Harnessing the Power of Geophysical Imaging to Recharge California's Groundwater

American Geophysical Union (AGU) | April 17th, 2025

Motivated by the availability of 20,000 line-km of airborne electromagnetic (AEM) data covering the Central Valley of California, we developed a workflow that uses resist

Motivated by the availability of 20,000 line-km of airborne electromagnetic (AEM) data covering the Central Valley of California, we developed a workflow that uses resistivity profiles from electromagnetic (EM) data to assess the suitability of areas for groundwater recharge. We defined a suitable area as one where “fastpaths” of coarse-grained material could efficiently move water from the ground surface to the water table. We defined recharge metrics and generated the corresponding maps by integrating resistivity profiles from AEM data, sediment type (from driller's logs), water level measurements, and water quality measurements. The workflow is publicly available through a web-based application, fastpath. We produced maps displaying recharge metrics on a 400 m × 400 m grid covering the Central Valley, with 80% of the cells sufficiently close to an AEM resistivity profile (within ∼3 km) to be assessed for recharge. Various decisions are made in the workflow that result in a range of values for determined metrics at any given location. The maps summarizing all metrics show that between 19% (2,000,000 acres) and 56% (7,000,000 acres) of the total area in the valley is land suitable for recharge. The landcover with the largest total area of land classified as suitable is cultivated crops. We estimated the total space available for recharge water to be ∼170 km3 which is two orders of magnitude greater than an estimate of the total volume of water likely to be available for recharge.

Helium isotope studies in the Mojave Desert, California: implications for groundwater chronology and regional seismicity

Chemical Geology (Elsevier) | November 7th, 2003

Hemet San Jacinto Stipulated Judgment

Superior Court of California, County of Riverside | April 18th, 2013

Background from "An Evaluation of California’s Adjudicated Groundwater Basins," Langridge et al, 2016 (UC Davis) Groundwater problems in the San Jacinto Basin were f

Background from "An Evaluation of California’s Adjudicated Groundwater Basins," Langridge et al, 2016 (UC Davis) Groundwater problems in the San Jacinto Basin were first addressed by the court in a 1954 judgment that allocated pumping rights for the Fruitvale Mutual Water Company in the upper San Jacinto Basin. Declining groundwater levels persisted into the 1970s, and local water purveyors attempted to develop a groundwater management plan to address the declines. Eastern Municipal Water District (EMWD), which had acquired the Fruitvale Company in 1972, worked with the water purveyors in the 1990s to implement an AB 3030 groundwater management plan for the West San Jacinto Groundwater Management Area. In 2001, a Memorandum of Understanding between the Department of Water Resources (DWR) and local agencies required a water management plan for the Hemet/San Jacinto Groundwater Management Area, the eastern portion of the San Jacinto Basin, and a plan was released in 2007. At the same time, the Soboba Band of Luiseño Indians, negotiating with the local agencies to specify their groundwater rights from the Hemet/San Jacinto Groundwater Management Area, also pushed for a management plan. These negotiations culminated in the 2008 Soboba Settlement Agreement Act that established their water rights. A 2013 stipulated judgment allocated pumping rights for public water agencies, provided for water rights outlined in the Soboba Settlement Agreement, incorporated the Water Management Plan, and mandated a Watermaster."

Henry Miller Water District Revised Groundwater Sustainability Plan, Kern County Subbasin

Henry Miller Water District | July 21st, 2022

This Groundwater Sustainability Plan (GSP) for the Henry Miller Water District (HMWD) Groundwater Sustainability Agency (GSA) has been prepared pursuant to Water Code §1

This Groundwater Sustainability Plan (GSP) for the Henry Miller Water District (HMWD) Groundwater Sustainability Agency (GSA) has been prepared pursuant to Water Code §10727. HMWD is located in the Kern County Subbasin (Basin 5-22.14) as defined by the Department of Water Resources’ (DWR) Bulletin 118. The Kern Subbasin is considered to be in a condition of critical overdraft and has been designated as a high priority basin. This GSP is one of the five GSPs being prepared in the Subbasin, which collectively has and will coordinate to avoid, to the best of their abilities, any and all Undesirable Results as a result of unsustainable groundwater management practices. HMWD formed its own GSA on March 15, 2017; it is the only Water District located within the GSA. HMWD GSA is one of five GSAs that are preparing a GSP within the Subbasin. This GSP, in coordination with the four other GSPs within the Subbasin, will provide a path to sustainability and the preservation of groundwater resources for all beneficial users of groundwater. Because the Subbasin has multiple GSPs, the GSPs are prepared under a coordination agreement. This Coordination Agreement exemplifies the ways that the various GSPs were able to work together to achieve a common goal: groundwater sustainability for the Subbasin. For example, the entire Subbasin has utilized Todd Groundwater’s services to analyze historic, current, and future groundwater conditions with a C2VSIM model. This Plan includes a description of the historic groundwater conditions in the Subbasin, a Subbasin water budget, sustainable management criteria for future monitoring, and projects and/or management actions that may be implemented to ensure groundwater sustainability is achieved by 2040 and maintained through 2070. Due to size, the file has been divided. Part 1, Part 2, Part 3, Part 4, Part 5

High resolution US water table depth estimates reveal quantity of accessible groundwater

Nature Portfolio (Springer Nature) | January 14th, 2026

Groundwater is the largest accessible freshwater on Earth, yet its quantity and distribution remain unknown. Here, we develop a high-resolution (approximately 30�

Groundwater is the largest accessible freshwater on Earth, yet its quantity and distribution remain unknown. Here, we develop a high-resolution (approximately 30 m) estimate of water table depth over the continental United States using machine learning that includes uncertainty. We estimate that there is 306,500 km³ (uncertainty range: 291,850–316,720 km³) of groundwater over North America. This represents our highest resolution estimate of accessible freshwater to date, supported by robust statistical performance. We calculate total and accessible groundwater storage, and results show that coarse resolution products are systematically biased in their estimates locally, where decisions are made, as well as at large scales. Our approaches are spatially extensive and locally relevant and thereby bridge a gap between remote sensing and point observations.

