The NGWA Pillars of Groundwater Innovation Conference: Alphabetical Content Listing

Role of the Vadose Zone in Subsurface Hydrology

Shlomo P. Neuman

Flow Near Wells in a Partially Saturated Geologic Media

Phoolendra Mishra
Reliable prediction of fate and transport of contaminants in subsurface requires the knowledge of hydraulic properties of subsurface in saturated and unsaturated zone.  Pumping tests are commonly used to estimate field scale properties of subsurface. The conceptualization of groundwater flow during unconfined pumping tests has been a challenging task that has spurred substantial theoretical research in the field hydrogeology for decades. In the last decade, research into developing unconfined aquifer test solutions has mostly focused on explicitly coupling the aquifer with the linearized vadose zone. Here we discuss recent work on coupled saturated-unsaturated analytical models for flow near pumping wells.

Scale-dependent Spatial Variability of Pedologic and Hydraulic Vadose Zone Properties: The Maricopa Case Example

Shlomo P. Neuman
Analyses of flow and transport in the shallow subsurface require information about spatial and statistical distributions of soil hydraulic properties (water content and permeability, their dependence on capillary pressure) as functions of scale and direction. Measuring these properties is relatively difficult, time consuming and costly. It is generally much easier, faster and less expensive to collect and describe the makeup of soil samples in terms of textural composition (e.g. per cent sand, silt, clay and organic matter), bulk density and other such pedological attributes. Over the last two decades soil scientists have developed a set of tools, known collectively as pedotransfer functions (PTFs), to help translate information about the spatial distribution of pedological indicators into corresponding information about soil hydraulic properties. One of the most successful PTFs is the nonlinear Rosetta neural network model developed by Marcel Schaap. I describe a recent application of Rosetta to soil sample data from an experimental site in southern Arizona and a novel geostatistical scaling analysis of Rosetta inputs and outputs conducted by Alberto Guadagnini, Monica Riva, Marcel Schaap and myself.

Uncertainty Quantification of Soil-Water Balance Predictions, Using Fuzzy-Probabilistic and Maximum Likelihood Bayesian Averaging

Boris Faybishenko
Multiple semi-empirical formulae have been developed for soil-water balance calculations of potential evapotranspiration (PET), actual evapotranspiration (ET), and infiltration (I), using meteorological data and hydraulic parameters. Selection of one these models and corroboration with field observations of infiltration and evapotranspiration is a challenging problem. In this presentation, I will discuss several types of uncertainties affecting soil-water balance calculations, and will present the results of Monte Carlo and fuzzy-probabilistic simulations of PET, ET, and infiltration (I), based on meteorological data for the Hanford and Savannah River sites. Then, will provide a comparison of using a fuzzy degree of similarity index (FDSI) and Maximum Likelihood Bayesian Model Averaging (MLBA) for the selection of a subset of models to express the uncertainty of calculations of PET, ET, and I for each site.

Role of the Vadose Zone in Subsurface Hydrology (cont.)

Shlomo P. Neuman

Heterogeneity Preserving Inversion Methods for Vadose Zone Flow Modeling

Marcel Schaap
Natural recharge to groundwater in semi-arid regions relies on unsaturated flow through an often deep vadose zone. Understanding and modeling such flow requires intimate knowledge of surface-atmosphere interactions (which includes complex patterns caused by seasonally active vegetation) but also the subsurface heterogeneity of hydraulic properties. It is expensive and labor intensive to measure such properties, especially for the extensive and deep vadose zones which are prevalent in the western United States and other densely populated semi-arid regions in the world. Pedotransfer functions (PTFs) offer a cheap means to estimate hydraulic properties from soil or sediment texture, but suffer from inaccuracies that would likely bias modeled deep vadose zone flow.

