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1.0 POND D HYDROLOGY CHECK <br />• [n response to comments concerning Pond D of the midterm review for Twentymile Coal Company (TCC) <br />and at the request of TCC, Montgomery Watson has provided the following: <br />• A signed copy of the Epps survey for Pond D that will be provided to the DMG by TCC <br />under separate cover. <br />• Pond D has been evaluated as follows: <br />Pond D watershed has been reviewed and divided into appropriate subwatersheds <br />delineating various stages of reclamation and disturbances. Subwatersheds have been <br />assigned hydrological and sedimentological parameters. This information is provided. <br />Utilizing information From the Epps survey and as-built information provided by TCC, <br />SEDCAD 4 modeling shows that Pond D meets water quality requirements when the ]0- <br />year, 24-hour storm event is applied to the watershed. <br />Also, utilizing information from the Epps survey and as-built information provided by <br />TCC, SEDCAD 4 modeling shows that Pond D spillway structures can safely pass the <br />peak Flow from the 25-year, 24-hour storm even[. <br />Modeling accounts for base flow including mine pumping (O.Scfs), springs (0.2cfs) and <br />possible increase in mine pumping (0.2cfs). <br />Modeling accounts For the fact that the pond always has water by setting the permanent <br />pond water elevation slightly above the lowest hole in the riser. <br />SEDCAD 4 computer printouts are provided along with Map 9A, which shows the delineated <br />subwatersheds <br /> <br /> <br />D-I <br />