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<br /> <br />Letter to Kurt Nielsen 2 Mav 23, 1999 <br />Specification for Structural Fills. Please affirm this assumption. The specification for the pond <br />embankment fill must be amended to incorporate the following: <br />a. A statement that plans and specifications cannot be changed without prior approval of [he DMG. <br />b. Specify testing methods and testing frequencies for the following pond zmbankment fill parameters: <br />grain size distribution, Atterberg limits, and moisture density relationships (Proctor tes'ting). <br />c. Provide a commitment to issue to DMG an engineer's certification upon completion of pond <br />installation that the facility was constructed in accordance with the approved design and <br />specifications. The certification must accompany a construction report including a tabulation of <br />tests conducted and testing results. <br />5. Provide a commitment to build the storm water pond as the first construction priority at the Piceance <br />processing facility location. This does not mean that processing facility construction cannot proceed <br />concurrently with pond construction, but that [he pond must be built and ready to receive runoff from the <br />disturbed area as quickly as possible once construction begins. <br />6. Using the Colorado Slate Engineer's regulations as a guide, [he storm water pond would likely be <br />classified as a minor class III impoundment requiring a spillway to pass the 50-year flood. Please provide <br />spillway capacity calculations and a design with rinr.~p snecifica[ions that will dzmonstrate [hat the 50-year <br />rood can be passed through the spillway if [he Flood . zre to r•c:::rwhen t`c pond is full. Also provide a <br />statement that the pond will not be used to store water except for [he three days following a rain event or in <br />the event of a large spill in [he plant area. <br />7. The DMG concurs that the calculations used to size the storm water pond are conservative. <br />However, it is not clear from the drawings provided [hat the drainage area contributing to the pond during a <br />100-year storm will be limited to the 7-acre plant site. Please provide a demonstration that the perimeter of <br />the plant site is at a drainage divide or that the perimeter will be adequately bermed to divert flows from [he <br />100-year storm around the site. <br />S. It is stated in the geotechnical report provided in support of the pond design that on site soils are less <br />desirable for use as compacted structural fill than an imported non-expansive granular material. The report <br />further indicates that all non-bedrock soils tested class as CL soils under the Unified Soil Classification <br />System. CL soils do not meet the specifications provided for the pond embankment fill. Will off site soils <br />be used in dam construction? If on site soils will be used, has a suitable borrow area been identified? <br />9. Table 6.5 from the Bureau of Reclamation's Design of Small Dams (3rd Edition) specifies a <br />maximum upstream slope of 2.5:1 for the type of soils specified for the storm water pond embankment <br />(using [he prudent assumption that there will be leakage past [he single geomzmbrane pond liner into [he <br />embankment fill). It is the DMG's position that the design should be modified to incorporate a 2.5:1 <br />inslope. This will necessitate resizing of the pond to maintain the same storage capacity that would be <br />available with a 2:1 inslope. <br />10. General Specification GC-13 - Geosyn[hetic Liner, was provided in support of the storm water pond <br />design. Even though the pond will not store process solution except in the event of a large spill, the liner is <br />