2021-06-17_PERMIT FILE - M2001046 (4)

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Mr.Joe Lamanna June 9, 2021 Page 2 generally consisting of clayey and silty sands; 2)sand and gravel alluvial deposits that underlie the overburden and overlie the bedrock;and 3)bedrock usually consisting of sandstone with local areas of claystone. These units are described in more detail below. 3.5.1 Overburden Unit The overburden at the site typically consists of two sub-units;a surficial brown clayey to silty sand that overlies a buff silty sand. These sub-units are described below. Surficial brown clayey to silty sand with local sandy clay. The surficial brown clayey to silty sand sub-unit is typically approximately 1 to 2 feet in thickness but locally is as thick as 8 feet. This sub-unit is usually slightly moist to moist, medium dense to dense with the top 6 to 8 inches containing significant organics. Of the samples tested,the percent passing the No.200 sieve ranged from 16.6%to 74.7%. Atterberg Limits testing resulted in Liquid Limits of 19 to 31 and Plasticity Indices of 3 to 11. Buff silty sand. The brown surficial sub-unit is underlain by the buff silty sand sub-unit. The buff silty sand sub- unit ranges from approximately 4 to 14 feet thick and is slightly moist to moist becoming wet at the water table. The silty sand is very loose to medium dense and locally becomes clayey with depth. Of the samples tested, the percent passing the No.200 sieve ranged from 10.9%to 39.1%. Atterberg Limits testing indicated the material was granular non-plastic. 3.5.2 Sand&Gravel Unit The sand and gravel is present throughout the site underlying the overburden and overlying the bedrock. This unit typically consists of gravelly,fine to coarse grained sand locally grading to sandy gravel. Where gravels were encountered,the size was typically%to 2 inches. This unit is typically medium dense to dense, but is also locally very loose to loose. This deposit ranges in thickness from approximately 26 feet to 60 feet. The sands are clean with fines content(silt and clay)generally ranging from approximately 2.0 to 4.1 percent averaging 3.0 percent(Big Rock Exploration, 2019). Local clay lenses were reported within the deposit by Big Rock Exploration (2019). 3.5.3 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 silty,fine to medium grained, sandstone with local claystone seams. For the sandstone samples,the percent passing the minus No. 200 sieve ranges from approximately 13.4%to 26.7%averaging 21.6%. For the claystone seams,the percent passing the No.200 sieve ranges from approximately 53.3%to 74.1%averaging 64.5%. The approximate top of bedrock contours are presented on Sheet 4 of the plans. 3.5.4 Groundwater Groundwater was encountered in all of the borings at approximately 7 to 12 feet below ground surface.The groundwater levels will vary seasonally and will typically rise during the irrigation season. Groundwater will be controlled with the proposed below grade slung wall. After slurry wall construction, groundwater mounding is anticipated on the upgradient (west and south)side of the site and a groundwater shadow(deeper water table) is anticipated on the downgradient (north and east)side the site. 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 as the slurry wall will control water level in the main cell and mining will be above the water table in the other cell.