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'• 4.0 CONCLUSIONS AND RECOMMENDATIONS Based on the results of this environmental site investigation, soil and groundwater beneath the site have been impacted by detectable concentrations of gasoline constituent compounds The greatest concentration of impacted sod appears to be present immediately beneath the former UST excavation These concentrations of gasoline hydrocarbons decline rapidly with depth below 15 feet Low concentrations of xylenes do extend to a depth of between 65 and 80 feet bgs The vertical extent of impacted soil was defined in this boring at a depth of 80 feet Groundwaterhydrocarbons The groundwater- grab beneath the site has been impacted by gasoline ydroc g grab sample collected contained relatively low concentrations of TPH-as-gasoline, toluene, ethylbenzene, and xylenes, and was free of detectable concentrations of benzene, oxygenates and 1,2-DCA Groundwater from the on-site domestic well did not contain detectable ' concentrations of any of the gasoline constituent compounds analyzed Based on these conclusions, Ramage Environmental recommends that a work plan be prepared, which includes the following course of environmental corrective action 1 Install three on-site groundwater monitoring wells These wells will be used to further evaluate the lateral extent of impacted groundwater and to establish a groundwater monitoring capability at the site 2 Monitor and sample groundwater from the three monitoring wells and the on-site domestic well on a quarterly basis for at least one year The groundwater samples should be analyzed for TPH-as-gasoline, BTEX, MTBE, DIPE, ETBE, TAME, TBA, and 1,2-DCA by EPA Method 8260B 3 Conduct a survey of sensitive receptors within a 2,000-foot radius of the site The survey should include the location of all wells, surface water bodies, schools, and other receptors within 2,000 feet of the site boundaries Information from the survey should be obtained from field reconnaissance within 500 feet of the site, local water purveyor(s), PHSIEHD, and the California Department of Water Resources (DWR) i 11 i