2015-11-09_HYDROLOGY - M1983194 - Laserfiche WebLink

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the oil shale and saline mineral deposits in the Eocene Parachute Creek Member of the Green River Formation which underlies the Uinta Formation. Nahcolite is the naturally occurring crystalline form of sodium bicarbonate. NS conducts nahcolite solution mining operations in the Parachute Creek Member of the Green River Formation on their Lease. 2.1.3 Site Geology The Parachute Creek Member of the Green River Formation is a dolomitic varved1 marlstone impregnated with varying amounts of kerogen known as oil shale. This member is subdivided into a series of rich (R) and lean (L) stratigraphic zones. In addition, this oil shale is rich in the sodium minerals nahcolite, halite, and dawsonite. These minerals occur in beds, nodules, aggregates, and as disseminated crystals. A cross -cutting boundary known as the Dissolution Surface (DS) demarks the depth of groundwater infiltration. Above the DS, groundwater has leached out sodium minerals; below the DS, saline minerals remain intact and the formation is dry. In the vicinity of the NS sodium lease, the DS occurs in the L-5 Zone at a depth of approximately 1,930 feet. The NS solution mining process is predominantly focused on a nahcolite bed in the L-5 Zone, known as the Boies Bed (BB). The Boies Bed can be subdivided into upper (UBB) and lower (LBB) sections, separated by a thin (approximately 4 foot thick) oil shale unit known as the Oil Shale Marker Bed (OSMB). The Boies Bed in the area of NS operations contains a facies change from halite to nahcolite. Nahcolite is solution mined from the Upper and/or Lower Boies Bed only when halite is absent from the target bed(s). Four aquifers have been identified in the subsurface of the NS Lease area. These include the Perched, A -Groove, B -Groove, and Dissolution Surface Aquifers. The Perched Aquifer is the product of a discontinuous, relatively impermeable Green River Formation tongue within the Uinta Formation sandstone at a depth of approximately 400 feet. Groundwater is typically first encountered near this depth as it accumulates on the very low permeability Green River tongue. The A -Groove and B -Groove Aquifers are approximately 40 feet thick, comprise the entire A -Groove and B -Groove lean stratigraphic zones, and are found at depths of approximately 1,440 and 1,640 feet, respectively. The Dissolution Surface Aquifer can be as much as 50 to 70 feet thick, extending approximately 50 to 70 feet above the DS. In the area of the NS sodium leases, the top of the Dissolution Surface Aquifer is found at a depth of approximately 1,890 feet in the upper L-5 Zone. The Perched, A -Groove, and B -Groove Aquifers are classified as 1 Varve: a sedimentary bed or lamina or sequence of laminae deposited in a body of still water (Iacustrine) within one year's time; seasonally deposited laminae. Daub & Associates, Inc. 3 NS LLC 2015 S A P Rev. 2