SITE INFORMATION AND CORRESPONDENCE_FILE 2

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6131 Pacific Ave December 1997 Page 2 water was measured at approximately 41 feet bgs. The report indicated that the wells were surveyed by a licensed surveyor to a site datum. The survey map was not included within the report of the investigation. Please submit the survey map for PHS/EHD's site record. Also,the recent monitoring results indicated the presence of a north-south hydraulic ridge which previously had not been reported. The recent groundwater sampling and monitoring results evidenced MTBE and di-isopropyl ether (DIPS). It is interesting to note that the concentrations of contaminants evidenced in MW4 were significantly higher than MW3,possibly related to the screened intervals or related to a more recent release of petroleum hydrocarbons. Monitoring well,MW4 is screened from 35 to 55 feet bgs while MW3 is screened from 45 to 65 feet bgs. MWI and MW4 w%**t are the two closest monitoring wells to the currently operating underground storage tanks and are the wells with detections of DIPS. Also,MW4 which is downgradient of the new tanks has, most recently,the highest confirmed detections of MTBE . As contamination has been evidenced off site,copies of all reports and correspondence should be forwarded to the off site property owners,until such time as the site is closed or the property owners request that copies are no longer forwarded to them. The reports failed to include any recommendations for further investigation and or remedial activities. As Shell Oil has been informed previously by PHS/EHD,all reports shall include conclusions and recommendations. The extent of the soil and groundwater contamination has not yet been defined. A work plan shall be submitted by January 30, 1999 which includes tabulated soil data and cross-sections depicting the distribution of soil contamination identified thus far and which proposes sufficient monitoring wells and soil borings to define the extent of groundwater and soil contamination. A corrective action plan shall be required pursuant to the California Health and Safety Code and the Underground Storage Tank Regulations. The work plan therefore, shall also include any additional vapor extraction wells and air sparge wells necessary to perform feasibility testing pursuant to the Underground Storage Tank Regulations. If you have any questions,please do not hesitate to contact me at (209) 468-0337. Donna Heran, REHS, Director Environmental Health Division Mary Meays,Senior REHS Marga�1,.ri., REHS Site Mitigation Unit Lead Senior cc: Pat Anderson,Central Valley Regional Water Quality Control Board cc: Ron Slate,PO Box 1146, Lodi CA 95241 cc: Vicki Iten, Porter Station Condominium Association, 8807 Thornton Road Suite M, Stockton CA 95209 cc: Diane Lundquest,Enviros PO Box 259 Sonoma CA 95476-0259