Arsenic and uranium mobilization in the unsaturated zone during flood MAR

Kira Waldman, University of California – Davis

Ag-MAR increases local groundwater storage by using excess surface water to flood farmland during nongrowing seasons. It is a promising strategy for alleviating water shortages caused by climate and overuse; however, it carries risks to groundwater quality due to perturbations in recharge regimes and geochemical conditions, potentially mobilizing geogenic arsenic and uranium. Previous research suggests that sediment heterogeneity, aquifer geochemistry, and rewetting cycles are critical factors influencing the release and retention of geogenic metal(loid)s from aquifer solids during artificial recharge. In this novel study, we examine the reaction mechanisms, behavior, and mobilization of geogenic arsenic and uranium in the vadose zone during a 1-month Ag-MAR experiment in a fallowed almond orchard in Modesto, California. We used three different recharge plots to investigate the following: the role of field-scale sediment heterogeneity in alluvial aquifer material, the geochemical conditions responsible for the mobilization of arsenic, and the effect of redox changes on the coupled impact of nitrate and uranium mobilization to groundwater quality. Through an integrated geochemical analysis of pore-water, soil, and monitoring well samples from the experiment, our work highlights the importance of understanding the processes controlling geogenic contaminant mobilization in Ag-MAR settings to protect regional water quality. Results will impact the site selection of farmland and operational Ag-MAR design to enhance water quantity while limiting degradation of groundwater quality throughout California’s Central Valley.

Ag-MAR suitability in the Tulare Lake Basin by noble gas and stable isotope derived parameters

Christopher Dory, University of California Davis, with Ate Visser, Jory Lerback, Luis Sanchez-Valle, Eddie Ocampo, Helen E. Dahlke

The Tulare Lake Basin of California has seen hundreds of well failures, persistent groundwater table drawdown, and increased dependence on streambed seepage for groundwater recharge. In order to ameliorate these issues, Managed Aquifer Recharge (MAR), a technique that intentionally places more water into groundwater aquifers for environmental benefit or later use water conveyance, has been proposed as a cheap ($.03 m-3 when flooding farm fields) alternative to reservoir expansion ($1.38-2.27 m-3) and seawater desalination ($1.54-2.43 m-3). Despite MAR being cost efficient, suitable high magnitude river flows, conveyance infrastructure, and funding are limited, creating a need for decision makers to identify recharge sites that not just increase groundwater storage but also provide multiple secondary benefits such as improved drinking water supply for communities negatively affected by well failures and groundwater depletion. However, little is known about the vulnerability of domestic and public drinking water supply wells to groundwater contamination from diffuse pollutant sources (e.g. nitrates from irrigation agriculture) and their remediation potential through recharge of clean source water. And while contaminant concentrations can be directly measured, this process is person-hour intensive. This study aims to reach a broader understanding of how groundwater recharge mechanisms and sources impact well water quality in the Tulare Lake Basin by correlation of water quality data with tritium-helium ages, oxygen isotopic analysis, and noble gas mass spectrometry. This broader understanding of well vulnerability will then enable decision makers to, along with the employment of existing demographic-based recommendations such as linguistic isolation, direct funds for the securing of clean and sustainable water in a more equitable manner.

Hydrological and hydrogeological considerations for redistribution agreements in severe drought: Limarí River Basin, Coquimbo, Chile  

Pedro Sanzana, Center for Advanced Research in Arid Zones in Chile, with Giulia dePasquale, Yerelin Cárcamo, Pablo Álvarez, Rosa Sanzana, Ignacio Aguirre

Water scarcity has had 35% of Chile’s population under a severe drought for over a decade. This dramatic situation has forced the coordination of nationwide strategies from ministries, agencies, and regional governments to formulate rules and agreements to regulate water resources. Local communities formed by surface or groundwater users have been pushing to reach agreements that prioritize human consumption and ecosystem services over productive uses such as industry, agriculture, and mining. As a result, water rights that are traditionally fixed have been prorated in basins where streams flow, enabling users to consume only 3 to 6% of their original volume. The new Chilean water code, implemented in April 2022, indicates that once a flow shortage evolves into a severe drought, the General Water Directorate can request a redistribution agreement in coordination with the local water communities. A lack of agreement between the parties will force the directorate to manage the basin and aquifer directly. Given the reduced precipitation and increased drought frequency due to climate change, it is expected that these redistribution agreements should be developed for most Chilean basins. This poster discusses the hydrological and hydrogeological considerations that should be included while elaborating on these redistribution agreements, including key policy and technical recommendations to ensure equitable water use. Although the primary study area is the semi-arid Limarí River basin in northern Chile, the conclusion aims to facilitate similar agreements everywhere.   

