Tulare Lake

Groundwater depletion in California’s Central Valley accelerates during megadrought

Nature Portfolio (Springer Nature) | December 19th, 2022

Groundwater provides nearly half of irrigation water supply, and it enables resilience during drought, but in many regions of the world, it remains poorly, if at all mana

Groundwater provides nearly half of irrigation water supply, and it enables resilience during drought, but in many regions of the world, it remains poorly, if at all managed. In heavily agricultural regions like California’s Central Valley, where groundwater management is being slowly implemented over a 27-year period that began in 2015, groundwater provides two–thirds or more of irrigation water during drought, which has led to falling water tables, drying wells, subsiding land, and its long-term disappearance. Here we use nearly two decades of observations from NASA’s GRACE satellite missions and show that the rate of groundwater depletion in the Central Valley has been accelerating since 2003 (1.86 km3/yr, 1961–2021; 2.41 km3/yr, 2003–2021; 8.58 km3/yr, 2019–2021), a period of megadrought in southwestern North America. Results suggest the need for expedited implementation of groundwater management in the Central Valley to ensure its availability during the increasingly intense droughts of the future.

Groundwater Depletion in the United States (1900-2008)

U.S. Geological Survey (USGS) | June 1st, 2013

A natural consequence of groundwater withdrawals is the removal of water from subsurface storage, but the overall rates and magnitude of groundwater depletion in the Unit

A natural consequence of groundwater withdrawals is the removal of water from subsurface storage, but the overall rates and magnitude of groundwater depletion in the United States are not well characterized. This study evaluates long-term cumulative depletion volumes in 40 separate aquifers or areas and one land use category in the United States, bringing together information from the literature and from new analyses. Depletion is directly calculated using calibrated groundwater models, analytical approaches, or volumetric budget analyses for multiple aquifer systems. Estimated groundwater depletion in the United States during 1900–2008 totals approximately 1,000 cubic kilometers (km3). Furthermore, the rate of groundwater depletion has increased markedly since about 1950, with maximum rates occurring during the most recent period (2000–2008) when the depletion rate averaged almost 25 km3 per year (compared to 9.2 km3 per year averaged over the 1900–2008 time-frame). 

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 in California

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

Groundwater Management and Safe Drinking Water in the San Joaquin Valley

Water Foundation | June 2nd, 2020

Groundwater Management Principles and Strategies to Monitor, Analyze and Minimize Impacts to Drinking Water Wells: A Framework for State Action to Support Drought Resilient Communities

California Department of Water Resources (DWR) | December 15th, 2021

This framework was developed in response to support drinking water access for groundwater-dependent communities.

This framework was developed in response to support drinking water access for groundwater-dependent communities.

Groundwater Quality in the Shallow Aquifers of the Tulare, Kaweah, and Tule Groundwater Basins and Adjacent Highlands areas, Southern San Joaquin Valley, California

U.S. Geological Survey (USGS) | January 11th, 2017

The Tulare Shallow Aquifer study unit covers approximately 2,320 square miles and consists of the Tulare, Kaweah, and Tule groundwater basins of the southern San Joaquin

The Tulare Shallow Aquifer study unit covers approximately 2,320 square miles and consists of the Tulare, Kaweah, and Tule groundwater basins of the southern San Joaquin Valley and adjacent highlands of the Sierra Nevada (California Department of Water Resources, 2003; Bennett and others, 2017). The freshwater aquifer system in the groundwater basins is composed of Quaternary-age alluvial and fluvial sediments primarily derived from the Sierra Nevada to the east and is divided into upper and lower zones by a clay-rich lacustrine unit, the Corcoran Clay (Faunt, 2009). The highlands have fractured rock aquifers composed primarily of Mesozoic-age granitic rocks. The hydrology of the southern San Joaquin Valley has been extensively altered by human activity, especially by agricultural development (Faunt, 2009). This study examined the quality of groundwater resources used for domestic drinking-water supply. Domestic wells in the study unit typically are drilled to depths of 150 to 500 feet (Bennett and others, 2017), which is shallower than the depths of public-supply wells in the same area (typically 300 to 1,400 feet deep; Burton and others, 2012). Water quality varies with depth in the groundwater system. This study was designed to provide a statistically representative assessment of groundwater resources used for domestic drinking water (Bennett and others, 2017). A total of 96 wells, distributed across the study unit, were sampled between November 2014 and April 2015. Previous groundwater studies in this area have found that nitrate, fumigants, microbial indicators, and several trace elements are present at elevated concentrations in some domestic wells (Burow and others, 1998; Jurgens and others, 2010; Harter and Lund, 2012; California State Water Resources Control Board, 2016).

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

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

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.

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

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.

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

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

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.