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kNj KLEINFELDER The actual round water gradient at Foothill Sanitary Landfill during October 1989 could g $ �Y not be calculated because the water level at MW-2 had dropped below the bottom of the well. The cause of this water level drop is unknown. The bottom of the well was sounded several times to recheck the observation, using the elevations measured in MW-1 and LW-1 and the elevation of the bottom of MW-2, an estimated range of the ground water gradient and flow direction was developed. Contours of the hypothetical ground water elevations, assuming that the water was at the very bottom of -2, are shown on Plate 4- 5. Contours of the hypothetical ground water elevations, assuming that water was 10 feet below the bottom of MW-2, are shown on Plate 4-6. It does not seem likely that ground water fell much more than 10 feet below the bottom of MW-2. These two contour maps indicate that the ground water flow direction in October 1989 was probably to the south- southeast and that the gradient was probably in the range of 0.9 to 1.5 percent. On February 5, 1990, the ground water gradient was approximately 0.21 percent to the south. Ground water elevations ranged from 56.09 to 61.37 feet above mean sea level. Contours of the ground water elevation are shown on Plate 4-7. On Aril 4, 1990, the round water gradient was approximately 0.22% to the south. g Ground water elevations ranged from 56.0 to 61.35 feet above mean sea level. Contours of the ground water elevations are shown on Plate 4-8. These four measurements of ground water levels indicated that ground water flowed in a generally southerly direction during 1989-1990. The ground water gradient is generally between 0.18% and 0.22%, based on the July, February and April measurements. The cause of the anomalously steep gradient in October 1989 that was responsible for MW-2 being dry is not known. From the four ground water elevation measurements, MW-1 appears to be upgradient of the landfill, and MW-2 appears to be downgradient of the landfill. 4.4.2 Background Water Quality Based on the four ground water elevations measured in 1989 and 1990, MW-1 appears to be well positioned to represent background water quality in the vicinity of the landfill. LW- 1 is spatially close to the landfilled area and, therefore, is not used to represent background water quality. Four samples were collected from MW-1 in July 1989, and were analyzed to assess the statistical variability in sample preservation and analysis. A statistical analysis of FOOTHILL 27