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eh ESPEY, HUSTON 8. ASSOCIATES, INC. • 13.2.2 Geohydrology As mentioned in the preceeding section, a total of 18 piezometers were installed on the site. The first three were installed in August 1979 by others and the remainder in May 1980 by EH&A. These wells were drilled to bedrock with a CME drilling rig using a solid stem auger or a hollow stem auger where soil samples were to be obtained. All wells were cased with 1 1/4 inch PVC pipe and sand packed to the surface. Static water levels were measured in these wells several days later. From this data a water table (potentiometric) map was developed (Fig. 13.23) illustrating the elevation in feet of the water surface above mean sea level. The other map on Fig. 13.23 illustrates the depth in feet of the water table below ground surface. Note that this data was collected in May 1980. This is neaz the end of the snow melt and was during a period during which several rainstorms occured. For this reason the data taken in May has been assumed to be the "worst case" for groundwater and used as the basis for design (see Sec. 133.2). Note further that this data was • collected to characterize the larger disposal azea and borings were taken uphill until they became dry. Borings 7, 12, and 14 were dry and no borings were made uphill from those (see Table 13.2.1). Examination of Fig. 13.2.3 reveals that the water table was found to be well below the ground surface throughout the disposal azea. At one point near the toe of the slope a reading of five feet below the surface was obtained. Improve- ments to the drainage system (deepening the natural drainage channel as part of the watershed diversion ditch) in conjunction with the natural permeability of the soil are expected to keep the potentiometric surface from rising above this level. 133 THE DESIGN 133.1 The Disposal Area Boundary The boundazy of the azea available for disposal is shown on Fig. 13.1.2. 13-4