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a • PROJECT DESCRIPTION The general location of the P3 and R1 portals is shown on Fig. 1. The proposed topography during mining and post-mining is shown in more detail on Figs. 2 through 5. The portal areas will be excavated into the existing hillsides and then backfilled after mining is completed. The post-mining topography will generally approximate the pre-mining topography. At portal R1 we have recommended minor revisions to the post-mining topography to flatten the final slopes (Fig. 4). Our analysis and recommendations are based upon Colorado Department of Minerals and Geology Regulations, Rule 4.14.2, General Grading Requirements. Rule 4.14.2 (b) requires backfill and grading to the most moderate slope possible, to eliminate the high wall which does not exceed either the angle of repose or such lesser slope as is necessary to achieve a minimum static safety factor of 1.3. Based upon information provided by Greystone, the portals will not be at the •~ lowest elevation of the underground mining. The portals will be sealed with masonry blocks and backfill. The sealing and backfilling is not anticipated to be water tight. Should the mined area fill with ground water, it is anticipated that most of the water will exit the mine area in historical seep locations. Should the mine fill with water above the portal elevations, seepage out the portal areas may occur. Greystone estimated that flows on the order of 25 gallons per minute are considered possible out of the portals for this condition. INVESTIGATION Field Investigation We visited the site on April 15, 1997 to observe conditions at the portal areas. A test trench had been previously excavated at each portal location to observe roof conditions. The trenches were excavated horizontally into the hillside to maximum ' depths on the order of 25 to 30 feet. Our field investigation included visual LORENCITO COAL COMPANY, LLC cTLrt zs,ess 3