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Groundwater Quality in the Sierra Nevada, California

U.S. Geological Survey (USGS) | December 23rd, 2014

Summary

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

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 increases public access to groundwater-quality information. The Sierra Nevada Regional study unit constitutes one of the study units being evaluated. The Sierra Nevada Regional (SNR) study unit covers approximately 25,000 square miles and includes the Sierra Nevada mountain and foothill regions. The study unit was divided into four study areas corresponding to the four major rock types present in the region: granitic rocks, metamorphic rocks, sedimentary deposits, and volcanic rocks (Shelton and others, 2010). In contrast to most other study units evaluated by the GAMA PBP, the SNR study unit consists primarily of fractured-bedrock aquifers. Most of the Sierra Nevada consists of granitic and metamorphic rocks. Groundwater is in fractures in the rocks. The fracture systems may be interconnected or isolated, resulting in variability in water levels, well yields, and water quality on local and regional scales (California Department of Water Resources, 2003). Sedimentary basins contain glacial, alluvial fan, fluvial, and lake sediments. Aquifers composed of different materials commonly contain groundwater with different chemical compositions.

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Groundwater Quality in the South Coast Interior Basins, California

U.S. Geological Survey (USGS) | May 14th, 2014

Summary

The South Coast Interior Basins (SCI) study unit covers approximately 653 square miles and consists of the Livermore, Gilroy-Hollister, Cuyama Valley, Castac Lake Valley,

The South Coast Interior Basins (SCI) study unit covers approximately 653 square miles and consists of the Livermore, Gilroy-Hollister, Cuyama Valley, Castac Lake Valley, Cuddy Canyon Valley, Cuddy Ranch Area, Cuddy Valley, and Mil Potrero groundwater basins (California Department of Water Resources, 2003). These basins were grouped into three study areas based on geography: Livermore (LIV), Gilroy (GIL), and Cuyama (CUY) (Mathany and others, 2009). Average annual precipitation across the study unit varies among the three study areas—from more than 20 inches (in.) along the northwest margin of the LIV study area to less than 8 in. in the northern parts of the CUY study area. The study areas are drained by the Arroyo de la Laguna canal in LIV, the Pájaro River and the San Benito River in GIL, and the Cuyama River in CUY. The primary aquifer system consists of Plio-Pleistocene sedimentary formations, Tertiary to Holocene-age alluvial sedimentary sequences, and unconfined Holocene- age and Pleistoceneage alluvium. The primary aquifer system is defined as those parts of the aquifers corresponding to the perforated intervals of the public-supply wells listed in the California Department of Public Health (CDPH) database. Public-supply wells in the study unit are typically drilled to depths between 200 and 600 feet, consist of solid casing from the land surface to a depth of about 50 to 350 feet, and are perforated below the solid casing. Water quality in the primary aquifer system may differ from that in the shallower and deeper parts of the aquifer system. Land use within 500-meter buffer areas around the wells in the study unit is approximately 44 percent (%) agricultural, 29% urban, and 27% natural. Agricultural lands are mostly orchards, row crops, vineyards, or pastures. The largest urban areas are the cities of Livermore and Gilroy. Recharge to groundwater basins occurs as infiltration of spring and streamflow, direct infiltration of precipitation and irrigation, subsurface inflow, and engineered recharge (percolation ponds and river regulation). The primary sources of groundwater discharge are water pumped for irrigation and municipal supply, discharge to rivers and streams, and evaporation.

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Groundwater Quality in the Western San Joaquin Valley Study Unit, 2010: California GAMA Priority Basin Project

U.S. Geological Survey (USGS) | June 9th, 2017

Summary

Water quality in groundwater resources used for public drinking-water supply in the Western San Joaquin Valley (WSJV) was investigated by the USGS in cooperation with the

Water quality in groundwater resources used for public drinking-water supply in the Western San Joaquin Valley (WSJV) was investigated by the USGS in cooperation with the California State Water Resources Control Board (SWRCB) as part of its Groundwater Ambient Monitoring and Assessment (GAMA) Program Priority Basin Project. The WSJV includes two study areas: the Delta–Mendota and Westside subbasins of the San Joaquin Valley groundwater basin. Study objectives for the WSJV study unit included two assessment types: (1) a status assessment yielding quantitative estimates of the current (2010) status of groundwater quality in the groundwater resources used for public drinking water, and (2) an evaluation of natural and anthropogenic factors that could be affecting the groundwater quality. The assessments characterized the quality of untreated groundwater, not the quality of treated drinking water delivered to consumers by water distributors. The status assessment was based on data collected from 43 wells sampled by the U.S. Geological Survey for the GAMA Priority Basin Project (USGS-GAMA) in 2010 and data compiled in the SWRCB Division of Drinking Water (SWRCB-DDW) database for 74 additional public-supply wells sampled for regulatory compliance purposes between 2007 and 2010. To provide context, concentrations of constituents measured in groundwater were compared to U.S. Environmental Protection Agency (EPA) and SWRCB-DDW regulatory and non-regulatory benchmarks for drinking-water quality. The status assessment used a spatially weighted, grid-based method to estimate the proportion of the groundwater resources used for public drinking water that has concentrations for particular constituents or class of constituents approaching or above benchmark concentrations. This method provides statistically unbiased results at the study-area scale within the WSJV study unit, and permits comparison of the two study areas to other areas assessed by the GAMA Priority Basin Project statewide. Groundwater resources used for public drinking water in the WSJV study unit are among the most saline and most affected by high concentrations of inorganic constituents of all groundwater resources used for public drinking water that have been assessed by the GAMA Priority Basin Project statewide. Among the 82 GAMA Priority Basin Project study areas statewide, the Delta–Mendota study area ranked above the 90th percentile for aquifer-scale proportions of groundwater resources having concentrations of total dissolved solids (TDS), sulfate, chloride, manganese, boron, chromium(VI), selenium, and strontium above benchmarks, and the Westside study area ranked above the 90th percentile for TDS, sulfate, manganese, and boron.

