Status of Groundwater Quality in the Santa Barbara Study Unit, 2011: California GAMA Priority Basin Project

U.S. Geological Survey (USGS) | September 30th, 2016

Groundwater quality in the 48-square-mile Santa Barbara study unit was investigated in 2011 as part of the California State Water Resources Control Board’s Groundwater

Groundwater quality in the 48-square-mile Santa Barbara study unit was investigated in 2011 as part of the California State Water Resources Control Board’s Groundwater Ambient Monitoring and Assessment (GAMA) Program Priority Basin Project. The study unit is mostly in Santa Barbara County and is in the Transverse and Selected Peninsular Ranges hydrogeologic province. The GAMA Priority Basin Project is carried out by the U.S. Geological Survey in collaboration with the California State Water Resources Control Board and Lawrence Livermore National Laboratory. The GAMA Priority Basin Project was designed to provide a statistically unbiased, spatially distributed assessment of the quality of untreated groundwater in the primary aquifer system of California. The primary aquifer system is defined as that part of the aquifer corresponding to the perforation interval of wells listed in the California Department of Public Health database for the Santa Barbara study unit. This status assessment is intended to characterize the quality of groundwater resources in the primary aquifer system of the Santa Barbara study unit, not the treated drinking water delivered to consumers by water purveyors. The status assessment for the Santa Barbara study unit was based on water-quality and ancillary data collected in 2011 by the U.S. Geological Survey from 23 sites and on water-quality data from the California Department of Public Health database for January 24, 2008–January 23, 2011. The data used for the assessment included volatile organic compounds; pesticides; pharmaceutical compounds; two constituents of special interest, perchlorate and N-nitrosodimethylamine (NDMA); and naturally present inorganic constituents, such as major ions and trace elements. Relative-concentrations (sample concentration divided by the health- or aesthetic-based benchmark concentration) were used to evaluate groundwater quality for those constituents that have federal or California regulatory and non-regulatory benchmarks for drinking-water quality. For inorganic, organic, and special-interest constituents, a relative-concentration greater than 1.0 indicates a concentration greater than the benchmark and is classified as high. Inorganic constituents are classified as moderate if relative-concentrations are greater than 0.5 and less than or equal to 1.0 and are classified as low if relative-concentrations are less than or equal to 0.5. For organic and special-interest constituents, the boundary between moderate and low relative-concentrations was set at 0.1. Aquifer-scale proportion was used as the primary metric for evaluating regional-scale groundwater quality. High aquifer-scale proportion is defined as the areal percentage of the primary aquifer system with a relative-concentration greater than 1.0 for a particular constituent or class of constituents. Moderate and low aquifer-scale proportions were defined as the areal percentage of the primary aquifer system that had moderate and low relative-concentrations, respectively. Two statistical approaches—grid based and spatially weighted—were used to calculate aquifer-scale proportions for individual constituents and constituent classes. Grid-based and spatially weighted estimates were comparable in this the study (within 90-percent confidence intervals). Grid-based results were selected for use in the status assessment unless, as was observed in a few cases, a grid-based result was zero and the spatially weighted result was not zero, in which case, the spatially weighted result was used. Inorganic constituents that have human-health benchmarks were present at high relative-concentrations in 5.3 percent of the primary aquifer system and at moderate concentrations in 32 percent. High aquifer-scale proportions of inorganic constituents primarily were a result of high aquifer-scale proportions of boron (5.3 percent) and fluoride (5.3 percent). Inorganic constituents that have aesthetic-based benchmarks, referred to as secondary maximum contaminant levels, were present at high relative-concentrations in 58 percent of the primary aquifer system and at moderate concentrations in 37 percent. Iron, manganese, sulfate, and total dissolved solids were the inorganic constituents with secondary maximum contaminant levels present at high relative-concentrations.

Strategic Salt Accumulation Land and Transportation Study (SSALTS) Final Phase 1 Report – Identification and Characterization of Existing Salt Accumulation Areas

Central Valley Salinity Alternatives for Long-Term Sustainability (CV-SALTS) | December 13th, 2013

The purpose of the Strategic Salt Accumulation Land and Transportation Study (SSALTS) is to identify the range of viable Central Valley alternatives for salt disposal to

