2018-05-22_PERMIT FILE - M2018027 (4)

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Mr. David W. Hunt May 13, 2018 Page 2 and overlie the bedrock; 3) Bedrock usually consisting of claystone and sandstone that is commonly weathered in the top 1 to 2 feet and is commonly interbedded and interlaminated. Overburden The overburden is typically a silty sand that locally grades to a clayey sand that is non-plastic or of low plasticity typically ranging from 0 to 3.5 feet in thickness. This unit is usually slightly moist to moist, loose to medium dense with the top 6 to 8 inches containing significant organics. Of the overburden samples tested,the range of percent passing the No. 200 sieve ranged from 9.3%to 41.2%with an average of 24%. Atterberg Limits testing ranged from granular non-plastic to Liquid Limits of 29 and Plasticity Indices of 9. For samples that were not granular non-plastic, the average Liquid Limit was 23 and the average Plasticity Index was 6. Table 1.1 reports the laboratory test parameters. Sand&Gravel The sand and gravel is present throughout the site locally occurring at the surface, but typically underlying the overburden and overlying the bedrock. This unit typically consists of slightly silty,fine to medium grained sand overlying a fine to coarse grained sand and/or gravelly sand. Local clayey sand was encountered along the east side of the site. Silty,fine grained sands were also locally encountered directly overlying the bedrock. Where gravels were encountered, the size was typically'/4 to'/2 inches. This unit is typically medium dense but locally dense, but is also locally very loose to loose typically in siltier and clayey areas particularly below the water table. This deposit ranges in thickness from approximately 24 feet to 55 feet, averaging approximately 40 feet along the slurry wall alignment. The sands are relatively clean with fines content(silt and clay)generally ranging from 1.0 to 13.8 percent averaging 7.1 percent. Bedrock The bedrock encountered in the exploratory borings was generally weathered in the upper one to two feet typically became harder in unweathered zones. The bedrock consisted of claystone and sandstones that were commonly interbedded and interlaminated. Local lignite was also encountered. The average percent passing the minus No. 200 sieve ranges from 37.7%to 94.8% respectively with plasticity indices ranging from 34 to 54. Groundwater Groundwater was encountered in all of the borings at approximately 12 to 17 feet below ground surface. The groundwater levels will vary seasonally and will typically rise during the irrigation season and when recharge is applied. Groundwater will be controlled with the proposed below grade slurry wall and by pumping down the water level on the interior of the slurry wall. After slurry wall construction, groundwater mounding is anticipated on the upgradient(south and southeast)side of the site and a groundwater shadow(deeper water table) is anticipated on the downgradient(north and northwest) side the site. The shadowing effect may be limited by the groundwater recharge on the southwest part of the site a planned future groundwater recharge basin planned on the northwest part of the site. Mining will be above the water table in both cells. From a geotechnical standpoint,the sand and gravel will form the majority of the mine slopes. These soils are generally strong and stable, particularly when dewatered. Dry mining is planned in both cells as the slurry wall will control water level in the main cell and mining will be above the water table in the other cell. STRUCTURES WITH 200 FEET OF DISTURBED AREAS The known, permanent, man-made structures within 200 feet of the proposed mine areas that are not owned by Mr. Hunt are listed below: • Mcglothlin, residence building • Green Valley Turf, residence building • Fleming,James, storage buildings • CDOT, Storage&Garage buildings • Various buildings owned by land owner