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<br />be established between the Dissolution Surface (1,400 feet below ground surface) and <br />the top of the mining interval. Therefore, the top of the mining interval will be at a <br />depth of 1,550 feet, i.e. the thickness of the overburden will be 1,550 feet. <br />The overburden consists of the following in areas with a surface elevation of <br />approximately 6,200 feet at the Piceance Site. <br />Table D-3 Overburden Summary <br />Depth Thickness Stratigraphic Unit Hydrologic Unit <br />(feet) (feet) <br />0-500 500 Uinta Formation Unsaturated <br />500-675 175 Uinta Formation Saturated -Upper portion of <br /> U er A uifer <br />675-830 155 Green River Formation Saturated -lower portion of <br /> U er A uifer <br />830-1055 225 Mahogany Zone Semi-confining Layer - <br /> (Green River Formation) Saturated <br />1055-1,400 345 Leached Zone Lower Aquifer <br /> (Green River Formation) <br />1,400-1,550 150 Saline Zone Confining Layer <br /> (Green River Formation) <br />Total <br />Thickness 1,550 feet <br />D.9 Underlying Stratum <br />The stratum directly underlying the mining interval is the Garden Gulch member of the <br />Green River Formation. Below the Garden Gulch Member are the Douglas Creek <br />Member and, in some areas, the Anvil Points Member of the Green River Formation. <br />These three members contain mainly sandstone, siltstone, marlstone, algal limestone, <br />and some lean, clay-rich oil shale. <br />D.10 Primary and Secondary Commodities <br />D.10.1 Commodities to be Mined <br />The principal products to be produced by American Soda are sodium bicarbonate and <br />sodium carbonate. Sodium bicarbonate (NaHCO,), also called baking soda, is used in <br />manufacturing effervescent salts and beverages, baking powder, sodium salts, <br />pharmaceuticals, cleaning preparations, laboratory reagents, antacids, and many other <br />products. Sodium carbonate, (Na2C0,), also called soda ash, is used in manufacturing <br />D-17 <br />