2011-09-09_REVISION - M1981185 (43)

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Mr. Wallace H. Erickson Response to August 22, 2011 Cazier Memorandum September 9, 2011 Page 12 13. The pond will be constructed in accordance with the following design specifications: • Obtain a water storage permit from the Division of Water Resources; • Drill 6 geotechnical borings at the locations shown on Figure 6.5 -1 to 20 feet deep or refusal to characterize foundation characteristics; • Conduct a geotechnical stability assessment of slopes steeper than 2(H):1(V); • The pond will be approximately 320 feet long, 100 feet wide and less than 8 feet deep; • The pond is designed with a a liner constructed from onsite cohesive soils or an appropriate geosynthetic liner; • Side slopes will be approximately 2:1; • The pond holding capacity is approximately 1.1 acre foot. (Detailed drawings are located at Attachment D -6, Figure D -1); • Water will be diverted from a stilling basin to be constructed at the Idaho Spring. Attachment D -6, Figure D -1; • A 12 -inch pipe (gravity drained) will divert water from the Spring when authorized; • Water will pumped and returned from the pond as necessary in accordance with Division of Water Resource water right stipulations and requirements using a 4 -inch discharge pipe; and, • Returned water will be discharged to a rip rap protected Idaho Spring channel. The two pipelines are illustrated on Attachment D -6, Figure D -1. Adequacy Issue No. 18. Page 4, Construction. Item 15 discusses the proposed gravity and pressurized HDPE pipelines will be in a trench not less than 18 inches deep. DRMS is concerned with both the gravity and pressure lines freezing during the winter and causing the pipe to rupture. This would lead to unintended subsurface discharges, possibly impacting the hydrologic balance and/or stability of roads and slopes in the vicinity of the pipeline. Please provide some discussion on precautions to be taken to prevent pipe freezing. Include an estimate of frost depth in the area. Response to Adequacy Issue No. 18. La Plata County design criteria specify a frost depth of 32 inches. Wildcat estimates frost depth in the area is less than four feet. Wildcat proposes burying the pipelines to a depth of no less than four feet, which is consistent with La Plata County recommended design criteria. Wildcat will modify Item 15 in the Construction section at Page 4 of Attachment D -6, as follows: DEN 97,591,786v1 9 -9 -11 GREENBERG TRAURIG, LLP • ATTORNEYS AT LAW • WWW.GTLAW.COM