Mapping saltwater intrusion with an airborne electromagnetic method in the offshore coastal environment, Monterey Bay, California

Journal of Hydrology (Elsevier) | April 1st, 2019

Study Region: The northern coast of the Monterey Bay, California, USA, extending from the coastline to 3.5 km offshore. Study Focus: Three-hundred and twenty line-kil

Study Region: The northern coast of the Monterey Bay, California, USA, extending from the coastline to 3.5 km offshore. Study Focus: Three-hundred and twenty line-kilometers of airborne electromagnetic (AEM) data were acquired offshore. These data spanned 20 km of coastline, extending up to 3.5 km offshore in water up to 18m in depth. Inversion of these data resulted in resistivity models extending to depths between 50 and 200m below sea level. The data were interpreted in conjunction with onshore monitoring well data, hydrologic and geologic reports, and electrical resistivity tomography (ERT) data to locate the freshwater/saltwater interfaces throughout the region. A resistivity-to-water-quality transform was established using well-based water quality and resistivity logging measurements. For resistivity values that could not be converted to water quality with this transform, local auxiliary information was used on a case-by-case basis to interpret the observed features. Some low resistivity anomalies were identified near the shore at depth, which were interpreted to be artifacts of the 1D assumption in the inversion scheme used for these AEM data. New Hydrogeological Insights for this Region: We found that the acquisition of AEM data provided valuable information about water quality in the offshore extents of the aquifers, a region inaccessible to traditional monitoring methods, but one that plays an important role in the modeling, prediction, and management of saltwater intrusion.

Monterey County Groundwater Management Plan

Monterey County Water Resources Agency (MCWRA) | May 17th, 2006

In 1992, California State Legislature adopted the Groundwater Management Act (California Water Code Part 2.7, §10753), originally enacted as Assembly Bill (AB) 3030 and

In 1992, California State Legislature adopted the Groundwater Management Act (California Water Code Part 2.7, §10753), originally enacted as Assembly Bill (AB) 3030 and amended by Senate Bill (SB) 1938 in 2002. The Groundwater Management Act provided the authority to prepare groundwater management plans and encouraged local agencies to work cooperatively to manage groundwater resources within their jurisdictions and groundwater basins. Monterey County Water Resources Agency (MCWRA), recognizing that management of its natural water resources is critical to ensuring a long-term sustainable and reliable good quality water supply, has prepared this Groundwater Management Plan (GWMP). The purpose of the GWMP is to provide a comprehensive overview of the Salinas Valley Groundwater Basin and to recommend various management strategies for the basin. Specifically, this document provides the framework for the management of groundwater resources in the Salinas Valley Groundwater Basin (exclusive of the Seaside and Paso Robles subareas) and acts as a guidance document for future groundwater projects. While this edition of the GWMP focuses on the Salinas Valley Groundwater Basin, MCWRA is responsible for the management of the water resources for all of Monterey County. Future GWMP versions will incorporate the additional groundwater basins in the County. This document has been prepared in accordance with existing regulations as outlined in the California Water Code (as referenced above) and was prepared in coordination with local agencies and interested residents through public outreach activities.

Municipal Service Review and Sphere of Influence Update for the Orange County Water District Including a Feasibility Analysis of the Potential Consolidation of Orange County Water District and Municipal Water District of Orange County

Local Agency Formation Commission of Orange County | November 15th, 2024

Ojai Basin Groundwater Management Agency Groundwater Management Plan – 2018 Update

Ojai Basin Groundwater Management Agency | August 30th, 2018

In September, 2014, Governor Jerry Brown signed into law a package of three bills (AB 1739, SB 1168, and SB 1319) known as the Sustainable Groundwater Management Act (“