Challenges and geometrical issues of integrated hydrological and hydrogeological modeling: A case study in Chile

—Pedro Sanzana, Giulia De Pasquale, Ignacio Aguirre

Integrated watershed management practices have become dependent on computational tools to support decision-making. These tools have been subject to upgrades in order to consistently simulate the environment. On one side, water resource models (such as WEAP) have recently become more complex by integrating modules that handle large quantities of spatiotemporal catchment data. On the other side, numerical models (such as MODFLOW) require users to correctly implement a modeling mesh that follows geometrical requirements. These changes have triggered a paradigm shift, leading hydrologists and hydrogeologists to take steps toward an integrated approach, adapting their conceptual models and evolving from the simplification of the hydrological cycle through fixed boundary conditions. In Chile, universities and consulting companies have implemented fully coupled models for water resources planning for more than 24 watersheds using the WEAP-MODFLOW framework in different spatial scales reaching basins up to 15,000 km2, including the Maipo River basin located near the country’s capital. These investigations highlight the need to assimilate new tools and strategies to produce realistic, accurate, spatiotemporal representations of the environment, catchments, and basins. A critical aspect is developing satisfactory surface, groundwater, and coupled (surface-groundwater) balances to provide reliable predictions. This poster discusses the issues raised by Refsgaard et al. (2010), Barthel and Banzhaf (2016), and Staudinger et al. (2019) from an interdisciplinary surface and groundwater perspective, using examples from the integrated modeling experiences carried out in different Chilean watersheds located in wide range of latitudes, ranging from the hyper-arid Atacama Desert, including the adjacent plateau (Altiplano), to Patagonia in the southern part of the country.

Up to the challenge: Operational strategies to maximize groundwater recharge on the Oxnard Plain during the drought-buster year of 2023

—Dr. Bram Sercu, United Water Conservation District

United Water Conservation District (United) has been diverting water from the lower Santa Clara River for MAR since 1927. A primary goal of United’s MAR program is to keep groundwater elevations sufficiently high to battle seawater intrusion in the coastal areas of the Oxnard basin and to control the elevated nitrate concentrations in some inland municipal wells during periods of drought. Groundwater elevations in the aquifers of the Oxnard and Pleasant Valley basins reached near-record lows following the 2012­–2016 and 2020–2022 drought periods, with minimal recovery observed during the wetter period between 2017 and 2019. Groundwater elevations near the coast remain below sea level, and seawater intrusion has intensified over the past decade. Record rainfall in 2023 provided an opportunity to maximize diversions of stormwater from the Santa Clara River and replenish local groundwater basins. However, the abundant supply of water generated several challenges, including high sediment transport in the river system impacting the facilities, surface clogging and groundwater mounding below the recharge basins following prolonged periods of maximum recharge, restrictions on storage in local surface water reservoirs, and limited down time for facility maintenance. Key operational strategies to maximize recharge include expanding facility monitoring and maintenance, optimizing recharge operations by implementing basin rotations and sediment removal, and maximizing contractual water deliveries. This presentation will detail reservoir releases, diversion and recharge operations during this extraordinary year, and the positive impacts on groundwater elevations in several basins within United’s service area.

Virus removal by soil aquifer treatment — a long history in Arizona

Charles P. Gerba, University of Arizona

Virus removal by soil aquifer treatment (SAT) systems are dependent upon numerous operational, water quality, soil, substrata, and biological parameters. Numerous field and laboratory studies have been conducted to assess virus removal by SAT in Arizona since the 1970s and continue to present time. The development of more sensitive detection methods has increased our ability to better quantify viruses and monitor their removal under field conditions. The application of modeling virus removal and molecular detection methods will allow us to better determine the removal credits of SAT treatment for virus removal by water recycling operations. This poster presents a review of studies on virus removal by SAT in Arizona over the last 50 years.

Estimating groundwater depth and storage responses to climate variability and human activities in western U.S.   

Qinyuan Dai, Arizona State University

Groundwater, a vital resource in the western U.S., relied upon by humans and ecological systems, faces severe depletion problems due to extensive pumping. Understanding the dynamics of groundwater depth and storage changes driven by climate and human activities is critical for sustainable water resources management. However, it is challenging to efficiently create large-scale groundwater level and storage maps due to the spatial and temporal discontinuity of in situ measurements and scarcity of monitoring wells. In this work, a machine learning–based spatial interpolation method is employed to generate monthly groundwater depth and storage change maps at a 1/8-degree resolution from 2002 to 2022 as well as a pre-development groundwater depth map in the western U.S. Our method integrates diverse data categories, including meteorology, climate index, geology, topography, hydrology, land cover, anthropogenic factors, in situ observations, and remotely sensed terrestrial water storage. The method fills the spatial and temporal gaps of groundwater depth and storage changes more accurately compared to the baseline method commonly used for interpolation (Kriging). Additionally, it identifies primary controlling factors of groundwater depth and reveals that attributions to these factors vary in space and time. This research aims to provide an easy-to-use dynamic groundwater depth and storage dataset and generate valuable insights into groundwater dynamics to support the sustainable management of groundwater resources.     