The purpose of the Strategic Salt Accumulation Land and Transportation Study (SSALTS) is to identify the range of viable Central Valley alternatives for salt disposal to provide input for consideration during development of the Salt and Nutrient Management Plan (SNMP) for the region under the jurisdiction of the Central Valley Regional Water Quality Control Board (Central Valley RWQCB). The findings will be used to guide discussions regarding establishment of regional salt management policies and the need for changes to the existing Central Valley RWQCB Water Quality Control Plans (Basin Plans) to facilitate salt disposal in a manner that is most beneficial to the region and consistent with the State Water Resource Control Board (SWRCB) Recycled Water Policy. This work is being conducted under the direction of the Central Valley Salinity Alternatives for Long- Term Sustainability (CV-SALTS) initiative, which is developing the SNMP for the Central Valley. The SSALTS project is being conducted in three phases: Phase 1: Identify and Characterize Existing Salt Accumulation Study Areas–Selection of representative Study Areas to serve as prototype situational examples to facilitate discussions regarding salt accumulation and disposal in the Central Valley. Each of these Study Areas is being characterized to establish baseline information that may be used to support development of salt disposal alternatives in subsequent project phases. Phase 2: Develop Potential Salt Management Strategies–SSALTS will develop potential long- term salt disposal alternatives in three parts: (1) In-Valley alternatives; (2) Out-of-Valley alternatives; and (3) hybrid alternatives that combine In-Valley and Out-of-Valley salt disposal options. Phase 3: Evaluate Potential Salt Disposal Alternatives to Identify Acceptable Alternatives for Implementation – Alternatives developed under Phase 2 will be evaluated using selected feasibility criteria (e.g., regulatory, institutional, economic, technological, etc.). The outcome of this evaluation will be the identification and prioritization of acceptable salt disposal alternatives for potential incorporation into Central Valley SNMP as salt management implementation measures. This draft report represents the findings of Phase 1. Subsequent phases of SSALTS will be implemented following completion of this phase.  

Strategic Salt Accumulation Land and Transportation Study (SSALTS) Final Phase 2 Report – Development of Potential Salt Management Strategies

Central Valley Salinity Alternatives for Long-Term Sustainability (CV-SALTS) | October 1st, 2014

The purpose of the Strategic Salt Accumulation Land and Transportation Study (SSALTS) is to identify the range of viable Central Valley alternatives for salt disposal to

The purpose of the Strategic Salt Accumulation Land and Transportation Study (SSALTS) is to identify the range of viable Central Valley alternatives for salt disposal to provide input for consideration during development of the Salt and Nutrient Management Plan (SNMP) for the region under the jurisdiction of the Central Valley Regional Water Quality Control Board (Central Valley RWQCB). The findings will be used to guide discussions regarding establishment of regional salt management policies and the need for changes to the existing Central Valley RWQCB Water Quality Control Plans (Basin Plans) to facilitate salt disposal in a manner that is most beneficial to the region and consistent with the State Water Resource Control Board (SWRCB) Recycled Water Policy. This work is being conducted under the direction of the Central Valley Salinity Alternatives for Long- Term Sustainability (CV-SALTS) initiative, which is developing the SNMP for the Central Valley. The SSALTS project is being conducted in three phases: Phase 1: Identify and Characterize Existing Salt Accumulation Study Areas–Selection of representative Study Areas to serve as prototype situational examples to facilitate discussions regarding salt accumulation and disposal in the Central Valley. Each of these Study Areas is being characterized to establish baseline information that may be used to support development of salt disposal alternatives in subsequent project phases. Phase 2: Develop Potential Salt Management Strategies–SSALTS will develop potential long- term salt disposal alternatives in three parts: (1) In-Valley alternatives; (2) Out-of-Valley alternatives; and (3) hybrid alternatives that combine In-Valley and Out-of-Valley salt disposal options. Phase3: Evaluate Potential Salt Disposal Alternatives to Identify Acceptable Alternatives for Implementation – Alternatives developed under Phase 2 will be evaluated using selected feasibility criteria (e.g., regulatory, institutional, economic, technological, etc.). The outcome of this evaluation will be the identification and prioritization of acceptable salt disposal alternatives for potential incorporation into Central Valley SNMP as salt management implementation measures. The Phase 1 report was finalized in December 2013. This report summarizes the findings of Phase 2. Phase 3 work will begin after the stakeholders have reviewed the Phase 2 report and provided comments.

Study of Potential for Groundwater Contamination from Past Dry Cleaner Operations in Santa Clara County

Santa Clara Valley Water District | September 20th, 2007

The threat of groundwater contamination posed by dry cleaning operations is primarily a legacy issue. Dry cleaners today have greatly improved usage and handling of solve

The threat of groundwater contamination posed by dry cleaning operations is primarily a legacy issue. Dry cleaners today have greatly improved usage and handling of solvents. Perchloroethylene (PCE) remains the most prevalent solvent used for dry cleaning. Dry cleaning machinery has evolved substantially and is designed to be leak-proof, air-tight, and to minimize waste generation. Dry cleaning facilities are subject to multiple permits, and are regularly inspected. A few dry cleaners have switched to “environmentally safe” solvents in their operations. Failures and operator error can nonetheless occur, representing a minor continuing threat to groundwater. The greater threat to groundwater quality is from past dry cleaning operations from as long as 50 years ago, a threat which remains significant today. This study catalogued the locations and years of operations for current and former dry cleaning operations in Santa Clara County. Past dry cleaner operational practices, solvent usage, groundwater subbasin vulnerability, and municipal supply well vulnerability are explored to develop a system to rank the relative risk of groundwater contamination from dry cleaner solvent releases. The systematic ranking of the threat posed by dry cleaners provides a means of prioritizing dry cleaning sites for further investigation. The ranking system will be useful to regulatory agencies for determining which cases warrant more aggressive investigation and remediation.

