Groundwater development leads to decreasing arsenic concentrations in the San Joaquin Valley, California

Science of the Total Environment (Elsevier) | January 18th, 2021

In the San Joaquin Valley (SJV), California, about 10% of drinking water wells since 2010 had arsenic concentrations above the U.S. maximum contaminant level of 10μg/L.

In the San Joaquin Valley (SJV), California, about 10% of drinking water wells since 2010 had arsenic concentrations above the U.S. maximum contaminant level of 10μg/L. High concentrations of arsenic are often associated with high pH (greater than 7.8) or reduced geochemical conditions. Although most wells have low arsenic(<3μg/L) and do not have changing arsenic concentrations, this study found that most wells with concentrations above 10μg/L had arsenic trends. Overall, about 24% of wells had time-series trends since 2010 and 59% had paired-sample trends since 2000. Most wells had decreasing arsenic trends, even in wells with higher arsenic concentrations. These wells often had co-detections of increasing nitrate and sulfate trends that reflect oxic groundwater likely derived from agricultural recharge. Wells with increasing arsenic trends were deeper or located in the valley trough where aquifer materials are more fine-grained and where reducing conditions favor arsenic mobility. Wells with arsenic trends also tend to be clustered near areas of higher well density. Groundwater pumping in these areas has likely increased the contribution of younger, more oxic groundwater in wells with declining arsenic or, less frequently, increased the contribution of higher pH or reduced groundwater in wells with rising arsenic. Projections of arsenic trends indicate that 37 wells with high arsenic presently will be below 10μg/L in ten years. Unfortunately, these improvements will be largely offset by 31 wells that are expected to increase above 10μg/L in addition to expected rises in nitrate in wells where arsenic decreased. This study shows how human-altered flow systems can impact the natural geochemical character of water in both beneficial and deleterious ways.

Groundwater Discharge by Evapotranspiration, Dixie Valley, West-Central Nevada, March 2009–September 2011

U.S. Geological Survey (USGS) | April 30th, 2015

Groundwater dominates snowmelt runoff and controls streamflow efficiency in the western United States

Nature Portfolio (Springer Nature) | May 3rd, 2025

Groundwater Dynamics in the Colorado River Limitrophe

Pacific Institute | May 23rd, 2013

The Colorado River, diverted and channelized and intensively managed, only rarely has enough water to flow even 20 miles past Morelos Dam, the last dam on the river, near

The Colorado River, diverted and channelized and intensively managed, only rarely has enough water to flow even 20 miles past Morelos Dam, the last dam on the river, near the California/Arizona/Baja California border. The river’s limitrophe reach – the roughly 22.5 mile stretch from Andrade to San Luis that separates Baja California from Arizona – is generally considered the uppermost extent of the remnant Colorado River delta, with some of the most extensive stands of native cottonwoods and willows left on the lower Colorado River and one of the few areas where the river still occasionally has enough water to exceed its banks and reach its floodplain. Because of this, there has been intense restoration interest in the limitrophe reach for more than a decade. In recent years, however, concern has grown that deteriorating groundwater conditions in the lower portion of the limitrophe will limit the success of restoration efforts. Groundwater Dynamics in the Colorado River Limitrophe describes and explains the changing groundwater conditions in and adjacent to the Colorado River’s limitrophe reach, and analyzes the impact of groundwater pumping on these overdraft conditions. The key question underlying this study asks how changing groundwater conditions in the limitrophe could affect the sustainability of planned habitat restoration projects. This study indicates that, even after the exceptionally dry period of 2005-2009, when surface flows failed to reach the gage at the downstream end of the limitrophe on 90 percent of days, more than a third of the channel through the limitrophe still exhibited connectivity with the water table, and roughly two-thirds of the limitrophe still had a water table that remained within the reach of the roots of cottonwoods and willows. The plunging water table at the downstream end of the limitrophe suggests that the final five miles of the river within the limitrophe may not respond to efforts to restore riparian habitat, at least not without a long-term commitment to supplemental irrigation, but areas upstream appear well-insulated from the recent drawdown and would benefit from restoration activity, such as that proposed by the recent Minute 319.

