Merced Groundwater Subbasin Groundwater Sustainability Plan (Revised)

Merced Subbasin Groundwater Sustainability Agency (MSGSA) | July 6th, 2022

Due to size, this file has been divided into six part. Part 1, Part 2, Part 3, Part 4, Part 5, Part 6

Due to size, this file has been divided into six part. Part 1, Part 2, Part 3, Part 4, Part 5, Part 6

Merced River Watershed Flood-MAR Reconnaissance Study

California Department of Water Resources (DWR) | November 15th, 2023

DWR, in partnership with the Merced Irrigation District (MID), is conducting a preliminary study using flood waters for managed aquifer recharge that can reduce flood ris

DWR, in partnership with the Merced Irrigation District (MID), is conducting a preliminary study using flood waters for managed aquifer recharge that can reduce flood risk, increase surface and groundwater supply reliability, and enhance ecosystems in the Merced River Basin. This Merced River Reconnaissance Study (study) is exploring the potential, feasibility, and effectiveness of Flood-MAR concepts, testing theories, and assessing strategies in overcoming barriers and challenges to project planning and implementation. The study will assess current conditions of the Merced River watershed and the vulnerability of these watershed management characteristics to a range of potential climate change futures. The study will also describe the public and private benefits that may be achieved through Flood-MAR strategies and quantify a range of benefits that Flood-MAR could provide in or adjacent to the Merced River watershed.

Mercury and Methylmercury in Fish and Water from the Sacramento-San Joaquin Delta: August 2016 – April 2017

San Francisco Estuary Institute (SFEI) | September 3rd, 2018

Monitoring of sport fish and water was conducted by the Delta Regional Monitoring Program (Delta RMP) from August 2016 to April 2017 to begin to address the highest prior

Monitoring of sport fish and water was conducted by the Delta Regional Monitoring Program (Delta RMP) from August 2016 to April 2017 to begin to address the highest priority information needs related to implementation of the Sacramento–San Joaquin Delta Estuary Total Maximum Daily Load (TMDL) for Methylmercury (Wood et al. 2010). Two species of sport fish, largemouth bass (Micropterus salmoides) and spotted bass (Micropterus punctulatus), were collected at six sampling locations in August and September 2016. The length-adjusted (350 mm) mean methylmercury (measured as total mercury, which is a routinely used proxy for methylmercury in predator fish) concentration in bass ranged from 0.15 mg/kg or parts per million (ppm) wet weight at Little Potato Slough to 0.61 ppm at the Sacramento River at Freeport. Water samples were collected on four occasions from August 2016 through April 2017. Concentrations of methylmercury in unfiltered water ranged from 0.021 to 0.22 ng/L or parts per trillion. Concentrations of total mercury in unfiltered water ranged from 0.91 to 13 ng/L. Over 99% of the lab results for this project met the requirements of the Delta RMP Quality Assurance Program Plan, and all data were reportable. This data report presents the methods and results for the first year of monitoring. Historic data from the same or nearby monitoring stations from 1998 to 2011 are also presented to provide context. Monitoring results for both sport fish and water were generally comparable to historic observations. For the next several years, annual monitoring of sport fish will be conducted to firmly establish baseline concentrations and interannual variation in support of monitoring of long-term trends as an essential performance measure for the TMDL. Monitoring of water will solidify the linkage analysis (the quantitative relationship between methylmercury in water and methylmercury in sport fish) in the TMDL. Water monitoring will also provide data that will be useful in verifying patterns and trends predicted by numerical models of mercury transport and cycling being developed for the Delta and Yolo Bypass by the California Department of Water Resources (DWR).

Mercury Contamination from Historical Gold Mining in California

U.S. Geological Survey (USGS) | October 31st, 2005

Mercury in Abiotic Matrices of Clear Lake, California: Human Health and Ecotoxicological Implications

Ecological Society of America (Wiley) | December 1st, 2008

Mercury (Hg) from Hg mining at Clear Lake, California, USA, has contaminated water and sediments for over 130 years and has the potential to affect human and environmen

