2017 NGWA Summit : Alphabetical Content Listing

Availability and Sustainability

On-Site Direct Potable Reuse: A New Approach to Improving Groundwater Sustainability

Adam Arnold, MASc
In many regions of the United States, and elsewhere, groundwater supplies are rapidly diminishing due to overuse or becoming increasingly contaminated. Groundwater is the conventional source for potable water in millions of houses and businesses without connections to centralized water systems. On-site direct potable reuse (DPR) is a new approach to reduce withdrawal of groundwater from aquifers via private wells and release of partially treated wastewater into the subsurface via septic systems. Specifically, the water that has been used by a home or small business is recycled to yield purified water that is safe for all indoor uses rather than being discharged to the septic system as a waste product. In addition to maintaining a potable water supply, on-site DPR could preserve and protect aquifers by reducing groundwater withdrawals that are not necessarily replenished by infiltration of septic system effluent, and by reducing subsurface release of pathogens, nutrients, and other contaminants.

New legislation passed in Ohio in 2014 added ‘recycled water’ as a source for private water systems serving fewer than 15 service connections or 25 people on average. An on-site DPR pilot study was run from 2013 through 2016, and the system is now indefinitely approved as a potable water source for the office building that it serves. Following an initial testing period with purified water discharged to the septic system, the water has been plumbed into the building since 2014 and approved for all indoor uses including drinking and cooking since 2015. Extensive testing overseen by regulators and reviewed by an international panel of water experts demonstrated the excellent quality of the purified water and reliability of the advanced water treatment process. To date, this on-site DPR system has reduced dependence upon the well and volumetric loading to the septic system by upwards of 1.5 million liters.

Quantifying the Change in Volume of Water in the Sparta Aquifer, Northern Louisiana

Samantha Wacaster
The Sparta aquifer, generally a confined aquifer, is the primary source of groundwater in north-central Louisiana. Increasing groundwater withdrawals at concentrated locations from wells screened in the Sparta aquifer, have resulted in regional water-level declines. Recent studies, including potentiometric maps and a groundwater flow model, have assessed the impacts of withdrawals on water levels in Sparta aquifer, and water levels and saltwater encroachment continue to be monitored at a network of wells screened in the aquifer in Louisiana. However, questions still persist regarding the volume of available water and the long-term sustainability of the aquifer. To address these concerns, the U.S. Geological Survey (USGS) is developing a web-based tool that can compile these products into a single platform, whereby water-resource managers can easily assess the status of available water resources for a given location. The tool will provide estimates of changes in the volume of water in the Sparta aquifer from 1900 predevelopment conditions through 2012. Storage change will be evaluated using two methods: 1) Geographic Information Systems analysis and comparison of previously published USGS structure maps and potentiometric surfaces of the Sparta aquifer; and 2) analysis of simulated water storage in the aquifer derived from a groundwater-flow model. The interactive web tool, once developed, will allow users to compare results from both methods in a publically available visual mapping platform. Knowledge of the change in water volume within the Sparta aquifer will be useful for assessing recharge rates and could improve public understanding of the impacts of withdrawals over time.

The Power of Networks: Increasing the Visibility of Local Groundwater Resources

Charles Dunning, Ph.D.
A growing number of communities and organizations are deploying water-level sensors in well networks designed to provide greater information about the spatial and temporal distribution of their groundwater resources. The goals of these networks may range from providing a basic understanding of the availability of water from their aquifer to focusing on immediate or emerging threats to groundwater availability. Development of these local networks is being encouraged by the relatively low cost and high capabilities of a new generation of water-level sensors, and the efficiencies and opportunities of data management in the cloud. The water-level data generated by these local networks have great value to local interests where other data are sparse; and the data from these local networks complement (at a greater resolution) data from monitoring networks established by state and federal agencies. A growing network sponsored by the New Mexico Bureau of Geology & Mineral Resources (the state geological survey) is an example of the value of local groundwater-level networks in increasing the visibility and understanding of local groundwater resources. This talk will suggest best practices in starting a network, recruiting participants, and using the data to address local flow patterns, risks to the resource and opportunities for utilization.

The Private Well Conference - A National Workshop on Private Well Issues

Steven D. Wilson
On May 23-25, 2017 the University of Illinois Private Well Class program hosted the first National Private Well Workshop for sanitarians, drillers, scientists, public health officials, educators, and other professionals. Over 110 experts, educators, and industry professionals attended and listened to nearly 40 presentations related to private well issues, outreach, education, challenges, industry perspectives, and partnering opportunities. Topics covered included well owner outreach and education, lead in private water systems, well construction issues, well owner concerns and questions, industry perspectives, laboratory concerns and testing, changing private well regulations, best practices, springs as water supplies, online tools, and the future of private well education, outreach, and public health protection. The most important issues identified, solutions offered, lessons learned, and successes presented at the conference will be shared in this presentation.

Unmanaged Aquifer Recharge: Revisiting Sustainable Yield in Northeast Illinois

Devin Mannix
Water supply planners often use estimates of sustainable yield of an aquifer to make decisions on future best management practices. The influence of wells with long open intervals on the Cambrian-Ordovician sandstones has long been documented, though early estimates of sustainable yield did not separate components of flow beyond water entering from natural recharge sources and sources internal to the system. Calibrating a transient head-specified MODFLOW model for northern Illinois to documented pumping rates yields improved estimates for the sustainable flow from recharge sources, as well as the individual contributions from both shallow aquifers and the Mt. Simon. Preliminary results indicate that before World War II, much of the water withdrawn from sandstone originated from shallow aquifers via wells uncased through bedrock, primarily the Silurian dolomite. The rate of this artificial recharge appears to decline in the post-war period, coinciding with wells being sealed in Chicago. Simultaneously, declining heads in the sandstone aquifers induce dewatering of the overlying Galena-Platteville dolomite and uppermost St. Peter Sandstone, with water removed from storage reaching a maximum with the peak of pumpage in 1979. Communities began switching to Lake Michigan water and head recovery occurred between 1980 and 2000; concurrently, rapid growth of subdivisions added a new source of artificial recharge in the form of private wells bypassing the Maquoketa Shale. Model simulations indicate that sandstone groundwater usage exceeds flow from outside northeast Illinois by about 40%, the remainder satisfied by water removed from storage and artificial recharge via wells with long open intervals. There is some question whether this artificial recharge can be considered sustainable, owing both to the transient nature of these wells and the removal of water from overlying aquifers. Regardless, a sustainable rate of water use has not been achieved as heads continue to decline in the region.

Communicating Groundwater Science

William Alley, Ph.D.

Groundwater Modeling

William L. Cunningham

A Devil of a Site

Karilyn Heisen, P.E.
At the Red Devil site in Mt. Vernon, New York, paint-related liquids were released and seeped into the subsurface, where they accumulated as a light non-aqueous phase liquid (LNAPL) on the water table. As a plume developed it seeped into the Bronx River, resulting in noticeable discharge of LNAPL, causing the site to be listed by New York State Department of Environmental Conservation (NYSDEC) for remediation. A numerical flow model of the site was developed to assess LNAPL movement and evaluate a proposed hydraulic barrier. Complexities at the site include: the LNAPL, which increases in viscosity as the lighter fraction evaporates and solidifies when exposed to air; limited access, including steep banks and an active railroad; an urban river, which periodically inundates the aquifer; and a century old retaining wall. LNAPL simulation was performed with DYNSWIM, a finite-element numerical flow model, which allows for simulation of two-phase flow. As the properties of the LNAPL were difficult to measure and varied spatially and temporarily, the model was used to simulate movement of the LNAPL with varying viscosity, dispersivity and residual saturation values. Model simulations were used to estimate mass in locations where it was difficult to collect data and to estimate changes in LNAPL under different remediation scenarios. Simulations showed that a proposed flow barrier could stop LNAPL migration to the river, but it would be costly and have a substantial impact on the local ecology. Construction of the barrier would require fill to be placed in the river and removal of existing trees. Instead, a more cost-efficient and sustainable approach was selected, which included limiting movement of LNAPL under the railway by pumping at the source, periodical removal of LNAPL through bailing of wells, and collection of material which enters the river and is trapped by a series of booms.

Benchmarking of FEHM Control Volume Finite Element Solver

Murray Fredlund, Ph.D., PE
The numerical modeling of groundwater and geothermal problems has seen increase in the past few years due to the increase in computational power and software. The size and complexity of solutions attempted has increased as computational abilities increase. Problems with larger number of total nodes, with complex geology involving faulting, as well as coupling of multiple processes are now being attempted. Las Alamos National Labs (LANL) has invested over 50 man-years of effort into the FEHM control volume finite element solver over the past number of decades. The code has been used on US EPA Superfund sites and has results published in various studies and areas. The code allows for complex coupling of processes as well as non-isothermal models to be solved of increased complexity than existing commercial codes. LANL and SoilVision Systems Ltd. have combined efforts to offer a groundwater and geothermal numerical modeling solution that allows solution of larger and more complex models. In order to gain confidence in the combined front end, solver, and back end visualization system, a number of benchmarks have been created in order to document performance. This paper presents the results of benchmarks created to test the performance of the new groundwater and geothermal modeling system. Performance of the system is discussed as well as challenges and hurdles encountered in the collaboration. The ability of the system to scale up to model field-scale systems will be discussed.

Developing a Regional Model of the Coastal Lowlands Aquifer System—Using Uncertainty Quantification as a Guide

Brian Clark
Traditional model development proceeds from model dataset construction to the process of deterministic history-matching (calibration), where the model inputs are adjusted to adequately reproduce past observations of system state, such as water levels, fluxes, and base flow. In contrast to traditional model development, uncertainty quantification (UQ) will guide the modeling process for the U.S. Geological Survey’s Coastal Lowlands Aquifer System (CLAS) study. The CLAS study area extends geographically along the Gulf of Mexico from the Texas/Mexico border through the Florida panhandle. Because of the large extent of the aquifer system and the importance of the groundwater resource to municipal, industrial, and agricultural supplies in the study area, many local-scale groundwater-flow models have been developed in recent decades. Information from these past models provides a jumping off point for model development through use of model-provided time series of pumping, aquifer properties, recharge, and other model parameters. Thus, the intent of the CLAS study is not to create a model from scratch, but to rely on local knowledge and data to efficiently create a new regional model based on the previous models. Early in the model development, initial estimates of parameter and boundary-condition uncertainty will be used to form the prior information of the model inputs, simply referred to as the prior statistical distribution, and will allow early estimation of model forecast uncertainty as well. As the model is improved, the knowledge of forecast uncertainty will help guide additional model refinement within an iterative process. For example, if an updated hydrogeologic framework dataset is implemented, the UQ may indicate how much that dataset improved the model’s reliability. The resultant model (or model ensemble) will help quantify groundwater resources in the CLAS and provide forecast uncertainty ranges to better evaluate the reliability of the model.

Groundwater and Nitrogen Modeling to Prioritize Management Strategies for Suffolk County’s Estuaries

Daniel O'Rourke, P.G.
Nitrogen loading to groundwater from surface activities has caused degradation of aquifer and surface water quality. In Suffolk County, New York, more than 70% of the county relies on on-site wastewater disposal systems such as septic systems and cesspools. Nitrogen loading from these systems impact both ground and surface waters. Due to the appearance of harmful algal blooms, the loss of sea grass as well as increasing nitrate concentrations in water supply wells of the sole source aquifer, evaluating nitrogen loading within the County is a priority.

Utilizing groundwater models allows for a better understanding of the impacts of historic, existing and potential future land uses on aquifer nitrogen concentrations and ultimate discharge to water supply wells and estuaries. Groundwater models were utilized to better understand nitrogen loading from various land uses within watersheds as well as the impact of potential nitrogen reduction strategies such as the use of innovative alternative onsite wastewater treatment (I/A OWTS), clustered/decentralized treatment, or traditional sewering. Nitrogen loading models have been coupled with groundwater models to simulate the fate and transport of parcel-specific nitrogen loading throughout the County.

Suffolk County has launched a Subwatersheds Wastewater Plan in which baseflow contributing areas (subwatersheds) were simulated for more than 180 surface water bodies. For each subwatershed, time of travel (from the water table to surface discharge) zones are quantified and nitrogen loading from surface activities including wastewater, fertilizer application and atmospheric deposition are calculated. The nitrogen loads were simulated as parcel based point sources using fate and transport groundwater models which ultimately provided discharge loads to the subwatersheds and more than 700 community water supply wells. Simulated nitrogen loads to surface waters were compiled with quantitative and qualitative data and utilized in a decision support tool to rank and prioritize the subwatersheds for future management strategies.

Groundwater Modeling for Closure of the Little Blue Run CCR Disposal Area

Brianne Hastings, P.G.
The Little Blue Run (LBR) disposal area is a 900+ acre impoundment that has been used since 1975 for the disposal of coal combustion residuals (CCR) from FirstEnergy’s Bruce Mansfield Generating Station. The disposal area consists of a valley fill impoundment supported by an earth and rock fill dam. The CCR materials in LBR consist of calcium sulfite scrubber material, granulated blast furnace slag, lime, and fly ash that are hydraulically placed.

A digital groundwater model was prepared for the facility to compare closure alternatives and to evaluate environmental implications of the facility after closure. The model consisted of nine layers and over 140,000 cells. It was constructed and calibrated to match observed aquifer conditions and groundwater levels within and surrounding LBR. 

As part of the selected long-term closure program, the CCR impoundment will be capped with a geosynthetic liner and soil cover. An anticipated result of closure is a significant drop in the water level and subsequent settlement within the CCR material inside the impoundment. Recognizing that significant settlement could impact the surface drainage and final cover system following closure, the groundwater model was used to predict post closure groundwater levels. A long-term simulation was run to predict the water table draw-down 50 years after the final cover system will be placed. The simulated timeline included disposal, site closure options, and liner placement.

The post-closure water level is predicted to drop more than 100 feet with the maximum amount occurring where the CCR deposits are the thickest. The reduction in water levels appears to be greatly dependent on the areal extent of standing water on top of the impoundment. The majority of water drawdown within the CCR occurs within the first 24 years after closure. This analysis assisted in the selection of the final closure design for LBR.

Groundwater Modeling of a Deep Coastal Aquifer System in Tanzania Guided by Hydrocarbon Exploration Data

Matthew Gamache, P.E., D.WRE
The water authority for the city of Dar es Salaam in Tanzania initiated work to explore the water supply potential of a regional coastal aquifer system in close vicinity of the City. As part of this work, the Kimbiji Aquifer System (KAS) has been characterized to determine its capacity and suitability as a sustainable source of clean drinking water for the City. The Kimbiji Aquifer Assessment (KAA) project drilled, logged and tested 9 exploration wells ranging in depth from 1,200 to 2,000 feet, interpreted 27 seismic survey profiles spanning 710 miles from the early 1980s, and used information from four deep hydrocarbon exploration wells, one of which is offshore in the Indian Ocean, to develop a conceptual hydrogeological model of the KAS.

The conceptual model was used as the basis for numerical model development. A three-dimensional groundwater model of the aquifer system was built, calibrated and applied to examine sustainability of aquifer development alternatives (including risk of seawater intrusion) and potential environmental impacts (stream reductions, wetland depletion). The regional-scale model, which covers 4,400 mi2 (73% of which are off-shore) simulates the hydraulic interaction between fresh and saline groundwater (with the deep aquifer interface estimated to be over 10 miles offshore) as well as discharges to surface water onshore.

Based on the modeling, the estimated quantities of groundwater that can be developed in the long-term from the KAS can be as high as 70 MGD, depending on how wellfield development proceeds. Different wellfield configurations were tested with the model, which indicated that sustainable yield is more likely to be constrained by available drawdowns in production wells and other operational constraints than by seawater intrusion. For the wellfield configurations selected for further development, the groundwater model was used to examine potential protection zones, potential environmental impacts, times of travel, and groundwater age.

Investigating Uncertainty of Groundwater/Surface-water Interactions in the Lower San Antonio River Basin, Texas

Linzy Foster
The quantification of model uncertainty provides important information regarding a model’s ability to predict a quantity of interest. Linear-based First-Order Second-Moment (FOSM) analysis is a technique that yields initial estimates of model predictive ability, also referred to as model reliability. In this study, a novel groundwater/surface-water model of the lower San Antonio River basin and surrounding areas is in development and is being paired with FOSM analysis to quantify the uncertainty surrounding simulated groundwater/surface-water exchange. In light of recent drought conditions, a predictive drought scenario of streamflow response to reduced rainfall and increased groundwater withdrawals will be investigated. The study’s main goal is to develop a tool that can assess spatial and temporal variations in flow occurring between the lower San Antonio River (and its major tributaries) and underlying aquifer units these streams traverse during 2006 through 2013. The modeling analysis may indicate reaches with potential for streamflow depletion within the basin. FOSM analysis is being applied through the use of PEST++ and pyEMU. Observations include groundwater levels within the Texas coastal uplands and Texas coastal lowlands aquifer systems and groundwater contributions to base flow in main-stream reaches. The results of this analysis will include simulated volumetric surface-water totals with associated uncertainty at the confluence of the San Antonio and Guadalupe rivers, which will provide improved understanding of how streamflow is affected by groundwater pumping within the basin.

MODFLOW Validation of FEFLOW Model to Assess Sea Level Rise and Climate Change Drive Effects: Miami Beach Case Study

Carlos Tamayo, Civil, Engineer, M.S.
Cities along the coastlines of the United States are currently being affected by sea level rise (SLR); thus, adaptation is crucial to assure resiliency. In Miami, FL, a large portion of densely urbanized areas within Miami-Dade County are experiencing major investments in infrastructure. Consequentially, the entire area is very vulnerable to effects of climate-change, such as SLR and hurricanes, among others.

Miami Beach, FL, is a quite interesting example to analyze considering that it experiences a lot of what was mentioned above. It is a densely urbanized coastal city that is exposed to extreme weather events, sea level rise, and its residents and infrastructure are in a very vulnerable position. Residential and commercial high rises, high end neighborhoods, and preserved historic buildings are the general makeup of the city. Moreover, highly permeable formations, shallow groundwater levels, rising sea levels, and tidal effects, create a perfect setting for saltwater intrusion (SI) to occur and worsen through the years.

As part of a larger study, a FEFLOW groundwater model is being developed for coupling with a Mike 21 surface water model for assessing interactions between them. The City is the testbed and the broader goal is to evaluate soft and hard engineering solutions for adapting to SLR.

For this specific study, the main goal is to validate the FEFLOW model by taking the developed conceptual model and running it in a MODFLOW environment. The same baseline and time-dependent scenarios are simulated to perform an accurate verification of the FEFLOW model and compare equivalent results. Scenarios will assess the influence of sea level rise, tidal flooding, and extreme storm events with projections for year 2100. This exercise will allow for the robust coupled model to be validated and refined in order to make it scalable and replicable in similar coastal environments.

Multiple Tracer Testing Approaches for Improved Groundwater Flow and Reactive Transport Modeling Input Parameters

Raymond Johnson, Ph.D.
At many U.S. Department of Energy Office of Legacy Management (LM) uranium mill tailings sites, initial groundwater flow and solute transport modeling was completed 20–25 years ago using field data that included hydraulic head information and a few aquifer pumping tests. Because the uranium tailings were either removed or placed in capped disposal cells, and the simulations assumed limited uranium sorption, these models did not consider ongoing uranium contaminant sources. Currently, several sites have uranium concentrations that exceed the prior model predictions, which has led to the identification of uranium sources in the subsurface that were not previously identified. In order to update the past models, tracer testing techniques are being considered to provide more accurate information on groundwater flow velocities, flow directions, ongoing uranium sources, uranium sorption potential, and dual-porosity issues related to aquifer grain coatings and cements.

Tracer testing will be completed in the summer or fall of 2017 using multiple tracers and techniques at LM’s Grand Junction, Colorado, Site, which is located on a shallow alluvial aquifer adjacent to the Gunnison River. This tracer testing will include the use of borehole dilution, push-pull, and cross-hole techniques that focus on identified areas with elevated solid-phase uranium concentrations. The test data will be analyzed to estimate groundwater flow directions, velocities, and uranium transport parameters (sorption and dual-porosity influences) and be compared to previous estimates. This presentation will discuss how these multiple tracer tests were completed, interpreted, and then used to provide updated input parameters for revising the site groundwater flow and reactive transport models (conceptual and numerical).

