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IPIPAC7 FIITIGATIOiJ PL.4p The foregoing sections detail the measures Atlantic Richfield will undertake to prevent subsidence to Dry Fork, Horse Creek and South Prang and measure ~~tream-flours to be able to detect any changes in water availability resulting from mining activities at the 1•lt. Gunnison Mine. Hoa+ever, there i5 the potential {however remote) that subsidence will af1`ect these streams in an adverse wa,y. The most catactrophic event which can be hypothesized is total loss of water in a stream channel into a subsidence crack. It is esti.nated that the length of a hypothesized subsidence crack could be.the width of ona~ mining panel (450 t.o 500 feet) because all panels are presently planned to be oriented at approximately 90 degrees to the general trend of Dry Fork. Atlantic Richfield will maintain 700 feet of st:eel well casing and a ~.uitable pump so that should water from the Dry Fork, Horse Creek or South Prong be inadvertently diverted into thEa mine Atlantic Richfield can quickly drill and case a hole from the surface to a sump in the mine and pump out *_he diverted water. All water handled in this manner will be released to the affected drainage at a location where it will not be rediverted to the mine. Appropriate water quality monitoring and treatment efforts (as necessary) will be used to insure non-degradation of •.vater quality. Because of the low contact tune betvreen the water and the coal and the absence of toxic or• undesirable materials in the overburden and coal in sufficient quantities to affect o-ratar quality no water quality problems are expected. If the surface source of water into tYie mine is readily identifiable the stream will be contained in a 36" culvert across the point of leakage. As necessary, portable flumes in conjunction with the perma- nent stream gaging stations will be used to delineate the point or area undergoing'o-rater loss. Once the surface source of ~.vater is defined, when feasible, the necessary pernics will be obtained and the culvert installed. This technique will be used first fur readily • (20)