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

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

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

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

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.

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.

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.

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.

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.

This dataset contains locations of surface water discharge and water quality sites.