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Adilk ► <br /> -54- <br /> the refuse pile had a sufficiently high permeability to prevent pore <br /> pressure buildup. This assumption has not been verified by appropriate <br /> drilling and monitor well installation. The applicant submitted a plan <br /> for the installation of monitoring wells above, within, and downslope <br /> from the coal processing waste pile. These locations should provide the <br /> necessary data. <br /> The applicant has agreed that if the monitoring results demonstrate that <br /> the ground water conditions encountered within the coal processing waste <br /> pile differ from those assumptions made in completing the stability <br /> analysis the analysis will be revised. If a revised stability analysis <br /> suggests that design revisions are necessary to achieve a static safety <br /> factor of 1 .5, the appropriate design revisions will be made. <br /> Mid-Continent Resources, Inc. , amended the permit application to propose <br /> the construction of a second coal processing waste disposal structure <br /> within the permit area. The site of the additional waste pile is located <br /> within the upper reaches of an unnamed, intermittent tributrary stream of <br /> Dutch Creek. The proposed five-year disposal facility is located <br /> approximately 1 1/2 miles southwest of the coal .processing plant. It is <br /> the intent of the operator to discontinue use of the existing coal <br /> processing waste pile upon approval and construction of the second <br /> structure, which is- projected to occur during 1983. Access to the <br /> proposed structure will be via an access road off the existing access <br /> road to the No. 4 mine bench. <br /> Mid-Continent Resources, Inc. had a geotechnical investigation and <br /> stability analysis prepared for the proposed structure by Geo-Hydro <br /> Consultants, Inc. Conceptual projections have also been prepared for an <br /> enlarged, longer life disposal configuration for the second structure. <br /> The geotechnical investigation and stability analysis were prepared in <br /> ccordance with the prudent state-of-the-art of slope stability analysis. <br /> In completing the analysis, Geo-Hydro Consultants, Inc. utilized material <br /> strength infonnation developed during the analysis of the original coal <br /> processing waste pile at the Coal Basin mines. The waste and bedrock <br /> materials encountered in both situations are analogous. The stability <br /> analysis projected a minimum static slope safety factor of 1 .82 for the <br /> proposed five-year pile configuration, which is designed to accommodate <br /> approximately 1,030,000 cubic yards of waste. <br /> The proposed waste pile plan includes the installation of an underdrain <br /> paralleling the existing thalweg drainage channel of the valley. In <br /> addition, several dendritic "finger" collector underdrains are also <br /> proposed to intercept seepage from an existing surface seep area <br /> discovered during the geotechnical investigation of the proposed site. <br /> Complete construction specifications and details are presented for the <br /> drain within the plan documents. Geo-Hydro Consultants, Inc. also <br /> prepared an analytical demonstration of the proposed subdrain system' s <br /> adequacy to accommodate the anticipated seepage encountered. in doing <br /> so, the applicant has demonstrated confornance with the variance <br /> require-nents of ;Rule 4.1U.3( 1 ) . <br />