Description: As a component of the ecological assessment for the Carson River Mercury Site, EPA conducted a survey of benthic macroinvertebrates to evaluate the potential adverse effects of mercury in surface water and sediment of the Carson River. Measures of benthic community response to mercury contamination derived from the benthic survey are presented in this the EcoRisk Assessment, Appendix C. A characterization of the existing environment at the sampling locations-including the habitat characteristics, fish and wildlife populations, and surrounding land use.
Rapid BioAssessment Protocol II (RBP) involves the standardized collection, enumeration, and identification of major benthic taxa to the family level in riffle/run habitats. Standard data sheets are used to record results at each sampling. location. Collections are compared to a reference location, and an evaluation is made as to the impairment, or lack thereof, of the benthic community from stressors within the watershed.
The biological condition of the community can be ranked according to three categories of impact: nonimpaired, moderately impaired, or severely impaired, where the degree of impairment implies less than optimal community structure, the loss of intolerant species, and dominance by a few tolerant taxa compared to background. RBP II also involves assessment of habitat characteristics such as stream flow, bottom conditions, and riparian vegetation. In addition, standard water quality parameters such as dissolved oxygen, temperature, pH, conductivity, color, and turbidity are determined. The RBP II was conducted on August 17 and 18, 1994 during a period of drought. Full metadata: https://edg.epa.gov/metadata/catalog/search/resource/details.page?uuid=%7BB5B5E4C2-FD2C-4856-97E3-5B599185ED43%7D
Description: EPA has collected soil, sediment, surface water and biota data to complete the remedial investigation (RI) at the Operable Unit (OU) No. 2 of the Carson River Mercury Superfund Site (CRMS). The goal of the study is to select a remedy that eliminates, reduces, or controls risks from site-related compounds of concern to human health and the environment. Specifically, the RI involves the investigation and study of the heavy metals contamination and the associated tributaries into the Carson River watershed resulting from site-related contaminant migration and to evaluate past and current releases and their impact to human health and the environment.
The Site includes mercury-contaminated soils at former mill sites, mercury contamination in waterways adjacent to the mill sites, and mercury contamination in sediments and banks fish and wildlife over more than a 80 mile length of the River, beginning near Carson City, Nevada and extending downstream to the Lahontan Valley and ultimately at its terminus at the USFWS Stillwater National Wildlife Refuge. Contamination at the Site is a legacy of the Comstock mining era of the late 1860s, when mercury was imported to the area for processing of gold and silver ore. Ore mined from the Comstock Lode was transported to the mill sites, where it was crushed and mixed with mercury to amalgamate the precious metals (Washoe Process). The mills were primarily located in Virginia City, Silver City, Gold Hill, Dayton, Six Mile Canyon, Gold Canyon, and adjacent to the Carson River between New Empire and Dayton. During the mining era, an estimated 7,500 tons of mercury were discharged into the River drainage, primarily in the form of mercury-contaminated tailings. Full metadata: https://edg.epa.gov/metadata/catalog/search/resource/details.page?uuid=%7B94BB835E-28D3-403D-8DD3-7A30021E6D9A%7D
Description: For the Ecological Risk Assessment Report, EPA collected these samples, consisting of benthic invertebrates (crayfish), from three contaminated locations in the Carson River upstream from Lahontan Reservoir (Santiago Ruins, Dayton State Park, and Fort Churchill) and one background location (Ruhenstroth Dam). As a component of the ecological assessment for the Carson River Mercury Site, a survey of benthic macroinvertebrates was conducted to evaluate the potential adverse effects of mercury in surface water and sediment of the Carson River. Measures of benthic community response to mercury contamination derived from the benthic survey are presented in this the EcoRisk Assessment, Appendix C. A characterization of the existing environment at the sampling locations-including the habitat characteristics, fish and wildlife populations, and surrounding land use.
Rapid BioAssessment Protocol II (RBP) involves the standardized collection, enumeration, and identification of major benthic taxa to the family level in riffle/run habitats. Standard data sheets are used to record results at each sampling. location. Collections are compared to a reference location, and an evaluation is made as to the impairment, or lack thereof, of the benthic community from stressors within the watershed. The biological condition of the community can be ranked according to three categories of impact: nonimpaired, moderately impaired, or severely impaired, where the degree of impairment implies less than optimal community structure, the loss of intolerant species, and dominance by a few tolerant taxa compared to background. RBP II also involves assessment of habitat characteristics such as stream flow, bottom conditions, and riparian vegetation. In addition, standard water quality parameters such as dissolved oxygen, temperature, pH, conductivity, color, and turbidity are determined.
The RBP II was conducted on August 17 and 18, 1994 during a period of drought. The EPA is publishing this data in support of the Carson River Mercury NPL Site in Nevada. Data was compiled and evaluated for the OU1 Remedial Investigation Report (EPA, 1994) as well as the OU2 Remedial Investigation Report (EPA, 2017), describing the nature and extent of contamination from the Site, primarily the Ecological Risk Assessment Report. The RI report also contains the Human Health Risk Assessment. Literature and other source Hg data are summarized in the RI for surface waters, sediments, and biological tissues. Full metadata: https://edg.epa.gov/metadata/catalog/search/resource/details.page?uuid=%7B2AF6806E-189F-454A-A792-9EF6A2BF240E%7D
Description: The dynamic nature of the annual volume of water discharged down the Carson River over a 10-year period, which included a century flood and drought, was examined in order to gain a better understanding of mercury movement, biological availability, and exposure to waterbirds nesting at Lahontan Reservoir. Total annual water discharge directly influenced total mercury (THg) in unfiltered water above the reservoir and downstream of a mining area, whereas methyl mercury (MeHg) at the same site was negatively related to annual discharge. Annual water storage at Lahontan Reservoir in the spring and early summer, as expected, was directly related to annual Carson River discharge. In contrast to the findings from above the reservoir, annual MeHg concentrations in water sampled below the reservoir were positively correlated with the total discharge and the amount of water stored in the reservoir on 1 July; that is, the reservoir is an important location for mercury methylation, which agrees with earlier findings. However, unfiltered water MeHg concentrations were about 10-fold higher above than below the reservoir, which indicated that much MeHg that entered as well as that produced in the reservoir settled out in the reservoir.
Avian exposure to mercury at Lahontan Reservoir was evaluated in both eggs and blood of young snowy egrets (Egretta thula) and black-crowned night-herons (Nycticorax nycticorax). Annual MeHg concentrations in unfiltered water below the reservoir, during the time period (days 90–190) when birds were present, correlated significantly with mercury concentrations in night-heron blood, snowy egret blood, and night-heron eggs, but not snowy egret eggs. A possible reason for lack of an MeHg water correlation with snowy egret eggs is discussed and relates to potential exposure differences associated with the food habits of both species. THg concentrations in water collected below the reservoir were not related to egg or blood mercury concentrations for either species.
The initial phase of this study was a 2-year evaluation of the effects of Hg on fish-eating birds nesting at Lahontan Reservoir and Carson Lake and at reference areas in northeastern Nevada (Henny et al. 2002). In the first year (1997), reproduction of snowy egrets (Egretta thula) and black-crowned night-herons (Nycticorax nycticorax) was studied via the ‘‘sample egg’’ technique (Blus 1984) (i.e., evaluate reproductive success of each clutch in relationship to the total Hg [THg] concentrations in the sample egg collected from that clutch). Both species laid eggs with comparatively low THg concentrations (Henny et al. 2002). Most eggs had THg concentrations below 0.80 lg/g wet weight (ww), the putative threshold concentration at which reproductive problems might be expected (Heinz 1979; Newton and Haas 1988).
The EPA is publishing this data in support of the Carson River Mercury NPL Site in Nevada. Data was compiled and evaluated for the OU2 Remedial Investigation Report (EPA, 2017), which describes the nature and extent of contamination from the Site. The report contains the Human Health Risk Assessment and Ecological Risk Assessment. Literature and other source Hg data are summarized in the RI for surface waters, sediments, and biological tissues. Full metadata: https://edg.epa.gov/metadata/catalog/search/resource/details.page?uuid=%7B7D976A08-2ACD-4951-B9C0-C82801FB04CB%7D
Description: This is a summary of mercury (Hg) data from fish collected in the Lahontan Reservoir area of the Carson River Basin. NDOW collected the fish and the EPA Region 9 Laboratory analyzed the tissue for mercury (Hg) for EPA's Impaired Waters Program, water resources managers and researchers working in the Carson River Basin. These data and the data tables provide results of the Lahontan Reservoir area, used by recreationalists and fishermen, in order to measure concentrations of Hg to evaluate potential human health exposure pathways. The original sources of Hg contamination in the Carson River Basin are from historic gold and silver mining and associated milling of the Comstock Lode near Virginia City, Nevada. Runoff and erosion from an estimated 236 'stamp mills', driven by flumes, resulted in a cummulative release of an estimated 7,500 Tons of elemental mercury into the Carson River Basin.
The elemental mercury, imported from mines in California and used to almalgamate the ore at the stamp mills, contaminated sediments throughout the Basin from the source area situated approximately between Carson City and Dayton, to the terminal wetlands in the Carson Sink. This area is the primary source of Hg pollution in the Basin, considering the naturally occurring mercury concentrations are close to the crustal average. During runoff and flood events, the River laterally cuts through the contaminated sediments in the overbanks and transports Hg with suspended sediments, and with concentrations rising with higher flow. When Lahontan Reservoir was built in 1915, it became a settling basin for suspended Hg from the Carson River, and while it retains up to 90 percent of influent sediments, the reservoir continues to pass significant concentrations of suspended and dissolved inorganic Hg and methylmercury (Me-Hg) downstream to the Carson Sink.
