Service Description: This feature class details a brief study undertaken by in-house staff about the nature of mercury species (forms) the span of the Carson River Mercury Site. The R9 EPA risk assessor requested mercury speciation data in sediment and soils along the River floodplain, specifically from the Fallon Pauite Shoshone Tribal Reservation, to support supplemental data for the OU2 risk assessment. This data set is comprised of the total mercury and methyl mercury values. The speciation fractions do not present well in the geospatial data. The speciation results from the Brooks Applied Lab are available in the report (see primary source document).
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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.
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Copyright Text: U.S. EPA
Spatial Reference: 102100 (3857)
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