SITE INFORMATION AND CORRESPONDENCE

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ivir. tric jenKs t may zuuy an onsite meeting ontMarch 2009. Soil closure requiretnts are outlined in a separate section of this letter. 3. During the February and August 2008 monitoring and sampling events, the average depth to groundwater measured was 12.6 feet and 14.6 feet below top of casing, respectively and was higher than those observed during historical monitoring events. This may have also facilitated fluctuations in 1,2,3 -TCP concentrations. Continued monitoring and comparison of 1, 2, 3 -TCP levels in relation to groundwater level is needed. 4. During 2008, high water levels combined with chloroform were detected in monitoring well MW -1. This may be due to a water main leak in the vicinity of the monitoring well; therefore, Central Valley Regional Water Board staff contacted the City of Stockton, Municipal Water Supply Department. The City of Stockton redirected the staff to California Water Service Company, which informed the Central Valley Regional Water Board that there was no water supply well within the 2000 -foot radius of the site. The nearest water supply well is located approximately one mile south from the site towards Stockton downtown and is non operational since 1980's. No malfunction or leakage has been reported from the water distribution system. Based on this information, further investigation is needed to discover the cause for high water and chloroform levels. 5. On 28 October 2008, during a meeting with the Central Valley Regional Water Board, JTF presented historical data from the Cone Penetration Test (CPT) investigation, which was conducted at the site in May 2005. After reviewing the CPT investigation data presented in Source Area Investigation and Downgradient Delineation Report, dated 15 August 2005, additional vertical delineation of groundwater is needed in deeper groundwater zone at approximately 50 feet bgs. Elevated levels of 1,2-DCP, and 1,2,3 -TCP were detected from grab groundwater samples collected from CPT boring CPT -052405, which was advanced to a depth of 50 feet bgs and is located at the northeast corner of the site. Concentrations of 1,2-DCP were detected at 170 pg/L, and 1,2,3 -TCP was detected at a concentration of 0.29 pg/L. Thus groundwater quality is degraded and a determination of the groundwater gradient and flow direction in deeper zone is necessary. In order to complete this assessment and to delineate the extent of COC's in deep groundwater, permanent groundwater monitoring wells need to be installed. A work plan for additional groundwater assessment is due by 10 July 2009. Historical CPT data should also be posted on the groundwater elevation and contour maps, in the future groundwater monitoring reports. 6. In the Report, JTF has proposed the following recommendations to revise the current Monitoring and Reporting Program (MRP) No. R5 -2004-0806- a. Removing fumigants by EPA Method 504.1 from the MRP, since 1,2,3 -TCP is being analyzed by SRL 524M -TCP. b. Changing the analytical suite of carbamate and urea pesticides (EPA 632) to bromacil only, since no other compounds have been detected in on-site and downgradient wells. C. Removing chlorinated herbicides from the MRP, as no chlorinated herbicides have been detected since February 2005. d. Removing triazine compounds from the MRP.