SITE INFORMATION AND CORRESPONDENCE

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PUBLIC HEALTH SERVICES o� SAN JOAQUIN COUNTY r` : JOG[RHASNd M.D..ALP.H Health Officer P.O. Box 2009 0 (1601 East Hazelton Avenue) 0 Stockton, California 95201 c�ticoaN�r (209)4683400 Richard Callistro August 19, 1992 Capital Projects Manager Office of the County Administrator 222 E, Weber Ave., Rm. 678 (_- Stockton, CA 95202-2778 Re: San Joaquin County Human Services Bldg. Site � a (Former 145 S. Sutter St., Stockton) Dear Mr. Callistro: We are in receipt of your letter of July 1, 1992, regarding the assessment activities at the above referenced site. You have requested that our agency approve a suspension of all site assessment,monitoring and cleanup activities for at least one year. We recognize the budget constraints and difficulties faced by all government agencies at this time; however, well over a year has elapsed since any investigation or monitoring has occurred on this site. In addition, it has been three years since the initial soil excavation and removal which was necessitated by construction of the Human Services Agency building. At that time, we discussed the need to continue assessment and documentation of the extent of the contamination as well as actions to cleanup the remaining contaminated soil and groundwater. As was also discussed at that time, our records show the County was aware of the presence of underground fuel storage tanks at this site when it was purchased in 1987. The presence of contamination, however, had not been identified at that time. As was noted in our correspondence to you of May 12 and June 12, 1992,quarterly monitoring is a minimum requirement for all sites with documented contamination. This site has significant groundwater contamination which has already spread off site and may continue to migrate resulting in more extensive contamination,a much more costly cleanup and greater liability for the county. Furthermore,the monitoring well (MW2) in the area of highest groundwater contamination (28,000 ppb Benzene) was dry at the time of the last sampling in August 1991, so it is impossible to even assess the contaminant levels in that area. Because the water table has dropped as much as 20 feet at the site, due to the current drought conditions, now may also be an opportune time to initiate cleanup of soil in the unsaturated or vadose zone. There are several technologies that have proven to be highly effective in removing contaminants from the vadose zone soil,thus removing a continuing source of contaminant release to the groundwater. This type of remediation can be accomplished much more quickly and effectively than groundwater remediation alone. To summarize our immediate concerns: 1) Existing information on the site is over a year old, therefore, the full extent and direction of off site migration of contaminants is unknown. In particular, a monitoring well(s) must be installed in or south of the area of highest contamination in order to assess the migration of contaminants in that area. 2) Conditions appear to be favorable at this time for removal of soil contaminants in the vadose zone which could lower the overall cost and duration of the groundwater cleanup. 3) State law requires certain minimum monitoring and assessment activities at sites with significant documented contamination. A DWim n of San Joaquin County Health C'uc Sery m