Modeling the dynamic penetration depth of post-1950s water in unconfined aquifers using environmental tracers: Central Valley, California

Journal of Hydrology (Elsevier) | December 5th, 2022

The penetration depth of post-1950s recharge (D-1950) in aquifers is a marker that is frequently used to identify groundwater that is susceptible to anthropogenic contami

The penetration depth of post-1950s recharge (D-1950) in aquifers is a marker that is frequently used to identify groundwater that is susceptible to anthropogenic contamination. Here, we compute D-1950 values at wells, interpolate them in space, and project them across time to map the moving front of modern recharge in four dimensions in the Central Valley aquifer system, California, USA. Tracers of groundwater age (tritium, carbon-14, noble gases, sulfur hexafluoride, and chlorofluorocarbons) were collected at 650 wells spatially distributed throughout the Central Valley and were fit to a lumped-parameter model that assumes a logarithmic age-depth profile in the aquifer. For samples where tritium was present (>0.3 tritium units), the model was used to predict D-1950 at wells screened above or across the modern-premodern interface (n = 484). Wells with samples where tritium was absent (≤0.3 tritium units) were used to define the depth beyond which groundwater is completely premodern (n = 166). Predicted D-1950 values were below the depth of screen bottoms for wells where groundwater is completely modern, and above the depth of screen tops for wells where groundwater is completely premodern. The interpolated surface of D-1950 is dynamic, less prone to extreme values, and produces maps with lower interpolation errors due to a higher spatial density of wells than maps based on the depth of premodern groundwater. Between 2005 and 2025, D-1950 is expected to deepen by 11 and 12 m in the northern and southern parts of the Central Valley, respectively. Areas where D-1950 increases rapidly are likely to see increases in nitrate and other anthropogenic contaminants associated with the downward moving front of modern water.

Modesto Subbasin Groundwater Sustainability Plan (Revised)

Publisher not available | July 12th, 2024

Submitted to the Department of Water Resources (DWR) in January 2022, the first version of this GSP was reviewed by DWR in January 2024 and determined to be incomplete (D

Submitted to the Department of Water Resources (DWR) in January 2022, the first version of this GSP was reviewed by DWR in January 2024 and determined to be incomplete (DWR, 2024). Two deficiencies were identified by DWR. The first of these involves provision of sufficient information (namely, analysis of potential impacts on wells) to support the selection of sustainable management criteria for chronic lowering of groundwater levels. The second involves provision of sufficient details on the projects and management actions to mitigate overdraft in the Subbasin and provide a feasible path to achieve sustainability. Corrective actions, including a resolution approved by both GSAs to arrest groundwater level declines by 2027 and raise groundwater levels after 2027, are incorporated into this revised July 16, 2024, GSP for resubmittal to DWR. This GSP is a revised version and does not represent a GSP update, which is slated for 2027. Due to size, this file has been divided. Part 1, Part 2, Part 3, Part 4

More with Less: Agricultural Water Conservation and Efficiency in California – A Special Focus on the Delta

Pacific Institute | September 8th, 2008

California farmers can grow more food and fiber with less water, according to the Pacific Institute report, More with Less: Agricultural Water Conservation and Efficiency

California farmers can grow more food and fiber with less water, according to the Pacific Institute report, More with Less: Agricultural Water Conservation and Efficiency in California – A Special Focus on the Delta. The report offers a comprehensive analysis of how to maintain a strong agricultural economy while improving the efficiency of water use and reducing groundwater overdraft and water withdrawals from the critically threatened Sacramento-San Joaquin Delta. The study finds agricultural water-use efficiency can be improved through careful planning, adopting existing, cost-effective technologies and management practices, and implementing feasible policy changes. The report also provides recommendations to overcome some of the financial, legal, and institutional barriers that can hinder farmers from implementing such adaptations and investments.

Multibenefit Land Repurposing Program Annual Report 2023

California Department of Conservation (CDoC) | April 9th, 2024

The Multibenefit Land Repurposing Program (MLRP) increases regional capacity for repurposing irrigated agricultural land to uses that reduce reliance on groundwat

The Multibenefit Land Repurposing Program (MLRP) increases regional capacity for repurposing irrigated agricultural land to uses that reduce reliance on groundwater while providing community health, economic well-being, water supply, habitat, renewable energy, and climate benefits. The program provides funding for regional block grants, tribal grants, and a Statewide Support Entity to provide technical assistance to block grantees and support progress toward program goals.