The EPA is publishing this data in support of the Carson River Mercury NPL Site in Nevada. Data was compiled and evaluated for the OU2 Remedial Investigation Report (EPA, 2017), which describes the nature and extent of contamination from the Site. The report contains the Human Health Risk Assessment and Ecological Risk Assessment. Literature and other source Hg data are summarized in the RI for surface waters, sediments, and biological tissues. Full metadata: https://edg.epa.gov/metadata/catalog/search/resource/details.page?uuid=%7B870A9666-B212-41C2-AE5A-E8DA1E7355D2%7D
Description: As a component of the ecological assessment for the Carson River Mercury Site, EPA conducted a survey of lizard samples collected from historic mill sites in the Carson River upstream from Lahontan Reservoir to evaluate the potential uptake of mercury in terrestrial food chains.
The EPA is publishing this data in support of the Carson River Mercury NPL Site in Nevada. Data was compiled and evaluated for the OU1 Remedial Investigation Report (EPA, 1994) as well as the OU2 Remedial Investigation Report (EPA, 2017), describing the nature and extent of contamination from the Site, primarily the Ecological Risk Assessment Report. The RI report also contains the Human Health Risk Assessment. Literature and other source Hg data are summarized in the RI for surface waters, sediments, and biological tissues. Full metadata: https://edg.epa.gov/metadata/catalog/search/resource/details.page?uuid=%7B04D20D55-7224-4DF8-AE27-435F36A27C49%7D
Description: EPA collected data in 2008 to evaluate the transport of mercury-contaminated water and sediment in the Carson River System in western Nevada. This report summarizes the analytical and field results from a pilot investigation performed to assess mercury contamination. Understanding the sources and transformations of mercury aided in planning future RI activities and pilot studies to assess mercury fate and transport in the Carson River and the Lahontan Reservoir. Soil samples from erosional banks along a 4-mile segment of the Carson River upstream of the Lahontan Reservoir were collected and analyzed in this pilot investigation to characterize mercury variability in exposed banks prone to erosion. This report presents the following information: Results of soil sampling and analysis, evaluation of data quality and compliance with the field sampling plan (FSP), discussion of the data, conclusions and recommendations for further study. The EPA is publishing this data in support of the Carson River Mercury NPL Site in Nevada. Data was compiled and evaluated for the OU2 Remedial Investigation Report (EPA, 2017), which describes the nature and extent of contamination from the Site. The report contains the Human Health Risk Assessment and Ecological Risk Assessment. Literature and other source Hg data are summarized in the RI for surface waters, sediments, and biological tissues. Full metadata: https://edg.epa.gov/metadata/catalog/search/resource/details.page?uuid=%7B31292C43-47C0-4F65-81ED-9A03263DEFFA%7D
Description: In order to collect samples which represent the levels of mercury occurring on the flood plain above Lahontan Reservoir, EPA collected surface and subsurface samples along several transects. Samples were collected along 3 transects which extended across the flood plain, perpendicular to the direction of flow. All of the transects were located below Brunswick Canyon in Dayton and Churchill Valley where the flood plain is most expansive and where there were no mills. Along each transect, 10 surface soil samples were collected and analyzed for total mercury. At the Fort Churchill gage, samples were also collected from the different stratigraphic intervals apparent in the bank of the flood plain (i.e., "FP005").
The EPA is publishing this data in support of the Carson River Mercury NPL Site in Nevada. Data was compiled and evaluated for the OU2 Remedial Investigation Report (EPA, 2017), which describes the nature and extent of contamination from the Site. The report contains the Human Health Risk Assessment and Ecological Risk Assessment Reports. Literature and other source Hg data are summarized in the RI for surface waters, sediments, and biological tissues. Full metadata: https://edg.epa.gov/metadata/catalog/search/resource/details.page?uuid=%7BA8983C25-7425-41FC-AE43-0BBD4A3410C3%7D
Description: This feature class is converted from GPS coordinates obtained using a GPSmap 60CSx unit from Garmin in the field by AEI Consultants. The attribute information is filled with contaminant (Arsenic, Lead, Mercury) concentrations of soils derived from the Shallow Subsurface Investigation provided by AEI Consultants dated on January 11, 2013. For more information on soil sampling field procedures, refer to the following source documents: AEI Consultants, Peter J. McIntyre, C.E.M., October 16, 2012, Draft Phase II Subsurface Investigation Work Plan Carson River Estates, Dayton, Nevada, report to Jack Yates, NDEP, Unpublished, AEI Consultants, Bryan Campbell, Program Manager, October 31, 2012, Identification of Revisions to the Draft Phase II Subsurface Investigation Work Plan Carson River Estates, Dayton, Nevada date October 16, 2012, Electronic mail correspondence to Jeff Collins, NDEP, Unpublished, AEI Consultants, Peter J. McIntyre, C.E.M., January 11, 2013, Shallow Subsurface Investigation, Property Identification: Carson River Estates, Dayton, Nevada, report to Chris Carlson, Sr. Vice-President, City National Bank, Unpublished.
Note: Generally, five composite sample points are respectively collected at the front and backyard in one parcel. However errors occurred in two parcels: APN=2952402 and APN=2952202. In the parcel 2952402, there are nine sample points. The other sample point (Sample ID=524-02-05) is found at the parcel 2952202 and overlied with one sample points (Sample ID=522-02-04) of the parcel 2952202. According to checking the Shallow Subsurface Investigation provided by AEI Consultants dated on January 11, 2013, the originial GPS coordinates of both sample points (Sample ID=524-02-05 and Sample ID=522-02-04) are the same. Full metadata: https://edg.epa.gov/metadata/catalog/search/resource/details.page?uuid=%7B0489CD28-538B-4FF5-8FB4-1646B7CF51C5%7D
Description: This feature class contains parcel boundaries and their environmental covenant status within the Carson River Estates subdivision in Lyon County, Nevada. An environmental covenant is an instrument used to define the appropriate activities and/or uses on real property that has been subject to contamination. It is a recordable instrument that is attached to the deed and runs with the property. It is almost always used on a property that was subject to clean-up action by a regulatory authority, either the Nevada Division of Environmental Protection (NDEP) or the US Environmental Protection Agency (US EPA).
In 2005 environmental covenants were created with the passage of Senate Bill No. 263 by the Nevada Legislature. The covenants meet a need to protect both the responsible party and regulatory agencies. Responsible parties must invest significant resources for removing contamination and constructing and maintaining engineering controls to limit the potential exposure from remnant contamination. Regulatory agencies on the other hand, such as NDEP or the US EPA, are responsible for enforcing and overseeing clean-up actions to assure protections remain in-place and are effective through their design life.
The Carson River Estates subdivision is located within Operable Unit 1 of the Carson River Mercury Site (CRMS).
Parcel boundaries were extracted from the Lyon County parcels layer, and then attributed with information pertaining to the environmental covenant (if applicable). Metadata: https://edg.epa.gov/metadata/catalog/search/resource/details.page?uuid=%7B85B385D7-057E-47B9-BB91-EA6D6AE262FE%7D
Description: The primary purpose of the sediment collection was to obtain vertical profile information from several areas in which no data existed and/or to compare with existing data to demonstrate the mercury and metals deposition resulting from the Comstock-era release (i.e., beginning in the 1860s). The specific areas targeted in the field work were from the Lahontan Reservoir, Sheckler Lake, and downstream areas potentially impacted by the historic river flows prior to construction of Lahontan Reservoir. In 2015, the Carson River and Lahontan Reservoir were at historic low levels as a result of a four-year drought. This presented the agency access to collect sediment core samples from areas that were normally below the waterline. EPA’s principal study question was whether mercury is indeed sediment bound and that Lahontan Reservoir, since it construction in 1915, serves as a mercury sink. The secondary purpose of the sediment sampling effort was to collect a range of mercury concentrations for assessing field screening equipment using Thermal Decomposition, Amalgamation, and Atomic Absorption Spectrophotometry (See EPA SW7473) and comparing the results to laboratory analytical data. The EPA is publishing this data in support of the Carson River Mercury NPL Site in Nevada. Data was compiled and evaluated for the OU2 Remedial Investigation Report (EPA, 2017), which describes the nature and extent of contamination from the Site. The report contains the Human Health Risk Assessment and Ecological Risk Assessment. Literature and other source Hg data are summarized in the RI for surface waters, sediments, and biological tissues. Full metadata: https://edg.epa.gov/metadata/catalog/search/resource/details.page?uuid=%7BE7CEC799-2C79-4550-AAC6-E396635EC826%7D
Description: The current conceptual site model (CSM) includes data gaps related to the extent of mercury contamination throughout the site, as well as the presence of other metal contaminants in soil. This study focuses on three areas in OU01: the Six Mile Canyon Area in Dayton, NV, the California Pan Mill Area in Virginia City, NV, and the Sacramento Mill Area just north of Virginia City, NV. Surface and near surface soils with COC concentration greater than the project action limits present a potential risk for direct contact and soil migration. Data gaps exist in the understanding the sources, extent, and migration pathways of contaminants at this area and the applicability of the Incremental Sampling (IS) and (X-ray Fluorescence (XRF) approach to comply with the LTSRP. The project will address these data gaps through incremental sampling and real time XRF.
Data was compiled and evaluated for the IS Study where field sample collection techniques were evaluated as part of this study using XRF. Sample processing included seiving, to compare ISM with the current LTSRP method based on four five-point composite samples per residential parcel. The goal to is to validate the CSM and improve the screening of vast areas of mercury-contaminated soils while continuing to evaluate the performance of X-ray fluorescence (XRF) instrumentation for the simultaneous analysis of mercury (Hg), lead (Pb) and arsenic (As) in soil affected by the mining operations associated with the Comstock Lode. however sample processing will be. The most effective processing and analytical techniques will be selected for use in a follow-up study which will evaluate field sample collection. It is anticipated that the most effective and efficient sampling and analysis techniques will be incorporated into future investigations for the Carson River area.
