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• iii iiiiiiiiniiiiii <br />999 <br />MINED LAND RECLAMATION DIVISION <br />Depart menl of Natu rah Resources <br />13t 3 Snerman 51.. Roorn 215 <br />Denver. CCU 80203 <br />303 866-3567 <br />FAX 303 8328106 <br /> <br />STATE OF COLORADO <br />J ~ ~ C/~YJI/I7rr73 <br />OF CO~O~ <br />}r--) U <br />/R 76 <br />Foy Rorer <br />Governor <br />DATE: February 8, 1990 <br />T0: Michael J. Boyd <br />FROM: John T. Doerfer \1'I v <br />Fretl R Banta <br />Division Dvector <br />RE: Hydrologic Adequacy Review, Platte Yalley Pit, C & M Companies, <br />File No. M-89-120 <br />I have reviewed the hydrologic aspects of the above-referenced permit <br />application as you requested. The proposed mine is a relatively large <br />alluvial sand and gravel operation which utilizes dewatering, It is adjacent <br />to the South Platte River near Brighton and the post-mining land use is a <br />lined water supply reservoir, My comments following review are provided below. <br />Exhibit F - Reclamation Plan <br />The reclamation plan proposes to seal the ponds created by mining by <br />constructing a compacted clay and overburden liner on the pit side slopes. <br />a. What is the source of clay referenced on cross-section B-B' and <br />shown on Exhibit F? Is this available on site? <br />b. Will the clay and overburden be placed in a random backfill or laid <br />in discrete homogenous layers? <br />c. What design specifications, as to permeability, thickness, <br />compaction, moisture density, Atterberg limits, and construction <br />procedures, are to be included in liner design? <br />d. Please clarify the depth and width dimensions of the liner key cut <br />into bedrock as shown on cross-section B-B'. <br />2. A dike is proposed to separate Cells A and B. <br />a. What is the expected water surface elevation in each cell? <br />b. What compaction criteria will be used during construction? Will <br />clay be incorporated into the dike similar to the liner? What is <br />the expected permeability of the dike material? <br />c. The dike is shown as a straight line structure. The Division <br />recommends you consider modifying dike configuration to round the <br />corners of the lakes, include an "S-shaped" curve in the dike, <br />andlor decrease side-slope angle at one-point in the dike to create <br />shallows which may improve fish habitat. <br />