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GETTLER - RYANINC'. st t March 3, 2003 Mr Ed Ralston ConocoPhillxps 76 Broadway Sacramento, CA 95818 R.E. Ozone Microsparge System First Semi-Annual Status Report Former Tosco(76) Service Station No. 6981 4707 Pacific Avenue, Stockton, California At the request of ConocoPhillips, Gettler-Ryan Inc (GR), has prepared this report documenting the status of operation for the year 2002 of an ozone microsparge remedial system, installed at the site to address hydrocarbon impacted groundwater (Figure 1) The remedial system was placed into operation on December 19, 2001 The system cycles ozone/air injection between ten of the thirteen (SP-1 through SP-13) sparge points (SP-1, SP-3, and SP-10 we currently not being used) (Figure 2) The schedule is currently set to cycle through each point 16 times per day, for between 5 and 15 ` minutes per point per cycle The schedule can be varied as part of the system evaluation process A description of the installation and startup of the remedial system can be found in GR's report Ozone Nlrcrovparge Well and System Installation Report, dated February 1, 2002 The primary constituents of concern at this site,are Total Petroleum Hydrocarbons as gasoline (TPHg) and benzene with methyl tertiary butyl ether (MtBE) as a minor contaminant Thirteen groundwater monitoring wells (MW-1 through MW-13), six vapor extraction wells (VW-1 through VW-6), and one groundwater extraction well (PTW-1) were installed on or near the site between January 1990 and August 1992 In February 1996, wells MW-3, MW-10, MW-12, and MW-13 were abandoned at the request of the city of Stockton This work was perforined to facilitate reconstruction of the intersection and widening of Pacific Avenue In August 1999, GR installed three groundwater monitoring wells (MW-14 through MW-16) and one vapor extraction well(VW- 7) These groundwater monitoring wells replaced the wells that were abandoned in February 1996 A vapor extraction system was installed at the site and was operational from September 1994 to the third quarter of 2001, and is currently in pulse mode Groundwater has been monitored on a quarterly basis since 1990 and sampled at the site on a quarterly or semi-annual basis since April 1993 Currently the wells are sampled on a quarterly basis 1 he quarterly sampling event before beginning the ozone sparge system was in conducted December 2001, while the last quarterly sampling event used in this evaluation occurred in December 2002 J he original laboratory data reports for the quarterly/semi-annual sampling events are included in the quarterly/semi-annual groundwater monitoring and sampling reports previously submitted under separate cover, and are not included in this report A summary table of historical analytical i esults is presented in Appendix 0 A 6747 Sierra Court , Suite J o Dublin , California 94568 9 ( 925 ) 551 -7555