General Comments: The location coordinates represent the center point of the Decision Unit (DU) as calculated by GIS. For DUs that cross roads or driveways (SMCD2 and SMCSCR-South) the midpoint may plot in the middle of the road. The center point for SMCCBS was selected manually due to the unusual shape of the DU. The calculated GIS center point falls outside of the DU. DU columns provided on each tab for easy sorting and QC check. It is not a critical data point since the DU name is embedded in the Sample ID. For Source Units (SU) samples, the DU column is N/A if the SU was located outside of a DU, this column is filled out if the SU was located inside of a DU. Date represents sample collection date.
Tab-Specific Comments: XRF field results did not use unique Lab ID sample #s so left that column blank. Did not establish specific XRF reporting limits for this project. Manually added a “U” for the XRF ND samples to match the lab formats. Region 9 lab results for the XRF comparison samples: Left all the ICP metals in the database. R9 lab DMA data only reported Pb, As, Se, and Hg per the team decision. SPLP Extraction #2 results for the samples selected for leaching analysis - removed the rows that identify the extraction procedure and contained no lab data. SPLP Extraction #3 results for the samples selected for leaching analysis - removed the rows that identify the extraction procedure and contained no lab data. Notes column indicates this is DI water extraction. Full metadata: https://edg.epa.gov/metadata/catalog/search/resource/details.page?uuid=%7B0F3FA73D-380A-4A8C-A670-7BF0F754A357%7D
Description: This dataset contains final results for XRF and select laboratory results for the 2019 Carson River Mercury Site Incremental Sampling Field Study. Incremental samples were collected from three separate areas within the CRMS: Six Mile Canyon Area near Mark Twain, NV; California Pan Mill in Virginia City, NV; and Sacramento Mill in Virginia City, NV. The purpose of the data collection was to help characterize the extent of Hg, Pb, and As in surface (0 to 6-inch) and in some locations subsurface (0 to 24-inch) soils in the three study areas. A secondary purpose of the study was to demonstrate incremental sampling techniques and field XRF analysis to EPA Region 9 and NDEP Staff. The XRF results columns in the attribute table were generated by XRF data collected in accordance with the EPA-Approved Quality Assurance Project Plan and are considered definitive results suitable for project decisions. 30-point incremental samples were sieved to the 100-mesh fraction, placed “interference free” XRF read bags, and analyzed with EPA Headquarters’ Niton XRF. At least two XRF measurements were collected on each side of the bag resulting in at least four readings that were used to calculate the sample bag average that appears in the XRF Results columns for Hg, Pb, and As. If triplicate results were collected for a given sample, the mean is reported in the XRF Results columns for Hg, Pb, and As and the results for each of the three replicates are detailed in the XRF Notes column. Full metadata: https://edg.epa.gov/metadata/catalog/search/resource/details.page?uuid=%7B1DB3DE0C-6216-44DB-8696-ACC20CD332A1%7D
Description: USGS conducted preliminary assays on aged (3 mo.) surface sediment (0-4 cm) collected from 13 sites during October 1998 in order to decipher general spatial trends in Hg-speciation, microbiology and relevant biogeochemistry. During the second field campaign sample processing and incubations were conducted at ambient temperature within hours of sediment collection to provide a more accurate measure of in-situ process rates and analyte concentrations. The third field sampling (October 1999), involving 14 sampling and was conducted with a similar approach as in June 1999. The latter two data sets provide a direct seasonal comparison (summer/fall, high/lo flow conditions) of Hg transformation dynamics in the CRS. Sediment depth profiles (0-16 cm) were investigated at four sites during June 1999 and at two of these four during October 1999. Eroding vertical bank material was sampled in the Hg-contaminated Fort Churchill region during both 1999 dates. Laboratory experiments were conducted using sediment collected during the latter two sampling dates.
The study purpose sought to: a) identify important zones of net methylmercury (MeHg) production and consumption within the CRS, b) determine which environmental factors most strongly influence these processes and c) provide estimates of seasonal variability. Measurements were made of microbial Hg-transformations (via radiotracer) and in-situ Hg speciation (total mercury (Hgt), MeHg, and particle-associated acid-extractable Hg(II)). Acid extractable Hg(II) was used as a surrogate measure for the Hg(II) most readily available to bacteria for methylation. A novel Hg-biosensor technique was also used to assess bioavailable Hg(II) in pore-water. A suite of ancillary microbial processes and sediment geochemical parameters were also measured to more fully characterize each site, and to relate these measurements to observed Hg-transformation rates and Hg-speciation.
The EPA is publishing this data in support of the Carson River Mercury NPL Site in Nevada. Data was compiled and evaluated for the OU2 Remedial Investigation Report (EPA, 2017), which describes the nature and extent of contamination from the Site. The report contains the Human Health Risk Assessment and Ecological Risk Assessment. Literature and other source Hg data are summarized in the RI for surface waters, sediments, and biological tissues. Full metadata: https://edg.epa.gov/metadata/catalog/search/resource/details.page?uuid=%7BA1F26D88-9A23-4B83-B238-9F6DA1F2120D%7D
Description: The Region 9 CRMS risk assessor specifically identified the need to obtain data for Tribal lands near Fallon, Nevada. Based on a 1994 study performed on OU1 samples, an estimated 12% of total mercury measurements is mercuric chloride (HgCl2). The Quality Assurance Project Plan (QAPP) summarized the OU1 historical analytical approaches for “speciation” with currently available methods summarized. Based on team scoping meeting with EPA Region 10 and the Region 9 Toxicologist, use of the Brooks Applied Lab (BRL) sequential extraction was selected primarily for reasons of comparability of approaches to simplify data assessment. (EPA Method 3200 was presented for comparative purposes.)
There are significant sources of uncertainty in “speciation” using any approach, as each is technically a procedurally defined fractionation that may include other mercury species not specifically identified. As an example of this uncertainty, under the OU1 study of the EPA Las Vegas Lab data, it was unclear which fraction would have captured mercury oxide or whether the residual chlorides caused minor amounts of sulfide to combine with the nitric acid fraction. While the Oak Ridge approach may have reported mercuric chloride in the elemental mercury fraction.
The primary factors driving the need for this speciation data were uncertainty about the quality of the historical OU1 data; applicability of the OU1 data at the locations below Lahontan Reservoir, and concerns expressed by the Region 9 CRMS risk assessor to better obtain direct measurement data near the Fallon Paiute-Shoshone Tribe. The data generated by this sampling were reviewed for laboratory quality control but decisions with the data were made by the EPA Region 9 CRMS risk assessor. Full metadata: https://edg.epa.gov/metadata/catalog/search/resource/details.page?uuid=%7B38160BA0-AA23-4653-9210-04F6FFDDFA75%7D
Description: This feature class contains soil sample points collected from the Onda Verde subdivision in Churchill County, Nevada. The Onda Verde subdivision is located within Operable Unit 2 of the Carson River Mercury Site (CRMS). Subdivisions located within the CRMS are required to undergo sampling per the Long Term Sampling and Response Plan. Full metadata: https://edg.epa.gov/metadata/catalog/search/resource/details.page?uuid=%7B83DB0DD0-1F38-41BF-B64D-44FEABFAD380%7D
Description: This feature class contains parcel boundaries and their environmental covenant status within the Onda Verde Subdivision in Churchill County, Nevada. An environmental covenant is an instrument used to define the appropriate activities and/or uses on real property that has been subject to contamination. It is a recordable instrument that is attached to the deed and runs with the property. It is almost always used on a property that was subject to clean-up action by a regulatory authority, either the Nevada Division of Environmental Protection (NDEP) or the US Environmental Protection Agency (US EPA).
In 2005 environmental covenants were created with the passage of Senate Bill No. 263 by the Nevada Legislature. The covenants meet a need to protect both the responsible party and regulatory agencies. Responsible parties must invest significant resources for removing contamination and constructing and maintaining engineering controls to limit the potential exposure from remnant contamination. Regulatory agencies on the other hand, such as NDEP or the US EPA, are responsible for enforcing and overseeing clean-up actions to assure protections remain in-place and are effective through their design life.
The Onda Verde subdivision is located within Operable Unit 2 of the Carson River Mercury Site (CRMS). Full metadata: https://edg.epa.gov/metadata/catalog/search/resource/details.page?uuid=%7B83771FE5-BB0F-4ECC-8783-DB27D70ECD75%7D
Description: EPA evaluated the total mercury representative of vegetables and/or fruit and colocated soil from several gardens located in Dayton and Silver City (OU1) for the purpose of the Human Health Risk Assessment investigation. EPA published this data in support of the Carson River Mercury NPL Site in Nevada.
Data was compiled and evaluated for the OU1 Remedial Investigation Report (EPA, 1994), which describes the nature and extent of contamination from the Site. The reports contain the Human Health Risk Assessment and Ecological Risk Assessment Reports. Literature and other source Hg data are summarized in the RI report for upland source areas. Full metadata: https://edg.epa.gov/metadata/catalog/search/resource/details.page?uuid=%7B737F2327-F990-467E-9B87-B8B5C14B5CA5%7D
Description: This feature class contains soil mercury sample points collected from the Riverpark subdivision in Lyon County, Nevada, along with the associated analytical data. The Riverpark subdivision is located within Operable Unit 1 of the Carson River Mercury Site (CRMS). Subdivisions located within the CRMS are required to undergo sampling per the Long Term Sampling and Response Plan (LTSRP). Full metadata: https://edg.epa.gov/metadata/catalog/search/resource/details.page?uuid=%7B78867837-59D0-4745-BDEB-AC17598F0A59%7D
Copyright Text: NDEP, Resource Concepts, Inc., Lennar Homes
Description: This feature class contains parcel boundaries and their environmental covenant status within the Riverpark Subdivision in Lyon County, Nevada. An environmental covenant is an instrument used to define the appropriate activities and/or uses on real property that has been subject to contamination. It is a recordable instrument that is attached to the deed and runs with the property. It is almost always used on a property that was subject to clean-up action by a regulatory authority, either the Nevada Division of Environmental Protection (NDEP) or the US Environmental Protection Agency (US EPA).
