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therefore, these upper reaches of Grassy and Little Grassy Creeks are determined to not be <br />AVFs. Although Scotchman's Gulch has sufficient unconsolidated stream-laid deposits <br />holding a stream, the Gulch does not meet the criteria of an AV:F based on insufficient water <br />for irrigation use and lack of subirrigation characteristics, as documented in Exhibit 2.06.8- <br />E1 of the permit application; therefore, Scotchman's Gulch near its confluence with Grassy <br />Creek is determined to not be an AVF. <br />Effect of Mining on Identified Alluvial Valley Floors <br />The PSCM will discharge mine disturbance runoff, coal spoil leachate, and underground <br />mine water into the stream channel in the Grassy Creek AVF via pond 002, and into the <br />stream channel in the Fish Creek AVF via pond 004. The runoff and leachate can be <br />expected to be alkaline, with the chemical constituents of greatest concern being dissolved <br />solids, mainly salts of sulfate. PSCM proposes no new disturbances or discharges in the <br />Little Grassy Creek AVF; therefore, there is no potential for material damage to this AVF. <br />Rule 2.06.8(5)(b) identifies one type of material damage on an AVF as an increase in <br />electroconductivity (an indicator of dissolved solids concentration) to a level above a <br />threshold value at which crop yields decrease. The Division considers that salt loading of <br />streams in the vicinity of the PSCM can reduce yields from irrigated or subirrigated crops <br />grown in an AVF if the electoconductivity of irrigation water exceeds 1,000 mmhos/cm or if <br />water in the root zone exceeds 1,500 mmhos/cm. <br />No changes are proposed for the Pond 004 watershed during PSCM mining; therefore, the <br />Division's evaluation of that watershed as described in the findings document for the Seneca <br />II Mine is applicable to the PSCM mine. That findings document describes the Seneca II <br />operator's analysis which indicated discharges from Pond 0041 during irrigation season are <br />likely to result in TDS in Fish Creek of 607 mg/l. The 607 mg/l TDS value equates to 809 <br />mmhos/cm, a value well below the 1,000 mmhos/cm material damage threshold (assuming a <br />0.75 conductivity to TDS conversion factor). <br />Table 2.05.6(3)-T1 of the PSCM permit application contains a mass-balance analysis that <br />indicates mixing of discharges from PSCM ponds with stream waters will result in maximum <br />TDS of 3,259 mg/l in the channel of the Grassy Creek AVF. Although 3,259 mg/l equates to <br />4,345 mmhos/cm, a value well above the 1,000 mmhos/cm material damage threshold, the <br />high TDS is a result of Seneca II surface mining activities that, as previously explained, are <br />exempt from AVF material damage rules 2.06.8(5)(a)(i) and (ii). The predicted TDS of <br />PSCM underground mine water is approximately 1,050 mg/l, which would dilute the high <br />TDS water whose source is Seneca II surface mining activities. <br />Based on the limited effects of PSCM discharges from underground mining activities on <br />surface water quality in the Fish Creek, Grassy Creek, and Little Grassy Creek AVFs, alluvial <br />ground water quality should not be significantly impaired. Sub-irrigation is expected to be <br />less affected by mine discharge than by irrigation using surface waters. A conservative <br />estimate of the expected effect of mining indicates that no material damage will result. <br />Peabody Sage Creek Mine 38 May 7, 2010