Groundwater Exchange Pools and Urban Water Supply Sustainability: Modeling Directed and Undirected Networks

American Society of Civil Engineers (ASCE) | August 1st, 2018

Groundwater basins are important sources of water supply and storage for many cities. Groundwater exchange pools offer additional opportunities for utilizing these

Groundwater basins are important sources of water supply and storage for many cities. Groundwater exchange pools offer additional opportunities for utilizing these common pool resources, but their potential role in urban water management is not clear, and modeling such exchanges can be challenging. This paper presents an analysis of the potential for groundwater basin exchange pools to contribute to urban water supply sustainability. Building on an existing model of urban water management in Los Angeles, the analysis assesses the potential for groundwater exchange pools to reduce scarcity and demonstrates a method for modeling two-way (undirected) flows within a directed-network model using linear programming. Results indicate that exchange pools can help alleviate shortages from operational changes (reduced imported water) in Los Angeles, but providing more parties with access to storage improves their effectiveness. Exchange pools could potentially provide 6–12% of total supplies and reduce shortages as much as 86%. Considerations for organizing exchange pools are discussed to explore policy implications for managing common pool resources. The analytical method for embedding undirected network flows within a larger directed-network model has wide applicability for water resource systems analysis applications, including modeling water markets and interbasin transfers. * U.C. Davis hosts a discussion of the content by the authors at California Water Blog. 

Groundwater Flow Model of the East and South Las Posas Sub-Basins – Preliminary Draft Report

Calleguas Municipal Water District (CMWD) | January 17th, 2018

INTERA Incorporated (INTERA) was retained by the Calleguas Municipal Water District (CMWD) to develop a numerical groundwater model of the East Las Posas Management Area

INTERA Incorporated (INTERA) was retained by the Calleguas Municipal Water District (CMWD) to develop a numerical groundwater model of the East Las Posas Management Area (ELPMA), which includes the locally-recognized east and south sub-basins of the Las Posas Valley Basin (LPVB). Groundwater in the ELPMA is found in a multiple-aquifer system characterized by intense faulting and folding, which is known to exert structural controls on groundwater flow and movement. The ELPMA is known to receive recharge from surface water flows in Arroyo Las Posas/Simi that runs east to west along the southern edge of the basin. Flows in the Arroyo have become perennial as a result of discharges from wastewater treatment plants and dewatering wells within and upstream of the ELPMA. Hence, understanding and modeling the surface-water/groundwater interaction along the Arroyo is an important component of the numerical model development. CMWD also owns and operates the Las Posas Basin Aquifer Storage and Recovery (ASR) Project, consisting of eighteen high capacity ASR wells and associated facilities located in the ELPMA that are used to inject and recover potable water purchased from Metropolitan Water District of Southern California (Metropolitan). Basin response to injection/extractions at the ASR well fields and the evaluation of storage capacity of the ASR well field are key considerations for this modeling project. 

Groundwater Geology and Hydrology of Death Valley National Park, California and Nevada

U.S. Department of the Interior (DOI) | December 3rd, 2012

Groundwater Hydraulics

American Geophysical Union (AGU) | January 1st, 1984

Published by the American Geophysical Union as part of the Water Resources Monograph Series, Volume 9. John Ferris's research has covered a broad range of hydrologic p

Published by the American Geophysical Union as part of the Water Resources Monograph Series, Volume 9. John Ferris's research has covered a broad range of hydrologic problems in groundwater, including pollution, storage, recharge, and pumping of groundwater; drainage design; hydraulics of aquifer systems; saltwater encroachment; and application of geophysics to groundwater development. These contributions have been made as a researcher and teacher of national and international renown during a career that has lasted more than four decades. During these four decades, the methodologies for application of hydraulics to solving groundwater problems have continued to evolve and improve. The development of aquifer test techniques and analytical solutions been coemonplace in the 1950's, 1960's, and early 1970's have increasingly been supplemented by the use of numerical methods and automated parameter estimation techniques.

Groundwater in California

Public Policy Institute of California (PPIC) | June 6th, 2024

Groundwater Level Monitoring and the Importance of Long-Term Water-Level Data

U.S. Geological Survey (USGS) | December 18th, 2001

Ground water is among the Nation’s most precious natural resources. Measurements of water levels in wells provide the most fundamental indicator of the status of this r

Ground water is among the Nation’s most precious natural resources. Measurements of water levels in wells provide the most fundamental indicator of the status of this resource and are critical to meaningful evaluations of the quantity and quality of ground water and its interaction with surface water. Water-level measurements are made by many Federal, State, and local agencies. It is the intent of this report to highlight the importance of measurements of ground-water levels and to foster a more comprehensive and systematic approach to the long-term collection of these essential data. Through such mutual efforts, the Nation will be better positioned in coming decades to make wise use of its extensive groundwater resources.