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� • i 1 31 Occurrence and Distribution of Detected TPH for Soil Sam les The October 2004 CAP relied upon the analytical data collected between 1997 and 2004, Table 2 ' summarizes all of these soil sample results The area of soil where petroleum-related constituents were detected extends laterally 140 by 110 feet (See Figure 3) and at depths from approximately 10 to 30 feet bgs Although no soil borings were advanced in the railroad corridor to the west of the site, the lateral extent of soil potentially affected by a release of petroleum constituents from the former UST is estimated to extend approximately the same distance from the former UST as was observed in soil borings advanced to the west of the former UST ' The highest concentrations of TPHd and TPHg occurred within the former tank cavity near the location of MW-2 In 1998 these TPHd concentrations in MW-2 were as high as 14,000 mg/kg, in a sample at I a depth of 20 5 feet The maximum TPHg soil concentration of 870 mg/kg was reported in this same location, MW-2 These soil samples were collected in the water table beneath the former UST cavity In 2004 soil samples collected in HA-8 and HA-9, at a distance of approximately 40 feet from MW-2, contained TPHd at levels of 690 to 1500 mg/kg The area where the maximum TPH concentrations were detected is defined by HA-9, SB-1, MW-2, ' SB-2, and MW-4 This area extends approximately 20 feet beyond the former UST excavation, or 40 ft from MW-2, and is associated with the migration of TPH residual in the water table TPHd concentrations were primarily detected between 15 feet bgs to 25 feet bgs and this depth is consistent ' with a water table elevation that has fluctuated between 8 feet and 14 feet in the six year period of monitoring Neither benzene nor methyl tertiary butyl ether(MTBE)has been detected in soil samples collected at the site Toluene, ethylbenzene, and xylenes have only been detected in the two soil samples collected from the boring for monitoring well MW-2 at concentrations up to 1 3, 0 11, and 4 2 mg/kg, ' respectively Based on the estimated lateral and vertical extent of TPH-affected soil and a review of the analytical results, the mass of residual TPH at the site is estimated at approximately 40,000 to 50,000 pounds, which equates to approximately 5,200 to 6,5Q0 gallons of residual TPH fuel remaining in site soil This estimate assumes that there is hydrocarbon material underneath the adjacent railroad tracks It is ' estimated that approximately 75 percent of the mass is located in an area approximately 60 feet in diameter around the location of the former tank excavation and at depths of 10 to 30 feet bgs ' 32 Occurrence and Distribution of Detected TPH for Water Samples Groundwater samples were collected from monitoring wells MW-2, MW-3, and MW-4 from 1998 through 2004 Analytical testing detected TPHd, TPHg, and one or more of the aromatic hydrocarbon compounds benzene, toluene, ethylbenzene, and xylenes, all of which are petroleum-fuel related analytes However,MTBE was not detected in groundwater samples collected from the site rWith the exception of the initial sampling of well MW-1, the June 2004 sampling, and the November 2004 sampling, groundwater samples collected from monitoring wells MW-1, MW-5, and MW-6, ' located just outside of the area of petroleum affected soil, did not contain concentrations of petroleum hydrocarbon constituents above analytical reporting limits 1 5 R 1C0NTGRANIstockton\CAP\CAP ADDENDUM