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f k H-A) CVL4 ER A41NES, <br /> Since the extension request OSMI engaged third party consultant Geosv ntec of Denver, to recommend <br /> analyses based on constituents in 'fable A of Regulation 41 that might he reasonably expected in historic <br /> machnnc ,hop wa,tc or modern drilling fluid. Based on Geo,v ntec', recommendation (Attachment y). <br /> OSMI sampled G\ -4 for the recommended constituents. Results were overwhelmingly below detection <br /> limits. Di-n-buty I phthalate was detected in a single anal}sis at 2.1 u(','L 0), with a groundwater standard <br /> of 700 ugiL. Bis(2-ethylhexyl)phthalate also known as DFl`IP was detected at 5.2 ug/L, an estimated <br /> value helovv the PQL. Because of the estimated value associated with DEHP, OSMI performed additional <br /> analysis including a blank and duplicate, ho\\ever the blank bottle broke during shipping. Therefore, <br /> OSMI undertook a third sampling event. Throughout the sampling events DEHP concentration varied <br /> from non-detect to I 1 ug/L (Attachments 2 and 3) <br /> OSNII has performed monthly sampling at SW-22 for DRO on a v isually contingent basis to evaluate the <br /> potential for organics impacts in Sneffels Creek Under the sheen rule(40 CFR 110). No sheen has been <br /> observed in SW-22, and therefore no laboratory analyses have been run. OSMI has notified the division <br /> of these results by letter within 15 days of the visual monitoring event. <br /> 3. Provide the rcitionule uv to whY the proposed locwton of'Git'-4R lrus ve/ected. Provide <br /> crcillultions rcgtilWing geologt% historic- use of'thc urcu, cincl gi-olinchrutcr flow irate and direction <br /> rind hoer theve rotnhcu-e to the origincil GW-4 locution. <br /> Response: OSMI no longer requests GW'-dR as a monitoring well. A well cannot be placed in the <br /> same y icinity as GW-4 without risking additional intersection of historic. ambient, organic rich <br /> groundwater. Given the tolloyy ing, OSMI proposes the Pond 3 is best monitored under already <br /> required sampling at Outfall 002A under C00000003 and monthly v isual inspection of the <br /> northern pond edge, results will be included in quarterly and annual reporting <br /> • Pond 3 was excavated to bedrock. During Pond 3 commissioning and leak testing, leaks <br /> were identified through a visible surface expression on the downgradient (north) edge of <br /> Pond 3. <br /> • Pond 3 is a polishing step, the water in Pond 3 is expected to be of high quality with the <br /> primary treatments occurring upgradient in ponds that are monitored with ground water <br /> wells. <br /> • Mine discharge is currently generally of higher quality than groundwater prior to <br /> treatment. <br /> • Pond ) is a lined facility whose discharge is monitored at Outfall 002A and regulated by <br /> the Colorado Department of Public Health and Environment. <br /> 4. They gocil for GIF-4 recltiire d br TR-10 trus to f tccilitule they monitoring of the pcissive inciter <br /> trccihncnt v;Yslen1 vpecificolIv for inipuets to woler dttcilit_v. Given unit pond 3 is lined uncl now ci <br /> vurfuce divclhurriritlg fucilit'V. Gbh'-4 nvottld serve cis a lecik detection vt'stetn, (in Environinenicil <br /> Pi-oteclion EUcllitl' (F_PF). Whot lroitld he the proposed repluceinent E.PEto ensttre thin pond 3 <br /> is,f ttncl ioning come c it t,if'G bi'--1 is to be abandoned.' <br /> 41 - <br />