In 2005 environmental covenants were created with the passage of Senate Bill No. 263 by the Nevada Legislature. The covenants meet a need to protect both the responsible party and regulatory agencies. Responsible parties must invest significant resources for removing contamination and constructing and maintaining engineering controls to limit the potential exposure from remnant contamination. Regulatory agencies on the other hand, such as NDEP or the US EPA, are responsible for enforcing and overseeing clean-up actions to assure protections remain in-place and are effective through their design life.
The Riverpark subdivision is located within Operable Unit 1 of the Carson River Mercury Site (CRMS). Full metadata: https://edg.epa.gov/metadata/catalog/search/resource/details.page?uuid=%7B1273B0CF-30FF-436A-8B2A-46E82B114AAE%7D
Description: This feature class depicts the locations and analytical data for the confirmation samples collected from existing grade to maximum depth 2 feet on each residential lot of Santa Maria Ranch Phase I subdivision. Sampling was conducted under NDEP oversight in accordance with the draft Long-Term Sampling and Response Plan (LTSRP).
Santa Maria Ranch is located within Operable Unit 1 of the Carson River Mercury Site. Full metadata: https://edg.epa.gov/metadata/catalog/search/resource/details.page?uuid=%7B3BBBF285-DA7D-4D01-BCF0-59B6D95D6DA7%7D
Description: This feature class depicts the approximate locations and analytical data of samples collected in a preliminary Phase II Environmental Site Assessment prior to construction and earthwork activities in development of Santa Maria Ranch Phase I residential subdivision (pregrade).
The Santa Maria Ranch subdivision is located within Operable Unit 1 of the Carson River Mercury Site. Full metadata: https://edg.epa.gov/metadata/catalog/search/resource/details.page?uuid=%7BD8944F6B-660C-4D29-AFB2-F95DD9324D42%7D
Name: Santa Maria Ranch Phase I Initial Borrow Samples
Display Field: SampleID
Type: Feature Layer
Geometry Type: esriGeometryPoint
Description: This feature class depicts the locations and associated analytical data of initial borrow samples collected in 2004 for Santa Maria Ranch Phase I residential subdivision.
The Santa Maria Ranch subdivision is located within Operable Unit 1 of the Carson River Mercury Site. Full metadata: https://edg.epa.gov/metadata/catalog/search/resource/details.page?uuid=%7BCAB255B6-CF6C-480B-BF9B-37F45399D928%7D
Description: This feature class depicts the locations and analytical data for the soil samples collected as part of a preliminary investigation of Santa Maria Ranch subdivison Phase II. The sampling program was performed by Converse Consultants for Dayton Land Developers L.L.C. in 2009. It is unclear if this portion of the subdivision is identified as Phase II, but geographically occupies that area of Santa Maria Ranch west of Daney Creek drainage.
Santa Maria Ranch is located within Operable Unit 1 of the Carson River Mercury Site. Full metadata: https://edg.epa.gov/metadata/catalog/search/resource/details.page?uuid=%7B14A7F65C-988C-4A86-9A68-2F679DB11577%7D
Description: This feature class depicts the locations and analytical data for the soil samples taken by Converse Consultants in 2006 in Santa Maria Ranch Phase III subdivision.
Santa Maria Ranch is located within Operable Unit 1 of the Carson River Mercury Site. Full metadata: https://edg.epa.gov/metadata/catalog/search/resource/details.page?uuid=%7BCD87591E-D11C-4C39-9B69-CEDCF0E4744C%7D
Description: This feature class depicts parcels within Phase I Santa Maria Ranch subdivision. The parcels were surveyed as part of the subdivision's development. The feature class includes the article of the Covenants Conditions & Restrictions (CC&Rs) addressing the potential soil contamination that might be found on the property and the limitations of the findings and conditions related to future soil excavation on the parcel. Santa Maria Ranch is located within Operable Unit 1 of the Carson River Mercury Site. Full metadata: https://edg.epa.gov/metadata/catalog/search/resource/details.page?uuid=%7BC814B416-47D0-4251-8A09-65063E72628A%7D
Description: This feature class depicts parcels within Phase II Santa Maria Ranch subdivision. The parcels were surveyed as part of the subdivision's development. The feature class includes the article of the Covenants Conditions & Restrictions (CC&Rs) addressing the potential soil contamination that might be found on the property and the limitations of the findings and conditions related to future soil excavation on the parcel. Santa Maria Ranch is located within Operable Unit 1 of the Carson River Mercury Site. Full metadata: https://edg.epa.gov/metadata/catalog/search/resource/details.page?uuid=%7B019E26CC-4AAB-40ED-943E-80A568CC02C8%7D
Description: This feature class depicts parcels within the Santa Maria Ranch subdivision that were surveyed during Phase III, including the article in the Santa Maria Ranch subdivision Covenants Conditions & Restrictions (CC&Rs) relevant to the potential for mercury contamination in the soil. Santa Maria Ranch is located within Operable Unit 1 of the Carson River Mercury Site. Full metadata: https://edg.epa.gov/metadata/catalog/search/resource/details.page?uuid=%7B7C88417E-43CA-45CD-AFB6-2C9408512269%7D
Description: The goal of the National Water Quality Assessment Program (NAWQA) is to determine within specific drainage basins both the character of water quality and the factors that effect that quality. Plans call for the program to be applied throughout the U.S. Initially, however, several pilot studies were established in diverse drainage basins to develop techniques for use in both groundwater and surface water studies. The Carson River Basin, Churchill and Lyon Counties, Nevada, is a pilot study area for groundwater. The Carson River originates on the east flank of the Sierra Nevada mountains and drains eastward to terminate in the Carson Sink. This report presents data from that study.
One of the objectives of the study is to investigate the relationship between water quality and the composition of the solid mineral material in contact with the water. A regional assessment of the geochemistry of surficial materials was obtained by soil samples. Subsurface assessment was obtained from drill core of shallow (at least to the depth of the water table) wells drilled specifically for this study.
Both groundwater and solid materials were sampled, but this report contains the analytical data only for the solid mineral materials that were collected. All analyses were performed in laboratories of the U.S. Geological Survey, Geologic Division, Denver, CO. Full metadata: https://edg.epa.gov/metadata/catalog/search/resource/details.page?uuid=%7BEC4FF2EE-50AC-4BBA-A7F1-EAD13475285A%7D
Description: This feature class is converted from GPS coordinates obtained using a GPSmap 60CSx unit from Garmin in the field by AEI Consultants. The attribute information is filled with contaminant (Arsenic, Lead, Mercury) concentrations of soils derived from the Shallow Subsurface Investigation provided by AEI Consultants dated on January 11, 2013.
Source documents; AEI Consultants, Peter J. McIntyre, C.E.M., October 16, 2012, Draft Phase II Subsurface Investigation Work Plan Carson River Estates, Dayton, Nevada, report to Jack Yates, NDEP, Unpublished, AEI Consultants, Bryan Campbell, Program Manager, October 31, 2012, Identification of Revisions to the Draft Phase II Subsurface Investigation Work Plan Carson River Estates, Dayton, Nevada date October 16, 2012, Electronic mail correspondence to Jeff Collins, NDEP, Unpublished, AEI Consultants, Peter J. McIntyre, C.E.M., January 11, 2013, Shallow Subsurface Investigation, Property Identification: Carson River Estates, Dayton, Nevada, report to Chris Carlson, Sr. Vice-President, City National Bank, Unpublished. Full metadata: https://edg.epa.gov/metadata/catalog/search/resource/details.page?uuid=%7B93512B9C-A76B-4751-8B41-D992B4325F07%7D
Description: This is a summary of mercury (Hg) data from the Lahontan Reservoir area of the Carson River Basin. USBR provided an information overview and reference source on mercury (Hg) in soils for water resources managers and researchers working in the Carson River Basin. These data and the data tables provide results of the Lahontan Reservoir area, focused on the camp sites and the beaches, in order to measure concentrations of Hg to evaluate potential human health exposure pathways. The original sources of Hg contamination in the Carson River Basin are from historic gold and silver mining and associated milling of the Comstock Lode near Virginia City, Nevada.
Runoff and erosion from an estimated 236 'stamp mills', driven by flumes, resulted in a cummulative release of an estimated 7,500 Tons of elemental mercury into the Carson River Basin. The elemental mercury, imported from mines in California and used to almalgamate the ore at the stamp mills, contaminated sediments throughout the Basin from the source area situated approximately between Carson City and Dayton, to the terminal wetlands in the Carson Sink. This area is the primary source of Hg pollution in the Basin, considering the naturally occurring mercury concentrations are close to the crustal average. During runoff and flood events, the River laterally cuts through the contaminated sediments in the overbanks and transports Hg with suspended sediments, and with concentrations rising with higher flow.
