SITE INFORMATION AND CORRESPONDENCE

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page 2, 242 Sutter Street Results from these and one previous site investigation indicate the following: 1. The vertical extent of the documented groundwater contamination onsite has not been defined. 2. The lateral extent of the shallow groundwater contamination has not been defined to the east, as a water sample was not collected from boring H in the shallow zone (40-feet bsg). 3. The vertical extent of the onsite soil contamination has not been defined. The deepest soil sample collected onsite that has been submitted for analysis was the 40-foot bsg sample collected from boring A, which had 250,000 ppb TPHg. 4. The soil data obtained from the shallow zones in boring H, in combination with the soil data obtained from the deeper zones of wells U-16 and U-17, which were installed as part of the investigation for the former Unocal site at 437 Minor Street, provide lateral, and vertical, soil definition in the down-gradient direction. 5. In addition, groundwater analytical data from the Unocal wells U-16 and U-17 provide definition of the deep groundwater contamination offsite in the down- gradient direction. The report recommends the installation of an additional monitoring well, screened deep, to be located onsite near boring J. SJC/EHD agrees with this recommendation. SJC/EHD also directs the following: 1. Vertical definition of the onsite soil contamination must be made. Soil samples must be collected every five feet during the boring of the deep onsite monitoring well, and select samples must be submitted for laboratory analysis. 2. A shallow groundwater monitoring well must be installed near boring H, to obtain definition of the lateral extent of the contamination in this zone. You are directed to submit a work plan to perform the above outlined work. The work plan is due May 20, 2002. In addition, submit to SJC/EHD copies of the boring logs for borings H, J and I. You are also directed to continue routine quarterly groundwater monitoring and sampling at this site until directed otherwise by SJC/EHD. The next event should take place in April 2002. Please note that 48-hours notice to SJC/EHD is required prior to the performance of any site fieldwork. The report noted, on page 4, that the ground surface elevations of the monitoring wells have been surveyed using an arbitrary benchmark. The State Water Resources Control Board now requires that all monitoring wells be surveyed to an established benchmark. Following the installation of the additional monitoring wells, you must have all the wells resurveyed to an established benchmark. If you have any questions please call Lori Duncan at (209) 468-0337. Donna Heran, REHS, Director Environmental Health Department �, A- G4- Lori Duncan, Senior REHS Margaret agorio, Supervising REHS LOP/Site Mitigation Unit IV LOP/Site Mitigation Unit IV cc: Marty Hartzell, CVRWQCB John T. O'Rourke, Hydro-Geo Consultants, Inc.