Groundwater Issues and Science Affecting Policy and Management in the Southwest: Alphabetical Content Listing

Drought Management/Managed Aquifer Recharge

Robert D. Marley

A New (old) Method to Measure Layered Vadose Zone Permeability at Field Scale for Managed Aquifer Recharge

Daniel Sola

Knowing the field scale vertical hydraulic conductivity of the vadose zone is a challenge, especially in arid settings with a thick vadose zone. Vertical hydraulic conductivity at the field scale can be determined by directly measuring the air permeability of the vadose zone. This approach to measuring the vadose zone permeability was first developed by Weeks (1978), prior to the availability of current numerical modeling capability. By measuring vadose zone pressure responses to changes in barometric pressure at various depths in nested probes, a numerical model can be calibrated. Probe depths can be used to bracket and quantify suspected low permeability horizons at depth. The natural, time-variable, barometric pressure is used as a model surface boundary and calibration is achieved by matching observed lag and attenuation of the atmospheric pressure ‘signal’ in each layer or depth as it propagates through the subsurface. The vertical gas permeability for each layer is determined using the calibrated model and, in conjunction with soil porosity and saturation, is used to compute the vertical hydraulic conductivity of vadose zone soils. This method has the advantage of measuring permeability over a large area and volume and avoiding problems with local heterogeneity. In arid settings where the soil water content is low, the vertical gas permeability obtained from the method essentially represents the intrinsic vertical permeability of the materials and thus is representative of the vertical permeability to water.

HGC originally adapted this method to directly determine landfill gas generation rates. We have used this method to measure vertical vadose zone gas permeabilities at over 50 sites to depths of up to 300 feet. Actual and theoretical examples of measuring vadose zone permeability using this method are presented.

Mitigating Drought Impacts on Estuary Inflows using Aquifer Storage and Recovery

James Dodson

Surface water in Texas is regulated under prior appropriation statutes recently amended to include provisions designed to protect instream flows and estuary inflows, but these provisions only apply to new or amended water rights. However, most river basins are already fully appropriated, leaving little real opportunity to utilize these new rules to achieve the instream flow and estuary inflow protection targets recently established through a process involving “Basin and Bay Area Stakeholder Committees (BBASC)” and expert science teams. The State of Texas continues to fund BBASCs to study adaptive management strategies designed to achieve the State’s goal of providing a “sound ecological environment” for Texas’ rivers and estuaries.

One adaptive management study recently commissioned by the Guadalupe-San Antonio (GSA)-BBASC investigated the use of two untapped categories of surface water flows – treated wastewater return flows and unappropriated water rights – and Aquifer Storage and Recovery (ASR) as a means of achieving the “Strategy Target Frequencies (STFs)” for the spring and summer freshwater inflow targets the GSA-BBASC established for the San Antonio Bay - Guadalupe Estuary System during drought periods.

A water availability model was used to calculate how much water from these two categories would be available for ASR storage during the “good years,” the total volume of ASR storage needed to meet the STFs for estuary inflows through a drought of record, and the volume of ASR recovery capacity required to deliver the stored water to the estuary during the spring and summer target periods. Modeling results were used to size ASR facilities to meet the STFs, and to prepare conceptual designs and cost estimates for a series of ASR facilities located along the lower Guadalupe River, just above the estuary. The project report included recommendations for state water policy changes needed to facilitate this innovative strategy.

Understanding the Role of Decision Support Tools for Assisting Managed Aquifer Recharge in California’s Central Valley

Zachary Sugg, Ph.D.

In 2014, California passed historic legislation requiring all high- and medium-priority groundwater basins in the State to be managed sustainably by 2042. Many consultants, nongovernmental organizations, and other entities are developing tools to support groundwater sustainability agencies (GSAs) -- the local agencies tasked with managing these basins -- in achieving their management goals. However, the efficacy of such tools and their role in changing long-term management decisions is rarely assessed. Using meeting observation, semi-structured interviews, and quantitative metrics, this research traces the development of a Groundwater Recharge Assessment Tool (GRAT) and its adoption by two major irrigation districts in the California Central Valley. In addition to assessing its effectiveness in meeting short- and long-term management goals, this study seeks to answer more fundamental questions about the tool’s functionality, including: Did the tool change management decisions and how? Who uses the tool and how do uses vary between users? What components of the tool were most effective and helpful for management decisions? What constrained the tool’s functionality? We conclude with thoughts on the broader applicability of such a tool for assisting managed aquifer recharge efforts elsewhere in the Southwest and welcome input from conference attendees to that end.

Groundwater Sustainability

Stacy Timmons

An Overview of the NMBGMR Collaborative Groundwater Monitoring Network and How to Get Involved

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. Many of the groundwater users in New Mexico know the importance of groundwater level monitoring and its applications in research and modeling. The Aquifer Mapping Program at the New Mexico Bureau of Geology and Mineral Resources is tapping into the willingness of water-interested New Mexicans to share data and resources to develop the Collaborative Groundwater Monitoring Network. This collaboration is achieved by collecting data from groups or well owners that are monitoring water levels, equipping or manually measuring wells, and providing education and outreach. With these partnerships, the Network is able to fill spatial and temporal gaps in the current groundwater level monitoring networks while promoting increased awareness of groundwater issues and providing an important dataset for making informed water management decisions.

