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page 2, 1612 Hammer Lane <br /> maximum contaminant level (MCL) have been detected in groundwater samples <br /> collected from monitoring well MW-7 in four of the six reported quarterly sampling events <br /> that have occurred since it was installed; and above the secondary MCL at one <br /> additional event. As stated before, all other monitoring wells at this site currently have <br /> screen intervals submerged below the groundwater surface; samples collected from <br /> these wells may not be representative of first water conditions. <br /> While the lateral extent of the groundwater contamination is not completely defined <br /> towards the east, it is probably as practically defined as it can be at this time. The <br /> contaminant concentrations reported from MW-7 are two to three orders of magnitude <br /> less than those reported in the vapor wells on site, which are the only other wells with <br /> screen intervals similar to that of MW-7. In addition, structures to the east of MW-7 <br /> leave little practical location for further fieldwork in that direction. The focus of the site <br /> investigation at this time should be on determining the best and most cost effective <br /> method of groundwater remediation. <br /> Cross-sectional isoconcentration maps B-B', depicting the site from east to west, <br /> inadvertently omitted well AS-1 and its related contaminant concentrations. Please have <br /> these maps re-drawn to include this well. <br /> The well survey submitted with the original SCM is not complete. This site is located <br /> close to an unincorporated area of the city and there are many nearby residences not <br /> provided with city water. All homes on Andrea Ave. have domestic wells, not just the <br /> two listed in the well survey table, and several of these would be less than 950 feet from <br /> the plume. One of these wells, located at 7740 Andrea Ave., was sampled by ARCO at <br /> the request of the homeowner and was non-detect for constituents analyzed. Homes <br /> directly north of the site, located on EI Camino Ave., while cross gradient to the site, are <br /> also not provided city water. Please have an updated well survey completed. <br /> Please proceed with submittal of a remedial action plan (RAP), including proposals for <br /> any required feasibility testing, for addressing the cleanup of the remaining groundwater <br /> contamination at this site. The RAP is due for submittal to SJCIEHD no later than <br /> April 28, 2006. <br /> If you have any questions or comments please call Lori Duncan at (209)468-0337. <br /> Donna Heran, RENS, Director <br /> Environmental Health Department <br /> Lori Duncan, Senior REHS Nuel C. Henderson, Jr., PG <br /> LOP/Site Mitigation Unit IV LOP/Site Mitigation Unit IV <br /> cc: James Barton, CVRWQCB <br /> Vernon Elarth, URS <br />