Multiple Benefits of Water Conservation and Efficiency for California Agriculture

Pacific Institute | July 29th, 2014

California farmers have made progress in updating and modernizing irrigation practices, but despite past efforts, great untapped potential remains to use water more effic

California farmers have made progress in updating and modernizing irrigation practices, but despite past efforts, great untapped potential remains to use water more efficiently. Water efficiency – defined as measures that reduce water use while maintaining the benefits water provides – has been shown to be a cost-effective and flexible tool to adapt to drought as well as to address longstanding water challenges in California. Moreover, today’s investments in efficiency will provide a competitive advantage in the future and ensure the ongoing strength of the agriculture sector in California. Water-efficiency strategies provide important benefits to farmers, ecosystems, and society. Some of the water saved represents new supply that can be dedicated to other uses. But there are also compelling reasons to seek reductions in total water withdrawals, e.g., allowing farmers to maintain and even improve crop yields and quality; protecting water quality; reducing fertilizer, water, and energy costs; and boosting profits. The multiple benefits associated with reducing both consumptive and non-consumptive water uses argues for a comprehensive approach for promoting water-efficiency improvements that allows us to address complex and interrelated water management challenges in California, including water-supply reliability, conflicts among water users, the risks of droughts, worsening water quality, and ecological degradation. This fact sheet and infographic, The Multiple Benefits of Water Efficiency for California Agriculture, describe some of these important benefits.

Multiscale Assessment of Agricultural Consumptive Water Use in California's Central Valley

American Geophysical Union (AGU) | May 4th, 2021

New Stone Water District GSA Groundwater Sustainability Plan

New Stone Water District (NSWD) | September 23rd, 2019

New water accounting reveals why the Colorado River no longer reaches the sea

Nature Portfolio (Springer Nature) | March 28th, 2024

Nitrogen Fertilizer Loading to Groundwater in the Central Valley

University of California, Davis (UC Davis) | October 31st, 2017

Nitrate‐nitrogen is the most common pollutant found in the Central Valley aquifer system of California. This project provides a long‐term assessment of past and curr

Nitrate‐nitrogen is the most common pollutant found in the Central Valley aquifer system of California. This project provides a long‐term assessment of past and current potential nitrogen loading to groundwater on irrigated and natural lands across the entire Central Valley of California using a nitrogen mass balance approach; assesses the long‐term implications for groundwater quality in the Central Valley (Sacramento Valley, San Joaquin Valley, and Tulare Lake Basin); evaluates potential best management practices to reduce groundwater nitrogen loading from irrigated lands; and provides a planning tool to better understand local and regional groundwater quality response to specific best management practices and policy/regulatory actions. The project complements other work to assess the vulnerability of Central Valley groundwater to nitrate contamination, sources of nitrate in groundwater, and how to reduce source loading.

Nitrogen Tracking and Reporting Task Force: Final Report

California Department of Food and Agriculture (CDFA) | December 6th, 2013

Agriculture in California is highly diverse in terms of food production, crop management, ecosystems, and climate. Nitrogen fertilizer is essential for crop food producti

Agriculture in California is highly diverse in terms of food production, crop management, ecosystems, and climate. Nitrogen fertilizer is essential for crop food production. Nitrogen fertilizer use over several decades in California has led to nitrates in groundwater. Recognizing that nitrates from agricultural nitrogen fertilizing materials have entered some California groundwater systems used for drinking water, CDFA convened the Nitrogen Tracking and Reporting Task Force in 2013 as part of a multi-pronged administration effort to address nutrient management and water quality. This Task Force was charged with implementing Recommendation 11 of several recommendations made to the Legislature by the State Water Board: “CDFA, in coordination with the Water Boards, should convene a Task Force to identify intended outcomes and expected benefits of a nitrogen mass balance tracking system in nitrate high-risk areas. The Task Force should identify appropriate nitrogen tracking and reporting systems, and potential alternatives, that would provide meaningful and high quality data to help better protect groundwater quality.” This charge was achieved through several measures including, among others, understanding and discussing the pros and cons of existing nitrogen tracking and reporting systems, identifying desirable components or elements of existing systems and evaluating the variability and complexity of California agriculture in relation to where existing systems have been implemented. Through several meetings, presentations by subject matter experts and discussion, the Task Force members came to general agreement on several components of an effective nitrogen tracking and reporting system. The recommended system addresses eight key topics including: (1) System Structure; (2) Data Elements; (3) Roles, Responsibilities and Data Accessibility; (4) Benefits of Participation; (5) Verifiability; (6) Societal Benefits of the Recommended System; (7) Limitations and (8) System Phase-in. This report presents the Task Force’s discussions and recommendations including intended outcome and anticipated benefits of such a tracking and reporting system for nitrogen use.