When Lahontan Reservoir was built in 1915, it became a settling basin for suspended Hg from the Carson River, and while it retains up to 90 percent of influent sediments, the reservoir continues to pass significant concentrations of suspended and dissolved inorganic Hg and methylmercury (Me-Hg) downstream to the Carson Sink. The EPA is publishing this data in support of the Carson River Mercury NPL Site in Nevada. Data was compiled and evaluated for the OU2 Remedial Investigation Report (EPA, 2017), which describes the nature and extent of contamination from the Site. Literature and other source Hg data are summarized in the RI, for surface waters, sediments, and biological tissues. The report contains the Human Health Risk Assessment and Ecological Risk Assessment. Full metadata: https://edg.epa.gov/metadata/catalog/search/resource/details.page?uuid=%7B16CCDC85-D925-4883-B651-DE1652F48168%7D
Description: EPA evaluated the total mercury representative of several subsurface locations in OU1 for the purpose of the Human Health Risk Assessment investigation. EPA published this data in support of the Carson River Mercury NPL Site in Nevada. Data was compiled and evaluated for the OU1 Remedial Investigation Report (EPA, 1994), which describes the nature and extent of contamination from the Site. The reports contain the Human Health Risk Assessment and Ecological Risk Assessment Reports. Literature and other source Hg data are summarized in the RI report for upland source areas. Full metadata: https://edg.epa.gov/metadata/catalog/search/resource/details.page?uuid=%7BDAA9BAE6-987D-40EF-87A0-EC41D7477953%7D
Description: In order to collect samples which represent the levels of mercury occurring at and near the mills and tailings piles (source areas), EPA collected surface and subsurface grab samples and transects. The EPA published this data in support of the Carson River Mercury NPL Site in Nevada. Data was compiled and evaluated for the Operable Unit 1 Remedial Investigation Report (EPA, 1994), which describes the nature and extent of contamination from the Site. The reports contain the Human Health Risk Assessment and Ecological Risk Assessment Reports. Literature and other source mercury data are summarized in the Remedial Investigation Report for upland source areas.
Description: EPA evaluated the mercury fractions (species) representative of several locations in OU1 for the purpose of the Human Health Risk Assessment investigation. In particular, the mercuric chloride fraction was of interest to toxicologists, because this is most bioavailable form of the compound in the terrestrial food pathway. EPA published this data in support of the Carson River Mercury NPL Site in Nevada. Data was compiled and evaluated for the OU1 Remedial Investigation Report (EPA, 1994), which describes the nature and extent of contamination from the Site. The reports contain the Human Health Risk Assessment and Ecological Risk Assessment Reports. Literature and other source Hg data are summarized in the RI report for upland source areas. Full metadata: https://edg.epa.gov/metadata/catalog/search/resource/details.page?uuid=%7BD6BD3AA5-BE5D-4109-8C06-77EB29E005A4%7D
Description: EPA evaluated the mercury fractions (species) representative of several locations in OU1 for the purpose of the Human Health Risk Assessment investigation. In particular, the mercuric chloride fraction was of interest to EPA toxicologists, because this is most bioavailable form of the compound in the terrestrial food pathway. EPA published this data in support of the Carson River Mercury NPL Site in Nevada. Data was compiled and evaluated for the OU1 Remedial Investigation Report (EPA, 1994), which describes the nature and extent of contamination from the Site. The reports contain the Human Health Risk Assessment and Ecological Risk Assessment Reports. Literature and other source Hg data are summarized in the RI report for upland source areas. Full metadata: https://edg.epa.gov/metadata/catalog/search/resource/details.page?uuid=%7BBFAB3ED7-CB7C-49B9-89A5-DED19CFA0816%7D
Description: Spatial variations in trace metal concentration are controlled by a complex set of parameters including reservoir sedimentation rates, dilution with pre-mining sediments, bed material mixing by shrink-swell processes, and factors that influence the sorption potential of the bed materials. Six years of below normal precipitation left much of the reservoir dry during the summer, 1992, and allowed for the precise delineation and mapping of the stratigraphic units that underlie Lahontan Reservoir.
The units were defined on the basis of spatial and topographic position, grain-size, composition, and the presence or absence of weathering zones. Once delineated, the units were mapped on 1: 12,000 scale aerial photographs. Subsequently, the photographic data were transferred to a stable base map for interpretation and analysis. Twelve stratigraphic units have been defined, nine of which post-date dam construction in 1915. One post-dam unit was deposited by eolian processes, while the remaining eight represent sedimentation in three lacustrine depositional environments: coastal, deep-water, and deltaic. Full metadata: https://edg.epa.gov/metadata/catalog/search/resource/details.page?uuid=%7BEA2F598A-B567-4B76-989C-5EE38D629095%7D
Description: This dataset contains final results for the XRF Demonstration of Method Applicability (DMA) conducted by the United States Environmental Protection Agency’s (EPA’s) Technology Integration and Information Branch (TIIB), Office of Superfund Remediation and Technology Innovation. Assistance on the DMA was provided to TIIB by ICF International, Inc. (ICF), and the Nevada Department of Environmental Protection. Field activities for the DMA were conducted in May 2017. The DMA was conducted in accordance with the EPA-approved Uniform Federal Policy-Quality Assurance Project Plan for Demonstration of Method Applicability, XRF Analysis of Mercury in Soil, Carson River Mercury Superfund Site, Revision 0 (UFP-QAPP), dated April 10, 2017. Full metadata: https://edg.epa.gov/metadata/catalog/search/resource/details.page?uuid=%7BA8C46F22-8CF8-41A1-AAC6-7462DC6B4550%7D
Description: Data collected from Lahontan Reservoir in 2006 demonstrated that unusually large concentrations of methylmercury were produced in the anoxic hypolimnion after the reservoir had stratified, leading to the development of the sampling and analysis plan to assess the frequency, spatial extent, and factors that may or may not control mercury methylation in Lahontan Reservoir. Limnology profiles of field parameters (temperature, dissolved oxygen, specific conductance, pH, oxidation-reduction potential, and turbidity) and water samples were collected at the deepest locations in each of the three reservoir basins. In addition, field parameters were measured and water samples collected from the Carson River inflow delta and from the two overflow basins.
Concentrations of hydrogen sulfide and the presence and relative abundance of sulfate-reducing bacteria were determined onsite, and water samples were collected for laboratory determination of 1) unfiltered and filtered concentrations of mercury, methylmercury, and organic carbon, 2) unfiltered concentrations of suspended solids, and 3) filtered concentrations of chloride, sulfate, nitrate, nitrite, orthophosphate, phosphorus, arsenite, arsenate, molybdenum, selenium, tungsten, and ultraviolet absorbing organic compounds. (1) Inflow Delta This location is near Silver Springs, NV, about .5 miles upstream of Lahontan Reservoir, and identified by the USGS as sampling location 392024119074801, LAHONTAN RES SAMPLE POINT NR CARSON R MOUTH; (2) Overflow Sub-Basin A This location is near Silver Springs, NV the on the Carson River, approximately 2.5 miles southeast of the Upper Basin reach of Lahontan Reservoir. This location is identified by the USGS as sampling location 392013119054001, LAHONTAN RES SAMPLE POINT NR OVERFLOW BASIN A; (3) Overflow Sub-Basin B This location is near Silver Springs, NV, about 1.5 miles west of the Middle Basin reach, Lahontan Reservoir, and identified by the USGS as sampling location 392316119114901, LAHONTAN RES SAMPLING PT NR OVERFLOW BASIN B; (4) Upper Basin This location is near Silver Springs, NV, approximately 0.65 northeast of the boat ramp and adjacent to the beach area, Lahontan Reservoir, and identified by the USGS as sampling location 392301119110801, LAHONTAN RES SAMPLE POINT NR UPPER BASIN; (5) Middle Basin This location is near Silver Springs, NV, about 0.6 miles southeast of Virginia Beach Rd, Lahontan Reservoir, and identified by the USGS as sampling location 392440119093101, LAHONTAN RES SAMPLE POINT NR MIDDLE BASIN; (6) Lower Basin This location is near Diatom, NV, about 0.1 miles west of the Karen Rd Beach Parking Area, Lahontan Reservoir, and identified by the USGS as sampling location 392730119040801, LAHONTAN RES SAMPLE POINT NR GATEHOUSE; The study also included field measurements of depth, water temperature, specific conductance, dissolved oxygen (DO), pH, turbidity, ORP, general water quality parameters, sulfate reducing bacteria, and the collection and analysis of samples from Lahontan Reservoir. Sampling and Analysis Plan final is dated 30 September 2010, approved by Mark Kutnink, Region 9 QAMO. An email from Carl Thodal, USGS Hydrogeologist, summarizing the findings is entitled "Thodal_Lahontan_limno_email_TL_27Mar15.msg".
The EPA is publishing this data in support of the Carson River Mercury NPL Site in Nevada. Data was compiled and evaluated for the OU2 Remedial Investigation Report (EPA, 2017), which describes the nature and extent of contamination from the Site. The report contains the Human Health Risk Assessment and Ecological Risk Assessment. Literature and other source Hg data are summarized in the RI for surface waters, sediments, and biological tissues. Full metadata: https://edg.epa.gov/metadata/catalog/search/resource/details.page?uuid=%7B3FF4B33E-8C04-4A79-96B9-85E359B9144E%7D
Description: The Carson River is a vital water resource for local municipalities and migratory birds travelling the Pacific Flyway. Historic mining practices that used mercury (Hg) to extract gold from Comstock Lode ore has left much of the river system heavily contaminated with Hg, a practice that continues in many parts of the world today.
