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U <br /> D p <br /> August 27, 2004 <br /> A 2904 <br /> ENVIR NiEtu548, <br /> 11 ; / 1 4 <br /> Ms. Lori Duncan FqW� 0 <br /> San Joaquin County <br /> Environmental Health Department AUG 3 0 2004 <br /> 304 East Weber Avenue, Third Floor E WRRDNA/IEl5 i IirH(TH <br /> Stockton, California 95201 SIT/SERVICES <br /> RE: Workplan for Additional Assessment <br /> Former ARCO Service Station 548 <br /> 1612 W. Hammer Lane <br /> Stockton, California 95209 <br /> Dear Ms. Duncan: <br /> URS Corporation Americas (URS), on behalf of Atlantic Richfield Company (ARCO—a BP <br /> affiliated company) has prepared this workplan to conduct an additional assessment at former <br /> ARCO service station No. 548 located at 1612 W. Hammer Lane in Stockton, California (site). <br /> This workplan has been prepared to investigate the vertical extent of groundwater contamination <br /> and to install monitoring wells that will intercept first groundwater as requested in the San Joaquin <br /> County Environmental Health Department (SJCEHD) letter dated, June 21 , 2004 (Appendix A). <br /> • One shallow monitoring well will be installed off site in the downgradient groundwater <br /> flow direction to monitor hydrocarbon impacts at first groundwater. <br /> • One deep monitoring well will be installed just downgradient of the highest known methyl <br /> tertiary butyl ether (MtBE) concentrations to assess the vertical extent of impacted <br /> groundwater. <br /> • Additional shallow monitoring wells will not be installed at this time. The existing <br /> network of vapor wells provides adequate coverage of upgradient and cross gradient <br /> groundwater conditions. Although these vapor extraction wells are constructed to be used <br /> as remediation wells and screened with large slot sizes (0.05 to 0. 10 inches), they do <br /> intercept first water, and samples collected from them should be considered representative <br /> of true groundwater conditions. <br /> URS Corporation <br /> Crown Corporate Center <br /> 2870 Gateway Oaks Drive, Suite 300 <br /> Sacramento, CA 95833 <br /> Tel: 916.679.2000 <br /> Fax: 916.679.2900 K:\WprocessV5 BP ARCO\00548\2004 well install\WP 04.doc <br />