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_ r P O Box 4353, Mountain View, CA 94040-4353 xs$4aRr nffixb�$3sF) RO-GEO CONSULTANTS, INC (654) 428-0588 • FAX (650) 428-0589 September 19, 2000 Project 3267-E San Joaquin County Environmental Health Division (PHS/EHD) 304 Weber Avenue, Third Floor Stockton, California 95202 Attention Ms Lori Duncan, RENS Subject Proposed Work Plan Extent of Soil/Groundwater Contamination 242 N. Sutter Avenue, Stockton, CA 95202 (APN 139-250-05; Site Code: 9327) Dear Ms Duncan, In response to your August 2, 2000 letter, we are herein presenting our proposed work plan to evaluate the horizontal and vertical extent of hydrocarbon contamination extending offsite, down-gradient from the subject property Our July 10, 2000 report defines the vertical and horizontal extent of the stabilized on- site petroleum plume The hydrocarbon-impacted soil at the captioned site 1s limited to an approximately 3,000 square foot area in the northeast corner of the property It extends to the northeast, ranging in depth from 30 to 40 feet, see Plate 1, Plot Plan The vertical extent of the hydrocarbon-impacted soil is apparently related to fluctuations in the groundwater level Initial, unstabilized groundwater levels at the site at the time of our investigation ranged from 22 to 26 feet below the ground surface During drought periods these levels may drop to 40 feet or more The underground storage tanks in the northeast corner of this site were abandoned 40 years ago, and the underground tanks at the Standard Oil Service Station were removed from this site 20 years ago, consequently, petroleum products do not appear to have migrated any significant distance since removal of their source. Studies of leakage from the underground storage tanks at the former UNOCAL Service Station, located north of the subject property, indicate that during a period of approximately 78 years, petroleum