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' I. Conclusions
<br /> ' This section provides a summary of the CSM elements, including sources, previous remedial alternatives, and
<br /> potential groundwater receptors. Also included is the recommended remedial alternative approved by the
<br /> CRWQCB-CVR to meet the remedial objectives at the site.
<br /> ' The primary sources for petroleum hydrocarbons at the site can be attributed to the five spills that have been
<br /> documented at the site from 1984 to 2001. These spills have resulted from either tank overflow activities or
<br /> from equipment malfunction at the tanks. Data from the site, including quarterly groundwater monitoring data,
<br /> ' indicate that the primary groundwater flow direction is to the north-northeast.
<br /> Subsurface investigations completed at the site have identified the presence of TPHd, TPHg, MtBE and
<br /> associated petroleum hydrocarbon constituents in both soil and groundwater beneath the site. Historically, the
<br /> highest petroleum hydrocarbon concentrations (TPHd, TPHg, and MtBE) detected in soil was 14,000, 2,700,
<br /> and 2.2 mg/kg, respectively. During the 4Q05, SPH was observed in one well (MW-40UA) and the highest
<br /> ' reported concentrations of TPHd, TPHg and MtBE in groundwater at the site were 190,000 gg/L (MW-40UA),
<br /> 21,000µg/L (EW-1), and 3,900 µg/L(MW-3UA),respectively.
<br /> In the Upper A zone, concentrations of TPHd in groundwater is not defined at the site except to the southeast
<br /> and southwest of the site. TPHg in groundwater are not defined to the north, northeast, northwest and south of
<br /> the site. MtBE and TBA in groundwater are not defined to the north, northwest,northeast and south of the site.
<br /> In the A zone, concentrations of TPHd in groundwater are not defined to the north, northeast, south and east;
<br /> 10 and MtBE and TBA in groundwater are not defined to the north(SECOR 2005c).
<br /> Based on quarterly groundwater concentrations, it appears that petroleum hydrocarbon impacts have not
<br /> significantly migrated into the B zone. The vertical extent of hydrocarbons in groundwater is defined by B zone
<br /> wells MW-12B, MW-13B, MW-22B, MW-23B, MW-50B, and MW-64B. As summarized in Table 2,
<br /> concentrations of TPHd for groundwater samples collected from the downgradient B zone well (MW-50B)have
<br /> tperiodically exceeded the RWQCB WQO of 100 µg/L, as outlined in the CAO.
<br /> Concentrations of TPHg,MtBE and TAME reported for groundwater samples at offsite boring locations in 2005
<br /> ' exceed the RWQCB WQOs. The horizontal extent of TPHd and TPHg in groundwater is delineated north of the
<br /> site; however, MtBE is not delineated north and northeast of the site. Concentrations of TPHd and MtBE in
<br /> groundwater decrease to the northeast from the site based on the results of the D and H-series borings. Data
<br /> 1 collected during the 2004 and 2005 offsite investigation indicate TPHd concentrations have decreased over time.
<br /> MtBE concentrations in groundwater samples collected from offsite borings installed between 2001 and 2004
<br /> indicate the offsite MtBE concentrations have not increased significantly, suggesting a stable plume.
<br /> ' A UST site assessment was conducted to evaluate soil and groundwater quality in the area surrounding the
<br /> former 1,000-gallon transmix UST, which was removed during March 2003. Low concentrations of petroleum
<br /> hydrocarbons in soil in MW-65B, MW-67UA, MW-68, and MW-69UA and previous soil borings PL-5, PL-6,
<br /> ' NSB-14 and NSB-16 indicate vertical definition, and lateral definition south and east of the former transmix
<br /> UST. Results of previous investigations suggest that soil impacts to the west of the former transmix UST are
<br /> commingled with the petroleum hydrocarbon impacts associated with the area northeast of the loading racks, as
<br /> summarized in Appendices E and F.
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<br /> BLASLAND,BOUCK&LEE,INC.
<br /> 3/28/06 engineers,scientists,economists 4-1
<br /> J:\D0006\44634_00161022_Conceptual Site Model.doc
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