North San Benito Groundwater Sustainability Plan

San Benito County Water District Groundwater Sustainability Agency (SBCWD) | November 30th, 2021

The North San Benito Groundwater Basin (Basin) is the plan area for this Groundwater Sustainability Plan (GSP), developed consistent with the Sustainable Groundwater Man

The North San Benito Groundwater Basin (Basin) is the plan area for this Groundwater Sustainability Plan (GSP), developed consistent with the Sustainable Groundwater Management Act (SGMA). This basin was formed in 2019 by consolidating the Bolsa, Hollister, and San Juan Bautista Subbasins of the Gilroy-Hollister Basin and the Tres Pinos Valley Basin. Including about 200 square miles, the Basin is predominantly in San Benito County with small areas in Santa Clara County. The Basin shares a boundary along the Pajaro River with the Llagas Subbasin in Santa Clara County. This GSP applies best available information to describe the plan area, groundwater resources, and associated surface water resources. Analysis of the groundwater basin condition, made with reference to sustainability indicators defined in SGMA, indicates that the North San Benito Basin has been managed sustainably, given availability of imported Central Valley Project (CVP) water. Projections have been made into the future (simulated with the numerical groundwater flow model) of existing conditions, climate change, and reasonably anticipated growth. These projections indicate that the Basin can continue to be sustainable, assuming reasonable availability of CVP water, with implementation of projects and management actions to avoid undesirable results. These projects and management actions do not include any long-term planned reductions in groundwater pumping.

North San Francisco Bay Shallow Aquifer Study Unit, 2012: California GAMA Priority Basin Project

U.S. Geological Survey (USGS) | July 20th, 2017

Groundwater quality in the North San Francisco Bay Shallow Aquifer study unit (NSF-SA) was investigated as part of the Priority Basin Project of the California

Groundwater quality in the North San Francisco Bay Shallow Aquifer study unit (NSF-SA) was investigated as part of the Priority Basin Project of the California Groundwater Ambient Monitoring and Assessment (GAMA) Program. The study unit is in Marin, Mendocino, Napa, Solano, and Sonoma Counties and included two physiographic study areas: the Valleys and Plains area and the surrounding Highlands area. The NSF-SA focused on groundwater resources used for domestic drinking water supply, which generally correspond to shallower parts of aquifer systems than that of groundwater resources used for public drinking water supply in the same area. The assessments characterized the quality of untreated groundwater, not the quality of drinking water. This study included three components: (1) a status assessment, which characterized the status of the quality of the groundwater resources used for domestic supply for 2012; (2) an understanding assessment, which evaluated the natural and human factors potentially affecting water quality in those resources; and (3) a comparison between the groundwater resources used for domestic supply and those used for public supply.

North San Francisco Bay Shallow Aquifer Study Unit, 2012: California GAMA Priority Basin Project (Version 1.1, February 2018)

U.S. Geological Survey (USGS) | February 23rd, 2018

Groundwater quality in the North San Francisco Bay Shallow Aquifer study unit (NSF-SA) was investigated as part of the Priority Basin Project of the California Grou

Groundwater quality in the North San Francisco Bay Shallow Aquifer study unit (NSF-SA) was investigated as part of the Priority Basin Project of the California Groundwater Ambient Monitoring and Assessment (GAMA) Program. The study unit is in Marin, Mendocino, Napa, Solano, and Sonoma Counties and included two physiographic study areas: the Valleys and Plains area and the surrounding Highlands area. The NSF-SA focused on groundwater resources used for domestic drinking water supply, which generally correspond to shallower parts of aquifer systems than that of groundwater resources used for public drinking water supply in the same area. The assessments characterized the quality of untreated groundwater, not the quality of drinking water. This study included three components: (1) a status assessment, which characterized the status of the quality of the groundwater resources used for domestic supply for 2012; (2) an understanding assessment, which evaluated the natural and human factors potentially affecting water quality in those resources; and (3) a comparison between the groundwater resources used for domestic supply and those used for public supply. The status assessment was based on data collected from 71 sites sampled by the U.S. Geological Survey for the GAMA Priority Basin Project in 2012. To provide context, concentrations of constituents measured in groundwater were compared to U.S. Environmental Protection Agency (EPA) and California State Water Resources Control Board Division of Drinking Water regulatory and non-regulatory benchmarks for drinking-water quality. The status assessment used a grid-based method to estimate the proportion of the groundwater resources that has concentrations of water-quality constituents approaching or above benchmark concentrations. This method provides statistically unbiased results at the study-area scale and permits comparisons to other GAMA Priority Basin Project study areas. In the NSF-SA study unit as a whole, inorganic constituents with human-health benchmarks were detected at high relative concentrations (RCs) in 27 percent of the shallow aquifer system, and inorganic constituents with secondary maximum contaminant levels (SMCL) were detected at high RCs in 24 percent of the system. The inorganic constituents detected at high RCs were arsenic, boron, fluoride, manganese, nitrate, iron, sulfate, and total dissolved solids (TDS). Organic constituents with human-health benchmarks were detected at high RCs in 1 percent of the shallow aquifer system. Of the 148 organic constituents analyzed, 30 constituents were detected, although only 1, chloroform, had a detection frequency greater than 10 percent. Natural and anthropogenic factors that could affect the groundwater quality were evaluated by using results from statistical testing of associations between constituent concentrations and values of potential explanatory factors. Groundwater age class (modern, mixed, or pre-modern), redox class (oxic or anoxic), aquifer lithology class (metamorphic, sedimentary, or volcanic), and dissolved oxygen concentrations were the explanatory factors that explained distribution patterns of most of the inorganic constituents best. Groundwater classified primarily as pre-modern or mixed in age was associated with higher concentrations of arsenic and fluoride than waters classified as modern. Anoxic or mixed redox conditions were associated with higher concentrations of boron, fluoride, and manganese. Similar patterns of association with explanatory variables were seen for inorganic constituents with aesthetic-based benchmarks detected at high concentrations. Nitrate and perchlorate had higher concentrations in oxic than in the anoxic redox class and were positively correlated with urban land use. The NSF-SA water-quality results were compared to those of the GAMA North San Francisco Bay Public-Supply Aquifer study unit (NSF-PA). The NSF-PA was sampled in 2004 and covers much of the same area as the NSF-SA, but focused on the deeper public-supply aquifer system. The comparison of the NSF-PA to the NSF-SA showed that there were more differences between the Valleys and Plains study areas of the two study units than between the Highlands study areas of the two study units. As expected from the shallower depth of wells, the NSF-SA Valleys and Plains study area had a lesser proportion of pre-modern age groundwater and greater proportion of modern age groundwater than the NSF-PA Valleys and Plains study area. In contrast, well depths and groundwater ages were not significantly different between the two Highlands study areas. Arsenic, manganese, and nitrate were present at high RCs, and perchlorate was detected in greater proportions of the NSF-SA Valleys and Plains study area than the NSF-PA Valleys and Plains study area.

