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�� W IN ZLER�KELLY l Mr lames Ueda j ' September 17, 2004 Page 2 ' Chemical Analysis Analytical Sciences Laboratory (Analytical Sciences) of Petaluma, California (a California-certified laboratory) analyzed groundwater samples for total petroleum hydrocarbons as gasoline (TPH-G) by EPA Method 8015M, and for benzene, toluene, ethyl benzene, and total xylenes (BTEX), and oxygenated fuel additives by EPA Method 8260B GROUNDWATER MONITORING AND SAMPLING RESULTS The groundwater elevation data and groundwater flow direction are presented in Tables 1 and 2 A groundwater contour map,provided as Figure 3, illustrates the groundwater elevation contours and ' flow direction at the site on August 13, 2004 As Figure 3 shows, the groundwater flow direction at the site was toward the northeast, at an approximate gradient of 0 01 ft/ft j i During purging activities, the parameters of pH, conductivity, temperature, and oxidation-reduction ' potential were monitored in the groundwater extracted from the wells A summary of these indicator parameters is provided in Table 3 Table 4 summarizes the analytical results of groundwater samples collected from monitoring wells at the site Figure 4 depicts the concentrations of TPH-G, benzene, tert-butyl alcohol (TBA), and methyl tert-butyl ether (MTBE) in the groundwater samples collected on August 13, 2004 Consistent with previous sampling events, the groundwater samples collected from MW-4 by EPA Methods 8015M and 8260B did not identify the presence of any petroleum related constituents ' above the laboratory's reportable detection limits MTBE was the only petroleum-related constituents detected in the groundwater samples collected from monitoring wells MW-1 through MW-3 The laboratory QA/QC included the use of method blanks to exclude false-positive analyses and the use of laboratory control samples to evaluate the percentage recovery of known analyte spikes The recovery percentages for all of the sample analytes were within acceptable ranges The complete laboratory report, QA/QC data, and the chain-of-custody form for the groundwater samples are included in Appendix B RECOMMENDATIONS The August 13, 2004 sampling event verified that the concentrations of petroleum hydrocarbons in the groundwater at the site are very low Furthermore, the deep well (MW-4) did not contain any petroleum-related constituents, indicating that the lower aquifer is not impacted Based on this, the site no longer represents a threat to groundwater, and Winzler& Kelly once again recommends that the site be closed