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DocuSign Envelope ID: 1 AACF3AD-1 B8E-4F1 13-13805-054D9472D4E9 <br /> TRI-STATE <br /> October 20, 2022 <br /> Page 3 <br /> Reach 2, Station 0+00 to 7+30 was constructed in 2011. As shown on the as-built certification submitted <br /> to the Division in the 2011 Annual Reclamation Report, the as-built demonstrates that Reach 2 was constructed <br /> to meet and/or exceed the design configuration of the channel. <br /> EPI and EP2 Stock Ponds <br /> The Final East Pit Ditch was modeled, designed, and constructed with two in-channel stock ponds, EP 1 <br /> and EP2 respectively. The stock ponds are designed and constructed as an additional layer of protection for the <br /> watershed. The typical design of the stock ponds(Figure 2.05-6)was less than 3-acre feet in volume,but typically <br /> less than 2-acre feet. The top of structure width was at least 10 feet, and the minimum open channel spillway <br /> width was 8 feet and grass lined. <br /> EP1 as shown on the as-built(Exhibit 7 Attachment 5 Map) was constructed with a total capacity of 1.3- <br /> acre feet. The top of the structure width is approximately 17 feet and the open channel spillway width is 17 feet. <br /> In 2021, an 8-inch straight pipe was installed in EP 1, two feet below the emergency spillway elevation, to allow <br /> the stock pond to passively discharge to maintain capacity within the pond. <br /> EP2 as shown on the as-built(Exhibit 7 Attachment 5 Map) was constructed with a total capacity of 2.4- <br /> acre feet. The top of structure width is approximately 40 feet and the open channel spillway width is 25 feet. <br /> Site Management <br /> Colowyo is continuously engaged in properly managing all post mine channels, stock ponds, and sediment <br /> ponds. Colowyo had identified earlier in 2022 that sediment was building up in Prospect Pond and had engaged <br /> a contractor to dredge the pond. During the week prior to the October 2, 2022 precipitation event, Colowyo's <br /> contractor removed all accumulated sediment from the pond and had completed the work on September 30, 2022. <br /> The Colowyo Mine site received 2.94 inches of precipitation from September 13, 2022 to October 1, 2022. <br /> This significant precipitation contributed water to EP1 and EP2 stock ponds prior to October 2, 2022. EP1 has <br /> a passive discharge system as previously noted (8-inch CMP) that had drained down the stock pond prior to the <br /> October 2 event. Colowyo was internally working on redesigning EP2 to install a passive drain system but had <br /> yet to finish the design work. Given this, Colowyo had identified that EP2 was full of water from these storm <br /> events and was actively pumping down EP2 to create additional capacity the week prior to the October 2, 2022 <br /> precipitation event. The pump was still in place when the Division inspected the EP2 stock pond on October 4, <br /> 2022 and is documented in the Division's photographs included in the October 4, 2022 inspection report. <br /> Further, in accordance with Rule 4.05.9(17), both stock ponds were inspected on September 14, 2022, as <br /> part of the quarterly impoundment inspection. Neither stock pond was noted to have any maintenance <br /> requirements or stability concerns during the September 14 inspection. This was documented on September 15, <br /> A Touchstone Energy <br /> Cooperative 1� <br />