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_ •~ ~..~ <br />~;,';n~1 <br />,> :, <br />, :-''A'TTACHMENT <br />' •~.. V• <br />~±j <br />SUBJECT: Hydrologic Impacts of the Proposed (12/8/94) Topography <br />at Marr Mine/Pit 1. <br />DATE December 23, 1994 <br />ANALYZED BY Hal Pranger, Hydrologist <br />Phil Reinholtz, Hydrologist ~~ <br />Hydrologic analyses were performed to determine the hydrologic <br />impacts (peak flow and total runoff) to Bush Draw and an unnamed <br />tributary as a result of the proposed alterations to the <br />postmining topography at the Marr Mine reclamation area (Pit 1). <br />These drainages included Bush Draw and an unnamed draw to the <br />east of the reclamation area. It was determined that peak flow <br />and runoff would increase by 0.7 percent in the Bush Draw <br />drainage (2618 acres) and decrease by 3.4 percent in the unnamed <br />tributary drainage (539.5 acres). The hydrologic impacts due to <br />the differences in the premine and proposed postmine topography <br />are negligible. <br />The results of these analyses are presented in the following <br />table: <br />Rain- C Unnamed Unnamed Draw Bush Draw Bush Draw <br />Fall N Draw (East) (East) Premine Postmine <br />Event Premine Postmine (2600 (2618 <br /> (539.5 (520.8 acres) acres) <br /> acres) acres) <br /> Peak/Runoff Peak/Runoff Peak/Runoff <br /> Peak/Runoff <br />10/24 6 3.7/2.9 3.6/2.8 10.9/14.0 11.0/14.1 <br /> 5 <br />10/24 7 31.4/11.0 30.3/10.6 48.2/53.0 48.6/53.4 <br /> 5 <br />10/24 8 105.2/26.2 101.9/25.3 133.3/126.4 134.2/127.2 <br /> 5 <br />100/24 6 34.6/13.4 33.4/12.9 56.8/64.5 57.2/64.9 <br /> 5 <br />100/24 7 108.6/29.2 104.85/28.23 142.0/141.0 143.0/142.0 <br /> 5 <br />100/24 8 226.8/53.0 219/51.2 2$2.5/255.3 284.5/257 <br /> 5 <br />Peak = Cubic feet per second; Runoff = Acre feet <br />10/24 Rainfall event = 1.7 inches <br />100/24 Rainfall event = 2.5 inches <br />