Between 1997 and 2013, the United States Geological Survey (USGS) collected and analyzed Carson River water for Hg and methylmercury (MeHg) concentrations resulting in a sixteen-year record of unfiltered total mercury (uf.THg), filtered (dissolved) Hg (f.THg), total methylmercury(uf.MeHg), filtered MeHg (f.MeHg), and particulate-bound THg (p.THg) and MeHg (p.MeHg) concentrations. This represents one of the longest continuous records of Hg speciation data for any riverine system, thereby providing a unique opportunity to evaluate long-term trends in concentrations and annual loads. During the period of analysis, uf.THg concentration and load trended downward at rates of 0.85% and 1.8% per year, respectively. Conversely, the f.THg concentration increased at a rate of 1.7% per year between 1998 and 2005, and 4.9% per year between 2005 and 2013. Trends inflow-normalized partition coefficients for both Hg and MeHg suggest a statistically significant shift from the particulate to thefiltered phase. The upwardly accelerating f.THg concentration and observed shift from the solid phase tothe aqueous phase among the pools of Hg and MeHg within the river water column signals an increased risk of deteriorating ecological conditions in the lower basin with respect to Hg contamination.
More broadly, the 16-year trend analysis, completed 140 years after the commencement of major Hg releases to the Carson River, provides a poignant example of the ongoing legacy left behind by gold and silver mining techniques that relied on Hg amalgamation, and a cautionary tale for regions still pursuing the practice in other countries. EPA funded work from 1997 through 2013.
Samples were collected at the Weeks Bridge location from April 1997 through February 1999, and at seven other Carson River locations from April 1998 through February 1999, and at Weeks Bridge and below Lahontan Reservoir from 2000 through 2013. Assist EPA in studying the transport of mercury-contaminated water and sediment in the Carson River system in western Nevada. The study included periodic measurements of streamflow, and the collection and analysis of water samples for total mercury, methylmercury, and suspended sediment at two Carson River locations. The study also included field measurements and the collection and analysis of samples from the north basin of Lahontan Reservoir.
EPA used the data to determine loadings of the dissolved and particulate fractions of total mercury and methylmercury into and from Lahontan Reservoir, to better understand sources and transformations of mercury in the Carson River system, evaluate the effects of reservoir stratification on methylmercury production, and ultimately to help determine whether remedial action is warranted to reduce the levels of mercury contamination in and near the Carson River. A journal article from Eric Morway, Carl Thodal and Mark Marvin-DiPascuale, USGS, summarizing the findings is entitled "Morway_Thodal_MMD_HgMeHg_2017.pdf". This study, a component of the Remedial Investigation for the Carson River Superfund Site, included collection and analysis of water samples for total mercury and methylmercury from Weeks Bridge above Lahontan Reservoir, located on the Carson River. The USGS Water Science Center has collected and analyzed water samples in the Carson River system through an Interagency Agreement with EPA. The EPA is publishing this data in support of the Carson River Mercury NPL Site in Nevada.
Data was compiled and evaluated for the OU2 Remedial Investigation Report (EPA, 2017), which describes the nature and extent of contamination from the Site. The report contains the Human Health Risk Assessment and Ecological Risk Assessment. Literature and other source Hg data are summarized in the RI for surface waters, sediments, and biological tissues. Full metadata: https://edg.epa.gov/metadata/catalog/search/resource/details.page?uuid=%7BCB42F6CA-6762-492B-9A43-961F1BD64122%7D
Description: The Carson River is a vital water resource for local municipalities and migratory birds travelling the Pacific Flyway. Historic mining practices that used mercury (Hg) to extract gold from Comstock Lode ore has left much of the river system heavily contaminated with Hg, a practice that continues in many parts of the world today.
Between 1997 and 2013, the United States Geological Survey (USGS) collected and analyzed Carson River water for Hg and methylmercury (MeHg) concentrations resulting in a sixteen-year record of unfiltered total mercury (uf.THg), filtered (dissolved) Hg (f.THg), total methylmercury(uf.MeHg), filtered MeHg (f.MeHg), and particulate-bound THg (p.THg) and MeHg (p.MeHg) concentrations. This represents one of the longest continuous records of Hg speciation data for any riverine system, thereby providing a unique opportunity to evaluate long-term trends in concentrations and annual loads. During the period of analysis, uf.THg concentration and load trended downward at rates of 0.85% and 1.8% per year, respectively. Conversely, the f.THg concentration increased at a rate of 1.7% per year between 1998 and 2005, and 4.9% per year between 2005 and 2013. Trends inflow-normalized partition coefficients for both Hg and MeHg suggest a statistically significant shift from the particulate to thefiltered phase. The upwardly accelerating f.THg concentration and observed shift from the solid phase tothe aqueous phase among the pools of Hg and MeHg within the river water column signals an increased risk of deteriorating ecological conditions in the lower basin with respect to Hg contamination.
More broadly, the 16-year trend analysis, completed 140 years after the commencement of major Hg releases to the Carson River, provides a poignant example of the ongoing legacy left behind by gold and silver mining techniques that relied on Hg amalgamation, and a cautionary tale for regions still pursuing the practice in other countries. EPA funded work from 1997 through 2013. Samples were collected at the Below Lahontan location from April 1997 through February 1999, and at seven other Carson River locations from April 1998 through February 1999, and at Weeks Bridge and below Lahontan Reservoir from 2000 through 2013. Assist EPA in studying the transport of mercury-contaminated water and sediment in the Carson River system in western Nevada.
The study included periodic measurements of streamflow, and the collection and analysis of water samples for total mercury, methylmercury, and suspended sediment at two Carson River locations. The study also included field measurements and the collection and analysis of samples from the north basin of Lahontan Reservoir. EPA used the data to determine loadings of the dissolved and particulate fractions of total mercury and methylmercury into and from Lahontan Reservoir, to better understand sources and transformations of mercury in the Carson River system, evaluate the effects of reservoir stratification on methylmercury production, and ultimately to help determine whether remedial action is warranted to reduce the levels of mercury contamination in and near the Carson River. A journal article from Eric Morway, Carl Thodal and Mark Marvin-DiPascuale, USGS, summarizing the findings is entitled "Morway_Thodal_MMD_HgMeHg_2017.pdf". This study, a component of the Remedial Investigation for the Carson River Superfund Site, included collection and analysis of water samples for total mercury and methylmercury from Weeks Bridge above Lahontan Reservoir, located on the Carson River.
The USGS Water Science Center has collected and analyzed water samples in the Carson River system through an Interagency Agreement with EPA. The EPA is publishing this data in support of the Carson River Mercury NPL Site in Nevada. Data was compiled and evaluated for the OU2 Remedial Investigation Report (EPA, 2017), which describes the nature and extent of contamination from the Site. The report contains the Human Health Risk Assessment and Ecological Risk Assessment. Literature and other source Hg data are summarized in the RI for surface waters, sediments, and biological tissues. Full metadata: https://edg.epa.gov/metadata/catalog/search/resource/details.page?uuid=%7B39A1C61C-E11B-4A94-B089-2345CE053F80%7D
Description: The primary purpose of the surface water collection was to correlate methylmercury information with sediment core data from several areas in which no data existed and/or to compare with existing data to demonstrate the mercury and metals deposition resulting from the Comstock-era release (i.e., beginning in the 1860s). The specific areas targeted in the field work were from the Lahontan Reservoir, Sheckler Lake, and downstream areas potentially impacted by the historic river flows prior to construction of Lahontan Reservoir. In 2015, the Carson River and Lahontan Reservoir were at historic low levels as a result of a four-year drought. This presented the agency access to collect sediment core samples from areas that were normally below the waterline. EPA’s principal study question was whether mercury is indeed sediment bound and that Lahontan Reservoir, since it construction in 1915, serves as a mercury sink. The secondary purpose of the sediment sampling effort was to collect a range of mercury concentrations for assessing field screening equipment using Thermal Decomposition, Amalgamation, and Atomic Absorption Spectrophotometry (See EPA SW7473) and comparing the results to laboratory analytical data. The EPA is publishing this data in support of the Carson River Mercury NPL Site in Nevada. Data was compiled and evaluated for the OU2 Remedial Investigation Report (EPA, 2017), which describes the nature and extent of contamination from the Site. The report contains the Human Health Risk Assessment and Ecological Risk Assessment. Literature and other source Hg data are summarized in the RI for surface waters, sediments, and biological tissues. Full metadata: https://edg.epa.gov/metadata/catalog/search/resource/details.page?uuid=%7B10011E58-4F8A-4300-9F24-87F01D796B76%7D
Description: The USGS collects data for this national program to inform public, State and local governments, public and private utilities and other Federal agencies involved with managing water resources. The NWIS Mapper provides the ability to export descriptive information and access data for most water-data sites in the National Water Information System (NWIS). These sites are or have been operated by USGS or in some cases by its cooperative partners. Includes methyl and elemental Hg in surface water. USGS Water Quality and Bottom Sediment Data, Co-located with Higgins, and Tuttle samples, and includes additional USGS gauges at Dayton, Lloyds Bridge, Weeks Bridge, Ft Churchill, BLW Lahonton Dam, and Fallon Canals.
The EPA is publishing this data in support of the Carson River Mercury NPL Site in Nevada. Data was compiled and evaluated for the OU2 Remedial Investigation Report (EPA, 2017), which describes the nature and extent of contamination from the Site. The report contains the Human Health Risk Assessment and Ecological Risk Assessment. Literature and other source Hg data are summarized in the RI for surface waters, sediments, and biological tissues. Full metadata: https://edg.epa.gov/metadata/catalog/search/resource/details.page?uuid=%7B7E7D376E-BD0E-488B-BEC8-FBC3203E59EF%7D
Description: USBR collected this data to evaluate the physical properties of the water (dissolved oxygen, pH, temperature, turbidity, specific conductance), common pathogens (coliform bacteria and Escherichia coli), and inorganic chemicals (such as heavy metals, fertilizers, and radiation). Organic chemicals such as common herbicides, pesticides and petroleum hydrocarbons were also monitored at sites showing the greatest potential for upstream industrial or agricultural contamination. In addition to this water quality investigation a separate project plan was initiated to address uptake of contaminates into vegetation (cattails) consumed by Tribal members. Sediment and plant material were collected from Reservation wetlands and analyzed for metals, radioactivity and organochlorine pesticides to test if there is a correlation between surface water, sediments and plant uptake. USBR collected the data to help the Fallon Paiute-Shoshone Tribe (FPST) gain information and help manage Tribal natural resources, a water quality investigation.
