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f , <br /> GROUND ZERO ANALYSIS, INC. <br /> 1714 Main Street <br /> Escalon, Califorma 95320 <br /> Telephone (209)838-9888 <br /> Facsimile (209)838-9883 e <br /> June 22,2006 <br /> aY►-�, <br /> Ms Vicky McCartney <br /> San Joaquin County Environmental Health Department a b � <br /> 304 E Weber Ave , Third Floor " <br /> Stockton, CA 95202 <br /> Subject Human Health Risk Screening Evaluation—Vapor Intrusion from Groundwater <br /> H&H Engineering and Construction Facility,212 Industrial Drive, Stockton, CA <br /> Dear Ms McCartney <br /> This letter report summatizes the results of a Human Health Risk Screening Evaluation conducted <br /> For the subject facility The put-pose of the evaluation was to determine whether residual <br /> concentrations of petioleuim hydiocarbon contaminants in groundwater might pose a significant risk <br /> to occupants of the property either under current use conditions or under assumed residential <br /> conditions The exposure pathway evaluated was inhalation of hydrocarbon vapors intruding a <br /> building The location of the site is shown on Figure I A site plan is presented on Figure 2 <br /> BACKGROUND <br /> Low levels of soil and groundwater contamination are present beneath the site as a iesult of a leaking <br /> undeiground storage tank The tante was removed in 1987 and several phases of subsurface <br /> investigation followed (1998-present) The initial investigation found the soil contamination was <br /> limited to the tank removal area, but additional work was needed to evaluate the groundwater <br /> Monitoring wells were installed and subsequent investigations have defined the extent of <br /> groundwater contamination Historically, groundwater has been contaminated with TPHg and <br /> BTEX compounds, predominantly benzene Contaminant concentrations in groundwater have <br /> declined greatly since the late 1990's and an analytical model predicted that concentrations of <br /> benzene above the MCL would most likely never migrate offsite Soil analytical results are <br /> summarized in Table i Groundwater analytical tesults are summarized in Table 2 Figure 3 depicts <br /> the area of groundwater impact <br /> At the suggestion of San Joaquin County Environmental Health Depaitment (EFID) Ground Zero <br /> submitted a request for case closure on September 27, 2005 (Second Semi-Annual 005 <br /> Gi oundwatei A10777t07 ing and.Sampling Report and Request fol Case Closin e) The clostue request <br /> included a "Checklist of Required Data for No Further Action Requests at Underground Storage <br /> Tank Sites' pursuant to California Regional Water Quality Control Board (RWQCB) "Tri-Regional <br /> Guidelines" In a letter dated April 4, 2006, EHD responded to the closure recommendation by <br /> oil <br /> G'GROUNDZ[1W-CIR[Sh1HHRSCGWTxi doc <br /> i <br />