ARCHIVED REPORTS XR0001072 - Laserfiche WebLink

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C A M B R I A SITE CONCEPTUAL MODEL Based on the data from previous CPT investigation, SJCEHD requested that an SCM be prepared Appendix A presents the requested SCM, which includes historical soil data tables and maps, historical groundwater tables, a groundwater contour map, isoconcentration maps, graphs of constituent concentrations versus time and trend analysis, boring logs, cross sections, remediation system data, and an exposure evaluation flowchart Mass estimates of TPHg, benzene, and MTBE in groundwater are included in Appendix B Figure 3 shows the maximum TPHg concentrations i�soil before remediation, and Figure 4 shows TPHg, benzene, and MTBE concentrations in soil after remediation Figure 5 presents TPHg, benzene, and MTBE concentrations in groundwater collected from the monitoring wells (during the second quarter 2004) and CPT borings Note that isoconcentration maps and mass estimates were not prepared for constituents in soil A majority of the soil data was collected prior to remediation at the site (Figure 3) As discussed above, the SVE system removed 17,628 pounds of hydrocarbons from the subsurface Subsequent soil data (Figure 4) demonstrate that there is minimal residual petroleum hydrocarbon impact to soil, and the remaining mass is not significant Cambria estimates that there are approximately 192 pounds TPHg, 23 pounds benzene, and 2 pounds MTBE remaining in groundwater(Appendix B) CONCLUSIONS Vertical and lateral soil delineation is complete at this site • Vertical groundwater delineation is complete at this site • Additional lateral groundwater assessment is warranted at depths below the monitoring- well screened intervals a Additional lateral groundwater assessment is warranted downgradient of well MW-9 • The shallow plume monitored by the existing groundwater monitoring wells is shrinking • No sensitive receptors have been identified within 2,000 feet of the site • The SVE system operating at the site from 1992 to 1996 was effective in removing n4 r 1 hydrocarbons from the subsurface soil (to 40 fbg) and subsequently reducing the plumei� .u�`!v in shallow groundwater ' r`� • Mass estimates suggest that less than 200 pounds of TPHg remain in groundwater 0778 3