Developing 3-Dimensional GIS Models for Visualizing Aquifer Systems in New Mexico

Colin Cikoski

A critical role for scientists in groundwater resource policy and management is educating and informing the public through accessible products. A new initiative for the New Mexico Bureau of Geology and Mineral Resources Aquifer Mapping Program, in public-private partnership with the Healy Foundation, seeks to provide accessible hydrogeologic information by developing interactive 3-dimensional visualizations of the geology and hydrogeology of major aquifer systems that can be accessed through common web browsers. We have preliminarily divided the state into 20 major aquifer systems, and for each we will compile existing hydrogeologic data into representative 3-dimensional GIS models. Each model will be uploaded to an ESRI Story Map, a webpage that can display interactive GIS data without requiring GIS-specific software. In the Story Map setting, each GIS model will be navigable, and hyperlinked text can be used to step through “slices” of the model that highlight specific aspects of the geology and hydrology. To date, we have developed representative models for our Estancia basin and Pecos slope aquifer systems. To construct each model, we developed digital elevation models for the upper and lower contacts of each hydrogeologic unit, then built 3-dimensional multipatch shapefiles between these surfaces using ESRI ArcGIS tools. For the Estancia basin, a regulatory MODFLOW model provided subsurface contact elevation control, while for the Pecos slope we processed digital geologic maps and cross-sections from a recent hydrogeologic study for contact control. Hydrologic data was available from published hydrogeologic studies and several water well databases. The crux of our general method of model development is locating adequate subsurface data for a given area. We anticipate significant challenges in developing models for less well-studied areas with sparse and/or imprecise subsurface data.

Energy Storage Investigation at Groundwater Banks

Lon House, Ph.D.

This is a summary of the recently completed California Energy Commission research project EPC 15-049, an Investigation of the Potential to Add Energy Services to Aquifer/Groundwater Storage Banks.

Two different technologies were assessed. Aquifer Pumped Hydro (APH) involved using the aquifer as the lower storage reservoir and a surface storage reservoir as the upper reservoir and retrofitting thegroundwater wells with reversible pump generators. Pumped Storage (PS) involved using a surface storage reservoir as the lower reservoir, an upper elevation reservoir as the upper reservoir, and pumps and hydroelectric generator to connect the two. The Willow Springs Water Bank (WSWB) in Southern California was the facility chosen for the investigation.

Due to the California hydrologic cycle, three different operating modes were assessed. During Wet Years the WSWB is recharging the aquifer and the projects were evaluated as a hydroelectric generators. During Idle Years the WSWB is neither recharging nor withdrawing water and projects were evaluated as pumped storage. During Dry Years the WSWB is withdrawing water continuously and the projects were evaluated as demand response (curtailing pumping load in response to electrical system needs).

The results of the analysis are that, for both technologies, the ability to curtail/adjust pumping and participate in demand response was the most valuable resource, more valuable than the ability to generate electricity. This can be accomplished by adding a surface storage reservoir to balance out water delivery needs when the pumps are curtailed without adding a generation component.

The Aquifer Pumped Hydro was not cost effective, due to technology costs and aquifer transmissivity making the round-trip efficiency dismal.

For Pumped Storage the ability to participate in fast ramping and demand response was significantly more valuable than operating as a bulk energy supplier but this option option needed the Dry Year demand response to be cost effective.

Groundwater in Unconfined New Mexican Aquifers

Alex Rinehart

Unconfined aquifers form a major source of freshwater in the Rio Grande and neighboring basins, and in the Ogallala aquifer of the Southern High Plains. It is, however, unknown how much water has been withdrawn during the historical record. In this study, we provide a systematic analysis of water level changes and basin-wide groundwater storage changes for the alluvial aquifers of Rio Grande basins and neighboring basins, and in the Southern High Plains of New Mexico from the 1950s to the 2010s. We review USGS, NMOSE, county-level and NMBGMR well and water level data to exclude pumping-effected measurments. For each basin studied, we estimate a correlation length of water level measurements and derive a specific yield from the literature. We then interpolate the water level measurements and find the differences through time between the interpolations. We exclude regions outside the correlation length of both well networks used for the two interpolations, and regions in bedrock or historical unsaturation and find the differences in water levels and storage on decadal time-steps. Not all of the reviewed basins had adequate well and measurement coverage to be used. Overall, groundwater storage in unconfined aquifers is declining in populated regions, especially in areas isolated from perennial rivers. Areas without intensive irrigated agriculture or major population centers have shown smaller decreases or remained roughly static. Observable recharge appears to only come from mountain fronts or from major rivers. The Southern High Plains have a dwindling water supply. Basins with the Rio Grande and large populations show loss of connection with river recharge through time.

Investigating Groundwater Sustainability in Valles Caldera National Preserve, New Mexico

Steve Rice, PG

Valles Caldera National Preserve in northern New Mexico is one of the newest units in the National Park System. Historically, surface water was sufficient for domestic and livestock uses. But, as with much of the western U.S., these resources are becoming increasingly less reliable. The National Park Service must therefore consider how much groundwater is available for the use and management of the Preserve while preserving the ecological integrity of the area’s springs, wetlands, and streams. The ongoing Jemez River Basin water-right adjudication and potential geothermal leasing on adjacent lands must also be considered in developing sustainable groundwater-management policies.

Lifetime Projections for the High Plains Aquifer in East-Central New Mexico

Alex Rinehart

Several thousand water level measurements spanning over 50 years, from over a thousand wells, were used to create aquifer lifetime projections for the High Plains Aquifer in east-central New Mexico. Projections are based on past water-level decline rates calculated over ten- and twenty-year intervals, for two scenarios. One scenario is the time until total dewatering of the aquifer, and the other is the time until a 30 foot saturated thickness threshold is reached, the minimum necessary to sustain high-capacity irrigation wells. Agricultural water use has determined water-level decline rates in the past - assuming future decline rates match those of the past ten to twenty years, the scenarios may be viewed as the usable aquifer lifetime for domestic and low-intensity municipal and industrial uses, and the usable lifetime for large-scale irrigated agriculture.

Projected lifetimes and progressively enlarging areas of zero saturation are shown on maps. Areas of declining water-levels and decreasing aquifer life are more reliable projections than areas where these quantities have increased. There is high confidence in the results in the region surrounding Clovis and Portales. Discrepancies between lifetime projections derived from the past and current conditions are largely due to differences between actual decline rates and those projected into the future from any given time period in the past. The results match very well across the state line with lifetime projections for the Texas Panhandle region. The effects of groundwater pumping and water-level declines in east-central New Mexico are similar to those observed in the High Plains aquifer across northwest Texas and western Kansas. Much of the region already has insufficient saturated thickness for large-capacity irrigation wells. Even when considering the lifetime of the entire thickness of the aquifer, projected lifetimes across much of the study area are a few tens of years or less.

