Groundwater Trading as a Tool for Implementing California’s Sustainable Groundwater Management Act

Environmental Defense Fund (EDF) | December 8th, 2017

Until recently, the State of California lacked comprehensive groundwater management policy. While many basins havebeen adjudicated in court or have adopted voluntary grou

Until recently, the State of California lacked comprehensive groundwater management policy. While many basins havebeen adjudicated in court or have adopted voluntary groundwater management programs following Assembly Bill 3030 and Senate Bill 1938, the vast majority of groundwater use remained unregulated. In 2014, the State Legislature passed the landmark Sustainable Groundwater Management Act (SGMA) in response to wide-ranging consequences of prolonged and unchecked groundwater pumping. While groundwater serves as an important primary and supplemental water supply for many water users, over-pumping can result in negative consequences, six of which are listed as “undesirable results” under SGMA: chronic aquifer overdraft, reduction of groundwater storage, seawater intrusion, degradation of water quality, land subsidence, and depletion of hydrologically connected surface water. SGMA requires local Groundwater Sustainability Agencies (GSAs) to develop and implement Groundwater Sustainability Plans (GSPs) to manage groundwater to avoid such consequences. To meet the requirements of SGMA, GSAs will need to employ a wide range of management tools. This paper focuses on one set of these tools: groundwater trading programs. Trading goes by many different names, including markets, cap and trade, transfers, credit programs, banking, pooling, and exchanges. For the purposes of this paper, we have elected to use the terms “trading” and “trading programs” as the broader categorization of incentive-based management tools. Trading can be executed through a wide range of exchange vehicles, including short- and long-term leases, permanent transfers, and other more advanced or unique arrangements, such as inter-annual water exchanges or dry-year options contracts.

Groundwater Transport: Handbook of Mathematical Models

American Geophysical Union (AGU) | January 1st, 1984

Published by the American Geophysical Union as part of the Water Resources Monograph Series, Volume 10. Concerns over groundwater pollution have resulted in the passag

Published by the American Geophysical Union as part of the Water Resources Monograph Series, Volume 10. Concerns over groundwater pollution have resulted in the passage of legislation during the last decade calling for pollution control and remedial measures to ensure proper drinking water quality. There are two main types of groundwater pollution caused by man: (1) pollution caused by the use of pesticides, herbicides, and fertilizers over agricultural lands, where the source of contamination covers a relatively large area, and (2) pollution caused by industries and municipalities, which is generally more localized. For the second type, because the contamination in the groundwater is localized, the design of any remedial measure requires knowledge of the extent of the contaminant plume. Various mathematical methods may be used for estimating the size, shape, and development of a localized contaminant plume. It is the need for these mathematical methodologies that forms the main impetus for the preparation of this monograph.

Groundwater Update 2013: San Joaquin River Hydrologic Region Report

California Department of Water Resources (DWR) | April 1st, 2016

The primary goal of the San Joaquin River Hydrologic Region (San Joaquin River region) groundwater update is to expand information about region-specific groundwater condi

The primary goal of the San Joaquin River Hydrologic Region (San Joaquin River region) groundwater update is to expand information about region-specific groundwater conditions for California Water Plan Update 2013, and to guide more informed groundwater management actions and policies. A second goal is to steadily improve the quality of groundwater information in future California Water Plan updates to a level that will enable regional water management groups (RWMGs) to accurately evaluate their groundwater resources and implement management strategies that can meet local and regional water resource objectives within the context of broader statewide objectives. The final goal is to identify data gaps and groundwater management challenges meant to serve as a guidepost for prioritizing future data collection and funding opportunities relevant to the region. This regional groundwater update is not intended to provide a comprehensive and detailed examination of local groundwater conditions, or be a substitute for local studies and analysis. However, where information is readily available, the update does report some aspects of the regional groundwater conditions in greater detail.

