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Ms.Kristi Shelton Page 5 of 6 CONCLUSIONS • The release/leak consisted of only petroleum. • The source of the contamination has been removed. • The release/leak did not occur in fractured bedrock. • The area is serviced by a public water system. • There is no free product. • The plume has been delineated as discussed in Ground Zero's Response to RWQCB Comments and Request for Case Closure dated September 22, 2010. The plume is not within 250 feet from the nearest drinking water well and does not exceed 250 feet from the source of release. o Benzene has typically ranged from below detection limits of 0.5 gg/L to 1.7 gg/L. With one anomalous result of 54 gg/L from the February 17, 2010 monitoring event. With the one exception,the benzene plume is stable. o Toluene, ethylbenzene, xylenes, MtBE, and TBA have never exceeded their respective MCLs. o Based on data from groundwater monitoring wells, there is no gross contamination of petroleum hydrocarbons. o TPHg has not exceeded 480 gg/L; and o TPHd has not exceeded 1,400 gg/L. • The contamination is beneath property zoned for commercial/industrial land use and the area is serviced by a public water system. • Water Quality Objectives (WQO) will be met within a reasonable timeframe as discussed in Ground Zero's Response to RWQCB Comments and Request for Case Closure dated September 22, 2010. • The area of soil contamination is limited in size and is not located under any existing structure. Additionally, there appears to be approximately eight feet of uncontaminated soil over the area. There are no occupied buildings over the contaminated soil column. An evaluation of potential soil-sourced vapor intrusion indicates that TPHg plus benzene risk levels were below the target hazard index. The incremental lifetime cancer risk due to benzene vapor intrusion falls between 10-4 and 10-6. Risks within this range are potentially acceptable, depending on site-specific considerations. • Concentrations of petroleum constituents in soil are less than those listed in the State Water Resource Control Board's Draft Low-Threat Site Closure Policy dated September 7, 2010. Soil analytical data are summarized in Table 4. G:\GROUNDZE\WCTOMATO\WCT-Investigation\Reports\QMR\2011\1 QM201 I.doc