SITE INFORMATION AND CORRESPONDENCE FILE 3

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DISCUSSION: LUpper Water Bearino Zone Depth to groundwater in the monitoring wells ranged from 6.08 to 8.95 feet below the top of the well casing and were within historical groundwater elevation fluctuation ranges. Depth-to-water measurements were converted to feet above mean sea level (MSL)and used to construct a groundwater elevation contour map(Figure 2). Southeastern groundwater flow was generally noted, at low gradients ranging from about 0.001 to 0.002 ft/ft. Variable, northeast, and southeast groundwater flow directions have generally been reported during previous monitoring events. GRO was only detected in samples collected from two offsite wells(MW-8 and MW-15, at concentrations of 340 gg/L and 130 gg/L, respectively). Benzene was only detected in one onsite well (MW-20, at 11 L gg/L). MTBE generally impacts the eastern portion of the site and offsite areas to the east and southeast. The highest MTBE concentrations were reported in offsite wells MW-8(440µg/L)and MW-15 (160 µg/L). MTBE concentrations in the other groundwater monitoring wells were relatively low(at and below 50 gg/L). TBA was not detected in any of the well samples collected during the second quarter 2010. Analytical results of GRO, benzene, MTBE, and TBA for groundwater samples collected from the shallow screened wells during the second quarter 2010 are presented in Figure 4. Lower Water Bearing Zone Depth to groundwater in the monitoring wells ranged from 7.12 to 8.42 feet below the top of the well casing and were within historical groundwater elevation fluctuation ranges. Depth-to-water measurements were converted to feet above mean sea level (MSL)and used to construct a groundwater elevation contour map(Figure 3). Northeast groundwater flow, at an average gradient of approximately 0.002 ft/ft, was observed on June 10, 2010. Northeast and northwest groundwater flow directions have been reported during previous monitoring events. Petroleum hydrocarbon and fuel oxygenate impact to the lower water bearing interval appears negligible. Benzene was detected in the samples collected from wells MW-12 and MW-21, at concentrations of 0.53 gg/L and 0.61 pVL, respectively. Low levels of DRO were reported in one well sample, however the laboratory noted that this concentration included compounds uncharacteristic of common fuels and lubricants. Analytical results of GRO, benzene, MTBE, and TBA for groundwater samples collected from the deeper screened wells during the second quarter 2010 are presented in Figure 5. RECOMMENDATIONS: In early June 2010, SJCEHD and Stratus personnel discussed future management of the environmental case at the subject site. SJCEHD noted that groundwater monitoring has been ongoing for quite some time, and indicated that their agency was likely to make a decision in the upcoming months regarding future site requirements. Specifically, the possibility of moving the site towards case closure, requiring a Feasibility Study/Corrective Action Plan(FS/CAP)report, and possibly performing a soil gas survey were topics mentioned by SJCEHD. It was requested that Stratus provide a recommendation regarding a future site management strategy. Using the groundwater analytical data collected during the second quarter 2010, Stratus has prepared estimates regarding the remaining mass of GRO and MTBE, which appear to be the primary contaminants impacting shallow groundwater at the site. Computation sheets which document these contaminant mass estimations, and figures that accompany this data, are provided in Appendix E. Based on the available data, Stratus estimates that 0.74 pounds of GRO and 1.11 pounds of MTBE remain dissolved in groundwater at the site. Given the relatively low mass of dissolved contaminants beneath the site, and the absence of groundwater sensitive receptors previously documented in the sife vicinity, it is our opinion that active groundwater remedial measures are not justified. Recent analytical data shows a general declining trend in levels of petroleum hydrocarbons and fuel oxygenates without active remedial efforts being K USA Gaso1me\08350wtc1y\2010\USA_835 2Q10.D0C STIMTUS