Mercury (Hg) from Hg mining at Clear Lake, California, USA, has contaminated water and sediments for over 130 years and has the potential to affect human and environmental health. With total mercury (TotHg) concentrations up to 438 mg/kg (dry mass) in surficial sediments and up to 399 ng/L in lake water, Clear Lake is one of the most Hg-contaminated lakes worldwide. Particulate Hg in surface water near the mine ranges from 10 000 to 64 000 ng/g; TotHg declines exponentially with distance from the Sulphur Bank Mercury Mine. From 1992 to 1998, no significant long-term trends for TotHg or methylmercury (MeHg) in sediments or water were observed, but peaks of both TotHg and MeHg occurred following a 1995 flooding event. Sediments and water exhibit summer/fall maxima and winter/spring minima for MeHg, but not TotHg. Sediment TotHg has not declined significantly a decade after remediation in 1992. At the mine site, aqueous TotHg reached 374 000 ng/L in unfiltered groundwater. Pore water sulfate in sediments varies seasonally from 112 mg/L in summer/fall (when Hg methylation is highest) to 3300 mg/L in winter. While TotHg is exceptionally high in both sediments and water, MeHg is substantially lower than would be expected based on the bulk Hg loading to the lake and in comparison with other sites worldwide. Total mercury in Clear Lake water does not exceed the Safe Drinking Water Act criteria, but it sometimes greatly exceeds human health criteria established by the Great Lakes Initiative, U.S. Environmental Protection Agency water quality guidelines, and the California Toxics Rule criterion. Methylmercury concentrations exceed the Great Lakes Initiative criterion for MeHg in water at some sites only during summer/fall. Relative to ecological health, Clear Lake sediments greatly exceed the National Oceanic and Atmospheric Administration’s benthic fauna Sediment Quality Guidelines for toxic effects, as well as the more concensus-based Threshold Effects Concentration criteria. Based on these criteria, Hg-contaminated sediments and water from Clear Lake are predicted to have some lethal and sublethal effects on specific resident aquatic species. However, based on unique physical and chemical characteristics of the Clear Lake environment, MeHg toxicity may be significantly less than anticipated from the large inorganic Hg loading.

Mercury in Every Mix

CALFED | May 1st, 2005

Mercury levels in nearshore fish from the Central Coast area: Important information for fish consumers

California State Water Resources Control Board (SWRCB) | April 11th, 2017

Several species of marine fish commonly caught in nearshore Central Coast waters may contain high levels of mercury. Several rockfish species, especially Black-and-Yellow

Several species of marine fish commonly caught in nearshore Central Coast waters may contain high levels of mercury. Several rockfish species, especially Black-and-Yellow, China, Copper, and Gopher, and sharks and bat rays are species of concern. People who routinely consume fish from nearshore waters are advised to follow the recent statewide coastal advisory released in November 2016 by the California Office of Environmental Health Hazard Assessment (OEHHA) regarding consumption of these and other species. The advisory recommends “no consumption” of several fish species for women 18-45 years and for children 1-17 years, and limiting consumption of some species for all population groups. The advisory can be found online at http://oehha.ca.gov/advisories/statewide-advisory-eating-fish-california-coastal-locations-without-site-specific-advice. Site-specific advice was also developed for Elkhorn Slough, and can be viewed at http://oehha.ca.gov/advisories/elkhorn-slough.

Mercury losses and recovery during a suction dredge test in the South Fork of the American River

California State Water Resources Control Board (SWRCB) | July 29th, 2005

Mercury has been used widely since the dawn of recorded history for gold mining. During California’s gold rush, gold miners used about 6 million kilograms or 6.6 thousa

Mercury has been used widely since the dawn of recorded history for gold mining. During California’s gold rush, gold miners used about 6 million kilograms or 6.6 thousand tons of mercury (Churchill, 2000) to recover over 3.6 thousand tons of gold (Bulletin 193). The weight of mercury used is roughly equal to the total weight of a 9-mile long line of 2,750, full sized pickup trucks (note: the pick up truck line equaling gold recovered would only be 5 miles long). The miners lost about half of the mercury to the environment. Using historical records,Churchill (2000) estimated that total mercury losses ranged between 2.3 million and 2.6 million kilograms for placer and lode mining in the Sierra Nevada Geomorphic Province. Consequently, elemental mercury from the gold rush is still found, sometimes in amounts that constitute a local hotspot (i.e., a location where visible elemental mercury is found) in Sierra Nevada watersheds where gold mining occurred. In March 2003, a recreational gold miner reported a mercury hotspot in the South Fork of the American River near Coloma, to State Water Resources Control Board staff. It was the first time a recreational gold miner had revealed a hotspot locations to agency staff. Coloma is California’s historic “Gold Discovery” site as James W. Marshall’s discovery there in January 1848 initiated the 1849 gold rush. Steve Franklin, the recreational gold miner who reported the hotspot, claimed to have recovered about a kilogram of mercury while gold mining from the hotspot during January and February 2003. Finding a hotspot near Coloma raised questions about its potential threat to human health, effects on local fi sh, and threat to water quality. Moreover, its discovery presented an opportunity to test the notion that recreational gold miners effectively clean up mercury hotspots while suction dredging for gold. There is no record of any attempts by state or federal agencies to clean up a mercury hotspot in a California river. But State and federal agencies have discussed whether encouraging or even providing support for recreational gold miners to clean up hotspots is viable and wise. The pros are that there is a potentially large, volunteer workforce. The cons are that oversight would be difficult and, up to now, no data supported the notion that suction dredges could recover mercury efficiently. Recreational gold dredging on public and private lands is a moderately popular activity in California. The Department of Fish and Game (DFG) issues several thousand permits annually to recreational gold dredgers. Along with gold, recreational dredgers recover iron (nails bolts, etc.), lead (fishing weights, buckshot, and spent bullets) and mercury (elemental mercury, mercury/gold amalgam, and mercury stained gold). Over the past several years, United States Forest Service (USFS), Bureau of Land Management (BLM) and State agency staff have discussed setting up a mercury recovery program for recreational dredgers. Incentives (e.g., cash for mercury, free dredging permits, new areas opened for dredging) were proposed in exchange for mercury turned in by recreational dredgers. Offering such incentives was and remains controversial for a variety of reasons and a mercury recovery program was not started. Moreover, an important drawback was that the efficiency of a standard suction dredge at recovering mercury was unknown. Consequently, no one knew if mercury would be lost along with waste sediment from a suction dredge. Clearly, a mercury recovery program that dispersed elemental mercury back into a stream in substantial amounts would be unacceptable. The hotspot presented an opportunity to determine the mercury recovery efficiency of a suction dredge. Studying the hotspot may also reveal bedrock characteristics and sediment transport conditions that cause hotspots, and the effects that concentrated mercury has on local fish. This report documents the results of a suction dredge test that was completed in September 2003 by State Water Board, USFS, and DFG staff.

