ARCHIVED REPORTS XR0005965 - Laserfiche WebLink

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• The second line of evidence that suggests an off-site source is the relative concentrations of TBA and MTBE in most groundwater samples (Table 3). In a recent technical conference involving speakers from various regulatory agencies in the San Joaquin Valley, Mr. John Noonan of the Fresno Regional Water Quality Control Board compared TBA and MTBE. According to Mr. Noonan, reformulated gasoline contains 11% MTBE but only a small percentage of TBA. Further, TBA can be derived by the breakdown of MTBE during the conversion of the ether to an alcohol. Because this process takes time, MTBE is usually far more abundant than TBA at operating gasoline stations where the tanks are continuing to leak. The fact that TBA concentrations are equal to or greater than MTBE concentrations in the Kwikee Foods wells suggests that the gasoline may be relatively old and that some of the MTBE has been degraded to TSA. The presence of degraded gasoline in the groundwater favors an non-operating off-site source. The extent of soil contamination now appears to be adequately delineated. We therefore recommend that the next phase of investigation be aimed at delineating the extent of groundwater contamination. Upgradient previously submitted a work plan to install three additional on-site monitoring wells and one off-site well. Based on the results of this investigation, we would now recommend two additional on-site wells and two offsite wells. One of the off-site wells should be located along the south side of the site, either in the sidewalk or in the parking lane of Country Club Boulevard. This work should be performed sometime in the second or third quarter of 1998 and coordinated with the regular quarterly monitoring of the existing wells. In view of the lack of soil contamination in the Geoprobe borings, we also recommend that the number of soil samples submitted for laboratory analysis be reduced in future drilling efforts. Lastly, we recommend repairing the well box covering KF-3. In its present condition, it cannot be secured against further contamination through accidental or intentional introduction of contaminants from surface sources. Further, it stands so far above the surrounding asphalt that it is likely to become further damaged by continuing vehicular traffic. 9