2021-05-12_REVISION - M2012032 (2)

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GLIRAY SILVER MINES 2. Section 3.1 states that the Oil and Grease sample results have not yet been received back from the lab. Please provide the Division with the results and a narrative once received. All G W-4 and S W-22 analytical results are presented in Attachments 2 through 4. As discussed in the revision request and adequacy review response extension request,organic material was noted in GW-4 during the development of the well. Initially this material was thought to be a small amount of drilling- related fluid from the drill rig. However repeated attempts to clean the well were not effective, leading OSMI to contact DRMS. DRMS requested analysis for DRO, GRO, MTBE, BTEX, and Oil and Grease. Oil and Grease results that had not been received are attached(Table 1)and generally reflect DRO results. DRO(C10-C28)was detected in GW-4 at 8.4 mg/L and SW-22 at 0.3 mg/L(an estimated value below the practical quantification limit). Oil and Grease was detected in GW-4 at 6.6 mg/L and was not detected at SW-22. Since the extension request OSMI engaged third party consultant Geosyntec of Denver,to recommend analyses based on constituents in Table A of Regulation 41 that might be reasonably expected in historic machine shop waste or modem drilling fluid. Based on Geosyntec's recommendation(Attachment 5). OSMI sampled GW-4 for the recommended constituents. Results were overwhelmingly below detection limits. Di-n-butyl phthalate was detected at 2.1 ug/L(J), which has a standard of 700 ug/L. Bis(2- ethylhexyl)phthalate was detected at 5.2 ug/L with no standard. OSMI has performed monthly sampling SW-22 for DRO on a visually contingent basis to evaluate the potential for organics impacts in Sneffels Creek under the sheen rule(40 CFR 1 10). No sheen has been observed in SW-22,and therefore no laboratory analyses have been run OSMI has notified the division of these results by letter within 15 days of the visual monitoring event. 3. Provide the rationale as to why the proposed location of GW-4R was selected. Provide evaluations regarding geology, historic use of the area, and groundwater flow rate and direction and how these compare to the original GW-4 location. Because a well cannot be placed in the same vicinity as GW-4 without risking additional intersection of historic, ambient, organic rich groundwater. Given the following, OSMI proposes the Pond 3 is best monitored under already required sampling at Outfall 002A under C00000003 the results of which will be included in quarterly and annual reporting. • Pond 3 was excavated to bedrock. • Pond 3 is a polishing step, the water in Pond 3 is expected to be of high quality with the primary treatments occurring upgradient in ponds that are monitored with ground water wells. • Mine discharge is currently generally of higher quality than groundwater prior to treatment. 2 1 P a g e