Groundwater Vulnerability Study Santa Clara County, California

Santa Clara Valley Water District | October 18th, 2010

The Santa Clara Valley Water District (District) is the primary water resources agency in Santa Clara County. This Groundwater Vulnerability Study was conducted to predic

The Santa Clara Valley Water District (District) is the primary water resources agency in Santa Clara County. This Groundwater Vulnerability Study was conducted to predict the vulnerability of groundwater to potentially contaminating land use activities to aid the District in its management and protection activities. Groundwater vulnerability is comprised of two key components: 1) groundwater sensitivity and 2) potentially contaminating activities. Groundwater sensitivity is generally defined as the relative ease with which a contaminant on or near the land surface can migrate to the aquifer of interest based on the intrinsic characteristics of the aquifer and the overlying unsaturated materials. Groundwater sensitivity is combined with the potentially contaminating activities risk to characterize overall groundwater vulnerability. The Study Area is comprised of three groundwater subbasins: the Santa Clara, the Coyote, and the Llagas. Each has unique hydrogeologic characteristics as well as unique current and historic land uses. Water-bearing units in the Study Area have been grouped into two major aquifer systems, the Shallow Aquifer and Principal Aquifer. Groundwater vulnerability was assessed separately for each aquifer. Generally, the Shallow Aquifer occurs above regional confining layers. The Principal Aquifer lies beneath the Shallow Aquifer and supplies most of the groundwater produced for beneficial uses in the Study Area. The Principal Aquifer occurs under semi-confined to confined conditions. In areas where confining layers do not exist or are not laterally and vertically extensive, only the Principal Aquifer occurs. Accordingly, in the recharge zones, depth to water was characterized as the first encountered groundwater for both the Shallow and Principal aquifers. In contrast, the Shallow and Principal aquifers were uniquely defined in the confined areas with the Shallow Aquifer characterized by the first encountered groundwater and the Principal Aquifer defined by the top screened interval of wells tapping the primary groundwater production zone. The southern area and lateral margins of the Santa Clara Subbasin are unconfined recharge areas. An extensive regional aquitard occurs in the northern interior portion of the subbasin. The Santa Clara Subbasin is currently highly developed with residential, commercial, and industrial areas. Due to the high density of urban land uses including major industrial manufacturing and processing facilities, point-source contamination is prevalent but generally contained in the Shallow Aquifer. This is due, in part, to the protection offered by the significant confining layers found in the northern portion of the subbasin. The Santa Clara Subbasin is currently undergoing continued urban expansion and redevelopment of formerly industrial areas to residential use. No significant laterally extensive confining layers exist in the Coyote Subbasin, and groundwater generally occurs under unconfined conditions. Compared with the Santa Clara Subbasin, the Coyote Subbasin is relatively rural, undeveloped, and mostly unincorporated with far fewer industrial/commercial contaminant release sites. Due to generally unconfined conditions, the Coyote Subbasin is hydrogeologically sensitive to groundwater contamination. Existing water quality impacts are related to agricultural practices and rural (e.g., septic) land use. Coyote Valley has a high potential for future residential and commercial development. Groundwater in the Llagas Subbasin occurs under unconfined to confined conditions. Generally unconfined recharge areas are found in the northern portion of the subbasin, while confining layers become more frequent and laterally and vertically extensive in the southern areas. Accordingly, the northern portion of the subbasin is relatively more hydrogeologically sensitive to groundwater contamination compared with the southern subbasin. The Llagas Subbasin has urban development focused in the north and south with the central portion of the subbasin comprised predominantly of agricultural development and large residential parcels. The Llagas Subbasin is currently impacted by high levels of nitrate associated with rural land use and agriculture and perchlorate from historic releases from a flare manufacturer. A comprehensive literature review was conducted to identify established methods to conduct vulnerability assessments. Based on the evaluation of available groundwater sensitivity assessment methods and an understanding of available hydrogeologic and water quality information for the Study Area, a statistical method was selected to quantify the sensitivity to contamination of the Shallow Aquifer and Principal Aquifer. Water quality data (i.e., nitrate concentrations and distribution) were used for calibration and verification purposes to identify and rank groundwater sensitivity factors. Based on the logistic regression statistical analysis, four factors were found to be the most important in characterizing groundwater sensitivity. These include 1) soil media characteristics in the vadose zone, 2) groundwater recharge, 3) depth to top of screen, and 4) annual groundwater production. Groundwater recharge in the Study Area includes a significant amount of artificial recharge conducted by the District. Traditionally, artificial recharge and groundwater production would not be considered intrinsic aquifer characteristics. However, for this Study, groundwater sensitivity did include consideration of quasiintrinsic characteristics such as artificial recharge and production. In addition to the objective statistical analysis, subjective refinements relative to artificial recharge areas and characterization of depth to water/aquifer were applied based on observation, technical judgment, and