Protecting Groundwater Quality in California: Management Considerations for Avoiding Naturally Occurring and Emerging Contaminants

Environmental Defense Fund (EDF) | September 20th, 2019

Quality of Groundwater Used for Domestic Drinking-Water Supply in the Coachella Valley, 2020

U.S. Geological Survey (USGS) | January 13th, 2023

Quality of Groundwater Used for Domestic Supply in the Modesto, Turlock, and Merced Subbasins of the San Joaquin Valley, California

U.S. Geological Survey (USGS) | January 6th, 2023

More than 2 million Californians rely on groundwater from privately owned domestic wells for drinking-water supply. This report summarizes a water-quality survey of domes

More than 2 million Californians rely on groundwater from privately owned domestic wells for drinking-water supply. This report summarizes a water-quality survey of domestic and small-system drinking-water supply wells in the Modesto, Turlock, and Merced subbasins of the San Joaquin Valley where more than 78,000 residents are estimated to use privately owned domestic wells. Results indicate that inorganic and organic constituents in groundwater were respectively present above regulatory (maximum contaminant level, MCL) benchmarks for public drinking-water quality in 37 percent and 9 percent of the aquifer area used for domestic drinking-water supplies (herein, “domestic groundwater resources”). The most prevalent inorganic constituents exceeding regulatory benchmarks were nitrate, uranium, and arsenic. The only organic constituents exceeding regulatory benchmarks were the fumigant constituents 1,2,3-trichloropropane (1,2,3-TCP) and 1,2-dibromo-3-chloropropane (DBCP), but the herbicides atrazine and simazine were detected at low concentrations below one-tenth of regulatory benchmarks in 30 percent of domestic groundwater resources. Total dissolved solids (TDS) and manganese exceeded aesthetic-based (secondary maximum contaminant level [SMCL]) benchmarks for drinking water in 3 percent and 13 percent of domestic groundwater resources, respectively. Per- and polyfluoroalkyl substances (PFAS) were detected in 23 percent of domestic groundwater resources, with 4 percent exceeding California state notification or response levels for specific compounds. Total coliform bacteria were detected in 20 percent of domestic groundwater resources. Elevated concentrations of nitrate, uranium, TDS, and pesticides (fumigant constituents and herbicides) are related to agricultural land use and were typically present at shallow depths up to 75 meters below land surface. Agriculturally derived constituents were detected in wells screened below the Corcoran Clay Member of the Tulare Formation (herein, “Corcoran Clay”) in the southeastern part of the study area, where the Corcoran Clay tends to be shallower and thinner than in areas to the northwest. Nitrate, uranium, and TDS were most prevalent in the northwest part of the study area proximal to the valley trough where soils are poorly drained and agricultural land uses are predominantly grain, alfalfa, and dairy farms. Pesticides tended to occur in groundwater below coarse-grained surficial deposits and within a northwest to southeast trending band along the eastern extent of the Corcoran Clay that typically demarcates the western extent of well-drained soils associated with perennial orchard crops. Elevated concentrations of arsenic tended to occur west of this band in reducing groundwater but also sometimes co-occurred with elevated nitrate in oxic groundwater, most likely because of geochemical conditions in agriculturally affected groundwater that can enhance the mobility of arsenic from aquifer sediments.

Quality of Water from Domestic Wells in Principal Aquifers of the United States, 1991–2004: Overview of Major Findings

U.S. Geological Survey (USGS) | November 5th, 2009

This report is one of a series of publications, The Quality of Our Nation’s Waters, which describes major findings of the NAWQA Program on water-quality issues of regio

This report is one of a series of publications, The Quality of Our Nation’s Waters, which describes major findings of the NAWQA Program on water-quality issues of regional and national concern. This report presents a national assessment of the quality of water in private domestic wells based on samples from about 2,100 wells located in 48 states and tapping 30 regional aquifers used for water supply. Compared to previous investigations of domestic well water quality, “Quality of Water from Domestic Wells in Principal Aquifers of the United States, 1991–2004 —Overview of Major Findings” greatly expands the number of contaminants assessed in domestic wells and improves geographic coverage of wells sampled. More than 43 million people—about 15 percent of the U.S. population—rely on domestic wells as their source of drinking water (Hutson and others, 2004). The quality and safety of water from domestic wells, also known as private wells, are not regulated by the Federal Safe Drinking Water Act or, in most cases, by state laws. Rather, individual homeowners are responsible for maintaining their domestic well systems and for monitoring water quality. The lack of regular monitoring of domestic wells makes periodic assessments at national, regional, and local scales important sources of information about this key source of drinking water. This study from the National Water-Quality Assessment (NAWQA) Program of the U.S. Geological Survey (USGS) assesses water-quality conditions for about 2,100 domestic wells. The sampled wells are located in 48 states and in parts of 30 regionally extensive aquifers used for water supply in the United States. As many as 219 properties and contaminants, including pH, major ions, nutrients, trace elements, radon, pesticides, and volatile organic compounds (VOCs), were measured. Fecal indicator bacteria and additional radionuclides were analyzed for a smaller number of wells. The large number of contaminants assessed and the broad geographic coverage of the present study provides a foundation for an improved understanding of the quality of water from the major aquifers tapped by domestic supply wells in the United States.

