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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 near the Montebello Oil Field, Los Angeles County, California

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

Summary

Groundwater quality and potential sources and migration pathways of chemical constituents associated with hydrocarbon-bearing formations were assessed by the U.S. Geologi

Groundwater quality and potential sources and migration pathways of chemical constituents associated with hydrocarbon-bearing formations were assessed by the U.S. Geological Survey for the California State Water Resources Control Board Oil and Gas Regional Monitoring Program (RMP). Groundwater samples were collected as part of the RMP from 21 preexisting wells used for public supply, monitoring, or irrigation in and near the Montebello Oil Field and analyzed for constituents associated with hydrocarbon-bearing formations and constituents used to identify recently recharged groundwater and older groundwater. The newly collected RMP data were supplemented with historical sample data from 849 groundwater wells and analyzed with respect to explanatory factors that have the potential to influence water quality. Potential sources and migration pathways of fluids (water, gas, or oil) from hydrocarbon-bearing formations that could affect groundwater quality in the Montebello Oil Field include large volumes of recycled produced water (water withdrawn from an oil well and brought to the surface that may include oil, water, and gas from the geologic formation and water or gas injected for enhanced recovery) that have been reinjected since the 1960s to enhance oil production, oil and gas wells with well-integrity issues, and oil and gas wells with an uncemented annulus that intersects groundwater resource zones. Trace amounts of dissolved petroleum hydrocarbons, thermogenic gas (propane through pentane range), or both, were detected in seven groundwater samples collected in 2014 and 2018 as part of the RMP. Five of those samples also contained manufactured volatile organic compounds and at least some modern-age groundwater (recharged during or after 1953), indicating that the hydrocarbons could have originated from surficial, or shallow, sources unrelated to oil and gas development. Two samples contained low concentrations of petroleum hydrocarbons (less than 0.1 microgram per liter) and did not contain detections of manufactured volatile organic compounds in pre-modern groundwater. These samples were collected from relatively deep wells (greater than 140 meters below land surface) with perforations completed in marine sediments that may contain water with similar compositions to produced water. The RMP sample results and available historical data in and near the Montebello Oil Field did not provide conclusive evidence that oil and gas development has adversely affected groundwater resources. All samples with detectable petroleum hydrocarbons, thermogenic gases, or both, were collected from sites that also are within 500 meters of anthropogenic hydrocarbon sources not associated with oil and gas development or sources. In addition, naturally occurring sources of hydrocarbons that exist at intervals shallower than, or are in areas outside of, economically productive oil- and gas-producing zones could affect groundwater quality. A definitive analysis of relations of groundwater quality to potential anthropogenic and natural explanatory factors was not possible because of the low density of new and historical sampling data, particularly in parts of the Montebello Oil Field where the largest relative risks to groundwater from hydrocarbon-bearing formations exist. Areas to consider for more detailed monitoring and analysis in the future that may present the largest relative potential risks to groundwater quality include (1) areas downgradient from historical surface ponds and sumps and (2) areas with co-located high net injection (oil reservoir injection exceeds production), old oil and gas wells that may be more likely to develop well-integrity issues than newer wells, and oil and gas wells with uncemented boreholes intersecting groundwater zones. To help fill gaps resulting from sparse groundwater wells, temperature and resistivity borehole log data could be analyzed to locate anomalies that identify potential areas where relatively warm or saline water from deeper hydrocarbon-bearing formations is present in groundwater.

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Groundwater quality near the Placerita Oil Field, California, 2018

U.S. Geological Survey (USGS) | September 26th, 2024

Summary

Groundwater-quality data and potential fluid-migration pathways near the Placerita Oil Field in Los Angeles County, California, were examined by the U.S. Geological Surve

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Groundwater Quality of the Lucerne Valley Groundwater Basin, California

U.S. Geological Survey (USGS) | July 7th, 2022

Summary

Anthropogenic activities, including groundwater withdrawals, return flow from irrigated agriculture, and treated wastewater-effluent disposal have the potential to affect

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Groundwater Quality Protection Strategy for the Central Valley Region, a Roadmap - Addendum 2015/2016

Central Valley Regional Water Quality Control Board (CVRWQCB) | May 7th, 2017

Summary

The Groundwater Quality Protection Strategy for the Central Valley Region, a Roadmap (GWQ Strategy) was developed through active stakeholder outreach and approved by the

