Ventura County: Environmental Stakeholder Representation in Groundwater Sustainability Agencies

Nature Conservancy | January 1st, 2016

The Sustainable Groundwater Management Act (SGMA) requires the preparation of groundwater sustainability plans (GSPs) for nine groundwater basins in Ventura Cou

The Sustainable Groundwater Management Act (SGMA) requires the preparation of groundwater sustainability plans (GSPs) for nine groundwater basins in Ventura County. The groundwater sustainability agencies (GSAs) that will prepare these plans consist of government agency and stakeholder representatives. Notably, in Ventura County, each basin is including specific representation of environmental interests in the GSP development process. The Fox Canyon Groundwater Management Agency (Fox Canyon) has included an environmental representative on its advisory committee and the other GSAs have included an environmental representative on their governing boards. The purpose of this organizational structure is to ensure that the groundwater needs of environmental uses are represented in the planning process.

Ventura Regional Groundwater Flow Model and Updated Hydrogeologic Conceptual Model: Oxnard Plain, Oxnard Forebay, Pleasant Valley, West Las Posas, and Mound Groundwater Basins

United Water Conservation District (UWCD) | July 2nd, 2018

United Water Conservation District’s (United) effort of the past six years to develop a significantly improved groundwater flow model for the Oxnard Plain and adjacent

United Water Conservation District’s (United) effort of the past six years to develop a significantly improved groundwater flow model for the Oxnard Plain and adjacent basins, as described in this report, is part of a broader effort by United and other agencies in the region to better understand the key factors that affect availability and usability of our area’s groundwater resources. Use of these resources, which have been supplemented for the past 90 years by spreading (artificial recharge) of surface water diverted from the Santa Clara River, has been key to the past growth and the future sustainability of cities and agriculture on the Oxnard coastal plain. Groundwater of suitable quality for a wide range of beneficial uses can be withdrawn from wells and delivered to cities or farms on the Oxnard coastal plain and in the Santa Clara River valley without construction of extensive, costly infrastructure projects (such as the aqueducts and surface reservoirs of the State Water Project), and provides a reliable water supply and resilience against potential major disruptions such as earthquakes and droughts. Although imported surface water from northern California began contributing significantly to the region’s municipal water-supply portfolio over the past half century, and desalination of brackish water or seawater may play an important water-supply role for the region in the future, neither of these alternative sources of water-supply can match the low cost and small environmental footprint of the existing groundwater resources, as enhanced by United’s recharge operations. Unfortunately, the relative accessibility, reliability, and low cost of groundwater for water supply has resulted in it being extracted from the aquifers underlying the Oxnard coastal plain at a faster rate than it has been replenished over the long term. This “overdraft” has resulted in corresponding groundwater-level declines in regional aquifers that have only been partly reversed during wet climatic cycles. In turn, these groundwater-level declines have resulted in seawater intrusion into the regional aquifers near the coast (since the 1930s), and could potentially exacerbate other water-quality problems or cause subsidence of land surface if allowed to continue. United coordinated with other regional water-supply stakeholders to plan and implement major projects in the 1950s, 1980s, and 1990s to mitigate the effects of overdraft, and these efforts have been partially successful. However, under California’s Sustainable Groundwater Management Act (SGMA) of 2015, groundwater sustainability plans (GSPs) must be developed and implemented by 2020 to provide long-term solutions that will prevent further negative impacts in “critically overdrafted basins,” including the Oxnard Plain and Pleasant Valley basins, and by 2022 for other groundwater basins in United’s service area. The geometry and physical characteristics of the aquifers, combined with the interactions of the stresses acting on those aquifers, within the regional groundwater basins are complex. The complexity is compounded by spatial and temporal variability of groundwater recharge and discharge. In order to forecast the effects of potential future water-supply alternatives with a sufficient level of certainty to evaluate and design new projects, it became evident to United in 2011 that the region needed a numerical groundwater-flow model that could discretely simulate each of the seven individual aquifer systems and six intervening aquitards that comprise the multi-layered regional aquifer system beneath the Oxnard and Pleasant Valley groundwater basins. The California Department of Water Resources notes that “while models are, by definition, a simplification of a more complex reality, they have proven to be useful tools over several decades for addressing a range of groundwater problems and supporting the decision-making process. Models can be useful tools for estimating the potential hydrologic effects of proposed water management activities” (Joseph and others, 2016). Numerical models of local groundwater basins developed by California Department of Water Resources in the 1970s, and by the U.S. Geological Survey in the 1990s, were useful for answering the questions about groundwater being asked at those times. However, these models assumed a greatly simplified hydrologic system, consisting of one, two, or three “lumped” aquifers, rather than explicitly modeling the seven aquifers (and six aquitards) that actually exist in the region. This oversimplification was necessary at the time due to limitations in available data, as well as limitations in computer processing power. Consequently, these models produced simulated groundwater elevations that did not always match measured groundwater elevations very well in some key areas, including near the coast and in recharge zones, reducing the reliability and increasing the uncertainty of forecasts for future conditions. Therefore, in 2012 United initiated, with financial and technical support from regional stakeholders, development of the numerical model described in this report (“Ventura Regional Groundwater Flow Model,” or VRGWFM), which discretely simulates each aquifer and aquitard underlying the Oxnard coastal plain as a distinct “layer” (in modeling terminology). The goal of this effort is to achieve significant improvement in calibration compared to previous models, allowing simulation of a greater range of natural and man-made hydrogeologic processes that have occurred in the past, and thereby increase the reliability of model predictions for the future. That said, the California Department of Water Resources warns, “there should be no expectation that a single ‘true’ model exists. All models and model results will have some level of uncertainty” (Joseph and others, 2016). For this reason, United is committed to continuous improvement of the VRGWFM as new data and improved methods become available, to minimize potential uncertainty. United would like to acknowledge the financial support provided by the Fox Canyon Groundwater Management Agency (FCGMA) and the Santa Clara River Watershed Committee, as well as the technical input and assistance provided by the FCGMA Technical Advisory Group (TAG), the Calleguas Municipal Water District’s technical staff and consultants, and the participants of the Expert Panel convened by United to review and provide guidance for improving the model (Dr. Sorab Panday, James Rumbaugh, and John Porcello). United would also like to acknowledge the various water and sanitation districts (including Ventura County Watershed Protection District), municipalities, and individuals that provided data to support development of the VRGWFM. We especially want to acknowledge the importance of the U.S. Geological Survey effort in the 1990s and 2000s to establish a regional groundwater monitoring-well network and construct the first MODFLOW model for the basins underlying the entire Santa Clara River and Calleguas Creek watersheds; their model was a critical “jumping-off point” for the VRGWFM. Finally, United’s Groundwater Department staff would like to recognize the foresight and patience of United’s Board of Directors, previous and present General Managers, and—most notably—former Groundwater Department Manager Tony Morgan, for their efforts in kicking off this modeling effort six years ago and guiding/pushing staff to completion of “Version 1.0” today.

