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As depicted (via bolded font and shading) in the foregoing Table 1-1, there are three instances <br /> where the respective MCL is exceeded per SPLP testing, as follows: <br /> • Lead (Pb)—in the Tailing Liquid <br /> • Manganese (Mn)—in the Crushed/Milled Waste Rock <br /> • Manganese (Mn)—in the Tailing Liquid <br /> The analytical results for Pb in the residual tailing liquid would represent a potential human health <br /> risk from "long term exposure" in drinking water. However, the tailing liquid is contained within <br /> the EPF (and likely significantly diluted via meteoric precipitation accumulation) and is proposed <br /> to be contained/managed throughout the course of the removal action. <br /> The analytical results for Mn in the crushed/milled waste rock and the tailing liquid, respectively, <br /> would also represent a potential human health risk from "long term exposure" in drinking water. <br /> Manganese, however, is subject to a Secondary Drinking Water Standard, and while contaminant <br /> levels exceeding the secondary MCLs may pose a potential risk to human health, manganese is <br /> primarily recognized as a contributor to potentially adverse aesthetic effects(e.g., odor, taste, and <br /> color) and to potentially adverse technical effects (e.g., corrosion and staining). <br /> Given the non-presence of an immediately proximal groundwater aquifer system and the lack of <br /> potable water supply wells within or proximal to Hukill Gulch (an ephemeral drainage), as well as <br /> the significant distance (e.g. in excess of Y.-mile) to the nearest receiving stream (Clear Creek), <br /> the net effect of either (or both) of these attributes (i.e., "aesthetic" or"technical'), particularly at <br /> the concentrations noted, can be considered negligible. <br /> DRMS Permit No. M2009-076 — Exhibit T provides a detailed discussion of the geologic setting <br /> of the Hukill Mill Site. In essence, the immediate locale exhibits a groundwater depression due <br /> to the drainage of the area facilitated by the Big Five Tunnel. The Hukill Mill Site has a nominal <br /> elevation (at the barrier wall) of approximately 8,320 ft. above mean sea level (amsl); whereas, <br /> the Big Five Tunnel invert elevation at this location is at approximately 7,600 ft. amsl, (m/1), <br /> indicative of an approximately 720-ft. (m/1) elevation differential. <br /> The Big Five Tunnel discharge is subject to treatment(at the Argo treatment plant)prior to release <br /> to Clear Creek, at a location approximately 3/4--mile south-southeast of the Hukill Mill Site. Thus, <br /> the potential for adverse impact to either surface water or localized groundwater(if present)from <br /> any de minimis release at the site can be considered to be negligible to non-existent. <br /> Based on the foregoing, and given the site specific conditions at the Hukill Mill Site (e.g., with the <br /> proximal area being drained by the Big Five Tunnel, present at approximately 720 ft. (m/1) <br /> vertically below the Hukill Mill Site EPF nominal surface elevation of 8,320 ft. amsl), the non- <br /> authorized waste rock materials do not warrant special consideration per se. Nevertheless, VRI <br /> will ensure that all such materials are at all times contained within the designated footprint area <br /> of the upgradient portion of the EPF throughout the conduct of the removal action. <br /> 7 <br />