2013-03-01_HYDROLOGY - P2010026 - Laserfiche WebLink

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miilidarcy in the remainder. The Saline Zone contains layers of nahcotite of various morphologies that alternate with kerogen -rich layers and are remarkably continuous across the basin. Nahcolite morphologies that appear In the Horse Draw mine occur in the same sequences at the East RDD. Thus, it is inferred that the physical conditions at Horse Draw mine persist wherever the saline zone exists, and since the Horse Draw mine is dry, it is inferred that the Saline'Zone is dry at the East RDD. During mining in the 1970s and 80s, operations were conducted on 4 separate working levels in the saline zone, all of which remained dry during mining. More recently, in 2009, Shell investigated the conditions inside the Horse Draw Mine Shaft and found that the mine remained dry after more than 25 years since the mine shaft was sealed at the surface. PART II. Permit Considerations (40 CFR §146.34) Geologic Setting The Piceance Creek Basin located in northwestern Colorado is an elongated structural. and stratigraphic depression, trending northwest - southeast. The basin is bounded by the Uinta Uplift to the north, White River Uplift to the east, Sawatch Uplift to the southeast, and the Douglas Creek Arch to the west. The Basin encompasses approximately 8.90 square miles, is asymmetric, and is structurally deepest In the northwest where crystalline basement rocks are estimated to be 24,000 feet below ground surface. The basin contains reserves of coal, natural gas, oil shale, and is also mined for the sodium mineral nahcolite. In the area of Shell's East RDD Project Site, the Piceance Creek Basin Is dominated by Uinta Formation outcrops that overlie the Green River Formation, both of Eocene age. The Uinta Formation is characterized by fine to medium grained sandstone interbedded with siltstone, sandy siltstone, many siltstone, and thin beds of coarse grained or pebbly sandstone. The underlying Green River Formation is locally divided into three members; the Douglas Creek Member at the base, Garden Gulch Member above, and Parachute Creek Member at the top. (Locally at the Shell East RDD site, the Douglas Creek Member has not been identified.) The Parachute Creek Member is the thickest and most economically important unit in the Green River Formation. The Parachute Creek Member has a large areal extent and contains all of the commercial resources of oil shale and nahcolite. Oil shale, which is kerogen- bearing manstone, and dolomite manstone; are - the dominant iithologiea ofthe Parachute Creek Na it colite beds and segregates are present in the Saline Zone, which occupies the lower part of the Parachute Creek Formation in basin center. Notable concentrations of dawsonite occur within the Saline Zone, and halite occurs sporadically in the upper Saline Zone and principally at the basin deposition center (i.e., not at the East RDD project). The Saline Zone constitutes the most Important resource interval in the entire Piceance Creek Basin. It not only contains tremendous quantities of oil shale but mineable concentrations of nahcolite and significant concentrations of dawsonite, and halite in basin center where the upper contact of the Saline Zone is overlain by the hydrostratigraphic L4 WBI. Recent resource assessments by the U.S. Geological Survey Indicate that the Saline Zone in the Piceance Creek Basin represents an in -place oil. shale resource of about 1.9 million barrels per acre and nahcolite resources on the order of 4.5 billion tons, or 542,541 tons per acre. The U.S. Department of interior indicated that dawsonite resources in the Saline Zone comprise approximately 195,000 tons per acre. The Saline Zone is bounded at the top by the Dissolution Surface, and at the base by a horizon that marks the lowermost occurrence of nahcolite in the R2 zone. Besides parts of the L4 and LO zones, the Saline Zone at the East RDD lease area also includes all of the R4, L3, R3, L2, R2, L1, R1, and LO stratigraphic zones. Permit CO32210 -00000 4 FINAL PERMIT Statement of Basis