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Groundwater Quality in the Western San Joaquin Valley, California

U.S. Geological Survey (USGS) | June 9th, 2017

Summary

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

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Groundwater Quality in the Yuba River and Bear River Watersheds, Sierra Nevada, California

U.S. Geological Survey (USGS) | September 27th, 2017

Summary

The Yuba River and Bear River Watersheds study unit (Yuba-Bear Watersheds) covers approximately 4,400 square kilometers on the western slope of the Sierra Nevada. Groundw

The Yuba River and Bear River Watersheds study unit (Yuba-Bear Watersheds) covers approximately 4,400 square kilometers on the western slope of the Sierra Nevada. Groundwater composes about 10 percent of overall water use in the region, but is the sole supply for many individual homes beyond the limits of public water supply infrastructure (Cosumnes, American, Bear, Yuba Integrated Regional Water Management Group, 2014). Recent drought conditions highlighted the vulnerability of private wells to diminished groundwater supplies in the study area and many wells required deepening (California Department of Water Resources, 2014).

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Groundwater-Quality Data in the North San Francisco Bay Shallow Aquifer Study Unit, 2012: Results from the California GAMA Program

U.S. Geological Survey (USGS) | October 23rd, 2014

Summary

Groundwater quality in the 1,850-square-mile North San Francisco Bay Shallow Aquifer (NSF-SA) study unit was investigated by the U.S. Geological Survey (USGS) from April

Groundwater quality in the 1,850-square-mile North San Francisco Bay Shallow Aquifer (NSF-SA) study unit was investigated by the U.S. Geological Survey (USGS) from April to August 2012, as part of the California State Water Resources Control Board (SWRCB) Groundwater Ambient Monitoring and Assessment (GAMA) Program’s Priority Basin Project (PBP). The GAMA-PBP was developed in response to the California Groundwater Quality Monitoring Act of 2001 and is being conducted in collaboration with the SWRCB and Lawrence Livermore National Laboratory (LLNL). The NSF-SA study unit was the first study unit to be sampled as part of the second phase of the GAMA-PBP, which focuses on the shallow aquifer system. The groundwater samples were analyzed for organic constituents (volatile organic compounds [VOCs], pesticides, and pesticide degradates); gross alpha and gross beta radioactivity). Naturally occurring constituents of special interest (perchlorate and 1,2,3-trichloropropane [1,2,3-TCP]); naturally occurring inorganic constituents (trace elements, nutrients, major and minor ions, silica, and total dissolved solids [TDS]); and radioactive constituents (radon-222 and gross alpha and gross beta radioactivity). Naturally occurring isotopes (stable isotopes of hydrogen, oxygen, boron, strontium, and inorganic carbon in water, tritium activities, and carbon-14 abundances) were measured to help identify the sources and ages of the sampled groundwater. In total, 207 constituents and water-quality indicators were measured.

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Groundwater-Quality Data in the Santa Cruz, San Gabriel, and Peninsular Ranges Hard Rock Aquifers Study Unit, 2011–2012: Results from the California GAMA Program

U.S. Geological Survey (USGS) | December 11th, 2014

Summary

Groundwater quality in the 2,400-square-mile Santa Cruz, San Gabriel, and Peninsular Ranges Hard Rock Aquifers (Hard Rock) study unit was investigated by the U.S. Geologi

Groundwater quality in the 2,400-square-mile Santa Cruz, San Gabriel, and Peninsular Ranges Hard Rock Aquifers (Hard Rock) study unit was investigated by the U.S. Geological Survey (USGS) from March 2011 through March 2012, as part of the California State Water Resources Control Board (SWRCB) Groundwater Ambient Monitoring and Assessment (GAMA) Program’s Priority Basin Project (PBP). The GAMA-PBP was developed in response to the California Groundwater Quality Monitoring Act of 2001 and is being conducted in collaboration with the SWRCB and Lawrence Livermore National Laboratory (LLNL). The Hard Rock study unit was the 35th study unit to be sampled as part of the GAMA-PBP. In the Hard Rock study unit, groundwater samples were collected from 112 wells and springs in 3 study areas (the Santa Cruz, the San Gabriel, and the Peninsular Ranges) in San Mateo, Santa Clara, Santa Cruz, San Benito, Los Angeles, Orange, Riverside, San Bernardino, and San Diego Counties. Eighty-three wells and 11 springs were selected by using a spatially distributed, randomized grid-based method to provide statistical representation of the study unit (grid wells), and 15 wells and 3 springs were selected to aid in evaluation of water-quality issues (understanding wells). The groundwater samples were analyzed for field water-quality indicators; organic constituents; one constituent of special interest (perchlorate); naturally occurring inorganic constituents; and radioactive constituents. Naturally occurring isotopes and dissolved noble gases were also measured to help identify the sources and ages of the sampled groundwater. In total, 209 constituents and water-quality indicators were measured.

