Name: LimnologyHgandMeHg_Lahontan_2012_USGS

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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. Metadata

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