Quality of Water from Public-Supply Wells in the United States, 1993–2007: Overview of Major Findings

U.S. Geological Survey (USGS) | July 12th, 2010

In this study by the National Water-Quality Assessment (NAWQA) Program of the U.S. Geological Survey (USGS), chemical water-quality conditions were assessed in source (un

In this study by the National Water-Quality Assessment (NAWQA) Program of the U.S. Geological Survey (USGS), chemical water-quality conditions were assessed in source (untreated) groundwater from 932 public-supply wells, hereafter referred to as public wells, and in source and finished water from a subset of 94 wells. The public wells are located in selected parts of 41 states and withdraw water from parts of 30 regionally extensive water-supply aquifers, which constitute about one-half of the principal aquifers in the United States. Although the wells sampled in this study represent less than 1 percent of all groundwater-supplied public water systems in the United States, they are widely distributed nationally and were randomly selected within the sampled hydrogeologic settings to represent typical aquifer conditions. All source-water samples were collected prior to any treatment or blending that potentially could alter contaminant concentrations. As a result, the sampled groundwater represents the quality of the source water and not necessarily the quality of finished water ingested by the people served by these public wells.

Quantifying anthropogenic contributions to century-scale groundwater salinity changes, San Joaquin Valley, California, USA

Science of the Total Environment (Elsevier) | June 15th, 2018

Total dissolved solids (TDS) concentrations in groundwater tapped for beneficial uses (drinking water, irrigation, freshwater industrial) have increased on average by abo

Total dissolved solids (TDS) concentrations in groundwater tapped for beneficial uses (drinking water, irrigation, freshwater industrial) have increased on average by about 100 mg/L over the last 100 y ears in the San Joaquin Valley, California (SJV). D uring this period land use in the SJV changed from natural vegetation and dryland agriculture to dominantly irrigated agriculture with growing urban areas. Century-scale salinity trends were evaluated by comparing TDS concentrations and major ion compositions of groundwater from wells sampled in 1910 (Historic) to data from wells sampled in 1993 –2015 (Modern). TDS concentrations in subregions of the SJV, the southern (SSJV), western (WSJV), northeastern (NESJV), and southeastern (SESJV) were calculated using a cell-declustering method. TDS concentrations increased in all regions, with the greatest increases found in the SSJV and SESJV. Evaluation of the Modern data from the NESJV and SESJV found higher TDS concentrations in recently recharged (post-1950) groundwater from shallow (b50 m) wells surrounded predominantly by agricultural land uses, while premodern (pre-1950) groundwater from deeper wells, and recently recharged groundwater from wells surrounded by mainly urban, natural, and mixed land uses had lower TDS concentrations, approaching the TDS concentrations in the Historic groundwater. For the NESJV and SESJV, inverse geochemical modeling with PHREEQC indicated that weathering of primary silicate minerals accounted for the majority o f the increase in TDS concentrations, contributing more than nitrate from fertilizers and sulfate from soil amendments combined. Bicarbonate showed the greatest increase among major ions, resulting from enhanced silicate weathering due to recharge of irrigation water enriched in CO2 during the growing season. The results of this study demonstrate that large anthropogenic changes to the hydrologic regime, like massive development of irrigated agriculture in semi-arid areas like the SJV, can cause large changes in groundwater quality on a regional scale.