Predicting Arsenic in Drinking Water Wells in Glacial Aquifer in Western and Central Minnesota, USA

Melinda Erickson, PhD, PE
Approximately 40% of available arsenic data for groundwater in western and central regions of Minnesota exceed the 10 μg/L drinking water standard. However, arsenic concentrations vary considerably over short distances and regionally across the state. A boosted regression tree (BRT) model was developed to predict the probability of arsenic occurring above the drinking water standard in groundwater at typical depths used for drinking water supply in glacial aquifers in western and central Minnesota. The BRT model, using about 75 predictive factors such as well construction characteristics, glacial material characteristics, and surficial characteristics (such as soil texture, soil chemistry, or land use), predicted probabilities of elevated arsenic in well water with about 65% total accuracy. Predictive factors determined to be influential for predicted probabilities included clay gap (distance from top of screen to overlying confining unit), nearest major river (a proxy for hydrological position in the landscape), horizontal hydraulic conductivity, and distance to the top of the bedrock from the bottom of the well. For example, smaller clay gaps were typically related to higher probability of elevated arsenic concentrations. The BRT model results were then used to generate maps illustrating elevated arsenic probabilities at the depth of a typical domestic drinking water well across the modeled regions. This a first application of BRT to model elevated arsenic probabilities in a glacial aquifer system.

Quantifying Future Groundwater Depletion, Climate Change and Irrigation Demand

Sasmita Sahoo, Ph.D.
A warming world, population rise, and increased demands for irrigation all compound to create pressures on groundwater resources. Multi-model integration is needed to evaluate these interactions, combining available observations with crop, climate and hydrological models. Major agricultural regions of the USA (e.g., High Plains aquifer) and North India (e.g., Punjab) rely heavily on groundwater, therefore better quantification and predictions of the impact of climate change on groundwater resources are urgently needed. Here we provide an assessment of historical and future climate change impacts on groundwater storage using two novel modeling approaches, machine learning and Bayesian model. We demonstrate the integration of climatic, crop and hydrological determinants of groundwater storage change in the High Plains and Alluvial aquifer of Punjab, India. The model is calibrated using historical (1980-2012) climate, streamflow, ocean temperature observations, and simulated crop water demand. Model runs using climate model projections and irrigation demand are used to simulate changes in future groundwater storage. The climate data is used directly in the model, also in a land surface hydrology model to predict streamflow, and in a biophysical crop model to predict irrigation demand. Climate data from two GCMs each with scenarios RCP 4.5 and 8.5 are used to generate future scenario inputs. The models are run in a high performance parallel computing environment to obtain estimates of future groundwater level change for hundreds of wells across each aquifer. Based on this combined climate-agriculture-groundwater model, changes in future groundwater storage are projected up to 2049. These results will be useful for identifying the locations of future groundwater stress, which will have implications for sustainable agricultural production, and will help inform management decisions in a rapidly changing and resource-constrained world. Overall, the major findings will be useful for immediate use to researchers and will improve decision-making in stakeholder communities.

Reactive Transport Modeling: A New Paradigm in Design of In Situ Treatment Systems

Robert D. Mutch Jr., P.Hg., P.E.
Application of three-dimensional, numerical, reactive transport modeling is emerging, we believe, as a new paradigm in the design process of in situ treatment systems. Its rapid emergence as a design tool is reminiscent of the paradigm that began to appear in the early 1980s when use of numerical groundwater flow modeling started to become standard practice in the design of groundwater extraction systems (despite the now apparent limitations in software and hardware at the time). In the last few years, reactive transport modeling has been applied with great success to evaluation and design of in situ chemical oxidation (ISCO), in situ chemical reduction (ISCR), and both aerobic and anaerobic in situ bioremediation (ISB) systems. Experience has shown that it can help optimize the performance of in situ treatment (IST) remedies, reduce the risk of outright failure, and save overall costs. A reactive transport model is built upon the foundation of a three-dimensional groundwater flow model and includes the ability to model the chemical interactions between injected substrates or chemicals and the contaminants of concern; between the injected chemicals and the aquifer skeleton; and other subsidiary reactions. As with any numerical model, best results are obtained when the model is calibrated to laboratory and field data. Several case studies will be briefly described where three-dimensional, reactive transport models were instrumental in the evaluation and design of full-scale ISCR, ISCO, and ISB systems.

Regional Hydrostratigraphic Unit Modelling Using Directional MCP Simulation

Nicolas Benoit
Regional Hydrostratigraphic Unit Modelling Using Directional MCP Simulation

N. Benoit1,2, D. Marcotte2, A. Boucher3, D. D’Or4 and A. Bajc5

1Geological Survey of Canada, Québec, Canada

2École Polytechnique de Montréal, Canada

3Advanced Resources and Risk Technology, LLC, Denver, USA

4Ephesia Consult, Belgium

5Ontario Geological Survey, Sudbury, Canada

In groundwater flow modelling, geological uncertainty characterization is a key input for risk assessment. The most influential geological uncertainty is attributed to the relative proportions, properties and spatial arrangement of the hydrostratigraphic units (HSU). The directional ordering of HSU is a critical component of sedimentary environments. This feature controls, to a large extent, the response of the system under a given external stimulus. Geostatistical algorithms, such as Bayesian Maximum Entropy method (BME) and Markov-type Categorical Prediction (MCP), present interesting features to impose directional constraints in categorical data simulation. In this study, we illustrate the ability of the MCP method to allow for trends and directional ordering in simulation. The MCP approach was tested first on a simple synthetic model and then applied to a regional 3D model in the Innisfil Creek sub-watershed. The required asymmetric transition probabilities between categories for MCP were extracted by Fast Fourier Transform computation from the transitional deterministic model. This model includes 15 hydrostratigraphic units displaying lateral variability and defined vertical ordering. The MCP realizations all reproduced hydrostratigraphic units in logical arrangements and proportions. The set of realizations appear globally unbiased with variations around the deterministic model. The resulting ensemble of geological models allows for the assessment of uncertainty of groundwater flow and transport as well as aquifer vulnerability and the delineation of wellhead protection areas.

Keywords : units ordering, categorical simulation, model uncertainty

The Ozark Plateaus Groundwater Model: Parameter Effects on Forecast Uncertainty

Leslie Duncan, PhD
Groundwater models are increasingly used to inform resource-management decisions. As such, it is important to understand how model uncertainty may affect scenario forecasts, particularly if such forecasts could suggest a wide range of possible management outcomes. In 2014, the U.S. Geological Survey (USGS) began developing a regional model of the Ozark Plateaus aquifer system to quantify groundwater availability and to evaluate impacts of climate variability and water-use changes. Water levels in wells screened in the aquifer system respond relatively rapidly to withdrawals and seasonal fluctuations in hydrologic drivers. Some water-level fluctuations exceed 100 ft, creating the need to lower pumps or drill new wells, and drought periods can cause alarm among water managers for municipal and industrial supply and within agricultural communities. Because of the aquifer system’s sensitivity to these fluctuations, the USGS will conduct linear-based, first-order, second-moment (FOSM) uncertainty analysis to estimate forecast uncertainty and to quantitatively evaluate which parameters have the greatest effect on forecast uncertainty. Complementary analysis based on the assumptions of FOSM will be used to estimate the value of additional information to reduce forecast uncertainty. The uncertainty analyses can be enlightening and often identify areas or parameters within the model that could reduce the range in forecast outcomes.

Using Machine Learning to Map Redox Conditions in the Mississippi Embayment Regional Aquifer System

Katherine Knierim, PhD
Redox conditions in the Mississippi embayment regional aquifer system were mapped at depth zones used for domestic and public supply using machine learning methods. About 3 million people rely on groundwater from this aquifer system for drinking water and redox processes exert important controls on groundwater quality in this system. Explanatory variables including environmental spatial datasets, groundwater-flow model output, and well characteristics were used to extrapolate groundwater quality (specifically redox conditions) to areas of the system without existing water-quality data. Machine learning methods are well suited to hydrologic studies because they allow input of continuous and categorical explanatory variables, can accommodate interactions among explanatory variables, and have performed better than linear regression methods for training data and also when tested on data not used as part of model training. In addition, machine learning methods are not constrained by hypothesis testing assumptions such as linear relations and data normality. Environmental explanatory variables included soil data (texture, drainage class, conductance, and geochemistry), climate (temperature and precipitation) and land use. Groundwater-flow model variables included groundwater flux, groundwater age, flowpath length, groundwater altitude, water use, and hydrogeologic unit texture. Well characteristic variables included hydrologic position relative to major surface-water drainages and well-construction data (length of and depth to top of the screened interval). Although there may be limitations to using environmental variables to explain groundwater quality for confined aquifers with long groundwater residence times (that is, old groundwater), if machine-learning methods can be used with environmental and well-characteristic variables, then groundwater quality can be more accurately predicted in areas lacking numerical groundwater-flow models.

Groundwater Monitoring

Scott Morie, PG, CGWP, CHMM

Acoustic Technology Provides New Groundwater-Level Monitoring Opportunities

Joseph Fillingham, Ph.D.
Acoustic groundwater-level monitoring systems are vital tools for creating and expanding data-dense, stakeholder-engaged monitoring networks. Telemetry enabled, acoustic groundwater-level sensors minimize contamination risk and operating complexity and benefit from the cloud, where automated plausibility and historical analysis provides accurate water level data despite local variables like obstructions, temperature change, and background noise, and maintains data quality control for long term monitoring. The technology is reshaping groundwater monitoring markets and practices since communities, agencies, and researchers are able to take advantage of previously untapped locations: the 15 million privately owned domestic and agricultural wells across the US. Low up front and operating costs, combined with rapid time intervals and automatic tagging of pump influenced readings reduce the cost per data-point over traditional methods, while creating new opportunities for evaluation and richer insight. Since the data can be shared with volunteers in formats designed for preventive maintenance, the effort and expense to start up and grow a spatially and temporally dense monitoring network is significantly reduced, while fostering community engagement between agencies and well owners around groundwater resource facts.

Analytical Study of Groundwater Flow in a Vertical Plane at the Interface Of Permafrost

Sairavichand Paturi
Groundwater dynamics in discontinuous permafrost aquifers is complex. The topography of permafrost redirects flow in difficult to predict directions that can be tens of degrees off from the regional flow direction. Large zones of permafrost vertically separate aquifers into supra and subpermafrost portions. The flow dynamics in each portion of the aquifer may be dissimilar due to different controlling boundary conditions. In areas of discontinuities in permafrost, known as open taliks, groundwater in the two portions of the aquifer may mix. These areas of mixing are the focus of this study, in particular the groundwater dynamics in taliks located in the floodplain of losing reaches of rivers. The study hypothesizes that groundwater flow in floodplain taliks of losing reaches of rivers will bifurcate between the supra and subpermafrost portions of a discontinuous permafrost aquifer. To test this hypothesis gradient magnitudes and flow directions were determined at several depths ranging from the water table to 150 ft. below ground surface using a linear interpolation scheme in various locations in a floodplain talik. Errors in water level measurements due to instrument errors as well as vertically moving wells were propagated into the gradient calculations by Monte Carlo analysis. Results from this research show a vertical divide in groundwater flow forms a short distance below the top of permafrost. Groundwater flow above the divide routes into the unconfined suprapermafrost portion of the aquifer. Water below the divide flows into the confined portion of the aquifer below permafrost. The position of the vertical groundwater divide may adjust in relation to the water table position. Additionally, methodology is presented for stochastically propagating measurement errors into gradient analyses by Monte Carlo analysis. Understanding the flow dynamics in discontinuous permafrost aquifers is key to the understanding of contaminant transport, aquifer recharge, and resource development in subarctic environments.

A New Methodology to Reduce Cost of Groundwater Monitoring Programs

Farid Achour, PhD
At contaminated sites, lengthy environmental clean-ups often involve a long-term program that can be costly. Responsible parties, through their consultants, should consider Cost-Effective Sampling (CES) methods that, in addition to their professional judgment, will tailor the monitoring program to directly support the cleanup and closure of the contaminated site. The goal should be to collect only those data needed to make operational and closure decisions. A successful optimization of a monitoring program should take into consideration the sampling frequency, analytic methods (temporal domain), and the sampling locations (spatial domain). To achieve such optimization, Ramboll Environ developed a methodology combining the concept of Regional Vector (RV) and multidimensional analyses such as Principal component Analyses, Factorial Discriminant Analyses, Correspondences Analyses and Dynamic Clouds Analysis.

These methods are hypothesis-free, and therefore, unbiased. They can be used to analyze multivariate data such as ground water level fluctuations and water chemistry simultaneously, collected over several sampling events in several wells. The purpose of the analyses is to evaluate and group wells based on the similarity in their temporal and spatial behavior. The methodology does not provide a "push button" solution, but requires the thoughtful and informed application of the various mathematical tools to provide output that can be used to meet the project requirements.

Application of Environmental Tracers in the Analysis of Flow in Discontinuous Permafrost Aquifers

Bridget Eckhardt
Groundwater systems and flow dynamics in cold regions are dictated by the presence of perennially frozen ground (permafrost) and seasonal freeze-thaw dynamics. Permafrost acts as a barrier to flow and a separation between aquifers above and below the permafrost. The complexity of groundwater flow in these systems increases in the discontinuous permafrost region where perennially thawed zones (open taliks) allow for connections between supra (above)- and sub (below)- permafrost groundwater which differ in quality and composition. This complexity poses difficulties in estimating groundwater quantity and quality and developing solutions for contaminant remediation. Changes in groundwater flow are expected to occur with the formation of new taliks, as a result of the warming climate. Knowledge of groundwater dynamics in these complex systems is crucial to groundwater sustainability and the future of groundwater modeling in Arctic and sub-Arctic regions of the world.

We present two studies focused on floodplain and sub-lake taliks in Interior Alaska that use chemical and physical tracers to characterize seasonal groundwater flow dynamics of supra- and sub-permafrost groundwater in discontinuous permafrost aquifers. Results from our study of the Tanana River floodplain near Fairbanks show that stable water isotopes, deuterium (δ2H) and oxygen-18 (δ18O), can be used to distinguish supra- and sub-permafrost groundwater. At a different study site consisting of two lakes with varying degrees of talik formation in the Goldstream Creek Basin near Fairbanks we combine the analysis of major cations and anions, alkalinity, basic field parameters, and stable water isotopes to distinguish sources of water and contributions to the lakes. Both studies demonstrate the complexity and seasonal variability of flow dynamics in open taliks as well as provide several conceptual models for the flow of groundwater within open taliks that can be used as a baseline for groundwater models in discontinuous permafrost regions.

Arsenic Concentration Variability in Newly Constructed Drinking Water Wells in Minnesota, USA

Helen Malenda
The State of Minnesota revised the well code in 2008 to require testing all new potable wells for arsenic (in addition to nitrate and bacteria). The well code requires testing at a certified laboratory before the well is used as a potable water supply. However the code does not require any particular sample collection method or sampling point. To better understand the influence that sample collection methods, sampling point, and timing have on measured arsenic concentration, arsenic concentrations were measured in 250 newly constructed wells over one year in several counties known to have prevalent elevated arsenic concentrations in groundwater. Study samples were collected in the following ways: 1) total arsenic samples (unfiltered) collected by well drillers in each respective driller’s common practice (from the drill rig or from plumbing); 2) initial total and dissolved (filtered) arsenic samples by MDH staff replicating driller sample timing, sampling point, and method; and 3) total and dissolved arsenic samples by MDH staff 3-6 months after well construction; and 4) total and dissolved arsenic samples by MDH staff 12 months after well construction. Initial total arsenic concentrations varied significantly from later sample concentrations, both total and dissolved. In contrast, initial dissolved sample concentration varied much less over time. Over one year, total initial arsenic samples switched between categories of above or below the 10 µg/L drinking water standard in more than 13% of wells. Dissolved arsenic samples switched between categories in only 7% of wells. Filtering initial arsenic samples reduces concentration variability over time.

Drilling and Installation of Deep Groundwater Monitoring Wells: Los Alamos National Laboratory, New Mexico

Mark Everett, PG
Los Alamos National Laboratory (LANL, or the Laboratory) is underlain by a complex basin-fill sequence of alluvial fan deposits, volcanic tuff, basaltic and dacitic lavas, and riverine deposits. On-going drilling and well installation activities have evolved to improve both the quality of hydrogeologic characterization and the performance of groundwater monitoring wells, ensuring they yield representative groundwater samples. Groundwater occurs as canyon-fill alluvial water, perched intermediate-depth water, and as a regional-scale aquifer that is the main water supply for the area. The regional aquifer below LANL is up to 1400 feet below ground surface (bgs). Therefore, monitoring wells at LANL, are among the deepest routinely installed in the US. Cost drivers include logistical challenges, and the variable drilling techniques required to characterize and install wells in this geologic environment.

Major challenges to the characterization approach at LANL are to obtain maximum information during drilling and to meet sample quality requirements while minimizing drilling costs. Current drilling practice makes limited use of fluid additives to supplement air circulation methods to advance through the vadose zone. Starting about 100 feet above the water table, drill casing is advanced to the regional aquifer using only air and municipal water for circulation. The ability to retract casing for video and geophysical logs allows for robust characterization of perched groundwater systems and accurate definition of the top of regional saturation.

Current well design emphasizes a minimal annulus, maximum screen slot size, and thorough well development to mitigate formation damage due to drilling. Careful subsurface characterization at depths ranging up to 1,400 feet bgs, while retaining the ability to collect representative groundwater samples, may have application at a number of sites throughout the environmental industry. Optimizing each well to meet program objectives while reducing total project costs benefits all environmental investigations. (LA-UR-17-23451)

Evaluating Water Levels in the Northern Atlantic Coastal Plain using National Groundwater Monitoring Network Data

Daryll Pope
The Subcommittee on Ground Water of the Federal Advisory Committee on Water Information has guided the development of the National Ground-Water Monitoring Network (NGWMN). The Network will provide water-level and water-quality data for groundwater resources at a scale appropriate for evaluating the USGS designated Principal Aquifers in the Nation. The Northern Atlantic Coastal Plain (NACP) is one of the first Principal Aquifers to have sufficient data available through the NGWMN data portal. The NACP extends from Long Island, New York to North Carolina. The NACP primarily consists of a series of seaward-dipping, semi-consolidated to unconsolidated sediment (aquifers) and interbedded clay units (confining units) that generally thicken to the southeast. In this presentation we show the current status of water levels in the NACP and the utility of NGWMN data to highlight temporal and spatial water-level changes.

Data currently available for the NACP in the NGWMN are provided by water resources agencies in seven states. Differences in the procedures used to collect data and classify sites are presented because they affect the use of the data. Available water-level data for wells in the NACP from the NGWMN are used to begin to address questions listed in the Network Objectives section of the NGWMN Framework Document (2013). Spatial variations in water-level changes are shown using maps of changes observed over the past 10 and 30 years, respectively. Selected hydrographs over the extent of the aquifer system are shown to complement the change maps. Water-level change maps over the past 30 years in each of the five major aquifers of the NACP show the variability within the aquifer system. The current status of water-levels is shown by visualizing the most recent water-level in comparison to long-term monthly statistics. Other potential uses of NGWMN data in the NACP will be briefly presented.

Gaining Insights Into Risks to Groundwater Using Big Data and Machine Learning

Jennifer Bauer
Efforts to improve insights related to the risks to groundwater coinciding with oil and gas development and infrastructure requires an understanding of the dynamics and interactions across the entire engineered-natural system. However, the heterogeneity and ambiguity of these data make it difficult to assess the broad range of potential risks posed to groundwater. But, successful applications of big data and machine learning in other scientific disciplines suggest these approaches are well suited to coping with these types of challenges faced when assessing risks to groundwater. Here, we will present some of our efforts and lessons learned integrating machine learning and big data analytics in various models and assessments to understand risk associated with oil and gas development and infrastructure as it pertains to groundwater.

