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i III IIIIIIIIIIIII III 999 STATE OF COLORf~DO DIVISION OF MINERALS ANU GEOLOGY I rrp.nlrm ..1 ..I N.n ui al Rr.~nin i . I tl t lhrimai~ Ct Ranni _'I'r I~rn.~, t'olnoulii .'IU!uf I'hnr~~: 1 In H IILO Vlf~.- I \\~ i tlt f i P. '~J 111 uL December 5, 1996 Mr. Juan Garcia Colowyo Coal Co. L.P. 5731 State Highway 13 Meeker, CO 81641 RE: Colowyo Coal Mine (C-81-019) Design Alternatives for Sediment Ponds Dear Mr. Garcia, I~~I~ I)EPARTMEtJT OF NATURAL RESOURCE Hny Rrimri .r~rrnr„ 1.~~~,~~, ti I,r~mrr,ld aer hacl H Long rnwr,rr,~, nn~~r L.r The Division received the design alternatives for the Gulch A Pond submitted by TerraMatrix. Included in the design is a description of the hydrologic, hydraulic, and sediment input parameters used to analyze the Gulch A Pond. It is my understanding that many of the parameters used in the Gulch A design will be used in modeling the remaining sediment ponds. Per our recent discussions, the Division has one concern regarding the particle size distribution used in the SEDCAD+ Model. The particle size distribution used by Colowyo can be broken down as follows; 52% Fine Sand 31% Silt 17% Clay Using the soil triangle of the basic soil textural classes developed by the U.S. Soil Conservation Service, this material is classed as Loam and nearly Sandy Loam. Please see attached soil classification chart for reference. The Division reviewed the soils resource information located in the permit. Within the Gulch A watershed boundary, may of the soils are classified as Clay Loam. [n particular, Table 3 page 2.04.9-14 depicts the chemical and physical da[a for the soils at the Colowyo Mine. This table breaks down the percent sand, silt and clay of the typical profiles as follows; 7%-58% Fine Sand (median 23%) 25%-54% Silt (median 35%) 16%-58% Clay (median 39%)