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� AMBRIA -7 -may request, during the first quarter 2005, groundwater samples all wells at the site were additionally analyzed for the fuel oxygenates tertiary butyl et�r,di-isopropyl ether,ethyl tertiary butyl ether, tertiary amyl methyl ether, 1,2-dichloroethane, ethylene dibronnde, and ethanol. None of the additional analytes were detected in site wells During the third quarter 2005 monitoring event, no TPHg or BTEX was detected in any of the sampled wells MTBE was detected in well MW-1 only at a concentration of 12 ppb Histoncal groundwater data and the third quarter 2005 groundwater elevation contour map are included in Appendix A SITE CONDITIONS Regional Geology- The subject site is located at the northern end of the San Joaquin Valley, a broad, flat valley filled with alluvium. The ground surface elevation of the subject site is approximately 35 feet above mean sea level (msl) In the vicinity of the site, the ground gently slopes toward the southeast Soil Types Soil types beneath the subject site are primarily fine-grained soils (silt and clay) with lesser amounts of coarse-grained sediments (sands) to the total explored depth of 45 fbg • Boring logs and cross-sectional diagrams are included in Appendix$ V kA, 'A re, „Y el vntcof n A-PPe,,zd'k B 11 --Z - J3 Hydrvgeology Groundwater occurs at approximately 25 5 fbg at the site Measured depths to groundwater in the site wells have ranged historically from 15 1 to 29 5 fbg, and groundwater elevations have ranged historically from 7 2 to 20 3 feet above ms] Shallow groundwater flow beneath the subject site is variable but generally is toward the southwest at a gradient ranging from 0 001 to 0 003 Groundwater depth and elevation data and the most recent groundwater contour map are included in Appendix A Hydrocarbon Distribution in Sod- Excluding detections that were over-excavated, maximum concentrations detected at the site in the vicinity of the northwestern former USTs are 27 ppm TPHg, 0 055 ppm benzene, and 34 ppm MTBE The lateral and vertical extent of these detections in soil has been defined by non-detect results in soil samples collected in the vicinity, including samples collected from the:CPT borings Excluding detections that were over-excavated, no TPHg, benzene, or MTBE has been detected beneath the former dispenser islands or piping at the site No TPHg, benzene, or MTBE was detected beneath the former USTs in the northeastern corner of the site 0323 4