Salinity distribution in heterogeneous coastal aquifers mapped by airborne electromagnetics

Soil Science Society of America (SSSA) | February 8th, 2011

Understanding the hydrologic setting of any given area is a challenging task, especially considering that the amount of available informaon is ofen very sparse re

Understanding the hydrologic setting of any given area is a challenging task, especially considering that the amount of available informaon is ofen very sparse relative to the size of the area and the complexity of the problem. We used geophysical transient electromagnetic (TEM) data from an airborne SkyTEM instrument to investigate discharge of freshwater from a river catchment into a coastal lagoon area, in support of large-scale hydrologic mapping of the HOBE hydrology research center. Existing hydrologic data indicate possible outflow from the catchment underneath the survey area, a hypothesis that was indeed backed up by our geophysical results. The results revealed a stratified geologic setting frequently incised by buried valleys beneath the lagoon. They also showed that the valleys are saturated with sea water, unlike the layers at the same depth that are probably saturated with brackish water. The salinity decreases with depth in large parts of the lagoon. The salinity distribution in the setting indicates the presence of intricate flow systems beneath the coastal area and the lagoon, and we propose that it is governed by the heterogeneity in the geologic setting. We also demonstrated how water depth as well as salinity can be accurately mapped using SkyTEM in combination with a robust and flexible inversion scheme.

Salinity of deep groundwater in California: Water quantity, quality, and protection

National Academy of Sciences (NAS) | July 12th, 2016

Deep groundwater aquifers are poorly characterized but could yield important sources of water in California and elsewhere. Deep aquifers have been developed for oil and g

Deep groundwater aquifers are poorly characterized but could yield important sources of water in California and elsewhere. Deep aquifers have been developed for oil and gas extraction, and this activity has created both valuable data and risks to groundwater quality. Assessing groundwater quantity and quality requires baseline data and a monitoring framework for evaluating impacts. We analyze 938 chemical, geological, and depth data points from 360 oil/gas fields across eight counties in California and depth data from 34,392 oil and gas wells. By expanding previous groundwater volume estimates from depths of 305 m to 3,000 m in California’s Central Valley, an important agricultural region with growing groundwater demands, fresh [<3,000 ppm total dissolved solids (TDS)] groundwater volume is almost tripled to 2,700 km3, most of it found shallower than 1,000 m. The 3,000-m depth zone also provides 3,900 km3 of fresh and saline water, not previously estimated, that can be categorized as underground sources of drinking water (USDWs; <10,000 ppm TDS). Up to 19% and 35% of oil/gas activities have occurred directly in freshwater zones and USDWs, respectively, in the eight counties. Deeper activities, such as wastewater injection, may also pose a potential threat to groundwater, especially USDWs. Our findings indicate that California’s Central Valley alone has close to three times the volume of fresh groundwater and four times the volume of USDWs than previous estimates suggest. Therefore, efforts to monitor and protect deeper, saline groundwater resources are needed in California and beyond.

Saltwater Intrusion in Los Angeles Area Coastal Aquifers— the Marine Connection

U.S. Geological Survey (USGS) | August 14th, 2002

Saltwater from the Pacific Ocean is seeping into some Los Angeles Basin coastal aquifers and replacing freshwater. Without treatment, this ground water does not conform t

Saltwater from the Pacific Ocean is seeping into some Los Angeles Basin coastal aquifers and replacing freshwater. Without treatment, this ground water does not conform to drinking-water or agricultural standards. This problem is significant because much of the water used by the nearly 10 million residents of Los Angeles County comes from ground-water sources. Although not all coastal aquifers in the region are at risk, the existing resources are vital and must be protected to maintain adequate supplies of potable water. In the 1950’s, construction began on the first of three “barriers” in an attempt to halt saltwater intrusion. Each barrier consists of a series of injection wells that essentially form a subsurface wall of freshwater designed to keep saltwater from penetrating further into aquifers. The barriers are only partly effective; saltwater continues to infiltrate in some areas. New studies show that the ground-water geohydrology of the coastal aquifers is more complex than previously imagined. U.S. Geological Survey (USGS) scientists, working in cooperation with the Water Replenishment District of Southern California and the Los Angeles County Department of Public Works, are expanding efforts to understand the geologic processes and fluid pathways that control saltwater intrusion.

