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Interpretation of Hydrostratigraphy and Water Quality from AEM Data Collected in the Northern Salinas Valley, CA

Marina Coast Water District | March 15th, 2018

Summary

Groundwater management, in the Monterey area of California, requires an accurate understanding of the hydrostratigraphy of the coastal aquifer system, as well as an unde

Groundwater management, in the Monterey area of California, requires an accurate understanding of the hydrostratigraphy of the coastal aquifer system, as well as an understanding of the groundwater quality variability within that system. The hydraulic properties of, and connectivity between, the individual units in the aquifer system determine potential routes for the movement of groundwater within and between aquifers. An understanding of the distribution of water quality within the aquifer system and an understanding of the hydrostratigraphy of the system are needed to evaluate the current state of groundwater resources, and to assess the potential impact of any proposed activity on the groundwater resources in the area. The focus of this study is the Northern Salinas Valley. Figure 1 shows the specific region of interest outlined in pink. The orange contour shows the extent of saltwater intrusion into the uppermost aquifers in this area, as determined from well data by the Monterey County Water Resources Agency as the regions where groundwater contains concentrations of chloride greater than 500 mg/L. But there is some question as to whether this contour accurately captures the extent of saltwater intrusion into these aquifers. The detection of water with anomalously low concentrations of total dissolved solids in five newly constructed monitoring well clusters suggests the presence of isolated lenses of fresher groundwater in the Dune Sand Aquifer and Perched Dune Sand Aquifer (outlined in light blue) and in the 180-Foot Aquifer (outlined in dark blue) (Hopkins Groundwater Consultants, 2016). The locations of seven wells from the Monterey Peninsula Water Supply Project (MPWSP) are also shown in Figure 1 as red diamonds, and wells owned by the Marina Coast Water District (MCWD) are shown as green circles. The two groundwater subbasins in the region of interest—the Monterey Subbasin and the 180/400 Aquifer Subbasin—are outlined in purple and blue, respectively. The objective of this study was to use the geophysical method, airborne electromagnetics (AEM), to evaluate the current understanding of the hydrostratigraphy in this area and to interpret the distribution of groundwater quality indicated by available well data. To evaluate the understanding of the hydrostratigraphy, a hydrostratigraphic model of the region of interest was first built using existing data, and was then updated with the information supplied by the AEM data. This approach was followed for two separate initial models. The first initial model was based on the North Marina Groundwater Model (NMGWM), developed by Geoscience Support Services as part of the MPWSP. The second initial model was built in-house using lithology data and hydrostratigraphic interpretations from a variety of previously published reports. Our interpretation of the distribution of groundwater quality in the region is based on statistical relationships built between water quality samples and borehole geophysical data collected in the wells shown in Figure 1.

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Investing In Clean Agriculture: How California Can Strengthen Agriculture, Reduce Pollution And Save Money

Pacific Institute | February 8th, 2005

Summary

Global competition, suburban encroachment, tighter regulations, and rising input costs are making farming in California more difficult and, in some cases, less profitable

Global competition, suburban encroachment, tighter regulations, and rising input costs are making farming in California more difficult and, in some cases, less profitable. At the same time, pesticide pollution from farming is causing significant harm to California’s surface and groundwater, air quality, and human health. But there is a way to reduce pesticide use, protect the environment, and help farmers stay competitive according to a new report, Investing In Clean Agriculture: How California Can Strengthen Agriculture, Reduce Pollution And Save Money, published today by the Pacific Institute. “Business as usual isn’t working for our state,” declared Dr. Gary H. Wolff, author of the report and Principal Economist and Engineer with the Pacific Institute of Oakland, California. “Our plan will reduce pesticide use, protect public health, preserve the environment, and help California’s farmers stay competitive in a rapidly changing economy. We think this will be a win for consumers, a win for taxpayers, and a win for agriculture.” A US Geological Survey study of groundwater wells in the San Joaquin-Tulare Basin found at least one pesticide in 59 of 100 samples. But current efforts to reduce pesticide pollution are caught up in the courts. The rebate approach creates a voluntary incentive to reduce pesticide use while leaving it up to farmers to figure out the best way forward. “The Pacific Institute’s innovative proposal will reward farmers who are willing to learn about farming practices that protect water quality,” noted Leland Swenson of the Community Alliance With Family Farmers. “It is a voluntary and incentive-based way for farmers to respond to water quality regulations and keep pesticides out of drinking water.” The report describes how farmers can be rewarded for learning voluntarily about sustainable agricultural practices. A modest increase in the statewide “mill” fee, now levied on pesticides, is returned to farmers who take a short course on sustainable agriculture techniques and storm runoff management. This helps farmers stay competitive while reducing pesticide use – which will protect human health, preserve the environment, and eventually save taxpayers money by reducing medical costs. “Everybody wins if we can reduce our dependence on pesticides,” said Jonathan Kaplan of NRDC. “As the head of California’s Department of Pesticide Regulation just stated, ‘Integrated Pest Management is good for our economy as well as our environment’.” Investing In Clean Agriculture: How California Can Strengthen Agriculture, Reduce Pollution And Save Money estimates that the voluntary program and fee increase could bring $60 million per year into the agricultural sector while also bringing the most cutting edge research on sustainable farming techniques to those in the field.

