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Ouray Silver Mines, Inc. 1900 Main St. Unit 1 t PO Box 564 Ouray, CO 81427 f I SILL ER 11111NIE To: Colorado Division of Reclamation. Mining K Safety 1313 Sherman Street, Rm 215 Denv er, CO 80203 From: Brian K. Briggs, P.E., Chief Executive Officer Date: August 14, 2021 Subject: PAR Response; Revenue Mine, Technical Revision No. 12 to DRMS 1 12(d) Mining Permit# M2012-032 Dear Mr. West. Ouray Silver Mines Inc. (OSMI) has completed the study of historic organic materials found in monitoring well GW-4 as discussed in the preliminary adequacy review (PAR) regarding the application for Technical Revision 12 to Permit M2012-032 for the Revenue Mine(also known as the Revenue- Virginius Mine). OSMI requested and received, several extensions to complete sampling and prepare this response. As presented in the TR12 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 OSM1 to both contact DRMS and to question the drill rig as a source. Archeological reports. provided under confidential cover in the TR 12 request revealed a historic machine shop in the vicinity of the well as a likely source. In this response OSMI requests to plug and abandon GW-4 based on the lack of regulated constituents above regulatory thresholds. OSMI also proposes monthty visual leak inspection of the northern edge of Pond 3 in lieu of drilling a replacement well for GW-4. Each of these proposals are discussed in addition detail below, followed by written responses to the thirteen items in the TR12 PAR. Abandonment of GW-4 The only constituent detected above groundwater standards in GW-4 was Bis(2-ethylhexyl)phthalate, also known as Ethylhexyl phthalate(BIS-2)or DEHP. However,the DEHP standard is below Practical Quantification Limits(PQLs) which are used to regulate activities(C.R.S. 41 5 (C)(4)). All detections of DEHP were below the lab PQL of 18.6 and below the State PQL (CDPHE Clean Water Policy 6) and are therefore below the regulatory threshold. Given this, and the lack of sheen expression in surface water, OSMI proposes to plug and abandon GW-4 and cease visually contingent monitoring at SW-22. Initially DRMS requested analysis for DRO, GRO, MTBE, BTEX, and Oil and Grease in GW-4 and SW- 22 (Table 1 in Attachment 2). DRO(CIO-C28) was detected in GW-4 at 8.4 im.;/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. Because DRO was detected but no regulated constituent identified, DRMS asked for additional analyses to identify potential impacts of the GW'-4 well organics (results presented in Tables 2 and 3 of Attachment 2, with laboratory reports in Attachment 3)and visually contingent monitoring of the SW-22 under the",peen rule'(inspections are presented in Attachment 4). Phone:(970)325-9830 ♦ Fax:(970)325-9824