2021-05-12_REVISION - M2012032 (2)

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GeosynteO' 13 South Tejon Street, Floor Colorado Springs,Colorado PH 727.647.1451 consultants www.geosyntec.com Memorandum Date: April 8, 2021 To: Todd Jesse, Ouray Silver Mine Copies to: Poppy Staub, Geosyntec Consultants Dave Folkes, Geosyntec Consultants Briana Greer, Solid Solution Geosciences, LLC From: David Riotte, Geosyntec Oakland Subject: GW-4 Sampling Plan Sampling Locations GW-4 and SW-22 Ouray Silver Mine The purpose of this memorandum is to present a summary of the recent sampling event conducted at groundwater monitoring well GW-4 and surface water sampling location SW-22 at the Revenue- Virginius Mine (the Mine), owned and operated by Ouray Silver Mines Inc. This memorandum also includes a recommended sampling strategy to evaluate those results. On February 15, 2021, groundwater and surface water samples were collected from GW-4 and SW-22, respectively. The samples were analyzed for gasoline range organics (GRO), specifically total volatile hydrocarbons (TVH) C6 to C10, as well as benzene, ethylbenzene, m-p-xylene, o- xylene, toluene, and methyl tert butyl ether (MTBE). The samples were also analyzed for diesel range organics (DRO), specifically, total petroleum hydrocarbons (TPH) C I 0 to C28. The laboratory results are provided as Attachment 1 to this memorandum. Based on the analytical results, MTBE and the GRO parameters were not detected at concentrations above the laboratory method detection limit in GW-4 or SW-22. However, TPH C10 to C28 (DRO) was detected in GW-4 and SW-22 at a concentration of 8.44 milligrams per liter(mg/L) and 0.3J' mg/L, respectively. The Mine reviewed the historical information to evaluate the potential origin of DRO in GW-4. The historical information indicated that a machine shop, was located just upgradient of GW-4. ' J indicates that the results is between the method detection limit and the practical quantifiable limit. GW-4 SW22 Sampling Plan RevFINAL