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i <br /> Project No 58080-06-02 <br /> May 5, 1995 <br /> 40 DATA EVALUATION AND DISCUSSION <br /> ' 4 1 Petroleum Hydrocarbons in Soil <br /> ' BTEX and petroleum hydrocarbons reported as TPHg and also reported as "unidentified <br /> hydrocarbons within the gasoline and diesel fuel ranges" (collectively referred to as petroleum <br />' hydrocarbons) exist in soil beneath the site The depths at which residual BTEX was detected range <br /> from approximately 28 feet to 43 feet bgs in the southern portion of the site and is limited to the <br />' depth of 25 feet bgs beneath the northern portion of the site With the exception of 15 mg/kg of <br /> petroleum hydrocarbons reported at approximately 50 vertical feet bgs in boring GB-6, the <br /> maximum vertical depth of detectable petroleum hydrocarbon migration appears limited to <br /> approximately 25 feet bgs in the northern portion of the site and 43 feet bgs in the southern portion <br /> The lateral limits of BTEX and petroleum hydrocarbon migration in soil are bounded by boring EB- <br /> T to the south and GB-I 1 to the west Beyond the northern and eastern site boundaries, BTEX and <br /> petroleum hydrocarbons were not detected in borings MW-5 and MW-4 Cross sectional views of <br /> the reinaming BTEX and petroleum hydrocarbon plumes are depicted on Figures 3 and 4 while the <br />' remaining lateral plume limits shown in plan view are depicted on Figure 6 Also depicted on <br /> Figure 6 is the estimated portion of the plume beneath the site that was subject to soil vapor <br /> extraction remediation Based on the analytical results from soil boring DTB1 (BTEX, TPHg and <br /> TPHd not detected at 25 feet bgs) and the evaluated vapor extraction radius of influence, it is <br />' estimated that soil remediation has been completed within the shaded portion of the site depicted <br /> on Figure 6 <br /> The volumes of remaining soil estimated to be impacted with BTEX and petroleum hydrocarbons <br />' (either as TPHg or as unidentified petroleum hydrocarbons) are approximately 900 and 2,200 cubic <br /> yards, respectively Based on an average combined BTEX concentration of 50 mg/kg in soil, it is <br /> estimated that approximately 168 pounds of BTEX mass exists beneath the site Assuming an <br /> -21- <br />