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I' 14 April 1998 • AGE-NC Project No. 95-0185 Page 2 of 4 transferred into two 40-m1 VOA vials containing 0.5m1 of 18% hydrochloric acid as a sample preservative and into one I-liter amber bottle without preservative. After collection, the samples were placed in a chilled container and transported under chain-of-custody to McCampbell Analytical, ' Inc. (MAI). Each sample was analyzed as follows: • By EPA Method 8015 M for total petroleum hydrocarbons quantified as gasoline and diesel (TPH-g and TPH-d), • By EPA Method 8020 for volatile aromatic compounds(benzene,toluene, ethyl-benzene and total xylenes: BTE&X) and methyl-tert-butyl ether (MTBE), and • By EPA Method 8260 for other oxygenated fuel additives tertiary butyl alcohol (TBA), di- isopropyl ether (DIPE), ethyl tertiary butyl ether (ETBE) and tertiary amyl methyl ether (TAME) and to confirm and quantify MTBE detected by EPA Method 8020. ' 3.0. FINDINGS ,. 3.1. GROUND WATER GRADIENT.AND FLOW DIRECTION The relative elevation of ground water in each well was calculated by subtracting the ground water depth from the surveyed casing elevation. Monitoring well casing elevations were surveyed relative to MW-4, which was assigned an arbitrary elevation of 60 feet. During the January, 1998 sampling event, the depth to ground water below the tops of the well casings at the site ranged from 20.93 to 21.20 feet. Ground water elevations have increased 0.6 and 0.09 feet in monitoring wells MW-3 and MW-4, and have decreased 0.04 feet in monitoring wells MW-1 and MW-2 since the last quarterly monitoring event. The ground water flow direction determined from the data collected during the January 1998 sampling event was toward the east, at a hydraulic gradient of 0.0095 ft/ft. The relative ground water elevations at the site are contoured on Figure 3 - Relative'Ground TVater Elevation. Ground water at the site has a very low gradient. At such a low gradient, normal measurement error can equal or even surpass the inferred elevation differences between wells, and can greatly influence the inferred ground water flow direction determination. The regional ground water flow direction is generally southwest. Small measurement errors'or minor changes of local recharge and/or LL` discharge of ground water mayhave produced the observed variation of ground water flow direction from the regional flow direction. ' Advanced GeoEnvironmental,Inc. 1