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._ MOUNTAIN COAL (OMPANV~.~.~. A Subsidiary of Arch Western Resotuoes, LLC July 07, 2005 RECEIVED JUl 112005 DiMaiat W Minerals antl Ged°6Y West Ells Mine P O Box 591 5174 Highway 133 Somerset; CO 81434 (970) 929.5015 Fax (970) 929-5595 Mr. Jeffery G. Coombe Colorado Department of Public Health and the Environment Water Quality Control Division, Enforcement and Compliance Section 4300 Cherry Creek Drive South Denver, CO 80222-1530 Re: Mountain Coal Company, LLC, (MCC), West Elk Mine, CDPS Permit No. CO-0038776, Response to the Division's Letter Dated June 28, 2005, for Outfa11016A. Deaz Mr. Coombe: Referencing your letter of June 28, 2005, and the attached meteorological information, MCC experienced two (2) Total Suspended Solids (TSS) excursions and reported those to be 42 mg/L for the highest 30-day average (January), and a maximum 7-day average of 80 mg/L (January 11, 2005). The following is an explanation of the events surrounding these excursions. January 1, 2005, the West Ells Mine was blanketed with approximately 20 inches of snow. This was the result of previous snow accumulation. Beginning on January 9th, rain began to fall and it continued through January 11th. The average 24-hour temperatures for the 9th, 10th, and 11th, did not fall below 34 degrees °F. The rainfall in combination with the previous snow accumulation and subsequent thaw was equal to or greater than the 10-yeaz 24-hour precipitation event of 1.9 inches. The precipitation total for January 2005 at the West Elk Mine was 5.13 inches, with neazly 3.0 inches of rain falling on the 9a', 10~', and l la'. Discharge Point 016 (Outfall 016) is a combined outfall for FW-1, MB-1, and potentially mine water in an open channel. When the sample was taken, January 11, 2005, water was dischazging from only MB-1, this flow combined with the melting of the watershed azea of ice and previous snow events (20 inches of snow equals approximately 2" of precipitation) and the rainfall, resulted in a rain on snow precipitation event greater than 1.9 inches which is equal to the 10-yeaz, 24-hour event. This value was calculated by using 1.0 inch of precipitation melting from the existing snowpack, and the 1.18 inches of rain falling on January 11, 2005, resulting in a precipitation event of 2.18 inches. The TSS value for January 11`~ (80 mg/L TSS) resulting from this precipitation event was responsible for both of the excursions. Normally, MCC would have noted the event on the Discharge Monitoring Report (DMR) however, MCC did not have the quarterly report (meteorological data) from IIv1I, Air Science to confirm the greater than 10-yeaz 24-hour precipitation event for the 11`x, when the DMRs were due to the WQCD. In going forwazd and being pro-active, MCC will ensure that IML Air Science has the quarterly meteorlogical report submitted to MCC prior to MCC submitting the CDPS DMRs to the Division. .