limitations in the nitrate data set. These refinements included subjectively ranking areas near artificial recharge areas as highly sensitive and using depth to first encountered groundwater to represent the depth to water factor for the Principal Aquifer in the recharge zones. This results in higher sensitivity in the recharge areas for the Principal Aquifer. Figures ES-1 and ES-2 show the sensitivity of the Shallow and Principal aquifers, respectively. Not surprisingly, the sensitivity assessment found that the Shallow Aquifer is more sensitive than the Principal Aquifer. In addition, the analysis indicates that the sensitivity of the Shallow and Principal aquifers is generally highest in the Llagas Subbasin, followed by the Coyote Subbasin, and Santa Clara Subbasin. Despite the protection afforded by the regional confining layer in the southern portion of the Llagas Subbasin, both the Shallow and Principal aquifers are highly sensitive to contamination due to high recharge rates and permeable soils. The sensitivity of the Shallow and Principal aquifers in the Coyote Subbasin are also relatively high due primarily to shallow aquifer conditions, high recharge rates, and large amounts of groundwater production. Although the confined zone in the Santa Clara Subbasin affords relatively good protection from surface contamination, the outer western confined zone appears to be highly sensitive to contamination due to the significant groundwater production in this area. Unlike the sensitivity assessment, it is not possible to statistically calibrate potentially contaminating activities risk. Accordingly, potentially contaminating activities are commonly identified and ranked based on subjective observation and experience (e.g., California Drinking Water Source Assessment and Protection Program). For the potentially contaminating activities risk ranking, emphasis was placed on accurately characterizing the maximum risks so as not to underestimate potential risks. The potentially contaminating activities risk analysis included four main risk factors or categories—general plan land use, potentially contaminating business activities, known contaminated sites, and supplemental data. Twenty-nine land use categories were selected and ranked with respect to groundwater impacts. Relative risk ranks were developed for 48 categories of business activities. Known and open contamination sites were given the highest ranking with a lower ranking for closed sites. Additional supplemental data for irrigated agriculture, septic system density, mines, landfills, and petroleum pipelines were also ranked and included in the analysis. These various risk factors were combined to generate the overall potentially contaminating activities risk distribution map. The potentially contaminating activities risk analysis found large portions of the Santa Clara Subbasin are at high risk due to its high level of development with commercial and industrial areas and many associated industrial and commercial contaminant release sites along with the lingering impacts of agricultural releases. Relatively lower overall risks are associated with the Coyote Subbasin, which is relatively rural, undeveloped, and mostly unincorporated with far fewer industrial/commercial contaminant release sites. Nonetheless, most of the subbasin shows a moderate level of risk associated with irrigated agriculture. It is important to note that the Coyote Valley has the most potential for future development and thus the most potential for an increase in risk in the future. Relatively lower overall potentially contaminating activities risk (compared with the Santa Clara Subbasin) is found in the Llagas Subbasin due to its more rural nature. Areas of relatively higher risk are associated with commercial and industrial development in the vicinity of the cities of Morgan Hill and Gilroy. Moderate risk is found in the central portion of the subbasin associated with irrigated agriculture. While continued conversion of rural to urban land use in the vicinity of the cities of Morgan Hill and Gilroy in the future will likely increase risk in these areas, the central portion of the subbasin is expected to remain relatively unchanged with respect to risk, given the established zoning. The sensitivity assessment and potentially contaminating activities risk were combined to create the overall vulnerability maps for the Shallow and Principal aquifers. Figures ES-3 and ES-4 show the vulnerability of the Shallow and Principal aquifers, respectively. As might be expected, the vulnerability of the Shallow Aquifer is greater than the Principal Aquifer in areas of confinement in the Santa Clara Subbasin. The density of commercial/industrial sites and known contamination release sites in the northern Santa Clara Subbasin make the Shallow Aquifer highly vulnerable to contamination. The Principal Aquifer has fewer areas of very high vulnerability compared with the Shallow Aquifer due to the relative lower sensitivity of the Principal Aquifer. The Llagas and Coyote subbasins exhibit high to very high groundwater vulnerability in both the Shallow and Principal aquifers. The high vulnerability is driven primarily by the high sensitivity in these two subbasins. Given the potential for future development in the Coyote Subbasin, the high degree of vulnerability of the subbasin requires the highest level of effort directed toward protection. Following completion of the vulnerability assessment, a web-based geographical information system tool was developed, which incorporated the sensitivity, potentially contaminating activities risk, and vulnerability maps. Additional maps are also provided to enhance the usefulness of the tool. The tool enables District staff to work interactively with the vulnerability study analysis. The tool enables District staff to evaluate potential impacts of land use changes, prioritize basin management activities, prioritize review of known contamination sites, update existing data layers, update or modify risk factors, and add supplemental data layers.

