Dawn Mining Company Millsite Soil Characterization

M. Vidyasagar; J.A. Johnson; H.R. Meyer; and C.A. Little (MFG, Inc.)

Dawn Mining Company (DMC) operated a mill near Ford, Washington to process uranium ore from the nearby Midnite Mine from 1957 to 1965 and from 1969 through 1982. The mill was permanently closed in 2001 and demolished in 2003. Residual radioactive materials in soil required additional cleanup to meet the requirements for termination of the DMC radioactive materials license. The project was regulated by the Washington Department of Health, Division of Radiation Protection (WDOH). The areas in the vicinity of the millsite requiring further soil cleanup are those primarily associated with soil radium-226 activity concentrations greater than 5.0 pCi/g above background for soil at ground surface and 15.0 pCi/g above background for soil at depth. These levels were previously outlined and approved in a 1999 Decommissioning Plan for the millsite. The Characterization Survey was designed to: 1) determine the nature and extent of radiological contamination relative to the clean-up criteria, 2) aid in evaluating remedial alternatives, 3) provide input data for pathway analysis and dose or risk assessment, 4) estimate occupational and public health and safety impacts during decommissioning, and 5) provide input into the design of Final Status Surveys. The characterization surveys encompassed the entire DMC millsite and adjacent areas outside the boundary possibly impacted by windblown tailings or other materials tracked off-site. Potentially impacted areas were divided into three classes, based on their respective remediation needs. The Characterization Survey consisted of four elements: (1) A GPS-based gamma scan in a shielded detector; (2) surface soil sampling; (3) sub-surface soil sampling; (4) and a correlation between shielded gamma measurements and Ra-226 activity concentration in soil. The Characterization Survey was completed in approximately 7 weeks.

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