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• • Mr. Ron Rowe Page 2 of 4 and groundwater sampling intervals to be agreed upon in consultation with PHS/EHD and RWQCB. • Monitoring well MW 13 to be properly destroyed under PHS/EHD permit. In addition to the above, you and Mr. Hartzell indicated your approval of the installation of proposed monitoring well MW 14. It is our opinion that the requested soil boring investigation is excessive with respect to depth and detail (CPT and discrete groundwater sampling at each location) and would not be an efficient financial expenditure. Our cost estimate for the soil boring portion of the workscope, as described above, is approximately $50,000. Previous soil sampling provides a general indication of the vertical extent of contamination peripheral to the former underground storage tanks. Borings VW3 and VW4/VW5 each penetrated the base of soil contamination, at 55 feet and 45 feet , respectively. We believe that a more reasonable and cost-effective definition of the vertical extent of soil and groundwater contamination can be accomplished with deeper borings located within the tankpit and east of the tankpit. In the other quadrants, we proposed more limited sampling to determine the effectiveness of the soil vapor extraction effort. Our cost estimate for the soil boring task described below is approximately $31,800: Within the tankpit, the purpose of sampling is to identify the effect soil vapor extraction has had on vadose contamination as well as to investigate the vertical extent of soil contamination. Boring CPT I/CBI will be advanced to a minimum depth of 110 feet. A CPT hole will be advanced as a preliminary lithological identification tool. The CPT boring will be twinned and soil samples collected from intervals of interest as identified from the CPT data and previous data. Soil sampling intervals will be agreed upon in consultation with PHS/EHD and RWQCB. Groundwater sampling is not proposed due to the potential for false positive results because of the penetration of contaminated soil. Groundwater samples from discrete intervals are proposed for the boring to be located directly downgradient of the former tankpit. Southwest of the tankpit, soil samples from vapor well VW3 were contaminated at 45 and 50 feet below grade but were non-detect at 55 feet. Samples from MW6 were contaminated from 20 to 40 feet as were samples from VW6. Deeper samples were not analyzed from these borings, however a sample from MW 1 at 50 feet was non-detect. These four borings are clustered within close proximity to each other. We propose to advance confirmation boring C132 to a depth of 60 feet at the location shown on the attached figure. We propose to collect and analyze soil samples at depths of 30', 37', 45', 55' and 60' in this boring. Soil samples from these depths will allow a comparison of current conditions with those predating soil vapor extraction. Additional soil samples may be analyzed depending upon subsurface conditions. No groundwater samples will be collected. rock\c1mureModadden.Ur