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Ozone Microsparge System First 5etni-Annual Status Report--76 Branded(Former BP)Facility No. 11195,Lathrop,California <br /> September 2 2003 <br /> MW-2, and MW-4 indicate an MtBE reduction of over 99%, 79%, and 35%,respectively. With the <br /> exception of a few reported concentrations that do not resemble TPHg, benzene and TPHg have <br /> remained non detect for the wells at and in the vicinity of the site. <br /> CONCLUSIONS AND RECOMMENDATIONS <br /> The results of the concentration versus time charts show that hydrocarbon concentrations have <br /> declined overall during the past six months of remedial system operation. The ozone sparging <br /> system is demonstrating success in reducing petroleum concentrations in the groundwater at this <br /> site. This includes MtBE, which is the compound of primary concern. Although initial increases in <br /> petroleum concentrations have been observed, primarily in impacted soil areas, they have been and <br /> are expected to be short term followed by continuous concentration decreases. <br /> The current ozone injection addresses the dissolved impact both onsite and offsite, and as a result, <br /> will decrease any continuing migration of dissolved hydrocarbons offsite. The ozone microsparge <br /> system will continue to operate and monitoring wells MW-3 and MW-10 will continue to be <br /> sampled on a monthly basis. Another semi-annual status report will be prepared and submitted <br /> following the receipt of 4"quarter 2003 data. <br /> s System Information <br /> Startup Date: December 20,2002 <br /> Months of Operation: 6 <br /> Number of ozone injection points: 15 (SP-1 through SP-15) <br /> Periodic groundwater sampling: MW-3, MW-10 <br /> 140193.16 4 <br />