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08 May 1997 <br /> AGE-NC Project No 96-0173 <br />' Page 2 of 4 <br />' 2 2 GROUND WATER SAMPLING <br /> Monitoring wells MW-1 through MW-4 were allowed to recover for a minimum of one hour prior <br />' to sample collection Ground water samples were collected utilizing new, disposable polyethylene <br /> bailers and new nylon rope Sufficient sample was collected from each well to fill three 40-m1 EPA- <br /> approved VOA vials, containing 0 5 ml 18% hydrochloric acid as a sample preservative, and a one- <br /> liter amber bottle Care was taken to ensure that visible air bubbles were not present in the vials after <br /> filling and capping Ground water sample containers were labeled with the well designation, date, <br /> time, and sampler's initials <br /> 1 <br /> 23 LABORATORY ANALYSIS OF GROUND WATER SAMPLES <br /> After collection, each sample was logged on a chain-of-custody form, placed in a chilled container <br /> and transported to Castle Analytical Laboratories (CAL), a California State-certified laboratory for <br />' analysis by EPA Method 8015-m for total petroleum hydrocarbons quantified as gasoline and diesel <br /> (TPH-g & TPH-d), and analysis by EPA Method 8020 for volatile aromatics (benzene, toluene, <br /> ethylbenzene and xylenes BTE&X) and methyl-tertiary butyl ether (MTBE) <br /> 3 0. FINDINGS <br /> 3 1 RELATIVE GROUND WATER ELEVATION AND GRADIENT <br /> The depths to ground water in wells MW-1 through N W-4 ranged between 30 22 and 30 74 feet <br /> below surface grade Between December 1996 and April 1997, ground water elevation increased an <br /> average of 5 33 feet Furthermore, the top of the screened intervals in wells MW-1 through MW-4 <br /> are between 0 22 and 0 74 feet above the ground water surface <br /> J <br /> The relative ground water surface elevation, as measured on 09 April 1997, is depicted in Figure 3 <br /> Due to the gentle ground water gradient encountered at the site, the gradient and flow direction were <br /> calculated by solving for the maximum gradient and direction as three-point problems using MW-I, <br /> MW-2 and MW-3 for one set and MW-1 MW-3 and MW-4 for the second set The results were <br /> averaged to determine the flow direction and gradient <br /> In December 1996, the gradient was calculated to be 0 002 ft/ft (approximately 11 feet per mile) and <br /> directed approximately N 67°E In April 1997, the gradient was calculated to be 0 001 ft/ft <br /> (approximately 5 feet per anile) and directed N 62'W Between December 1996 and Apiil 1997, <br /> ground water flow direction beneath the site rotated approximately 85' towards the northwest <br /> I <br />