Mapping Deep Channel Deposits in the Ogallala Aquifer Using Electrical Resistivity Surveys

John Jansen, Ph.D., PG

The Ogallala formation was deposited as an extensive braided stream system that drained the eastern slope of the Rocky Mountains. The thickness of the sand and gravel deposits is highly variable with the thickest deposits filling stream valleys eroded into the underlying land surface. The thickness varies from about 0 to over 500 feet in a few buried channels.

The aquifer has been extensively pumped for decades and significant dewatering has occurred. In portions of the aquifer the saturated thickness is becoming a limiting factor controlling the production of a well and the sustainability of the supply. While the mining is not sustainable, wells in deeper portions of the aquifer with coarser sands will provide higher yields for longer periods as the thinner parts of the aquifer are dewatered but the deeper parts of the aquifer still contain saturated permeable material. While it is not possible to predict the thickness of the Ogallala based on surface topography, there are geophysical methods that can be used to map the thickness of permeable sand and gravel units above the underlying units.

A high resolution electrical resistivity survey conducted in west Texas for an industrial client. The client had an extensive well field to provide cooling water for an industrial facility but regional declines in water levels continues to reduce the capacity of most of the wells. Seven miles of resistivity lines were used to map the deeper portions of the aquifer. Subsequent test borings confirmed the channels, which varied from about 180 to about 270 feet deep, with the coarsest formation in the deepest part of the channels. A horizontal well was constructed in one of the deeper channels. The additional submergence provided by siting the well in the deeper channels and coarsest sands helped increase the production from the horizontal well.

Potentiometric Surface Maps in the Middle Rio Grande Basin: Rising Water Levels in the Production Zone

Lucas Curry

Groundwater pumping in the Middle Rio Grande Basin has resulted in groundwater level declines in the local aquifer’s production zone of more than 120 feet from pre-development (1950s) water levels. The USGS New Mexico Water Science Center, in cooperation with the Albuquerque Bernalillo County Water Utility Authority (ABCWUA), measures groundwater levels at monitoring wells throughout the Middle Rio Grande Basin. These data are used to develop potentiometric-surface maps depicting static groundwater elevation contours of the production zone. Published potentiometric-surface maps for water years 2002, 2008, and 2012, and preliminary results for water year 2016 show the effects of ABCWUA’s water resource management strategies on the aquifer and can be used to quantify groundwater elevation changes over time. Specifically, the groundwater-monitoring network and potentiometric-surface maps show a rise in groundwater levels, of over 30 feet in some areas, since 2008 corresponding to a significant reduction in groundwater pumping. These maps are a useful tool for water resource management and for the evaluation of management strategies, such as those documented in ABCWUA’s “Water 2120” plan. Other applications of the maps include estimating water availability for projected population growth, evaluating the resiliency of Albuquerque’s water supply to the impacts of climate change, and testing model accuracy in predicting long-term effects of groundwater withdrawal.

Simplified Stream Accretion Modeling for Sustainable Groundwater Management: An Interactive Approach

Deborah L. Hathaway, PE

Stream depletion/accretion assessment is critical to developing basin-wide plans for sustainable groundwater management. Groundwater models are commonly used to quantify schedules for stream depletion or accretion from existing groundwater uses, projected changes in groundwater use, or conjunctive use scenarios to meet groundwater management goals. Development of a groundwater model can be a multi-year and expensive process, compounded by the analysis and processing of multiple scenarios and permutations. This process can be streamlined, yielding useful approximations, by simulating a set of baseline actions and using convolution and superposition to explore combinations of actions through an interactive interface. Results, qualified by limitations of linear approaches in non-linear systems, help decision makers understand groundwater dynamics and stream interactions associated with groundwater management actions. This approach is illustrated for the Scott Valley in California.

Hypothetical groundwater management options were analyzed to provide a screening-level comparison of the magnitude and timing of flow increase to the Scott River. Four hypothetical groundwater management options are presented, including delayed groundwater pumping, managed winter recharge, augmentation wells and reduced irrigation pumping. Potential flow benefits are reviewed to understand the scale of the project or projects that may be required to satisfy water rights and to protect aquatic resources. The actions differ notably in the timing of flow benefits. The timing of benefits is a critical factor in judging the suitability of management actions for meeting flow objectives. A graphical comparison of groundwater management flow impacts is facilitated with an interactive spreadsheet-based tool, including user-controlled on/off switches and sliders to select and scale the magnitude of projects. Results may be compared to user-specified monthly flow enhancement targets. The rapid comparison of stream depletion/accretion results, drawing from simulation of selected baseline actions, can provide useful information for stakeholder discussion during the process of developing groundwater sustainability plans.

Siting, Design and Construction of a Horizontal Well for Industrial Water Supply in the Ogallala Aquifer

James Beach, PG

The Ogallala Aquifer has been extensively pumped for decades and significant dewatering has occurred in many areas of Texas. In portions of the aquifer, decreased saturated thickness is becoming a limiting factor controlling the production capacity of vertical wells. While there is a finite volume of water in the aquifer, horizontal wells in deeper portions of the aquifer containing coarser sands might provide a more economically feasible approach to groundwater production for longer periods even as saturated thickness of the aquifer become smaller.

This paper presents the approach that was used for siting, designing, and construction of a horizontal well for industrial client. The industrial user has an extensive well field to provide cooling water for a facility but regional declines in water levels continues to reduce the capacity of most of the vertical wells. The approach to siting and designing a horizontal well entailed evaluation of estimated saturated thickness, permeability, and other strategic considerations as well as groundwater modeling. After the preliminary evaluation, approximately seven miles of geophysical resistivity lines were used to map the deeper portions of the Ogallala aquifer. Subsequent test borings were used to further refine the lithology and target the best channels. The horizontal well contains 500 feet of 12-inch screen placed about 190 feet below land surface and produced over 650 gpm with only 42 feet of initial saturated thickness at the well site. Water level measurements from four vertical wells are received daily by the groundwater conservation district for monitoring purposes.

