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Seclion 4 <br />PolenlialforRock to be Toxic Forming <br />0 These assessments are discussed below. <br />4.2.1 Screening-Level Evaluation <br />This section presents a screening-level evaluation of the potential for development <br />rock to form leachate that may be toxic to human health or the environment. As <br />requested by DRMS (DBMS 2008), this screening-level evaluation was conducted by <br />comparing MWMP data to Colorado groundwater standards in Colorado Department <br />of Public Health and Environment (CDPHE) Water Quality Control Commission <br />Regulation No. 41 (Tables 1 through 3). Standards presented in these tables are based <br />primarily on U.S. EPA National Primary and Secondary Drinking Water Standards. <br />The majority of standards listed in Table 1 (Domestic Water Supply - Human Health <br />Standards) are maximum contaminant levels (MCLs) for public drinking water <br />supplies, as established by the National Primary Drinking Water Regulations. Table 2 <br />standards (Domestic Water Supply - Drinking Water Standards) are also for public <br />drinking water supplies, as established by the National Secondary Drinking Water <br />Standards. Table 3 standards (Agricultural Standards) were developed for <br />agricultural use of groundwater for the protection of livestock and crops. <br />Table 4-4 presents the comparison of MWMP leachate data to the Colorado <br />groundwater standards. This screening-level comparison indicates that a number of <br />constituents were detected that are greater than the Colorado groundwater standards. <br />Below is a list of constituents detected in MWMP leachate that were detected at <br />• concentrations greater than the screening criteria for the development rock samples: <br />¦ DM-V4WR-1: arsenic, molybdenum, selenium, sulfate, uranium, vanadium. <br />¦ DM-V4WR-2: antimony, arsenic, molybdenum, selenium, sulfate, uranium, <br />vanadium. <br />¦ DM-V4WR-3: arsenic, molybdenum, selenium, sulfate, uranium, vanadium. <br />It should be noted that groundwater in the vicinity of the Van 4 Mine is not classified <br />with respect to designated uses (CDPHE Regulation 42); and therefore, the human <br />health, drinking water and agricultural criteria are not formal standards for <br />groundwater at the site. In addition, current groundwater uses in the vicinity of Van 4 <br />Mine does not include Human Health, Drinking Water and Agricultural uses (CDM <br />2009c). Additional information regarding current and future uses of groundwater in <br />the area is included in Hydrogeologic Evaluation of the Van 4 Mine, San Miguel, Colorado <br />(CDM 2009c). <br />4.2.2 Volume of Percolation through Rock Piles <br />The screening-level analysis presented previously shows that under the water to rock <br />ratios used in the MWMP analyses, leachate from the piles would be expected to <br />contain concentrations of several metals such that the development rock and ore <br />might be considered toxic-forming. To further evaluate if the development rock <br />should be considered as a toxic-forming material, this section evaluates the potential <br />• <br />4-9