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Site Characterization- Second Event Page 11 Former Karlson Trucking Facility Project No. 191.2 April 27, 2000 3.0 Conclusions & Recommendations 3.1 Conclusions The conclusions presented below are based on an interpretation of the data collected during the completion of this investigation, previous soil and groundwater data collected at the site, as well as historical and County environmental data: 1. The bearing and gradient of the groundwater surface based upon measurements from MW-1, 3, & 7 was N76.9°W at 0.0002 ft/ft. This is consistent with earlier measures of groundwater gradient. MW's-6 & 7 situated down-gradient from the suspected point of release, contained low detectable levels of diesel oil range petroleum hydrocarbons. While a "non-detect" delineation was not reached in the down-gradient direction, the contaminant levels in these two wells were three orders of magnitude lower than those from MW-4, suggesting that the wells were installed near the distal margins of the contaminant plume. 2. The non-detectable levels of PNA contaminants from well MW-4 by EPA method 8270 suggests that the site has not been impacted by this type of contaminant. This might suggest that the contaminant is not diesel, however, given the suspected source of the release (one or more above or below ground diesel tanks), another possible or likely explanation is that the contaminant is actually a heavily degraded diesel. The lack of PNA's as a site contaminant is further supported by the analysis of the soil gas survey points which did not contain detectable PNA's indicative of diesel. (See site map for suspected diesel tank and dispenser location). The RWQCB has adopted a general clean-up goal for diesel of 0.1 mg/l. The level of understanding of the contaminant at the site to date suggests that it exhibits a carbon distribution which is typical of both a diesel and dielectric oil. The lack of BTEX range petroleum hydrocarbons and Polynuclear Aromatic Hydrocarbons would suggest that the contaminant is either a light oil or (more likely) a highly degraded diesel. In any event, given its character and lack of specific chemicals generally used as indicators of poor groundwater quality (PNA's and BTEX range petroleum hydrocarbons) it is our opinion that the clean-up goal for the site be reconsidered to reflect the relatively immobile and degraded nature of the contaminant. 2937 Veneman Avenue,Suite B240 Geo-Phase Environmental Inc. Phone: (209)569-0293 Modesto, Ca 95356 Fax: (209)569-0295