SITE INFORMATION AND CORRESPONDENCE FILE 2

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Rodger Liston Darpetro Inc. - - - - - 749 E. Charter Way, Stockton, California Page 5 of 7 would change considerably. Another major weakness of CGG presenting the 1997 TBA and MTBE maps to show migration onto the site from the south is that well BM-3 was not tested in 1997; the 1998 maps, with BM-3 data included , demolish the argument. In 1997 the interpretation may have been somewhat reasonable, but with the knowledge and data available in 2004, the 1997 maps - lacking data for the significant monitoring point at BM-3 - cannot be accepted today as valid plume models for 1997. It is the opinion of EHD that the data presented by CGG has more than one possible interpretation and can even be utilized to interpret the source of contamination to be the subject site . While an adequate site conceptual model may demonstrate CGG's interpretation to be correct, EHD finds the revised SCM to still be less than compelling ; indeed EHD interprets the data to indicate that the current UST system onsite may have been the source of the contaminants centered on monitoring well BM-3, as was noted in the discussion of the TBA and MTBE concentration maps . Other data supporting an on site source are as follows: 1 . Mapping of the first occurrences of MTBE in the BM wells shows a bull's eye near BMA , BM-3 and BM-5 , as was noted in EHD's 05 September letter; 2. Mapping the highest MTBE concentrations detected in each well also shows a bull's eye on or near BM- 1 , . BM-3 and BM-4; 3. In 2000 , the spill buckets were replaced on the USTs without permit or regulatory oversight; reportedly the spill buckets had been leaking ; 4 . During the November 2000 inspection of the UST system, numerous violations were noted ; 5. During installation of pans under the dispensers in November 2003, soil samples were collected and analyzed — MTBE and petroleum hydrocarbons were detected , soil from under the dispenser closest to BM-3 had the highest concentrations; 6. Since replacement of the spill buckets, MTBE concentrations in the impacted BM wells have generally declined . It should be noted that an EHD inspector reported no odor or staining was noted in a pea-gravel sample collected 4 feet below the replaced spill buckets on 27 June 2001 . Pea gravel , with its lack of fines and low surface area to volume ratio would have a much lower sorbtion rate than normal soil. EHD believes the data to indicate that most of the MTBE and associated contaminants were released on your site during your tenure on the property and/or during USA's operation on the property, and that you should be moving ahead to finish the site characterization and perform appropriate remediation of impacted ground water. In view of this discussion, EHD will reconsider CGG's work plan for a soil gas survey around the UST system , if your consultant concurs, with revised depths of investigation to better address possible release points from the system. Sampling points should be in close proximity to the suspected source and should be at a depth most likely to pick up vapor from a release from the suspected source. Please submit the revised work plan by 10 May 2004 . Review of the quarterly reports causes some concern with the quality of work performed during ground water monitoring events . As noted in the EHD letter dated 03 November 2003 , deficiencies with the monitoring procedures during the October 2003 ground water monitoring event had been noted by EHD . EHD visited the site as the second-to-last well