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i 30 June 1999 AGE-NC Project No.95-0185 Page 2 of 6 2.3. PRELIMINARY SITE INVESTIGATION In December 1995,AGE advanced five soil probe borings at the site. Free hydrocarbon product was encountered in ground water samples collected from the site. However, soil samples indicated that hydrocarbon-impacted soil was limited to the capillary fringe or lower vadose zone. Locations of the probe borings are illustrated on Figure 2. In June 1996, AGE installed four ground water monitoring wells. Between June 1996 and February 1999, 11 ground water monitoring and sampling events were performed at the site. The following is a summary of the ground water sampling results and findings: • TPH-g was detected from wells MW-1 and MW-4 at concentrations ranging to 730 ,ug/l; TPH-g was detected from wells MW-1 and MW-4 at concentrations ranging to 220,000µg/1 on site and 26,000µg/l off site and BTEX compounds were detected from wells MW-1 and MW-4 at concentrations ranging to 54 µg/l (xylene). • Fuel oxygenating compound di-isopropyl ether was detected from well MW-1 at concentrations ranging to 27 gg/l; methyl tertiary butyl ether was detected from well MW-4 at concentrations ranging to 6.5 ,ug/l and di-isopropyl ether was detected from well MW-4 at concentrations ranging to 24,ug/l. • Ground elevations have increased approximately four to five feet of the monitoring period, at some points increasing dissolved hydrocarbon concentrations near the ground water wells. Additional background information prepared by AGE is summarized in the Preliminary Evaluation and Investigation Report, dated 15 August 1996 submitted to the PHS-EHD. Additional analytical ground water data prepared by AGE is summarized in the March 1999 (dated 10 June 1999) Quarterly Report submitted to PHS-EHD. 2.3. REGIONAL GEOLOGIC SETTING The property is situated within the Great Valley Geomorphic Province of California, a large, elongate, northwest trending, asymmetric structural trough. The Great Valley Province has been . filled with thick sequences of sediment ranging in age from Jurassic to Quaternary, creatingYa nearly lyirig'alluvial plain; exfending-from the Tehachapi Mountains in tine south to the Klamath Mountains in the north.-The western and eastern boundaries of this province are comprised of the California Coast Range and the Sierra Nevada, respectively. Rocks composing the basement complex of the province have not been completely defined but are believed to be metamorphic and Advanced GeoEnvironmental,Inc.