Historical Seawater Intrusion Map Pressure 180-Foot Aquifer - 500 mg/L or Greater Chloride Areas

Monterey County Water Resources Agency (MCWRA) | April 11th, 2018

History and Sources of Co-Occurring Pesticides in an Abstraction Well Unraveled by Age Distributions of Depth-Specific Groundwater Samples

American Chemical Society (ACS) | November 24th, 2019

When groundwater-based drinking water supply becomes contaminated, the timing and source of contamination are obvious questions. However, contaminants often have diffuse

When groundwater-based drinking water supply becomes contaminated, the timing and source of contamination are obvious questions. However, contaminants often have diffuse sources and different contaminants may have different sources even in a single groundwater well, making these questions complicated to answer. Age dating of groundwater has been used to reconstruct contaminant travel times to wells; however, critics have highlighted that groundwater flow is often complex with mixing of groundwater of different ages. In drinking water wells, where water is typically abstracted from a large depth interval, such mixing is even more problematic. We present a way to overcome some of the obstacles in identifying the source and age of contaminants in drinking water wells by combining depth-specific sampling with age tracer modeling, particle tracking simulations, geological characterization, and contaminant properties. This multitool approach was applied to a drinking water well, where bentazon and dichlorprop contamination was found to have different pollutant sources and release histories, even though both pesticides can be associated with the same land use. Bentazon was derived from recent application to a golf course, while dichlorprop was derived from agricultural use more than 30 years ago. The advantages, limitations, and pitfalls of the proposed course of action are then further discussed.

History and Sources of Co-Occurring Pesticides in an Abstraction Well Unraveled by Age Distributions of Depth-Specific Groundwater Samples

American Chemical Society (ACS) | November 24th, 2019

When groundwater-based drinking water supply becomes contaminated, the timing and source of contamination are obvious questions. However, contaminants often have diffuse

When groundwater-based drinking water supply becomes contaminated, the timing and source of contamination are obvious questions. However, contaminants often have diffuse sources and different contaminants may have different sources even in a single groundwater well, making these questions complicated to answer. Age dating of groundwater has been used to reconstruct contaminant travel times to wells; however, critics have highlighted that groundwater flow is often complex with mixing of groundwater of different ages. In drinking water wells, where water is typically abstracted from a large depth interval, such mixing is even more problematic. We present a way to overcome some of the obstacles in identifying the source and age of contaminants in drinking water wells by combining depth-specific sampling with age tracer modeling, particle tracking simulations, geological characterization, and contaminant properties. This multitool approach was applied to a drinking water well, where bentazon and dichlorprop contamination was found to have different pollutant sources and release histories, even though both pesticides can be associated with the same land use. Bentazon was derived from recent application to a golf course, while dichlorprop was derived from agricultural use more than 30 years ago. The advantages, limitations, and pitfalls of the proposed course of action are then further discussed.

How are Western water districts managing groundwater basins?

California Agriculture (UCANR) | March 13th, 2018

Making the transition from open-access groundwater rights to sustainable groundwater management is a formidable task for newly formed groundwater sustainability agencies

Making the transition from open-access groundwater rights to sustainable groundwater management is a formidable task for newly formed groundwater sustainability agencies in California. As agencies begin to decide how to make equitable water allocations, how to monitor groundwater use and what mix of supply- and demand-side mechanisms to adopt to satisfy sustainability criteria, the groundwater management strategies in place across other basins in the western United States are worth studying. We surveyed 18 groundwater districts in California and other Western states to identify the management approaches and practices they have instituted. The conclusions we draw suggest a correlative rights framework of water allocation with phase-ins for heavy users; metered pumping; flexible arrangements for trading and carrying over allocations for multiple years; and incentivizing groundwater recharge, including recharge from deep percolation from crops. Rigid formulas for significantly reducing groundwater use in medium- and high-priority basins are likely to have significant negative effects on the regional economy.

How are Western water districts managing groundwater basins?

California Agriculture (UCANR) | March 13th, 2018

Making the transition from open-access groundwater rights to sustainable groundwater management is a formidable task for newly formed groundwater sustainability age

Making the transition from open-access groundwater rights to sustainable groundwater management is a formidable task for newly formed groundwater sustainability agencies in California. As agencies begin to decide how to make equitable water allocations, how to monitor groundwater use and what mix of supply- and demand-side mechanisms to adopt to satisfy sustainability criteria, the groundwater management strategies in place across other basins in the western United States are worth studying. We surveyed 18 groundwater districts in California and other Western states to identify the management approaches and practices they have instituted. The conclusions we draw suggest a correlative rights framework of water allocation with phase-ins for heavy users; metered pumping; flexible arrangements for trading and carrying over allocations for multiple years; and incentivizing groundwater recharge, including recharge from deep percolation from crops. Rigid formulas for significantly reducing groundwater use in medium- and high-priority basins are likely to have significant negative effects on the regional economy.