Implementation of a Non-Traditional Groundwater Level Monitoring Network in New Mexico

Sara Chudnoff, PG
In the southwest U.S., we face a future of warmer annual average temperatures, with increasing variability in precipitation, reduced groundwater recharge, and increasing demand on groundwater. However, because of limited funding, groundwater level monitoring programs in New Mexico have been shrinking over the past several years. Maintaining or growing current groundwater monitoring networks in New Mexico are expanding with “non-traditional” methods. In 2016, the New Mexico Bureau of Geology and Mineral Resources (NMBGMR), through a public-private funding partnership, began the Collaborative Groundwater Monitoring Network (network). The goal of the network is to fill spatial and temporal gaps in groundwater level monitoring, while promoting increased awareness of water issues and providing an important dataset for making informed water management decisions. This collaboration is achieved by collecting data from parties that are monitoring water levels, equipping or manually measuring wells, and providing education and outreach to parties interested in learning to monitor water levels. These data are made available to the public through the NMBGMR webmap.

Improved Monitoring for Remediation Effectiveness with Water Quality Sondes

Adam Hobson, P.G.
Remediation of contaminated groundwater is often a prolonged and expensive process from initial characterization to achieving remedial action objectives. Rapid assessment of the performance and effectiveness of remedial technologies can shorten the remediation process resulting in reduced costs, contaminant exposure, and corresponding risk. In this case study, a monitoring program was implemented to rapidly assess the migration of an in situ groundwater remediation technology applied to contaminated groundwater in shallow fractured bedrock under an active manufacturing building. Due to the manufacturing activities, access to the subsurface with vertical wells or other technologies was not practical, resulting in a limited understanding of the fate and transport of the contamination. To remediate the contamination, injection of a remediation reagent composed of fine particles of activated carbon was proposed. Due to the restricted access, the reagent would be injected along the perimeter of the building and up-gradient of the suspected source area. Initially, monitoring the effectiveness of the remedial solution was proposed to be through quarterly groundwater quality sampling of selected near-source down gradient wells. However, this approach would result in over one year of monitoring, analysis, reporting, and decision making to establish the effectiveness of the remediation. In an effort to accelerate the remediation process and avoid unnecessary delays, we deployed a network of water quality sondes and telemetry units to measure turbidity as a surrogate for the presence of the remediation reagent. Using the near real-time data, we rapidly demonstrated the limited and irregular distribution of the reagent to the target remediation zone (which was subsequently borne out by the groundwater quality sampling) and gained a better understanding of the groundwater flow system, thereby guiding future corrective actions and reducing delays in the remediation process.

Lead and Manganese in Untreated Drinking Water from Aquifers in the Atlantic and Gulf Coastal Plain, Eastern USA

Jeannie Barlow, PhD
Concentrations of lead and manganese in 258 untreated drinking-water samples collected in 2013 from aquifers in the Coastal Plain were compared to select factors related to hydrologic position, mineral saturation, and geochemical conditions. Statistical comparisons between the concentrations and the explanatory factors were used to identify the factors most important to the occurrence of lead and manganese in groundwater. Lead and manganese were selected because: 1.) both trace metals and neurotoxins; 2.) both were detected at elevated concentrations in greater than 2 percent of samples collected within the study area. The lead and manganese concentrations were evaluated in terms of hydrologic position, well depth, and geochemical indicators including pH, dissolved oxygen, specific conductance, and select trace metals. Sample results from 258 wells completed in three principal aquifers in the Coastal Plain aquifer systems were included in the analysis. Elevated concentrations of lead were associated with relatively younger, high-oxygen, low-pH waters which occurred closer to recharge zones (relatively shorter flow paths). Elevated concentrations of manganese were associated with relatively older, low-oxygen, low-pH waters which occurred further away from recharge zones (relatively longer flow paths). Based on these associations, dissolved oxygen and pH, both relatively easy to measure in groundwater, can be used to identify locations within aquifers in the Coastal Plain systems that may be more susceptible to elevated manganese and lead concentrations.

Montana in the National Ground-Water Monitoring Network

John LaFave
The Framework for the National Ground-Water Monitoring Network (NGWMN) calls for the use of existing state and local groundwater monitoring programs (SOGW, 2013). The Montana Bureau of Mines and Geology (MBMG) maintains a statewide groundwater monitoring network that collects water-level and water-quality data from Montana’s principal aquifers—including the heavily-developed Intermontane Basins aquifers and the less-intensively-developed, but widely-used Alluvial, Lower Tertiary, Upper Cretaceous, Lower Cretaceous, and Paleozoic aquifers. Montana’s network design is based on aquifer extents and development, and provides current data about long-term trends in groundwater storage and quality.

The MBMG shares data through its Ground Water Information Center (GWIC) website (http:// mbmggwic.mtech.edu/), and web mapping applications. Data also are available through web services hosted on ESRI’s ArcGIS Server or Geoserver.

The MBMG selected its NGWMN wells based on Framework Document and “Tip Sheet” guidance available from the NGWMN web page (http://cida.usgs.gov/ngwmn/learnmore.jsp). Candidate wells had at least five years of water-level record and a monitoring frequency of at least quarterly. Other criteria included the aquifer extent, groundwater development, flow system position, and monitoring well density.

The selection process identified 227 wells for inclusion in the NGWMN. Each well’s hydrograph was evaluated against local hydrogeologic and land-use data to assign it to a Background, Suspected Changes, or Documented Changes subnetwork. Most wells show little-to-no anthropogenic influence and became part of the Background subnetwork. Hydrographs with anthropogenic signals (Documented Changes subnetwork) showed:

  • Seasonal irrigation recharge—mostly from the irrigated alluvial aquifers.
  • Seasonal irrigation withdrawals—mostly from the irrigated intermontane basins and buried glacial aquifers.
  • Long-term depletion—locally from the upper Cretaceous Fox Hills-Hell Creek aquifer system in eastern Montana.

Data from Montana NGWMN wells are available through the NGWMN Data Portal (https://cida. usgs.gov/ngwmn/).

Radium Mobility and the Age of Groundwater in Drinking-Water Supplies from the Cambrian-Ordovician Aquifer System

Paul Stackelberg
Groundwater ages which ranged from modern (< 50 yrs) to ancient (> 1 Myrs) were combined with raw water-quality data from 80 public-supply wells to evaluate the evolution of geochemical conditions that mobilize high concentrations of radium (Ra) in potable portions of the Cambrian-Ordovician (C-O) aquifer system. Findings indicate that it is the combination of anoxic, Fe-reducing conditions and increasing mineralization that favor the mobilization of Ra coupled with the length of time water is in the aquifer system that results in the frequent occurrence of combined Ra (226Ra + 228Ra) at concentrations exceeding the USEPA MCL of 5 pCi/L. Strongly correlated concentrations of 224Ra and 228Ra comprised a larger proportion of the total Ra (Rat = 224Ra + 226Ra + 228Ra) concentration in samples from upgradient recharge areas where arkosic sandstones are common, whereas 226Ra comprised the larger proportion in samples from downgradient confined regions. 226Ra distribution coefficients decreased substantially with anoxic conditions and increasing ionic strength (mineralization) indicating Ra is mobilized to solution from solid phases of the aquifer as sorption capacity is diminished. The rate of release of 226Ra from solid phases by alpha-recoil mechanisms exceeds the rate of Ra sequestration by adsorption processes or co-precipitation with barite. Although 226Ra occurred at concentrations greater than 224Ra or 228Ra, the ingestion exposure risk was greater for 228Ra owing to its greater toxicity. In addition, 224Ra added substantial gross alpha-particle radioactivity (GAA) to potable samples from the C-O aquifer system. Thus, monitoring for Ra radionuclides and GAA is equally critical in the recharge area as downgradient, with GAA measurements being completed within 72 h of sample collection to capture alpha-particle radiation from the short-lived 224Ra.

The National Groundwater Monitoring Network – A Progress Report and an Invitation to Participate

Robert P. Schreiber, PE, BCEE, D.WRE
The National Ground Water Association (NGWA), along with partner organizations, continues its strong support of the U.S. National Groundwater Monitoring Network (NGWMN), a wonderful example of cooperation between the Federal government, states, other governmental entities, the private sector, and academia. Each year, the NGWA Groundwater Summit provides an opportunity to update the membership on progress being made toward full implementation of the NGWMN, and to encourage participation in the ongoing effort. Therefore, this presentation will include a status report, while also serving as an introduction for other related presentations that will demonstrate the value of the NGWMN. The progress report will address the following topics: a description of the group that spearheaded the formulation of the NGWMN; the purposes and objectives built into the design framework for the NGWMN; a short outline of the approach taken by the NGWMN; a summary of the funding history for the NGWMN; some statistics demonstrating the growth from pilot phase to today; and, a statement of the value-added as the NGWMN begins to grow enough to meet its design purposes/objectives. This progress report will be capped off by an invitation to participate in the NGWMN process, with identification of specific roles and the ways to get involved. These will include roles not only within the U.S. effort, but also interactions with other countries’ similar efforts.

Tidal Influence on Remediation Sites: Understanding Predominant Gradients and Flow Inversion Effects on Mass Flux

Robert J. Stuetzle, P.Geo.
Many remediation sites across the globe are located in coastal settings or along the banks of tidally influenced rivers. Furthermore, the effects of tides on those nearby surface water bodies manifest themselves in the groundwater flow system. Understanding and quantitatively incorporating tidal influence into the conceptual site model (CSM) is key to predicting groundwater flow, contaminant transport, and mass flux at the site. Without correction for tidal effects, manually measured groundwater monitoring data can appear erratic, both spatially and from one event to the next. Mass discharge estimates can be challenging in these environments, due to daily groundwater flow inversions near the receiving surface water body, which tend to produce significant natural attenuation of plume fronts prior to discharge. Temporary deployment of transducers for continuous water level monitoring in a subset of existing monitoring wells and in the adjacent surface water body, has shown to provide the data necessary to develop correction factors for subsequent manual water level measurement events. Calculation of tidal efficiency and tidal time lag, once quantified, can normalize the hydraulic head data such that a true synoptic potentiometric surface can estimated. Beyond correcting for temporal variation to create snapshots of potentiometric surfaces in time, the continuous monitoring data can be used in conjunction with numerical modeling to understand the transient dynamic nature of tidally influenced systems, including flow inversions, net discharge flow, transient transport and mass flux. This combined approach provides a more comprehensive assessment of site risks and, ultimately, more realistic remediation goals. This presentation reviews site specific data where detailed head measurements and modeling techniques were used to obtain a comprehensive understanding of tidal influenced systems.

Groundwater Remediation, including Combined Remedies

Seth Kellogg, PG

A Quantitative Approach for Passive Removal of LNAPL from Groundwater

Kevin Svitana, Ph.D.
Persistent light non-aqueous phase liquids (LNAPLs) are one of the more problematic challenges for obtaining site closure or no further action status at remediation sites. The source of the LNAPLs can be varied, ranging from leaking underground petroleum storage tanks to manufacturing facilities where long-term oil loss from equipment creates LNAPL accumulations beneath factory floors. Active recovery using pumping or periodic vacuum recovery from wells or sumps typically are employed as a remedial action, but usually have disappointing results because the LNAPL re-accumulates to thicknesses that exceed the 0.01 foot action level recognized by many states shortly after active recovery ceases. This paper presents a simple passive approach to removing persistent LNAPL using non-woven hydrophobic oil absorbing fabrics. The method was explored in a laboratory setting to assess physical properties of the sorbent cloth. Parameters that included sorptive capacity, buoyancy and LNAPL wicking were measured and observed. From the observations it was determined that the cloth could be rolled and secured with cable ties for placement in the wells/sumps. Two sorbent placement designs were developed; one where the rolled sorbent freely floated on the well/sump fluid surface and a second where the sorbent roll was placed in the fluid column at a fixed depth. The rolled sorbents were then applied at two manufacturing facilities that have had persistent LNAPLs present for over a decade. In both instances, LNAPLs were reduced to thicknesses below the action level in less than two months. At both locations, the sorbents were removed and LNAPL thicknesses were gauged one month later. In most wells LNAPL did not re-accumulate; where it did re-accumulate, it was less than 50% of the original thickness. The application of this approach to quantify mobility and migration analysis for site closure will be presented.

Challenges of Treating PAH Compounds Down to Part Per Trillion Levels on a Remediation Site

Jason Downey, PE
Challenges of Treating PAH Compounds
Down to Part Per Trillion Levels on a Remediation Site

As discharge regulations continue to tighten across North America, solution providers are required to evolve and adapt products and designs to meet new regulations.

In 2015, newterra developed a process design and created a treatment plant for remediating a heavily contaminated Superfund site situated on the environmentally sensitive shore of Lake Superior. As a former Manufactured Gas Plant (MGP), the site contained large volumes of weathered LNAPL and DNAPL that were collected and treated along with the heavily impacted groundwater and solids drawn from multiple extraction wells on the property.

The effluent from the treatment plant discharged to Lake Superior and was subject to strict permit requirements with discharge limits in the part per trillion range for the difficult to treat PAH compounds.

This presentation will guide the audience through the treatment objectives and challenges faced in developing the solution for this site. The presenter will walk through the process steps of bench testing, pilot testing and full scale design of the treatment plant – and share the lessons learned through commissioning and startup.

By sharing our challenges, technology selection process and experience from this project, delegates will be able to apply and build on the lessons we learned for their own remediation/water treatment initiatives.

Development of Klozur SP with a Built in Activator: Safe Storage / Mixing and Maintaining Treatment Effectiveness

Brant Smith, Ph.D.
Background:

Activated Klozur® persulfate has been implemented for over 10 years to successfully remediate sites impacted with a wide assortment of contaminants of concern ranging from petroleum hydrocarbons, oxidizable chlorinated solvents, and reducible organics such as carbon tetrachloride and 1,1,1-trichloroethane. The ability to treat different contaminants has been attributed to the activation method and the formation of the sulfate, hydroxyl, and superoxide radicals. Conventional methods of activating persulfate include iron chelates, alkalinity, heat, zero valent iron, and hydrogen peroxide. As these chemistries react with persulfate, it has required that the activator reagents be stored and mixed separately from the persulfate.

Certain sites can benefit from having the persulfate and activator delivered as a single bag and mixed into a single solution. However, activators can promote the decomposition of persulfate. This is the intended result in the subsurface needed to generate the oxidative and reductive radicals but should be eliminated or minimized when stored or once mixed into solution.

Objectives:

The objective of this work was to identify a blended activator-persulfate system that could be safely stored, transported, and batched together while still effectively treating the different contaminants of concern.

Summary:

This presentation will discuss the existing methods of activating persulfate, conditions used to generate oxidative and reductive pathways, and then review key stability data and treatment efficacy of an all-in-one blend containing Klozur SP and a novel activation system. The stability data will show that the blend can be safely stored and transported. Stability and losses measured over time upon mixing will be compared to that of different organic activators. Finally the treatment efficacy of different activation systems in treating common contaminants of concern such as 1,4-dioxane, TCE, carbon tetrachloride, and benzene will be presented.

Keywords: ISCO, Klozur, persulfate, activation, organic

Evolving Regulatory Requirements, Health Effects & Cost-Recovery/Affirmative Litigation Options for PFAS

Richard Head
PFOA and PFOS are fluorinated organic chemicals, part of a larger group of chemicals referred to as perfluoroalkly substances (PFASs), that have been discovered in dozens of drinking waters supplies throughout the country resulting in EPA or state mandated multi-million dollar clean up projects. There source of PFAS contamination in drinking water is typically the result of direct releases from manufacturing facilities into the ground or air or firefighting foams containing PFASs that were used at Air Force bases, airports and firefighting training facilities. In response to the discovery of this recent contamination and the public outcry over health effects associated with PFASs, EPA lowered its Health Guidelines for PFAS and states are also beginning to implement their own regulatory response to this growing problem. This presentation will discuss the extent of the problem, legal and scientific issues relating to remediating drinking water supplies contaminated with PFASs, health effects from PFAS exposure and cost-recovery/affirmative litigation options for municipalities whose drinking water supplies are contaminated with PFASs.

Extended Release Low Solubility Potassium Persulfate Laboratory and Field Applications

Jennifer Lindsey
In situ chemical oxidation (ISCO) using activated Klozur SP® persulfate has been applied at thousands of sites to treat a wide assortment of environmental contaminants of concern. Potassium persulfate is another commercially available persulfate that, once activated, releases the same remediation potential as sodium persulfate but has several different key characteristics. Two of these critical characteristics are a theoretical solubility that is over an order of magnitude lower than sodium persulfate and the use of the potassium salt which would be beneficial at a limited number of sites that have regulatory guidance on sodium (Na) concentrations in groundwater.

Laboratory tests were conducted in a series of batch and column studies. Batch tests included comparing solubility under different conditions, and evaluating characteristics of several activation methods. Column studies were conducted evaluating the treatment efficacy of common aqueous phase contaminants such as MTBE and 1,4-dioxane, and potential longevity under difference treatment conditions.

Field application included hydraulic placement of activated Klozur KP at 3 locations to address dissolved petroleum constituents and chlorinated volatile organic compounds at a former drum storage area. The targeted vertical profile was between approximately 7 to 11 m below ground surface, where a relatively large contaminant mass was concentrated in a relatively small aquifer volume. Injected solutions included a total of 1,350 kg of Klozur KP and 200 kg of ferrous lactate. Post injection monitoring for 1 year indicated successful distribution of activated Klozur KP and resulted in reductions of up to 99% contaminant concentrations.

The laboratory and field data show that persulfate derived from potassium persulfate is capable of treating a multitude of contaminants of concern and that potassium persulfate exhibits key characteristics that can be used by design engineers and implementers for a variety of site specific applications.

Groundwater and PFAS: State of Knowledge and Practice

Seth Kellogg, PG
Per- and polyfluoroalkyl substances (PFASs) are a unique class of emerging drinking water contaminants that have shown widespread occurrence in groundwater and surface water resources, and due to their toxicological characteristics are increasingly the focus of environmental protection agencies worldwide. Starting in October 2016, 37 scientists and engineers voluntarily collaborated through the National Ground Water Association to develop information for the broader groundwater community. Using a consensus-driven process that included a public comment period, their efforts resulted in Groundwater and PFAS: State of Knowledge and Practice, published earlier in 2017.

NGWA published this PFAS document to assist members and other groundwater professionals who may be tasked with investigating the transport pathways and extent of PFASs in groundwater and surface water, assessing potential risks to receptors, or designing and constructing engineering controls to manage subsurface PFAS contamination. The main purpose of this document is to summarize the current state of knowledge and practice regarding PFAS fate, transport, remediation, and treatment, recognizing that knowledge in this field is advancing. This document also aims to summarize current technologies, methods, and field procedures being used to characterize sites and test remediation and treatment technologies.

Groundwater Remediation System Capture Analysis: Examples from Multiple Sites

Jason R. House, CG, PG
Groundwater remediation systems are subject to periodic review by site remediation personnel, clients, and regulators. Since remediation systems run the gamut from small and simple systems to large and complex systems, a one-size fits all approach may not be warranted or appropriate. There are many ways to evaluate capture and a multiple lines-of-evidence approach helps to ensure that groundwater capture and the correlated containment and cleanup objectives are being met. This presentation will provide examples from various federal, state, and voluntary remedial action sites on groundwater capture evaluation each with differing levels of complexity related to hydrogeology, system design, and contaminant types. The approaches and methods used will be discussed and outcomes evaluated. General project costs for each of the types of evaluations will be provided to illustrate level of effort versus site complexity.

Heat Enhanced Hydrolysis

Gregory Beyke, PE
Electrical Resistance Heating (ERH) provides two main mechanisms of contamination removal: vaporization and degradation. While many people are familiar with using ERH for contaminant source area remediation, ERH can also enhance hydrolysis. Hydrolysis is a key mechanism of contaminant degradation that breaks contaminant chemical bonds through a reaction with water. Hydrolysis occurs through either a water substitution or elimination reaction pathway. Hydrolysis is a reaction in which a molecule is cleaved in two by the addition of a water molecule.

Some hydrolysis reactions can be faster at high or low pH (alkaline or acidic). Some compounds undergo rapid neutral hydrolysis that is independent of pH. In addition, elevated temperatures speed up the hydrolysis reaction rate defined by the Arrhenius equation. ERH has been used as the method for temperature increases to escalate the rate of hydrolysis.

A half-life is how long it takes for half of a compound to be destroyed through the hydrolysis reaction. Seven half-lives produce 99% destruction; ten half-lives is 99.9% destruction. A half-life faster than 10 days is ideal and half-lives as long as about 40 days are still fast enough to be cost-effective.