Groundwater/Surface Water Interaction

Ronald Green, Ph.D., PG

Aquifer Systems that Recharge the Texas Reach of the Rio Grande/Rio Bravo

Ronald Green, Ph.D., PG

The Texas reach of the Rio Grande/Rio Bravo is recharged by a number of major and minor aquifers that are sourced in Texas and Mexico. Recent studies have added to understanding the relative importance and magnitude of recharge that each aquifer contributes to the river. This understanding illuminates the need to better understand how different factors impact the watersheds that recharge the aquifers and how water-resource management decisions can alter the water budget of the Rio Grande/Rio Bravo valley and watershed. Challenges to refining these conceptualizations are that the aquifers and watersheds that discharge to the river exhibit highly variable recharge rates and mechanisms. Much of the variability in recharge is due to fact that these watersheds span large changes in elevation and many occur in arid and semi-arid climates which adds a high level of complexity to the nature of recharge mechanisms and rates. Compounding this complexity, the water budgets of many of the major watersheds and aquifers that discharge to the river are being altered by large-scale groundwater extraction and changes in land use. Development of sound conceptualizations of recharge and discharge from these aquifers will enable better informed management of the Rio Grande/Rio Bravo water resources.

Groundwater Management in Texas: Considering Flows to Springs and Streams

Larry French, PG

Texas law requires that groundwater conservation districts consider “impacts on spring flow and other interactions between groundwater and surface water” in managing groundwater resources. The Texas Water Development Board recently quantified groundwater – surface water relationships in the 9 major aquifers and 21 minor aquifers that extend beneath 81 percent of the land area of Texas.

We used “hydrologic landscape regions” to estimate groundwater flow to surface water based on data from nearly 600 U.S. Geological Survey stream gauging stations. This approach yielded a statewide average net groundwater flow to surface water of 9.3 million acre-feet per year, or about 30 percent of all surface-water flows. Groundwater contributions to surface water are greatest in east Texas and around major springs in the Hill Country and west Texas. The Gulf Coast Aquifer discharges the most groundwater to surface water, with an estimated flow of 3.8 million acre-feet per year. The Edwards (Balcones Fault Zone) Aquifer discharges the greatest volume of baseflow per square mile of aquifer area. Springs and seeps in west Texas also contribute locally significant baseflow to streams. About half of Texas aquifers contribute less than 50,000 acre-feet per year to surface-water flows.

The Edwards (Balcones Fault Zone), Edwards-Trinity (Plateau), and Pecos Valley aquifers contribute more than 50 percent of the baseflow of streams flowing across their outcrop zones. Eighteen major and minor aquifers contribute between 20 and 50 percent of the flow to streams flowing over their outcrop zones. Eight minor aquifers contribute between 14 and 20 percent of the flow to streams flowing over their outcrop zones. The Rita Blanca Aquifer, contributes zero percent to streamflow and is classified as non-tributary. Each of the state’s aquifers has local areas that may differ from the regional, aggregate designation.

Hydrologic and Temperature Indicators of Surface Water Groundwater Exchange, Sandia Canyon Wetland, Los Alamos NM

Kevin Reid, PG

The Sandia Canyon wetland is approximately 16,000 m² and largely sustained by year-round NPDES permitted outfall water from the Los Alamos National Laboratory. From 1956 to 1972 the wetland received effluent containing hexavalent chromium resulting in elevated chromium concentrations in the sediment and alluvial groundwater. Reducing conditions within the wetland favor chromium to exist as the more stable and less toxic valence state of Cr(III). Due to the low solubility of Cr(III) most of the inventory is thought to be adsorbed to sediments or organic material. In addition to outfall discharge, the wetland receives storm water runoff from an impervious developed landscape in response to precipitation events. Understanding the hydrologic pathways through the wetland is important for analysis of the geochemical stability of the chromium inventory within the wetland sediments. Particularly how groundwater-surface water exchange could potentially transport chromium out of the wetland downstream to receptors. Within the wetland there are twelve alluvial wells installed in four transects of three wells each and three surface water gage stations. Water levels and discharge were measured continuously. Geochemical samples were collected quarterly. Nine of twelve alluvial wells show water level responses to runoff events. Two of twelve wells show temperature responses to runoff events. These results indicate there is connectivity of the surface water and alluvial groundwater. The set of three wells which did not have as strong correlation were located in the widest section of the wetland where flow is more dispersed within ponded and highly vegetated areas. Although there is connectivity of surface water and alluvial groundwater, the geochemical monitoring results show chromium remains stable as Cr(III) within the alluvial system. LA-UR-17-27384

Preferential Flow Pathway Controls on Groundwater Discharge in the Devils River of Texas

Nathaniel Toll

Groundwater in the Devils River Basin in central Texas is discharged almost entirely into the Devils River. The characteristics of groundwater discharge to the Devils River are dominated by karst features, geomorphological features, and geologic structures. Karst features are postulated to have developed in alignment with river channels over long periods of time and have resulted in preferential flow pathways or conduits. These conduits are located in close proximity to surface channels of the rivers, major tributaries, and minor channels at relatively shallow depths. The dendritic nature of the stream channel network implies that an equally complex preferential flow network exists in the basin. Recent experiments in developing conceptual and numerical models of this surface-water/groundwater system have led to several interesting observations. Permeability exists at several different scales in the study area. Discrete representation of the conduit network is required to calibrate both groundwater-level fluctuations and spring discharges to the Devils River. Conduits of low-order streams must be included in the models to replicate the base-flow response seen in the Devils River. Groundwater flow and sustainability of the Devils River watershed appears to be controlled by the morphology of the area more than the bulk hydraulic properties of the host rocks. The ability of the models to replicate Devils River discharge was only achieved when the groundwater model attained the apparently correct distribution, morphology, and alignment of conduits relative to the watershed topography. Production of groundwater in the basin results in a proportional reduction in the flow of the Devils River. The impact is most pronounced during low-flow conditions. This has large impacts on the ecology of the river system as small decreases in groundwater levels and discharge can extinguish spring clusters in the river potentially destroying refuges for fauna and flora under low-flow conditions.

