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~: ~ ~~. i COLOWYO COAL COMPANY L.P. 5731 State Highway 13 Meeker, Colorado 81647 (970)824-1572 (970) 824-1598 FAX James A. Kilter Senior Environmental Engineer September 23, 1997 Mr. Byron Walker Environmental Protection Specialist Colorado Division of Minerals and Geology 215 Centennial Building 1313 Sherman Street Denver, Colorado 80203 ~_ III Illlllllllllllllt /~ .Energy ,_ Co(oa-yo Cool Conr~tany L.~ ' ~` w° RECEIVED SEP 2 5 1997 71Vi$iC(I OI nunCiB!0 ~. GCCIOnY RE: Colowyo Coal Co. L.P., (C-81-019) Follow up to CDMG Inspection of September 22 and 23, 1997 Receipt of Precipitation Data Dear Mr. Walker: During the referenced Partial CDMG Inspection we indicated that once precipitation data was available we would forward the data to the Division for your information and review. The data would be extremely useful in characterizing the precipitation events that occurred from September 18 through September 22, 1997. If you will recall the severity of rainfall events occurring during September 18 and 19, 1997 led to our telephone call on September 19, 1997 notifying the Division of problems with the Prospect Pond (CDPS discharge point 007). I have included with this letter the summary data for our three precipitation gage locations covering the period July, August and through September 22, 1997. The Section 34 station is located approximately 2000 feet NE of the shop facility. The Gossard station is located at the Gossard loadout. The Section 16 station is located at the 101 dragline substation located approximately 3300 feet south of the north limit of the pit. The Section 16 station is representative of the events that would impact the watershed above the Prospect Pond. The Section 34 station is representative of the minesite in general and, of course, the Gossard site is representative of the Loadout. The 10 year, 24 hour precipitation event at Colowyo is 1.8 inches. The 25 year, 24 hour precipitation event at Colowyo is 2.3 inches and the 100 year, 24 hour precipitation event at Colowyo is 2.8 inches. Of particular relevance to the severity of the storm leading up to the events at Prospect pond is the data for the 24 hour rainfall occurring during the period from 0500 of 9/18/97 to 0500 of 9/19/97. Approximately 2.38 inches of precipitation fell during this 24 hour period, exceeding both the 10 year and the 25 year, 24 hour precipitation events! During the same 24 hour time period, approximately 1.88 inches of precipitation fell at the section 34 station. This would indicate that the entire minesite experienced rainfall exceeding the 10 year, 24 hour precipitation event. Also during the same time period, the Gossard loadout received approximately 1.65 inches of precipitation, or very nearly equivalent to the 10 year, 24 hour event.