In September, 2014, Governor Jerry Brown signed into law a package of three bills (AB 1739, SB 1168, and SB 1319) known as the Sustainable Groundwater Management Act (“SGMA”). SGMA provides a framework for sustainable management of groundwater supplies by local authorities, with a limited role for state intervention only if necessary to protect the resource.  The Act requires the formation of local groundwater sustainability agencies that must assess conditions in their local water basins and adopt locally-based management plans. SGMA provides local agencies with the tools and authority to require registration of groundwater wells, measure and manage extractions, require reports and assess fees, and request revisions of basin boundaries, including establishing new subbasins.  High- and medium-priority basins, as defined by the State of California Department of Water Resources (“DWR”), must adopt groundwater sustainability plans within five to seven years, depending on whether the basin is in critical overdraft. Statewide groundwater basins are prioritized based on eight criteria: (1) overlying population, (2) projected growth of overlying population, (3) public supply wells, (4) total water wells, (5) overlying irrigated acreage, (6) reliance on groundwater as the primary source of water (7) impacts on the groundwater, including overdraft, subsidence, saline intrusion, and other water quality degradation, and (8) any other information determined to be relevant by the DWR.  Consistent with its Enabling Legislation, the Ojai Basin Groundwater Management Agency (“OBGMA” or “Agency”) has worked to preserve the quantity and quality of groundwater in the Ojai Valley Groundwater Basin (“Ojai Basin”) for sustainable long-term use since the agency’s establishment in 1991. (The Agency’s Enabling Legislation, SB 534, approved by the Governor October 8, 1991, is also referred to herein as the “OBGMA Act.”) These management efforts have resulted in the protection and maintenance of the long-term water supply for the common benefit of all water users in the Basin. As a result, the Ojai Basin has operated within its “sustainable yield” for the past several decades with no evidence of “undesirable results.”  Per OBGMA Resolution No. 2014-4, adopted by its Board of Directors on December 4, 2014 (copy included as Appendix A), OBGMA is designated as the Groundwater Sustainability Agency (“GSA”) for the Ojai Groundwater Basin. In addition, SGMA identifies OBGMA as an “exclusive local agency” within its statutory boundaries for purposes of implementing the requirements of the Act. (Water Code § 10723(c)(1).) Since OBGMA, in compliance with its Enabling Legislation, already performs many of the planning and management tasks required by SGMA, and sustainable conditions have persisted in the Basin for more than a 10-year period. OBGMA determined it would comply with SGMA by making the Alternative Demonstration of groundwater sustainability authorized by Water Code § 10733.6(b)(3).  To comply with SGMA, OBGMA issued its December 23, 2016 “Report Supporting Alternative Demonstration Made Pursuant to Water Code 10733.6(b)(3). The report contained a physical description of the Basin, including groundwater levels, groundwater quality, information on groundwater-surface water interaction, data on historical and projected water demands and supplies, monitoring and management provisions. The report demonstrated how the Ojai Basin has operated within its “sustainable yield” for the past several decades with no evidence of “undesirable results.”  In sum, OBGMA’s management of the Basin pursuant to its Enabling Legislation has allowed the Agency to make the Alternative Demonstration authorized by SGMA. This 2018 Update to the Agency’s Groundwater Management Plan, undertaken in compliance with its Enabling Legislation, is part of the Agency’s ongoing efforts to preserve the long-term quantity and quality of groundwater in the Ojai Basin for the common benefit all users in the Basin. 

Pajaro Valley Basin Management Plan Groundwater Sustainability Update 2022

Pajaro Valley Water Management Agency (PVWMA) | November 17th, 2021

Pajaro Valley Water Management Agency Basin Management Plan Update

Pajaro Valley Water Management Agency (PVWMA) | February 14th, 2014

Pajaro Valley Water Management Agency Revised Management Plan

Pajaro Valley Water Management Agency (PVWMA) | February 14th, 2002

Pure Water Soquel Groundwater Model Simulation Results

Soquel Creek Water District | June 22nd, 2018

This technical memorandum discusses model simulation groundwater levels, groundwater budget, and particle tracking results to support the Environmental Impact Rep

This technical memorandum discusses model simulation groundwater levels, groundwater budget, and particle tracking results to support the Environmental Impact Report of the Pure Water Soquel project involving replenishment of advanced purified recycled water within Soquel Creek Water District’s (SqCWD’s) service area. Six model simulations have been run using the calibrated GSFLOW model for the Santa Cruz Mid- County Basin (the Basin) where SqCWD’s service area is located. These simulations have different pumping and active replenishment distributions, as follows: Two Projected Existing Conditions (No Project) simulations with SqCWD’spumping distribution reflecting future demand without additional replenishment at proposed recharge wells. Two Project simulations with SqCWD’s pumping distribution reflecting future demand and pumping re-distribution with the addition of replenishment at the Monterey and Cabrillo College Dr. sites (referred to as the Cabrillo-Monterey simulations). These simulations also represent potential replenishment at the Twin Lakes Church site instead of one of the two Cabrillo College Dr. sites. The Twin Lakes Church site is approximately 500-750 feet to the west of the Cabrillo College Dr. sites. Two Project simulations with the same pumping distribution as the Cabrillo- Monterey simulations, but with replenishment at the Monterey and Willowbrook sites (referred to as the Monterey-Willowbrook simulations).Simulation groundwater levels are evaluated for the following effects: Comparison of groundwater levels at coastal monitoring wells to protective elevations estimated to prevent seawater intrusion from further occurring in groundwater supply aquifers. Groundwater levels in the recharge wells to assess whether model results are consistent with estimated capacities for the well, recognizing that site specific testing will be needed to confirm recharge well capacities. Groundwater levels at nearby wells to evaluate effects on operation of those municipal, private, and institutional wells.Simulation groundwater budgets are evaluated for following effects: • Flows entering and leaving the Basin, including flows to and from groundwater in storage and flows offshore to prevent seawater intrusion. • Flows between groundwater and surface water. This memo does not include results for a Cumulative simulation. Information from the City of Santa Cruz to define its Aquifer Storage and Recovery project to be cumulative with Pure Water Soquel is not available or developed at this time. This memo includes results from particle tracking based on the above simulations performed to support the Salt and Nutrient Anti-degradation Study and permitting of the recharge wells. This involves particle tracking of simulated purified, replenishment water to evaluate the fate of the water as it travels in subsurface aquifers. Particle tracking is also used to evaluate travel times of purified, replenishment water, which requires refined analysis near the recharge wells. A scope to superimpose analytic element solutions for recharge and nearby extraction wells onto GSFLOW results to facilitate travel time calculations was approved by SqCWD Board December 18, 2017 and results should be forthcoming in July 2018.

