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r , Addendum To Closure Report- Chevron Station#9-1848 July 9, 1999 4 Appendix A and Appendix B of the Closure Report Include tabulated soil and groundwater chemical analytical data, respectively 5 TPHg and benzene Isoconcentration maps (Figures 5 through 8) that indicate Impacted soil remaining in place in the vicinity of the former gasoline USTs, dispenser Islands, and the current gasoline USTs are attached Hydrocarbon Impact was not encountered in off-site borings Vertical extent of hydrocarbon Impact beneath the site is depicted on Figure 4 Areas of impact were defined from 3 to 9 feet bgs (dispenser islands and former waste oil UST), 16 to 25 feet bgs (former fuel UST pit), and 18 to 25 feet bgs (current fuel UST pit) 6 Mass balance calculations for TPHg and benzene in soil are attached Approximately 814 pounds (lbs) of TPHg, and 1 7 lbs of benzene remain in the soil beneath the site Approximately 0 7 Ibs of dissolved TPHg,0 007 lbs of benzene, and 0 27 lbs of MtBE remain in the groundwater beneath the site 7 Clean-up efforts were limited to source removal GR's Closure Report discusses remediation activities and effectiveness in sections VI and VIII, "Rational For Closure " 8 Engineered remediation was not undertaken at this site 9, 10 Reasons why "background" was not attained and the rationale why groundwater conditions will not be adversely affected are discussed in the Sign Off sections of GR's Closure Report, section VIII Based upon the data presented in GR's Closure Report and the information provided above, it is our opinion that no further action is warranted and this site should be closed There does not appear to be a threat to human health from contaminants that remain in place beneath the site Groundwater impact appears limited to the area beneath the subject site only At the request of SJCPHS, GR investigated one domestic supply well and one municipal supply well in the vicinity of the subject site These wells were identified as the closest sensitive receptors that could be impacted by the dissolved hydrocarbon plume GR was able to contact and discuss the condition of the wells with their owners According to the property owner of the domestic well located 0 1-mile northeast of the site (well ID #1, Figure 1, in the Closure Report), a domestic supply well does not exist, nor has ever existed at this location City of Manteca municipal well#4, located approximately 0 5-mile northeast of the site (well ID #2, Figure 1, in the Closure Report), has been out-of-service (inactive) for 5 years Ms Dianne Martin, Water Quality Engineer for the City of Manteca Public Works Department (PWD) indicated the PWD will not activate or allow access into the wellhead for collection of a water sample 346392 02