Laserfiche WebLink
<br />/r.JM,wx>! :Lm,.. : P'w +,. a~.ti.-w 1L.ns~n }lu,~ _ <br />- imnitCi Ot .10011 wa[Cr Jaall[V nn the ~COnnt1 and •uf'aeewafCr OUa11lV. Tne aVa11UOIC dam <br />indicare that a small proportion of the overburden may produce acid [hrough the oxidation <br />of pyrite. Based on laboratory tests on overburden cores. calcite is almost ubiquitous. <br />Calcite serves two funcions. First. it buffers the aH of the water. which overall tends to <br />stow [he oxidation of pvrite. slowing the produricn of acid. Second, it will neunafize the <br />acid that is produced, T'ne core samples chat cxhPoited low paste pH's are surrounded by <br />non-acid producinc, calcite-bearing rocks. The water that contacu the low•paste pH <br />materials will have first reacted wi[h calcite. and the[efore developed a pH-buffer capacity <br />of its own. The groundwater monitoring dam indicate chat mixed overburden and <br />interburden waters have near neutral pH's. Sampk pH's less than 6 are assa:iated onW with <br />the lower Dakota coal. Where the coal's permeability is high enough to produce about 5 <br />gpm during sampling, the acid-producing reactions do not appear to be tiast enough to <br />maintain the pH of the water less than 5. Oxidation rates may increase because of the <br />mining process. However, the supply of oxidation is only one of the constraints on the <br />production of acid. Other constraints are imposed by the quantity of caliite present, and <br />the reactivity of the pvrite. The paste-pH test. conducted under oxidizing conditions, <br />indicates that a very small proportion of the overburden is lisely to produce acid. The aad <br />that is produced will bE quickW neutralized. During [he mining process. WFC wtil test the <br />overburden and if acidic layer are encountered they wil] be mixed with non-acidic layers <br />• to neutralize any acid Forming ctfecrs. <br />Potential imrmcts of replaced spoil on ¢roundwater aualirv. Tne aaalvsis of geochetnical <br />coatrals on groundwater quality suggests that the water chemistry and mnccntra[ioas of most <br />elements of concern are controlled by mineralagic reactions that will resisi changes in watcr <br />chemistry. Production of acid may occur in very local settings and is probably most <br />prevalent in the coal which will be mined. Calculations indicate that neutralizarion or the <br />acid will occur rapidly with milting of water. or with movement of acidic water inm caicite- <br />bearing rocks. Also. the analysis conducted indicates that chemipl changes are apt likely <br />to occur. <br />Effects of mining on the local ~~eomorohologv_. Impacts From mining on the local <br />geomorphology will be tong form. but appear to be of minimal signiticant.'e. The <br />recsmblished reach oY' the drainage which will be mined will result in a shover, stirittly <br />steeper stream channel. The potential For increased sediment loads in the drainage (once <br />pond 007 is removed) should be otTset by the staple banksides and the reactivety sma{1 <br />change in overall gradient The increased runoff and consequent erosion potential on <br />disturbed basins in the mining area due to the temporary loss of ropso7 strimure should be <br />of minimai significance. Conrour ripping, mulching and revegetation have been demonstrat- <br />ed to minimize sotl erosion and wdl be used to mitigate the increased runoff potential until <br />the topsoil structure is developed. <br />I' ;'~ ^' <br />I <br />Attachment 2.04.7-5-15 <br />