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<br /> <br />Letter to Kurt Nielsen 2 May 23. 1999 <br />Specification for Structural Fills. Please affirm [his assumption. The specification for [he 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 the DMG. <br />b. Specify testing methods and testing frequencies for the following pond embankment fill parameters: <br />grain size distribution, At[erberg limits, and moisture density relationships (Proctor testing). <br />c. Provide a commitment to issue to DIvIG 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 [he 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 the 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 State Engineer's regulations as a guide, the 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 riprap specifications that will demonstrate that the 50-year <br />fined can be passed through the spillway if the flood were to occur when the pond is full. Also pro:~ide a <br />statement that the pond will not be used to store water except for the three days following a rain event or in <br />the event of a large spill in the 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 [o the pond during a <br />100-year storm will be limited [o 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 the <br />100-year storm around the site. <br />8. 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 no[ meet the specifications provided for the pond embankment fill. Will off site soils <br />be used in dam construction? [f 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 (3`d Edition) specifies a <br />maximum upstream slope of 2.S:1 for the type of soils specified for the storm water pond embankment <br />(using the prudent assumption that [here will be leakage past the single geomembrane pond liner into the <br />embankment fill). It is the DMG's position that the design should be modified to incorporate a 2.7:1 <br />inslope. This will necessitate resizing of the pond to maintain the same storage capacity that would be <br />available with a 2: l inslope. <br />10. General Specification GC- 13 - Geosynthetic 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 lame spill, the liner is <br />