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ATC Associates Inc 1117 Lone Palm Avenue, Suite B Modesto, California 95351 (YVATC209.579-2221 A S S O C I A T E S I N C fax 209-579-2225 Summary Table of Mass Removal VET System Dates Total TPHg Benzene MTBE Hours removed removed removed lbs lbs lbs 10/25/04-10129/04 40 18625 313 0 002 11/29/04-12/03104 36 4949 066 0 005 ' 01/03/05-01107/05 3375 — 654 0 010 02/07/05-02/11/05 37 9472 040 0 003 03114/05-03/18/05 40 2980 030 0 002 04/11/05-04/15/05 40 6459 031 0 004 ' Cumulative 226 75 424 85 11 34 0 026 5.0 DISCUSSION Based upon monitoring of the influent vapor with a PID during the vapor extraction events and analytical results of vapor samples collected from well MW2, approximately 436 pounds of petroleum hydrocarbon constituents were removed during the vapor extraction test The approximate 436 pounds of petroleum hydrocarbons removed during the vapor extraction events exceeds the approximately 180 7 pounds of petroleum hydrocarbons estimated to be present in soils in ATC's Addendum to Site Conceptual Model and Corrective Action Plan, ' Diesel Performance, 2804 Fremont Street, Stockton, California, dated March 5, 2004 In correspondence dated March 17, 2004, EHD considered ATC's initial estimate of mass to be low The data collected during the remediation events support this Additionally the possible ' volatilization of dissolved phase petroleum hydrocarbons in groundwater may be attributed to a portion of the mass ' Concentrations of TPHg have recently decreased to below 100 micrograms per bier in the groundwater sample collected from NMI and MW2 and were not detected in the groundwater samples collected from MW3 through MW7 during the second quarter 2005 groundwater monitoring event Concentrations of benzene and MTBE were detected below the stated MCLs in the groundwater samples collected from MW 1 through MW7 during the second quarter 2005 ' groundwater monitoring event s\e�ftl\62577-mrewi Pergrgx \ntenm rem doc 5