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ATTACHMENT F:MAPS AND CROSS SECTIONS OF GEOLOGIC STRUCTURE OF AREA Geologic Cross Sections Figure F-3 shows the local surficial geology for the area surrounding the STIG-LEC facility. This figure is a combination of the Sacramento and the San Francisco-San Jose Quadrangle Geologic Maps of the State of California. A regional cross section showing some of the local folds and faults is shown in Figure F-4. Two perpendicular geologic cross sections were developed using geophysical logs from exploratory gas wells to show the local subsurface geology in the STIG-LEC facility area. Figure F-5 shows the location of the wells used to develop the cross sections. The cross sections are shown in Figures F-6 and F-7. The cross sections intersect the STIG-1 well and extend to a depth of 6,000 feet,which is well below the 4,650-foot total depth of STIG-1,the proposed depth of LEC-1,and the USDWs. The cross sections show the shallow dip of approximately 2 degrees to the southwest. Most units also thicken basinward,toward the west or southwest,with the exception of the Meganos Gorge Fill unit,which thins away from the STIG-1 well toward the northwest and southeast. History of Local Hydrocarbon Production The creation of structural traps from the region's tectonic history and sedimentary traps from historic deposition created opportunities for hydrocarbon production. Numerous exploratory wells have been drilled in the area since the 1950s to evaluate this potential. Although numerous small hydrocarbon fields—primarily gas fields—have been identified in the region (Figure F-8), seven of the eight deep wells drilled for hydrocarbon exploration within the 2-mile AOR were destroyed within days or weeks of completing the drilling and/or testing programs for each well (see Table C-1). The one active gas well within the AOR (Piacentine#1-27) is still producing gas,although not at the levels observed during its initial operation. Injection Zone The lower sand member of the Domengine Formation was originally selected as the target injection unit for the STIG-1 well because: • Salinity is greater than 10,000 mg/L TDS. • It had been demonstrated to have adequate injectivity. • It is confined by a regionally extensive shale unit. • Injection was not expected to have (nor has it shown to have) any influence on existing water wells or local groundwater resources. Additional discussion of the Domengine Formation is included in Attachment 1. SAC/371322/082550021(ATTACH MENT-F.DOC) F-3