Sustainability of irrigated agriculture in the San Joaquin Valley, California

National Academy of Sciences (NAS) | October 25th, 2005

The sustainability of irrigated agriculture in many arid and semiarid areas of the world is at risk because of a combination of several interrelated factors, including

The sustainability of irrigated agriculture in many arid and semiarid areas of the world is at risk because of a combination of several interrelated factors, including lack of fresh water, lack of drainage, the presence of high water tables, and salinization of soil and groundwater resources. Nowhere in the United States are these issues more apparent than in the San Joaquin Valley of California. A solid understanding of salinization processes at regional spatial and decadal time scales is required to evaluate the sustainability of irrigated agriculture. A hydro-salinity model was developed to integrate subsurface hydrology with reactive salt transport for a 1,400-km2 study area in the San Joaquin Valley. The model was used to reconstruct historical changes in salt storage by irrigated agriculture over the past 60 years. We show that patterns in soil and groundwater salinity were caused by spatial variations in soil hydrology, the change from local groundwater to snowmelt water as the main irrigation water supply, and by occasional droughts. Gypsum dissolution was a critical component of the regional salt balance. Although results show that the total salt input and output were about equal for the past 20 years, the model also predicts salinization of the deeper aquifers, thereby questioning the sustainability of irrigated agriculture.

Temporal changes in the vertical distribution of flow and chloride in deep wells

National Groundwater Association (NGWA) | July 4th, 2005

The combination of flowmeter and depth‐dependent water‐quality data was used to evaluate the quantity and source of high‐chloride water yielded from different depth

The combination of flowmeter and depth‐dependent water‐quality data was used to evaluate the quantity and source of high‐chloride water yielded from different depths to eight production wells in the Pleasant Valley area of southern California. The wells were screened from 117 to 437 m below land surface, and in most cases, flow from the aquifer into the wells was not uniformly distributed throughout the well screen. Wells having as little as 6 m of screen in the overlying upper aquifer system yielded as much as 50% of their water from the upper system during drought periods, while the deeper parts of the well screens yielded 15% or less of the total yield of the wells. Mixing of water within wells during pumping degraded higher‐quality water with poorer‐quality water from deeper depths, and in some cases with poorer‐quality water from the overlying upper aquifer system. Changes in the mixture of water within a well, resulting from changes in the distribution of flow into the well, changed the quality of water from the surface discharge of wells over time. The combination of flowmeter and depth‐dependent water quality data yielded information about sources of high‐chloride water to wells that was not available on the basis of samples collected from nearby observation wells. Changing well design to eliminate small quantities of poor‐quality water from deeper parts of the well may improve the quality of water from some wells without greatly reducing well yield.

The Cost of Regulating Active Landfills for Water Quality

California State Water Resources Control Board (SWRCB) | January 3rd, 2016

This report to the legislature was prepared pursuant to Chapter 718, Statutes of 2010 (SB 855, Committee on Budget and Fiscal Review), which requires the State Water Reso

This report to the legislature was prepared pursuant to Chapter 718, Statutes of 2010 (SB 855, Committee on Budget and Fiscal Review), which requires the State Water Resources Control Board (State Water Board) to submit to the budget committees in each house of the legislature a report on the costs of regulating water quality at active landfills. The State Water Board and Regional Water Quality Control Boards (Regional Boards, collectively, the Water Boards) analyzed the cost of resources required to implement State and Federal statutes, regulations, and policies at these facilities. This report provides an overview of the Water Boards’ Land Disposal Program, followed by a cost analysis. The Water Boards’ Land Disposal Program provides regulatory oversight to 439 active landfills and 235 other waste management facilities in the State. Active landfills are all landfills that still pose a threat to the environment, even if they have stopped accepting waste. Active landfills are classified as operating or non-operating, with non-operating landfills including proposed, closing, and closed landfills. There are an estimated 1600 legacy landfills that were not included in the cost analysis for this report. Legacy landfills are waste management units that were closed, abandoned, or inactive prior to the adoption of revised State Water Board regulations in November 1984. In response to the legislative requirements, the results of this analysis show the cost of regulating the 439 active landfills to be approximately $18.1 million. The Land Disposal Program also regulates other waste management facilities as an integral part of the program, and tracks these facilities along with active landfills. Based on this analysis, the cost of regulating the 235 other waste management facilities is approximately $7.6 million. In total, implementation of the Land Disposal Program would cost approximately $25.7 million (not including legacy landfills). In Fiscal Year 2011-2012, the total expenditures incurred by the Land Disposal Program were approximately $10.6 million. As this presents an approximately $15.2 million shortfall in funding, the program prioritizes work based on threat to water quality, complexity, and level of activity at the facility. Working within existing resource constraints, the Land Disposal Program is currently implementing a series of efficiency measures to improve program effectiveness. A discussion of these efforts concludes this report.

