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West Elk Mine <br />and 3E in Exhibit 66 identify the watersheds in the Sylvester Gulch Facilities Area. Map 54B <br />shows the ditch and culvert locations in conjunction with the Sylvester Gulch Facilities Area. The <br />following sections deal with each specific hydrologic protection measure. <br />Studies have been completed to estimate the peak runoff and flood volume for storms having <br />specific recunence intervals for the West Elk Mine azea. Exhibit 44 is the report used in the design <br />of the original sedimentation ponds (MB-1, MB-2, and MB-3), ditches and culverts by Merrick and <br />Company. This report was submitted to the State Engineer for the approval of the three <br />sedimentation ponds MB-1, the original MB-2, and MB-3, and the freshwater pond, FW-1. <br />Approval was received on February 3, 1981, and is included in Exhibit 45. Exhibit 66 contains the <br />new designs for ponds MB-ZR and MB-3. The Exhibit 43 and Exhibit 44 designs are no longer <br />valid for these ponds. Exhibit 66 contains an as-built drawing that reflects the addition of a dike in <br />the pond to create a north and south cell. However, the drawings included in Exhibit 43 do <br />accurately reflect other structures associated with MB-1 (i.e., the primary and emergency <br />spillways). Exhibit 66 also contains the design information for SG-1 located at the Sylvester Gulch <br />Facilities Area. See Exhibit 46 for the original design specifications and for the current designs for <br />MB-4, Unit Train Loadout Sedimentation Pond. Pond MB-4 was relocated in 1998 from the east <br />side of the train load-out to an azea west of the load-out between two sets of train tracks. The <br />relocated sediment pond is constructed of concrete and is preceded by an oil skimmer and a <br />sediment trap. Design criteria for Ponds MB-5 aze contained in Exhibit 47, and an as-built survey is <br />contained in Exhibit 66. Ponds MB-2 and MB-6 no longer exist and were replaced by new pond <br />MB-2R. Design criteria for the Refuse Pile Expansion (RPE) pond, designated the "RPE" pond, are <br />included in Exhibit 70. <br />Hvdrologic Design ofRunoffPonds <br />Seven storm drainage sediment control structures are used as settling ponds for storm water runoff <br />from the mine site. These ponds have been designed according to CDMG regulations (see Exhibits <br />43, 47, 66, and 70). <br />These ponds have been constructed to contain an estimated three yeazs of sediment storage volume <br />and a runoff storage volume resulting from the 10-yeaz 24-hour rainfall event. Sediment will be <br />excavated, allowing for addifional storage, when sediment has reached the maximum storage <br />capacity. Sediment volumes aze estimated by a quarterly visual evaluation. The smaller ponds MB- <br />3, MB-4, and MB-5, usually dry during a portion of the yeaz and sediment levels, relative to the <br />primary dischazge structure elevations, can be visually detemuned. The lazger ponds usually <br />contain water and visual evaluations aze less accurate. These ponds, MB-1, MB-2R, and SG-1 will <br />be surveyed at least every three yeazs to determine the actual sediment levels. <br />The CDMG requirements for the emergency spillway sizing aze 25-yeaz, 24-hour storm flows, or <br />100-year, 24-hour storm flows, depending on the size of the structure. The spillways for MB-3, <br />MB-4 and MB-5 were sized based on the 25-yeaz, 24-hour storm, while MB-1, MB-2R, and SG-1 <br />were sized for the 100-yeaz, 24-hour storm event in accordance with the requirements of the State <br />Engineer. Drainage basins for the spillway sizing aze shown on Map 54, Sediment and Drainage <br />• Control Facilities. The RPE pond has been designed to completely contain the runoff from a 100- <br />yeaz, 24-hour storm event. Designs aze included in Exhibit 70. <br />2.05-26 RevisedJvne 1005 PRI G <br />