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Development of a Groundwater-Simulation Model in the Los Angeles Coastal Plain, Los Angeles County, California

U.S. Geological Survey (USGS) | September 28th, 2021

Summary

The Los Angeles Coastal Plain (LACP) covers about 580 square miles and is the largest coastal plain of semiarid southern California. The LACP is heavily developed with mo

The Los Angeles Coastal Plain (LACP) covers about 580 square miles and is the largest coastal plain of semiarid southern California. The LACP is heavily developed with mostly residential, commercial, and industrial land uses that rely heavily on groundwater for water supply. In 2010, the LACP was home to about 14 percent of California’s population, or about 5.4 million residents. The LACP is also a major commercial and industrial hub with industries including manufacturing, aerospace, entertainment, and tourism. There has been a heavy reliance on groundwater from the LACP for many years. An average of 305,000 acre-feet per year (acre-ft/yr) of groundwater was used annually from the LACP from 1971 to 2015. The need to replenish the groundwater basins within the LACP was recognized as far back as the 1930s, when spreading grounds were first used to replenish groundwater basins and store water underground during times of water surplus to meet demands in times of shortage. Seawater intrusion resulting from freshwater pumping was first observed in the 1940s. As a result, injection of imported water through wells at what is now the West Coast Basin Barrier Project began on an experimental basis in 1951. Managed aquifer recharge from the spreading grounds and barrier wells is now a substantial component of the LACP’s groundwater supply. The average annual recharge from water spreading from 1971 to 2015 was about 120,000 acre-ft/yr, and the average annual injection into the barrier wells was about 33,000 acre-ft/yr. Other inflows include areal recharge, underflow from San Gabriel and San Fernando Valleys, and onshore flow from the ocean. The average annual recharge from these sources was 100,000 acre-feet (acre-ft) from 1971 to 2015. Additionally, cross-boundary flow from Orange County into the western Orange County subareas of the LACP was simulated as 48,000 acre-ft from 1971 to 2015. This study, conducted in cooperation with the Water Replenishment District of Southern California (WRD), involved an assessment of the historical and present status of groundwater resources in the LACP and the development of tools to better understand the groundwater system. These efforts were built upon results from previous studies and incorporate new information and developments in modeling capabilities to provide a more detailed analysis of the aquifer systems. This study includes a comprehensive compilation of geologic and hydrologic data (Chapter A), development of a chronostratigraphic model that provides a detailed description of the LACP aquifer systems (Chapter B), characterization of the groundwater hydrology of the LACP, including a down-hole analysis of grain size using lithologic and geophysical logs (Chapter C), and development and application of the Los Angeles Coastal Plain Groundwater-flow Model (LACPGM) to simulate past groundwater conditions, estimate groundwater-budget components and flow paths, and approximate future groundwater conditions under different scenarios (Chapter D).

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DGMETA (Version 1): Dissolved Gas Modeling and Environmental Tracer Analysis Computer Program

U.S. Geological Survey (USGS) | January 8th, 2021

Summary

DGMETA (Dissolved Gas Modeling and Environmental Tracer Analysis) is a Microsoft Excel-based computer program that is used for modeling air-water equilibrium conditions f

