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Colowyo, C1991 -019, PR3 adequacy No. 3 19 July 22, 2011 <br />Our letter on April 22, 2011 explained that the 18% factor is based on Williams and Clark's <br />(1994) spoil Iysimeter study which found that approxiinate 18% of annual precipitation <br />recharge spoil at a Routt County mine. The lithologic differences between Danforth Hills area <br />and the lowere Williams Fork Formation that are cited on page 23 of CCC May 20, 2011 <br />response letter would not cause a significant difference in spoil permeability (and, <br />consequently, spoil saturation rate) because the effective porosity in the spoil is between <br />particles of spoil, rather than inside the particles of spoil. Also, a spoil infiltration study found <br />the Colowyo spoil infiltration rate was not less than infiltration rates at mines developed in the <br />Lower Williams Fork coal sequence (Table 10. item 6 of Exhibit 7 of the Colmwo permit <br />application). <br />6. To be consistent with the 15% swell factor noted in Table 2.05.6 -5, please use in the spoil <br />resaturation calculations a spoil porosity value of 15 %, rather than 35 %. <br />fhe Dia i>ion's III grout contrnrnt t,as a request to use in the ( Ill lunr Lite pit becktiII .sutural ion <br />Cale ulru ion Ihal Call entla is cuntallied on pal-,e 37, a cultie for rlhxrire pot ,,II. IY,, Ihat is <br />shown on that pm -e. AIn >I of the 111)a and resul t ing saturat ion in spoil ra ill ocau beloeen the <br />particle, It'I'm1. rather dam lhmu,_h pall icics of,poiI; Ihcl(lolC The porosity bGween spoil <br />particle,, is Ibe eft CON c porosit\.:md ctfcCoN C porosity is the appropriate pomsita %aluc fin' <br />pertl)IIuing a ,poil ,aturnion Culcul:aion. It seems rcaxnnablc in a spoil saturation C,Ileulution N <br />add 5 percentage points fur iaef feetn c porosity inside spoil particles that may become partially <br />saturated. resulting in 20" 10 porosity for the percentage of spoil backfill than will become <br />saturated (15 "o effective porosity between particles, plus 5% partially saturated particles.) A <br />value of 20" o is consistent with the values of 20" o that is referred to on page 133 as the <br />"effective" porosity, and is used on that page in a calculation of the spoil saturation rate. <br />"rhe Division accepts the Cullum Lite spoil saturation calculation on page 133, with the <br />changes requested elsewhere in this letter to the surface water infiltration rate and subtracting <br />pitwall seepage from the spoil saturation calculation. Based on the adequaev of the calculation <br />of spoil saturation on page 133 (with the requested changes). and the imadeglacr of the <br />calculation of spoil saturation on page 137 (due to its use of total porosity), the Division <br />requests that you delete the second, third, fourth, and fifth paragraphs from page 137. These <br />paragraphs contradict the calculation on page 133, making the prediction of spoil saturation <br />unclear. Also, some of the information in the referenced paragraphs on pogo 137 repeats <br />intorn itiou that is provided on page 133, resulting in the spoil saturation analysis not being <br />concise. Rule 2.03.2( 1 ) requires information in the permit to be clear and concise. <br />7. The predicted spoil recharge rate of 3.1 inches per year (see previous comment 5) is <br />significantly greater than the maximum bedrock recharge rate of 1.1 inches per year; therefore, <br />it is probable that as spoil backfill resaturates, the spoil leachate- saturated zone at the downdip <br />