COMPLIANCE INFO_FILE 9 - Laserfiche WebLink

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siltstone/claystones (Tnsc1), and it underlies most of the central Site 300 GSA. Ground water elevations in this unit range from 491 ft. above mean sea level (MSL) to 515 ft. above MSL. Unconfined groundwater flows southward in the Qt-Tnsc1 hydrologic unit. Where groundwater in this hydrologic unit discharges to the stream channel alluvium in the Corral Hollow streambed, the groundwater flow direction follows the streambed toward the east. The lowest stratigraphic unit, Tnsc1, serves as a confining layer between the Qt-Tnsc1 hydrologic unit and the underlying Neroly lower blue sandstone (Tnbs1) hydrologic unit, as indicated by water chemistry and hydraulic head differences between the two units. Water level elevations in the Qt-Tnsc1 hydrologic unit are higher than in the underlying Tnbs1 hydrologic unit. Although the Tnsc1 stratigraphic unit has low porosity and primary permeability, our observations of mineral coatings on fractures in cores indicate that it has moderate fracture (secondary) permeability. Neroly Lower Sandstone (Tnbs1) Hydrologic Unit: The Tnbs1 hydrologic unit underlies the Qt-Tnsc1 hydrologic unit throughout the central General Services Area. Groundwater elevations within this unit range from 493 ft. above MSL to 514.7 ft. above MSL. Within the Tnbs1 hydrologic unit, groundwater is confined and flows in a southerly direction, oriented subparallel to the bedding planes of the bedrock. Groundwater in the Tnbs1 regional aquifer is hydraulically isolated from overlying shallow (Qt-Tnsc1) aquifer by the Tnsc1 confining layer. Data from wells completed in the Tnbs1 unit in the central GSA indicate that saturated conditions exist beneath most of the GSA. Mineral data from groundwater collected from ten wells completed exclusively in the Tnbs1 hydrologic unit were used to characterize this unit. Groundwater in the Tnbs1 water-bearing zone is dominated by the sodium cation and contains no dominant anions. In general, groundwater from the Tnbs1 hydrologic unit is higher in sodium that water from the Qt-Tnsc1 hydrologic unit. Two groundwater monitor wells, W-873-01 and W-873-03, are located downgradient of Building 871. Well W-873-03 is completed in the shallow Qt- Tnsc1 aquifer and well W-873-01 is completed in the deeper Tnbs1 regional aquifer. No aromatic hydrocarbons (BTXE compounds) have ever been detected in groundwater samples collected from these wells. No analysis for total fuel hydrocarbons has been performed on groundwater samples from these wells. - 9 -