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Jac Donald Peterson Former Reeve's Exxon Page 2 of 3 from the on-site former UST systerii-with contaminants released from the pipeline north said to be north of the subject site. The EHD,does not concur with this interpretation for the following reasons:, • There has been no report or demonstration of a release from the pipeline believed to be north of the subject site; • The results of the 'fingerprinting' of the hydrocarbon extracts are not consistent between samples, have uncertainty associated with the interpreted identities or are not identified, and none are demonstrated to'!have originated from any product or crude product transported through the pipeline; and • The interpretation of a release from the pipeline appears (to the EHD) to have been inferred from two samples — HB-9 and HB-11, both of which are south of samples impacted by high to -moderate concentrations of.'TPH-g and BTEX. The sample from HB-11 contained 1200 mg/kg TPH-g and 1100 mglkg7PH=mo. While it may eventually be shown that there are commingling plumes north of the subject site, the EHD does not consider the currently available data to be more than the basis for a hypothesis at this time and believes the down-gradient extent of impacted groundwater still requires delineation; and to this end directs that additional investigation of the plume of impacted groundwater in the down-gradient direction be conducted. The EHD notes that recently the Central Valley Regional Water Quality Control. Board (CVRWQCB) has not been concurring with closure recommendations from the EHD for sites that do not have the plumes fully,assessed, especially in the down-gradient direction — even where significant physical barriers greatly complicate further investigation in the down-gradient direct. i E The low concentrations of TP_Hg and BTEX detected in the 10' bgs soil sample in SB-15 located approximately fifteen feet down gradient (north-northeast) of SB-14 indicate that the lateral extent of impacted soil in this area may be. on the order of 15 feet or so, assuming homogeneous soil properties. Ground water samples.'.collected from.SB-14 and SB-15, as well as SB-16 at 14' bgs indicate that elevated levels of.,TPH-ho and TPH-g, as well as other petroleum constituents have impacted the ground water in these areas. The grab ground water sample colfected from SB-15 indicates that impacted ground water in this area is not delineated. The impact to'ground water dowry gradient of the former waste oil UST and upgradient of the former fuel USTs',;must be more fully characterized; the EHD recommends that a i monitoring well be placed between SB-14 and SB-15.. A work plan to address this issue is due at EHD before December 1, 2006. Please follow the Tri Regional Guidelines — Appendix A, Table 2 protocol for the required laboratory E analysis and EPA Methods for waste-oil tante constituents for investigating the waste oil UST release. These analyses were not conducted.for the SB-14 and SB-15 samples and are to be included in the analytical regimen for the next phase;of work related to the former waste oil UST release. Future work in the former waste oil UST area should also include assessing for cadmium and lead, detected at, elevated concentrations in sample "0" in the former UST pit. The data from SB-11, approximately 18 feet from "G" may demonstrate lateral extent, but does not address vertical extent in soil or impact on groundwater.." The ISR/SCM did not include a ground water iso-concentration map for TPHg. Please provide one immediately. Additionally, a complete soil data table should have been included in the ISR/SCM. -Please compile a complete soil data table and submit it to the EHD immediately. The dates the borings were advanced and the depths the soil samples were collected from are to be included in the soil table. This most recent soil analytical data-indicates that elevated concentrations of petroleum constituents are still present in the soil at the site. This residual soil contamination.is undefined and may still be impacting and degrading the groundwater at this site. Additional investigation is needed to define r