DGMETA (Dissolved Gas Modeling and Environmental Tracer Analysis) is a Microsoft Excel-based computer program that is used for modeling air-water equilibrium conditions from measurements of dissolved gases and for computing concentrations of environmental tracers that rely on air-water equilibrium model results. DGMETA can solve for the temperature, salinity, excess air, fractionation of gases, or pressure/elevation of water when it is equilibrated with the atmosphere. Models are calibrated inversely using one or more measurements of dissolved gases such as helium, neon, argon, krypton, xenon, and nitrogen. Excess nitrogen gas, originating from denitrification or other sources, also can be included as a fitted parameter or as a separate calculation from the dissolved gas modeling results. DGMETA uses the air-water equilibrium models to separate measured concentrations of gases and isotopes of gases into components that are used for tracing water in the environment. DGMETA calculates atmospheric dry-air mole fractions (mixing ratios) for transient atmospheric gas tracers such as chlorofluorocarbons, sulfur hexafluoride, and bromotrifluoromethane (Halon-1301); and concentrations of tritiogenic helium-3 and radiogenic helium-4, which accumulate from the decay of tritium in water and the decay of uranium and thorium in rocks, respectively. Sample data can be graphed to identify applicable models of excess air, samples that contain excess nitrogen gas, or samples that have partially degassed, for example. Monte Carlo analysis of errors associated with dissolved gas equilibrium model results can be carried through computations of environmental tracer concentrations to provide robust estimates of error. In addition, graphical routines for separating helium sources using helium isotopes are included to refine estimates of tritiogenic helium-3 when terrigenic helium from mantle or crustal sources is present in samples. Environmental tracer concentrations and their errors computed from DGMETA can be used with other programs, such as TracerLPM (Jurgens and others, 2012), to determine groundwater ages and biogeochemical reaction rates. DGMETA also produces output files in a format that meets the U.S. Geological Survey open data requirements for documentation of model inputs and outputs. DGMETA is a versatile and adaptable program that allows users to add solubility data for new gases, modify the existing set of gas solubility data, modify the default set of gases used for modeling, choose calculations based on real (non-ideal) gas behavior, and select various concentration units for data entry and results to match laboratory reports and study objectives. DGMETA comes with a set of gases widely used in hydrology and oceanography and many gases include multiple solubilities from previous work. Seventeen dissolved gases are included in the default version of the program: noble gases (helium, neon, argon, krypton, and xenon), reactive gases (nitrogen, oxygen, methane, carbon dioxide, carbon monoxide, hydrogen, and nitrous oxide), and environmental tracers (chlorofluorocarbon-11, chlorofluorocarbon-12, chlorofluorocarbon-113, sulfur hexafluoride, and Halon-1301).

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Discussion Regarding Sources and Ages of Groundwater in Southeastern California

U.S. Department of Energy (DOE) | March 3rd, 2000

Summary

A planned groundwater storage project for future drought relief has been assessed in the Fenner Gap area of the Fenner, Cadiz, and Bristol watershed region of southeaste

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Dispute Resolution Processes - Thinking Through SGMA Implementation: A Water in the West Series

Stanford University | October 9th, 2019

Summary

Groundwater serves as the primary water supply for more than two billion people worldwide (Famiglietti 2014) and supplies approximately 40% of irrigation water supply gl

Groundwater serves as the primary water supply for more than two billion people worldwide (Famiglietti 2014) and supplies approximately 40% of irrigation water supply globally (Siebert et al. 2010). This heavy reliance on groundwater aquifers has led to the unsustainable depletion of groundwater resources at the regional and global scale resulting in an increasing number of conflicts over groundwater resources (Jarvis 2014). Similar to global trends, a long-term overreliance on groundwater in California has resulted in historically low groundwater levels in basins throughout the state. Groundwater level declines have had widespread impacts, including drying of domestic wells, land subsidence and the loss of supply wells. In 2014, California passed the Sustainable Groundwater Management Act (SGMA) to address the impacts resulting from chronic groundwater overdraft in the state. SGMA requires formation of local Groundwater Sustainability Agencies (GSAs). GSAs must develop and implement Groundwater Sustainability Plans (GSPs, Plan) to achieve sustainability within 20 years of Plan implementation. Achieving sustainability requires local agencies, stakeholders and water users to make many difficult and potentially contentious decisions such as regulating pumping, levying pumping fees and finding and purchasing alternative water supplies to meet legislated sustainability goals. These decisions are prone to conflict, particularly when pumping restrictions are viewed as infringing on property rights, or when fees are charged to support local management. Traditionally, many of these decisions have been resolved through court adjudications, many of which have been long and expensive processes in California (Szeptycki et al. 2018) and elsewhere (USDA 2018). In recent decades, the Alternative Dispute Resolution (ADR) movement has fostered use of alternative processes, including direct negotiation among the parties, facilitation, mediation and arbitration in lieu of, or supplemental to, adjudication to resolve environmental conflicts. The U.S. Department of Agriculture (USDA) mediation program has the explicit goal of helping “avoid expensive and time-consuming administrative appeals and/ or litigation” (USDA 2018). Other government departments like the Department of Energy and the U.S. Environmental Protection Agency also have mediation programs with similar goals. Many of the local GSAs established under SGMA are multi-entity GSAs formed through Joint Powers Authorities Agreements (JPAA) or through Memorandums of Understanding Agreements (MOUA) – we refer to these agreements collectively as “Agreements.” Additionally, the jurisdictional area of many GSAs does not span the entire groundwater basin. SGMA requires sustainability at the basin-scale, so many GSAs will need to collaborate internally (among member agencies within a GSA) and externally (with other GSAs in their basin) to develop and implement GSPs which are “together likely to achieve the groundwater sustainability goal for the basin,” (California Water Code (CWC) § 10733(b)). Newly formed GSAs have additional layers of potential conflict that may not be present in interpersonal or even other inter-organizational contexts with well-established processes and precedents, including questions of who has the authority, what process(es) should be followed when exercising that authority and what the constraints on the exercise of that authority are. These questions are particularly pertinent when agencies with similar or overlapping authorities are working together – as is common practice under SGMA. Questions regarding authority, tight legal and regulatory timelines, a lack of existing precedents and the need to represent agency and constituent interests have the potential to exacerbate conflicts under SGMA. In some cases, where authoritative interpretations of legal authority and limits have not been established yet, litigation may be necessary and warranted. When institutions have to coordinate and cooperate, as JPAs do, identifying processes and forums for resolving conflicts is crucial (Marta et al. 2014). However, developing effective mechanisms for resolving conflicts and using them can be challenging. Learning from the experiences of past water management agencies in California, as well as the natural resource conflict resolution literature more broadly, may help GSAs develop robust dispute resolution plans with processes to incentivize and streamline their resolution.

