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 Groundwater Used for Domestic Supply in the Northern San Joaquin Valley, California

U.S. Geological Survey (USGS) | July 28th, 2021

 Groundwater provides more than 40 percent of California’s drinking water. To protect this vital resource, the State of California created the Groundwater Ambient Moni

 Groundwater provides more than 40 percent of California’s drinking water. To protect this vital resource, the State of California created the Groundwater Ambient Monitoring and Assessment (GAMA) Program. The Priority Basin Project (PBP) of the GAMA Program provides a comprehensive assessment of the State’s groundwater quality and provides increased public access to groundwater-quality information. Private domestic and small-system drinking-water wells in the Northern San Joaquin Valley (NSJV) were the target for this assessment. These wells tend to pump water from shallower parts of alluvial aquifers compared to deeper, long-screened public-supply wells in the region. 

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.

Rapid groundwater decline and some cases of recovery in aquifers globally

Nature Portfolio (Springer Nature) | January 24th, 2024

Rapid subsidence over oil fields measured by SAR interferometry: Geophysical Research Letters

American Geophysical Union (AGU) | September 1st, 1998

The Lost Hills and Belridge oilfields are in the San Joaquin Valley, California. The major oil reservoir is high porosity and low permeability diatomite. Extraction of la

The Lost Hills and Belridge oilfields are in the San Joaquin Valley, California. The major oil reservoir is high porosity and low permeability diatomite. Extraction of large volumes from shallow depths causes reduction in pore pressure and subsequent compaction, forming a surface sub- sidence bowl. We measure this subsidence from space using interferometric analysis of SAR (Synthetic Aperture Radar) data collected by the European Space Agency Remote Sensing Satellites (ERS-1 and ERS-2). Maximum subsidence rates are as high as 40 mm in 35 days or > 400 mm/yr, measured from interferograms with time separations ranging from one day to 26 months. The 8- and 26-month inter-ferograms contain areas where the subsidence gradient exceeds the measurement possible with ERS SAR, but shows increased detail in areas of less rapid subsidence. Synoptic mapping of subsidence distribution from satellite data powerfully complements ground-based techniques, permits measurements where access is difficult, and aids identification of underlying causes

Recharge Area Identification, Utilization, and Protection Resource Management Strategy

California Department of Water Resources (DWR) | April 29th, 2024

This resource management strategy (RMS) advances water supply augmentation, resilience, and equity in California by providing summaries of the state of knowledge, applica

This resource management strategy (RMS) advances water supply augmentation, resilience, and equity in California by providing summaries of the state of knowledge, applications, and available information and resources on recharge area identification, utilization, and protection.

Recharge Area Protection (Resource Management Strategy)

California Department of Water Resources (DWR) | July 29th, 2016

Recharge areas are those areas that provide the primary means of replenishing groundwater. Good natural recharge areas are those where good quality surface water is able

Recharge areas are those areas that provide the primary means of replenishing groundwater. Good natural recharge areas are those where good quality surface water is able to percolate through the sediments and rocks to the saturated zone which contains groundwater. If recharge areas cease to function properly, it will limit groundwater replenishment and/or groundwater quality for storage or use. Protection of recharge areas requires a number of actions based on two primary goals: (1) ensuring that areas suitable for recharge continue to be capable of adequate recharge rather than being covered by urban infrastructure, such as buildings and roads, and (2) preventing pollutants from entering groundwater to avoid expensive treatment that may be necessary prior to beneficial use. Protection of recharge areas is necessary to maintain the quantity and quality of groundwater in the aquifer. However, protecting recharge areas by itself does not provide a supply of water. Recharge areas are functioning properly when aquifer storage capacity is available, sufficient permeable surface is present, and the adequate supply of good quality water to recharge the aquifer is available. Protecting existing and potential recharge areas allows them to serve as valuable components of a conjunctive management and groundwater strategy.