In pursuit of the question “How much subsurface heterogeneity must be accounted for in vadose zone flow modeling?” we quantify the effectiveness of several methods for generating “fields” of subsurface hydraulic properties as needed for 1D to 3D numerical simulations. The main line of the presentation will deal with a detailed study carried out at Maricopa, Arizona. The study site is a 50×50 meter and 15 meter deep vadose zone at which a 28-day constant-rate infiltration experiment was conducted in 2001. Moisture content at this site was measured with neutron thermalization at 400 locations daily during the infiltration period, and at irregular intervals 100 and 200 days prior to and after infiltration, respectively. Our research shows that direct simulations based on PTF-estimated heterogeneous fields of hydraulic properties poorly represent the measured infiltration plume. However, several types of model inversions using different generalizations of heterogeneity present in the PTF estimates yield acceptable results and offer a potential means to limit the collection of site-specific data. In addition to the Maricopa site, we will also briefly outline surface soil-climate-deep vadose zone interactions for managed systems (a hypothetical golf course) and rangelands for long (10-25 year) time series. Much of this work is still ongoing, but presently these simulations indicate that the type of surface soil and the amount of winter rain strongly affects the amount of deep vadose zone infiltration. Conversely, surface soils as well as the amount of summer rain (the North American monsoon) have very limited effect on long-term nonriparian infiltration.

Unexpectedly Rapid Migration of Perchlorate Through a Thick Vadose Zone Under Low Rainfall Conditions

Daniel B. Stephens, Ph.D., PG
Perchlorate, a highly water soluble compound, has been detected in groundwater near Rialto, CA where the depth to groundwater is about 250 to 400 feet below ground surface. Mean annual precipitation is about 15 inches. The soils are highly permeable alluvial gravels with sparse vegetation. Assumptions that diffuse recharge is about 0.5 to 5% of mean annual precipitation, an assumption used in regional groundwater studies, cannot explain the depth of perchlorate migration through the vadose zone. Model studies and field data show that even under non-ponded conditions, perchlorate can migrate to much greater depths than otherwise expected. This behavior is attributable to localized focused recharge, the high permeability of the alluvium, and the absence of vegetation during site operations. The high local recharge, more than 50% of mean annual precipitation in places, also explains why shallow soil sampling did not detect significant concentrations of perchlorate in some areas.

Water Flow and Solute Transport in Deep Vadose Zone—Implications from Direct Observations

Ofer Dahan
Assessment of water percolation and solute transport in the vadose zone is considered a major challenge in hydrologic sciences. It is often characterized by unstable flow that is highly sensitive to hydraulic conditions. In laboratory experiments where the flow characteristics through a well-defined medium may be controlled, close predictions may be achieved. Nevertheless, in natural field conditions the lithologic heterogeneity as well as the erratic nature of hydraulic conditions increase flow instability and imposes a great obstacle to proper prediction. Often conventional models relay solely on parameters that are measured on the domain boundaries, with no direct validation in time and dimension scales that correspond with actual flow dynamics in the modeled domain.

A vadose-zone monitoring system (VMS), which was developed recently, allows continuous monitoring of the hydrological and chemical properties of percolating water in the deep vadose zone. The data which is collected by the system allow direct measurements of the water percolation fluxes and detect the chemical evolution of the percolating water across the entire unsaturated domain. Up to date, the system has been successfully implemented in several studies on water flow and contaminant transport in various hydrological and geological setups. These include floodwater infiltration and groundwater recharge, agricultural impact on groundwater quality, evolution of landfill leaches, and control of remediation processes in contaminated sites.

Direct observations on flow and transport processes which were measured in a variety of natural deep vadose zones under various hydraulic conditions allowed evaluation of few assumptions that are commonly used in vadose zone modeling. For example, water percolation in a natural vadose zone occurs as wetting waves through a relatively narrow range of water content amplitudes that does not exceed field capacity values, even if land surface is flooded with high water head for long periods (weeks to months). This phenomenon greatly influences solute and contaminant transport in unsaturated conditions. Percolation under low water content that never reaches saturation does not allow complete leaching of solutes from the unsaturated zone. Moreover, it allows salinity/contaminant accumulation in sections of the porous domain that never gets fully saturated, even in relatively homogeneous domains such as sand dunes. The incomplete leaching creates major differences between the chemical composition of sediment sample extracts and mobile water phase. Evidences of this phenomenon were observed over a wide range of geological and hydrological scales. Apparently this phenomenon impacts flow and transport models that use chemical composition of sediment samples for calibration and validation process. Another example is related to transport in unsaturated clay sediments. Direct measurements of water percolation velocities showed that percolation rates in unsaturated clay are several orders of magnitude faster compared to any other natural sediment, such as sand or alluvium (natural gravel). It has been found that fast water percolation velocities were related directly to desiccation cracks that form naturally in unsaturated clay. Apparently these observations contradict the common notion that attributes lower sensitivity to aquifers underlying clay soils.