The Groundwater Quality Protection Strategy for the Central Valley Region, a Roadmap (GWQ Strategy) was developed through active stakeholder outreach and approved by the Central Valley Water Board (September 2010 Resolution R5-2010-0095.) The GWQ Strategy is intended to provide a long range planning document that defines the regulatory programs to be enhanced, and identify ways to expand on all partnering opportunities to protect groundwater quality. Within the GWQ Strategy, actions were identified to implement groundwater quality protection. In the five years since the GWQ Strategy was approved, work has been completed on some actions, progress has been made on others, and new or emerging issues have been identified. This Addendum to the GWQ Strategy is intended to provide an update on any sections where changes may have occurred such as: new regulations or policies, programs have been added or modified, and new or emerging issues have been identified. In this Addendum, only the sections and/or subsections have been updated where new information was available since the GWQ Strategy was approved. The sections that have had the most extensive changes are sections 3, 4, and 6. In the last five years, there have been many legislative actions, bond initiatives, and new statewide policies that warranted updates to subsection: 3.2. Section 4 describes the Groundwater Quality Protection Programs the Central Valley Water Board implements. The most extensive updates to this section was to describe changes in program implementation for subsections, 4.1.1 Confined Animal Facilities, 4.1.2 Irrigated Lands Regulatory Program, and the addition of a new Oil Field Program under section 4.1.7. Section 6 is the Roadmap that identifies actions to be taken to improve groundwater quality. Updates to this section modify the numbering system used to identify the actions and includes nine new actions that have been prioritized using criteria from the GWQ Strategy. Some of these actions are directly related to new regulations, on-going drought related issues, or continuation of work identified in the GWQ Strategy in 2010.

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Groundwater Quality Protection Strategy: A "Roadmap" for the Central Valley Region

Central Valley Regional Water Quality Control Board (CVRWQCB) | January 8th, 2010

Summary

The California Regional Water Quality Control Board, Central Valley Region (Central Valley Water Board) recognizes that past regulatory approaches have not protected all

The California Regional Water Quality Control Board, Central Valley Region (Central Valley Water Board) recognizes that past regulatory approaches have not protected all groundwater from historical and current practices associated with land applications of waste. For example, in some areas of the Central Valley Region groundwater produced from some aquifers that serve individual and community drinking water systems have been polluted and are unsafe to drink. In response, the Central Valley Water Board adopted Resolution R5-2008-0181 directing staff to develop a Groundwater Quality Protection Strategy (Roadmap) through an active stakeholder process. Developing a Roadmap for the Central Valley Region is not initiating a new regulatory program. This Roadmap is intended to be an overarching framework or an outline for long range planning. By presenting it to the Central Valley Water Board it allows the Board review and approval of the overarching plan as well as an opportunity to provide direction to staff. Further, it defines the regulatory programs to be enhanced, and identifies ways to expand on all partnering opportunities with other federal, state, and/or local agencies to protect groundwater quality. Following approval of the Roadmap, workplan(s) will be developed for the higher priority future actions to provide a more detailed description of tasks, timelines, and resources required to implement those actions. In order to make this Roadmap useful to the public, policy-makers, and the Central Valley Water Board, a starting point to map a course for the future had to be identified. The starting point for the Roadmap is the background (Section 3) information on agencies and organization, the Central Valley Region’s basins, and primary constituents of concern. Current Groundwater Quality Protection Programs (Section 4) being implemented by the Central Valley Water Board describe how groundwater quality is being protected now. To assist in the evaluation of existing groundwater quality protection programs and identification of future actions, Stakeholder’s Concerns and Issues (Section 5) were also considered. The final section of the Strategy is the “Roadmap” (Section 6) which focuses on future actions that can be implemented within the next five to twenty years. To illustrate the Roadmap, a description is provided of three basic elements: a) future actions; b) how the actions are prioritized; and c) resource needs to implement the actions. Implementation of future actions, are not limited to the Central Valley Water Board. Future actions may be implemented by: the Central Valley Water Board; other agencies or organization; or through a partnership between agencies.

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Groundwater residence time estimates obscured by anthropogenic carbonate

American Association for the Advancement of Science (AAAS) | April 21st, 2021

Summary

Groundwater is an important source of drinking and irrigation water. Dating groundwater informs its vulnerability to contamination and aids in calibrating flow models. He

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Groundwater salinity mapping using geophysical log analysis within the Fruitvale and Rosedale Ranch oil fields, Kern County, California, USA

Hydrogeology Journal (Springer) | September 26th, 2018

Summary

A method is presented for deriving a volume model of groundwater total dissolved solids (TDS) from borehole geophysical and aqueous geochemical measurements. Whil

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Groundwater Quality in the South Coast Interior Basins, California

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

Groundwater Quality in the Western San Joaquin Valley, California

Groundwater Quality near the Montebello Oil Field, Los Angeles County, California

Groundwater quality near the Placerita Oil Field, California, 2018

Groundwater Quality of the Lucerne Valley Groundwater Basin, California

Groundwater Quality Protection Strategy for the Central Valley Region, a Roadmap - Addendum 2015/2016

Groundwater Quality Protection Strategy: A "Roadmap" for the Central Valley Region

Groundwater residence time estimates obscured by anthropogenic carbonate

Groundwater salinity mapping using geophysical log analysis within the Fruitvale and Rosedale Ranch oil fields, Kern County, California, USA

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