2007-12-19_REVISION - M1988112 (17)

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ARCADIS BBI. negligible risk exists, then there is strong support for a no further action recommendation. It should be noted that any exceedances observed during the screening process is not necessarily indicative of risk, but rather an indication that further evaluation may be necessary before a definitive decision can be made. Exposure Assessment In an exposure assessment, receptors are linked to the source via exposure pathways. The irrigation ponds at San Luis Mine will be surrounded by fencing and as such, key receptors were identified to be waterfowl and terrestrial birds that may be exposed via the ingestion of water exposure pathway. Seven different avian species: mallard duck, lesser scaup, red tailed hawk, spotted sand piper, marsh wren, American robin, and Gambel's quail, were evaluated for surface water ingestion at the San Luis Mine. Daily water ingestion rates were determined using the following equation from USEPA (1993) that determines average daily water intake based on body weight. IRWater = 0.059*BWro.67 Where: IRWater = ingestion rate of water (Uday) BWr =body weight of ecological receptor (kg). The calculated daily water intake for each receptor can be seen Table 1. Effects Assessment A key component of a wildlife risk assessment is the identification of appropriate toxicity reference value (TRV). A TRV is an exposure level that is considered not to pose unacceptable risk of deleterious effects to a receptor class. TRVs may be developed for different routes of exposure such as ingestion or dermal contact. They may be obtained from appropriate regulatory criteria or be developed as an exposure dose (expressed as mg/kg-BW/day for oral intake), a concentration in food, water, or air (expressed as mg/kg, mg/L, and milligram per cubic meter [mg/ml, respectively), or a body burden. This assessment focused on water ingestion, so TRVs were selected from Sample et. al. (1996). Tables 2 and 3 summarize the data associated with the irrigation ponds and TRVs were available for barium, boron, fluoride, and manganese. For these four metals, Sample et. al. (1996) reported values in mg/kg/day for a given test species. TRVs were scaled to account for differences in body weights between the organism used to establish the TRVs and the ecological receptor chosen for evaluation. This was accomplished by using the following equation (Sample and Arenal, 1999): TRVW = TRVs * (BWs/BWr)1-1.2 where: TRVW = weight-adjusted TRV (mg/kg-day) TRV, = literature-based TRV (mg/kg-day) p:WmjD&1212-mvmriksanlulsY?wlrislpemdtmewrnent-westpilmanWnenMrepot&pdfs*pendot-ftmA rppMUmlu'sminememo Page: _Wy n, zaozdoc 2/5