Improving flood-MAR flexibility: Toward tailored high-flow diversion criteria in California rivers         

Kirsten Ondris, University of California – Davis

Implementation of flood-managed aquifer recharge (flood-MAR) requires flexible, coordinated efforts to divert excess surface water from winter and spring runoff. Currently, the California State Water Resources Control Board uses the 90th percentile of the most recent 30-year daily streamflow record to determine the availability of surface water for diversion to underground storage. However, the 90th percentile as a statewide criterion has grown increasingly controversial given the hydrologic diversity of California river systems and the heightened ecological sensitivity of particular streams, such as those in the San Joaquin Basin. In this study, we aim to develop river-specific high-flow diversion criteria to protect ecosystem functions associated with key aspects of the natural flow regime and improve flexibility in diversions. Via a case study of the Tuolumne River in the San Joaquin Basin, we calculate the availability of flood flows (magnitude, frequency, duration, and timing) in exceedance of the 90th percentile streamflow below La Grange Reservoir (USGS gauge 11289650) using the most recent 30-year record. These metrics are compared to recommended functional flow metrics and surface water rights to determine periods of streamflow abundance available for recharge. This analysis will yield revised estimates of the annual streamflow available for recharge on the Tuolumne River. It will also provide a framework to select river-specific high-flow diversion criteria for other streams in California. 

Climate resiliency through the City of Boise’s recycled water program       

Dan Stanaway, Kristene Wilder, Brown and Caldwell

Water scarcity and growing demands in the western U.S. are transforming conventional approaches to the treat-and-discharge mentality. The City of Boise’s Recycled Water Program (RWP) seeks to augment groundwater by using 5 million gallons per day (mgd) of recycled water from treated industrial effluent for reuse and aquifer recharge in the Treasure Valley, Idaho, thereby increasing water sustainability and enhancing water security. The RWP requires a cross-disciplinary approach that includes permitting, research, innovation, and pilot testing for treatment, aquifer recharge, utility formation and workforce development, land acquisition, policy and partnership development, and community engagement. Two primary technical approaches are being developed to meet the RWP objectives. First, treatment technologies are being pilot tested to develop a process for producing fit-for-purpose water quality from industrial water within permit guidelines, a process that considers antidegradation and compatibility with native groundwater. Second, groundwater recharge planning is tasked with determining the most feasible locations and methods, infiltration and/or injection. MAR planning, site characterization, and modeling used to enhance groundwater resources are some of the primary components of the RWP. Site characterization uses data from surface and borehole geophysics, infiltration testing, drill cutting samples, test wells (for groundwater sampling), and flow and transport modeling. This information will be used to support the full-scale recharge approach. A successful program will meet the City’s objective of a more diversified, secure water supply portfolio and limit daily inflows to existing publicly owned treatment works while increasing water supplies through MAR.

Movement and quantification of Escherichia coli in a MAR site

Hannah Collins, Arizona State University

Groundwater is an important source of drinking water in Arizona and, according to the Arizona Municipal Water Users Association, it makes up 40% of drinking water supplies of the state. MAR is considered an important method to maintain, replenish, and store groundwater using reclaimed and/or surface water. The Riparian Preserve at Water Ranch (RPWR) in Gilbert, Arizona, recharges treated wastewater that can contain fecal contamination. Wildlife animal activities near the pre-treated wastewater pond may additionally trigger fecal contamination in the recharged water. According to the U.S. Environmental Protection Agency, fecal-contaminated water is unsuitable for drinking and can contain pathogens that threaten public health. Escherichia coli (E. coli) is often selected as an indicator of fecal contamination level in water. Some strains of E. coli are pathogenic and can cause gastrointestinal illness in humans. The goal of this study is to assess potential concerns of public health and environmental quality by quantifying and characterizing the transport of E. coli from a wastewater recharge pond at the RWPR through the soil into groundwater. To this end, E. coli was quantified in the pond 21 times over a 15-month period (from July 2022 to September 2023), correlated with environmental factors, and analyzed during soil column experiments to determine the minimum required vertical distance of soil to prevent it from reaching the water table and contaminating groundwater. E. coli concentrations were variable and high retention was observed in the clay soil collected from the RPWR.

i-SMART is an innovative, integrated, modular, efficient, and cost-effective technology for ASR

—Dr. Ayaz Hasan, King Sattam University, Al-Kharj, Saudi Arabia

Over the past decade, numerous ASR feasibility studies have been conducted. These studies utilized the results of water quality monitoring and groundwater models, generating a significant amount of data related to hydrogeology, geology, geochemistry, well design, and operational processes. The i-SMART technology is a cost-effective, modular, real-time solution integrated into subsurface water storage systems (SWSS) that guarantees a secure and sustainable drinking water supply for cities and towns during peak demands and emergencies. The technology consists of four critical components: the SMART wellfield, the SMART operations and monitoring system, geodatabase and GIS mapping, and numerical modeling system. The i-SMART technology has been applied successfully to develop a conceptual design of a large-scale dewatering system and helped in planning the excavation and construction of underground railways by using predictive simulation of drawdowns with time. It is also used to estimate sustainable pumping rates (flow rates) by optimizing well spacing and reducing well interference.