SITE INFORMATION AND CORRESPONDENCE

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' IiT ATC Associates Inc. 1117 Lane Palm Avenue, Suite 201 ' Modesto, California 95351 209-579-2221 ( .VAfC. Fax: 209-579-2225 A S S O C I A T E S I N C.: 1 presence of petroleum hydrocarbons and to determine the groundwater gradient direction and magnitude. Each boring was completed as"a monitoring well. Analytical data indicated that soil samples collected from boring MW2 contained detectable concentrations of petroleum hydrocarbons. Petroleum hydrocarbons were also detected in the groundwater sample collected from monitoring well MW2. A groundwater sample collected from MW3 contained very low concentrations of only a few of the petroleum analytes. Petroleum hydrocarbons were not ' detected in the groundwater sample obtained from MW4. Field activities and analytical results ` are summarized in ATC's Summary Report of Additional Subsurface Investigation, dated ' February 24, 2000. i In December 2001, soil boring VEW1 was advanced to approximately 35 feet bgs, and borings i VEW2 and VEW3 were each advanced to an approximate depth of 45 feet bgs. Borings MVV5, 1 MW6, and MW7 were each advanced to approximate depth of 65_feet bgs and were completed as 2-inch diameter groundwater monitoring wells. Soil borings.VEW1, VEW2, and VEW3 were completed as 2-inch diameter vapor .extraction wells. Boring CPT1 was then advanced to approximately 100 feet bgs utilizing a truck-mounted Cone Penetrometer Testing (CPT) rig: In 2002, ATC performed a soil vapor extraction (SVE) pilot test using mobile extraction equipment which yielded a radius of influence:(ROI) of approximately 30 feet at a vacuum of f 11.5 inches of water. Approximately 2.64 pounds of total petroleum hydrocarbons were removed from the subsurface. Field activities and analytical results are presented in ATC's Remedial Investigation FeasibilityStudy dated November 19, 2002. The documents, Site Conceptual Model and Corrective Action Plan dated January 5, 2004 and Addendum to Site Conceptual Model and Corrective Action Plan dated March 5, 2004 were prepared by ATC and submitted to the SJCEHD. From October 2004 to August 2006, ATC performed multiple high-vacuum vapor extraction episodes using mobile extraction equipment. The vacuum .strength and test duration were [ varied and various combinations of wells from which extraction was conducted resulted in the extraction of 700 pounds of hydrocarbons. The data generated during the multiple vapor extraction episodes was used to design.of a semi-permanent system. E In December 2006, ATC completed permitting and began installation of a permanent VES. During the week of January 8, 2007, ATC personnel initiated trenching and system plumbing activities to install the subsurface conveyance piping that directs extracted hydrocarbon vapor from monitoring well MW2 to the nearby remediation equipment compound. The VES system consists of a 5 horse power (hp), totally enclosed, fan cooled (TEFC) positive displacement blower motor and a Solleco 100 SCAT electric catalytic oxidizer (CATOX) capable of 100 cubic feet per minute (cfm) flow and a vacuum of 12 inches of mercury. The equipment was mounted a on a trailer, enclosed within a fence, and connected to monitoring well.MW2, which serves as the VES extraction well. i The SVE system was started on January 17, 2007, and operated until February 13, 2009, when volatile organic vapor concentrations became too low to justify sustained continuous-operation. Since the initial start-up of the SVE system on January 17, 2007, the system operated for a total of 16,500 hours and successfully removed an estimated 5,436.7$ pounds of Total S:lenvironmental1625771031quarierly12009 02.doc 2 I J