Groundwater-dependent ecosystem map exposes global dryland protection needs

Nature Portfolio (Springer Nature) | July 17th, 2024

Groundwater-Flow and Land-Subsidence Model of Antelope Valley, California

U.S. Geological Survey (USGS) | October 27th, 2014

Antelope Valley, California, is a topographically closed basin in the western part of the Mojave Desert, about 50 miles northeast of Los Angeles. The Antelope Valley grou

Antelope Valley, California, is a topographically closed basin in the western part of the Mojave Desert, about 50 miles northeast of Los Angeles. The Antelope Valley groundwater basin is about 940 square miles and is separated from the northern part of Antelope Valley by faults and low-lying hills. Prior to 1972, groundwater provided more than 90 percent of the total water supply in the valley; since 1972, it has provided between 50 and 90 percent. Most groundwater pumping in the valley occurs in the Antelope Valley groundwater basin, which includes the rapidly growing cities of Lancaster and Palmdale. Groundwater-level declines of more than 270 feet in some parts of the groundwater basin have resulted in an increase in pumping lifts, reduced well efficiency, and land subsidence of more than 6 feet in some areas. Future urban growth and limits on the supply of imported water may increase reliance on groundwater. In 2011, the Los Angeles County Superior Court of California ruled that the Antelope Valley groundwater basin is in overdraft—groundwater extractions are in excess of the Court-defined safe yield of the groundwater basin. The Court determined that the safe yield of the adjudicated area of the basin was 110,000 acre-feet per year (acre-ft/yr). Natural recharge is an important component of total groundwater recharge in Antelope Valley; however, the exact quantity and distribution of natural recharge, primarily in the form of mountain-front recharge, is uncertain, with total estimates ranging from 30,000 to 160,000 acre-ft/yr. Technical experts, retained by parties to the adjudication, used 60,000 acre-ft/yr to estimate the sustainable yield of the basin, and this value was used in this study. In order to better understand the uncertainty associated with natural recharge and to provide a tool to aid in groundwater management, a numerical model of groundwater flow and land subsidence in the Antelope Valley groundwater basin was developed using old and new geohydrologic information. The groundwater-flow system consists of three aquifers: the upper, middle, and lower aquifers. The three aquifers, which were identified on the basis of the hydrologic properties, age, and depth of the unconsolidated deposits, consist of gravel, sand, silt, and clay alluvial deposits and clay and silty clay lacustrine deposits. Prior to groundwater development in the valley, recharge was primarily the infiltration of runoff from the surrounding mountains. Groundwater flowed from the recharge areas to discharge areas around the playas where it discharged from the aquifer system as either evapotranspiration or from springs. Partial barriers to horizontal groundwater flow, such as faults, have been identified in the groundwater basin. Water-level declines owing to groundwater development have eliminated the natural sources of discharge, and pumping for agricultural and urban uses have become the primary source of discharge from the groundwater system. Infiltration of return flow from agricultural irrigation has become an important source of recharge to the aquifer system.

