Dames & Moore, 1999 - USDA Forest Service

mechanisms, PCOCs originating from past activities at the Site could be potentially transported to
ecological receptors.
PCOCs present in primary and secondary source materials (surface water, sediment. soil. and biota that have
been exposed to primary source materials including tailings) may be released via several mechanisms.
including incorporation into the food-web. PCOCs released to surface water and/or sediment can be
contacted or ingested by aquatic and terrestrial receptors. Tedal receptors may directly contact or ingest
surface soil at the site. Surface runoff could transport surface soil PCOCs to surface water and sediment.
potentially exposing aquatic receptors. Through predation, compounds of concern in plant or animal tissues
can be acquired by other animals.
EPA (1994) indicates that for ecological receptors, dermal exposure pathways to media such as sediment
are very difficult to document as complete and that for many receptors (e.g., small mammals grooming
fur) ingestion of PCOCs will likely occur before actual dermal contact. This is especially true for metals
which are not permeable to the skin except in ionic form. For this reason, dermal exposure will be
considered to be adequately addressed for ecological receptors as modeled oral doses.
Likewise, inhalation exposure pathways are not well characterized for ecological receptors, no dust
measurements were available, and there is no data for absorbance efficiency for wildlife. Because PCOC
exposure for ecological receptors cannot be accurately quantified, potential exposure via this route will be
considered as an uncertainty to the risk characterization.
Exposure Pathways Analysis
Exposure pathways that are potentially complete at the Site include:
Surface Water. Direct surface water contact (dermal and respiratory) and ingestion are
potentially complete pathways to aquatic and terrestrial receptors, respectively.
Sediment. Limited sediment accumulation exists in Railroad creek because, of the high
gradient and water flows. However, in those small area where sediment does exist, it
could pose an exposure pathway to certain benthic invertebrates. Because sediment will
be substantially washed off food items consumed by terrestrial receptors (Beyer 1994),
sediment ingestion is not of concern for these animals.
Tailings Piles and Soil. Ingestion of tailings pile surface soil by biota and uptake of
PCOCs by vegetation are potentially complete exposure pathways at these sites.
Ground Water. Ground water pathways are not complete for ecological receptors (as it
is not directly contacted until it becomes surface water) and will not be considered hrther
because surface' water is addressed directly.
Biota. Direct ingestion of biota (including vegetation, aquatic insects, fish, small
mammals, etc.) by higher trophic level ecological receptors is a potentially complete
exposure pathway at this site. Concentrations of PCOCs measured in fish tissues (PNL.
1992; Ecology, 1993; Ecology, 1994) are the integrated products of the complete
exposure pathways and also reflect physiological processes such as elimination and
depuration. As such, this pathway was accounted for by direct sampling (by others).
G:\wpdur\00JLrpo~Uloldol-2\n\7O.doc 7-43
17693-005-019Uuly 27.1999.5:16 PMDRAFT FINAL RI REPORT
'