Thermally enhanced hydrolysis is generally the most cost-effective remediation method for halogenated alkanes and many fumigants and pesticides. Thermally enhanced hydrolysis is also an important degradation reaction for pesticides, TNT, RDX, and trace amounts of Mustard Gas. ERH can now provide a reduced cost solution for heat enhanced hydrolysis of contaminants in soil and groundwater.

Research behind heat-enhanced hydrolysis of energetics and field case studies will be presented.

Impacted Groundwater to Drinking Water: Large Potable End Use Groundwater Remediation System Design & Permitting

Kirk Craig, P.E.
In drought stricken areas such as the southwestern United States, where populations are predicted to continue to increase significantly for decades to come, the scarcity of available drinking water is an ever-growing threat. Today in California, heavy fees are imposed on impacted groundwater that is extracted and not used as drinking water or restored and reinjected into the aquifer. This session will present the current design and permitting requirements associated with a 2,000 gallon per minute groundwater extraction and treatment system (GETS) in California. The GETS will remediate several contaminants by utilizing a complex interaction of treatment technologies including granular activated carbon for VOCs, ion exchange resin for perchlorate, advanced oxidation for 1,4-dioxane and reverse osmosis for treatment of total dissolved solids and selenium. In addition to cleaning up impacted groundwater, the GETS will serve as a valuable new potable water supply that will decrease the region’s reliance on imported water. Due to the site’s location and the end use of the GETS, numerous local, state and federal permitting requirements are associated with the system design, construction and operation of the system including permitting under the California Division of Drinking Water’s 97-005 Policy. The extensive 97-005 permitting process is required due to the end-use of the GETS as potable water.

This presentation will then discuss where and why drinking water end uses for impacted groundwater are applicable to urban areas. It will touch upon what specific interests should be considered with respect to reclaimed groundwater, whether state-specific regulatory guidance should be developed and what we can learn from the associated policy implemented by California.

In Situ Bioremediation Optimization in Fractured Bedrock using 3D Visualization and Analysis

Eric Dieck
Previous operations at a former industrial site have contributed chlorinated volatile organic compounds (CVOCs) and 1,4-dioxane to a mixed, 132-acre plume in a fractured shale bedrock aquifer. An in situ bioremediation program was implemented in the source area. 3D visualizations of the hydrogeologic setting and analyte spatial data were generated in Earth Volumetric Studio (EVS) software to gain a better understanding of contaminant migration pathways and remediation performance.

An accurate conceptual site model (CSM) was constructed in EVS displaying the bedrock stratigraphy and fracture network. Prior to remediation, a dye tracer test was conducted to provide further understanding of the fracture network and contaminant transport to improve remedial design. 3D models were generated to document the time elapsed dye distribution and transport within fracture regimes. The remedial approach was developed to accommodate observed groundwater velocities and target the preferential pathways identified during the tracer test. 3D visualization and analysis were performed on the contaminant mass and distribution, amendment distribution, and redox conditions. Modeled contaminant plume volumes in EVS were also used for mass calculations over time, providing a quantitative assessment of biodegradation.

Simultaneous display of both the hydrogeologic framework and groundwater chemistry data provided both a qualitative and quantitative assessment of bioremediation performance. 3D visualization illustrated contaminant migration along the fractured bedding-plane partings and tectonic fractures, position of subcropping discrete fracture zones with respect to source areas and injections, and evolving redox conditions. Delivery of amendments to targeted pathways and source areas within the fracture network was visually confirmed through 3D display. Mass reduction and dechlorination were assessed using the 3D volumetric contaminant and daughter product plume models. The ability to display geochemistry data within a 3D hydrogeologic setting provided a powerful tool identifying active biodegradation zones and assessing hydrogeologic conditions promoting or inhibiting the remediation of the source area.

Iterative High-Resolution Site Investigation and Remediation

George Losonsky, PhD, PG
Subsurface investigation and in situ remediation technologies have historically been linked. The limitations of conventional drilling technologies led to investigations yielding insufficient data density to characterize site heterogeneities, and remediation systems with insufficient numbers of delivery points accurately placed to overcome impediments to site remediation imposed by heterogeneity. The demand for cost-effective remedial strategies has spawned an expanding array of direct push technology (DPT) tools for both investigation and remediation. Geophysical and hydrogeologic measurement tools combined with discrete sampling allow geoscientists to collect high resolution site characterization (HRSC) data and develop an enhanced conceptual site model (CSM) that accurately reflects transport and storage properties of contaminants in soil and groundwater. Subsequent refinement of the CSM using high resolution data allows remediation geoscientists to target the contaminant mass adequately within the full array of porosity and permeability textures common in both naturally deposited and anthropogenic formations.

While a complete HRSC in advance of remediation is an appropriate goal and defines an environmental management paradigm shift, many legacy, abandoned, and underfunded sites do not offer the luxury of this approach. Iterative cycles of site characterization, CSM refinement and remediation become fruitful when implemented using high density data and DPT investigative tools.

An example site in Louisiana has been the subject of iterative investigations which identified a retail gas station as the source of a petroleum hydrocarbon plume in groundwater seeping into and impacting a down-gradient stream. A dense DPT grid of in-situ chemical oxidation (ISCO) injection points near the stream bank identified localized pockets and channels of non-aqueous phase hydrocarbons not easily discernable using a traditionally drilled network of monitoring wells. Pressure and flow monitoring allowed injection of large volumes of oxidant into heterogeneous sediments. Data collected throughout the remediation effort led to a revised CSM and a cost-effective remedial strategy.

Preventative Groundwater Treatment - Aggressive Source Area Chemical Oxidation

Patrick Hicks
An aggressive source area chemical oxidation application was used as a preventative measure for continuing groundwater contamination at a former bulk fueling facility. Historical operations since the 1940’s resulted in wide-spread distribution of primarily fuel hydrocarbons. Initial remedial investigations comprised of 44 borings to a depth of 7.6 m revealed contaminant mass distribution was restricted primarily to surface soils. However, the contaminant mass was distributed over a relatively large (750 sq m) area of surface soils, potentially endangering the shallow groundwater quality beneath the area due to percolating rainfall. The area could not be addressed with excavation as active rail spurs straddle the east and west boundaries. Total Petroleum Hydrocarbons Diesel range (TPH-D) concentrations in surface soil approaching 14,500 mg/kg was the primary focus for contaminant mass destruction.

A corrective measures study recommended application of In Situ Chemical Oxidation (ISCO) using activated Klozur SP sodium persulfate to destroy residual TPH-D mass. A Soil Oxidant Demand (SOD) test was performed on soil and groundwater from the site to ensure sufficient oxidant would be applied to address both the non-target and target demands. Appropriate permitting for injections was secured. Preparation of field equipment, including injection well installation was completed prior to injection. The first injection of approximately 94,635 liters of 20% Klozur SP and 20 % NaOH solution was performed in 2016, followed by monitoring of oxidant persistence for 60 to 90 days. Subsequent TPD-D monitoring indicated a concentration reduction between 50% and 95% in treated soils. The TPH-D mass reduction was more pronounced along the perimeter of the targeted injection area. A second round of ISCO injections focused on the remaining TPH-D mass is planned, and results will be presented.

Remediating the Largest Superfund Site in the Country – the Main San Gabriel Basin

Ken Manning
The San Gabriel Basin is the largest USEPA groundwater Superfund site in the country. With the groundwater basin providing 90% of the drinking water supply to 1.4 million residents, and an extended drought limiting basin supply, remediating the five separate areas each with distinct contaminant signatures is top priority for the region. The ongoing multi-decade effort required an innovative approach to remediation that included the first perchlorate treatment facility in the nation to be permitted for drinking water supply. Additionally, these efforts required water agencies to be the first to navigate a strict, newly formed California policy for permitting extremely impaired sources entitled Policy 97-005. Several of the large scale 97-005 cleanups projects required the use of the multiple technologies for treatment of contaminants including VOCs, perchlorate, NDMA, 1,4-dioxane, CrVI and 1,2,3 TCP. 

Thinking Outside the Boxcar: Combined Remedies using Single Application of Multi-Functional Amendments

Matthew Burns
The combined remedy approach to groundwater remediation optimizes contaminated site cleanup as measured by technical efficacy and sustainability. Regardless of the potential for improving site cleanups, there are several obstacles limiting the implementation of combined remedies. The obstacles primarily stem from an inability of liability owners to easily determine if economic costs are synergistic or additive and from regulatory hesitancy to codify needed timing and technology sequencing flexibility within design documents. These obstacles can often be circumvented by employing multi-component and multi-functional remedial amendment formulations delivered with a single application.

 

Case studies are presented that demonstrate efficacy of this combined remedies approach. The sustainability of the approach is also assessed by evaluation of economic viability, social productivity and environmental protection. The case studies include combined abiotic and biotic degradation of chlorinated ethenes and ethanes compounds, combined reductive and microaerophilic treatment of chlorinated benzenes, and combined chemical oxidation and biodegradation of petroleum compounds. Case studies are supported with conventional concentration trends and advanced diagnostics including compound specific isotope analysis (CSIA) and genetic-based molecular biological tools (MBTs).

Use of Permeable Reactive Barrier to Bioremediate a Petroleum Hydrocarbon Groundwater Plume

Eric Henry, LEP, LSP
Circa 1980s release of gasoline at a large throughput fueling facility at an Interstate Rest Area produced a groundwater plume which impacted a downgradient wetland area. Previous remediation efforts at the facility sufficiently addressed petroleum impact to the vadose zone but the groundwater plume persisted. Dissolved volatile petroleum hydrocarbons (VPH) were detected in monitoring wells located at a wetland area approximately 200 feet from the sources (underground storage tank systems). The natural reducing conditions at the wetland were exacerbated by the petroleum hydrocarbon groundwater plume resulted in the concentration of arsenic and beryllium in shallow soils. Remediation of the groundwater plume was complicated due to the active fueling operation and presence of approximately 25 feet of fill material [boulders, blast rock, and concrete from the circa 1960s construction of the Interstate highway] overlying the saturated zone. A permeable reactive barrier (PRB) was installed orthogonal to groundwater flow approximately 100 feet up-gradient of the affected wetland to bioremediate the groundwater plume. A mixture of granular activated carbon product (BOS 200®), calcium sulfate, and water was injected throughout the saturated zone to establish the PRB. Post-installation monitoring data indicate that the remedy is performing as designed. The conceptual site model, PRB design and installation data, and approximately 18 months of post-PRB installation performance monitoring will be presented.

Groundwater and Integrated Water Management

Accessible County Level Water Resource Fact Sheets: Experiences from Louisiana

Vincent White
Accessible water-resources data and analysis are essential for the proper management of a community’s water resources. Knowledge of water availability, quality, development potential, and the impact of development is necessary for water-resources planning and protection. Water-resources information for Louisiana and many other states are presented in a variety of technical reports, each with a particular geographical scope and topical focus. Information in these reports often includes the whole state or a multi-county area. Basic information on surface water, ground water, and water quality in a single county of interest often has to be gleaned from several reports, many of which may be in limited circulation and difficult to locate. Many stake-holders and decision-makers are often not in a position with respect to resources and time-required to research and synthesize the available literature. Furthermore, difficulties in acquiring and analyzing data runs the spread from an apparent or actual absence of information for a county to an information overload induced by reports conducted using different terminology in slightly different study areas in different decades. Concise summaries are needed to provide the information needed to make decisions about current and future development which meets the needs of local stakeholders of all segments and avoids the excesses of under-information and over-information.

The Water Resources of Louisiana Parishes project is about 70 percent finished achieving this goal with the publication of an online and hard-copy fact sheet for each of Louisiana’s 64 parishes (equivalent to a county). These 64 publications, which are generally 6 pages in length, provide summaries of groundwater and surface-water availability, water quality, current and historical water usage, and an extensive list of references for readers looking for more in-depth treatments of the topic.

A Southern California Water Market- Managing in a Time of Scarcity

William Greg Hamer, CHG, CEG
California's recent severe drought along with historical population growth has increased the need for creative water supply solutions. As the need for reliable water supplies increases so does the cost per acre-foot. In response to this, new and creative arrangements are being developed between water users and purveyors. Informal and formal water markets are increasing. In the arid Mojave River Basin in southern California, a growing water rights market provides a good solution to match supply with demand.

Adjudication of the Mojave River Basin is helping to reduce groundwater overdraft. Under the adjudication, nearly all groundwater pumpers have had to gradually reduce their pumping. As agricultural, municipal and industrial water users are faced with reduced supplies, a local water market has developed for both annual water allotments and permanent water rights. The value of annual and permanent water rights are related to the cost of imported water, which is also available in the basin, although in limited supply. The Mojave water market is helping to promote better planning for droughts, water conservation, and increased water system reliability.

Disposal of Produced Water into Depleted Oil Reservoirs: Economic Use and Risk of USDW Pollution

Javier Vilcaez
Produced water from unconventional hydrocarbon reservoirs is characterized by high concentrations of total dissolved solids (TDS) and variable concentrations of heavy metals whose concentrations in most cases largely exceed EPA maximum contaminant levels (MCLs). However, produced water is also characterized by containing indigenous microbial communities which are well adapted to extreme deep subsurface (high temperate, pressure and salinity) conditions. Disposal of produced water into depleted oil reservoirs and deep saline aquifers are two common practices to prevent the pollution of underground source of drinking water (USDW) by contaminants contained in produced water. We are developing a new method to stimulate microbial crude oil biodegradation via methanogenesis in depleted oil reservoirs injected with produced water. This method has the potential to enhance the recovery of oil from depleted oil reservoirs. Its potentiality will be discussed based on our experimental results showing that the addition of stimulating nutrients to produced water of certain microbial composition can trigger crude oil biodegradation via methanogenesis if such produced water is injected into depleted oil reservoirs of different microbial composition. The risk of USDW pollution by heavy metals due to the possible upward migration of disposed produced water into deep saline aquifers will be discussed based on our experimental results showing that the mobility of heavy metals is much higher in brine than in freshwater and that salinity promotes the desorption of heavy metals in deep carbonate saline aquifers.

Groundwater and Global Energy Security

Yu-Feng Lin, Ph.D., P.G., GISP
Groundwater extraction for irrigation, industry, and drinking has a considerable impact on global energy consumption. In Punjab Province, India, up to 50% of electricity in the growing season powers groundwater pumps. In China, CO2 emissions from groundwater extraction is >0.5 % of the national total. With an expanding global population, and increased living standards, larger urban areas and anticipated economic growth, significant stress will be put on maintaining sustainable energy generation and use.

How best to deal with these challenges requires reassessment of energy policy, infrastructure, and efficiency. The U.S. Energy Information Administration reports production of renewable energy is the fastest-growing sector and will be for many decades to come. Production and utilization of fossil fuels is often limited by their geographical distribution. In contrast, geothermal energy is distributed more widely in volcanic rocks and groundwater. Estimated total amount of heat contained in hot dry rock is ~10 billion quads, 300 times greater than fossil fuels. Some studies have predicted that the growth of geothermal energy could be average 6.5% annually to 2040.

Heating, ventilation and cooling of buildings is a significant contributor to greenhouse gas emissions (~33% worldwide). Energy usage in buildings accounts for 34.8% of the total in the US and 27.5% in China. To power a building requires energy be converted into different forms, mechanical energy to electricity to heat, and potential energy to mechanical energy, electricity to heat, nuclear energy to mechanical energy to heat, etc. These conversions result in significant energy losses that ultimately lower overall efficiency. However, the use of groundwater (aquifers) to store and transfer heat would be much more efficient, but require the installation ground-source heating exchange system. To address energy efficiency issues, the role of groundwater in global energy security will be evaluated.

Ground Water Modeling Analyses to Inform Aquifer Management Decisions in the Nebraska Panhandle

Thad Kuntz, PG

In the Nebraska Panhandle, two modeling efforts have been developed to provide decision support information, tools, and analyses of water resources management decisions. The Western Water Use Management Modeling covers the Southern Nebraska Panhandle and was created for two Natural Resources District's (NRD) and the Nebraska Department of Natural Resources (NeDNR). The Upper Niobrara-White Ground Water Model covers the Northern Nebraska Panhandle and was created for the Upper Niobrara White NRD and the NeDNR. The NRDs are governmental entities with locally elected Board of Directors that are responsible for regulating and managing ground water pumping over several counties.

These modeling efforts encompass nearly the entire Nebraska Panhandle between the Wyoming, Colorado, and South Dakota borders. The primary surface water bodies within the models are the North Platte River, South Platte River, Niobrara River, and Lodgepole Creek. The principal ground water system in the area is the High Plains Aquifer that locally consists of alluvial, aeolian (Nebraska Sandhills), Ogallala, and Arikaree aquifers. Each modeling effort utilizes three partially integrated models that consist of a surface water operations model of the North Platte and Niobrara Rivers; a regionalized soil water balance model to determine consumptive use; and a ground water model to simulate the ground water/surface water system and the effects of well pumping.

Recent analyses of the Ogallala and Arikaree aquifers have been conducted using the ground water models to simulate different ground water pumping allocations and climate scenarios which provide estimates of future aquifer drawdown, saturated thickness, and percent saturated thickness used. Ultimately, the results of these analyses are used to help educate and inform the public, open up a dialog on aquifer management, and provide the NRD Boards with information to aid their aquifer management decisions to determine future ground water pumping allocations.

Impact of Awareness-Raising and Citizen Pressure on US Groundwater Governance

Andrew Stone
Who make decisions about how groundwater resources are managed? Who has water allocation authority or the authority to restrict pumping? By what legislative or legal process was that authority obtained? Groundwater governance is a dynamic and evolutionary process involving collective influences on policy and management. Decisions about the use of groundwater are rooted in political structure, historical precedent, hydrogeological conditions, legal rights and vested interests. Groundwater governance does not start from a blank page but is built on past influences.

In recent years, citizens, community interest groups, non-governmental organizations (NGOs), and professional associations have had considerable influence on the way in which groundwater resources are managed. Greater public awareness about the significance of groundwater has been a motivating force on public involvement. Issues such as hydraulic fracturing, bottled water and emerging contaminants have forced elected representatives to pay attention to resource protection and allocation policies.

Information, awareness and education about groundwater, much of it provided by NGOs and professional associations, has helped widen the suite of groundwater stake-holders. It is no longer just senior staff in state and federal agencies or the direct vested interests of groundwater end-users who have the ear of the political policymakers. Individuals and organizations with environmental, ecological, health related and socioeconomic priorities have shown they can impact decisions about groundwater use and source protection.

Groundwater governance strategies are principally developed to achieve sustainability while protecting a diverse range of vested interests by balancing economic, environmental and social issues within institutional political frameworks. Many agencies and units of government play a role in creating, implementing and policing groundwater regulations which are the basic building blocks of groundwater governance. Citizen pressure and the interventions of associations and NGOs can have a major influence on regulations and policy.

Implementing SGMA – An Update on California’s Foray into Groundwater Regulation

Leslie Dumas, P.E.
In November 2014, the California governor signed the Sustainable Groundwater Management Act (or SGMA), 100 years after the passing of the Water Commission Act of 1914 which established California’s surface water rights system. Effective January 1, 2015, SGMA establishes a new structure for sustaining groundwater and, for the first time, attempts to manage groundwater use in the State outside of the legal courts. While the goal of SGMA is unmistakable, the Act itself provided a clear timetable for implementation along with a mixed bag of useful tools for sustainable groundwater management and conflicting directions which have the potential to stymie implementation. Now two years into the process and facing the first major regulatory deadline, State regulators are scrambling to develop and clarify guidelines and regulations while water agencies and public entities grapple with the implications of the Act, work to overcome differences to form the required governance structures for sustainable groundwater management, and initiate tentative steps towards meeting key sustainability deadlines. In general, SGMA compliance consists of 6 key steps: (1) prioritizing basins; (2) identifying basins in critical overdraft; (3) determining if basin or subbasin boundaries require modification; (4) developing Groundwater Sustainability Agencies; (5) preparing Groundwater Sustainability Plans; and ultimately (6) sustainably managing California’s groundwater basins. When completed, the Groundwater Sustainability Plans developed under SGMA will be California’s first truly integrated water resource plans. Presented herein are summaries of progress made to date relative to complying with SGMA, problems that have arose and solutions suggested, and an assessment of what SGMA implementation will really mean for California as it tries to achieve groundwater sustainability by the year 2040.

