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�./ `.✓ Stantec 76(Former BP)Service Station No. 11192 March 10, 2011 Page 4 On August 8 through 10, 2001, GRI supervised the installation of three off-site and one on-site groundwater monitoring wells (MW-8 through MW-11). Well MW-11 was constructed in a deeper (intermediate)water-bearing zone beneath the site. With the exception of MTBE in the 14-foot soil sample from boring MW-11 (1.7 ppm) and MTBE in the groundwater sample from well MW-11 (110 ppb), soil and groundwater samples did not contain analytes above laboratory method reporting limits (MRL). (GRI, Monitoring Well Installation Report dated September 2001). Between December 3 and 7, 2001, SECOR performed dual-phase extraction (DPE) pilot testing at the site. The DPE test was performed on wells MW-3 and MW 7 over a 110-hour period. Flow rates during the test varied from 10.90 to 33.41 scfm, and vacuum rates varied from 24 to 25 inches of mercury (in Hg). Over the course of the five-day event, a total of zero lbs of TPHg, 0.01 lbs of benzene, and 6.64 lbs of MTBE were removed from beneath the site. Results of DPE testing indicated a vacuum radius of influence between 36 and 60 feet. Approximately 20,830 gallons of groundwater were extracted during the DPE event. Based on the low mass removal achieved with this test, SECOR concluded that DPE was not an effective remedial alternative for this site (SECOR, Dual Phase Extraction Summary Report dated February 2002). On April 23, 2002, the SJCEHD expressed concern with high concentrations of tertiary-butyl alcohol (TBA) in wells MW-3 and MW-7. On May 9, 2002, GRI confirmed the presence of high concentrations of TBA in the wells (over 200,000 pg/L) and attributed the raised concentrations to MTBE metabolism. In correspondence dated July 22, 2002, the SJCEHD required that the groundwater samples from wells MW-3 and MW-7 be analyzed for the full scan of analytes by Environmental Protection Agency (EPA) Method 8260B. According to the SJCEHD, other degradation constituents are likely present if MTBE metabolism is occurring in the areas of wells MW-3 and MW-7. GRI began sampling MW-3 and MW-7 for the full scan of analytes by EPA Method 8260B during the first quarter 2003. In December 2002, GRI oversaw the installation of groundwater monitoring wells MW-12 and MW-13, the installation of ten ozone sparge (OS) points (SP-A through SP-H, SP-J, and SP-K) completed at a depth of 30 ft bgs, and drilled two additional CPT probes (CPT-2 and CPT-3) to a maximum depth of 140 ft bgs. The CPT rig was equipped with an on-board computer system that provided a real-time analysis of the subsurface conditions. The CPT device created a soil stratigraphy log of the boring by comparing the CPT tip resistance to sleeve friction on the CPT cone. TPHg and BTEX constituents were not detected above the laboratory MRLs in the CPT groundwater samples. MTBE and methanol were detected in the 75-foot groundwater sample from CPT-2 at concentrations of 2.0 and 2,700 ppb, respectively. MTBE was detected in the 100-foot groundwater sample from CPT-3 at a concentration of 6.8 ppb. MTBE and TBA were detected in the 125-foot sample from CPT-3 at concentrations of 290 and 88 ppb, respectively (GRI, Groundwater Monitoring Well, CPT, and Ozone Microsparge System Installation Report dated May 2003). An OS system was installed, connected to the sparge wells, and was brought on-line on December 20, 2002 by GRI. The OS system currently operating at the site consists of a K-V Associates (KVA) "C-Sparge" ozone microsparging system that cycles a mixture of ozone and air into each sparge point. (GRI, Groundwater Monitoring Well, CPT, and Ozone Microsparge System Installation Report dated May 2003). SENSITIVE RECEPTORS A water supply well survey was performed in 1989. Results indicated the presence of one private water supply well located approximately 900 feet from the site (direction unknown), and one public 11192 CPT Investigation WP 3-2011.doc