Satellite Imagery Applications for Hydrogeology

Errol L. Montgomery, Ph.D.

Satellite Imagery Applications for Hydrogeology

Errol L. Montgomery, Ph.D.
Information from space–based sensing and imaging systems has been widely available in digital format from the mid-1970s. The systems for processing and viewing digital image data became more readily available in the 1980s. This information has been used for such diverse hydrologic purposes as analysis of distribution of hydrogeologic units; estimation of areal extent, depth, and sediment content of water in lakes and streams; distribution, health, and abundance of riparian and phreatophytic vegetation; establishment of environmental baselines; estimation of ocean temperatures; and investigations for occurrence of water on other planets. Much of the preliminary analysis is now automated using commercially available processing software. Processed images can be used to describe hydrologic features and may require calibration through ground truthing. Time series images from earliest availability to the present provide information for numerical analysis of changes in hydrologic features.

Satellite Imaging for Tailings Impoundment Water Balance

Janis Blainer-Fleming

Tailings impoundments are disposal locations for sediments resulting from mineral processing at mining industry facilities. Tailings are commonly transported to impoundments as a water slurry. Evaporation loss is the single largest output component of tailing impoundment water balances for locations in the arid southwest of the United States. Previous estimates of evaporation loss for an example site were based on regional climate data and were in the range of 15 to 20 percent of water delivered. Satellite images obtained at approximate one month intervals were analyzed to estimate relative moisture of the tailings impoundment surface. The relative moisture results coupled with local-scale evaporation data were used to refine previously estimated evaporation loss. Results indicate that evaporation losses at the example site were larger than previously estimated and range from 30 to 40 percent of water delivered.

The Role of Groundwater in Hydroclimatological Prediction

Dennis P. Lettenmaier
TBA

Satellite Imagery Applications for Hydrogeology (cont.)

Errol L. Montgomery, Ph.D.

CONUS-Wide Operational Landscape ET at 1 km for Drought and Hydrologic Applications

Gabriel Senay
USGS EROS has started producing monthly ET at 1 km spatial resolution since 2000 using the MODIS sensor data stream and the operational simplified surface energy balance (SSEBop) model. Monthly ETa products are being made available for USGS  scientists for download from a  Geo Portal. An overview of the model development, evaluation results and applications for drought monitoring and water balance studies will be presented.

Four Decades of Earth Observation Data Related to Mining Activity and Changing Hydrology in Mongolia

Donald Bills
The U.S. Geological Survey has submitted a proposal to the NASA 2013 Research Opportunities in Space and Earth Sciences (ROSES) Program to evaluate the rapidly changing hydrology of Mongolia related to the recent mining boom. The goal of the proposal is to create new knowledge through a suite of state-of-the-art maps and models demonstrating the status of mining and its impacts on water and land resources using 40+ years of multi-sensor, multi-date remote-sensing data from MODIS Terra/Aqua, GRACE, and Landsat. Observations have demonstrated that the volume and quality of Mongolia’s water resources are in a state of rapid decline. In an assessment report from 2012, Mongolia’s government identified declines of over 100 meters in many of the region’s groundwater resources. They have also seen about 15 percent of their known lakes, streams, and spring resources dry up or stop flowing. These unprecedented changes are significantly impacting both human and ecosystem water availability and needs. The root cause of these declines remains poorly understood, but an initial assessment by the USGS indicates that there are likely four primary stressors: land-use change, urbanization, regionally changing climate, and the recent mining boom. This project seeks to create a spatial data and knowledge storehouse using Earth Observation data to enable informed decision making through a suite of decision support tools that will make it possible to provide predictive assessments of the water resources and land use impact of future mining in Mongolia as well as in other countries. The products and knowledge gained through this project in Mongolia will be of immense benefit to understanding environmental and ecological impacts of mining globally. The Mongolian government and the international research and development community can use this information to ensure sustainable development, protect resources, and support mitigation programs as mining and other industrialization activities continue to develop.