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Identification of Bacteria in Groundwater Used for Domestic Supply in the Southeast San Joaquin Valley, California, 2014

U.S. Geological Survey (USGS) | June 22nd, 2021

Summary

Groundwater is an important source of drinking water in California. Water-borne diseases caused by microbial contamination are a growing concern. The MI test, a membrane

Groundwater is an important source of drinking water in California. Water-borne diseases caused by microbial contamination are a growing concern. The MI test, a membrane filtration method for the chromogenic-/-fluorogenic detection of total coliforms and Escherichia coli, was used for samples collected January to April 2014 from 42 domestic wells in the southeastern San Joaquin Valley. The wells were sampled as part of the Groundwater Ambient Monitoring and Assessment Program Priority Basin Project (GAMA-PBP), a cooperative study between the U.S. Geological Survey and the California State Water Resources Control Board. Polymerase chain reaction analysis and sequencing of deoxyribonucleic acid (DNA) were used for 34 target and nontarget colonies that grew on the MI media from samples collected from 13 of the domestic wells to identify what genera of bacteria could exist in groundwater used by domestic wells. Gene sequences obtained using the Sanger method were entered into the basic local alignment search tool (BLAST) database, and 17 genera of bacteria were identified. Of these, 13 genera contain species that are human pathogens or opportunistic human pathogens. All the genera that include human pathogens are naturally present in soil, plants, or water; one of the pathogens also can be found in fecal matter. Six of the human pathogens were from non-target colony growth on the MI media. Target and non-target microbial growth on MI media are indicators of the possible presence of pathogenic bacteria even if the bacteria naturally are from soil rather than from a fecal source.

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Identification of Bacteria in Groundwater Used for Domestic Supply in the Southeast San Joaquin Valley, California, 2014

U.S. Geological Survey (USGS) | June 22nd, 2021

Summary

Groundwater is an important source of drinking water in California. Water-borne diseases caused by microbial contamination are a growing concern. The MI test, a membrane

Groundwater is an important source of drinking water in California. Water-borne diseases caused by microbial contamination are a growing concern. The MI test, a membrane filtration method for the chromogenic / fluorogenic detection of total coliforms and Escherichia coli, was used for samples collected January to April 2014 from 42 domestic wells in the southeastern San Joaquin Valley. The wells were sampled as part of the Groundwater Ambient Monitoring and Assessment Program Priority Basin Project (GAMA-PBP), a cooperative study between the U.S. Geological Survey and the California State Water Resources Control Board. Polymerase chain reaction analysis and sequencing of deoxyribonucleic acid (DNA) were used for 34 target and nontarget colonies that grew on the MI media from samples collected from 13 of the domestic wells to identify what genera of bacteria could exist in groundwater used by domestic wells. Gene sequences obtained using the Sanger method were entered into the basic local alignment search tool (BLAST) database, and 17 genera of bacteria were identified. Of these, 13 genera contain species that are human pathogens or opportunistic human pathogens. All the genera that include human pathogens are naturally present in soil, plants, or water; one of the pathogens also can be found in fecal matter. Six of the human pathogens were from non-target colony growth on the MI media. Target and non-target microbial growth on MI media are indicators of the possible presence of pathogenic bacteria even if the bacteria naturally are from soil rather than from a fecal source.

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North San Francisco Bay Shallow Aquifer Study Unit, 2012: California GAMA Priority Basin Project

U.S. Geological Survey (USGS) | July 20th, 2017

Summary

Groundwater quality in the North San Francisco Bay Shallow Aquifer study unit (NSF-SA) was investigated as part of the Priority Basin Project of the California

Groundwater quality in the North San Francisco Bay Shallow Aquifer study unit (NSF-SA) was investigated as part of the Priority Basin Project of the California Groundwater Ambient Monitoring and Assessment (GAMA) Program. The study unit is in Marin, Mendocino, Napa, Solano, and Sonoma Counties and included two physiographic study areas: the Valleys and Plains area and the surrounding Highlands area. The NSF-SA focused on groundwater resources used for domestic drinking water supply, which generally correspond to shallower parts of aquifer systems than that of groundwater resources used for public drinking water supply in the same area. The assessments characterized the quality of untreated groundwater, not the quality of drinking water. This study included three components: (1) a status assessment, which characterized the status of the quality of the groundwater resources used for domestic supply for 2012; (2) an understanding assessment, which evaluated the natural and human factors potentially affecting water quality in those resources; and (3) a comparison between the groundwater resources used for domestic supply and those used for public supply.

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