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20 July 2005 r AGE-NC Project No. 95-0109 Page 4 of 5 3.3. OZONE SPARGING REMEDIATION Ozone injection operation began at the site on 14 October 2004. The ozone system currently injects ozone for a 2-hour duration into one ozone injection point at a time. The injection pressure was measured at 10 psi and the ozone injection rate was approximately 10 cubic feet per hour. 4.0. DISCUSSION AND CONCLUSIONS Based upon data collected from the site, AGE finds: • Ground water on-site and off--site was inferred to be flowing towards the south. The ground water gradient averaged 0.001 ft/ft on-site and off-site. • TPH-g was detected at the southern edge of the site, in ground water samples from wells MW-S, MW-9 and MW-14, at concentrations as great as 6,100 pg/1 (MW-9). • Benzene was detected in the two samples collected from on-site well MW-9 and off-site well MW-14, west of the site, at concentrations of 2.9 µg11, and 32 µg/l, respectively. • TPH-g and BTEX compounds were not detected for the sixth consecutive quarter in recently installed monitoring wells MW-20, MW-21 and MW-22. The lateral and vertical extent of petroleum hydrocarbon-impacted ground water has been defined. • The fuel additive 1,2-DCA was detected in samples collected from off-site well MW-9 and a on-site well MW-14 at concentrations ranging between 19 µg/1 (MW-9) and 9.3 µg11 (MW-14).Dissolved 1,2-DCA was not detected in any of the most recently installed ground water monitoring wells nor the newer deeply-screened wells. 1,2-DCA was not detected this quarter in the samples collected from off-site well MW-16. The lateral and vertical extent of the 1,2-DCA contamination appears to be defined. 5.0. RECOMMENDATIONS Based upon data collected from the site, AGE recommends: • Continued quarterly ground water monitoring as required by Clean-up and Abatement Order No. 93-701.The next ground water monitoring event will be scheduled for September 2005. • Continuation of ozone sparging remediation and installation of additional ozone wells to address the dissolved hydrocarbon ground water plume.The continuation of ozone injection and installation of additional wells were approved by CVRWQCB letter,dated 11 July 2005. Advanced GeoEnvironmental,Inc.