GENERAL48922 - Laserfiche WebLink

Home Browse Search

-.iU - Leaching of Dissolved So.Lids from Spo.i1 Matorial The applicant has prepared an estimate of changes in water quality resulting from the percolation of water through the .spoil material, this information is contained in Section 2.5.3 of the permit application. The changes in water quality which will be realized in Trout Creek (in terms of total dissolved solids) are minor, due to the relatively Large volume of "dilution water" available both instream, and as a result of contributions from the alluvial ground water located on the western side of Trout Creek. The net degradation of water quality in Trout Creek, even in terms of low flow conditions (worst-case), from the incremental mining to be petf~~med in this~•permit term should not Limit its use for irrigation. !'aae 2.5-l~r~l of the permit application presents the results of water 7uality modeling done on Trout Creek at the Edna mine. Predicted increas%~s in TUS are presented for r_ach month of the year. The maximum anticipated increase in TDS i= seen in Flay, wheL"c TDS incrcasas from 340 mg/1 to 388 mg/1. This is in the spring when Trout Creek waters are spread over irrigated crops in the vicinity of the mine. This slight increase in TDS is considered insignificant as it relates to crop yields. The water i,ri11 still be of very good quality for flood irrigation l>ucposes. The water quality of the ground water contained in the alluvium on the astern side of Trout Creek will also degrade as a result of mining. This degradation will be more severe than that projected for the surface waters of Trout Creek, since an analgous volume of "dilution water' is not available in the alluvium. Conversely, the severity of impact will be more local in scope. T,he applicant has predicted that the TDS concentrations in the alluvial aquifer are expected to eventuallu increase from the current levels to somewhere between 2,000 and 1,000 mg/1 (see page 2.5-97 of the permit application). Alluvial waters containing elevated levels of dissolved solids will therefore enter into Trout Creek, prior to use. The alluvial waters should become tremendously diluted instream, resulting in TLLS levels well below unsuitable irrigation limits. This statement is true for both average conditions and during the irrigation season. The dilution should therefore minimize the likelihood of impacting withdrawals from Trout Creel: for irrigation use. There is also the potential for the degraded alluvial ground water to impact the productivity of subirrigated crops. Because Trout Creek is a discharge point for the alluvial ground water, this impact should be realized only on the East side of the stream. In the vicinity of the permit area, there arc only tr.~o irrigated crop fields on the East side of Trout Creek.. They are located immediately downslope of the West Ridge area. The tdest Ridge area was previously mined out and left un- recIaimed. As a result, precipitation easily infiltrates into the unreclaimed spoils, flows through the spoils, Leaching salts as it goes, and discharges into the Trout Creek alluvium. P6M proposes to mine through these unreclaimed spoils and recover a deeper coal seam. Subsequent reclamation should greatly cut down on the infiltration potential through topsoiling and reveyetation practices. Follow- ing successful reclamation, the quality of the alluvial water immediately downslope of [Jest Ridge should actually improve. This is because less r.~ater should infiltrate into the spoils and discharge into the alluvium, thereby allowing for greater dilution. The crop Lands in question have been under the influence of this increased discharge of degraded water for many years. Even through actual monitoring is lacking, there has been no apparent reduction in crop productivity. Since the water quality is likely to improve, no future reduction in crop productivity is an ticinated.