Groundwater-Quality Data in the North San Francisco Bay Shallow Aquifer Study Unit, 2012: Results from the California GAMA Program

U.S. Geological Survey (USGS) | October 23rd, 2014

Groundwater quality in the 1,850-square-mile North San Francisco Bay Shallow Aquifer (NSF-SA) study unit was investigated by the U.S. Geological Survey (USGS) from April

Groundwater quality in the 1,850-square-mile North San Francisco Bay Shallow Aquifer (NSF-SA) study unit was investigated by the U.S. Geological Survey (USGS) from April to August 2012, as part of the California State Water Resources Control Board (SWRCB) Groundwater Ambient Monitoring and Assessment (GAMA) Program’s Priority Basin Project (PBP). The GAMA-PBP was developed in response to the California Groundwater Quality Monitoring Act of 2001 and is being conducted in collaboration with the SWRCB and Lawrence Livermore National Laboratory (LLNL). The NSF-SA study unit was the first study unit to be sampled as part of the second phase of the GAMA-PBP, which focuses on the shallow aquifer system. The groundwater samples were analyzed for organic constituents (volatile organic compounds [VOCs], pesticides, and pesticide degradates);  gross alpha and gross beta radioactivity). Naturally occurring constituents of special interest (perchlorate and 1,2,3-trichloropropane [1,2,3-TCP]); naturally occurring inorganic constituents (trace elements, nutrients, major and minor ions, silica, and total dissolved solids [TDS]); and radioactive constituents (radon-222 and gross alpha and gross beta radioactivity). Naturally occurring isotopes (stable isotopes of hydrogen, oxygen, boron, strontium, and inorganic carbon in water, tritium activities, and carbon-14 abundances) were measured to help identify the sources and ages of the sampled groundwater. In total, 207 constituents and water-quality indicators were measured.

Groundwater-Quality Data in the Santa Cruz, San Gabriel, and Peninsular Ranges Hard Rock Aquifers Study Unit, 2011–2012: Results from the California GAMA Program

U.S. Geological Survey (USGS) | December 11th, 2014

Groundwater quality in the 2,400-square-mile Santa Cruz, San Gabriel, and Peninsular Ranges Hard Rock Aquifers (Hard Rock) study unit was investigated by the U.S. Geologi

