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Section 4 <br />Pofenfia/fol-Rock lobe Toxic Fo1ming <br />• ¦ Threatened or endangered species, or suitable habitat for those species, are not <br />present in the Van 4 Mine development rock areas. Therefore, complete mitigation <br />of potential risks to all individual wildlife organisms is not warranted. <br />¦ It is unlikely that potential adverse effects to wildlife related to direct contact risks <br />would cause a significant impact to overall populations and community of the <br />referenced species. <br />4.1.2 Further Assessment of Arsenic in Development Rock <br />As discussed in the BLM document and consistent with screening level approaches, <br />site-specific data can be used to reduce uncertainties in the exposure assumptions <br />used to develop the RMCs (BLM 2004, p.13). In particular, to further evaluate <br />detected concentrations of arsenic in waste rock and its potential as a toxic-forming <br />material with respect to workers, RMC input parameters were adjusted using the <br />following site-specific information: (1) exposure to multiple metals and media and (2) <br />bioavailability. <br />Exposure to Multiple Metals and Media. RMCs have been calculated based on <br />potential for both non-cancer and cancer health effects. Health protective levels for <br />arsenic are 65 and 12 milligrams per kilogram (mg/kg) for non-cancer and cancer <br />health effects, respectively. For non-cancer health effects, BLM RMCs have been <br />divided by 11 metals and "n" medial to account for multiple chemical and media <br />• exposures. Such a calculation is conservative for the Van 4 Mine because most metals <br />are present only at concentrations well below their respective RMCs indicating little if <br />any potential for adverse health effects. Even so, all arsenic concentrations are below <br />the non-cancer "RMC" of 65 mg/kg. From a non-cancer viewpoint, development rock <br />at the Van 4 Mine is not toxic-forming for direct contact. <br />RMCs based on cancer risk assume possible exposure to arsenic in groundwater, soil <br />and air and the number of media included in the calculations is therefore three (3). <br />Thus, the RMC for arsenic in soil is about one third of the value that would be <br />calculated assuming exposure to soil alone. In telephone correspondence with Dr. <br />Karl Ford of the BLM (author of the BLM RMC document), (CDM 2009a), Dr. Ford <br />indicated that the appropriate number of media for the worker scenario was one (1). <br />This input to the calculations is appropriate because: <br />1. Groundwater is present only at depth and no contact with groundwater is <br />possible for a worker or camper that visits the site; <br />2. Possible exposure to arsenic suspended as dust in ambient air is estimated in <br />the equation for calculation of the RMC based on cancer risk; and <br />3. Possible exposure to other carcinogens observed in development rock <br />(cadmium and nickel) is accounted for in the calculations. <br />Media include soil, air, groundwater, sediment and surface water. Only soil and air are relevant to the <br />Sunday Group mines, as discussed in the text. <br />4-3