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(USGS Station #6242), and Yellow Creek near White River (USGS Station #6255). Historical <br /> surface water data for these stations can be found at usgs.gov. <br /> 2.1.2 Geologic Setting <br /> The NS sodium lease site is located near the depositional center of the Piceance Creek Basin in <br /> northwestern Colorado. The site is immediately underlain by sandstones, siltstones, and <br /> marlstones of the Eocene Uinta Formation. The dominant economic resources in the area are <br /> the oil shale and saline mineral deposits in the Eocene Parachute Creek Member of the Green <br /> River Formation which underlies the Uinta Formation. The saline mineral nahcolite is the <br /> naturally occurring crystalline form of sodium bicarbonate. NS conducts nahcolite solution <br /> mining operations in the Parachute Creek Member of the Green River Formation on their Lease. <br /> 2.1.3 Site Geology <br /> The Parachute Creek Member of the Green River Formation is a dolomitic varvedl marlstone <br /> impregnated with varying amounts of kerogen and subsequently referred to as oil shale. This <br /> member is subdivided into a series of rich (R) and lean (L) stratigraphic zones. In addition, this <br /> oil shale is enriched in the sodium minerals nahcolite, halite, and dawsonite. These minerals <br /> may occur in beds, nodules, aggregates, and as disseminated crystals. A cross-cutting boundary <br /> known as the Dissolution Surface (DS) demarks the depth of groundwater infiltration. Above <br /> the DS, groundwater has leached out sodium minerals; below the DS, saline minerals remain <br /> intact and the formation is dry. In the vicinity of the NS sodium lease, the DS generally occurs in <br /> the L-5 Zone at a depth of approximately 1,930 feet. <br /> The NS solution mining process is predominantly focused on a nahcolite bed in the L-5 Zone, <br /> known as the Boies Bed (BB). The Boies Bed can be subdivided into upper (UBB) and lower <br /> (LBB) sections, separated by a thin (approximately 4-foot-thick) oil shale unit known as the <br /> Oil Shale Marker Bed (OSMB). The Boies Bed in the area of NS operations contains a bottoms- <br /> up facies change from halite to nahcolite. Nahcolite is solution mined from the Upper and/or <br /> Lower Boies Bed only when halite is absent from the target bed(s). <br /> Four aquifers have been identified in the subsurface of the NS Lease area. These include the <br /> Perched, A-Groove, B-Groove, and Dissolution Surface Aquifers. The Perched Aquifer is the <br /> product of a discontinuous, relatively impermeable Green River Formation tongue within the <br /> Uinta Formation sandstone at a depth of approximately 400 feet. Groundwater is typically first <br /> encountered near this depth as it accumulates on the low permeability Green River <br /> marlstone/oil shale tongue. <br /> Varve: a sedimentary bed or lamina or sequence of laminae deposited in a body of still water <br /> (lacustrine)within one year's time; seasonally deposited laminae. <br /> Daub &Associates, Inc. 3 NS LLC 2022 SAP <br />