Imaging Current and Ancient Subsurface Water and Ice on Mars

Victor Baker

A variety of satellite imagery is being applied to studies of the current and paleo-hydrogeology of the planet Mars. Gamma ray spectroscopy and radar sounding document extensive planetary-scale deposits of subsurface water ice. Visible and near-infrared imagery show evidence of very ancient outbursts of subsurface water, some of which generated megaflooding on early Mars that induced global climatic change. The University of Arizona’s High Resolution Imaging Science Experiment (HiRISE) has recently generated images showing ongoing seepage of what are probably brines on present-day Mars. It is now clear that Mars, like Earth, has had a dynamic hydrological cycle, operating on a planetary scale, over the entire history of the planet, and that this cycle involved complex interactions of both groundwater and surface water components interacting with an evolving atmosphere and cryosphere.

Successful and Efficient Groundwater Investigations and Remedial Work

Fletcher Driscoll, Ph.D., PG

Observations from 40 Years of Project Management

Al Quagliotti
In the environmental consulting profession we have historically judged project managers by financial performance.  In the 1970s the criteria for project success was “on time, within specification and under budget”.  The business community then embraced “quality” and shortly thereafter, “customer satisfaction”.  Today’s projects often include “stakeholders” which might include our client, numerous regulatory agencies, public interest groups and neighbors.  Project managers must wear a variety of hats, serve numerous masters, and are generally not equipped to manage a project to the satisfaction of all these stakeholders.  Many environmental firms provide training; however, most concentrate on technical competence and/or financial management.  It should be our mandate as senior environmental professionals to reach out and serve as mentors to younger professionals in our firms, even in the absence of a structured program.

This paper will present examples of “good project management” practices that resulted in unexpected and unfavorable consequences for the consultant, project manager, client or other stakeholders.  The presentation will conclude with the description of a successful project involving decades of work and a long list of stakeholders.

Plume Mapping Requires Consideration of Unique Groundwater Conditions and Chemical Properties

James Mercer

Complex site hydrogeology results in variations in chemical distributions at hazardous waste sites. Different permeable units have different unique plumes due, in part, to different flow directions and properties. Plumes in these different hydrologic units should not be aggregated. Different chemical properties prevent uniform distribution of chemicals. The transport properties of chemicals such as sorption and degradation determine how rapidly and how far each individual chemical will migrate. Different chemical release locations and dates further contribute to unique chemical migration extent and distribution. Consequently, combining multiple chemicals with different properties and distributions a priori is technically inappropriate. Combining multiple measurements of different chemicals over an extended time period (1) prevents interpretation of individual chemical plumes, (2) can result in connecting outlier data points that would otherwise be excluded, (3) combines data of different quality, and (4) does not consider active or passive remediation that will have an effect on older data, often lowering concentrations. The selected contouring method also has an impact on the shape and size of plumes. Further, selection of the numerical value of the outer contour will determine the size of plumes and may incorporate uncertain data.

Successful and Efficient Groundwater Investigations and Remedial Work

Fletcher Driscoll, Ph.D., PG

A consultant’s technical and scientific expertise can only be effective at a contaminated site if the work is carefully and strategically managed throughout the life of the project. Managers on behalf of both the client and consultant must have the capability to identify the potential environmental liabilities, define and adopt strategies to address the risks, and focus the investigation and remedial work on the most important elements. It is vital that the client authorize sufficient monetary support to ensure that the data collected are adequate, technically defensible, and presented in a well-written and easily-understood report. The consultant must ensure that the investigation expenditures are focused on only the identified risks and then presents the data in a report that addresses these risks. Long experience in providing expert witness testimony and the review of thousands of consultant reports for contaminated sites indicates that the adoption of an effective project strategy, collection of an adequate and well-defined data base, and the installation of an effective remedial system will lead to an overall lower project cost, efficient site remediation, and fairer resolution during litigation.