San Andreas Fault Stress Change Due To Groundwater Withdrawal in California's Central Valley, 1860-2010

American Geophysical Union (AGU) | December 28th, 2021

We investigate the spatial and temporal effects of groundwater removal in California's Central Valley on ground surface deformation and on stress changes on the nearby ce

We investigate the spatial and temporal effects of groundwater removal in California's Central Valley on ground surface deformation and on stress changes on the nearby central San Andreas fault (CSAF). In particular, we focus on two outstanding questions: (a) What are the spatial distributions of Coulomb failure stress (ΔCFS) on the CSAF? (b) What are the effects of viscoelasticity on uplift and ΔCSF over time? We focus on the well studied 2006–2010 drought, estimating the change in groundwater storage and the resulting uplift and stress change through a numerical model for the Earth. Viscoelastic effects are examined through an estimate of historical groundwater change from 1860-1961 and a hydrological model from 1961-2003 added to the 2006–2010 drought estimates. Here we find that lower crust or upper mantle viscosity variations enhance uplift and stress changes and that CSAF stress changes may accumulate with time, especially with droughts and groundwater consumption.

San Antonio Creek Valley Groundwater Basin Groundwater Sustainability Plan

San Antonio Basin Groundwater Sustainability Agency | December 16th, 2021

The Sustainable Groundwater Management Act (SGMA), effective as of January of 2015, created a new statewide framework for managing California’s groundwater at the loca

The Sustainable Groundwater Management Act (SGMA), effective as of January of 2015, created a new statewide framework for managing California’s groundwater at the local level through the formation of Groundwater Sustainability Agencies (GSAs). SGMA requires the development and implementation of a Groundwater Sustainability Plan (GSP) for each groundwater basin in the state that has been designated as high or medium priority. A GSP presents strategies for maintaining or bringing a groundwater basin into a sustainable condition within the next 20 years. SGMA exempts de minimus pumpers (e.g., individual domestic well owners who extract up to 2 acre-feet per year [AFY]) from most of the SGMA requirements and does not require metering. The San Antonio Basin Groundwater Sustainability Agency (SABGSA) was formed in 2017 for the purpose of sustainably managing groundwater and developing this GSP for the San Antonio Creek Valley Groundwater Basin (Basin). The SABGSA member agencies are the San Antonio Basin Water District and Los Alamos Community Services District. The Basin occupies approximately 123 square miles in western Santa Barbara County (see Figure ES-1). It is bounded on the north by the Casmalia Hills and Solomon Hills, on the east by the San Rafael Mountains and a watershed divide separating the adjoining Santa Ynez River Valley groundwater basin, on the south by the Purisima Hills and Burton Mesa, and the west by the approximate western boundary of Barka Slough. This GSP describes the physical setting of the Basin; quantifies historical, present, and future water budgets; develops quantifiable management objectives that account for the interests of the Basin’s beneficial groundwater uses and users and identifies a group of projects and management actions that will allow the Basin to achieve sustainability within 20 years of plan adoption. This document also includes the list of references and technical studies, documentation of the stakeholder engagement process undertaken in the development of this plan, and several supporting appendices. Due to size, the file has been divided. Part 1, Part 2, Part 3, Part 4, Part 5, Part 6

San Gorgonio Pass Subbasin Groundwater Sustainability Plan

San Gorgonio Pass Groundwater Sustainability Agency | January 28th, 2022

San Joaquin Valley Conveyance Study

California Department of Water Resources (DWR) | November 24th, 2025

This San Joaquin Valley Conveyance Study analyzes water conveyance needs in the San Joaquin Valley (Figure ES-1). The purpose of this study is to: •Describe the impa

This San Joaquin Valley Conveyance Study analyzes water conveyance needs in the San Joaquin Valley (Figure ES-1). The purpose of this study is to: •Describe the impacts of subsidence on San Joaquin Valley conveyance facilities. •Evaluate the need for improved or expanded conveyance facilities throughout the San Joaquin Valley.  

