2016-09-26_REVISION - M2004031 (4)

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Rationale for Recommendation to Approve Page 17 September 26, 2016 In this matter there is no requirement to differentiate between groundwater and surface water for DWR compliance purposes, only total quantity. Therefore, AM -01 demonstrates compliance with Section 34-32.5-116(4)(h) C.R.S., and Rule 3.1.6(1)(a). ll. Comment that the spillway elevation of 5040.8 feet is 4.8 feet higher thcur the elevation of the Orr drain outlet to the reservoir, and could letrd to reverse flows if/ivlren the reservoir is filled. (Equity Funding LLC— second comment period) The design high water elevation of the reservoir is 5036.0 feet. 5036.0 feet is also the design elevation of the Orr drain outlet, and the design elevation of the proposed reservoir drain structure, which will consist of three 24 inch diameter pipes, intended to convey flows from the Orr drain, and any other sources, from the reservoir back to the Platte River. Under normal operating conditions the elevation of the reservoir should never exceed 5036.0 feet and therefore reverse flow through the drain from the inlet, set at 5036.5 feet should not occur. During a major flood event which overwhelms the reservoir drain and causes the reservoir to exceed the design high water level, reverse flow through the drain is to be prevented by raising the drain inlet utilizing the elevation control "stop -blocks". The emergency pillway referred to in this comment was designed to meet the requirements of, and approved by, the Urban Drainage District. This emergency spillway structure is intended for use only as a failsafe during a major flood event to prevent head -cutting from flood flows from the reservoir back to the South Platte River, which could potentially lead to the failure of the pit wall and capture of the South Platte River. The elevation of the ground surface at MW -2, adjacent to the Orr property in the vicinity of the Orr drain, was surveyed at 5041.59' (0.79 feet higher than the spillway elevation). Because the spillway elevation is below the existing ground elevation of the Orr property in the vicinity of the drain inlet, the impact from any reverse flow from the drain structure, if it occurred, would be expected to be minimal and localized to the immediate excavated area of the drain inlet on the operator's property if the drain inlet is properly closed off. Conclusion Therefore, on September 26, 2016, the Office determined the application satisfied the requirements of Section 34-32.5-115(4) C.R.S., and issued its recommendation to approve AM - 01 to the Hazeltine Pit, Permit No. M-2004-031, over public objections.