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-7- <br />The disturbance of these overburden and interburden materials could impact the <br />quality of the ground and surface water, and affect the suitability of the <br />overburden as a plant growth medium. <br />The overlying and underlying strata of the Hoyle coal seam and the overlying <br />strata of the Sudduth coal seam will be adequately mixed within the spoils <br />during mining. The strata underlying the Sudduth seam is a shale. The <br />weathering of this shale will be minimal due to the low permeability of the <br />strata and the limited exposure at the pit bottom. Thus, the contribution of <br />dissolved solids to the ground water system will be minimal. Most of the coal <br />was removed from the site during mining and thus reduced the potential <br />toxicity. <br />Given the proposed operations plan for the Bourg Mine, overburden strata which <br />have toxic constituents will be adequately mixed and diluted within the <br />spoils. The multiple handling of the overburden will provide this mixing, <br />thus reducing the potential that these elements will affect plant growth. <br />Oxidized coal from outcrops will have to be selectively handled. To reduce <br />the toxic effects of the oxidized coal, this material should be placed above <br />the pre-existing water table and out of the root zone of plants. The operator <br />has supplied a map showing the pre-existing ground water levels, Figure 7. <br />This map, in conjunction with a map of the reclaimed surface contour, will <br />delineate those areas which would be suitable for isolating the oxidized coal. <br />The operation is in compliance with the requirements of this section. <br />V. Hydrologic Balance: Surface Water - Rules 2.04.5, 2.04.7, 2.05.3, <br />. an . <br />Hydrologic information for the Bourg Strip Mine is located in section I, pages <br />1 through 31, and supporting information and designs are located in Appendix A <br />of the application. A detailed description of the surface water resources and <br />the impacts of mining on surface water can be found in Section IX titled <br />"Probable Hydrologic Consequences of Mining and Cumulative Hydrologic Impacts <br />Study" of this permit document. <br />Increased surface water sediment yields generated by mining would ordinarily <br />cause a notable impact on the quality of water in Mann Draw. Increases in <br />suspended solids from disturbed runoff will be mitigated through the use of <br />sediment ponds. <br />The sediment control system which is intended to reduce affected water <br />sediment loads was designed in accordance with Rule 4.05. Runoff volumes were <br />calculated using procedures outlined in Chapter 10 of the National Engineering <br />Handbook, Section 4, to ensure that the ponds could detain the runoff produced <br />from a 10-year, 24-hour precipitation event. Peak rates of runoff were <br />calculated using the method outlined in Procedures for Determining Peak Flows <br />in Colorado, SC S, 1977. Using these rates, emergency spi ways were esigne <br />or~5=year, 24-hour event. Although some questions arose over the <br />steepness of the spillway channel, it was decided that the design was in <br />compliance, since the design peak flow was not routed and did not consider the <br />effects of attenuation due to pond storage. <br />