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1 <br /> ATTACHMENT 4: <br /> INSTALLATION OF VERTICAL DELINEATION SOIL BORING <br /> The vertical delineation soil boring (VDSB-1) was completed by Precision Sampling, Inc <br /> ' (Precision) on July 14, 1997 The Precision sampling ng utilizes a hydraulic hammer to drive the <br /> hollow,cylindrical EnviroCoreTM sampling rods into the ground to collect continuous soil cores Two <br /> ' nested sampling rods were driven simultaneously the small- diameter inner sampling rods were used <br /> to obtain and retrieve the soil cores, and the larger-diameter outer rods served as temporary drive <br /> casings This equipment provides a technique for collecting soil samples below the water table while <br /> minimizing the potential for cross-contamination from groundwater encountered in the boring <br /> Soil samples were collected from 5 5, 9 5, 18, 21, 26, 31 5, 35, 40 5, and 45 feet bgs to <br /> determine if a pathway for vertical migration of hydrocarbons in shallow groundwater was present <br /> During the installation of the boring, the water within the outer casing was removed following the <br /> completion of the boring to 34 feet and 40 feet to reduce the possibility of cross-contamination <br /> between lithologic layers Dewatering of the well was not successful at the shallow depth but was <br /> ' successful at 40 feet bgs The boring log is included in this attachment <br /> Soil samples collected using the EnviroCoreTM stainless steel sleeves were sealed, placed on ice, <br /> and transported to Sequoia Analytical, Inc (Sequoia), along with appropriate chain-of-custody <br /> documentation All of the soil samples were analyzed for TPH as gasoline (USEPA Method 8015, <br /> ' modified) and BTEX with MTBE(USEPA Method 8020,modified) A summary of analytical results <br /> for VDSB-1 is included in Table 1 of the main report A copy of the analytical report is included in <br /> this attachment. <br /> ' No hydrocarbons were detected at 5 5 feet bgs TPH as gasoline was detected at a maximum <br /> concentration of 510 mg/kg at 18 feet bgs Samples collected from 21 and 26 feet bgs contained 2 6 <br /> mg/kg and 3 2 mg/kg of TPH as gasoline, respectively No hydrocarbons were detected in soil <br /> ' samples collected from 315, 35, 40 5, or 45 feet bgs <br /> Silt and clay present in the subsurface are likely acting as a barrier to vertical migration of <br /> petroleum hydrocarbons present in the soil and groundwater in the shallow subsurface No further <br /> ' vertical delineation is recommended <br /> GM-XCHMONADATACHEVRON CHEV N Z RBENIAM COM-ACT Andre doe <br /> GERAGHTY& MILLER,INC �� <br />