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Divergent effects of climate change on future groundwater availability in key mid-latitude aquifers

Nature Portfolio (Springer Nature) | July 24th, 2020

Summary

Groundwater provides critical freshwater supply, particularly in dry regions where surface water availability is limited. Climate change impacts on GWS (groundwater stora

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Diverse stakeholders create collaborative, multilevel basin governance for groundwater sustainability

California Agriculture (UCANR) | March 13th, 2018

Summary

The Sustainable Groundwater Management Act (SGMA) is introducing significant changes in the way groundwater is governed for agricultural use. It requires the format

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Documentation of a Groundwater Flow Model (SJRRPGW) for the San Joaquin River Restoration Program Study Area, California

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

Summary

To better understand the potential effects of restoration flows on existing drainage problems, anticipated as a result of the San Joaquin River Restoration Program (SJRRP

To better understand the potential effects of restoration flows on existing drainage problems, anticipated as a result of the San Joaquin River Restoration Program (SJRRP), the U.S. Geological Survey (USGS), in cooperation with the U.S. Bureau of Reclamation (Reclamation), developed a groundwater flow model (SJRRPGW) of the SJRRP study area that is within 5 miles of the San Joaquin River and adjacent bypass system from Friant Dam to the Merced River. The primary goal of the SJRRP is to reestablish the natural ecology of the river to a degree that restores salmon and other fish populations. Increased flows in the river, particularly during the spring salmon run, are a key component of the restoration effort. A potential consequence of these increased river flows is the exacerbation of existing irrigation drainage problems along a section of the river between Mendota and the confluence with the Merced River. Historically, this reach typically was underlain by a water table within 10 feet of the land surface, thus requiring careful irrigation management and (or) artificial drainage to maintain crop health. The SJRRPGW is designed to meet the short-term needs of the SJRRP; future versions of the model may incorporate potential enhancements, several of which are identified in this report. The SJRRPGW was constructed using the USGS groundwater flow model MODFLOW and was built on the framework of the USGS Central Valley Hydrologic Model (CVHM) within which the SJRRPGW model domain is embedded. The Farm Process (FMP2) was used to simulate the supply and demand components of irrigated agriculture. The Streamflow-Routing Package (SFR2) was used to simulate the streams and bypasses and their interaction with the aquifer system. The 1,300-square mile study area was subdivided into 0.25-mile by 0.25-mile cells. The sediment texture of the aquifer system, which was used to distribute hydraulic properties by model cell, was refined from that used in the CVHM to better represent the natural heterogeneity of aquifer-system materials within the model domain. In addition, the stream properties were updated from the CVHM to better simulate stream-aquifer interactions, and water-budget subregions were refined to better simulate agricultural water supply and demand. External boundary conditions were derived from the CVHM. The SJRRPGW was calibrated for April 1961 to September 2003 by using groundwater-level observations from 133 wells and streamflow observations from 19 streamgages. The model was calibrated using public-domain parameter estimation software (PEST) in a semi-automated manner. The simulated groundwater-level elevations and trends (including seasonal fluctuations) and surface-water flow magnitudes and trends reasonably matched observed data. The calibrated model is planned to be used to assess the potential effects of restoration flows on agricultural lands and the relative capabilities of proposed SJRRP actions to reduce these effects.