Recommendations to Address the Expansion of Seawater Intrusion in the Salinas Valley Groundwater Basin

Monterey County Water Resources Agency (MCWRA) | October 12th, 2017

This report provides a discussion of the current knowledge and related background information surrounding seawater intrusion pathways and potential impacts ther

This report provides a discussion of the current knowledge and related background information surrounding seawater intrusion pathways and potential impacts thereof on the Salinas Valley Groundwater Basin. This document also serves as a body of evidence to catalogue the findings used to support the recommendations presented herein. Staff is making six recommendations, with each focused on a component that influences, or could be impacted by, the advancement of seawater intrusion. The recommendations are being presented in an order that builds upon the foundational knowledge laid out in the background section of this report, rather than in an order of priority. Each recommendation can be implemented on its own or in concert with the others, and the relative importance of each will be discussed individually in this report. However, the recommendations have been conceptualized as a comprehensive solution that, along with continued operation of projects that have been constructed for the same purpose, have the strongest potential to ensure success in slowing or halting further seawater intrusion when implemented simultaneously.

Resistivity imaging reveals complex pattern of saltwater intrusion along Monterey coast

Journal of Hydrology (Elsevier) | February 22nd, 2017

A coastal region represents a dynamic zone where fresh groundwater in the coastal aquifers interacts with saline ocean water. The location of the freshwater-saltwater int

A coastal region represents a dynamic zone where fresh groundwater in the coastal aquifers interacts with saline ocean water. The location of the freshwater-saltwater interface is governed by the density and pressure differences on the two sides of the interface and the subsurface hydrologic properties that control fluid movement. Saltwater intrusion is the process in which this interface moves landward, with saltwater then occupying parts of the aquifer that were once fresh. While this process has been observed and documented throughout the world for over a century (Bear et al., 1999), climate change, growing water demands, and manipulation of natural hydrologic systems have led to saltwater intrusion being considered a significant threat to future freshwater resources globally (Kinzelbach et al., 2003; Barlow and Reichard, 2009; Werner et al., 2013). Saltwater intrusion can have a number of significant economic and environmental impacts, including diminished freshwater storage capacity, contamination of freshwater production wells, soil salinization, and decreased nutrient laden freshwater discharge to marine ecosystems (Johannes, 1980; Taniguchi et al., 2002; Werner et al., 2013). A number of steps can be taken to attempt to slow the rate of saltwater intrusion, including spatial and temporal changes in the extent of groundwater pumping, in landuse, in surface water diversions, and in artificial recharge (Abarca et al., 2006). What is needed however is a way to prioritize these actions, or combinations of actions, so as to optimize the impact on saltwater intrusion. This requires an accurate understanding of the current distribution of freshwater and saltwater, that can be used to predict future locations in response to these, and other, actions (Sanford and Pope, 2009). Saltwater intrusion is traditionally mapped and monitored using measurements made in wells and predictive flow models (Werner et al., 2013). There are a number of limitations with these methods. Measurements made in wells provide point data, which may fail to capture the spatial complexity in subsurface conditions. Improving spatial coverage with additional wells can be cost prohibitive (Ogilvy et al., 2009). Additionally, salinity measurements from wells can be flux-averaged concentrations, and head measurements in wells are affected by the density of the water column so can be misinterpreted in the presence of unknown salt water, and are susceptible to measurement, instrument, and time lag errors (Carrera et al., 2009; Post and Von Asmuth, 2013). Models are generally calibrated by matching historic head values in wells and/or matching salinity values from well samples (Carrera et al., 2009), thus all the limitations of well data are carried over into the model calibration. Given these limitations there is significant opportunity for additional methods of mapping and monitoring the distribution of saltwater in the subsurface for improved management of coastal aquifers.