2018-10-16_PERMIT FILE - M2018039 (2)

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Mr. Jared Ebert RE:Lamb Lakes Site M-2018-039 October 15, 2018 trees include Siberian elm, ash, and rabbit brush. Along the lake shore, cottonwoods, willow, and Russian olive are dominant. Rule 6.4.19—Exhibit S —Permanent Man-made Structures 13. Proof of offering structure agreements to all owners of man-made structures within 200 feet of the affect land is provided in Attachment D. However, not all adjacent property owners with structures have accepted the applicant's structure agreement offer. As structure agreements become finalized, they will be provided to the Division. Since structure agreements could not be obtained from all structure owners within 200 feet of the affected area, slope stability shall be addressed prior to slurry wall construction. The lake cavities have been previously mined and reclaimed and no highwalls exist, nor will be created, on the site. According to the 1987 Home Office Pit Amendment by Sterling Sand & Gravel Company, the pits were mined to bedrock and reclaimed for wildlife habitat. To enhance the wildlife habitat, lake side slopes were reclaimed to 3H:1 V slopes, with flatter 4H:1 V slopes within five feet of the normal lake water surface. Wave erosion has altered the slopes slightly, but slopes below the water line appear to be 3H:1 V or flatter as recommended by the Division for slope stability. The existing reclaimed lake slopes have remained stable since reclamation was finalized. It is expected that even once the lakes are dewatered, the slopes will remain stable during slurry wall construction. Lake draw-down rates will be controlled to prevent slope failure during dewatering. Since the geotechnical properties of the slope material is not known, and the slopes are not available for sampling, a slope stability sensitivity analysis will be performed using typical slope backfill materials to guide lake draw-down rates. Once dewatered, the slope material will be sampled and evaluated for stability during slurry wall construction and reservoir operation. In addition to the slope material, the adjacent top of bank material will be sampled and evaluated for stability as part of slurry wall design. The applicant believes that, in its current reclaimed condition, the property is stable. Even if failure of the lake slopes occurs during dewatering, with the bulk of existing slope material in place, slope failure would not extend to the original mining highwall or outside of the proposed permit boundary. Once dewatering is complete, material analyses and stability evaluations will be performed as part of the reservoir construction and the applicant commits to providing the analyses and evaluation results to the Division prior to construction. Rule 1.6.2 —Notice Requirements 14. Proof of publication in newspaper is provided in Attachment C. Page 6 of 7