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n <br /> Mr Ronald Rowe Project 22640-100 001 <br /> May 21, 1999 <br /> Page 4 <br /> HydroPunch samples from B-2 at 64 ft bgs and 74 ft bgs did not contain petroleum <br /> hydrocarbons The sample at 90 ft contained TBA at 69 ug/1 The sample collected at 102 <br /> ft bgs contained TPHG at 6,300 ug/l, benzene at 1,300 ugh and TBA at 130 ug/1 <br /> Groundwater samples collected from monitoring wells contained TPHG, BTEX, TBA and <br /> MTBE TPHG concentrations were 970 ugh and 170,000 ug/l Benzene concentrations <br /> were 100 ugh and 17,000 ugh in MW-8 and MW-9, respectively MW-8 contained TBA <br /> at 55 ugh and MTBE at 0 9 ug/1 <br /> Analytical results are summarized on Tables 1 through 4 Copies of certified analytical <br /> reports (CARS) and chain of custody (COC) documentation are presented in Appendix E <br /> CONCLUSIONS AND RECOMENDATIONS <br /> Petroleum hydrocarbon impacts were detected in soil and groundwater samples collected <br /> during the assessment Soil impacts are greatest in boring B-1 (MW-9) at 74 ft bgs <br /> Groundwater impacts 1n HydroPunch samples were highest in B-1/HP-1 at 70 ft bgs and in <br /> B-2/HP-2 at 102 ft bgs Impacts detected in monitoring well MW-8 are three orders of <br /> magnitude lower than those in MW-9 <br /> EMCON recommends sampling groundwater monitoring wells MW-8 and MW-9 to verify <br /> the previously detected concentrations of TPHG, BTEX, and fuel oxygenates If the <br /> concentrations remain high, additional assessment should be completed to further define <br /> the vertical and lateral extent of impacts It is possible this additional assessment could be <br /> performed using Geoprobe HydroPunch sampling, whereby discrete soil and groundwater <br /> samples can be collected <br /> If previously detected hydrocarbon concentrations are not verified (i e , significantly <br /> lower), then an appropriate plan of action for mitigating the hydrocarbon impacts should be <br /> developed and discussed with the San Joaquin County Department of Public Health <br /> Services Environmental Health Division <br /> Sincerely, <br /> EMCON <br /> Mark Cas, R G 6561 ay J nson, R G 5867 <br /> Project Manager m Project Supervisor <br /> CP1E IAPACHEIREPORTs1APACP102 D0C-98Usg 1 sEmcon <br />