ARCHIVED REPORTS_WELL INSTALL AND QUARTERLY GROUNDWATER MONITORING REPORT 2008

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' Well Installation and Quarterly Groundwater Monitoring Report Second Quarter 2008 1950 West Fremont Street, Stockton, California ' 3.5.2 Semi Volatile Organic Compounds SVOCs were not detected at or above respective laboratory RLs in the samples collected from the site during the June 2008 investigation. ' 3.5.3 NDMA NDMA was not detected at or above the laboratory RL in the samples collected from the site during the June 2008 investigation. 3.5.4 Metals With the exception of barium, nickel, and vanadium, CAM 17 metals were not detected at or above the ' laboratory RLs. Barium and vanadium were detected at concentrations well below their respective MCLS. Nickel was detected at only one concentration (0.11 mg/L) slightly exceeding the MCL (0.10 mg/L)in well MW-3. 4.0 CONCLUSIONS AND RECOMMENDATIONS Based on the Second Quarter 2008 groundwater monitoring event, which followed the installation of the 1 monitoring wells (MW-1 through MW-3)in June 2008, and slug testing,the findings were as follows: ■ No VOCs were detected, including MTBE; ' ■ No SVOCs were detected,including NDMA; ' Of the metals detected (barium, nickel, and vanadium), only nickel exceeded its respective MCL (0.1 mg/L),with a concentration of 0.11 mg/L found at down-gradient well MW-3; ' ■ The direction of groundwater flow at the site is towards the north with a hydraulic gradient of 0.004 feet/feet; and ' ■ Hydraulic conductivity values for the site were calculated to range from 0.056 ft/d at well MW-1 to 1.65 ft/d at well MW-2. ' The results confirm that nickel, NDMA and MTBE are not migrating off-site in groundwater at concentrations exceeding their respective regulatory criteria. Based on the results and with considerations of cost-efficiency, we recommend that the analytical suite for subsequent quarterly groundwater monitoring events be reduced to only those chemicals previously Project 102790 11 July 2008