2009-05-19_REVISION - M1981021 (32)

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Section 4 Potential for Rock to be Toxic-Forming levels. Although the ore material could be considered a potentially toxic forming material given • this screening evaluation, it is a marketable material and is only temporarily stored at the site for brief time periods between production and off-site shipment for processing. Accordingly, further considerations regarding ore material are not warranted. For potential human exposure in development rock, the only detected metal with a concentration that exceeds its respective RMC is arsenic. Specifically, BLM RMCs for arsenic are exceeded for resident, camper and worker scenarios, but not for ATV driver or surveyor scenarios. For these latter scenarios, this screening level evaluation indicates that development rock is not a toxic-forming material with respect to direct contact risks. Additional information is provided below to further assess the exposure of the worker to arsenic at the Sunday Mines Group. The camper is not considered separately because the RMt_ for this scenario is higher than for workers. Thus, conditions protective of the worker will also be protective of the camper. A residential scenario is not considered since this type of land use is not anticipated. Future use of the site is designated as "non-motorized recreation". The total metals data are also compared to BLM wildlife RMC values. The BLM RMCs are species-specific, and this screening-level evaluation considers RIV[C values for deer mouse, cottontail, bighorn sheep, white-tailed deer, mule deer, elk, cattle,, and sheep. The screening- level evaluation shows that most metals in development rock occur at concentrations that are lower than their respective screening criteria. However, cadmium concentrations exceed the screening levels at some locations. These include the Sunday Mine development rock area, and one location at the Topaz Mine development rock area. Although local areas are present where cadmium concentrations exceed the BLM screening levels, potential toxicity to wildlife are not discussed further in this document for several reasons: ¦ The development rock areas where cadmium locally exceeds the wildlife screening; criteria are very small relative to home and/or foraging ranges for most ecological receptors of interest, which reduces the potential exposure levels. ¦ Threatened or endangered species, or suitable habitat for those species, are not present in the Sunday Mines Group Development Rock Areas. Therefore, complete mitigation of potential risks to all individual wildlife organisms is not warranted. ¦ It is unlikely that potential adverse effects to wildlife related to direct contact risks would cause a significant impact to overall populations and community of the referenced species. 4.1.2 Further Assessment of Arsenic in Development Rock As discussed in the BLM document and consistent with screening; level approaches, site-specific data can be used to reduce uncertainties in the exposure assumptions used to develop the RMCs (BLM 2004, p.13). In particular, to further evaluate detected concentrations of arsenic in waste rock and its potential as a toxic-forming material with respect to workers, RMC input parameters were adjusted using the following site-specific information: (1) exposure to multiple metals and media and (2) bioavailability. Exposure to Multiple Metals and Media. RMCs have been calculated based on potential for both noncancer and cancer health effects. Health protective levels for arsenic are 65 and 12. milligrams per kilogram (mg/kg) for noncancer and cancer health effects, respectively. For 4-2 TA64985-Denison MineslTask Order 3 - DMO Sampling and Analysis Plan%Task 3.12 • Soil, Ore, Rock Data Aasessment ReporOSunday Rock R:ponunsl reponlReportlFinal Sunday Mines Group Soil Ore Rock Data Assessment Repon_051509.doc