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ATC Associates Inc. <br /> 1117 Lone Palm Avenue, Suite 201 <br /> Modesto,California 95351 <br /> 209-579-2221 <br /> A s s o e`t A t e s 1..N c Fax.209-579-2225 <br /> MW1. Analytical data indicated that soil and groundwater' samples contained detectable <br /> concentrations of petroleum hydrocarbons. Field activities and analytical results are detailed in <br /> ATC's Summary Report of Additional Subsurface Investigation, dated January 8, 1999. <br /> In December 1999, ATC personnel supervised the advancement of soil borings MW2, MW3, <br /> and MW4 each to a depth of approximately 65 feet bgs to evaluate groundwater .for the <br /> presence of petroleum hydrocarbons and to determine the groundwater gradient direction and <br /> magnitude. Each boring was completed as a monitoring well. Analytical data,indicated that soil. <br /> samples collected from boring MW2 contained detectable concentrations of petroleum <br /> hydrocarbons. Petroleum ' hydrocarbons were also detected in the groundwater sample <br /> collected from monitoring well MW2. A groundwater sample collected from MW3 contained very <br /> low concentrations of only a few of the petroleum analytes. Petroleum hydrocarbons were not . <br /> detected in the groundwater sample obtained from MW4. Field activities and analytical results j <br /> are summarized; in 'ATC's Summary Report'of Additional Subsurface Investigation, dated + <br /> February 24, 2000. <br /> In December 2001, soil boring VEW1 was advanced to approximately 35 feet bgs, and borings <br /> VEW2.and VEW3 we're each advanced to an approximate depth:of 45 feet bgs. Borings MW5,. <br /> MW6, and MW7 were each advanced to approximately 65 feet bgs and were.completed as 2= <br /> inch diameter groundwater monitoring wells. .Soil borings VEW1, VEW2, and VEW3 were <br /> completed as 2-inch diameter vapor extraction wells. Boring CPT1 was advanced to <br /> approximately 100 feet bgs utilizing a truck-mounted Cone Penetrometer Testing (CPT) rig. <br /> In 2002, ATC performed a soil vapor extraction .(SVE) pilot test using mobile extraction <br /> equipment that yieldea a radius of influence (ROI) of approximately 30 feet at a vacuum of 11.5 <br /> inches of water. Approximately 2.64 pounds of total petroleum- hydrocarbons were removed <br /> from the subsurface during the pilot test. Field activities and analytical results are presented in <br /> ATC's Remedial Investigation Feasibility Study dated November 19, 2002. <br /> From October 2004 to August 2006, ATC performed additional SVE system tests to provide !! <br /> information from which an efficient and effective'.permanent SVE system could be designed. <br /> In December 2006, ATC. completed permitting and began installation of"a SVE system with <br /> startup of the system occurring on January 17, 2007. The system continued operating until <br /> February 13, 2009, when volatile organic vapor concentrations. became too low to justify <br /> sustained continuous operation. On July 14, 2409, after 151 days of non-operation, the SVE <br /> system was restarted in order to conduct a'rebound test, Concentrations of volatile'organic <br /> compounds (VOCs) measured from the influent air stream were determined to not significantly <br /> increased beyond the concentrations measured prior to the system shut down in February <br /> 2009. The SVE'system rebound test supported historical..dat6 that indicated influent vapor, <br /> phase hydrocarbon concentrations had decreased to levels that warranted terminating system <br /> operations. The test also suggested that cycling the system' would not be a cost effective <br /> alternative. <br /> S:lEnviromenta1162577-Diesel PerAREPORTS\WP-Well Abandonment2 <br />