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FARR ASSOCIATES The volume of petroleum-affected residual soils for the Tank 3 area was estimated assuming the contamination resides between depths of 35 and 60 feet bgs, within the 390 ft area shown on Figure 9 Based on these assumptions, a total volume of residual ly-contammated soil for Tank 3 is estimated to be approximately 360 cubic yards For Tank 4, the estimated area of residual soil contamination is shown on Figure 9 The surface area of this contamination is estimated to be 650 ft' Within this area, the contamination is estimated to reside between 5 and 25 feet bgs Therefore, the total volume of residually-contaminated soil associated with Tank 4 is estimated to be 450 cubic yards These soil volume estimates are conservatively large, primarily due to the long time period between the early 1990s, when the data used to support the volume estimates was collected, and today Significant biodegradation has occurred and residual petroleum concentrations have decreased substantially during this long time period, thus decreasing the 1 volume of residually affected soil at the Site Using the above information,the total estimated mass of residual Site soil contamination was icalculated to be approximately 172 kg, as summarized in Table 5 It should be emphasized that the low concentrations of petroleum compounds in soil described here pose no health risk, nor any risk to water quality at the Site Of the residual estimated soil contamination, the vast majority (over 96% of total mass) of the contamination is due to TPH, and not the BTEX compounds (79% TPH-o, 14% TPH-k, 3 4% TPH-d and 0 8% 1 PH-g) ' 62 Evaluation of Risk and impact to Water Quality The existence of soils with residual petroleum contamination in the vicinity of Tanks 3 and 4 does not pose a risk to groundwater quality at the Site, as evidenced by the lack of detectable chemicals of concern in samples from monitoring wells immediately adjacent to the petroleum- affected soils The majority of residual soil contamination is below the water table and has not adversely impacted the quality of groundwater at nearby monitoring wells, MW-1 and MW-2 7.0 WELL ABANDONMENT AND SITE CLOSURE Upon approval of the findings in this report, a plan tar well abandonment according to all applicable regulatory requirements will be prepared and submitted to San Joaquin County PHSIEHD for approval Based on the site data, no post-closure monitoring is recommended 8.0 SUMMARY AND CONCLUSIONS Given the history of site investigations and remediation, and the site data on soils, soil-gas, and groundwater quality, it is apparent that the former Union Ice facility at 425 North Union Street, ' Stockton, has met the criteria for site closure It is recommended that a no-further-action letter be issued for this site on the condition of proper abandonment of the five (5) site monitoring I wells C 1MyFiles\AnnelwpwmlprojectslumonlClosurcRpt wpd 1 1