Vina Groundwater Subbasin Groundwater Sustainability Plan

Vina and Rock Creek Reclamation District Groundwater Sustainability Agencies | December 15th, 2021

The Vina GSA and Rock Creek Reclamation District GSA and the stakeholders within the Subbasin recognize that this GSP is not the finish line; it is the starting line for

The Vina GSA and Rock Creek Reclamation District GSA and the stakeholders within the Subbasin recognize that this GSP is not the finish line; it is the starting line for sustainable management of the Subbasin. As conditions within the Subbasin change, the GSAs within the Subbasin are committed to an open, transparent, and all-inclusive adaptive management strategy aimed at tackling the important local issues that they face. At the heart of SGMA is the power for locals to solve local problems with local resources. All parties in the Subbasin are committed to doing just that.

Volatile organic compounds in groundwater used for public supply across the United States: Occurrence, explanatory factors, and human-health context

Science of the Total Environment (Elsevier) | March 11th, 2022

This systematic assessment of occurrence for 85 volatile organic compounds (VOCs) in raw (untreated) groundwater used for public supply across the United States (U.S.), w

This systematic assessment of occurrence for 85 volatile organic compounds (VOCs) in raw (untreated) groundwater used for public supply across the United States (U.S.), which includes 43 compounds not previously monitored by national studies, relates VOC occurrence to explanatory factors and assesses VOC detections in a human-health context. Samples were collected in 2013 through 2019 from 1537 public-supply wells in aquifers representing 78% of the volume pumped for public drinking-water supply. Laboratory detection limits for VOCs generally were less than 0.1 μg/L. Detections were reported for 36% of the sampled principal-aquifer area (38% of sampled wells) and were most common in wells in shallow, unconfined aquifers in urban areas that produce high proportions of modern-age and oxic groundwater. The disinfection by-product trichloromethane (chloroform) was the most commonly detected VOC associated primarily with anthropogenic sources (24% of the sampled area, 25% of sampled wells), followed by the gasoline oxygenate methyl tert-butyl ether (8.4% of area, 11% of wells). Carbon disulfide (12% of area, 14% of wells) was examined separately because of likely substantial contributions from natural sources. Newly monitored VOCs were each detected in

Volatile Organic Compounds in the Nation’s Ground Water and Drinking Water Supply Wells

U.S. Geological Survey (USGS) | August 29th, 2014

This national assessment of 55 volatile organic compounds (VOCs) in ground water gives emphasis to the occurrence of VOCs in aquifers that are used as an important supply

This national assessment of 55 volatile organic compounds (VOCs) in ground water gives emphasis to the occurrence of VOCs in aquifers that are used as an important supply of drinking water. In contrast to the monitoring of VOC contamination of ground water at point-source release sites, such as landfills and leaking underground storage tanks (LUSTs), our investigations of aquifers are designed as large-scale resource assessments that provide a general characterization of water-quality conditions. Nearly all of the aquifers included in this assessment have been identified as regionally extensive aquifers or aquifer systems.(2)  The assessment of ground water (Chapter 3) included analyses of about 3,500 water samples collected during 1985–2001 from various types of wells, representing almost 100 different aquifer studies. This is the first national assessment of the occurrence of a large number of VOCs with different uses, and the assessment addresses key questions about VOCs in aquifers. The assessment also provides a foundation for subsequent decadal assessments of the U.S. Geological Survey (USGS) National Water-Quality Assessment (NAWQA) Program to ascertain long-term trends of VOC occurrence in these aquifers.

