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Mr. Joe Carpio - 7 - May 11, 1987 <br />In order to accurately describe the proposed change in the pond into a <br />permanent impoundment, the description on page 4.05-7 and 4-16 should be <br />revised as appropriate. <br />16. Geochemical analyses of the coal and overburden indicate that there is a <br />potential for acid drainage from the mine to occur at some point in the <br />future. Recognizing that the mine is currently dry, it is not unusual <br />for mining operations to dewater an overlying perched aquifer. If this <br />were to occur or if water is encountered as the mine expands to the <br />northeast, drainage from the mine could be acidic enough to have <br />deleterious effects to the surrounding environment. Therefore, the <br />applicant should devise a contingency plan to treat any sediment pond <br />inflow whose pH is less than 6.0 units. <br />17. The applicant's proposal to install a diversion ditch at the crest of the <br />highwall fill needs to be evaluated in terms of overall slope stability. <br />Based on a preliminary review, it appears that this type of drainage <br />control structure could significantly decrease the stability of the fill <br />by increasing the amount of water percolating through the <br />highwall/backfill interface. The applicant may wish to consider <br />alternative means of controlling erosion on the regraded fill such as <br />flat or gently sloping terraces which reduce slope length without <br />concentrating runoff within an unlined ditch situated at the crest of the <br />fill. <br />18. On April 29, 1987 as part of the notice-of-intent, the Division received <br />reouests from you to keep the coal storage bins for hay storage purposes <br />and to keep the weight sale to weigh hay trucks. It is necessary to <br />incorporate this information into the application document in both the <br />reclamation plan and in the post-mining land use discussion. <br />19. Based upon additional information submitted by La Plata Coal, the <br />Division has revised the preliminary reclamation cost estimate for the La <br />Plata No. 1 Mine as follows. <br />Task No. 4 -Compaction of portal bench and access road cut. The <br />size of the water truck was reduced from 7,000 <br />gallons to 3,500 gallons, resulting in an hourly <br />truck cost reduction from $99.77/hr to $50.70/h r. <br />This worked out to a task cost reduction from <br />$16,297.36 to $12,009.13. <br />Task No. 11 - Portal sealing and backfilling. The number of <br />entries was reduced from 4 to 3 (one has been sealed <br />and is used as the "shop"); and the dimension of each <br />entry was reduced from 20'w x 8'h to 20'w x 6'h. The <br />net effect of these changes on the estimate was a <br />reduction in cost from $7,104.00 to 53,996.00. <br />