Northern and Central Delta-Mendota Regions Revised Groundwater Sustainability Plan

San Luis & Delta-Mendota Water Authority (SLDMWA) | June 24th, 2022

Within the Delta-Mendota Subbasin, six (6) GSPs have been developed in a coordinated fashion with the goal of achieving sustainability for the Subbasin as a whole. The GS

Within the Delta-Mendota Subbasin, six (6) GSPs have been developed in a coordinated fashion with the goal of achieving sustainability for the Subbasin as a whole. The GSP Groups preparing the coordinated GSPs include: the Aliso Water District GSP Group, Farmers Water District GSP Group, Fresno County GSP Group, Grassland GSP Group, Northern & Central Delta-Mendota Region GSP Group, and San Joaquin River Exchange Contractors GSP Group. This GSP has been developed for the Northern and Central Delta-Mendota Regions, which are comprised of the following eight Groundwater Sustainability Agencies (GSAs): Central Delta-Mendota, City of Patterson, DM-II, Northwestern Delta-Mendota, Oro Loma Water District, Patterson Irrigation District, West Stanislaus Irrigation District, and Widren Water District. The Northern & Central Delta-Mendota Region GSP has been developed by these GSAs to meet SGMA regulatory requirements while reflecting local needs and preserving local control over water resources. This GSP provides a path to achieve and document sustainable groundwater management within 20 years following adoption, promoting the long-term sustainability of locally-managed groundwater resources now and into the future. Due to size, this file has been divided. Part 1, Part 2, Part 3

Not All Rivers Are Created Equal: The Importance of Spring-Fed Rivers under a Changing Climate

Water (MDPI) | June 12th, 2021

In the Western United States, volcanic spring-fed rivers are anticipated to become increasingly more important for salmonids and other native fishes, as these rivers wil

In the Western United States, volcanic spring-fed rivers are anticipated to become increasingly more important for salmonids and other native fishes, as these rivers will retain cold-water habitats as the climate warms. Despite this, little is known about the hydro-biogeochemical interactions within these ecosystems. A review of existing literature on spring-fed rivers, coupled with a decade of research on volcanic spring-fed rivers of northern California, finds that these systems are exceptionally productive and exhibit stable environmental conditions. These unique conditions stem from hydrogeologic processes typical of young volcanic terrains. Aquatic macrophytes, common to some nutrient-rich spring-fed systems, play a disproportionate role in hydrologic and geomorphic processes by facilitating ecological interactions and velocity conditions that improve juvenile salmonid growth. We find that volcanic spring-fed rivers are also resilient to climate change, due not only to their ability to dampen water temperature changes through deep groundwater flow but also because of their nutrient-driven high ecosystem productivity, which may enable cold-water species to metabolically compensate for marginal increases in water temperature. Understanding the fundamental geomorphic and ecological differences between these rare ecosystems and their numerically dominant runoff rivers is essential for developing long-term conservation strategies for cold-water species under a rapidly changing climate.