Successful and Efficient Groundwater Investigations and Remedial Work

Fletcher Driscoll, Ph.D., PG

Ignore the Details and Varying Uncertainty of Well Data at Your Own Peril

Marvin F. Glotfelty, RG

Groundwater investigators can utilize indirect methods (such as geophysical surveys) for hydrologic data collection, and stochastic analyses or data management tools enable us to thoroughly organize and assess the hydrologic data.  However, groundwater investigations inevitably rely on information derived from borings and/or wells. Too often, the considerations and limitations of information from drilling programs and wells are ignored by investigators. Wells should not be considered only as a set of data points to be plotted on a site map to represent hydrogeologic and water quality conditions at various locations. A flaw in this perspective is a disregard for the vertical dimension (well depth and perforated interval) of each well, the impact of the well’s annular seals (or the lack thereof), or the methods and materials used for well drilling, installation, and development. In addition to the construction attributes of wells, inappropriate hydrogeologic interpretations often result from failure of an investigator to embrace sound fundamental scientific principles, such as differentiating precision versus accuracy, validity of significant digits in reporting measured data, and recognition that conceptual models based on extrapolated or interpolated data cannot be assigned the same level of reliability as actual measured or observed values. Clarification of things we can measure and rely upon with certainty—versus the things we assume, interpret, or project with some degree of uncertainty—will enable us to avoid the pitfalls of hydrologic understanding/misunderstanding that can lead to misinterpretation of groundwater conditions and poor design of groundwater supply or remedial infrastructure.

The Ethics of Scoping and Pricing

Tyler Gass

Although most clients are aware of the challenges faced by environmental consultants who have been asked to develop a scope of work for an environmental site characterization program or the remediation of a contaminated site, clients will often request, even their most favored consultants, to competitively bid on work. In most circumstances price becomes one of the primary factors driving the selection of the environmental consultant to perform the work. Therefore, to compete, consultants are faced with a decision to trim the scope of work below what may be necessary to achieve the client’s needs, or come up with an imaginative low-cost proposal, knowing that any loss of profit will be made up with subsequent changes in scope. Alternatively, some consultants will deliberately prepare a realistic scope of services and cost proposal for those services, believing that it is the consultant’s ethical obligation to provide the client with a program that has the best chance of achieving the client’s needs, without significant changes to the original proposed scope of service and price.

The issue of ethics in the environmental consulting field is subject to a range of opinions. While a code of professional ethics is generally inherent in the culture of any professional services firm, for the individual professional scientist and engineer, the ethical challenge of pricing and scoping becomes more complex. Frequently the individual must demonstrate his/her ability to bring in new project work, while at the same time address the question of whether to provide the client with the information and services they truly need versus a scope of work and price the client would find more palatable.

This presentation will illustrate the challenges faced by consultants, and the dilemmas faced by clients in selecting consultants, using several case studies based on the author’s observations and experience during 40 years of providing environmental and hydrogeologic services.

The Influence of Black Swans on the Effectiveness of Remediating Groundwater Contamination

Donald Siegel, Ph.D.
Black swans, outliers, dominate science far more than predictable outcomes. Neither the environmental consulting nor regulatory industries appreciate that, ironically, predictable success constitutes the black swan in groundwater cleanup. Even the National Research Council recently concluded that groundwater cleanup to drinking water standards has nationally been a broad failure in typical complex hydrogeologic settings. Payne and others in their book Remediation Hydraulics abandoned the notion that representation of the subsurface through large-scale averages and steady-state observations can adequately support groundwater remedy designs. Groundwater consultants in their cleanup efforts would better serve themselves and their clients by coupling parsimonious site characterization to natural and induced geochemical tracer tests, and regulatory agencies would better serve the public by recognizing that groundwater cleanup can be futile in many settings except to low brownfield standards.

Wrap-Up

Fletcher Driscoll, Ph.D., PG
This will be a wrap-up of this session's topic.

What’s New in Groundwater Modeling?

Mary P. Anderson, Ph.D.

A Revolution in Progress

Mary P. Anderson, Ph.D.