The Evolution of Unmanned Aerial System (Drones) in Water Science

Richard Brose

With the advent of the Federal Aviation Administration development of certification requirements for operators of unmanned aerial systems in 2016, combined with the explosive growth of hardware and software for aerial imaging, the use of unmanned aerial systems (commonly referred to as “drones”) has opened a new method to obtain, observe, and document both the existence of, and changes in, surface and groundwater resources and their associated ecosystems. While aerial photography has been used for decades to provide a “birds eye” view of the earth’s surface, the readily available newest aerial technologies enable real-time data acquisition of ongoing processes affected by changes in surface and groundwater conditions and their impacts on ecosystem changes. Aerial imagery platforms, including visual documentation, infra-red imaging, LIDAR, and other technologies are evaluated and the opportunities provided by each technology are discussed. Evolving software options that include redundant flight opportunities, geo-imaging, geo-spacial data acquisition, telemetry, and cloud data integration into projects are reviewed, as is the utility of the integration of evolving technologies in the applicability to project activities. The review provides a coherent and succinct summary of the current tools and software available to assess, document, and catalogue the many remote sensing options available to the professional scientist evaluating both surface and groundwater systems.

Uncertainty in Runoff and Recharge for Surface-Water/Groundwater Models in the Arid and Semiarid Edwards Plateau, Central Texas

Beth Fratesi, Ph.D.

The volume and distribution of recharge is arguably the most critical source of uncertainty in both surface-water and groundwater models, as recharge estimates often carry high potential for error. This uncertainty is magnified when attempting to quantify recharge in arid and semi-arid environments, where precipitation may be insufficient to instigate distributed recharge. Precipitation is often intensely concentrated in space and time, and recharge occurs in pulses through paths of preferential flow such as sinks or stream beds. If karstic conduit flow is well developed in the groundwater system, the boundary between the flashy baseflow elements and direct runoff can be blurred. Often, integrated surface-water/groundwater models are developed in an attempt to gain insight on recharge mechanisms and rates. Unless this uncertainty is adequately constrained, models cannot be trusted to generate meaningfully accurate insights for use in water-resource management planning. Furthermore, most surface-water modeling methods are built on assumptions and conceptual models developed for engineering purposes in humid areas, few of which can be applied without alteration to arid and semi-arid environments. Integrated surface-water/groundwater models have been used to explore recharge, runoff, and the related sources of uncertainty for both processes in the arid and semi-arid Edwards Plateau in central Texas. This experience provides insight on how to constrain conceptual and numerical models used to simulate surface-water and groundwater flow under variable precipitation and recharge conditions. Elements of the surface-water/groundwater models that constitute the greatest sources of uncertainty include (1) channel transmission losses to groundwater; (2) magnitude of precipitation; (3) the presence and size of a “tension zone” soil storage element in which water is vulnerable to evapotranspiration but not infiltration; (4) the calculation method for actual evapotranspiration; and (5) the level of discretization compared to the temporal and spatial variability of the system.

Valuing Groundwater Recharge as an Attribute of Watershed Restoration: A Focus on Willingness to Pay for Project Attributes

Adrienne Soder

A healthy watershed provides benefits to all its residents, including improvements in surface and groundwater quality and quantity, groundwater recharge, agricultural irrigation, recreation, and ecosystem services. Quantifying benefits received from a healthy watershed using market values has, in the past, been difficult. However, the largest landscape-level forest restoration project in the U.S., the Four Forests Restoration Initiative, is now providing an opportunity to quantify the values of watershed services affected by restoration. The purpose of this study is to estimate monetary values for attributes of watershed restoration projects to assist decision-makers with budget allocation when considering future restoration projects. This study focuses primarily on benefi ts offered to those residing in the Salt-Verde Watershed managed by Salt River Project (SRP), a major energy and water provider in the Phoenix metropolitan area. Values are obtained by utilizing nonmarket valuation, an economic method that allows estimation of monetary values of goods and services, such as groundwater recharge, not typically traded in a traditional market. We apply the Choice Experiment (CE) methodology of non-market valuation to survey residents of the Salt-Verde Watershed regarding their preferences for attributes of watershed restoration. We plan to use a mixed logit model to obtain marginal willingness to pay from the online survey results. The results are intended to directly inform SRP’s decision-making regarding restoration projects in semi-regions in Arizona.

Meet and Greet

Multi-Jurisdictional, Integrated Water Management

Alex Rinehart

Brackish Groundwater Desalination Projects in Texas: The El Paso and San Antonio Strategies

Brad Cross, PG

Water in the arid southwest United States is becoming scarcer and with populations continuing to grow, more marginal aquifers will need to be tapped. The State of Texas has a tremendous resource in brackish groundwater that can be found throughout the state, including West Texas, North-Central Texas, Central Texas, and the Southern Coastal region. Brackish water has total dissolved solids (TDS) greater than 1,000 milligrams per liter (mg/l) and is becoming an attractive resource to a number of communities throughout the state. This presentation provides an overview of the groundwater management strategies for the Cities of San Antonio and El Paso with a summary of the use of brackish groundwater, associated desalination operations, and the disposal of concentrate.

GIS-Based Dynamic Database for Water Rights Administration in the Gila River Valley, NM

April Jean Tafoya

Water resources and water rights in the Southwest are legally and operationally intertwined, requiring water right administrators and hydrologists to work within state and federal legislation with diverse water right users, including municipal, agricultural and tribal stakeholders. In 2014 a Federal Court mandated the creation of a “Dynamic Database” to represent four irrigation districts, two Indian tribes, and a minerals corporation in the Gila River Valley which spans public, private and tribal land in southern New Mexico and Arizona. The project scope includes farm and river bottom land mapping, agricultural system efficiency assessment, water right abstracting, conducting stakeholder meetings with water right users, and map production for the irrigated agricultural lands along the Gila River. The authors developed a GIS-based interactive Dynamic Database for New Mexico which will ultimately be utilized in management of the Globe Equity Decree, providing a template for spatial databases to be used in water right administration. The database is designed to be user friendly, accessible, adaptable, spatial, accurate, and capable of distilling thousands of legal documents into a linked attribute table for stakeholders, and legal and technical experts to query. The Dynamic Database will be utilized in multijurisdictional integrated water management by the Gila Water Commissioner after a technical and legal review process. Water budgeting for the future of our shared resources involves allocation of surface and ground water rights for competing interests; interactive GIS-based databases provide accessibility and clarity for stakeholders, legal counsel, technical experts and government agencies.