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Is there an urban pesticide signature? Urban streams in five U.S. regions share common dissolved-phase pesticides but differ in predicted aquatic toxicity

Science of the Total Environment (Elsevier) | June 15th, 2021

Summary

Pesticides occur in urban streams globally, but the relation of occurrence to urbanization can be obscured by regional differences. In studies of five regions of the Unit

Pesticides occur in urban streams globally, but the relation of occurrence to urbanization can be obscured by regional differences. In studies of five regions of the United States, we investigated the effect of region and urbanization on the occurrence and potential toxicity of dissolved pesticide mixtures. We analyzed 225 pesticide compounds in weekly discrete water samples collected during 6–12 weeks from 271 wadable streams; development in these basins ranged from undeveloped to highly urbanized. Sixteen pesticides were consistently detected in 16 urban centers across the five regions—we propose that these pesticides comprise a suite of urban signature pesticides (USP) that are all common in small U.S. urban streams. These USPs accounted for the majority of summed maximum pesticide concentrations at urban sites within each urban center. USP concentrations, mixture complexity, and potential toxicity increased with the degree of urbanization in the basin. Basin urbanization explained the most variability in multivariate distance-based models of pesticide profiles, with region always secondary in importance. The USPs accounted for 83% of pesticides in the 20 most frequently occurring 2-compound unique mixtures at urban sites, with carbendazim+prometon the most common. Although USPs were consistently detected in all regions, detection frequencies and concentrations varied by region, conferring differences in potential aquatic toxicity. Potential toxicity was highest for invertebrates (benchmarks exceeded in 51% of urban streams), due most often to the neonicotinoid insecticideimidacloprid and secondarily to organophosphate insecticides and fipronil. Benchmarks were rarely exceeded in urban streams for plants (at 3% of sites) or fish (<1%). We propose that the USPs identified here would make logical core (nonexclusive) constituents for monitoring dissolved pesticides in U.S. urban streams, and that unique mixtures containing imidacloprid, fipronil, and carbendazim are priority candidates for mixtures toxicity testing.

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Joint Report to the Legislature on the Department of Fish and Wildlife and State Water Resources Control Board pilot project to address the Environmental Impacts of Cannabis Cultivation (Watershed Enforcement Team)

California State Water Resources Control Board (SWRCB) | March 16th, 2015

Summary

This report is in response to the 2014-2015 Supplemental Report for item 3600-001-0001-Department of Fish and Wildlife (Department or CDFW), which provides the following

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Kern County Subbasin Staff Review of 2025 Draft of Groundwater Sustainability Plans

California State Water Resources Control Board (SWRCB) | September 5th, 2025

Summary

The Kern County Subbasin (subbasin or basin) is a critically overdrafted subbasin in the southern portion of the San Joaquin Valley with an area of about 1.78 million acr

The Kern County Subbasin (subbasin or basin) is a critically overdrafted subbasin in the southern portion of the San Joaquin Valley with an area of about 1.78 million acres. The subbasin is currently managed by 20 GSAs. DWR determined the subbasin’s 2022 GSPs were inadequate and referred the subbasin to the State Water Board in March 2023, which initiated the state intervention process. The subbasin GSAs submitted their revised, adopted GSPs to the Board in December 2024, and Board staff determined that these updated GSPs did not resolve all the deficiencies identified by staff in the previous GSPs. On February 20, 2025, the State Water Board held a hearing to determine whether to designate the subbasin as probationary. In recognition of the substantial progress the subbasin made, the Board continued the hearing to September 17, 2025, giving the GSAs additional time to resolve the remaining deficiencies and directing the GSAs to submit revised draft GSPs to the Board by June 20, 2025 for review. On June 20, 2025, the GSAs submitted seven amended draft GSPs to the Board (2025 Draft GSPs). Board staff reviewed the 2025 Draft GSPs and conclude that the GSAs substantially, though not completely, address the deficiencies identified in the previous GSPs. Staff recommends returning the subbasin to DWR for review of the updated GSPs pursuant to Water Code section 10733.4 if the GSAs resolve three of the remaining issues: (1) providing an adequate mitigation program for drinking water wells impacted by any constituent for which a minimum threshold is established in the GSPs, including 1,2,3-TCP, where groundwater management activities cause concentrations to exceed those minimum thresholds; (2) providing an adequate mitigation program for state small water system wells (or domestic wells with more than four service connections) impacted by groundwater management activities; and (3) eliminating the Kern Non-Districted Land Authority GSA Joint Exercise of Powers Agreement May 2026 sunset provision, which would result in unmanaged areas of the subbasin that are a potential basis for state intervention.

