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Distribution of Mercury in US EPA Region IX REMAP Study Areas

Robert K. Hall 1, Anthony Olsen 2, Daniel T. Heggem 3, Peter Husby 4, and Linda Chambers 5

1 USEPA Region IX, San Francisco, CA 94105
2 USEPA NHEERL-WED 200 SW 35th St., Corvallis, OR 97333
3 University of Nevada, Reno, NV 89557
4 USEPA Region IX Laboratory, Richmond CA 94804
5 USEPA Region IX, San Francisco, CA 94105

Mercury distribution within U.S. EPA Region IX Regional Environmental Monitoring and Assessment Program (R-EMAP) study units is associated with geology and land-use practices. Stream water and sediment data indicate mercury is mobilized from weathering of ore bearing rock, and atmospheric deposition. In the Humboldt River Watershed Total Mercury (HgT) in sediment is detected at 26 of 34 sites ranging in concentration from 0.07 - 1.50 mg/Kg. Lowest Effects Level (LEL) for aquatic organisms in sediments of 0.2 mg/Kg is exceeded at 6 sites, which are located downstream from historical mine sites and downwind from current mining activity. Mining facilities in the Humboldt Basin reported, in the 1998 USEPA Toxic Release Inventory (TRI), emitting an estimated 13,560 lbs. of mercury directly into the atmosphere and over 9 million lbs. are contained in tailings and waste rock piles. In the Central Valley, CA, irrigation canals, ditches and drains, HgT is found in 15 of 50 sites ranging from 0.1-0.32 ug/L in water and 0.07-0.66 mg/Kg dry weight sediment. HgT is associated with abandoned mercury and gold mines in the Coast Ranges and Sierras. In the Walker River and Muddy River watersheds, HgT in sediment is found at 7 of 28 sites ranging from 0.07 - 0.78 mg/Kg, and in 4 of 37 sites ranging from 0.07 - 0.80 mg/Kg respectively. One site in the Muddy River has detectable HgT concentration in water of 0.41 ug/L.

Keywords: mercury, Toxic Release Inventory (TRI), mercury deposition

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