2011-05-12_PERMIT FILE - P2010026 (3)

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2.0 HYDROGEOLOGIC CONTEXT This section outlines the hydrogeology of the East RDD site to give context to the monitoring program. This program is designed to characterize baseline ground water conditions, develop conceptual models of ground water flow and chemistry, and monitor for potential hydrologic consequences associated with implementation of the Pilot in situ pyrolysis project. Ground water samples are analyzed for a large suite of inorganic and organic constituents ("analytes") to establish baseline water quality. Inorganic constituents include major ions (such as sodium, calcium, magnesium, potassium, bicarbonate, sulfate and chloride), and trace constituents which are significant as tracers or potentially as regulated species. Organic analytes include regulated compounds expected to be formed by pyrolysis, and for which a baseline must be established. 2.1 Geology Oil shale in northwest Colorado is found mainly in the Garden Gulch and Parachute Creek members of the Eocene Green River Formation, and to a much lesser extent in the overlying Uinta Formation. The Garden Gulch is a relatively clay-rich zone with very low permeability. The Parachute Creek, which is the most significant oil shale unit, consists of layers of dolomitic marlstone and kerogen, with a clay-bearing marlstone near the center of the Member. Many of the marlstone-dominant units contain fine layers of kerogen, and the kerogen-dominant units may bear many fine layers of marlstone. The stratigraphy of the Parachute Creek is divided into kerogen-rich (R) zones and kerogen-lean (L) zones (Figure 2-1). The Uinta Formation consists mostly of siltstone and sandstone units with occasional kerogen-rich "tongues". Owing to the relative paucity of kerogen in marlstone-dominant units, the L-zones tend to be brittle and therefore are fractured. Kerogen-rich R zones on the other hand tend to be ductile, and generally are unfractured. These features provide important hydrological controls, as the L- zones are water bearing intervals with fracture-controlled permeability, whereas the R-zones form seals with extremely low permeability both laterally and vertically. While remnants of the saline mineral nahcolite can be found throughout the Parachute Creek Section, the lower Parachute Creek in basin center has high concentrations of nahcolite plus additional saline minerals dawsonite and halite, the presence of which provide extremely low permeability. The vertical and lateral extent of this so-called "Saline Zone" has been reduced over time by the dissolution of soluble saline minerals by flowing ground water. Such dissolution is most evident in the L3 stratigraphic zone where breccias and contorted beds are common. The saline zone occupies only part of the L3 on its margins, yet extends from base of the L3 to the lower portion of the L5 in basin center. What is locally called the "Dissolution Surface" is the point below which there is no evidence of saline mineral deposition. Extreme low permeability makes the Saline Zone a regional no-flow boundary for ground water. The Pilot will target a portion of the Saline Zone well below the Dissolution Surface and all water- bearing units above the Dissolution Surface. 2.2 Surface Water Hydrology Stream flow is ephemeral in the uplands surrounding the East RDD areas. Drainage ways lose flow due to infiltration into soils and shallow alluvium. In the larger drainages, flow is intermittent to ephemeral, and those drainages lose which flow to the alluvium may regain flow downstream where the alluvium thins or the saturated zone intersects the channel base. Summer precipitation is largely consumed by evapotranspiration so that only high intensity storms produce significant summer stream flow. EAST RDD ENVIRONMENTAL MONITORING, SAMPLING AND ANALYSIS PLAN 2