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T <br /> 5 <br /> 23 September 1997 <br /> AGE-NC Project No 95-0184 <br /> Page 2 of 8 <br /> f <br /> 23 SUBSURFACE INVESTIGATION <br /> An initial subsurface assessment was performed by WaterWork Corporation One soil boring was <br />' advanced to a depth of approximately 35 feet below surface grade (bsg) near tank A Ground water <br /> was encountered at 32 feet bsg Details of the mitial investigation were summarized in a Preliminary <br /> Assessment Report dazed 12 January 1990, prepared by WaterWork <br /> Five soil borings (B I through B5)were drilled at the site by Geological Audit Services, Inc between <br /> I I 1 and 14 February 1994 Borings B I through B4 were completed as ground water monitoring wells <br /> MW-i through MW-4, respectively Free product was encountered in MW-4 and removed between <br /> September and November 1994 Total petroleum hydrocarbons quantified as gasoline (TPH-g) and <br /> volatile aromatics(benzene,toluene,ethylbenzene and xylenes,BTE&)6 were detected in each well <br /> TPH as diesel (TPH-d) was detected in MW-4 <br /> 3.0. PROCEDURES <br /> 3 1 GROUND WATER MONITORING - 10 OCTOBER 1995 <br /> On 10 October 1995, the depth to water in each monitoring well was measured relative to the top <br /> of the well casings using a Solinst water level meter An interface probe was also used to check for <br /> free product in MW-4 A pressure release was noted associated with monitoring wells MW-1,MW-2 <br /> and MW-3 when the locking caps were removed Ground water was allowed to stabilize in each well <br /> before depth measurements were collected The relative elevation of ground water in each well was <br /> calculated by subtracting the depth to ground water from the surveyed casing elevation (Table 1) <br /> The relative ground water elevations were then plotted to determine the'ground water flow direction <br /> and giadient Ground water samples were not collected <br /> 3 2 INSTALLATION OF WELLS AND BORING <br /> 3 2 1 Drilling and Sampling <br /> From 19 to 26 February 1996, six borings were advanced at the site All borings were drilled using <br /> a truck-mounted CME-75HT drill rig The dnll ng and two-man and three-man crews were supplied <br /> by Mitchell Drilling Environmental Corp of Rancho Cordova, California Boring MW-7 was <br /> advanced to a depth of 60 feet and was completed as a ground water monitoring well Boring VW-1, <br /> drilled at an angle of 30° from vertical directed N 34°E, was advanced to a vertical depth of 55 feet <br /> bsg with a horizontal run of 318 feet and was backfilled to surface grade Borings VW-2, VW-3 and <br /> VW-4 were advanced vertically to a depth of 55 feet and were completed as vapor extraction <br /> Advanced GeoEnvironmental,Inc <br />