Natural and Anthropogenic Contaminants

William Alley, Ph.D.

Mobilization of Naturally Occurring Uranium to Water Supply Wells, Southern Tucson Basin

Michael Barden

Uranium concentrations exceeding the federal MCL were encountered in water during routine sampling from two community supply wells located south of Tucson, Arizona. The wells are situated adjacent to an area of recently developed agricultural fields on the western margin of the Tucson basin. A study conducted to evaluate the situation and compliance alternatives included extensive examination of the geological and hydrogeological setting and geochemical characterization of groundwater to determine the source of elevated uranium concentrations and appropriate measures to deal with the problem.

Trace metal composition of alluvial basin-fill sediments is poorly known, but various uraniferous sources are present in the area and uranium content in surficial materials is known to typically be about 5 mg/kg and range up to about 22 mg/kg. Uranium is naturally occurring in the alluvial sediments and groundwater underlying the area. Uranium solubility in groundwater depends strongly on the presence of potential complexing agents in solution, such as carbonate, phosphate and sulfate, as well as on the pH and oxidation-reduction conditions. Uranium is most mobile in oxic and alkaline groundwater where it forms highly soluble uranyl-carbonate complexes. The association of elevated uranium concentrations in groundwater with nitrate has been widely noted and a variety of mechanisms are known by which nitrate can directly or indirectly result in potential uranium mobilization. Evaluation of the hydrogeology and groundwater chemistry, including geochemical modeling using PHREEQC, indicate that the source of the observed uranium concentrations in the water supply wells is most likely due to increased concentrations of bicarbonate and calcium associated with irrigation return flow from the adjacent agricultural fields that has resulted in desorption of uranium from aquifer solids through formation of a highly soluble calcium-uranyl-carbonate complex. The area of elevated uranium concentrations appears to be restricted to the area impacted by irrigation return flows.

Observed Variability in Groundwater Quality in the Rincon Valley, NM through High-Frequency Monitoring

Laura Bexfield

Since 2014, the USGS National Water Quality Assessment Project has been collecting high-frequency (daily) data for water-quality parameters at three wells in the Rincon Valley, New Mexico, to better understand how groundwater quality changes over short (daily to monthly) and long (seasonal to decadal) timescales. After daily purging of the two monitoring wells and one irrigation well, single measurements of water temperature, specific conductance (SC), pH, and dissolved oxygen are transmitted to the National Water Information System, where they are available for near real time viewing (https://waterdata.usgs.gov/nm/nwis/current/?type=quality&group%20Key=basin%20cd). Water levels are recorded every 15 minutes. Groundwater samples are collected annually for analysis of major and trace elements, nutrients, pesticides, and selected environmental tracers. Bimonthly sampling (planned to begin in 2018) is intended to help correlate high-frequency water-quality parameters with constituents of interest, including dissolved solids, nitrate, and uranium.

Land use in the Rincon Valley, located along the Rio Grande in southern New Mexico, is dominantly agricultural, and water management in the valley is highly dependent upon the annual availability of surface water for crop irrigation. Water levels in all three study wells, which represent different depths (6.7 to 18 m) and positions within the groundwater flow system, have generally risen over the period of record. However, the sites differ with respect to the direction of multi-year SC trends, as well as the seasonality and general variability of water-quality parameters. Annual dissolved-solids concentrations typically correlate with multi-year SC trends, but annual concentrations of individual major and trace elements, nutrients, and pesticides tend to be variable. Age tracers indicate that the sites have differing fractions of young (post-1950) recharge and older regional groundwater. Temporal patterns in water quality at the three sites likely illustrate the effects of various hydrologic factors and conditions, including the release, pumping, and application of water for crop irrigation.

Pre-Regulatory Closed Landfill Care: Albuquerque’s Experience

Ken Ziegler

Minimally regulated closed municipal solid waste landfills continue to pose threats to human health, environment, and groundwater even after more than 30 years of closure. The City of Albuquerque Environmental Health Department Environmental Services Division (ESD) has been overseeing and managing closed landfills for over 25 years. Most of the landfills were former gravel pits that were filled and closed prior to State and Federal landfill requirements. These closed landfills did not have subsurface liners, known waste inventory, or information on landfill management during filling. Issues related to these landfills include landfill gas production, migration, and mitigation; settlement and erosion; development on and near; and potential impacts to human health and the environment.

Long term monitoring shows methane production within the waste remains consistent at levels near 35% with maximum amounts measured around 60%. Volatile organic compounds, specifically chlorinated alkenes, remain as threats to groundwater and vapor intrusion. A landfill gas extraction system, soil vapor extraction system, air injection system, and a groundwater pump and treat system has been installed, operated, and maintained at the closed Los Angeles Landfill. ESD has established guidelines for development in and around closed landfills that require assessment and abatement of landfill gas and/or waste.

Oversight and management of these closed landfills cannot be overlooked by municipalities, counties, and state agencies in spite of minimal regulatory requirements. These closed landfills continue to pose threats to groundwater resources and as such development of ordinances, policies, regulations, and guidelines may be necessary to address these long term legacy contaminant sources.

Presence of Pharmaceutical Compounds in Water, North Central New Mexico

Patrick Longmire, Ph.D.

