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Shell has conducted extensive hydraulic testing in the Piceance Basin to refine the intervals of • fracture and flow resulting in hydrostratigraphic zones that differ from the historical definition of stratigraphic zones whereby the water - bearing intervals (WBI) considered to be equivalent to stratigraphic subdivisions. Based on this differentiation of hydrostratigraphic units from stratigraphic units, The WBIs are generally seen to be thicker than the stratigraphic units of the same names. In particular, the L4 WBI is much thicker than the L4 defined solely on the basis of geologic stratigraphy. For purposes of this Permit, the following geologic setting and definition of geologic units pertinent to the UIC permit, the hydrostratigraphic definition of each WBI will be described for strata from the surface to the Dissolution Surface. The balance of the stratigraphic section below the L4 (including the R4, L3, R3, L2, R2,1_1, and R1) will be referred to as the "R4 Seal" because this part of the stratigraphic section corresponds to the impermeable Saline Zone (Figure 3). Table 2.1 provides a description of the hydrostratigraphy of the East RDD. Uinta Hydrostratigraphic Zone The Uinta Formation consists of discontinuous layers of silty sandstone, siltstone, maristone and lenses (or tongues) of kerogen - bearing maristone. It forms the surficial bedrock over most of the northern Piceance Basin. At the East RDD, the hydrostratigraphic sequence of the Uinta consists of a 260 foot thick, tow permeability zone overlying a 684 foot thick water - bearing interval. R8 Hydrosfrafigraphic Zone The R8 oil shate (a hydrostratigraphic "seal" in Shell terminology) is the next hydrostratigraphic unit and is approximately 60 feet thick within the East RDD. It is composed of interbedded oil shales and occasional interbeds of siltstone, marlstone and volcanic tuff. Oil shale and maristone are typically laminated and tan to dark brown in color. A- Groove (1.7) Hydrostratigraphic Zone Within the East RDD, the A- Groove or L7 hydrostratigraphic unit/WBI is approximately 114 feet thick. It is composed of tan to yellowish -tan lean oil shale and silty maristone, and has a distinct "weathered" appearance R7 (Mahogany Zone) Hydrostrafigraphic Zone The R7 hydrostratigraphic unit/seal is approximately 62 feet thick at the East RDD. The kerogen -rich oil shale unit is usually laminatd or structuretess; however, blebby oil - is present, especially in the richest beds. ' B- Groove (L6 Hydrostratigraphic Zone) Similar to the A- Groove, the B- Groove or L6 hydrostratigraphic unit (WBI) is composed of marlstone, silty marlstone and lean to low -grade oil shale. Most of the B- Groove has a weathered or ieaahed appearance and the upper one -half often contains a thick (5 to 10 feet) rubble horizon. The approximate thickness of the B- Groove at the East RDD is 161 feet. R6 Zone Hydrostratigraphic Zone • The R6 hydrostratigraphic zone /seal is approximately 40 feet thick at the East RDD. The unit is composed primarily of oil shale, vuggy oil shale, and maristone. Dissolution features are minor and 'rare in the R6 zone at the East RDD site. L5 Zone Hydrostratigraphic Zone The L5 hydrostratigraphic zone/WBI is similar lithologically-to the overlying R6 zone, however, it has a lower average oil shale content and is therefore more brittle and contains more fractures. Throughout the East RDD, the L5 zone is above the saline zone and is about 142 feet thick. Stratification in these rocks is generally laminated, sometimes structureless. Permit CO32210 -00000 6 FINAL PERMIT Statement of Basis