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.

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.

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.

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.

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.

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.

This dataset includes the field measurements and laboratory analyses of surface water, seston, and sediment collected from Lake Powell, within Glen Canyon National Recreation area (GLCA), during high flow (May-June 2014) and low flow (August 2015) conditions. The study area includes 12-13 sampling sites that follow a transect spanning the entire length of the reservoir from the Colorado River inflow to the Glen Canyon dam, as well as the San Juan River arm, the Escalante River arm and West Canyon. Bed sediment samples were analyzed for mercury speciation, methylmercury production and degradation rates, total reduced sulfur, iron speciation, organic content, and 16S rRNA gene templates as a proxy for microbial abundances. Water samples were collected from 3-5 depths at each site and analyzed for: total mercury (filtered and particulate), methylmercury (filtered and particulate), dissolved organic and inorganic carbon with 13C isotopic ratios, nutrients, anions, cations, trace metals, particulate carbon (with 13C isotopic ratios) and particulate nitrogen (with 15N isotopic ratios). Water quality sonde (EXO) field measurements included specific conductivity, temperature, pH, dissolved oxygen, fluorescent dissolved organic matter, chlorophyll, and turbidity. Fish samples were also collected during November 2014 from Good Hope Bay (upper reservoir), Wahweap Bay (lower reservoir), and the San Juan arm and assayed for total mercury for comparison with previous striped bass samples collected by the state of Utah. There are nine files (*.csv) in this dataset: 1) data dictionary ; 2) sediment data; 3) water data; 4) seston data; 5) fish data; 6) EXO main channel profile data ; 7) EXO off channel profile data; 8) quality assurance data; and 9) molecular data.

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.

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.

The data represent a shallow mercury chronology using sediment core from a playa lake system situated in a high-altitude setting in northwest Argentina. Archive samples were used from sediment core (LP07-1A) that was collected from a location (lat -22.362100°, lon -66.003600°) in the center of the playa-lake Laguna de Pozuelos in the dry season of 2007, when the water level was 2 to 3 cm. The samples were taken over 1 to 2 cm intervals and had been dried and homogenized. Sediment total mercury analyses were conducted by digesting sediment (0.30 g) in boiling concentrated nitric/sulfuric acid (ratio 3:1), followed by 12 hour oxidation with bromine monochloride, tin chloride reduction, gold amalgamation, and detection by CVAFS.