Improving Groundwater Management in Myanmar through Capacity Building

Michael Grzybowski
Myanmar is a former military state known as Burma, which was closed for the last half century and recently opened in 2011. Myanmar has been developing fast and the lack of access to basic information on hydrogeology and urban services has resulted in pollution of their shallow aquifer systems. An additional issue is there are no formally trained hydrogeologists within the country. Thus, the objective of this research project was to conduct a hydrogeological reconnaissance and to take the first steps towards capacity building in hydrogeology. The City of Mandalay is located within the flood plain of the Irrawaddy River. The inhabitants of this area depend primarily on both dug and tube wells as their source of water (drinking, cooking, and washing). Many of these wells are located in close proximity to anthropogenic sources of contamination, such as wastewater. Thus, an understanding of the hydrogeology and the interaction between this alluvial aquifer and the Irrawaddy River is critical in order to better manage their groundwater. The sand and gravel alluvial aquifer has a high hydraulic conductivity (K) based on three slug tests and numerical modeling using the analytical element model, GFLOW (Haitjema, 1995). The ranges in K are from 2 meters/day to 67 meters/day. Thus, the first task was to develop a conceptual hydrogeological model in order to have a basic understanding of the local hydrogeology, and delivering it through open-source platforms that would allow our colleagues in Myanmar to build on it. Through a grant from the National Groundwater Association’s Developing Nations Fund, a two week workshop was conducted. Open-source software such as QGIS, GFLOW, and Topodrive were used as potential tools that can help facilitate the development of a capacity building program in hydrogeology.

Locating and Monitoring Private Domestic Wells to Improve Public Health

Fran Kremer, PhD
Private domestic wells are a source of drinking water for 15 percent of the US population. These water sources have little to no water quality monitoring but potentially significant health impacts. An approach has been developed to improve methods for estimating areas with high reliance on private domestic water wells, from a national to local scale. To address the potential for point source contamination, a GID application has been developed to relate sources to receptors. Additionally, a pilot is being developed to crowdsource data using citizen science to: monitor water quality in wells, including the use of sensors; input data in a geospatial platform; assess potential sources of contamination; develop recommendations to limit well contamination. This will provide useful temporal and spatial data on localized and watershed-level impacts to this drinking water source. The data will not only assist homeowners in protecting their water supply but also provide key data for local, state, and federal agencies in improving watershed management and public health.

Maximizing Groundwater Sustainablity in a Highly-Urbanized Southern California Groundwater Basin

David S. Gould, P.E.
In Southern California, increasing demand for water is forcing water agencies to look harder at the integration of surface and groundwater resources. In recent years an extended drought period has resulted in declining groundwater levels in the Verdugo Groundwater Basin in Southern California and reduced water supply reliability. Crescenta Valley Water District (CVWD) conducted a detailed Feasibility Study to evaluate the potential for artificially recharging the Basin to increase the amount of groundwater in storage. The results of the study will help improve the reliability of the water supply for thousands of residents in the area. The feasibility study received special notice from the California Department of Water Resources as an exemplary project. Surface water flows, including stormwater, were identified as a viable water source for recharge. Potential recharge locations, required recharge facilities, and administrative and regulatory opportunities and constraints were considered in the development of specific alternatives. Alternatives were then ranked and a conceptual design for the preferred alternative was prepared. The preferred alternative is for recharge of storm runoff using subsurface infiltration galleries installed beneath a local park. Key challenges to recharge include wide variations in surface water flow rates following storms (large peak flows would be difficult to capture), high turbidity levels that can clog recharge facilities, and varying water quality, as surface runoff from urban areas may contain oils, metals, and fertilizers. These challenges were considered and addressed in the development of the preferred recharge alternative. CVWD monitored surface water flows and water quality and developed an initial recharge gallery design. Inflatable rubber dams will be used to divert flows from storm channels to recharge facilities. Implementation of the recharge program will improve water supply reliability and groundwater quality in the Basin and form a key component in the overall Basin water resources management.

Opportunities and Challenges for Incorporating Threshold Effects in Linked Surface/Groundwater Management

S Andrew McGuire
The accelerating impacts of landuse changes driven by development in areas outside of urban centers have highlighted the imperative for integrated management of surface and groundwater resources. Although judicial rulings have provided government agencies authority to utilize the potential impacts of groundwater reduction on surface waters to inform management decisions, these agencies are not equipped with standardized processes to gather the information necessary to exercise their authority. This gap has created regulatory uncertainty and fostered conflict around linked surface and groundwater resources (LSGR) management. Lake Beulah is a multi-basin marl lake in Walworth County, Wisconsin where concerns over the potential impact of groundwater withdrawal on lake water quality resulted in a lengthy legal battle between lake residents, local government, and the Wisconsin Department of Natural Resources (WDNR). In this study we first employed the US Army Corps of Engineers reservoir/lake model BATHTUB in combination with geochemical model PHREEQC to identify an impact threshold value for groundwater reduction for Lake Beulah. Groundwater withdrawal reduces the resilience of Lake Beulah to nutrient loading through the established Ca2+ - P co-precipitation mechanism, and effects were not uniform across basins. It remains to be seen as to whether state agencies in Wisconsin will utilize decision frameworks in making management decisions in LSGR systems. Ongoing challenges to court rulings and interpretations of agency authority continue to obfuscate whether WDNR will be allowed to consider the cumulative effects of multiple wells in assessing significant adverse impacts. A critical discussion of the utility of decision support frameworks outlines the need for boundary work to identify how it can be used to effectively govern LSGR.

Providing Accessibility and Usability of MODFLOW Models for Water Managers

James Schneider, Ph.D.
Graphical user interfaces (GUIs) for the construction and calibration of a groundwater model are widely available and tailored to be easily understood by trained hydrogeologists. However, with limited, highly specific examples, these models are not delivered to the water manager with a related GUI that would allow for the full integration of the model into water management activities. Rather, models have traditionally been developed and used to conduct a single set of model scenarios that are the basis for a report that the water manager receives - this report is destined to gather dust on a shelf. We envision a paradigm shift in the way groundwater models are used to manage water. Models can and should be delivered with an easy-to-use GUI that can be used many times over to keep the model up-to-date and can run as many hypothetical scenarios as the water manager can dream up.

There are two fundamental requirements for this approach: 1) an intimate understanding of the water manager’s objectives for constructing the model, and 2) a very detailed understanding of the format of specific MODFLOW packages that may be incorporated into the model, and the ability to produce computer code that will manipulate the data in these packages. This is in addition to the traditional components that generally include the ability to construct and calibrate a groundwater model that is scientifically defensible.

This presentation will explore several projects that we have completed in Nebraska that have put water managers in the “decision making” driver’s seat. It has also empowered them with a tool that can keep their models current. They are now able to answer management questions in real-time in their own office faster and more efficiently than if they employed the hydrogeologists necessary to otherwise conduct these evaluations.

Toxic Levels of Lead and Copper in Groundwater Can Be Caused by Stray Electrical Current

Todd Giddings, Ph.D., PG
Throughout Pennsylvania and most other states, both lead and copper are not usually found in groundwater at toxic levels. News from the Flint, Michigan corrosive water crisis has caused homeowners with a water well to test their tap-water. A few homeowners and commercial building owners are finding toxic levels of lead and copper. This presentation will explain how stray electrical current flowing through their water piping is causing the toxic levels of lead and copper found in their tap-water, when their source groundwater is not corrosive and contains non-detect levels of lead and only trace levels of copper. Stray electrical current is a little-known cause of corrosion that dissolves lead from solder and dissolves copper from the piping. Several case-history examples will be used to show the major stray electrical current causes and some corrective actions. The electrochemical process that dissolves the two metals will be explained.

Using High Resolution, High Accuracy Topography Data to Improve Water Management on the High Plains Aquifer

Douglas Hallum, P.G.
The Nebraska GIS Council has been on a decade long mission to collect and employ discrete return topographic LiDAR in Nebraska for a variety of purposes, including water management decision-making. Nebraska will soon deploy select LiDAR deliverables publicly, and is helping farmers, researchers and regulators utilize gathered LiDAR data to promote effective management of Nebraska’s water resources. This talk explores select case studies within the High Plains Aquifer of Nebraska where LiDAR-derived topography is being utilized to improve water management decisions. Selected studies include examples where: agricultural water research is improved by defining sub-parcel scale watersheds that can be used to better interpret and understand the results of scientific studies, irrigation of crops is improved by mapping slope at high spatial resolution that when combined with other data, improves irrigation effectiveness and can help minimize groundwater pumping and mitigate input costs, and integrated water management decisions are improved by helping to better observe and understand likely consequences of water management decisions on ranching operations.

Invited Hydrogeophysics Papers from SAGEEP

John Jansen, Ph.D., PG, PGp

Applied Geophysics to Create Insight and Reduce Uncertainties

Peter Thomsen
Delineating the architecture of aquifers and aquitards is essential when modelling and managing groundwater resources. The geophysical method time-domain electromagnetic (TDEM) has over the last two decades shown to be an efficient tool in areas with sparse data coverage.

Water scarcity due to climate changes and over abstraction make it very important to establish groundwater sustainability plans based on accurate hydraulic flow models. Often scattered and uneven spatially distributed boreholes and general geological maps are the only information available knowledges of subsurface conditions. Geophysical data, including TDEM, are therefore used in order to minimize model uncertainties.

TDEM is a non-intrusive, effective and cost-efficient method for obtaining information about the subsurface to 400m and sometimes even deeper. With the TDEM method, the hydrogeology can be described as variations in electrical resistivity. By comparing the resistivity with information from boreholes, the distribution of the different sediments can be described and thus create a valuable base for defining the basin boundaries or setting up flow models.

Due to high contrast in conductivity of fresh and brackish groundwater, the TDEM method is particularly suitable for mapping the mixing zone between fresh and saline water, which is important when sustainably managing groundwater abstraction in coastal areas or well fields influenced by saltwater intrusion.

When designing Aquifer Storage and Recovery (ASR) solutions, the TDEM method can be used for delineating areas having hydraulic conditions suitable for infiltration of surface water or treated waste water. In same way, data can help minimizing uncertainties when designing where to extract recharged resources.

The presentation will showcase different case studies where the TDEM method has played a key role in creating insight in the hydrogeological conditions. The method has been applied since the early 90’s and is the basis for the development of airborne systems for large scale mapping purposes.

Characterizing the Spiritwood Valley Aquifer using Helicopter Time-Domain Electromagnetics

Jean Legault
Buried valley aquifers, consisting of permeable sand and gravel deposits in eroded bedrock valleys, are important sources of groundwater supply in many regions of the United States and Canada. Buried valley aquifers have been difficult to define because they are often partially eroded, have complex lithology and are hidden by other shallow sand and gravel aquifers within thick glacial overburden. One example of a buried valley aquifer is the Spiritwood system that is an important supply of water both in the US and Canada.

Investigations of the Spiritwood aquifer in southern Manitoba by the Geological Survey of Canada and other workers, have demonstrated the value of helicopter time domain electromagnetic (TDEM) surveys in aquifer mapping and characterization using the contrasts between Quaternary glacio-lacustrine sand-gravels (high resistivity) that are relatively permeable and clay-tills (low resistivity) that are relatively impermeable, as well as the deeper, much less resistive Cretaceous Pierre Formation Shale basement rocks. This success provided the impetus for the North Dakota State Water Commission to fly a VTEM helicopter EM survey in the Jamestown, ND region in October, 2016.

The VTEM data collected over the Spiritwood-JT block allowed for geological mapping from near surface to depth, in spite of relatively weak resistivity contrasts (<10X). These data were inverted with a layered-earth algorithm to produce resistivity-depth models. These models were able to resolve the location and depths to the top and bottom of the Spiritwood aquifer throughout the central portion of the block providing more detailed pictures of the aquifer’s geometry. In addition to resolving the main aquifer as well as its deeper channels, the VTEM data and models highlighted several smaller, previously undiscovered aquifers that cross-cut/branch-off from the main Spiritwood channel. These are interpreted as probable transverse low-K barriers that were apparent from the existing test drilling and aquifer testing.

Combined use of Transient Electromagnetics, Passive Seismic, and Nuclear Magnetic Resonance Methods to Characterize an Unconsolidated Aquifer on Cape Cod, Massachusetts

Carole D. Johnson
Very few deep boreholes exist near the coast on Cape Cod. In 2016, the U.S. Geological Survey drilled a borehole to bedrock in Falmouth, Massachusetts, to improve understanding of the glacial history and hydrologic properties of the Cape Cod aquifer. Prior to drilling, candidate sites were investigated using transient electromagnetics (TEM) and passive seismic horizontal-to-vertical spectral ratio (HVSR) methods to estimate depths to bedrock and the freshwater/saline-water interface. At the Falmouth site, the TEM results indicated saline water at 49 m below land surface (bls) and bedrock at 92 m bls. The HVSR results indicated bedrock at 88 m bls.

The borehole was drilled using the sonic drilling method, requiring injection of freshwater during drilling. Bedrock was encountered at 93 m bls. The borehole was completed to bedrock using polyvinyl chloride (PVC) casing. Differencing of electromagnetic (EM) logs collected ~10 and 100 days after drilling delineated intervals where formation water displaced drilling fluids in discrete zones of higher porosity and k. These zones were confirmed with borehole nuclear magnetic resonance (NMR) logs that provided water content and k estimates every 0.5 m. NMR results indicate that porosity ranges from 0.19 to 0.42 with an average of 0.33, and k ranges from 0.5 to 405 meters per day (m/d) with an average of 54 m/d, results that are consistent with local- and aquifer-scale measurements. HVSR- and TEM- derived depths to bedrock were within 5 and 1 percent of the drilled depth, respectively. The TEM-estimated saturated thickness and fresh/saline-water interface was within 2 percent of the contact interpreted from the EM logs.

These results demonstrate the utility of combined TEM and HVSR methods for mapping the subsurface conductivity structure and thickness of unconsolidated aquifers and the efficacy of NMR logging to provide continuous logs of hydrologic properties in PVC-cased boreholes.

Estimating the Distribution of Hydraulic Properties Using Resistivity Models Derived from Airborne Geophysics

Andrew Genco
The Ramotswa transboundary aquifer is shared between South Africa and Botswana. An extended drought throughout the region has increased the need to understand this shared water resource. An airborne electromagnetic (AEM) survey was conducted to generate new information about the aquifer in order to support water security and facilitate its sustainable management between the two countries. Using the AEM survey results, the three-dimensional spatial distribution of the dolomite aquifer was interpreted and estimates of the aquifer’s distribution and range of porosity and hydraulic conductivity were made. Porosities throughout the dolomite were estimated using a modified version or Archie’s Law specific to carbonates. Transmissivity values were previously calculated in the Ramotswa Well Field, from both constant rate and step pumping tests, and were used in conjunction with resistivity data, extrapolated over the well field, to calculate the relationship between hydraulic conductivity and resistivity for the aquifer. Minimal hydraulic data was collected on the ground within the study area, presenting a challenge for relating the electrical resistivity data to hydraulic properties, especially over a large and heterogeneous aquifer. The distribution of hydraulic conductivity in the aquifer was geoelectrically estimated using a generalized log-log linear electrical-hydraulic correlation function, the slope of which is dependent on the geologic and geochemical environment.

Identification of the Optimal Locations for Artificial Infiltration

Max Halkjaer
pls note: we would like to be part of the special session on geophysics. Reference John Jansen

text:

Inhomogeneity of topsoil often exceeds what can be verified by boreholes. Non-invasive Geophysical investigations can efficiently increase our knowledge and thereby minimized structural uncertainties in near surface hydraulic modelling.

High resolution geophysical multi coil Ground Conductivity Meter DualEM421 investigations have shown to be a successful tool for detailed mapping of the soil conductivity within the upper 5-7 m. Combined with shallow boreholes, hydraulic head measurement and simple infiltrations test, detailed description of the hydraulic conditions of the near surface groundwater is obtained. Surveys can be scaled according to size of area and needs for resolution.

Experiences shows a strong relation between electrical conductivity measured with DualEM421 and geological conditions which again are strong related to hydraulic conductivity obtained by infiltration test e.g. double ring infiltrometer test. Site specific relation leads to significant improvement of data input for near surface 3D geological and hydraulic modelling, and thereby optimizes the assessment of hydraulic consequences for specific LID/SuDS and aquifer recharges solutions.

Knowledge of the spatial distribution of high permeable sand layers and less permeable clay layers is crucial when pointing out the optimum location for artificial infiltration.

LID/SuDS solutions for handling rainwater are often a necessity and an integrated part in the development of urban and suburban areas. Aquifer storage and recovery (ASR) is a commonly used tool for sustainable water resource management. Beside rainwater the reuse and infiltration of treated wastewater is an important source for maintaining water availability in water stressed environment.

Presentation will showcase example from both urban and suburban investigation, where integrated investigation has provided an improved knowledge and minimized uncertified when planning LID/SuDS solutions.

Recommended Basic Borehole Geophysics for Hydrologic Investigations in a Fractured Bedrock Aquifer

Rick A. Hoover, PG
Hydrogeologists do not always receive a great exposure to borehole geophysics within many educational institutions, just as geophysicists do not get a lot of exposure to hydrogeology. Yet an often-heard inquiry from the hydrogeologist starts with “I have a 6-inch casing stick-up, but I don’t know much else about this well…” ending with “is there anything geophysics can do for me?” The geophysical choices can be many, and the answer sometimes depends on the person answering. Using a case history from a fouled groundwater supply well, constructed in the 1940’s, this presentation will look at a classic hydrologic suite of log measurements recommended to help the hydrogeologist understand the well and aquifer. In this particular instance, the well log was long lost to history, along with the well depth, yield, and water bearing zones and lithology. The geophysical investigation was designed to identify basic well characteristics to aid well rehabilitation. The basic logging suite recommended included Temperature, Caliper, Spontaneous Potential, Single Point Resistance, Normal Resistivity (8”, 16”, 32”, and 64”), Fluid Resistivity, Natural Gamma Radiation, Heat Pulse Flow Meter, and Optical Televiewer. None of the geophysical measurements is unusual. However, the combination provides well details and insight into geology and hydrogeology penetrated by this well. This recommended basic suite of borehole geophysical measurements should be included in all fundamental hydrogeologic investigations. The presentation will review the measured results for this well and compare the information to data gathered during the well rehabilitation process.

Seismic Attribute Processing to Find Deep Aquifers

John Jansen, Ph.D., PG, PGp
The scarcity of water in arid and semi-arid regions has increased interest in sources of water much deeper than traditionally considered economic. Many projects have targeted fresh to brackish water sources at depths of 2,000 to over 5,000 feet. In many formations the potential yield of a well varies based on stratigraphic changes making it difficult to predict the potential yield of a given location without more information. The cost of drilling to such depths limits the availability of data and makes developing these resources risky and expensive.

Seismic reflection surveys collect data on the propagation of seismic waves to depths of several thousand feet. Developed by the oil and gas industry, seismic data can be used to map structural features in fine detail. Modern processing and interpretation techniques can map aquifer units, faults, and other structural features that can control well yield. With a little more processing, the shape of the waveforms can identify changes in the stratigraphy, porosity, and pore fluid characteristics in a unit. Seismic attribute processing can be used to identify permeable features such as narrow channel sand deposits at depths of thousands of feet to target permeable zones.

The cost to acquire reflection data is relatively high, which has limited the application of the method for water supply applications. Fortunately many areas have libraries of existing reflection data from previous oil and gas exploration activities. This data can often be purchased for a few thousand dollars per mile and used to map units that can potentially serve as aquifers.

Several case histories will be presented to demonstrate how modern interpretation methods can be used on 2D or 3D seismic reflection data to map features such as sand channels, faults, and pinch outs in aquifer units and direct drilling programs toward higher yielding sites.

Karst Hydrology

Benjamin Miller

Development Of A Freshwater Lens Assessment Protocol For Karst Islands

Robert M. DiFilippo, P.G.
Karst Islands like those found in the Philippine Archipelago present extreme challenges for stakeholders to manage their water resources in a sustainable manner. Anthropogenic Climate Change, land development, point source pollution and increased population have all combined to alter the water balance on these fragile islands. Karst features, shallow depth to groundwater and the potential for dissolution, contribute greatly to these challenges. Combined, these factors pose an array of complex research challenges. A field reconnaissance, and semi-structured interviews were completed on Bantayan Island in 2016. Drawing upon current groundwater characterization practices the research posits a novel approach for these hydrogeologic environs. With the application of the Freshwater Lens Assessment Protocol (FLAP) credible output for the characterization of the islands groundwater resources will be determined and integrated into an Adaptive Water Resource Management framework, empowering stakeholders to make informed decisions on sustainable abstraction strategies.

