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L - <br /> City of Stockton A68108.01B <br /> July 18, 1997 Page 9 <br /> impacted soil. The greatest concentrations of PPC detected in this volume (15,000 mg/kg <br /> of TPH-G) suggests this PPC impacted soil is a potential source for groundwater <br /> contamination. <br /> The concentrations of PPCs detected in the groundwater sample suggest that the <br /> groundwater may already be impacted. The presence of groundwater contamination should <br /> be confirmed by performing a groundwater assessment prior to formulating a remediation <br /> plan. A groundwater assessment normally would require the installation of monitoring wells <br /> and at least four quarters of groundwater monitoring. Information collected during the <br /> groundwater asssessment may be used .with a risk based assessment to support a site <br /> classification of "low risk", facilitating site closure. <br /> n 7.0 CONCLUSIONS <br /> • The extent of PPC migration in soil appears to be limited to a roughly cylindrical <br /> volume between 16 and 32 feet BSG with a radius ranging from 3 to 10 feet; <br /> Groundwater beneath the site appears to be contaminated with,PPCs; <br /> 8.0 RECOMMENDATIONS <br /> 1 <br /> a <br /> • Copies of this report should be forwarded to SJCPHS for review and comment; and <br /> • Additional investigation based on the concentrations of PPCs remaining in soil and <br /> their potential to impact groundwater should be performed. <br /> 9.0 LIMITATIONS <br /> Finding and recommendations presented in this report are based on the assumption that <br /> subsurface conditions and chemical concentrations do not deviate from those disclosed in <br /> r. the field and laboratory testing. If variations from these findings are found, Twining should <br /> be notified so that supplemental conclusions and recommendations, may be provided. <br /> The purpose of a geologic/hydrogeologic study is to reasonably characterize existing site <br /> conditions based on the geology/hydrogeology of the area. In performing a such study, it <br /> Y <br /> is understood that a balance must be struck between a reasonable inquiry into the site <br /> ' conditions and an exhaustive analysis of each conceivable environmental characteristic. No <br /> �' investigation is thorough enough to describe all eolo geolo is h -dro is conditions of interest <br /> at a given site. <br /> �J g / Y g g <br />{i s <br />