The EPA is publishing this data in support of the Carson River Mercury NPL Site in Nevada. Data was compiled and evaluated for the OU2 Remedial Investigation Report (EPA, 2017), which describes the nature and extent of contamination from the Site. The report contains the Human Health Risk Assessment and Ecological Risk Assessment. Literature and other source Hg data are summarized in the RI for surface waters, sediments, and biological tissues. Full metadata: https://edg.epa.gov/metadata/catalog/search/resource/details.page?uuid=%7B2DD357F8-1E09-4519-8B83-5C31751E8511%7D
Description: This is a summary of mercury (Hg) data from the Lahontan spillway area of the Carson River Basin. USBR provided an information overview and reference source on mercury (Hg) in soils for water resources managers and researchers working in the Carson River Basin. These data and the data tables provide results of the Lahontan spillway area, focused on the wetlands used by recreationalists and hunters, in order to measure concentrations of Hg to evaluate potential human health exposure pathways. The original sources of Hg contamination in the Carson River Basin are from historic gold and silver mining and associated milling of the Comstock Lode near Virginia City, Nevada. Runoff and erosion from an estimated 236 'stamp mills', driven by flumes, resulted in a cummulative release of an estimated 7,500 Tons of elemental mercury into the Carson River Basin. The elemental mercury, imported from mines in California and used to almalgamate the ore at the stamp mills, contaminated sediments throughout the Basin from the source area situated approximately between Carson City and Dayton, to the closed terminal wetlands in the Carson Sink.
This area is the primary source of Hg pollution in the Basin, considering the naturally occurring mercury concentrations are close to the crustal average. During runoff and flood events, the River laterally cuts through the contaminated sediments in the overbanks and transports Hg with suspended sediments, and with concentrations rising with higher flow. When Lahontan Reservoir was built in 1915, it became a settling basin for suspended Hg from the Carson River, and while it retains up to 90 percent of influent sediments, the reservoir continues to pass significant concentrations of suspended and dissolved inorganic Hg and methylmercury (Me-Hg) downstream to the Carson Sink. This data was collected to help achieve goals set by the CWA that requires individual States to identify impaired water bodies and create enforceable WQ objectives to protect surface water quality within State bounds (CWA Sections 303d and 305 b). These objectives were to focus on priority toxic pollutants, pursuant to CWA Section 307a. The EPA is publishing this data in support of the Carson River Mercury NPL Site in Nevada.
Data was compiled and evaluated for the OU2 Remedial Investigation Report (EPA, 2017), which describes the nature and extent of contamination from the Site. Literature and other source Hg data are summarized in the RI, for surface waters, sediments, and biological tissues. The report contains the Human Health Risk Assessment and Ecological Risk Assessment. Full metadata: https://edg.epa.gov/metadata/catalog/search/resource/details.page?uuid=%7B8DACDCA6-0500-45E1-A94E-70AEB7EB6BD2%7D
Description: Investigations of wetlands in Lahontan Valley have documented concentrations of inorganic contaminants in water, sediment, and biological samples in excess of concentrations associated with adverse effects to fish and wildlife. Under the auspices of the Truckee-Carson-Pyramid Lake Water Settlement Agreement, the Department of the Interior has implemented a program to acquire rights for water to restore and maintain a portion of the historic wetlands in Lahontan Valley. Although inflow to wetlands will be partially restored, the effects of increased inflow to wetland contamination is uncertain.
In 1990, the Nevada State Office, in conjunction with Stillwater National Wildlife Refuge (NWR), instituted a monitoring program on Stillwater NWR to assess implications of inorganic contaminants to fish, wildlife, and human health and to assess changes in inorganic contaminant concentrations in wetlands maintained With freshwater and agricultural drainage water. This program entailed the measurement of water quality parameters and the determination of trace element concentrations in water, sediment, and biological matrices. These data and the data tables provide results of the Stillwater National Wildlife Refuge, Indian Lakes and Fallon National Wildlife Refuge, focused on the wetlands in order to measure concentrations of Hg to evaluate potential human health and ecological exposure pathways.
The original sources of Hg contamination in the Carson River Basin are from historic gold and silver mining and associated milling of the Comstock Lode near Virginia City, Nevada. Runoff and erosion from an estimated 236 'stamp mills', driven by flumes, resulted in a cummulative release of an estimated 7,500 Tons of elemental mercury into the Carson River Basin. The elemental mercury, imported from mines in California and used to almalgamate the ore at the stamp mills, contaminated sediments throughout the Basin from the source area situated approximately between Carson City and Dayton, to the closed terminal wetlands in the Carson Sink. This area is the primary source of Hg pollution in the Basin, considering the naturally occurring mercury concentrations are close to the crustal average. During runoff and flood events, the River laterally cuts through the contaminated sediments in the overbanks and transports Hg with suspended sediments, and with concentrations rising with higher flow.
When Lahontan Reservoir was built in 1915, it became a settling basin for suspended Hg from the Carson River, and while it retains up to 90 percent of influent sediments, the reservoir continues to pass significant concentrations of suspended and dissolved inorganic Hg and methylmercury (Me-Hg) downstream to the Carson Sink. The EPA is publishing this data in support of the Carson River Mercury NPL Site in Nevada. Data was compiled and evaluated for the OU2 Remedial Investigation Report (EPA, 2017), which describes the nature and extent of contamination from the Site. Literature and other source Hg data are summarized in the RI, for surface waters, sediments, and biological tissues. The report contains the Human Health Risk Assessment and Ecological Risk Assessment. Full metadata: https://edg.epa.gov/metadata/catalog/search/resource/details.page?uuid=%7B19E9A28F-63AE-409F-B200-64C2EA65C223%7D
Description: This feature class depicts Comstock-era mill locations within the Carson River Mercury Site (CRMS). These locations were obtained in order to define the investigation area boundaries of Operable Unit 1 (OU1) within CRMS. Completion of this dataset took place over several years and phases, as described below. EPA surveyThe first mill survey took place in 1993 by EPA, contracted by Piedmont Engineering.113 mills were identified in this survey. Later, Nevada Division of Environmental Protection (NDEP) conducted historic research on Comstock-era mills to expand upon this dataset, identifying an additional 87 mill sites, bringing the total number of mills in the dataset to 200. This process is described below.NDEP Historical ResearchMill site locations were determined based on georeferenced maps procured from the EPA, NDEP, Storey County and the UNR digital map library. All maps were georeferenced based on available landmarks by heads-up digitizing techniques. The maps utilized had varying degrees of accuracy based on their date of production. Some maps utilized dated back to the 1860's.Once all historic maps were scanned, imported and georeferenced, all map sources were evaluated and mill site locations were digitized based on the preponderance of evidence (by comparing mill locations as shown on the various source maps) to determine each mill's location.A vector layer of mill sites was thus constructed using georeferenced raster layer resources. This layer of mill sites contains the locations of 188 historic Comstock Era mills as well as 12 additional tailings locations that are not directly associated with a mill site. 33 additional sites were identified; these consisted of sites that were known to exist but not located on historic maps, as well as cyanide mills. Broadbent and Associates, Inc. field surveysIn 2012 NDEP contracted Broadbent and Associates, Inc. to survey all mill sites defined in this dataset. The contractor successfully verified the remains and evidence of 73 mills. Inconclusive mill evidence was found for 98 of the sites in the dataset. For 65 mill sites, the contractor was not given permission by the landowner to access the property and therefore the mill site location was not surveyed. Survey status is unknown for 1 mill. The contractor provided a feature class of all 236 mills accompanied by a detailed report on their survey efforts, listed below:Broadbent and Associates, Inc., Eric M. Seitz, Project Manager. January 31, 2013, Final Report – Comstock Archaeological Mill Site Inventory, Unpublished. NDEP reviewed this report and the associated feature class to confirm each mill point location and provide attribute information on the survey status of each mill site. NDEP added the attrtibute field "Field Verified" to provide information on the field verification status of each site. A value of "No" indicates the site was not surveyed in the field. This was due to to access limitations and denials for sites located on private property. A value of "Yes" indicates the site was surveyed and evidence of the mill was found. A value of "Surveyed" indicates the site was surveyed but inconclusive or little evidence of a mill was found. Full metadata: https://edg.epa.gov/metadata/catalog/search/resource/details.page?uuid=%7B2B0702C8-8F71-430E-8458-87EBA042B90A%7D
Copyright Text: NDEP Bureau of Corrective Actions, EPA
Description: The TIGER/Line shapefiles and related database files (.dbf) are an extract of selected geographic and cartographic information from the U.S. Census Bureau's Master Address File / Topologically Integrated Geographic Encoding and Referencing (MAF/TIGER) Database (MTDB). The MTDB represents a seamless national file with no overlaps or gaps between parts, however, each TIGER/Line shapefile is designed to stand alone as an independent data set, or they can be combined to cover the entire nation. The TIGER/Line shapefiles include both incorporated places (legal entities) and census designated places or CDPs (statistical entities). An incorporated place is established to provide governmental functions for a concentration of people as opposed to a minor civil division (MCD), which generally is created to provide services or administer an area without regard, necessarily, to population. Places always nest within a state, but may extend across county and county subdivision boundaries. An incorporated place usually is a city, town, village, or borough, but can have other legal descriptions. CDPs are delineated for the decennial census as the statistical counterparts of incorporated places. CDPs are delineated to provide data for settled concentrations of population that are identifiable by name, but are not legally incorporated under the laws of the state in which they are located. The boundaries for CDPs often are defined in partnership with state, local, and/or tribal officials and usually coincide with visible features or the boundary of an adjacent incorporated place or another legal entity. CDP boundaries often change from one decennial census to the next with changes in the settlement pattern and development; a CDP with the same name as in an earlier census does not necessarily have the same boundary. The only population/housing size requirement for CDPs is that they must contain some housing and population. The boundaries of all incorporated places are as of January 1, 2013 as reported through the Census Bureau's Boundary and Annexation Survey (BAS). The boundaries of all CDPs were delineated as part of the Census Bureau's Participant Statistical Areas Program (PSAP) for the 2010 Census.NDEP extracted the Virginia City Census-Designated Place boundary polygon from the TIGER/Line database in 2020. Full metadata: https://edg.epa.gov/metadata/catalog/search/resource/details.page?uuid=%7B06BC7814-390C-4C5C-B943-0248FE0A7011%7D
Description: This feature class contains Comstock-era tailings locations throughout Operable Unit 1 (OU1) of the Carson River Mercury Site (CRMS) within Lyon and Storey Counties, Nevada. Piedmont Engineering was contracted by NDEP to conduct an archeological survey of Comstock-era mining and milling features. These locations were obtained in order to define the investigation area boundaries of the Carson River Mercury Site. The field survey took place in 1993; NDEP later created the geospatial data representing the surveyed features. Additional features were added by NDEP using historical documents and aerial imagery. The hardcopy Piedmont Engineering maps of Comstock-era mills and tailings sites were georeferenced by NDEP. Tailings polygons were digitized in ArcGIS Desktop. The original hardcopy maps were drawn at a scale of 1:2400 (written as 1" = 200' in the maps). Full metadata: https://edg.epa.gov/metadata/catalog/search/resource/details.page?uuid=%7BC714D8F6-61A4-4E17-85A5-6D0C79EFD101%7D
Description: EPA has compiled a significant volume of soil, sediment, surface water and biota geodata, collected either directly, by our contractors and in many cases by our Federal, State and Tribal agency partners (grantees) to complete the remedial investigation (RI) and Feasibility Study at the Operable Unit (OU) 2 (i.e., the river, the floodplain and biota). EPA’s goal for the OU2 area is to select a remedy in 2020 that reduces, or controls risks to human health and the environment. Specifically, this RI involves the investigation and evaluation of the heavy metals (mercury, arsenic and lead) contamination and associated drainages in the Carson River Basin which has resulted from contaminant migration from the Carson River Mercury Mines Site.
