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Site Characterization-Second Event Page 6 Former Karlson Trucking Facility Project No. 191.2 March 2,2001 4.0 Conclusions & Recommendations 4.1 Conclusions The conclusions presented below are based on an interpretation of the data collected during the completion of this investigation, including information from prior work: 1. Groundwater samples from both borings contained detectable levels of what appear to be non-petroleum organic materials. Moreover, no staining, odor or other field evidence was found to suggest petroleum fuels were present. 2. The sampling equipment was steam cleaned prior to use, and was thoroughly washed between the collections of samples. It is also noted that in both borings there is fairly clear trend of lower reported contaminant levels with increasing sample depths. Together,these facts make it appear unlikely that cross-contamination is at issue. In a verbal communication with the laboratory technician who performed the analyses, he stated that the patterns observed on the chromatograms are similar to others he observed in area where rotting wood or wood leachate was in contact with shallow groundwater. He could not state that this was the case in this instance, but he seemed confident that the contaminant was not similar to what has been detected in prior samples collected at this site. Based on interpretation of aerial photos of the Property from 1975 and 1983, it appears that the locations of one soil borings (SB 14) lies in area where wood apparently was previously stored in stacks. The other new boring (SB-13 is situated within an almond orchard. It was not possible to further explore this possibility using additional lab analyses of these groundwater samples, as at least two additional liters of water would have been needed for each sample point. These sample volumes were not available. 3. While not fully proved, it appears that borings SB-13 and SB-14 are located beyond the down-gradient limit of the diesel groundwater plume. The "zero-line" would this be situated between the borings SB-13 and SB-14, and MW-6. 4.2 Recommendations Based on the conclusions discussed above, Geo-Phase Environmental Inc. suggests that no additional borings or wells be required to characterize this site. We also suggest that a risk assessment commence to assess the future implications of the residual contamination. A new groundwater monitoring event should be also be completed. 2937 Veneman Avenue,Suite B240 Geo-Phase Environmental Inc. Phone: (209)569-0293 Modesto,Ca 95356 Fax: (209)569-0295