Archeologists to study Comstock mill sites in contamination review
Submitted by editor on Mon, 04/25/2011 - 1:25pm
Environmental agencies have opened a new phase in their investigation into mercury contamination in the Carson River and Washoe Lake watersheds that has been associated with a historic Comstock Lode gold and silver mining.
The Nevada division of Environmental Protection and the U.S. Environmental Protection Agency will employ archeologists to characterize gold and silver mill sites that were active during the 1859 to 1900 Comstock era. The milling process concentrated naturally-occurring arsenic and lead, and also added mercury to the ore to separate gold and silver from the native rock.
Mercury is a naturally occurring metal typically found in the form of cinnabar ore which contains mercuric sulfide. Mercury in lakes and rivers is converted into methyl mercury by certain bacteria. Fish ingest methyl mercury by swimming or feeding in contaminated water. Methyl mercury accumulates in fish tissue and is carried up the food chain to larger fish, animals and humans. Methyl mercury is dangerous because the concentration of methyl mercury increases as it goes up the food chain.
In the intervening century since the mills were active, wind and water have eroded and redistributed these contaminants to soil and water courses, as well as stream, river, lake and floodplain sediments. Original mill site locations are still potential hotspots for mercury, arsenic and lead contamination; therefore, it is important to know exactly where each former mill site was located.
The original Carson River Mercury Superfund Site investigation in the 1990s identified over 130 mill sites and that list has now grown to almost 250. Click here to read more.
