SITE INFORMATION AND CORRESPONDENCE_FILE 2

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GeoHydrologic Consultants, Inc. The results of ozone treatment on secondary water quality parameters are shown in Table 7 of the Prima Report located in Appendix B. 4.3.5 Ozone Demand The ozone demand for soil was 112— 115 mg ozone/kg of soil, and this result was anticipated given the low concentrations of COCs and total organic carbor. in the site soil sample. The ozone demand for groundwater was 337 —350 mg ozone/L of groundwater, and this result was lower than anticipated. Based on the concentrations of COCs in untreated soil and the stoichemetries for ozone reaction, the theoretical ozone demand was 1,850 mg/L. A possible explanation is that COCs were not completely destroyed in the empirical ozone demand test, rendering the measured ozone demand lower than expected. The ozone demand for soil and groundwater are shown in Figure's 1 and 2, respectively, of the Prima Report located in Appendix B. 4.3.6 Attenuation of Bromate and Cr(VI) Because bromate and Cr(VI) were observed during ozone treatment additional tests were conducted to determine whether these compounds are likely to attenuate within the treatment area at the site (once ozone treatment stops) and downgradient of the site. 4.3.6. 1 Cr(VI) Untreated soil and soil treated with a low dose of ozone reduced up to 1.9 mg Cr(Vl)/kg soil, while treated with a high dose of ozone reduced up to 1.4 mg Cr(VI)/kg soil. These results indicate that the soil 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, however, a trend of attenuation had clearly been established. The results of available Cr(VI) reducing capacity test are shown in Table 9, and the long-term Cr(VI) attenuation test results are presented in Table 10 of the Prima Report located in Appendix B. 4.3.6.2 Bromate 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. In contrast no attenuation was TOC 4172 Rench Scale lest Page 14