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demonstrated that a long-term static safety factor of 1.5 was achieved. The analysis is provided as Appendix 3.9-A. 31'T'S ~85 w final pit is located in approximately the mi dle of Section 36, TSN, R66W. A positive drainage system was created rzomzne<rsege--top-t~ the ridge bottom. Exhibit 3.9-1 was constructed using a computer model developed by Exploration Computer Services, Inc., and was used with the following items considered; the topography of the area before mining, the depth of the overburden, the depth of the coal, the mining methods used, past experience in reclamation and a 338 swell factor for the material. The final postmining contours were achieved by shooting the highwall and grading material from both sides (highwall and spoil) of the pit. This enabled the reclaimed slopes to more closely resemble the premining topography. Grading of the final pit began downslope of the pit area designated for disposal of unsalvageable facilities material. Exhibit 3.9-3 shows a comparison of cross-sections for the final pit area before and after backfilling. The location of the cross-sections are shown on Exhibit 3.9-1. Exhibit 3.9-9 shows a comparison of the premining and postmining slope profiles in the vicinity of the backfilled pit. A review of the profiles indicate that five percent of the premining slope segments equaled or exceeded a 508 slope (individual slope segments were • based on five-foot vertical intervals), particularly along the lowermost portion of the pit area. To ensure long-term stability of the final pit area, the reclaimed pit slope profile does not exceed a maximum of 338. The majority of the reclaimed 338 slope segments have been placed in the upper 250 feet of the profile where the watershed is smallest to minimize the potential for erosion. The remainder of the 338 slopes have been dispersed over the middle section of the final slope profile. Additionally, the stability of the hillslope will be monitored by installing a minimum of three stability monitoring pins. Two of the pin will be installed on the reclaimed spoil approximately 100 ft. south of the highwall edge. The third pin will be placed on undisturbed ground just west (downgradient) of the pit. The pins will be installed along a common east-west line. The pins will be installed once final reclamation activities (i.e., fertilizing, seeding, etc.) have been completed and any influence from freeze/thaw action is absent. The position (east/west coordinates and elevation) of the pins will be monitored quarterly for the first year following installation, and annually thereafter. The timing of the monitoring will be planned so that freeze/thaw action does not influence the position of the pins. Results of the monitoring will be • provided in the Annual Hydrology Report. Renewal-3 3.9-2 June 13, 1997