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• Ms Margaret Lagroio August 11,2004 Subsurface Assessment Report Project No 2033-15600-01 Joe's Truck Plaza, 15600 South Harlan Road,Lathrop,CA Page 10 immediate vicinity of, and downgradient from, the former USTs The vertical and lateral extent of soil impact appears to be adequately characterized, and additional evaluation of soil impact does not appear warranted Soil analytical data collected during this investigation do not alter the understanding of the lateral extent of soil impact developed in the SCM, and do not substantially alter the estimated mass of hydrocarbons remaining in the soil as presented in the SCM MTBE was reported in the grab groundwater sample collected from boring CPT-5 at 11 feet bgs It has been our experience that when wells are installed at locations where grab groundwater samples initially show low concentrations such as was reported in boring CPT-5, the wells usually report non-detect (ND) concentrations (below laboratory limits) Because we believe that a well installed in the vicinity of boring CPT-5 would return a ND result, we believe that boring CPT-5 adequately characterized the lateral extent of MTBE impact within Sand A to the northeast The vertical extent of impact appears to extend to approximately 40 feet bgs downgradient of the former USTs Low concentrations of dissolved MTBE were reported in grab groundwater samples collected within Sand B in boring CPT-8, but the lateral and vertical extent of this impact has been adequately characterized Dissolved MTBE was not reported in Sand C Analytical data from the grab groundwater samples collected during this investigation did not substantially alter our understanding of the lateral extent of dissolved MTBE impact in the first encountered groundwater In addition, these analytical data do not appear to substantially alter the estimate of dissolved mass remaining beneath the site Given that the lateral and vertical extent of dissolved MTBE impact appears to be adequately characterized, and there are no groundwater receptors within 2,000 feet of the site, additional characterization of dissolved MTBE does not appear warranted LIMITATIONS This report was prepared in general accordance with accepted standards of care that existed at the time this work was performed No other warranty, expressed or implied, is made Conclusions and recommendations are based on field observations and data obtained from this work and previous investigations It should be recognized that definition and evaluation of geologic conditions is a difficult and inexact art Judgments leading to conclusions and recommendations are generally made with an incomplete knowledge of the subsurface conditions present More extensive studies may be performed to reduce uncertainties This report is solely for the use and information of our client unless otherwise noted P Voe's Truck PlazalReportslCPT report 08-2004 doc