Reduction of Nitrates in Groundwater – Agricultural Expert Panel Report

California State Water Resources Control Board (SWRCB) | September 9th, 2014

Recommendations to the State Water Resources Control Board pertaining to the Irrigated Lands Regulatory Program The Agricultural Expert Panel (Panel) was convened to a

Recommendations to the State Water Resources Control Board pertaining to the Irrigated Lands Regulatory Program The Agricultural Expert Panel (Panel) was convened to address thirteen questions posed by the State Water Resources Control Board (State Water Board). The questions were primarily technical in nature, and are abbreviated below. 1. How can risk to or vulnerability of groundwater best be determined in the context of a regulatory program such as the Irrigated Lands Regulatory Program (ILRP)? 2. Evaluate and develop recommendations for the current approaches taken to assessing risk to or vulnerability of groundwater. 3. How can risk to or vulnerability of surface water best be determined in the context of a regulatory program such as the ILRP? 4. Evaluate and develop recommendations for the current approaches taken to assessing risk to or vulnerability of surface water. 5. What management practices are expected to be implemented and under what circumstances for the control of nitrogen? 6. What management practices are recommended for consideration by growers when they are selecting practices to put in place for the control of nitrogen? 7. Evaluate and make recommendations regarding the usage of various nitrogen management and accounting practices. 8. Evaluate and make recommendations regarding the most effective methods for ensuring growers have the knowledge required for effectively implementing recommended management practices. 9. What measurements can be used to verify that the implementations of management practices for nitrogen are as effective as possible? 10. Evaluate and make recommendations regarding the usage of various verification measurements of nitrogen control. 11. Evaluate the relative merits, and make recommendations regarding the usage of, surface water measurement systems derived from either receiving water or a discharge monitoring approach to identify problem discharges. 12. Evaluate and make recommendations on how best to integrate the results of the Nitrogen Tracking and Reporting System Task Force with any above recommendation regarding management practices and verification measures. 13. Evaluate and make recommendations on the reporting requirements to report budgeting and recording of nitrogen application on a management block basis versus reporting aggregated numbers on a nitrate loading risk unit level.

Regional nitrate and pesticide trends in ground water in the eastern San Joaquin Valley, California

American Society of Agronomy (ASA) | September 18th, 2008

Protection of ground water for present and future use requires monitoring and understanding of the mechanisms controlling long-term quality of ground water. In this stu

Protection of ground water for present and future use requires monitoring and understanding of the mechanisms controlling long-term quality of ground water. In this study, spatial and temporal trends in concentrations of nitrate and pesticides in ground water in the eastern San Joaquin Valley, California, were evaluated to determine the long-term effects of agricultural and urban development on regional ground-water quality. Trends in concentrations of nitrate, the nematocide 1,2-dibromo-3-chloropropane, and the herbicide simazine during the last two decades are generally consistent with known nitrogen fertilizer and pesticide use and with the position of the well networks in the regional ground-water fl ow system. Concentrations of nitrate and pesticides are higher in the shallow part of the aquifer system where domestic wells are typically screened, whereas concentrations are lower in the deep part of the aquifer system where public-supply wells are typically screened. Attenuation processes do not seem to significantly affect concentrations. Historical data indicate that concentrations of nitrate have increased since the 1950s in the shallow and deep parts of the aquifer system. Concentrations of nitrate and detection of pesticides in the deep part of the aquifer system will likely increase as the proportion of highly affected water contributed to these wells increases with time. Because of the time of travel between the water table and the deep part of the aquifer system, current concentrations in public-supply wells likely reflect the effects of 40- to 50-year-old management practices.

Remote sensing is a viable tool for mapping soil salinity in agricultural lands

University of California, Davis (UC Davis) | April 7th, 2017

Report of Waste Discharge and Technical Report

Westlands Water District | July 10th, 2019

This Technical Report is in support of a Report of Waste Discharge (ROWD) for an agricultural aquifer storage and recovery (Ag-ASR) program for Westlands Water District

This Technical Report is in support of a Report of Waste Discharge (ROWD) for an agricultural aquifer storage and recovery (Ag-ASR) program for Westlands Water District (Westlands or District). The District is located in western Fresno and Kings Counties in the San Joaquin Valley. With the new Sustainable Groundwater Management Act (SGMA) signed into law in 2014, Westlands is pursuing means to recharge groundwater within the District’s boundaries, which coincide with the Westside Subbasin (Groundwater Subbasin Number 5-22.09). Due to the presence of poor quality shallow groundwater, fine-grained soils, and the Corcoran Clay restrictive layer, surface recharge opportunities are limited (Schmidt, 2009). Direct injection using Ag-ASR wells holds promise as a more widely implementable recharge method in the District.