SITE INFORMATION AND CORRESPONDENCE_FILE 2

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GeoHydrologic Consultants, Inc. seen within the treatment zone. The results of the long-term bromate attenuation test are presented in Table 1 1 of the Prima Report located in Appendix B. 4.4 Conclusions The ozone bench scale study demonstrated that site petroleum hydrocarbons in soil and groundwater can be successfully destroyed with ozone treatrriunt. in both the low dose (1,600 mg) and high dose (2,600 mg)ozone treatments greater than 99%of COCs were destroyed in the groundwater, with less than I%detected in off-gases. The entire Prima Bench Scale Test Report which presents soil and groundwater sampling results, and the effectiveness of this bench scale study, is attached in Appendix B. Cr(VI) and bromate were generated with treatment of ozone at concentrations that exceeded the maximum contaminant levels (MCLs) in groundwater for Cr(VI) of 0.050 mg/L and bromate of 0.010 mg/L. The results of the Cr(VI) attenuation study indicated that the soil from the Site has some ability to reduce Cr(VI) and that ozone may affect the ability of the soil to attenuate Cr(VI), but the magnitude of the effect depends on the amount of ozone applied. The results of the long-term Cr(VI) attenuation test showed that Cr(VI) readily attenuated in simulated downgradient conditions with complete removal of Cr(VI) in only seven days. In contrast, the concentration of Cr(VI) initially increased within the treatment area, but then slowly attenuated. Complete removal had not occurred with 60 days. The results of the long-term bromate attenuation tests showed that bromate appeared to attenuate slowly in tests simulating downgradient conditions; by 28 days the bromate concentration had decreased from 0.31 mg/L to 0.16 mg/L, still well above the MCLs for bromate (0.010 mg/L). In contrast no attenuation was seen within the treatment zone during the study. Other secondary parameters behaved as expected, with alkalinity decreasing and pH increasing. 5.0 CONCLUSIONS AND RECOMMENDATIONS The ozone bench scale study demonstrated that site petroleum hydrocarbons in soil and groundwater can be successfully destroyed with ozone treatment however ozone sparging generated elevated concentrations of Cr(VI) and bromate at concentrations that exceeded the California MCL for these compounds. In addition, the attenuation study conducted for the CC(VI) and bromate which was formed demonstrated that both of the compounds were relatively slow to attenuate downgradient to concentrations below the MCL and attenuation within the treatment zone either showed very slow attenuation rates with respect to Cr(VI) or no appreciable attenuation with respect to bromate. Therefore, based on these results ozone sparging is no longer being proposed for the Site because of the elevated risk that ozone sparging activities will create a new Cr(VI) and bromate plume within the treatment area at concentrations that will exceed the California MCLs for these compounds. Based on the recent developments at the Site which included removal of the USTs, fuel lines, and dispensers it does not appear that the Site will be used for retail fuel sales in the TOC#172 Bench Scale Test Page 15