Evaluating Best-Practice Capacities for a Carbonate Island Karst Aquifer: Northern Guam Lens Aquifer, Guam, USA

John Jenson, PhD
The Northern Guam Lens Aquifer (NGLA) provides 90% of Guam’s drinking water. Recent modeling results provided insights into how the existing water-production system might respond to new development and natural changes in recharge, but local policy makers and water managers have also asked “What is the ultimate volume of water that could be sustainably withdrawn from the aquifer if we had the best possible production system?” Answering this question requires, first, specifying a best-practice production system—which we define as one that is constructed and operated to deliver maximum production attainable for a given quality standard, constrained, of course, by the available technology and capital. Second, it requires reliable knowledge of the natural limits imposed by recharge and aquifer properties.

We present results from an ongoing modeling study directed at estimating aggregate production that could be achieved by a system of about the same number of vertical wells as in the present system but in which well locations and well-field production are chosen to maximize production for specified standards of salinity. Natural limits are imposed by specifying the same recharge and aquifer properties employed in the recent successful modeling study of the existing system.

Although an ideal production system as defined above may not be feasible in the near term, if ever, an estimate of the total production that could be obtained by such a system for specified salinities provides helpful insights for long-term planning and future decisions regarding sustainable management of the NGLA.

For a Better Understanding and Management of Karstic Aquifers: Characterization of the Properties of the Big Spring Karstic System (Missouri)

Alain Mangin, Ph.D.
The results obtained from the study of karstic systems over the last several decades have clearly emphasized their specificities. These specificities are mainly due to the organization of voids in the karst, which, due to the mechanisms of their emplacement, are distributed in an extremely heterogeneous way. The result is an anisotropic permeability, but above all structured according to their position within the karst massif. Moreover, all the voids do not have the same function with respect to the movement of fluids. In saturated media (saturated karst), some voids (“the drains”) have a transmissive function and ensure the propagation of waters. Other systems that are connected to the drainage give an account of their storage and corresponds to the storage function. These properties result in a highly non-linear hydrodynamic behaviour with all its consequences: sensitivity to initial conditions, high unpredictability, and impossibility of using simple deterministic modelling. Due to the permeability contrasts between drains and ancillary systems, depending on the duration of the events (floods), only parts of the aquifer are involved in the hydrodynamics. Therefore, over time the karstic aquifer possesses a variable geometry.

To better study, exploit, and manage karstic aquifers, a new approach using systemic analysis is currently used by Ramboll Environ. The overall behaviour of the aquifer is no longer considered to be the result of the sum of spatially individualized behaviours, which is assumed and imposed by the differential approach, but as the sum of the interactions of these individual behaviours that most of the time are unknown. The karst is thus conceived as a set of dynamic processes (flows) whose study and understanding must lead to the identification of its properties, allow a description, and ultimately facilitate its exploitation and management. While this concept is easy to understand, and seems able to solve the difficulties encountered, its implementation remains subtle.

The Ramboll Environ approach derives from a philosophy different from the conventional hydrogeological approach and requires abundant robust collection of continuous data, using transducers of the various parameters that monitor the functioning of the karstic aquifer (discharges, water levels, rainfall, etc.). This approach involved the development of a set of methods and high-performance software to extract information from the collected data in order to recognize the physical signatures that are responsible for the observed hydrodynamic behaviour, and thus, whatever the difficulty encountered, including non-linearities, characterize the dynamics of systems and predict their behaviours. These methods are called correlative and spectral analyses, continuous or discontinuous wavelet analyses, rescaled range analysis, fractal or multifractal analyses and attractor analyses.

The application of these analyses to Big Spring, Missouri allowed the establishment of an “Identity Card” of the spring, encompassing all information necessary for an optimal management of the spring.

Hydrogeology of the Finegayan Basin, Northern Guam Lens Aquifer, Guam

Ida Shalilian
The Finegayan Basin of the Northern Guam Lens Aquifer is already well developed, but is expected to undergo additional economic development in the near future, with expansion of US military activities on Guam. The purpose of this study was to better understand the natural plumbing that controls groundwater recharge, transmission, and discharge of the basin, preliminary to exploration for new groundwater production wells. A field survey showed that the single greatest concentration of freshwater discharge from the northwest coast issues from a coastal cave that lies precisely at the end of a major fault. An initial estimate suggested discharge from the cave of up to 5.3 Mgal/day, which would constitute of 32% of basin recharge. Given the 4.8 Mgal/day of withdrawal from the basin, discharge of 5.3 Mgal/day would further constitute 45% of the remaining total basin discharge of 11.7 Mgal/day. The calculated hydraulic gradient along the fault for 5.3 Mgal/day discharge, assuming hydraulic conductivity of 75,000 m/d along the fault, a minimum width of 10 m for the conductive zone, and an average thickness of 30 m for the freshwater lens, is 9 x 10-4. This is consistent with a regional hydraulic gradient of about 3 x 10-4 estimated from previous modeling studies. The estimate of 5.3 Mgal/day for this single discharge point also compares reasonably with a recent finite-element model estimate of 31 Mgal/day discharge from the coastal zone centered around the cave. Additional, more-sophisticated field measurements of discharge are recommended to test the accuracy of the 5.3 Mgal/day estimate for the cave discharge. This presentation offers a hypothesis for the influence of the fault on the drainage of the Finegayan Basin and makes concomitant recommendations for revision of the basin boundaries to reflect the hypothesized influence of the fault, based on the Carbonate Island Karst Model.

Photolinears, Fractures, and Fallacies: What Can We Assume About the Structures of ASR Host Strata?

Michael Alfieri, P.G., P.Hg., CGWP
There is a general misconception by some in the geologic, and non-geologic communities, that terms “photolineaments” (or “photolinear”) and fractures are synonymous. This fallacy can be very detrimental to scientific/geologic interpretations. For example, a potable well placed at the intersection of two photolineaments may not be productive and would be a costly error if is not ground-truthed, because aerial interpretation of soil tones, for example, can be easily confused with intersecting deer trails. A photolineament assessment is a screening tool which requires verification prior to any further geologic interpretations or opinions. While in other areas of the country there is a higher correlation between photolinears and fractures/fracture systems, due to the cover materials, thicknesses, and karst in Florida, this degree of correlation does not exist. In the State of Florida, there have been four major regional photolinear assessments. To date, the authors are unaware of any literature references documenting the verification of these aerial interpreted features. This has led to the misuse of these assessments in geologic interpretations. The case study discussed herein describes the verification of a photolinear assessment completed in Hillsborough County, Florida and demonstrates how the misuse of photolinear assessments can impact geologic interpretation.

Keywords: “ground-truthed”, “ground-truthing”, photolineament, photolinear, fractures, fissures, joints, faults, fracture trace, geology, stratigraphy, karst, sinkholes, conduits, ground penetrating radar (GPR), seismic refraction, seismic reflection, standard penetration test (SPT) borings, cone penetrometer test (CPT) soundings, and Hillsborough County, Florida

Responses of Karst Springs to Precipitation Reflect Land Use, Lithology, and Climate

Alan E. Fryar
Numerous studies have documented how discharge (Q), water temperature (Tw), and chemistry of karst springs respond to precipitation (P). Fewer have compared responses between regions with differing land use, lithology, and seasonal precipitation patterns. We monitored Tw, specific conductance (SC), and stage (correlated to Q) at Blue Hole spring in Versailles, Kentucky, for 574 d. Blue Hole drains a gently rolling, primarily urban basin developed on flat-lying limestone; there are no pronounced wet or dry seasons. We monitored Tw and stage at three springs (Zerouka, Sidi Rached, and Ribaa), plus stable isotopes of water at Zerouka, in the Middle Atlas region of Morocco for 423 d. The Middle Atlas plateau consists of tabular, faulted dolomitic limestones. The landscape is forest and rangeland; the climate is Mediterranean with dry summers. Average local P during each study period was similar for Blue Hole (2.15 mm/d) and the Middle Atlas (2.38 mm/d). The number of events (defined as total P ≥ 2.5 mm with gaps ≤ 8 h) and maximum hourly P were greater for Blue Hole, whereas median values of event P and event duration were greater for the Middle Atlas. At Blue Hole, the difference between maximum and minimum Tw values during events (ΔTw) was as much as 5.58°C. Tw responses for Middle Atlas springs were more subdued (maximum ΔTw 0.74°C at Ribaa). For storms at Blue Hole, ΔTw increased and minimum SC decreased as maximum Q increased. Stage at Sidi Rached and Zerouka tended to decline gradually from spring to summer before rebounding. Deuterium and oxygen-18 at Zerouka fluctuated with time but did not show pronounced seasonality. We attribute regional differences to the greater extent of impervious cover in the Blue Hole basin and the lower intensity of storms and the lesser extent of carbonate weathering in the Middle Atlas.

Vadose Hydrology at Jinapsan Cave, Northern Guam

Kaylyn Bautista
Six years of monthly data were analyzed from an active tropical limestone cave in Guam, the southernmost Mariana Island in the western Pacific Ocean. The purpose of this study was to characterize rates and variability of vadose percolation in the Plio-Pleistocene Mariana Limestone, which occupies about 75% of the surface of the Northern Guam Lens Aquifer (NGLA). A ground survey grid was established on the surface above the cave, a vegetated talus slope beneath the >150-m-high cliff behind the cave. Cave and vadose zone 3-D models were constructed from the surface survey and a cave interior survey. Cross sections display talus slope features, inferred epikarst and vadose layer dimensions, cave floor slope, and structural and geomorphic features of the cave, including a brackish water-table pool at the cave bottom. A plan-view map displays significant boulder talus and limestone-forest trees, cave entrance location, and the underlying cave boundary and fractures mapped on the cave ceiling. Thicknesses of the talus and vadose bedrock sections range from 1.3 to 17.0 meters and 1.7 to 46.4 meters, respectively. Drip rate and discharge rate data from 7 cave stations are presented in graphs showing varying responses between percolation and changes in rainfall during wet (Jun-Nov) and dry (Dec-May) seasons. Six stations exhibited seasonal drip responses to wet-dry rainfall. One (the slowest) displayed mostly perennial dripping, with several overflow occurrences. Average drip rate, plotted on a log scale, divided stations based on order-of-magnitude into inferred hydrologic preferential pathway categories: fracture flow (fast; 103-104 drips/hr); fracture-fissure (fast; 102-103 drips/hr); small fissure flow (medium; 101-102 drips/hr); and matrix flow (slow; <101 drips/hr).

Volatilization of Trichloroethene from Groundwater in Karst, Mitigating a Human-Health Concern in a Show Cave

Jarrett Ellis
Vapor intrusion of Volatile Organic Compounds (VOCs) such as trichloroethene (TCE) is a human health risk as contaminants volatilize into confined spaces and occupants are unknowingly exposed. Many studies have focused on vapor intrusion in buildings, but few have addressed vapor intrusion in commercial caves. Missouri is known as the “Cave State” with thousands of known caves, several of which are commercial caves offering guided tours.

 In 1990, the U.S. Geological Survey (USGS) detected TCE in a spring within a commercial show cave near a Superfund site, subsequently (2002) the Missouri Department of Natural Resources (MDNR) detected TCE in air inside the cave. TCE levels inside the cave became a concern after the U.S. Environmental Protection Agency (USEPA) lowered allowable TCE concentrations in air, resulting in the owner closing the cave for several months during 2016. Collaborative efforts between the USGS, USEPA, MDNR, cave owner, and a potentially responsible party (PRP), investigated TCE transport within the cave system using a network of airflow and temperature monitors and periodic water and air sampling.

Volatilization from groundwater in the karst system beyond the mapped cave extent generates substantial TCE concentrations in cave air. During the summer when outside air concentrations are higher than cave air, convection moves this TCE-contaminated air “downcave” though toured areas to the cave mouth. During the winter when outside temperatures are lower than the cave, flow reverses with fresh air entering the cave mouth dramatically decreasing TCE concentrations inside the cave. In the summer nearly 20% of the TCE flux occurs in the cave air. Concentrations peak during fall and spring when outside temperature approximates cave temperature and airflow stagnates. A mitigation system was designed to reproduce “winter-like” airflow that have historically produced the lowest TCE concentrations in air and allowed the cave to reopen for tours.

Managed Aquifer Recharge

2013 Chino Basin Recharge Master Plan Implementation

Garrett Rapp, PE
In 1998, the Chino Basin Watermaster (CBWM) developed an Optimum Basin Management Program (OBMP) to enhance the safe yield and reliability of the Chino Groundwater Basin. One goal of the OBMP is to develop and implement a comprehensive recharge program. CBWM and the Inland Empire Utilities Agency (IEUA) have been developing, implementing, and updating recharge master plans (RMPs) to augment the managed recharge and sustainability of the Chino Basin. The first RMP, completed in 2005, increased storm and recycled water recharge by 14,000 acre-ft/year. CBWM and IEUA completed an RMP update in 2013 (2013 RMPU), planning to increase storm and recycled water recharge by an additional 12,000 acre-ft/year.

Surface water models for the watersheds overlying the Chino Basin were developed to: estimate the benefits of the recharge projects throughout the basin, understand the interaction of recharge facilities on the same stream system, optimize the scale of the projects, estimate the recharge from low impact development projects, and estimate downstream impacts on the Santa Ana River. This methodology is transferable to most areas where increasing groundwater recharge is desirable.

The facilities included in the 2013 RMPU range from redesigns of passive storm water retention basins to new stormwater storage and transfer facilities. The project stakeholders include regional and retail water agencies, private companies and 300 overlying pumpers. CBWM and IEUA are currently implementing the 2013 RMPU. The recommended 2013 RMPU projects are presently in design, and CBWM and IEUA anticipate that construction will be completed by 2020.

This talk will focus on the process used by CBWM and IEUA to conduct and implement their recharge master plans, the use of surface water modeling as a tool for evaluation, how well the master plan facilities performed compared to the plan, and how this same master plan process can be extended elsewhere.

Applying the HPT-GWS System for Evaluation of Managed Recharge in Unconsolidated Aquifers

Wes McCall, PG
A modified HPT probe has been designed with multiple injection ports that also may function as sampling ports. This probe is called the Hydraulic Profiling Tool-Ground Water Sampler. Field testing of the HPT-GWS was conducted in an alluvial aquifer system in central Kansas, at depths approaching 30m. The injection pressure logs were monitored to define the hydrostratigraphy and determine permeable zones in the formation where groundwater could be successfully sampled. Water quality parameters were monitored to stability prior to sampling. Changes in water quality parameters versus depth were observed and used to guide selection of depth intervals for sampling major element cations/anions as well as arsenic, barium and uranium.

During field work, subtle variations in the EC log across the coarse-grained aquifer were observed where the corrected HPT pressure log was flat. A strong relation also was observed between groundwater specific conductance and bulk formation EC in the coarse-grained aquifer facies. Modeling of field data found that the DP EC logs follow Archie’s Law in the aquifer facies even at the relatively low dissolved ion concentrations observed. Negative EC anomalies were observed where fresh water recharge was occurring below local storm water retention basins. Conversely, positive EC anomalies were observed where brine from the underlying shale bedrock was impacting the water at the base of the aquifer. These results demonstrate that the HPT-GWS can be used to define formation hydrostratigraphy at the centimeter-scale and sample for contaminants at multiple depths (profiling) in unconsolidated, permeable formations. The system also could be used to effectively assess seawater/brine impact and evaluate sites for placement of aquifer recharge basins or wells. Additionaly, the logs and profile samples may be useful in assessing the changes in groundwater geochemistry and extent of artificial recharge in unconsolidated aquifers.

Hexavalent Chromium Concentrations In Urban Runoff, Soil Moisture And Groundwater In The Los Angeles Basin

Anthony Daus
Between 2000 and 2007 a water augmentation study was performed in the Los Angeles Basin to assess the potential impact from recharging groundwater with urban storm water runoff. Six background locations were selected to monitor storm water runoff, vadose zone soil moisture and underlying groundwater quality for a large suite of parameters including total chromium and hexavalent chromium (Cr6+). The sites selected represented industrial, commercial, residential and recreational land uses. Storm water runoff, soil moisture and groundwater were sampled over a seven year period. While Cr6+ in stormwater was generally less than 1 µg/L, soil moisture concentrations varied over several orders of magnitude spatially and temporally with concentrations well in excess of the current MCL (10 µg/L). Underlying groundwater showed varying degrees of Cr6+ impacts from ND to 10’s of µg/L. The potential sources of Cr6+ and it’s mobility in the vadose zone as well as the potential implications for locating groundwater augmentation facilities is examined.

On-Farm Storage Reservoir Water as a Potential Water Source in Managed Aquifer Recharge in Eastern Arkansas

Deborah Leslie, PhD
The Mississippi River Valley Alluvial Aquifer is the primary source of irrigation for agriculture in eastern Arkansas. However, alluvial aquifer declines in Arkansas, mainly attributed to irrigation, continue to impact production costs and groundwater sustainability. Agricultural producers are constructing on-farm reservoir - tailwater recovery (R-TWR) systems to reduce their reliance on groundwater. Reservoirs store surface water and, when coupled with a tailwater recovery system, underground pipes, and groundwater wells, function as a complete irrigation system. Currently, more than 700 R-TWR systems have been identified in two eastern Arkansas areas designated as Critical Groundwater Areas (CGA). In relation to water conservation measures, it would also be beneficial to devise methods that increase aquifer recharge. Infiltration (injection) galleries have been suggested as a strategy for managed aquifer recharge on site. Infiltration galleries could be installed within the unsaturated zone of the alluvial aquifer, which has expanded in CGA due to declining groundwater levels. Preferential gallery locations include areas with a thin confining clay layer and with a large enough depth to groundwater for sufficient treatment time in the unsaturated aquifer. On-farm reservoir water, which primarily consists of winter-spring precipitation, could serve as a source of recharge water during the non-growing season. The quality of the injected reservoir water would need to be improved through soil aquifer treatment within the unsaturated sand lithology before reaching the water table. The objective of this research is to identify the potential of R-TWR systems to enhance water quality, while also considering reservoir infrastructure, orientation, age, erosion control, etc. Initial water quality results, including herbicide concentrations, will be presented. Potential testing locations for infiltration galleries which reflect areas that have a thin confining clay layer, a suitable depth to groundwater, and an adjacent reservoir water supply within the Cache River CGA will also be discussed.

Mississippi Alluvial Plain Groundwater Project

Michael W. Bradley

Characterizing Groundwater and Surface-Water Interaction in the Mississippi Delta Using Hydrograph Separation

Courtney Killian
Understanding the relationship between groundwater withdrawals and aquifer response can allow for the estimation of changes in groundwater availability over time and help determine best water-resource-management practices to sustain groundwater and surface water resources for agricultural irrigation, ecological flow, and other uses. An increase in groundwater withdrawals from the Mississippi River valley alluvial (MRVA) aquifer for agricultural irrigation has resulted in stream and groundwater level declines in the Mississippi Delta region, in northwest Mississippi. In 2016, the U.S. Geological Survey (USGS) began a study to better understand the effects of pumping on groundwater availability in the alluvial aquifer. Two USGS continuous continuous-gaging stations and co-located piezometers provided hydrologic data to characterized groundwater/surface-water interaction at two sites in the Delta. The sites are located at the Sunflower River at Sunflower, Mississippi and the Tallahatchie River at Money, Mississippi. Baseflow, the amount of groundwater that contributes to streamflow, was estimated at each site using hydrograph-separation and trend-analysis techniques provided in the USGS Groundwater Toolbox open-source software. Recently collected streambed resistivity data provided insight into the variability of hydraulic connectivity along streambeds and values were compared with the hydrograph separation and trend analysis results. This combination of techniques allowed for better characterization of the hydrogeologic conditions and the groundwater/surface-water interactions at the selected site. Characterizing hydrologic relations such as this will help refine a regional groundwater model of the Delta that will aid water-resource managers in future decisions pertaining to groundwater availability of the alluvial aquifer.

