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Section 4
<br />Potential for Rock to be Toxic-Forming
<br />0 4.2.1 Screening-Level Evaluation
<br />This section presents a screening-level evaluation of the potential for development rock and ore
<br />to form leachate that may be toxic to human health or the environment. As requested by DRMS
<br />(DRMS 2008b), this screening-level evaluation was conducted by comparing MWMP data to
<br />Colorado groundwater standards in CDPHE Water Quality Control Commission Regulation
<br />No. 41 (Tables 1 through 3). Standards presented in these tables are based primarily on U.S.
<br />EPA National Primary and Secondary Drinking Water Standards. The majority of standards
<br />listed in Table 1 (Domestic Water Supply - Human Health Standards) are maximum
<br />contaminant levels (MCLs) for public drinking water supplies, as established by the National
<br />Primary Drinking Water Regulations. Table 2 standards (Domestic Water Supply - Drinking
<br />Water Standards) are also for public drinking water supplies, as established by the National
<br />Secondary Drinking Water Standards. Table 3 standards (Agricultural Standards) were
<br />developed for 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 groundwater
<br />standards. This screening-level comparison indicates that a number of constituents were
<br />detected that are greater than the Colorado groundwater standards. Below is a list of
<br />constituents detected in MWMP leachate that were detected at concentrations greater than the
<br />screening criteria for each of the development rock and ore stockpiles:
<br />¦ Topaz Mine Development Rock (samples DM-TPWR-1 to DM-TPWR-3): arsenic, chloride,
<br />molybdenum, nitrate, nitrite, pH, selenium, sulfate, uranium, vanadium.
<br />• ¦ Sunday Mine Development Rock (samples DM-SUWR-1 to DM-SUWR-3): antimony, arsenic,
<br />molybdenum, nitrate, nitrite, selenium, sulfate, and vanadium.
<br />¦ St. Jude Mine Development Rock (samples DM-SJWR-1 to DM-SJWR-3): arsenic, fluoride,
<br />molybdenum, nitrate, pH, selenium, sulfate, uranium, and vanadium.
<br />¦ West Sunday Mine Development Rock (samples DM-WSWR-1 to DM-WSWR-3): arsenic,
<br />cadmium, chloride, molybdenum, nitrate, nitrite, pH, selenium, sulfate, uranium, and
<br />vanadium.
<br />¦ Composite Ore Stockpiles (samples DM-ORE-1, DM-ORE-2): antimony, arsenic, copper, lead,
<br />molybdenum, nitrate, selenium, sulfate, uranium, and vanadium.
<br />¦ Sunday Mine Low Grade Ore (sample DM-SU-Lowgrade): antimony, arsenic, molybdenum,
<br />selenium, sulfate, and vanadium.
<br />Overall, ore samples (i.e., DM-ORE-1, DM-ORE-2, and DM-SU-Lowgrade) leachate metals
<br />concentrations are greater than the development rock leachate metals concentrations which are
<br />expected given that the ore has increased mineral content. It should be noted that groundwater
<br />in the vicinity of the Sunday Mines Group is not classified with respect to designated uses
<br />(CDPHE Regulation 42); and therefore, the human health, drinking water and agricultural
<br />criteria are not formal standards for groundwater at the site. In addition, current groundwater
<br />uses in the vicinity of Sunday Mines Group do not include Human Health, Drinking Water and
<br />I& Agricultural uses (CDM 2009c). Additional information regarding current and future uses of
<br />cm 4-9
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