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Pomba Property Subsurface Investigation Retort Page: S Groundwater was encountered at depths of 9 to 12 feet below grade in Geoprobe'� ' borings B9, B 10, B i 1, and B 12. All of the Geoprobe"' borings were terminated in the coarse sand Unit (lower sand). Boring B-9, installed to determine the vertical extent of the contamination, passed through the thin shallow, confined to semi- confined, sandy unit (upper sand) and was terminated in the well-sorted sand present at the base of the borings (lower sand). ' All three monitoring wells also terminate in the lower sand, The thin shallow, confined to semi-confined, sandy unit (upper sand) is not recognizable in boring MW3. Based on depth to water measurements conducted during the July 1999 monitoring event, ground water flow was north 23 degrees east with a gradient if 0.0124 feet per feet on July 23, 1999. n' Pombo Groundwater Elevations (7-23-99) Well lCollar Elevation DTW GW Elevation ' MW-1 52.69 9.24 43.45 MW-2 52.78 9.34 43.44 MW-3 54.3 9.3 45 ' Jul 23 1999 groundwater elevations and flow direction are h July g sown on Figure 4 Groundwater Gradient Map. 1 � 3.2 Soils Contamination Laboratoryresults of analyses of soil samples collected in y p this investigation are presented in Appendix A and summarized in the tables "Geoprobe"-Laboratory i' Soil Sample Results (July 6, 1999)" and "Laboratory Soil Sample Results (July 20, 1999)". Gasoline and volatile aromatic hydrocarbons were detected in the ' laboratory sample collected from boring B-11 at a depth 10 feet, located east of the previously removed underground fuel tank. The 10 foot sample in boring B- 11 occurs in the thin shallow, confined to semi-confined, sandy unit (upper sand) discussed above. The analytical laboratory reported non-detectable concentrations ' of gasoline, BTEX, and MTBE for all other soil samples. ' 3.3 Groundwater Contamination Laboratory results of analyses of groundwater samples collected in this investigation are presented in Appendix A and summarized in the tables "GeoprobeOP-Laboratory Water Sample Results (July 6, 1999)" and "Laboratory Well Water Sample Results (July 23, 1999". Low concentrations of contaminants were detected in the shallow Geoprobe t ground water samples. 6.5 mg1I gasoline r range petroleum hydrocarbons, 33 ug/1 benzene, 49 ug/l toluene, 170 ug/1 ethyl ' benzene, and 470 ug/l total xylenes, were detected in the groundwater sample I