Coupling Modeling with Monitoring to Assess Water Availability in the Mississippi Alluvial Plain

Wade Kress
The Mississippi Alluvial Plain (MAP) is one of the most important agricultural regions in the United States, and crop productivity relies on groundwater irrigation from a system that is poorly understood. Groundwater use from the Mississippi River Valley alluvial aquifer (MRVA) has resulted in substantial groundwater-level declines and reductions in baseflow in streams within the MAP. These impacts are limiting well production and threatening future water availability for irrigation in the region. Accurate and ongoing assessments of water availability in the MAP region are critically important for making well-informed management decisions about sustainability, establishing best practices for water use, and identifying predicted changes to the regional water system over the next 50-100 years. To provide stakeholders and water-resource managers with information and tools to better understand and manage available water resources within the MAP, the U.S. Geological Survey (USGS) initiated a regional water availability project funded by the Water Availability and Use Science Program (WAUSP). The MAP project couples modeling with monitoring to improve the characterization of the alluvial aquifer system in an existing numerical-groundwater-simulation model. The premise of the investigation is to evaluate the existing groundwater model and produce an estimate of the uncertainty of the model inputs, such as hydraulic conductivities, storage, streams, recharge, and water use. Based on the uncertainty results, additional data are collected (monitoring) to improve the model. After which, the uncertainty will be estimated again, and the process will be repeated as necessary. Through this iterative method of modeling and monitoring, a more dynamic, ‘living’, numerical model will be available to more accurately represent groundwater flow in the system. The MAP groundwater model can then be used to help manage water resources, evaluate potential future effects of water-use changes, conservation practices, construction of diversion-control structures, and climate change.

Development of Monthly Water Budget Estimates for the CONUS and Application to the Mississippi Alluvial Plain

Meredith Reitz
As water resources become increasingly strained in the US and globally, the development of reliable methods of water availability estimation becomes ever more critical for making informed water use management decisions. Here we present new monthly 1km-resolution estimates of the set of water budget components of evapotranspiration (ET), surface runoff, snow storage, and recharge for the modern time period of 2000-2013. We use a combination of remote sensing products and empirical estimates from ground-based data, to leverage both the spatial/temporal resolution of remote sensing and the overall magnitude checks from field data. For ET we use a combination of the MODIS-based USGS SSEBop data set and long-term ET magnitude estimates based on water balance data. We estimate runoff with an empirical regression against soil and surficial geology data, and use the SNODAS snow water equivalent product of the National Snow and Ice Data Center to incorporate snow storage. Recharge and groundwater storage change are then estimated as the balance of the precipitation for the month. After presenting the methods and CONUS-scale maps, we show an application of this work to understanding water availability in the Mississippi Alluvial Plain region, which has seen significant impacts on water resources due to irrigation and groundwater pumping. Our monthly timescale estimates are compared with results from other methods, and synthesized into a summary of water budget trends in the region.

Evaluation of Recharge and Evapotranspiration Estimation Methods in the Mississippi Alluvial Plain

David Ladd
The Mississippi River Valley alluvial aquifer which underlies the Mississippi Alluvial Plain (MAP) is heavily used for irrigated agriculture and is one of the top three aquifers in the U.S. in terms of groundwater withdrawals for irrigation. Recharge and evapotranspiration (ET) are critical components of the overall water budget in the MAP area. Variations in the magnitude and spatial distribution of these water-budget components due to differing estimation methods could affect the results of the groundwater flow model developed for the Mississippi Embayment Regional Aquifer System (MERAS) used to simulate flow in the MAP area. A comparison of available methods to estimate recharge and ET points out the variability in estimates of these water budget components in the MERAS area. The results for recharge estimates from the PRISM-based calculations used in the original MERAS model are compared to those from the Soil-Water-Balance (SWB) model and from long-term Empirical Water Budget (EWB) estimates. The recharge estimates are examined in areas of differing irrigation intensity, and compared to field-based estimates where available.

Geophysical Surveys to Characterize Geologic Controls on Aquifer Recharge and Surface Water–Groundwater Exchange

Ryan Adams
The U.S. Geological Survey (USGS) developed a groundwater-flow model of the Mississippi Embayment Regional Aquifer System (MERAS) that incorporated multiple aquifers including the Mississippi River Valley alluvial (MRVA) aquifer. In addition to groundwater withdrawal, two major fluxes in the model are recharge from precipitation and surface water-groundwater exchange. In order to determine appropriate values for recharge to the MERAS model, the USGS has utilized two published datasets- the geomorphology of Quaternary deposits and local soil surveys. At a regional scale, recharge in the MERAS model correlate well with large-scale geomorphological features. However, there is little spatial variability, so local-scale variations in recharge are not adequately represented. Higher resolution data such as soil coverages provide a more spatially-variable estimates of recharge, but, soil-survey data often characterize the shallow soil horizon and do not reflect the generalized geomorphological features in which the horizon lies. In addition, streambed sediments may differ greatly from the mapped geomorphologic areas and shallow soils due to alteration from stream mechanics. Thus, geomorphologic maps and soil information are both types of surficial information that may not accurately reflect the underlying hydrogeology that controls infiltration of recharge water or the composition of streambed sediments.

In 2016-17, the USGS conducted several waterborne geophysical surveys to characterize the near-surface (<12 m) lithology that controls recharge to the MRVA aquifer and surface water-groundwater exchange at selected locations within the Mississippi Alluvial Plain (MAP). Two-dimensional vertical profiles of resistivity identified differences in geoelectrical properties of the streambed. High resistivity values are associated with coarse grained sediments and low values are indicative of fine grained materials. These resistivity-derived lithologies were then transformed using several techniques to inform the estimated hydraulic conductivity of the simulated streambed and refine the characterization of streamflow interactions in the MERAS groundwater-flow model.


Initial Assessment of Agricultural Water Management Scenarios in the Mississippi Delta

Connor Haugh
The Mississippi River alluvial plain in northwestern Mississippi (referred to as the Delta), once a floodplain to the Mississippi River covered with hardwoods and marshland, is now a highly productive agricultural region of large economic importance. Water for irrigation in the Delta is supplied primarily by the Mississippi River Valley alluvial aquifer. Although the aquifer has significant storage capacity, there is evidence that the current rate of water use is exceeding the available supply from, the aquifer. In an effort to better understand the impacts of different water-management scenarios on water availability and to identify additional monitoring needs in the Delta, the U.S. Geological Survey and the Mississippi Department of Environmental Quality are collaborating to update and enhance an existing regional groundwater-flow model. As a result of this collaboration, the model has been updated through 2013 with the most recent water-use data, precipitation and recharge data, and streamflow and groundwater-level data. The updated model has been used to evaluate alternative water-supply scenarios in order to assess impacts to the alluvial aquifer and identify data needs for future groundwater management modeling. Alternative water-supply options assessed to date include: 1) increased irrigation efficiency; 2) tailwater recovery and on-farm storage; 3) surface-water augmentation; 4) inter/intra-basin surface-water transfers; and 5) groundwater transfer. A relative comparison approach was used to calculate the simulated water-level response due to each scenario. Water-level response is the difference between water-levels simulated by the alternative-supply scenario and those simulated by a base case or “no action” scenario. Water-level response in the alluvial aquifer varied for each scenario based on the location and magnitude of the implemented alternative-supply option. These initial model results will serve to develop and assess conjunctive water-management-optimization scenarios as well as improve and enhance current and future monitoring activities within the Delta.

Quantifying Water Use in the Mississippi Alluvial Plain

Drew Westerman
The Mississippi Alluvial Plain (MAP) is one of the most important agricultural regions in the United States with an estimated water-use demand for irrigation to be over 10 billion gallons per day. Crop productivity relies on groundwater irrigation from the Mississippi River Valley alluvial (MRVA) aquifer - an aquifer system that is not fully understood in terms of water-level response to pumping, sources of recharge and the water budget components. Withdrawals from the MRVA aquifer have resulted in substantial declines in groundwater-levels and reductions in stream baseflow, and a realization that continued rates of withdrawal may not be sustainable to maintain the aquifer as a source for irrigation in the region. To address this need in the MAP, the U.S. Geological Survey has initiated a regional water-availability study to improve characterization of the MRVA aquifer system. Understanding the water-use demands within the MAP region is imperative before questions of water availability and sustainability can be addressed. Water-use represents one of the largest components of the water budget and is significant variable in groundwater-flow models. The USGS plans to improve water-use estimates by establishing a regional water-use monitoring network and enhancing the existing State networks within the MAP region. These data along with multiple remotely-sensed (or GIS) data variables will be evaluated geostatistically to develop a dynamic irrigation water-use model to provide a consistent and improved estimate of water-use throughout the MAP. The irrigation water-use model will include variables such as; remotely-sensed data, climate data, crop types, soil types, and amount of irrigated acres to estimate water-use both spatially and temporally for the MAP region. Improving estimates of water use will improve groundwater-flow model predictions, and help guide management strategies to improve sustainability of water resources to meet the needs of humans and ecosystems.

Using a model’s purpose to guide model updates: The case of the Mississippi Alluvial Plain aquifer

Jeremy White
Uncertainty and data-worth analyses evaluate the reliability of computer model outputs and estimate which model inputs are contributing most to model output uncertainty. These analyses direct decision makers to well-informed decisions and allow practitioners to estimate data importance for reduced model output uncertainty.

These techniques have been applied to the existing Mississippi Embayment Regional Aquifer System (MERAS) model to guide data collection and model dataset construction for the proposed Mississippi Alluvial Plain (MAP) aquifer model. The focus of the MAP model is to forecast aquifer water levels and surface-water/groundwater (SW-GW) exchange under different climatic and water-use conditions. Forecasts of interest (FOIs) simulated by the MERAS model include water levels and SW-GW exchange along major surface-water features under conditions of less recharge and increased water use. Preliminary results from the uncertainty analysis indicate streambed conductance values may better constrain uncertainty in water-levels and streamflow, which can be used to guide data collection in the field. These results will be presented and discussed in the context of data collection and model data preparation.

Poster Reception

After the Dam Comes Down: Groundwater-Stream Interactions & Water Quality of Restored and Unaltered Reaches in Ohio

Krista Brown
Over that past decade, dam removals have become increasingly popular, as many dams near the end of their life expectancy. With an anticipated increase of dam removals in coming years, this study aims to develop an understanding of groundwater-stream interactions and water quality in former reservoirs after dam removal. Low head dams were removed in 2009 on Plum Creek and Kelsey Creek, tributaries to the Cuyahoga River. Kelsey Creek reservoir remains unaltered and consists of a stream channel flowing through riparian-wetland environments, while Plum Creek reservoir underwent channel restoration in 2011. At Kelsey Creek, 20 piezometers and 3 wells were installed within the former reservoir. Since October 2013, hydraulic heads have been recorded semi-weekly for aquifer modelling and water samples have been taken in the wells and stream. Water quality is being evaluated with field-measured parameters and ion chromatography. Plum Creek is being used to understand the water quality effects of channel restoration.

At Kelsey Creek, interaction between the stream and shallow groundwater is evident. The stream tends to contribute shallow groundwater flow toward the western side of the site and north, parallel to the stream. The well closest to the stream shows variability in specific conductance, indicating bidirectional groundwater-stream exchange and all wells show rapid response to precipitation events. Hydraulic conductivity calculated using the Hvorslev method ranged 2.84x10-2 to 7.38x10-6 m/s and poorly correlate with the bulk sediments in Kelsey Creek.

Despite the wetland and groundwater-stream exchange in the unrestored Kelsey Creek, there is little change in stream water quality within the former reservoir site, similar to the restored Plum Creek site. This suggests that there is little water quality benefit to be gained from stream restoration at dam removal sites. Left unaltered, Kelsey Creek provides flood control and groundwater recharge in wetland areas.

An Interactive Excel Spreadsheet To Calculate Time-Varying Efficiencies for Pump-and-Treat Wells

Prashanth Khambhammettu, PE
An interactive excel spreadsheet has been developed to estimate time-varying efficiencies for pump-and-treat wells (extraction and injection) at a contaminated site. The spreadsheet uses convolution and superposition techniques to calculate water levels in each well based on the pumping at the well, interference from neighboring pumping wells, effect of a neighboring river, and time-varying linear and non-linear well losses. Aquifer and well loss parameters can be interactively adjusted until the calculated water levels match measured data. Well efficiency is automatically calculated by the spreadsheet as a function of the time-varying well loss parameters and the expected theoretical drawdown.

This spreadsheet is currently being used at two operating units of a contaminated site.

In the first operating unit, water levels in an unconfined aquifer respond to pumping, and fluctuating stage in a neighboring river. Here, the spreadsheet is used to calculate efficiencies for 160 pump-and-treat wells. The second operating unit is inland and not impacted by the fluctuations in the river stage. However, the pumping wells in this operating unit are periodically cleaned resulting in sudden increases in well efficiencies. The spreadsheet tool was successfully able to model the water levels and efficiencies at these pumping wells after factoring in the maintenance history.

This spreadsheet tool can be used at other contaminated sites, provided, the local geology and hydrological processes are consistent with the underlying theoretical assumptions. The interactive and visual nature of the tool enables better communication with stakeholders and regulators.

Assessment of Rainwater Harvesting Potential on Groundwater Recharge in Vellore City, India.

Siddharth Singh
The study suggests the importance of inclusion of rainwater harvesting in Groundwater level in the state of Tamil Nadu, India. To serve the purpose, groundwater levels of two observation wells in the Katpadi and Vellore City blocks of Vellore district, Tamil Nadu, India were modeled using two different approaches of Multiple Linear Regression (MLR) and Neural Network Analysis (ANN). Different input parameters were selected on the basis of previous studies and cross correlation analysis (CC). Volume of rainwater harvested was calculated by employing image classification technique on different images of the study area obtained from Google Earth’s historical database. During CC volume of rainwater harvested emerged as an important parameter. Results of MLR model suggested inclusion antecedent rainfall conditions produced the best results. ANN modeling suggested that present condition and absence of antecedent conditions produced the best model. In comparison, on the basis of coefficient of determination ANN produced better model than MLR analysis. Considerably better results were obtained for more recent years suggesting that rainwater harvesting may have reduced fluctuations in groundwater levels. The study presented itself as the motivation for other states to follow the successful scheme of Tamil Nadu government of mandating rainwater harvesting in all the structures.

Development of a New, Direct-Push-Based, Geophysical and Geochemical Approach for Groundwater Tracer Tests

Rob Rice, MS
Groundwater tracer tests are often employed to measure parameters used to model groundwater movement and contaminant fate. A new, direct-push-based approach to conducting tracer tests was evaluated in a sandy gravel aquifer next to the Gunnison River at the U.S. Department of Energy Office of Legacy Management's, Grand Junction, Colorado, Site. This aquifer is of interest due to past contamination from uranium processing, and the need for groundwater flow and contaminant transport parameters. The new method incorporates simultaneous vertical logging of electrical conductivity (EC), and hydraulic properties, along with groundwater sampling at specific intervals using a direct-push drilling rig. A lithium bromide tracer was injected into the alluvial sand and gravels and subsequently monitored using this new approach. The tools and approach were assessed for viability of mapping the tracer movement. A Geoprobe Hydraulic Profiling Tool – Groundwater Sampler (HPT-GWS) was used to log vertical changes in both EC and hydraulic properties using measured hydraulic back pressure. These logs, with extracted groundwater samples, were used to locate the tracer plume. Where logs indicated a spike in EC, a groundwater sample was obtained. Sample-specific conductance measurements were made in the field and used to approximate the position of the conductive bromide tracer. The presence of bromide was later verified through laboratory analysis. Vertical EC variations within the saturated zone were observed in three downgradient logs using the HPT-GWS. Comparison of EC and hydraulic pressure (HP) profiles allowed for identification of high conductivity zones and possible presence of the tracer. Continuous sediment cores were used to identify lithology that might influence the groundwater flow and tracer movement and resulting EC values. The use of an HPT-GWS for assessment of hydrogeological parameters such as groundwater flow direction and velocity, contaminant dispersion, and aquifer lithology, can enhance characterizations of chemical and physical processes occurring in the aquifer.

Estimation of Spatial Distribution of Specific Yield by Using Hydraulic Tomography and Gravity Measurements

Jui-Pin Tsai
Specific yield (Sy) is an important aquifer parameter especially highly correlated to the groundwater resources estimation. Sy is typically obtained through filed sampling. However, obtaining the detailed spatial distribution of Sy through a large amount of field point samples for a field area is an arduous task. To efficiently derive the distribution of Sy for a field area, this study proposed a method that integrates hydraulic head and gravity measurements based on hydraulic tomography (HT). A synthetic case is used to demonstrate the capability of the developed method. Our preliminary results show that gravity measurements are helpful to constrain the estimated distribution of Sy. By comparing the results estimated by the proposed method with that of original HT, the uncertainty of the distribution of Sy estimated by the proposed method is improved. Our studies show that the proposed method is practicable and could be useful to reduce the uncertainty of field-scale characterization.

Exposure History Dependence of Microbial Mediated Substrate Transformation in Groundwater

Larry McKay, Ph.D.
The capacity of natural microbial communities to transform a substrate in groundwater has been shown to increase after repeated exposures to the substrate; herein referred to as the “memory effect”. The objectives of this study were to determine: (1) how long the memory effect can last and (2) how the memory effect can alter the structure and function of natural microbial communities. Ethanol substrate was injected into a single groundwater test well for six consecutive weeks to establish a memory effect. The groundwater control well, located up-gradient of the test well, was not injected with ethanol during the first six weeks. Ethanol transformation in the test well was not significant the first week whereas ethanol transformation was significant during weeks two through six. The test and control wells were then monitored for eight additional weeks under ambient conditions. During week 14, ethanol was injected into both the test and control wells. Ethanol transformation was significant in the test well whereas ethanol transformation was not significant in the control well. These results demonstrated that the memory effect lasted at least eight weeks in the test well.

Here we present the hydrological, geochemical, and microbiological data and analyses in hand from the study site and the experimental well pair. This includes: (1) the magnitude and variability of hydraulic conductivity, hydraulic gradient, and effective porosity, (2) the potential for diffusive mass transport, (3) the temporal variability of specific discharge, (4) ethanol transformation to acetate and removal of nitrate and sulfate, (5) utilization/limitation of metal nutrients and/or co-factors, (6) microbial community structure (16S rRNA sequencing), and (7) microbial community function (GeoChip). Finally, we discuss the implications of the memory effort in terms of groundwater remediation with emphasis on the immobilization of redox sensitive metals and radionuclides.

Fraction of Young Water as an Indicator of Aquifer Vulnerability Along Two Regional Flow Paths in the Memphis Aquifer

James Kingsbury
Wells along two flow paths beginning in the outcrop area and ending at public-supply wells in the confined parts of the Memphis aquifer were sampled for age-date tracers, inorganic and organic constituents to characterize the sources of water and the vulnerability of the Memphis aquifer to contamination across a range of hydrologic and land-use conditions in southwest Tennessee. Young groundwater (< 60 years) was present at 13 of the 16 wells sampled in both unconfined and confined parts of the aquifer. These age-dating results generally were consistent with previous studies at Memphis, Tennessee, that documented leakage of shallow water into the Memphis aquifer locally where the overlying confining unit is thin or absent. Mixtures of young and old water were most prevalent where long-term pumping for public supply has lowered groundwater levels and induced downward movement of young water. The fraction of young water was correlated to the occurrence of anthropogenic organic contaminants, but relatively few contaminants were detected and concentrations were low because of the large fraction of old water at most locations. Long-term water-quality data collected from 1990 to 2015 for one of the flow-path wells in the confined part of the aquifer indicate that the fraction of young water is increasing over time as withdrawals for public supply are increasing. End member mixing models of shallow and deep groundwater based on the fraction of young water from age-tracer results suggest that over time the young fraction has increased from about 5 percent in 1990 to almost 20 percent in 2015. In general the vulnerability of this aquifer is low because of the predominance of old water at most locations, but as demand for water for various uses increases over time, the vulnerability of the aquifer is likely to increase.