Warming and snow loss increase reliance on old groundwater in a Colorado River headwater

Nature Portfolio (Springer Nature) | April 8th, 2026

Atmospheric warming is reducing snowpack, with uncertain effects on mountainous streamflow, a crucial water resource. Despite limited historical observations of groundwat

Atmospheric warming is reducing snowpack, with uncertain effects on mountainous streamflow, a crucial water resource. Despite limited historical observations of groundwater–streamflow interactions above 2,500 m, new measurements in the Upper Colorado River headwaters indicate declining groundwater storage that is dated decades to millennia old. Here we use integrated hydrologic modelling spanning water years 2015–2021 to determine whether the loss of old-age groundwater buffers streamflow during low-snow years and whether that loss is exacerbated with warming. Results show that old-groundwater contributions to streams remain relatively steady through time, unlike the more variable contributions from young groundwater. Numerical experiments of increased surface air temperatures (+2.5 °C and +4 °C) increase rain–snow fractions and evapotranspiration and decrease runoff ratio by 2–3% per degree Celsius increase. As streamflow declines with warming, the age of groundwater supporting it gets older, in part owing to intermediate-aged (1–3 year) groundwater declining twice as fast. Simulations show that water table depths at higher elevations (>3,700 m) decline disproportionately and fail to recover even during wet years. These findings suggest altered groundwater–streamflow interactions with warming and snow loss, with implications for water resources.

Water availability and land subsidence in the Central Valley, California, USA

Hydrogeology Journal (Springer) | November 17th, 2015

The Central Valley in California (USA) covers about 52,000 km2 and is one of the most productive agricultural regions in the world. This agriculture relies heavily on sur

The Central Valley in California (USA) covers about 52,000 km2 and is one of the most productive agricultural regions in the world. This agriculture relies heavily on surface-water diversions and groundwater pumpage to meet irrigation water demand. Because the valley is semi-arid and surface-water availability varies substantially, agriculture relies heavily on local groundwater. In the southern two thirds of the valley, the San Joaquin Valley, historic and recent groundwater pumpage has caused significant and extensive drawdowns, aquifer-system compaction and subsidence. During recent drought periods (2007–2009 and 2012-present), groundwater pumping has increased owing to a combination of decreased surface-water availability and land-use changes. Declining groundwater levels, approaching or surpassing historical low levels, have caused accelerated and renewed compaction and subsidence that likely is mostly permanent. The subsidence has caused operational, maintenance, and construction-design problems for water-delivery and flood control canals in the San Joaquin Valley. Planning for the effects of continued subsidence in the area is important for water agencies. As land use, managed aquifer recharge, and surface-water availability continue to vary, long-term groundwater-level and subsidence monitoring and modelling are critical to understanding the dynamics of historical and continued groundwater use resulting in additional water-level and groundwater storage declines, and associated subsidence. Modeling tools such as the Central Valley Hydrologic Model can be used in the evaluation of management strategies to mitigate adverse impacts due to subsidence while also optimizing water availability. This knowledge will be critical for successful implementation of recent legislation aimed toward sustainable groundwater use. *Erratum: Water availability and land subsidence in the Central Valley, California, USA, Faunt, C.C., Sneed, M., Traum, J. et al. Hydrogeol J (2017) 25: 2215

Water availability and subsidence in California’s Central Valley

University of California, Davis (UC Davis) | September 5th, 2015

California’s Central Valley covers about 52,000 square kilometers (km2) and is one of the most productive agricultural regions in the world. More than 250 different c

California’s Central Valley covers about 52,000 square kilometers (km2) and is one of the most productive agricultural regions in the world. More than 250 different crops are grown in the broad alluvial filled structural trough, with an estimated value exceeding $20 billion per year (Faunt 2009) (Figure 1). Central Valley agriculture depends on state and federal water systems that divert surface water, predominantly originating from Sierra Nevada snowmelt, to agricultural fields. Because the valley is semi-arid and the availability of surface water varies substantially from year to year, season to season, and from north to south, agriculture, as it grew, developed a reliance on groundwater for irrigation.

Water Available for Replenishment 2018

California Department of Water Resources (DWR) | April 12th, 2018

Water Blueprint for the San Joaquin Valley Economic Impact Analysis: Phase One Results

Water Blueprint for San Joaquin Valley | February 15th, 2020