Tracing enhanced oil recovery signatures in casing gases from the Lost Hills oil field using noble gases

Earth and Planetary Science Letters (Elsevier) | August 15th, 2018

Enhanced oil recovery (EOR) and hydraulic fracturing practices are commonly used methods to improve hydrocarbon extraction efficiency; however, the environmental effects

Enhanced oil recovery (EOR) and hydraulic fracturing practices are commonly used methods to improve hydrocarbon extraction efficiency; however, the environmental effects of such practices remain poorly understood. EOR is particularly prevalent in oil fields throughout California where water resources are in high demand and the disposal of large volumes of produced water may affect groundwater quality. Consequently, it is essential to better understand the fate of injected (EOR) fluids in California, and other subsurface petroleum systems, as well as any potential effect on nearby aquifer systems. Noble gases can be used as tracers to understand hydrocarbon generation, migration, and storage conditions, as well as the relative proportions of oil and water present in the subsurface. In addition, a noble gas signature diagnostic of injected (EOR) fluids can be readily identified. We report noble gas isotope and concentration data in casing gases from oil production wells in the Lost Hills oil field, northwest of Bakersfield, California, and injectate gas data from the Fruitvale oil field, located within the city of Bakersfield. Casing and injectate gas data are used to: 1) establish pristine hydrocarbon noble-gas signatures and the processes controlling noble gas distributions, 2) characterize the noble gas signature of injectate fluids, 3) trace injectate fluids in the subsurface, and 4) construct a model to estimate EOR efficiency. Noble gas results range from pristine to significantly modified by EOR, and can be best explained using a solubility exchange model between oil and connate/formation fluids, followed by gas exsolution upon production. This model is sensitive to oil–water interaction during hydrocarbon expulsion, migration, and storage at reservoir conditions, as well as any subsequent modification by EOR.

Two-dimensional, steady-state model of ground-water flow, Nevada Test Site and vicinity, Nevada- California: U.S. Geological Survey Water-Resources Investigations Report 82-4085

U.S. Geological Survey (USGS) | July 1st, 1962

Using machine learning to predict 1,2,3-trichloropropane contamination from legacy non-point source pollution of groundwater in California's Central Valley

Elsevier | May 6th, 2023

1,2,3-tricholoropropane (TCP) is an impurity common in nematicides applied to agricultural soils from the 1940s to the 1980s. Evidence from animal studies indicates t

1,2,3-tricholoropropane (TCP) is an impurity common in nematicides applied to agricultural soils from the 1940s to the 1980s. Evidence from animal studies indicates that TCP is a probable human carcinogen. TCP leaches through the soil into groundwater where it persists and contaminates thousands of wells in Asia, Europe, and North America. In California, TCP contaminates drinking water wells, with the highest levels of TCP beneath agricultural land used to grow grapevines. This study performs a mass balance and evaluates the ability of three types of tree-based machine learning models to predict TCP concentration in California's Central Valley aquifer system: classification and regression trees (CART), Random Forest (RF), and Boosted Regression Trees (BRT). To construct the models, multiple spatial explanatory variables were used, including historical agricultural land use data, irrigation levels, precipitation, soil type, groundwater age, redox state, and the presence of the co-contaminant nitrate. To estimate the amount of TCP applied to farmland in California, state historical pesticide and land use documents were used in the mass balance. Between 110,000 and 4,300,000 kg of TCP are estimated to have accumulated in the subsurface. Machine learning models indicate that the most important explanatory variables to predict TCP contamination of groundwater are precipitation, redox state, and the presence of the co-contaminant nitrate. Additionally, a 1000-m buffer area offers a slightly higher predictive performance as compared to 500-m and 1500-m buffers. Furthermore, the RF model outperforms CART and BRT for predictive performance. Finally, modeling using decision trees can predict TCP contamination levels in areas where monitoring is lacking, help target future TCP monitoring efforts, and aid in identifying areas to avoid when drilling new drinking water wells.