Laserfiche WebLink
drops below the 6,652.2 elevation. The "T" is the dewatering device, and discharging water <br />flows through the bottom of the "T" — this assures that "clean" water is discharged from LCSS to <br />• Pond 002. The 10 -year, 24 -hour peak elevation is 6,768.8 feet. <br />As noted above, the emergency spillway invert elevations are 6,665.0 and 6,655.0 for UCSS and <br />LCSS, respectively. Peak water levels for inflow from the 10 -year, 24 -hour storm events are less <br />than the invert elevations. These calculations indicate that in accordance with Rule 4.05.9(2)(b), <br />there is no discharge through the emergency spillway as the result of a 10 -year, 24 -hour storm event. <br />The calculated 25 -year, 24 -hour event peak discharge from the UCSS is 7.2 cfs (see Addendum <br />2.05.3- E2.E -2). The spillway invert is at the 6,665.0 foot elevation, while the peak stage in the <br />SEDCAD demonstration is at 6,665.3 feet. The top of the embankment is 6,667.0 feet. Both the <br />spillway crest and outslope will be protected with a rock riprap liner. The channel utility design (see <br />Addendum 2.05.3- E2.E -3) was used to size the rock riprap. Rock riprap size was determined using <br />the PADER (Pennsylvania Department of Environmental Resources, Stover, 1990) method. Given <br />the uncertainty in determining riprap D for steep slopes with the PADER Method, SCCC adds an <br />additional 3- inches to the model recommended D size. The D for the spillway crest is 4.0 inches; <br />the D5o for the spillway outslope is 4.5- inches. <br />The calculated 25 -year, 24 -hour event peak discharge from the LCSS is 36.5 cfs (see Addendum <br />2.05.3- E2.E -2). The spillway invert is at the 6,655.0 foot elevation, while the peak stage in the <br />• SEDCAD demonstration is at 6,656.1 feet. The top of the embankment is 6,757.5 feet. Both the <br />spillway crest and outslope will be protected with a rock riprap liner. The channel utility design (see <br />Addendum 2.05.3- E2.E -3) was used to -size the rock riprap. Rock riprap size was determined using <br />the PADER method. As noted above, SCCC adds an additional 3- inches to the model recommended <br />D size. The D for the spillway crest is 4.5 inches; the D for the spillway outslope is 9- inches. <br />The designs presented in Addendum 2.05.3- E2.E -3 indicate that the emergency spillways maintains <br />the necessary freeboard specified in Rule 4.05.9(7)(d). <br />5.0 Summary <br />The capacity of the two coal stockpile sumps (UCSS and LCSS) are attributed to embankment <br />construction. Since the sumps will not be permitted as CDPS structures, there are no effluent limits <br />and Rule 4.05.2(7) is not applicable. Both the principal and emergency spillways have been <br />designed to assure compliance with the requirements of Rule 4.05.9. <br />The embankments were designed to be stable and provide adequate freeboard and, therefore, the <br />structures comply with the appropriate rules and regulations for a sedimentation structure. Sage <br />Creek Coal Company will periodically inspect the structure for sediment storage, structural integrity <br />• and hazardous conditions. Maintenance or remedial work will be performed in accordance with the <br />approved mine permits. <br />2.05.3 -E2.E5 12/09 <br />