San Luis Obispo Valley Groundwater Sustainability Management Plan

San Luis Obispo Groundwater Sustainability Agencies | October 1st, 2021

This document fulfills the GSP development requirement for the SLO Basin. This GSP describes and assesses the groundwater condition of the SLO Basin, develops quantifiab

This document fulfills the GSP development requirement for the SLO Basin. This GSP describes and assesses the groundwater condition of the SLO Basin, develops quantifiable management objectives that account for the interests of the SLO Basin’s beneficial groundwater uses and users, and identifies a group of projects and management actions that will allow the SLO Basin to achieve and maintain sustainability in the future. GSP approved by DWR 4/27/23

San Mateo Plain Groundwater Basin Assessment

San Mateo County | July 12th, 2018

On behalf of the County of San Mateo, EKI Environment & Water, Inc., Todd Groundwater, and HydroFocus, Inc. (the Project Team) have prepared this report to summarize

On behalf of the County of San Mateo, EKI Environment & Water, Inc., Todd Groundwater, and HydroFocus, Inc. (the Project Team) have prepared this report to summarize the efforts and results of the San Mateo Plain Groundwater Basin Assessment (Project). The Project was conducted by the County, with the support of the Project Team, to comprehensively evaluate the San Mateo Plain Groundwater Subbasin as defined by the Department of Water Resources (DWR).

San Pasqual Valley Groundwater Basin Groundwater Sustainability Plan

San Pasqual Valley Groundwater Sustainability Agency | September 30th, 2021

The San Pasqual Valley Groundwater Sustainability Agency (SPV GSA), which comprises the City of San Diego (City) and the County of San Diego (County), developed this Gro

The San Pasqual Valley Groundwater Sustainability Agency (SPV GSA), which comprises the City of San Diego (City) and the County of San Diego (County), developed this Groundwater Sustainability Plan (GSP) to comply with California’s Sustainable Groundwater Management Act (SGMA) and its requirement to sustainably manage the San Pasqual Valley Groundwater Basin (Basin). SGMA,  which became effective January 1, 2015, provides a framework to regulate groundwater for the first time in California’s history by requiring local agencies to form GSAs and providing those GSAs with the necessary tools to manage ground-water use (California Water Code [CWC] Section 10720, et seq.). The overarching aim of SGMA is to establish and achieve the “sustainability goal” for the Basin through the development and implementation of a GSP. SGMA defines sustainable groundwater management as “the management and use of groundwater in a manner that can be maintained during the planning and implementation horizon without causing undesirable results” (CWC Section 10721). The GSP is required to include measures to achieve sustainable conditions by 2042. The City Council and the County Board of Supervisors each adopted the Memorandum of Understanding: Development of a Groundwater Sustainability Plan for the San Pasqual Valley Groundwater Basin establishing the SPV GSA as the single multi-agency GSA for the Basin. The Memorandum of Understanding further clarified the collaborative approach to developing and implementing the GSP with stakeholders’ input. SGMA requires both the County and City to adopt this GSP by January 31, 2022. Similarly, future GSP amendments must be adopted by both the City Council and County Board of Supervisors. While groundwater use in the Basin is currently sustainable, this GSP includes monitoring requirements, established thresholds, and projects and management actions that, once implemented, would ensure the sustainable management of groundwater resources in perpetuity. Due to size, this file has been divided into six parts. Part 1; Part 2; Part 3; Part 4; Part 5; Part 6