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Pombo Ranch Property Second Quarter Groundwater Sampling Report May 2005 Page: 3 GROUNDWATER MONITORING WELL REPLACEMENT On February 28, 2005 M.J. Kloberdanz & Associate started an excavation of the source area of contamination closest to the former underground gasoline tank. A Photo Ionization Detector was used to screen contaminated soils from clean soils and to assist in worker health and safety. The impacted soils exhibited a dark gray discoloration and gasoline odor, which was confirmed with the Photo Ionization Detector. Soils near the original release were impacted below a depth at about 5 feet below grade. Away from the point of release, the depth to impacted soils increased to an average of 8 feet below surface grade. Soils above 8 feet in depth were then segregated into a "clean pile" for reuse as fill in the excavation. Groundwater was measured at a depth of about 12 feet from the surface in the January 2005 quarterly monitoring event. Depth to water was estimated at least 12 feet from ground surface in the area of the former UST on February 28`'limiting the vertical extent of the excavation to 12 feet below grade surface. Apparent contamination extended in a north to northeast direction and the lateral limits of the excavation resulted in an irregular shape 65' to the east of the former underground tank and 50 to 62 feet north of the 65'south lateral line (see Figure 2). Monitoring well MW-4, located within the area of excavation was destroyed. The well was re-installed in the same approximate location and is identified as MW-4B. The well was constructed the same as former MW-4, 20 feet deep with 15 feet of screen (Appendix Q. The well had not been surveyed at the time this report was drafted so it was not used in the gradient calculations this quarter. However, the survey map was received on the day of this printing and is included in Appendix C. CONCLUSIONS AND RECOMMENDATIONS Shallow ground water flow was to the northeast and southwest with very flat gradients. Low concentrations of gasoline petroleum hydrocarbons and volatile aromatic hydrocarbons were detected by the analytical laboratory in water samples collected from the monitoring well MWS located down gradient from the former underground storage tanks. Low concentrations of fuel oxygenates were detected in the water sample collected from the monitoring well MW413 located at and immediate down gradient from the former underground storage tanks. The contamination is defined laterally and vertically. The dissolved oxygen low in the vicinity and down gradient of the release indicates that the biological breakdown of the groundwater contamination is occurring. The San Joaquin County/ Environmental Health Division modified and approved on November 3, 2004, the M.J. Kloberdanz work plan for the over excavation and removal of impacted soils in the source area. Quarterly monitoring will continue to confirm the breakdown of the remaining contaminants.