Dames & Moore, 1999 - USDA Forest Service

5.0 NATURE AND EXTENT OF CONTAMINATION
This section discusses the nature and extent of contamination identified in the surface water of Railroad
Creek, Copper Creek, and associated tributaries, groundwater in the mine-affected area. soil in Holden
Village and maintenance yard areas, sediment in Railroad Creek and Lake Chelan. and other media
associated with the Site. The discussion is based on analytical results collected historically from previous
investigations at the Site and data collected during the RI conducted in 1997 and 1998. Included in ,this
section are field measurements and laboratory analytical data collected in accordance with the approved
draft RI Work Plan, SAPS, and QAPPs for the RI as presented in Section 1 .O. Issues that were identified
during data validation reviews that resulted in data qualification affecting data interpretation are
incorporated in the analytical discussions for each media.
5.1 BACKGROUND AND CHEMICAL SPECIFIC ARARS AND TBCS
Background conditions were assessed for Site media where feasible to assess chemical constituents that
exist in the area but are not related to mining activities at the Site. Assessment of background conditions
included the collection and analysis of samples from areas in and near the Railroad Creek drainage where
mining activities by Howe Sound Company are believed not too have occurred. Statistical analyses of the
data were performed using the statistical methods established under MTCA and associated other
published statistical guidance. The MTCA statistical methods utilized adequately address background
conditions assessed under CERCLA. The establishment of cleanup levels under MTCA considers Site-
specific characteristics under certain circumstances. Site-specific cleanup levels may be established
based on background concentrations of compounds of concern (COCs) at a site provided that adequate
data are available to appropriately calculate background concentrations as specified in the Washington
Administrative Code (WAC) 173-340-708(11).
Two types of background are defined by MTCA. Natural background is defined as the concentration of
hazardous substances consistently present in the environment which has not been influenced by localized
human activities. Area background is defined as the concentration of hazardous substances that are
consistently in the environment in the vicinity of the Site which are the result of human activities
unrelated to releases on the Site. Natural background was not evaluated due to the physical
characteristics of the Site and historical prospecting and mining-related activities that have occurred in the
area unrelated to the Howe Sound Company and the Holden Mine. Area background was assessed for
media where feasible.
Site data were compared to background constituent levels to assess if Site-specific sample concentrations
are above area background values. A preliminiuy list bf chemical specific Applicable or Relevant and
Appropriate Requirements (ARARs) and To Be Considered (TBC) numerical chemical guidance for surface
water, groundwater, soil, and sediment are presented and discussed and are for identifying potential
compounds of concern (PCOCs) for the Site. The PCOCs identified are further evaluated in the ecological
and human health risk assessments.
The intent of this section is to present and compare available background data and chemical-specific
ARARs and TBC,guidance for compounds identified in surface water, groundwater, soil, and sediment. A
more detailed discussion of ARARs and TBC values will be provided in the Remedial Action Objectives
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