Mercury on a landscape scale—Balancing regional export with wildlife health

U.S. Geological Survey (USGS) | June 26th, 2018

The Cosumnes River watershed requires a 57–64 percent reduction in loads to meet the new Delta methylmercury (MeHg) total maximum daily load allocation, established by

The Cosumnes River watershed requires a 57–64 percent reduction in loads to meet the new Delta methylmercury (MeHg) total maximum daily load allocation, established by the Central Valley Regional Water Quality Control Board. Because there are no large point sources of MeHg in the watershed, the focus of MeHg load reductions will fall upon non-point sources, particularly the expansive wetlands considered to be a primary source of MeHg in the region. Few management practices have been implemented and tested in order to meet load reductions in managed wetlands, but recent efforts have shown promise. This project examines a treatment approach to reduce MeHg loads to the Sacramento-San Joaquin River Delta by creating open-water deep cells with a small footprint at the downstream end of wetlands to promote net demethylation of MeHg and to minimize MeHg and Hg loads exiting wetlands at the Cosumnes River Preserve. Specifically, the deep cells were were located immediately up gradient of the wetland’s outflow weir and were deep enough (75–91 centimeter depth) to be vegetation-free. The topographic and hydrologic structure of each treatment wetland was modified to include open-water deep cells so that the removal of aqueous MeHg might be enhanced through (1) particle settling, (2) photo-degradation, and (3) benthic microbial demethylation. These deep cells were, therefore, expected to clean MeHg from surface water prior to its discharge to the Cosumnes River and the downstream Delta.

Mercury Risks to Wildlife in California Lakes: Statewide Survey Finds Fish-Eating Birds at Risk in Many Lakes

U.S. Geological Survey (USGS) | May 22nd, 2015

Numerous water bodies in California are listed under the Clean Water Act as being impaired by mercury contamination. Mercury generally poses risks both to humans who co

Numerous water bodies in California are listed under the Clean Water Act as being impaired by mercury contamination. Mercury generally poses risks both to humans who consume fish from these water bodies and to wildlife species at the top of the aquatic food chain. The SWAMP has recently completed statewide surveys of contaminants in sport fish from California lakes, rivers, and coastal waters. These surveys generated information regarding potential human exposure to mercury, but did not include monitoring to assess risks to wildlife. This study was performed to address critical information gaps related to mercury risks to wildlife in California lakes. Western grebes and Clark’s grebes were chosen as the wildlife indicator species. These grebe species are widely distributed and breed in lakes throughout California, are piscivorous (fish-eaters) near the top of the lake food chain, and become flightless after they arrive at their summer locations. This makes them excellent indicators of lake-specific contaminant exposure. Mercury concentrations were measured in grebe blood at all of the lakes, and in grebe eggs where they could be collected. Mercury also was measured in the small fish species that grebes eat and in sport fish in order to determine whether correlations between fish and grebes could be used to estimate risk to grebes in cases where direct measurements of mercury in grebes are not available. Grebes, prey fish, and sport fish were sampled at 25 lakes throughout California (Figure 1) during the spring and summer of 2012 and 2013, seasons when breeding occurs and birds are vulnerable to mercury - induced impairment of reproduction. Mercury concentrations were measured in blood from 354 grebes at 25 lakes, 101 grebe eggs at 7 lakes, 505 prey fish from14 species at 25 lakes, and 230 sport fish from 5 species at 24 lakes. T he lakes included in the survey were selected to be a representative sampling spanning the entire state, a range of mercury contamination, and a variety of sizes, shapes, and elevations.