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--------------=----- - -------------------6ETTLER - RYA-N-- - --------------- ---- INC. September 2,2003 Mr. Edward Ralston ConocoPhiilips 76 Broadway Sacramento, CA 95818 RE: First Semi-Annual Status Report 2003 -Ozone Microsparge Remedial System 76 Branded(Former BP)Facility No. 11195 16500 South I-5,Lathrop, California At the request of ConocoPhillips, Gettler-Ryan Inc. (GR),has prepared this report documenting the status of the initial six months of operation of an ozone microsparge remedial system, installed at the location referenced above (Figure 1) to address petroleum hydrocarbon impacted groundwater. The ozone system was placed into operation on December 20, 2002. A description of the installation and startup of the remedial system can be found in GR's report Groundwater Monitoring Well Installation and Ozone Microsparge System Installation And Startup Report, dated May 20, 2003. The primary chemical of concern at this site is methyl tertiary butyl. ether (MtBE), with Total Petroleum Hydrocarbons as gasoline (TPHg) and benzene as a minor concern. Groundwater sainpling began at the site in 1992 after the installation of groundwater monitoring wells MW-1 through MW-5. Wells MW-6 through MW-21 were added in 1993, 1998, and 2002. Monitoring well MW-7 was destroyed in 1995. There is also one conductor casing well in the tank pit backfill (CC-WS) which was installed in 1998. From January 2000 through February 2003, weekly groundwater purging events were performed on CC-WS. The 20 existing monitoring wells are currently being monitored and sampled quarterly. The quarterly sampling event prior to beginning operation of the ozone sparge system was conducted on November 18 and 19, 2002, while the last quarterly sampling event documented in this report was performed on May 12 and 13, 2003. Historical sampling data tables for the quarterly sampling events which occurred from December 1992 through May 2003 are presented in Appendix A. Ozone Micro Sparging—System Overview The C-Sparge m ozone microsparging system, manufactured by K-V Associates, was placed into operation on December 20, 2002. Ozone microsparging is a process where ozone in air is introduced into the groundwater at low flow rates (2-6 cubic feet per minute) through specially designed macroporous plastic spargers to create"microbubbles." As these microbubbles rise within the column of water,the dissolved volatile organic compounds(VOCs) are rapidly oxidized. 6747 Sierra Court , Suite J Dublin , California 94568 ( 925 ) 551 - 7555