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<br />RESPONSE TO DMG COMMENTS REGARDING POND B <br />I.0 POND B HYDROLOGY CHECK <br />In response to comments concerning Pond B From the Department of Mining and Geology (DMG) and at <br />the request of Twentymile Coal Company (TCC), Montgomery Watson has provided the following: <br />• Pond B has been evaluated as follows: <br />Pond B watershed has been reviewed and divided into appropriate subwatersheds <br />delineating reclamation, disturbed and undisturbed areas. subwatersheds have been <br />assigned hydrological and sedimentological parameters. This information is provided. <br />Pond B was evaluated as a single pond. <br />Using pond as-built information from the Epp survey and 1999 survey information <br />provided by TCC, SEDCAD4 modeling was utilized to predict Pond B will meet water <br />quality requirements when the 10-year, 24-hour storm even[ is applied to the watershed. <br />Also, utilizing information from the Epp survey and as-built information provided by <br />TCC, SEDCAD4 modeling was utilized to show that the Pond B spillway structure can <br />safely pass the peak flow from the 25-year, 24-hour storm event. <br />Pond B was modeled with a single open notch spillway for both the 10-year and 25-year <br />storm events. <br />Modeling accounts for the fact that the pond always has water by setting the permanent <br />pond water elevation at the invert of the open notch spillway. <br />• SEDCAD4 computer printouts are provided along with Map 9B, which shows the delineated watersheds. <br /> <br />