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Ouray Silver Mines Inc. <br /> Technical Revision 11 March 26, 2020 <br /> TR08—Allowed OSMI to infiltrate of mine discharge to groundwater following passive <br /> treatment in a sulfate reducing bioreactor. <br /> 2 PROJECT DESCRIPTION <br /> The following Project Description provides more detailed information of each of the proposed <br /> revisions as well as supporting documentation, where necessary. <br /> 2.1 Water Monitoring Program <br /> The mine is proposing changes intended to improve the utility of water quality information. All <br /> sampling locations at the mine are presented on Table 1. <br /> OSMI is expanding its voluntary surface water sampling program to better its understanding of <br /> impacts to Sneffels Creek. Samples will be collected during the three main flow periods: high <br /> flow, low flow, and the rising limb of flow. In addition to the surface water locations currently <br /> sampled, SW-3, SW-4, SW-15, and SW-16,the mine will also sample the following shown on <br /> Figure 1: <br /> • The Atlas Drainage (SW-1); <br /> • Sneffels Creek downstream of the confluence with the Governor Basin drainage(SW-2); <br /> and <br /> • Sneffels Creek upstream of the confluence with the Governor Basin drainage and <br /> downstream of the Walker/Ruby Trust Mine(SW-17). <br /> OSMI proposes four new underground locations along the Revenue Tunnel ditch as shown on <br /> Figure 2. OSMI is updating the underground water monitoring locations to better capture <br /> changes in water quality and quantity due to mining activities once the mine becomes <br /> operational. Currently, underground sampling occurs at six locations (UG-1 through UG-6), <br /> which were selected to characterize water associated with the major vein sets intersecting the <br /> Revenue Tunnel. Changes to the sampling program are summarized on Table 2 and below: <br /> • Sampling at UG-1 and UG-3 will be discontinued; <br /> • Sampling at UG-4 will change from quarterly to annual during high flow due to a lack of <br /> flow in the western end of the ditch; <br /> • New locations UG-7 and UG-9 will be established as voluntary sampling locations; <br /> • New location UG-8 will be sampled quarterly; and <br /> • New location UG-10 will be sampled annually. <br /> There are no proposed changes to UG-2, UG-5, and UG-6. <br /> OSMI is proposing one change to the groundwater parameter list with standards. Currently, <br /> dissolved ortho phosphorus is a listed parameter. The mine would like to remove this parameter <br /> and replace it with dissolved total phosphorus as shown on Table 3 for two reasons: <br /> • Colorado surface water standards are based on total phosphorus not ortho phosphorus; <br /> and <br /> • Due to ortho phosphorus' short hold time (48 hours), difficulty getting to and from the <br /> mine in winter months, and shipping limitations in the area, daily shipping typically <br /> Page 4 of 8 <br />