SITE INFORMATION AND CORRESPONDENCE

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Potential Pesticide Plume -2- 5 October 1992 DDRW, Tracy 3. The representativeness of the ground water samples is questionable because Well No. 1 was perforated in multiple intervals in the Lower Tulare. Unlike monitor wells which have discrete screen intervals, supply wells commonly draw water from several zones. Therefore, it is unknown what horizon within the Lower Tulare may be polluted. 4. The ground water samples from Well No. 1 cannot be confirmed because the well was abandoned. 5. Well No. 1 is not down gradient from potential on-site source areas for pesticides. It is up gradient from the existing and old industrial wastewater ponds and is approximately 4500 feet cross gradient from the pesticide waste burial trench. 6. Well No. 1 began accumulating sand within a few years after installation in 1942 and after 1949, use of the well ceased. The overall contribution of this well , in drawing down contamination from the Upper Tulare, may be minimal because the well was in service for only a few years. Off-site deep agricultural supply wells, that have been in service longer than Well No. 1 , may have a greater effect on drawing down contamination into the Lower Tulare. Second, we are concerned that the EPA's position presented in the 23 July 1992 Project Manager's Meeting has changed with respect to pesticide ground water contamination. During this meeting, the Project Managers discussed the findings of the Well Evaluation and Abandonment program. The Regional Board stated that the installation of monitor wells in the Lower Tulare were unnecessary at this time. EPA's only concern was that contamination should not migrate into the Lower Tulare. We believe that EPA's concern was addressed with the June 1992 abandonment of Well No. 1 when the potential conduit for cross contamination from the Upper to the Lower Tulare was sealed. EPA did not express concern regarding a potential pesticide plume in the Lower Tulare Formation at the 23 July 1992 Project Manager's Meeting. Issuance of this letter with a position different than that presented by the EPA during the Project Manager's Meeting suggests that the EPA Project Manager was unprepared to discuss this issue which made the Meeting ineffective. We believe that EPA's change in position is not constructive for maintaining a team effort to the cleanup at the DDRW, Tracy site, unless new significant technical information is available to support that position. We believe that an investigation of the Lower Tulare should be postponed until the completion of the Comprehensive RI of the Upper Tulare Formation. Until the investigation of potential on-site source areas for Dieldrin, DDD and DDE contamination is completed and until a transport pathway can be identified and supported with technical data, we believe that other more pressing issues, such as the complete capture and treatment of the off-site volatile organic constituent (VOC) plumes, should be the primary concerns of the Project Managers.