Endocrine disruptor chemicals (EDC) and pharmaceutical and personal care products (PPCP) are contaminants of significant concern found in aquatic environments worldwide. Numerous hydrophilic EDC and PPCP have been measured in treated and non-treated wastewater, surface water, and groundwater throughout the United States and Europe during the past several decades. Since the mid-1940s, Los Alamos National Laboratory (LANL) and Los Alamos County, New Mexico have released treated wastewater to three major watersheds that provide recharge to the regional aquifer beneath the Pajarito Plateau. Santa Fe and Española also discharge treated wastewater to the Santa Fe River and Rio Grande, respectively. Over 105 sampling stations located across the Pajarito Plateau and along the Rio Grande and Santa Fe River are routinely analyzed for 32 PPCP using EPA method 1694. Analytical results show variable types and concentrations of PPCP present at most sampling locations. These water-soluble chemicals undergo limited adsorption/partitioning onto mineral surfaces and solid organic matter and typically migrate in groundwater without any retardation. Commonly detected PPCP present in treated wastewater include acetaminophen, caffeine, carbamazepine, DEET, diazepam, diclofenac, dilantin, fluorextine, gemfibrozil, hydrocodone, meprobamate, methadone, salicylic acid, and sulfamethoxazole. Acetaminophen, caffeine, and sulfamethoxazole are detected at the highest frequency in groundwater and surface water downstream from discharge sources. Several of the LANL monitoring wells containing PPCP also have contaminants associated with industrial-derived effluents such as chromate, sulfate, chloride, and nitrate. This contaminant relationship shows the presence of similar groundwater-flow paths in the vadose zone (305 meters thick) and regional aquifer. Presence of PPCP in groundwater at Los Alamos refines the conceptual model for fate and transport of mobile contaminants migrating through the deep vadose zone to the regional aquifer.

Quality of groundwater used for public supply in principal aquifers of the Southwestern U.S.

Celia Rosecrans

In 2013, the National Water-Quality Assessment (NAWQA) Project of the U.S. Geological Survey began a sampling effort focused on the quality of groundwater used for public supply in 20 principal aquifers across the Nation. Portions of four of these nationally identified principal aquifers─the Basin and Range basin-fill aquifer, the Basin and Range carbonate-rock aquifer, the Rio Grande aquifer and the High Plains aquifer─are located within the Southwestern U.S. NAWQA sampled 238 public supply wells from these four aquifers during 2013 to 2016. Samples were analyzed for a comprehensive suite of water-quality constituents, including major and trace elements (including hexavalent chromium), nutrients, pesticides, volatile organic compounds (VOCs), radionuclides, microbial indicators, pharmaceuticals, hormones, and groundwater age tracers. No exceedances of human-health benchmarks for drinking water were present in the samples collected for pesticides or VOCs. The most common exceedances frequencies of water-quality benchmarks relative to secondary standards were for salinity-related constituents: 30% of samples had high concentrations of dissolved solids, whereas exceedances of chloride, sulfate, and fluoride, ranged from 8% to 13%. The most common exceedance of a human-health benchmark for drinking water was for arsenic (12%). Exceedances for uranium (4%) and nitrate (0%) were low; these results contrast with previous NAWQA studies of shallow groundwater in these aquifers, where exceedances of human-health benchmarks for constituents such as arsenic, uranium, and nitrate occurred more frequently. Results are being evaluated to assess the relation of groundwater quality with natural and human-related factors. Most constituents that have exceedances of water-quality or human-health benchmarks in the four identified principal aquifers are derived chiefly from geologic sources, and generally are observed at higher concentrations in older, more geochemically evolved groundwater.

Quality of groundwater used for public supply in the aquifers of the Edwards-Trinity aquifer system

Marylynn Musgrove

The Edwards-Trinity aquifer system is an important source of groundwater for public supply. The aquifer system underlies about 77,000 square miles, largely in Texas and also in small parts of Oklahoma and Arkansas. In 2016 and 2017, the National Water-Quality Assessment (NAWQA) project of the U.S. Geological Survey collected raw-water samples from 75 public-supply wells in the Edwards-Trinity aquifer system as part of a sampling effort focused on the quality of groundwater used for public supply in principal aquifers across the Nation. The Edwards-Trinity aquifer system, which ranks 11^th among the Nation’s principal aquifers for groundwater withdrawal for public supply, is characterized as three related aquifers in carbonate and clastic Cretaceous-age rocks: the Trinity aquifer, the Edwards aquifer, and the undifferentiated Edwards-Trinity aquifer. Twenty-five public-supply wells were sampled in each of the three aquifers, which allows for comparison across the aquifers. The wells were selected for sampling under a nationally consistent design that uses equal-area grids to achieve a spatially unbiased dataset, and were sampled for a comprehensive suite of analytes (major and trace elements, nutrients, pesticides, volatile organic compounds, radionuclides, microbial indicators, pharmaceuticals, hormones, and selected isotopes and groundwater age tracers). Results of this sampling effort are being incorporated into ongoing efforts by NAWQA to characterize the occurrence of contaminants of concern for human health, to identify the primary factors controlling that occurrence, and to improve understanding of groundwater processes that are important to management of water resources.

Registration

Transboundary Aquifers

Laura Bexfield

Geochemical and isotopic investigation of deep groundwater in the Mesilla Basin, New Mexico

Andrew Robertson

The Mesilla Basin/Conejos-Médanos aquifer system, extending from southern New Mexico to Chihuahua, Mexico, is a priority transboundary aquifer under the 2006 United States-Mexico Transboundary Aquifer Assessment Act. Declining water levels, deteriorating water quality, and increasing groundwater use by municipal, industrial, and agricultural users raise concerns about long-term aquifer sustainability. Relative contributions of present-day and “paleo” recharge to sustainable fresh groundwater yields has not been determined and evidence suggests that a large source of salinity at the distal end of the Mesilla Basin is saline discharge from deep groundwater flow. The magnitude and distribution of those deep saline flow paths are not determined.

The contribution of deep groundwater to discharge and salinity in the shallow groundwater and surface water systems of the Mesilla Basin will be determined by collecting groundwater samples and analyzing for geochemical and isotopic tracers, including the radioisotopes of argon and krypton. Analytes include major ions, trace elements, the stable isotopes of water, strontium and boron isotopes, uranium isotopes, the carbon isotopes of dissolved inorganic carbon, noble gas concentrations and helium isotope ratios. Dissolved gases are extracted and captured from groundwater wells using membrane contactors in a process known as ultra-trace sampling. Gas samples are analyzed for radioisotope ratios of krypton and argon by ATTA or low-level counting.

