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+� Bulk Transportation Page 4 <br /> Site Conceptual Model& Closure Report <br /> GPE Project No. 606.3 <br /> August 28, 2009 <br /> ti..r <br /> confirmation soil samples were collected and tested. The seven samples were <br /> 'r collected from the bottom of the pit and sidewalls. An additional five samples <br /> were collected from the stockpile. Four of these samples were composited for <br /> laboratory analysis. <br /> Upon completion of the excavation and soil sampling, the over-excavated pit <br /> was subsequently backfilled with clean material. <br /> The highest concentration of diesel contamination was 2,400 mg/Kg from a <br /> sample in the pipe trench. Composite samples of the spoil material suggested <br /> that the average concentration of diesel fuel in the excavated material was 700 <br /> mg/Kg. Based on the volume of soil removed, and the analytical results of the <br /> �., composite soil samples, Hygienetics estimated that 144 pounds of diesel <br /> hydrocarbons were removed and stockpiled. <br /> In 2007, NRC Environmental Services re-sampled the spoil pile to determine if <br /> the material was suitable for disposal on site. Two samples were collected and <br /> one contained 22 mg/Kg of diesel hydrocarbons and the other contained 6.4 <br /> mg/Kg. The material was left in-place pending additional natural attenuation. <br /> �. In July of this year, Geo-Phase Environmental, Inc. collected two 4-point <br /> composite soil samples of the material from the spoil soil. These samples <br /> (designated SPS & SPN) were collected under the supervision of Harlin Knoll <br /> of the San Joaquin County EHD. The samples were tested for the presence of <br /> diesel-range hydrocarbons, but the laboratory reported no detectable <br /> concentrations, suggesting that the material has been fully remediated. <br /> Site Investigations <br /> The following is a timeline of events summarizing the remedial investigation <br /> �- pertaining to this release: <br /> October 2002 <br /> The UST was removed under County permit, and confirmation soil samples <br /> from the vicinity of the pipe trench and dispensers indicated that elevated <br /> concentrations of diesel fuel were present. The County EHD issues a "Notice <br /> of Unauthorized Release" on November S, 2002. <br /> �. April 2003 <br /> A work plan was submitted describing methods and protocols to be used to <br /> over-excavate the tank pit. Hygienetics Services prepared the plan which is <br /> %W entitled Revised Work Plan — Additional Excavation and Con irrnation Soil <br /> Sampling, Former Underground Storage TaUk Site. <br /> ti. 2937 Veneman Ave.,#B240 Geo-Phase Environmental Inc. Phone (209) 569-0293 <br /> Modesto,CA 95356 Fax(209) 569-0293 <br />