Numerical Simulation of Ground-Water Flow and Assessment of the Effects of Artificial Recharge in the Rialto–Colton Basin, San Bernardino County, California

U.S. Geological Survey (USGS) | July 1st, 2001

Nutrient Chemistry in the Elizabeth Lake Subwatershed: Effects of Onsite Wastewater Treatment Systems on Groundwater and Lake Water Quality, Los Angeles County, California

U.S. Geological Survey (USGS) | April 16th, 2024

Nutrient (nitrogen [N] and phosphorus [P] chemistry) down-gradient from onsite wastewater treatment system (OWTS) was evaluated with a groundwater study in the area surr

Nutrient (nitrogen [N] and phosphorus [P] chemistry) down-gradient from onsite wastewater treatment system (OWTS) was evaluated with a groundwater study in the area surrounding Elizabeth Lake, the largest of three sag lakes within the Santa Clara River watershed of Los Angeles County, California. Elizabeth Lake is listed on the “303 (d) Impaired Waters List” for excess nutrients and is down-gradient from more than 600 OWTS. The primary objective of this study was to develop a conceptual hydrogeological model to determine if discharge from OWTS is transported into shallow groundwater within the Elizabeth Lake subwatershed and contributes nutrients to Elizabeth Lake in excess of the total maximum daily load limit.

Nutrients in the Nation’s Streams and Groundwater, 1992–2004

U.S. Geological Survey (USGS) | June 6th, 2011

This report is one of a series of publications, The Quality of Our Nation’s Waters, which describes major findings of the NAWQA Program on water-quality issues of regio

This report is one of a series of publications, The Quality of Our Nation’s Waters, which describes major findings of the NAWQA Program on water-quality issues of regional and national concern. This report presents an assessment of the occurrence and distribution of nutrients in the Nation’s streams and groundwater based on water-quality data from about 500 streams and over 5,000 wells collected from 1992 through 2001. Other topics addressed include the relation of nutrient conditions to aquatic life in streams, changes in nutrient conditions from 1988 through 2004, and implications for future changes. The information in this series is intended primarily for those interested or involved in resource management and protection, conservation, regulation, and policy-making at regional and national levels. In addition, the information is relevant to those at a local level who wish to know more about the general quality of streams and groundwater in areas near where they live and how that quality compares with other areas across the Nation.

Oases of the future? Springs as potential hydrologic refugia in drying climates

Ecological Society of America (Wiley) | June 1st, 2020

Natural springs in water‐limited landscapes are biodiversity hotspots and keystone ecosystems that have a disproportionate influence on surrounding landscapes despite t

Natural springs in water‐limited landscapes are biodiversity hotspots and keystone ecosystems that have a disproportionate influence on surrounding landscapes despite their usually small size. Some springs served as evolutionary refugia during previous climate drying, supporting relict species in isolated habitats. Understanding whether springs will provide hydrologic refugia from future climate change is important to biodiversity conservation but is complicated by hydrologic variability among springs, data limitations, and multiple non‐climate threats to groundwater‐dependent ecosystems. We present a conceptual framework for categorizing springs as potentially stable, relative, or transient hydrologic refugia in a drying climate. Clues about the refugial capacity of springs can be assembled from various approaches, including citizen‐science‐powered ecohydrologic monitoring, remote sensing, landowner interviews, and environmental tracer analysis. Managers can integrate multiple lines of evidence to predict which springs may become future refugia for species of concern, strengthening the long‐term effectiveness of their conservation and restoration, and informing climate adaptation for terrestrial and freshwater species.

Occurrence and sources of radium in groundwater associated with oil fields in the southern San Joaquin Valley, California

American Chemical Society (ACS) | August 7th, 2019

Geochemical data from 40 water wells were used to examine the occurrence and sources of radium (Ra) in groundwater associated with three oil fields in California (Fruitva

Geochemical data from 40 water wells were used to examine the occurrence and sources of radium (Ra) in groundwater associated with three oil fields in California (Fruitvale, Lost Hills, South Belridge). 226Ra+228Ra activities (range = 0.010–0.51 Bq/L) exceeded the 0.185 Bq/L drinking-water standard in 18% of the wells (not drinking-water wells). Radium activities were correlated with TDS concentrations (p < 0.001, ρ = 0.90, range = 145–15,900 mg/L), Mn + Fe concentrations (p < 0.001, ρ = 0.82, range = <0.005–18.5 mg/L), and pH (p < 0.001, ρ = −0.67, range = 6.2–9.2), indicating Ra in groundwater was influenced by salinity, redox, and pH. Ra-rich groundwater was mixed with up to 45% oil-field water at some locations, primarily infiltrating through unlined disposal ponds, based on Cl, Li, noble-gas, and other data. Yet 228Ra/226Ra ratios in pond-impacted groundwater (median = 3.1) differed from those in oil-field water (median = 0.51). PHREEQC mixing calculations and spatial geochemical variations suggest that the Ra in the oil-field water was removed by coprecipitation with secondary barite and adsorption on Mn–Fe precipitates in the near-pond environment. The saline, organic-rich oil-field water subsequently mobilized Ra from downgradient aquifer sediments via Ra-desorption and Mn/Fe-reduction processes. This study demonstrates that infiltration of oil-field water may leach Ra into groundwater by changing salinity and redox conditions in the subsurface rather than by mixing with a high-Ra source.