Effectiveness of the ultra-trace sampling device and method was evaluated by comparing results of tritium concentrations to the krypton-85 content. Good agreement between the analyses, especially in samples with undetectable tritium, indicates that the ultra-trace procedure is effective and confirms that introduction of atmospheric air has not occurred. The geochemistry data indicate a complex system of geochemical endmembers, and mixing between these endmembers. Ongoing work seeks to better constrain groundwater ages and mixing models through the coupled use of conventional aqueous geochemical and isotopic analysis and the ultra-trace constituents.

Integration of Science and Policy in the Management of Transboundary Water Resources with Specific Approaches on Transboundary Aquifers along the U.S. and Mexico

Gilbert Anaya

The International Boundary and Water Commission (or IBWC), United States and Mexico, is an international body that was created to address the various boundary and water issues as they may arise. The 1944 Water Treaty addresses the allocation and distribution of shared rivers for the Rio Grande, Tijuana, and Colorado River. During the application of these treaties, the IBWC can seek to address an issue or new concept by convening binational meetings with leaders from each country and develop solutions that may lead to concurrence and commitment under an IBWC Minute. IBWC Minutes are binding upon both governments and become part of the Treaty. To date, IBWC has signed 322 Minutes.

Many of these Minutes include the allocation and distribution of shared surface waters. There is only one reference to transboundary groundwater resources within the IBWC framework. Under the 1944 Water Treaty, Minute No. 242 was signed in 1973. The Minute noted that a groundwater agreement would be developed in a subsequent agreement. The U.S. and Mexico also agreed to establish a buffer at San Luis, Arizona, and San Luis, Sonora that would limit groundwater pumping within 5 miles of the border.

Collaborative efforts related to groundwater were focused on data collection that were based on Minute No. 242 and a subsequent agreement of the IBWC signed in 2009, known as a Joint Report of the Principal Engineers, to prepare and support binational transboundary aquifer studies along the border. The IBWC framework serves to bring scientists together, to conduct joint investigations, foster information exchange, and work under a framework that is mutually agreed to and respected by both countries. The role of the IBWC may be to help bring the science and policy discussions together in a forum that could lead to the development of a framework document for groundwater.

The Transboundariness Approach and Prioritization of Transboundary Aquifers between Mexico and Texas

Rosario Sanchez

Transboundarines refers to a new approach that identifies and measures the priorization of transboundary aquifers using criteria that expands its physical boundaries. This approach redefines the aquifer value considering its socio-economic and political conditions adding additional variables to the transboundary context. Transboundariness is applied to the hydrogeological units/aquifers between Mexico and Texas obtaining the following results. First, the criteria used to measure it and corresponding scores, agree with the current level of attention to transboundary aquifers/hydrogeological units in the region, providing a quantifiable metric system that could be tested with other transboundary aquifers in the world. Second, this approach provides a holistic and integrative perspective for transboundary aquifer assessment and priorization scheme, offering transboundary management alternatives that consider contextual dimensions and time scales in addition to the physical aquifer conditions. Third, this prioritization exercise expands the criteria currently used to prioritize transboundary aquifers (groundwater dependency and contamination vulnerability) into a more identifiable regime of groundwater links to the community as a whole. Finally, results reflect not only the reality in which the transboundary aquifers between Mexico and United States in Texas are being used (or neglected), at which scale and rate; but also, the socio-political reality of the populations that depend on these vital resources for current and future development. Future research should encourage the analysis of sustainable groundwater scenarios for the high-priority aquifers as well as the development of transboundary governance schemes, to move toward managing transboundary aquifers in a truly binational way.

Using Heat as a Tracer to Estimate Deep Saline Groundwater Inputs to the Rio Grande in the Mesilla Basin, New Mexico, USA

Jeff Pepin

Profiles of temperature with depth below ground surface are used to locate groundwater upflow zones and to estimate associated salinity fluxes from deep (greater than 1 km) parts of the Mesilla Basin regional aquifer to the Rio Grande. The Mesilla Basin in southern New Mexico, western Texas, and northern Chihuahua, Mexico, where it is known as the Conejos-Médanos Basin, was designated by the United States as a priority transboundary aquifer in part because of the presence of the Rio Grande within the basin. Declining water levels, deteriorating water quality, and increasing use of water resources on both sides of the international border raise concerns about the sustainability of regional water supplies. The Rio Grande wintertime chloride concentration more than doubles (120 ppm to 280 ppm) as the river flows through 70 miles of the Mesilla Basin. Previous researchers attributed this reduction in water quality to the upwelling of deep sedimentary brines and geothermal waters within the basin. However, the spatial distribution of these upflow zones and their groundwater flow rates are poorly understood. Temperature profiles from 373 existing boreholes within the basin are affected by the advection of heat, resulting in characteristic thermal signatures at upflow zones. At least three distinct upflow zones near regional faults have been identified. The Bredehoeft and Papadopulos (1965) one-dimensional heat-transport analytical solution is applied to upflow-zone profiles to estimate their corresponding vertical groundwater flow rates. Temperature, heat flow, and salinity maps are constructed to approximate the areal extents of identified upflow zones. These areal estimates are then combined with the vertical groundwater flow calculations and salinity data to quantify volumetric salinity fluxes to the shallow aquifer system and Rio Grande. The results of this study will inform understanding of the impact of deep saline groundwater on regional water supplies for the Mesilla Basin.

Welcome and Keynote: Holly Richter, Ph.D.

Holly Richter, Ph.D.

Adaptive Management of Groundwater Resources in the Arid Southwest

Holly Richter, Ph.D.

Increasing water demands, combined with extended drought within the arid Southwest, have resulted in widespread increases in aquifer depletion. While the complexity and uncertainty associated with groundwater systems limits well-informed decision-making in many cases, this presentation will provide a general framework for stakeholder engagement that builds progressive momentum toward identifying longer term solutions.