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Lahar Hazard Zones for Eruption-Generated Lahars in the Lassen Volcanic Center, California

U.S. Geological Survey (USGS) | September 25th, 2012

Summary

Lahars, Indonesian for volcanic mudflows or debris-flows, are a rapidly flowing mixture of rock debris and water that originates on the slopes of a volcano. Lahar generat

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Lake Tahoe Nearshore Water Quality Protection Plan

California State Water Resources Control Board (SWRCB) | November 6th, 2014

Summary

In October 2013, the Desert Research Institute, UC Davis, and University of Nevada at Reno released the Lake Tahoe Nearshore Evaluation and Monitoring Framework Report (R

In October 2013, the Desert Research Institute, UC Davis, and University of Nevada at Reno released the Lake Tahoe Nearshore Evaluation and Monitoring Framework Report (Report) (NeST 2013). The Report presents a conceptual understanding of nearshore environment processes, assesses the heterogenic nature of the nearshore, highlights the lack of data available to characterize the environmental status of the Lake Tahoe nearshore, and emphasizes that current agency implementation efforts will benefit the nearshore environment. This Lake Tahoe Nearshore Water Quality Protection Plan (Plan) outlines the Lahontan Regional Water Quality Control Board’s (Regional Water Board) response to the changes in the Lake Tahoe nearshore environment as informed by the Report. Based on the Report findings and recommendations, the Regional Water Board will proceed with the following actions: (1) continue implementing programs that benefit nearshore environmental quality; (2) establish and implement an integrated nearshore monitoring plan to track change in the nearshore environment and track pollutant inputs to the nearshore; (3) evaluate localized “hotspots” where nearshore change has been documented and assess causes of observed degradation; (4) investigate climate change influence on nearshore water quality; and (5) assess the need for revised or new water quality standards to protect nearshore water quality. In establishing and maintaining nearshore water quality protection policies, the Water Board will continue to coordinate with other government agencies and the public. Because available resources are insufficient to fully implement all recommendations, a dedicated annual funding source must be found to adequately protect and enhance Lake Tahoe’s precious nearshore. The Plan elements and funding needs are presented in Attachment 1. The Plan also serves as response to a Legislative request in the 2012-2013 Budget Act specific to the Water Board’s approach to the nearshore.

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Land Subsidence in the Southwestern Mojave Desert, California, 1992–2009

U.S. Geological Survey (USGS) | July 8th, 2017

Summary

Groundwater has been the primary source of domestic, agricultural, and municipal water supplies in the southwestern Mojave Desert, California, since the early 1900s. Incr

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Land subsidence, groundwater levels, and geology in the Coachella Valley, California, 1993-2010

U.S. Geological Survey (USGS) | June 15th, 2014

Summary

Land subsidence associated with groundwater-level declines has been investigated by the U.S. Geological Survey in the Coachella Valley, California, since 1996. Groundwate

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Land use and land cover influence on water quality in the last free-flowing river draining the western Sierra Nevada, California

Journal of Hydrology (Elsevier) | November 10th, 2005

Summary

Land use and land cover across 28 sub-basins within the Cosumnes Watershed, CA (1989 km2) were correlated to nitrate-N and total suspended solids (TSS) loading between w

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Page : 55

Interpretation of Hydrostratigraphy and Water Quality from AEM Data Collected in the Northern Salinas Valley, CA

Investing In Clean Agriculture: How California Can Strengthen Agriculture, Reduce Pollution And Save Money

Is there an urban pesticide signature? Urban streams in five U.S. regions share common dissolved-phase pesticides but differ in predicted aquatic toxicity

Joint Report to the Legislature on the Department of Fish and Wildlife and State Water Resources Control Board pilot project to address the Environmental Impacts of Cannabis Cultivation (Watershed Enforcement Team)

Kern County Subbasin Staff Review of 2025 Draft of Groundwater Sustainability Plans

Lahar Hazard Zones for Eruption-Generated Lahars in the Lassen Volcanic Center, California

Lake Tahoe Nearshore Water Quality Protection Plan

Land Subsidence in the Southwestern Mojave Desert, California, 1992–2009

Land subsidence, groundwater levels, and geology in the Coachella Valley, California, 1993-2010

Land use and land cover influence on water quality in the last free-flowing river draining the western Sierra Nevada, California

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