The Human Health and Ecological Risk Assessments, contained within the RI, evaluated past and current releases and their impact to human health and the environment. The primary concern is the effect of mercury contamination from the mining operations on the residences near the former stamp mills, the fisheries, waterfowl, water plants and recreational users of the Carson River (“River”) Basin. The OU1 area Superfund Site consists of mining wastes and releases from approximately 236 abandoned gold and silver mines from three basic source areas: the main stem of the River starting at New Empire (Morgan Mill) to Dayton, the Comstock Lode in Gold, Six and Sevenmile Canyons and several mills around Washoe Lake. Mercury from the former mill sites, has contaminated soils at and near the former mill sites, sediments in the drainages and the floodplain, the river banks, the fish and wildlife over more than a 130-mile length of the River extending downstream to the Lahontan Valley and ultimately at its terminus at the USFWS Stillwater and Fallons National Wildlife Refuges.
Contamination from the Site is a legacy of the Comstock mining era of the late 1860s, when mercury was imported to the area for processing of gold and silver ore. Ore mined from the Comstock Lode was transported to the individual mill sites, where it was crushed and mixed with mercury to amalgamate the precious metals before refining. The mills were located in the drainages in and around Virginia City, Silver City, Gold Hill, Dayton, Six Mile Canyon, Gold Canyon, and along main stem of the Carson River between New Empire and Dayton. An estimated 7,500 tons of mercury were discharged into the tributaries and River, primarily in the form of mercury-contaminated tailings. Full metadata: https://edg.epa.gov/metadata/catalog/search/resource/details.page?uuid=%7B50E821EC-2D16-411F-9227-8B2FCCCC809A%7D
Description: This feature class depicts the boundaries of Operable Unit 1 (OU1) within the Carson River Mercury Site (CRMS), including the four Area of Investigation boundaries. NDEP lead an initiative to refine the boundaries shown on maps identifying the Carson River Mercury Superfund Site (CRMS) from the initial site identification and description as the Carson River hydrographic basin beginning in Carson City, NV to its terminal points in Churchill County, NV. This description of the CRMS was used in many of the early site investigation studies and reports and continued to be used in all public education and long-term site management controls until approximately 2012. Using site contaminant fate and transport determinations from the CRMS OU1 Remedial Investigation (RI) and Conceptual Site Model (CSM), it seemed inappropriate to include the much larger area of the hydrographic basin as being potentially impacted by site contaminants of concern (CoC). NDEP created protocols to estimate areas that are likely to have been impacted by CoCs and created maps using these protocols to redraw the CRMS boundary limits. In the development of these protocols, NDEP used: Historic records and documentation of probable source areas; The 2012 archaeological mill site research and field study conducted by Broadbent & Associates to locate the historic source areas; Soil and sediment transport mechanisms identified in the CSM and general soil transport and sedimentology principals to predict areas where CoCs have likely been located at and downstream of the historic sources. The overall area of transport was estimated to be reasonably large to include possible anthropogenic activity as well as historic and future natural events such as flooding and channel migration. Additionally, NDEP added a “buffer” to extend the potential areas beyond the conservatively defined primary areas of potential contamination to further address unknown and future effects. These buffers have been identified separately from the primary areas of concern and labeled as such on maps using these protocols. These revisions were formalized in the 2013 Explanation of Significant Differences to the OU-1 Record of Decision (RoD) to adopt the new site definition and boundaries identified by NDEP as new estimates of the CRMS extents. NDEP identified four geographic areas of prime importance to the CRMS. Originally labeled by NDEP as “Risk Areas”, the intent of this terminology was to indicate these were the areas understood to have the most likely “risk” of contamination. Under consultation with EPA R9 risk assessment staff, the term has been changed to “Area of Investigation” to avoid confusion that any actual quantitative level of human or ecological risk has been determined for these areas. They are only estimates of potential contamination and new or additional information that contradicts these boundaries as being insufficient will be used to adopt new boundaries as appropriate. The four Areas of Investigation have become the foundation for the residential soil sampling program mandated by the OU-1 RoD. Summarized briefly; Investigation Area 1 (IA 1)- This includes all areas in the Carson River drainage basin from about the area of the historic settlement of Empire in Carson City, NV downstream to the existing or historic terminal points of the river at Carson Lake, Carson Sink, Indian Lakes and the Stillwater National Wildlife Refuge that lie outside the buffer zones of the other three Investigation Areas. It is least probable that CRMS CoCs will be located in these areas. It is unlikely that any sampling will be requested on areas developed within IA 1, but it might be requested in special circumstances, especially near and around the source areas of the contamination where historic activities could potentially have caused contamination beyond the typical boundaries as identified by the CSM. Investigation Area 2 (IA 2)- This area is defined as a buffer that lies 100 feet along a normal horizontal to the Investigation Area 3 boundary. For Comstock-era mill sites and isolated tailings piles, this translates to the area between 350 feet and 450 feet from the center point of the historic feature. For the 100-year FEMA floodplain and areas of irrigation, this is the area beginning at the limit of the flood plain boundary or irrigated land along a normal to 100 feet. Investigation Area 3 (IA 3)- This area is defined as a buffer that lies 100 feet along a normal horizontal to the Investigation Area 4 boundary for Comstock-era mills or isolated tailings piles. For Comstock-era mill sites and isolated tailings piles, this translates to the area between 250 feet and 350 feet from the center point of the historic feature. It is also defined as the limits of the FEMA 100-year floodplain or past or current flood irrigation practices. A tributary of the Carson River must have a Comstock-era mill site or tailings pile located along it to be mapped in IA3 and only the portion of the tributary downstream of the historic feature is included, not including the IA3 area and buffer drawn around the historic feature itself. If a tributary does not have FEMA 100-year flood plain defined, then IA3 has been defined as the area 100 feet along a normal to Investigation Area 4 boundary of that tributary. Investigation Area 4 (IA 4)- This area represents the highest likelihood of mercury contamination. Multiple steps were used to define the extent of this area, described below: The area within a 250 feet radius from the center point of a Comstock-era mill Comstock-era tailings pile polygon with a 250 ft buffer The centerline of the current channel of the Carson River enclosed in a polygon 100-feet wide (50 feet either side). Tributaries to the Carson River, where Comstock-era mills and tailings piles were located are enclosed in a polygon 50-feet wide (25 feet either side) from the approximate center of the tributary channel. Irrigation canals are enclosed in a polygon 20 feet wide (10 feet either side) from the approximate center of the ditch. Full metadata: https://edg.epa.gov/metadata/catalog/search/resource/details.page?uuid=%7B0DB20F30-957E-409A-B485-B941B46A2A7E%7D
Description: This feature class represents a future study area. EPA plans to determine the nature and extent of contamination in Washoe Lakes and the Steamboat Creek headwaters. EPA has identified 13 mill sites in this area. Full metadata: https://edg.epa.gov/metadata/catalog/search/resource/details.page?uuid=%7BDBF5DDED-80B1-4318-A713-2DF1C9E1095C%7D