Groundwater quality in the 2,400-square-mile Santa Cruz, San Gabriel, and Peninsular Ranges Hard Rock Aquifers (Hard Rock) study unit was investigated by the U.S. Geological Survey (USGS) from March 2011 through March 2012, as part of the California State Water Resources Control Board (SWRCB) Groundwater Ambient Monitoring and Assessment (GAMA) Program’s Priority Basin Project (PBP). The GAMA-PBP was developed in response to the California Groundwater Quality Monitoring Act of 2001 and is being conducted in collaboration with the SWRCB and Lawrence Livermore National Laboratory (LLNL). The Hard Rock study unit was the 35th study unit to be sampled as part of the GAMA-PBP. In the Hard Rock study unit, groundwater samples were collected from 112 wells and springs in 3 study areas (the Santa Cruz, the San Gabriel, and the Peninsular Ranges) in San Mateo, Santa Clara, Santa Cruz, San Benito, Los Angeles, Orange, Riverside, San Bernardino, and San Diego Counties. Eighty-three wells and 11 springs were selected by using a spatially distributed, randomized grid-based method to provide statistical representation of the study unit (grid wells), and 15 wells and 3 springs were selected to aid in evaluation of water-quality issues (understanding wells). The groundwater samples were analyzed for field water-quality indicators; organic constituents; one constituent of special interest (perchlorate); naturally occurring inorganic constituents; and radioactive constituents. Naturally occurring isotopes and dissolved noble gases were also measured to help identify the sources and ages of the sampled groundwater. In total, 209 constituents and water-quality indicators were measured.

Groundwater: The Water-Budget Myth

National Academy of Sciences (NAS) | June 1st, 1982

Water-resource scientists are concerned that some basic principles are being overlooked by water managers. Rather than discuss the scope of groundwater hydrolog

Water-resource scientists are concerned that some basic principles are being overlooked by water managers. Rather than discuss the scope of groundwater hydrology, we have chosen to focus on a common misconception to illustrate the point. Perhaps the most common misconception in groundwater hydrology is that a water budget of an area determines the magnitude of possible groundwater development. Several well-known hydrologists have addressed this misconception and attempted to dispel it. Somehow, though, it persists and continues to color decisions by the water-management community. The laws governing the development of groundwater in Nevada as well as several other states are based on the idea that pumping within a groundwater basin shall not exceed the recharge. It is the intent of this paper to re-examine the issue.

Groundwater/Aquifer Remediation (Resource Management Strategy)

California Department of Water Resources (DWR) | July 29th, 2016

Portions of aquifers in many groundwater basins in California have degraded water quality that does not support beneficial use of groundwater. In some areas, groundwater

Portions of aquifers in many groundwater basins in California have degraded water quality that does not support beneficial use of groundwater. In some areas, groundwater quality is degraded by constituents that occur naturally (e.g., arsenic). In many urban and rural areas, groundwater quality degradation has resulted from a wide range of human (anthropogenic) activities. Groundwater remediation is necessary to improve the quality of degraded groundwater for beneficial use. Drinking water supply is the beneficial use that typically requires remediation when groundwater quality is degraded. Contaminants in groundwater can come from a many sources, naturally occurring and anthropogenic. Examples of naturally occurring contaminants include heavy metals and radioactive constituents, as well as high concentrations of various salts from specific geologic formations or conditions. Climate change that results in altered precipitation, snowfall patterns, and rising sea levels may exacerbate salt water intrusion and flooding of low-lying infrastructure and urban facilities. These phenomena will add new challenges to protection of groundwater from contamination. In addition, groundwater can be contaminated by anthropogenic sources with organic, inorganic, and radioactive constituents from point and non-point sources. These anthropogenic sources include industrial sites, mining operations, leaking fuel tanks and pipelines, manufactured gas plants, landfills, impoundments, dairies, septic systems, and urban and agricultural activities. The contaminant having the most widespread and adverse impact on drinking water wells is arsenic, followed by nitrates, naturally occurring radioactivity, industrial/commercial solvents, and pesticides. Groundwater remediation removes constituents, hereafter called contaminants, which affect beneficial use of groundwater. Groundwater remediation systems can employ passive or active methods to remove contaminants. Passive groundwater remediation allows contaminants to degrade biologically or chemically or disperse in situ over time. Active groundwater remediation involves either treating contaminated groundwater while it is still in the aquifer (in situ) or extracting contaminated groundwater from the aquifer and treating it outside of the aquifer (ex situ). Active in situ methods generally involve injecting chemicals into the contaminant plume to obtain a chemical or biological removal of the contaminant. Ex situ methods for treating contaminated groundwater can involve physical, chemical, and/or biological processes.