Groundwater Impacts and a Complete Exposure Pathway: Vapor Intrusion (VI) Case Studies with Mitigation Options

Bryant Hoffer, LPG, CHMM
Groundwater impacts leading to Vapor Intrusion (VI) continues to be a hot-button topic in the environmental industry. As more information pertaining to VI becomes available, state and federal regulators, environmental consultants, environmental attorneys, insurers, and site owners are considering numerous approaches to sample, evaluate impacts, and mitigate the potentially complete pathway.

Various parameters of groundwater impacts affect the potential for a complete VI exposure pathway. These parameters include contaminant concentrations, depth to groundwater, lateral distance from groundwater impacts to occupied buildings, lithology of the unsaturated zone, and the individual characteristics of the Potential Contaminant (PC) at the Site.

There are several mitigation techniques currently available for sites with a complete/potentially complete VI exposure pathway. While numerous techniques are available for new construction (such as a vapor barrier, preemptive passive/active systems, and other new industry-specific products), the most common/effective strategy for existing buildings continues to be the installation/operation of Sub-Slab Depressurization Systems (SSDSs). These SSDSs introduce a pressure differential between the indoor air and sub-slab air. This pressure differential prevents the site PCs from entering the occupied building.

This poster will enable the reader to discover new sampling techniques, how to evaluate analytical data to determine the VI potential (with a focus on contaminant concentrations, depth to groundwater, and lithologic conditions), and learn about the common VI mitigation techniques. This poster will include case studies in which groundwater impacts have led to a potentially complete VI exposure pathway and the VI mitigation techniques used to effectively mitigate VI.

Informatics of Water-Level Measurements for the Mississippi River Valley Alluvial Aquifer, USA

William Asquith, Ph.D., P.G.
The Mississippi River Valley alluvial aquifer (MRVA) underlies much of the Mississippi River alluvial plain (MAP). A large regional study by the U.S. Geological Survey (USGS) of the hydrogeology and numerical groundwater-flow models of the MAP is on going (c. 2016–2021). The poster describes some research into the MRVA water-level database (16,756 wells; 285,429 measurements). A complex history of MRVA data collection exists over the past century by the USGS and equally important, numerous other local, state, and federal agencies. Data anomalies potentially represent erroneous information and hinder scientific study—Objective large-scale identification of such data is the primary focus of groundwater informatics for the MRVA. Two types of anomalous data are sought: (1) time-series outliers and (2) spatial outliers. Time-series data permit well-hydrograph visualization and temporal trend analyses using generalized additive (GAM) and support vector machine (SVM) models. Measurements exceeding a residual magnitude of 20 feet are flagged as outliers and relayed to database administrators (DBAs) for further scrutiny. Spatial outlier detection is based on period-of-record minimums using a two-dimensional (2D) GAM. Wells with data "out-of-place" in a local region are flagged as outliers and relayed to DBAs for further scrutiny. Patterns in decadal means for 2000 and 2010 are depicted. Exploratory long-term monitoring network identification using a 2D-SVM is made. Wells "supporting" the 2D-SVM are more informative than those not supporting it.

Modeling Preferential Fluid Flow through Deep Tropical Soils

Kalle Jahn
Deforestation and the expansion of agricultural land is occurring at a rapid pace throughout much of South America. Understanding the impacts of this trend on local hydrogeology is key to mitigating potential negative effects on ecosystem health and sustaining future agricultural opportunities. Tanguro Ranch is located in a Brazilian region of extensive land use conversion, and it’s deep, well-weathered soils are primary controls on the regional hydrogeology. In the last two decades, approximately half of the ranch land has been converted to soy and maize crop that requires heavy fertilization with both phosphate and nitrate. Previous studies at Tanguro have observed higher groundwater solute concentrations in agricultural watersheds, but no significant increases in stream solute concentrations. This has been attributed to vertical preferential flow paths that enhance nutrient transport to groundwater and reduce direct lateral surface and subsurface transport to nearby stream channels. This study quantifies the role of these vertical flow paths by pairing multi-year soil moisture and meteorological data with soil macropore data to develop detailed subsurface transport models. Soil moisture data are collected on a daily basis from 9-meter deep pits using time-domain reflectometers. Local meteorological data are collected from two weather stations located on the ranch. Macropore distribution and preferential flow data were assessed using tension infiltration and dye tracers. Modeled fluid fluxes will be integrated with soil pore water and groundwater chemistry to develop a regional model of flow from agricultural fields to groundwater to the stream network. These models contribute to our understanding of subsurface nutrient fate and transport through deep, tropical soils, and also help assess potential groundwater quality impacts from future climate and land use changes.

Novel Modeling Approach for Sites with Complex, Well‐Characterized Geology

Jessica Barros, PE
A groundwater model was generated to inform the design of a groundwater remedy involving a slurry wall and extensive groundwater extraction well network. The site is underlain by a gently sloping alluvial plain, where hydrogeologic zones consist of mostly fine‐grained low permeability units with localized high permeability regions that form a heterogeneous and interbedded aquifer system.

C Tech’s Mining Visualization System (MVS) software was used to develop a comprehensive geologic model from 233 highly‐detailed boring logs. Initially, a 3D finite difference grid was created in MVS and imported into Modflow USG. This version consisted of 56 layers, each representing a zone of uniform hydraulic conductivity. An attempt was made to simulate the complex geology using the MVS pinchout feature; however, this resulted in many discontinuous lenses and associated model computation/converging challenges. Ultimately, it was determined that this approach was not the best fit for modeling the site’s well‐characterized, heterogeneous geology.

The final version of the model was constructed using a 3D rectilinear grid, generated in MVS, which consists of approximately 120,000 active cells. MVS was used to assign one of four hydrologic conductivity zones (sand with fines, clay, sand, or gravel) to each cell in the model based on imported boring log data. Exporting the hydraulic conductivity zone data from MVS and importing this information into Groundwater Vistas presented particular challenges. Additionally, a boundary condition data gap was identified through model use and resulted in additional field investigation and model refinement.

Surface and Downhole Geophysics for Determination of Light Non-Aqueous Phase Liquid Migration in Faulted Dolomite

Corey Miller
The determination of LNAPL migration and groundwater flow patterns by identifying and mapping subsurface preferential pathways such as faults, fractures, air/water-filled voids, or solution cavities that may impact groundwater movement is crucial from both an environmental and engineering perspective. The primary goal of this research was to determine the feasibility of detecting LNAPL migration in a highly-weathered and faulted dolomitic environment through a combination of surface electrical resistivity imaging (ERI) and induced polarization (IP) methods, and a detailed suite of borehole geophysical logs. Appropriate ERI and IP electrode geometries have been taken into account for a target depth of approximately 130-feet bgs. Surface geophysical data have been integrated with downhole geophysical data from eight wells that include electric (8”, 16”, 32”, and 64” normal resistivity), natural gamma, fluid resistivity, temperature, optical televiewer, caliper, and heat pulse flow meter logs. These data were compared to structural geologic features identified with ERI and IP data to determine preferential pathways in which both groundwater and LNAPL likely migrate throughout this site. A second goal of this research was examine the observe any variations in ERI, IP, and borehole geophysical responses over areas which contain documented LNAPL in large, known volumes, and infer whether these variations in geophysical responses are caused by the significant LNAPL presence. This research discusses observed variations in both surface and downhole geophysical responses and how these variations relate to interpreted subsurface structural features and LNAPL migration.

Use of Monte-Carlo Analysis to Estimate Cost to Closure for Environmental Sites

James Berndt, LPG
One of the first questions often asked by parties responsible for environmental clean-up costs is “how much will it cost to bring this site to closure?” The second question usually asked is “how long will it take?” These are important questions for property owners, developers, their consultants, and legal counsel working with the various parties. An understanding of remedial costs and timeframes are needed when trying to estimate the value of environmental liabilities, for insurance companies setting reserves for environmental claims, and for site owners and legal counsel looking at the impact of environmental costs to a business.

There are a number of approaches to estimating cost-to-closure, from simplistic “best guesses” to more sophisticated cost modeling techniques using Monte Carlo simulations. The challenge for accurately determining cost for closure comes down to the client risk tolerance, regulatory acceptance, available reserves, timeframes, and other variables. Cost modeling provides a more statistically rigorous analysis of all the potential costs and their likelihood of being incurred as the site proceeds to closure. The interpretation of the results provides a mathematically defensible estimate of the cost-to-closure. However, like with all models, it is only as good as the data used to build it. The more that is known about a site, the more confidence can be placed on the model results.

Using a Groundwater Model To Analyze Depletion Mapping For The Mississippi Alluvial Plain Groundwater Project

Steven M, Peterson
The Mississippi Alluvial Plain (MAP) is among the most productive agricultural regions in the United States. This agriculture is enhanced through substantial groundwater irrigation, resulting in groundwater level declines in parts of the area. Efforts are currently (2017) underway to update the information and science available to support water-resources decisions and sustain future water availability. Groundwater models representing the major regional groundwater flows in a larger area encompassing the MAP have been published from 2009-2017. Even prior to integration of new data and approaches, these groundwater models also can be used in their current state to map depletions, which are like responses to increased stresses.

For a depletion mapping analysis, a model of an area for a specified time period is first run under a baseline condition. Simulated groundwater flows to various simulated boundary conditions are recorded, such as for streams, groundwater levels, and wells. Next, a new well is added to one model cell, the model is rerun, groundwater flows to various boundaries are again recorded, and the results are compared with the baseline condition. Results are commonly expressed as the change in the boundary flow as a percentage of the new well’s flow. Subsequently, the new well is moved from one cell to the next, and each cell is mapped. Depletion maps have been used to establish water resources management boundaries in Nebraska for more than a decade. In addition, these maps reveal characteristics of the groundwater system of an area and of the simulation representing that system. Depletion maps generated for the MAP area demonstrate where the new wells caused increased groundwater level declines (loss of storage) or decreased groundwater discharge to streams. The depletion maps also show some characteristics and details of the groundwater model inputs, such as variations in the hydraulic conductivity assigned to simulated streams.

Stepwise Modeling of Groundwater Flow

Hendrik Haitjema, Ph.D.

Summit Plenary Session

Neven Kresic, Ph.D., PG

Surface Water/Groundwater Interaction

A Case of Oysters – Understanding and Quantifying Surface/Groundwater Interactions

Sorab Panday
The Apalachicola-Chattahoochee- Flint (ACF) River basin lies mostly in Southwestern Georgia with portions in Alabama and Florida. Aquifers in the upper parts of the basin are not very productive and surface-water reservoir systems provide water for consumptive use. Lower portions of the basin overlie the highly productive Upper Floridan Aquifer (UFA) which supplies water for irrigation. Agricultural pumping from the UFA has increased significantly since the early 1970s and is vital to the economy of Southwest Georgia.

The Chattahoochee and Flint Rivers flow through Southwestern Georgia into Lake Seminole at the Florida-Georgia Stateline. The Apalachicola River begins at Lake Seminole and flows into Apalachicola Bay which is a major producer of oysters in Florida. The ACF River basin has recently faced severe multi-year droughts and flow in the ACF River has declined in recent years. The oyster industry in Apalachicola Bay was declared a disaster in 2012. That spurred the State of Florida to file a complaint against Georgia in the Supreme Court of the United States for equitable apportionment and injunctive relief. The complaint pointed at increased consumption by Georgia as the cause of adverse impacts to the Bay and requested the Court to cap Georgia’s overall consumptive water uses to levels existing in 1992. This presentation provides an overview of the case and review of the tools and techniques used to evaluate and quantify the impact of groundwater pumping versus other factors (including weather and anthropogenic activities) on flow at the Florida-Georgia Stateline and into Apalachicola Bay. These methods were presented at trial before a special master and the case will be argued before the U.S Supreme Court.

Empirical Linear Model for Base Flow Forecast as a Function of the Rainfall Moving Average

Edson Wendland
Climatic variation may result in insufficient input of water in the water balance in a region, resulting in inconsistencies in the water rights permits. During droughts such reference discharges may not reach the water rights permits, requiring groundwater extraction to compensate this deficiency in surface water bodies. The aim of this study is to determine the integrated water availability (surface and groundwater), using an empirical linear model, proposed as a function of the average rainfall of previous periods related to the aquifer regulation time. Correlation and spectral techniques were employed for time-series analysis of precipitation (P) and base flow discharge (Q) in the Ribeirão da Onça watershed, to determine response times of Q as a function of P. The proposed methodology was developed for precipitation and discharge observed from 2003 to 2014 in a watershed with an area of 65 km2. The obtained results indicate that the aquifer stores the rainfall water with regulation times of approximately 60 days for the subsurface flow, and approximately 2 years for the base flow. The methodology was also tested for two sub-basins of the Jacaré-Guaçú River watershed, with areas of 1867 and 3519 km2.The proposed methodology allows the estimation of a sustainable reference discharge making it possible to predict the base flow variation during recession periods, since it is defined as a function of past rainfall.

Groundwater Models to Improve the Ecology of a Saline Floodplain

Juliette Woods, PhD
Complex hydrological environments present management challenges where surface water-groundwater interactions involve interlinked processes at multiple scales. One example is Australia’s River Murray, which flows through a semi-arid landscape with highly saline groundwater. In this region, the floodplain ecology depends on freshwater provided from the main river channel, anabranches, and floodwaters. However, in the past century access to freshwater has been further limited due to river regulation, land clearance, and irrigation. A programme to improve ecosystem health at Pike Floodplain, South Australia, is evaluating management options such as environmental watering and groundwater pumping.

Due to the complicated interdependencies between processes moving water and salt within the floodplain, a series of inter-linked models have been developed to assist with management decisions. The models differ by hydrological domain, scale, and dimensionality. Together they simulate surface water, the unsaturated zone, and groundwater on regional, floodplain, and local scales. Outputs from regional models provide boundary conditions for floodplain models, which in turn provide inputs for the local scale models.

Two linked numerical groundwater models simulate floodplain processes in detail. One simulates 3D groundwater flow and solute transport across Pike Floodplain, while the other simulates density-dependent flow and transport in a cross-section through a riverine freshwater lens. The results are interpreted based on (i) ecohydrological requirements for key species of tree, and (ii) impacts on river salinity for downstream users. When combined, the models provide an integrated and interdisciplinary understanding of the hydrology and management of saline floodplains.

Hydrogeologic Evaluation of a Radial Collector Well as a Water Supply for the City of Manchester, New Hampshire

James Wieck, PG
A case study is presented describing hydrogeologic evaluation of a radial collector well installed adjacent and beneath the Merrimack River in Hooksett, New Hampshire. The well includes an approximately an 70-foot-deep, 16-foot-diameter vertical caisson, and six horizontal laterals constructed in a fan-like pattern beneath the riverbed. Laterals are an average of 200 feet in length. Phases of subsurface exploration and preliminary withdrawal testing were performed to collect stratigraphic and hydraulic information for design of the radial collector well, and provide monitoring locations for water quality and level response monitoring. Data collected supported application for a New Hampshire Large Groundwater Withdrawal permit and water supply permitting for the City of Manchester, New Hampshire.

Hydrogeologic evaluation included a step drawdown and two over 30-day constant rate withdrawal tests to evaluate groundwater capture, sustainable yield, and potential adverse impacts. Groundwater-surface water interactions and relative contributions to the withdrawal were evaluated. Constant rate tests were conducted during summer and winter conditions to evaluate effects of seasonal variations in viscosity on yield, capture, and groundwater-surface water interactions. Relative contributions of surface water and groundwater were also evaluated based on water quality including anion and cation data.

Hydraulic head data were collected from over 25 monitoring wells and selected residential water supply wells including wells screened in shallow and deep overburden and bedrock. Hydraulic head and water temperature data were also collected from the caisson and three multilevel monitoring locations constructed within the riverbed. Riverbed monitoring data were also used to identify the presence of restrictive layers within the riverbed.

The results of the withdrawal testing indicate a sustainable withdrawal rate of over 5,000 gallons per minute, with over eighty percent of the withdrawal from induced infiltration. The relative percentage of contributions to the well varies by up to 10 percent dependent upon temperature.

Impact of Hyporheic Exchange on Stream Temperature in Restored Systems

Ethan Bauer
One of the leading topics of discussion over the years in regard to stream health and water quality is stream temperature. The common school of thought within the industry is that the best and most effective way to regulate stream temperature is by blocking incident solar radiation via shading by riparian vegetation. There is much evidence to support this practice; it is known that solar radiation is the primary contributor for thermal loading within a stream (Johnson 2004). However, the practice of establishing a riparian community capable of providing significant vegetative shading is expensive and difficult to accomplish in the short term. A possible alternative lies in the practice of enhancing hyporheic connection in restored systems. It has been acknowledged that hyporheic exchange does alter the mechanics of stream temperature regulation (Forney, Soulard, & Chickadel, 2013), though its influence is rarely included in temperature analyses. To better understand the impact of hyporheic exchange, pre and post-restoration stream temperatures were compared for Kurtz Run and its tributary in Lancaster County, Pennsylvania. The floodplain restoration was completed by LandStudies, Inc. in 2012 and resulted in significant improvement of hyporheic connection within the system. Temperature data for 2011 and 2014 (represent pre and post-restoration conditions) was taken from five on site pressure transducers and solar radiation data was retrieved from a public NASA database. The daily maximum temperature was then plotted against total daily solar radiation to determine a relationship. After the completion of both a graphical and statistical analysis of the relationship between the datasets, it was determined that the influence of solar radiation on daily maximum stream temperature was reduced by an average 53% in the restored system. Better understanding of the potential impact of hyporheic exchange on stream temperature could significantly impact dominant restoration practices for both designers and regulators.

Understanding Surface Water and Groundwater Interactions at a Mining District Superfund Site near Silverton, CO

Rory Cowie, PhD
The US Environmental Protection Agency (EPA) has placed the Bonita Peak Mining District (BPMD) on the National Priorities List (NPL) making it eligible for a remedial investigation under the Superfund program. The BPMD consists of 48 historic mines or mining-related sources located in headwaters of the Animas River Watershed near Silverton, CO. The mine sites are located within a volcanic caldera complex with hydrothermally altered fractured bedrock. Surface and sub-surface rock and water interactions across the mining district produce acidic waters which enable the mobilization and transport of metals into the local surface waters.This talk will focus on the methods and techniques used to develop a conceptual model of the hydrologic fluxes within the mining district. Specifically, the talk will highlight the data needs to address complexities of water inputs, flow paths, and discharges in multiple headwater catchments interconnected by both natural (i.e. fracture flow) and anthropogenic (mine workings) hydrologic pathways. Challenges of combining data from physical parameters (i.e. rainfall, discharge, groundwater elevations) with analytical chemistry results, and maps of geologic structures and mine workings will be discussed.

Wintertime Infiltration and Snowmelt Processes of Black Spruce Peatlands in the Boreal Plain

Toomas Parratt
Understanding surface water groundwater interactions within the Boreal Plains is vital to reclaiming peatlands within Alberta’s Athabasca Oil Sands. After multiple years of field observations, it became apparent that many of the long held assumptions regarding wintertime hydrology and groundwater infiltration were false, especially within the peatlands. During the wintertime, it was discovered that the biological activity of the black spruce trees warmed the subsurface soil beneath the snowpack and thus prevented the ground from freezing. Further multiple wintertime events were observed where canopy snowmelt would directly infiltrate into the peat and not accumulate within the snowpack or sublimate as previously believed.

A conceptual model of how black spruce trees impact the winter hydrology of peatlands will be presented. The importance of incorporating ecology into physically based model which simulate the interactions between surface water and groundwater will be discussed. Brief modeling examples using the USDA Simultaneous Heat and Water (SHAW) model will be used to demonstrate the differences in groundwater recharge between black spruce, lodgepole pine, and burnt forested ecosites, including the additional processes that are required to properly simulate black spruce peatlands. Finally the importance of ecohydrology will be emphasised by demonstracting how simulating groundwater infiltration under varying tree species will provide reclamation specialists an important tool for designing future peatlands.

The Hydrogeology of Tennessee

Thomas Ballard, P.G. (CA, TN, LA); CHG (CA)

NGWA Groundwater Summit is being held in conjunction with Groundwater Week.

Find out more about NGWA and our events.

National Ground Water Association
601 Dempsey Road
Westerville, Ohio 43081
USA
Phone 614 898.7791
(toll-free within the United States 800 551.7379)
Fax 614 898.7786
Email ngwa@ngwa.org

Websites:

http://www.ngwa.org/ —home site of NGWA

http://www.wellowner.org — information for well owners