2024-10-15_PERMIT FILE - C1981038

Home Browse Search

RL?70FF AND SEDIHE`1TATION CALCirLATI0N5 E."lERGENCY COAL STOCKPILE File 077-353 I • December 17, 1979 The drainage area of the eaergency coal stockpile was surveyed by conventional weans and was determined to be 4.78 acres. Runoff expectations for a 10-year 24-hours storm were taken from work by Charles Leaf, P.E. Detailed work may be found in "Colorado Westaoreland Inc., Orchard Valley `line, Modification of Onderground Coal Mining and Reclaaation Permit - submitted June 18, 1479" Section 784, page 22. The previous work was done for Westaoreland Canyon, and it was judged that the emergency coal pile was is close enough vicinity to use similar values. Based on this information, runoff amounts are: .04 acre-feet for disturbed lands acre 0.01 acre-feet for undisturbed lands acre Expected runoff, assuming the entire area as disturbed, 1s 0.04 acre-feet X 4.78 acres = 0.19 acre-feet acre Expected sediment volume is based on 30 CFR 817.46b(2). The volume required . way vary from 0.10 acre-feet to a minimum of 0.035 acre-feet. The acre acre regulations state that to use the minimum, sufficient sediment control measures are used to reduce sediment. Colorado Westaoreland Inc. proposes to use the minimum of 0.035 acre-feet. This is based on the eaergency, acre temporary nature of the pile and close monitor•:ng of sec Went levels. The expected sediment volume for [he area is 0.035 acre-feet R 4.i8 acres 0.16 acre-feet. acre Total storage capacity adding the runoff and sediment values Ss 0.19 acre-feet _ 0.16 acre-feet = 0.35 acre-feet. The sedimentation pond would have a storage capacity o_' 0.22 acre-feet. Aa additional 0.14 acre-fee[ is provided within the beraed area directly north of the rail spur. This will provide 0.22 acre-_`eet + 0.14 acre-_'eet = 0.36 acre-feet. As stated previously, the sedimentation pond till be closely monitored and as per 30 CFR 817.46(h) the pond wi L' be cleaned at the level shove on stockpile a: ea drawings attached. • ine runoff/sedimentation storage areas will be devatered with a pump. The devatering will be after a runoff detention. time of '4 ^ours, and will Se - done in such a manner as to ciniaize disturbance a surrcund_ng areas. 111 drawings, calculations, and surveying for this emergency stockpile area has Seen directed by a registered professional engineer.