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CAMBRIA <br /> S <br /> Quarterly groundwater monitoring and sampling has been performed at this site since January <br /> 1995 Depth to water at this site has ranged from approximately b to 13 feet below grade (fbg) <br /> and groundwater flow direction has vaned at the site but has predominantly been either toward <br /> the northeast or southwest <br /> WORK PLAN <br /> Technical Rationale for Proposed Scope of Work <br /> • After the former USTs were removed and overexcavation was performed (1995), soil <br /> samples collected from the finished excavation contained residual levels of petroleum <br /> hydrocarbons A map and table displaying these data are included in Appendix A <br /> • Shallow overexcavation was also performed along the southern edge of the northern <br /> dispenser islands in 1995 Soil sampling analytical data from this area of the site <br /> indicates the overexcavation efforts were effective in removing the majority of the <br /> petroleum hydrocarbon impacted soil <br /> • A OWE system operated at this site from June 2001 until October 2003 Groundwater <br /> influent data collected while the GWE system was in operation show only a slight <br /> decline in petroleum hydrocarbon concentration during this operational period The slow <br /> decline in petroleum hydrocarbon concentration may be due to residual petroleum <br /> hydrocarbons in shallow soil in the vicinity of the former UST complex <br /> • The former UST complex was backfilled with 2-inch diameter gravel from 11 to 15 fbg <br /> and then clean, compacted, fill material above that Well RW-IA was installed in the <br /> former UST excavation This well has contained elevated levels of petroleum <br /> hydrocarbons and methyl tertiary butyl ether (MTBE) since it was installed It is <br /> possible that impacted groundwater has introduced petroleum hydrocarbons into the <br /> clean backfill material in the former UST area <br /> • Available soil analytical data (shown on Figure 2) and historical groundwater monitoring <br /> data suggest the southern portion of the site is where the highest levels of petroleum <br /> hydrocarbons have been detected <br /> 0783 2 <br />