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Documentation of Model Input and Output Values for the Geohydrology and Mathematical Simulation of the Pajaro Valley Aquifer System, Santa Cruz and Monterey Counties, California

U.S. Geological Survey (USGS) | July 14th, 1990

Summary

As part of a study of the geology and hydrology of the Pajaro Valley aquifer system, Santa Cruz and Monterey Counties, California, a three-layer mathematical mode

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Domestic well vulnerability to drought duration and unsustainable groundwater management in California's Central Valley

Environmental Research Letters (IOP) | March 18th, 2020

Summary

Millions of Californians access drinking water via domestic wells, which are vulnerable to drought and unsustainable groundwater management. Groundwater overdraft and th

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Draft EIR Monterey Amendment to the State Water Project Contracts (Including Kern Water Bank Transfer) and Associated Actions as Part of a Settlement Agreement (Monterey Plus)

California Department of Water Resources (DWR) | April 1st, 2015

Summary

The California Department of Water Resources (Department), as the lead agency under the California Environmental Quality Act (CEQA), prepared the environmental impact rep

The California Department of Water Resources (Department), as the lead agency under the California Environmental Quality Act (CEQA), prepared the environmental impact report (EIR) for the Monterey Amendment to the State Water Project Contracts (Including Kern Water Bank Transfer) and Associated Actions as Part of a Settlement Agreement (Monterey Plus) (Monterey Plus EIR). The Department certified the Monterey Plus EIR on February 1, 2010. Several parties challenged the adequacy of the Monterey Plus EIR under CEQA. In 2014, the Monterey Plus EIR was found by the Sacramento County Superior Court (Court) to comply with CEQA in all aspects except with respect to the development, use, and operation of the Kern Water Bank (KWB). The Court specified that the Department is to correct the deficiencies and recertify the EIR without reopening the non-defective portions of the EIR. Upon recertification, only those portions of the Revised EIR (REIR) that are new or changed shall be subject to challenge under CEQA by petitioners or other interested parties. For these reasons, the Department has developed this three-volume Monterey Plus Draft Revised EIR. Document A1 presents all the changes to the Monterey Plus EIR made as a result of the Department’s reanalysis of the Kern Fan Element (KFE) property transfer and new analysis of the KWB development and continued use and operation. Since DWR decertified the Monterey Plus EIR, pursuant to the Court’s order, the Revised EIR also includes, without modification, the 2007 Draft EIR (Document B, including Volumes I and II) and the 2010 Final EIR (Document C, including Volumes I and II). Together, the three documents constitute the Monterey Plus Draft Revised EIR (Figure P-1). The Draft Revised EIR focuses on the development and continued use and operations of the KWB near Bakersfield. Potentially significant impacts before mitigation were related to groundwater levels and quality, Kern River water quality, the Cross Valley Canal, terrestrial biological resources, erosion, hazardous materials, waterborne disease, cultural and paleontological resources, greenhouse gas emissions, and cumulative impacts. Potentially significant and unavoidable impacts were related to cumulative growth-related impacts. The Draft Revised EIR identifies hazardous sites on or near KWB Lands that have been remediated.

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Page : 31

Development of a Groundwater-Simulation Model in the Los Angeles Coastal Plain, Los Angeles County, California

DGMETA (Version 1): Dissolved Gas Modeling and Environmental Tracer Analysis Computer Program

Discussion Regarding Sources and Ages of Groundwater in Southeastern California

Dispute Resolution Processes - Thinking Through SGMA Implementation: A Water in the West Series

Divergent effects of climate change on future groundwater availability in key mid-latitude aquifers

Diverse stakeholders create collaborative, multilevel basin governance for groundwater sustainability

Documentation of a Groundwater Flow Model (SJRRPGW) for the San Joaquin River Restoration Program Study Area, California

Documentation of Model Input and Output Values for the Geohydrology and Mathematical Simulation of the Pajaro Valley Aquifer System, Santa Cruz and Monterey Counties, California

Domestic well vulnerability to drought duration and unsustainable groundwater management in California's Central Valley

Draft EIR Monterey Amendment to the State Water Project Contracts (Including Kern Water Bank Transfer) and Associated Actions as Part of a Settlement Agreement (Monterey Plus)

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