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Historic placer gold mining has impacted the landscape of the lower Trinity River and introduced mercury into sedimentary environments within the watershed. The data presented in this preliminary report were collected to assess the impact of historic placer mining. Restoration project activities at Hocker Flat proposed by the Trinity River Restoration Program (TRRP) have the potential to release mercury and enhance mercury methylation. The USGS has collected sediments, tailings, and water samples in the Hocker Flat area in seven sampling events between October 2002 and June 2004. Mercury concentration in biota have also been assessed and a brief summary of biota results to date are presented. Only the results for mercury and methyl mercury c in placer tailings, sediment, and water are presented and discussed. Other physical and chemical variable that control mercury methylation, such as sulfate and total organic carbon concentration, are not evaluated because all analytical data have not been received.

 

The purposes of this project are to identify materials with elevated mercury concentrations, determine the speciation of mercury in such materials, and obtain preliminary information on ranges of mercury concentrations in all types of material and environments found on the site. The sampling scheme implemented so far has been designed for these purposes. It is not designed to determine spatial variations in mercury concentrations, and cannot be used reliably for this purpose.