Groundwater modeling is undergoing a revolution driven by the need to incorporate uncertainty in the conceptual model, numerical model, and in model calibration. Additionally, new GIS packages and new ways of modeling (e.g., with unstructured grids) provide powerful tools to improve how we model. In this session, we will explore some of these exciting new developments in groundwater modeling. In the past, groundwater modelers focused on simulating a single version of reality. However, modelers now acknowledge that unavoidable gaps in hydrogeological field data mean that there is uncertainty in the conceptual model that underlies every numerical groundwater model. Moreover, modelers are gradually accepting that inverse (parameter estimation) codes, which incorporate uncertainty analysis as part of the calibration, provide a better way to calibrate models. Furthermore, new GIS tools help in formulating the conceptual model while unstructured grids allow much needed flexibility in constructing the numerical model. New codes are available for complex problems involving saltwater intrusion in coastal aquifers and advances are being made in representing heterogeneities in subsurface properties, which is critical in delineating contaminant pathways. Ongoing research is also yielding a suite of codes for analyzing transport of contaminants with efforts toward aquifer remediation.

Developing the Conceptual Model

Neven Kresic, Ph.D., PG

Conceptual site models (CSMs) are now increasingly developed in a quantitative manner from the beginning of most commercial projects and are ready to be translated into numeric models effortlessly, at any stage of the project. Using a quantitative CSM and a numeric model simultaneously is invaluable for assessing uncertainties in both, and provides a very much needed feedback for their improvement. Notwithstanding that a professional hydrogeologic judgment is irreplaceable at the end, this presentation focuses on application of geostatistical, probabilistic, and visualization programs for CSM development and includes discussion on various interactions between conceptual and numeric models, as well as their potential misuse.

Uncertainty and Parameter Estimation

Randall Hunt, Ph.D., PH
No matter how sophisticated the groundwater model, a model is by definition a simplification of reality—a simplification that tries to accurately characterize mostly unseen water flowing in an unknowably complex earth under future stresses that can only be guessed at. Therefore, it is not surprising that groundwater models can no longer be considered “crystal balls” foretelling the future, but rather are best discussed in the context of their inherent uncertainty. Although general uncertainty concepts are widely understood, best practices for conveying uncertainty estimates are not well established. Parameter estimation techniques provide a quantitative framework that can form a common language and provide metrics for discussing model uncertainty. As a result, parameter estimation approaches are an increasingly indispensable part of 21st century groundwater modeling.

What’s New in Groundwater Modeling? (cont.)

Mary P. Anderson, Ph.D.

Effects of Small-Scale Preferential Flow Paths on Solute Transport: Observation and Modeling

Chunmiao Zheng
Preferential flow paths at decimeter and smaller scales are pervasive in the heterogeneous geological media.  Recent studies have shown that they exert a dominating control on solute transport.  However, their characterization in the field and the incorporation into solute transport models have been a significant challenge.  This presentation will review the recent advances in field techniques and model development that have improved our ability to characterize and predict solute transport in highly heterogeneous  aquifers containing small-scale preferential flow paths and relative flow barriers.

Topic Wrap-Up

Mary P. Anderson, Ph.D.
This will be a closing statement for the morning's topic.

Understanding Saltwater Intrusion Processes: New Insights Learned from Laboratory Observations Coupled to Numerical Predictions

T. Prabhakar Clement, Ph.D.
 

Sea level rise and reductions in groundwater flow due to droughts are the two important climate change-induced hydrological variables that can severely aggravate freshwater management problems in coastal aquifers. In this presentation we will present several laboratory and numerical datasets to illustrate the impacts of these two climate change-induced hydrological variables on saltwater intrusion processes. We will summarize the results of recent research efforts where we have tested three counterintuitive hypotheses related to the saltwater intrusion problem. In this presentation we will provide laboratory and/or numerical data to verify these hypotheses, and also discuss the new insights learned from these research studies.

Unstructured Grids

Sorab Panday, Ph.D.
An unstructured grid version of MODFLOW called MODFLOW-USG has recently been released to provide flexibility in gridding for MODFLOW solutions. Additional tools surrounding this code that have been developed and are under further development include various grid generation schemes, graphical user interfaces (GUIs), particle tracking routines, zone budget routines, parameter estimation routines, and dual domain flow and transport simulation capabilities among others. This presentation summarizes the current version of MODFLOW-USG —how it works, when and where it should be used, and current and future development plans.