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p' RULE 2 PERMITS <br /> :`"4,4 . 4041W14,14,1VFh 4,, 4,,,v, .'$41.00,0xa.,1?k:Tdly<A, F.044.;44^ tKbt v%44. <br /> estimated that in excess of one million cubic yards of unconsolidated material was down cut, <br /> slumped, and transported by Wilson Creek during spring 1984. An analysis of TSS during June, <br /> 1984 showed a concentration of 40,000 mg/1 in Wilson Creek. <br /> The spring runoff period is especially important in analyzing suspended sediment data. Both <br /> drainages showed tremendous increases in concentrations on May 27, 1975. These high values are <br /> probably a result of a storm event occurring within or just prior to the sampling period. <br /> Nevertheless, the values were not exceedingly high or even approaching values obtained in urban <br /> runoff studies. <br /> Data (see Exhibit 7A) collected by the USGS on Wilson Creek for the period October, 1979 <br /> through September, 1980 also show the tremendous seasonal variability. These data are presented <br /> in Table 2.04.7-23. Exact locations for both sample periods, the previous VTN and the current <br /> USGS studies, were assumed to be comparable. The USGS data encompass an entire year. Again <br /> the seasonal fluctuations are apparent and storm event related concentrations increase dramatically <br /> over the ambient periods. <br /> Storm events not only move surface particles through overland flow, but also create bottom scour <br /> which is reflected in the increases. Also, the 1980 data was collected during an exceptionally wet <br /> year compared to 1974-75. This is the prime cause for mean values being higher. The Colowyo <br /> Coal Company Permit Application contains information regarding sediment yield from the mine <br /> site proper to Streeter Gulch. These estimates of erosion using a rainfall factor of 30.0 were an <br /> average of 3.17 tons/acre/year broken down into component parts of undisturbed and disturbed <br /> areas. The total acres contributing drainage to Streeter Gulch were 1367 with a maximum of 181 <br /> acres being disturbed at any one time. Exhibit 7 contains this information. <br /> Striffler and Rhodes (1981) conducted field tests at eleven surface coal mines in Colorado to <br /> determine erodibility and- infiltration capacity. of reclaimed land and overburden piles at each <br /> mine. Their report "Hydrologic and Erosional Characteristics of Regraded Surface Coal Mined <br /> Land in Colorado" is briefly summarized here. The report is included in Exhibit 7 in its entirety. <br /> Striffler and Rhodes conducted field tests at the Colowyo Mine on six plots randomly selected and <br /> determined a mean soil loss of topsoil of 0.54 tons/acre/year. Overburden erosion was calculated <br /> at 3.66 tons/acre/year. These values are considerably less than those accepted by the Colorado <br /> Mined Land Reclamation Board. Field tests result in a calculated R-factor of 20.0 for use in <br /> the Universal Soil Loss Equation. This value is also considerably less than the values of 30.0 <br /> accepted by the CMLRB. <br /> Potential Impacts from Mining-Water Quantity <br /> General and Permit Areas <br /> The Colowyo surface mining activities are not expected to cause significant contamination, <br /> diminution, or interruption of any underground or surface sources of water in the general area of <br /> the mine. (Please refer to the Leonard Rice 1979 report found in Exhibit 7. For additional <br /> information) <br /> OP <br /> Rule 2 Permits 2.04-30 Revision Date: 12/20/19 <br /> Revision No.: TR-135 <br />