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<br />1 <br />r <br /> <br /> <br /> <br /> <br /> <br />1 <br />~~ <br /> <br />1 <br /> <br /> <br /> <br />1 <br />1 <br />Farmer's mine. During this investigation the water level in the <br />flooded mine was measured at an elevation of 7,036 feet. <br />Analysis of a water sample collected in the Farmer's mine <br />indicated a total dissolved solids content of 3,100 mg/1 and an <br />increased content of sulfates (2,120 mg/1). <br />The Farmer's mine water quality is similar to the quality of <br />Spring No. 25, located near Farmer's mine in Section 19 (T 13 S, <br />R 91 W). Spring No. 25 is issuing water from bedrock. The water <br />quality in deep monitoring wells DH - 60 and DH - 65 have higher <br />contents of total dissolved solids than the water in the Farmer's <br />mine, however, the sulfate content is typically lower. <br />Therefore, it is assumed that changes of water quality in the <br />flooded mine over a long period of time would be expressed by a <br />slight increase of sulfates and of total dissolved solids. <br />A more detailed study of post-mining water quality will be <br />performed after at least one year of in-mine monitoring is <br />available. <br />However, the fact that no discharge of water from the <br />flooded mine is anticipated, most of the negative impacts on <br />local water quality related to the discharge of mine water into <br />the local drainages will be eliminated. <br />6.0 CONCLUSIONS <br />The present water inflow into the Orchard Valley underground <br />coal mine is very low. It was estimated that at the end of 1984 <br />only about four (4) gallons per minute of water were discharging <br />into the mine. This inflow rate is smaller than experienced in <br />other mines within the general area. It is believed that the <br />reason for the low water inflow is the absence of major aquifers <br />above the mined coal, general hydrogeologic conditions of the <br />site (recharge potential, in particular) and the absence of <br />significant surface streams within the mined area. <br />The water inflow into the mine wi 11 be increasing with the <br />mine expansion. Most of the increased inflow will be related <br />proportionately to the increase in mine area. Only in the <br />western part of the future mine (to be opened after 1989) is an <br />increased water inflow anticipated. This increase will be due to <br />mining near the coal subcrop into the stream beds of Stevens <br />Gulch and East Roatcap Creek and due to the driving of entries <br />underneath these streams where the thickness of the overburden is <br />less than 500 feet. The water inflow into the future mine was <br />calculated as approximately 8.7 gpm at the end of 1989 and 33.5 <br />gpm at the end of the mine life. <br />The predicted impact of water seepage into the mine on local <br />water users is considered insignificant on East Roatcap Creek. <br />The impact on Stevens Gulch is significant only during a short <br />period of time. CWI is preparing mitigation measures to address <br />the potential impacts assessed in this report. <br />' I I 13 muia ~. r. e~~ i:m si cn vi:, <br />