The Sierra Zinc Mine and Mill is a former lead and zinc mine located approximately 24 miles north of Colville,Washington and approximately 17 miles south of Northport, Washington. Features at the site include a tailings pile, a waste rock pile, dilapidated mill and barn buildings, assay office, and a flowing adit. The South Fork Deep Creek flows adjacent to the site.
The mine was in operation sporadically from 1906 to its closure in the 1950s. During operations at the site, a large quantity of tailings were generated and deposited north of the mill building. The tailings pile covers approximately 25 acres at the site.
In 2001, START completed preliminary assessment/site inspections (PA/SIs) at a number of mine and mills in the Upper Columbia River area. During the PA/SI, samples were collected from the tailings pile and waste rock pile for off-site fixed laboratory analysis.
In 2003, the Washington State Department of Natural Resources (WDNR) completed an Inactive and Abandoned Mine Land Investigation at the site. Two samples were collected from the tailings pile for off-site fixed laboratory analysis. In addition, surface water samples were collected from the on-site flowing adit in September 2001 and June 2002 for off-site fixed laboratory analysis.
The Removal Site Evaluation (RSE) was conducted July 8 through 11, 2013. During the RSE field event, START screened tailings, soil, and waste rock using a field-portable x-ray fluorescent (XRF), installed borehole on the tailings pile to assist in determining the volume of material, collected 24 samples for off-site fixed laboratory analysis, collected surface water from the on-site adit, collected surface water and sediment from nearby South Fork Deep Creek, and sampled an adjacent residential drinking water well. A subset of the soil samples were also submitted for Synthetic Characteristic Leaching Procedure (SPLP) to determine if the material was leachable to groundwater.
Concurrent with EPA's RSE, on behalf of the responsible party (The Goldfield Corporation), RMC conducted an investigation of the site and surrounding area. As part of their investigation, RMC collected surface soil, groundwater, surface water, and sediment samples were collected for off-site fixed laboratory analysis.
