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1 <br /> ARCADIS GERAGHTY&MILLER <br /> EXECUTIVE SUMMARY <br />' This report presents the results and findings of a supplemental site characterization field <br /> investigation, file reviews, and analyses conducted by ARCADIS Geraghty & Miller, Inc, on <br />' behalf of Union Oil Company of California (UNOCAL), between August, 1998 and March, <br /> 1999, regarding the former UNOCAL service station number 0187, located at 437 East Miner <br /> Avenue, Stockton, Califomia (the Site) Two nests of monitoring wells were installed, each <br /> consisting of three wells installed at discrete depths One well nest (NP-1) was installed near <br /> the previously identified source area and the other (NP-2) was installed offsite approximately <br /> 75 east of the Site This report describes the field installations, data collection techniques, and <br />' resulting data analysis and conclusions Additionally, the historical record of data and events <br />' regarding the Site have been examined, analyzed, and presented The results of a sitewide <br /> groundwater morntoruig event conducted February 5, 1999 are also presented and evaluated <br /> The primary petroleurr. hydrocarbon sources, relating to the dispensing of gasoline <br />' products at the Site, have been removed <br /> Based on data from two continuously sampled 100+foot deep bonngs (NP-1 and NP- <br /> 2) advanced at the Site, impacts from the Site release occurred during at a tune when <br /> groundwater levels were lower and groundwater has subsequently risen into the zone of <br /> impacted soils This interpretation is consistent with historic local water level changes <br /> General water quality in the vicinity of the Site is poor and does not meet California <br />' State standards (MCLs) for acceptable drinking water All of the wells at the Site have Total <br /> Dissolved Solids concentrations above the Cahfo-nia State Maximum Contaminant Level The <br />' Site hes in a location that has been mapped as within the influence of an intruding salt water- <br /> front <br /> aterfront documented in the 1997 San Joaquin County Flood Control & Water Conservation <br />' Report <br /> v <br />