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S E C 0 R ' Conceptual site Model Chevron Service Station#9-6171 March 25, 2005 Page 21 6.4 Former Regal! Service Station #603 — 6425 Pacific Avenue The site, a former Regal Service Station, was subleased from Wickland Oil Company by Exxon, Inc in the late-1980's It was developed into the former Exxon service station #7- 0136 64.1 Site History IIn October 1988, Town and Country (T&C) removed three USTs during a station upgrade During excavation activities, gasoline-range hydrocarbons were encountered in native soil I beneath the old USTs In an attempt to remove the contaminated soil, the excavation was deepened to approximately 22 feet This resulted in the removal of approximately 550-600 yd of stockpiled soil from the site 6.42 Sampling and Analyses In October 1988, six soil samples were collected at 18 feet bgs from the ends of the UST pit Based on the laboratory analyses of these soil samples, the UST pit was excavated further to a depth of approximately 28 feet bgs and an additional six soil samples were I collected The TPHg concentrations from the 12 soil samples ranged from below the method detection limits to 5,100 ppm (S-16-WW) The BTEX concentrations from the 12 soil samples ranged from below the method detection limits to 120 ppm (S-17-5), 650 ppm I (S-28-B), 1,100 ppm (S-27-A), and 960 ppm (S-28-B), respectively In December 1988, six soil borings (131 through 136) were advanced and 24 soil samples were collected from around the tank excavation Analyses of the six soil boring samples reported TPHg concentrations from below the method detection limits to 11,000 ppm (133) and to 1,000 ppm (133) TPHd was detected at a maximum concentration of 1,000 ppm in a Isoil sample collected from B3 The concentrations of BTEX ranged from below the method detection limits (62) to 73 ppm (133), 140 ppm (133), 78 ppm (133), and 360 ppm (133) respectively The 24 remaining samples were sent to McLaren Laboratories for analysis of TPHg, TPHd, BTEX, and total lead The results of the analysis are unknown to SECOR Groundwater grab samples were collected from borings B1 through B5 In boring B6, no I groundwater sample was collected due to the presence of floating product Groundwater monitoring wells MW1 through MW3 were installed at boring locations B4 through B6 Groundwater samples collected from wells MW1 through MW3 contained concentrations of TPHg from below the method detection limits to 5,000 ppm (136) TPHd was not reported in any of the samples at or above the detection limit, although elevated concentrations of petroleum hydrocarbons caused the elevation of detection limits in some of the samples for example, B6 The concentrations of BTEX in groundwater were reported as follows . benzene ranged from 0 4 ppm (134) to 79 ppm (136), toluene ranged from 0 4 ppm (134) to I N 1FifeslProiectslChevron\RetaiM9-61711Site Conceptuai ModeRFINAL_CSM doe I