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3.3 Depth to Groundwater and Groundwater Flow Directions As shown in Table 2, the depth to groundwater on March 30 ranged from 59 to more than 65 feet This is 5 to 10 feet less than in November 2004 The vise in the water table is due to above normal precipitation in the area and the lack of agricultural pumping A groundwater elevation map for each aquifer was constructed from the data in Table 2 to illustrate the groundwater flow direction Figure 10 shows the elevation in the 1" Riverbank aquifer The elevation of the piezometne surface in this aquifer increases northward from—35 31 feet in GT-6 to —35 64 feet in GT-20, implying northward groundwater flow The hydraulic gradient averages about 0 0045 ft/ft In the 2nd Riverbank aquifer, the piezometric surface is approximately 0 2 to 0 4 feet shallower than in the 1St Riverbank aquifer The elevation difference in GT-17, for example, is--35 29—(-35 06) = 0 23 feet However, the difference is not uniform in all wells, so that the piezometric surface in the 2nd Riverbank aquifer slopes eastward rather than northward (Figure 11) The piezometric surface is also slightly less planar, with a westward bend in the contours in the vicinity of the UST cavity due to a somewhat low static water level in GT-14 In general, the gradient is a very flat 0 0018 ft/ft Note that the calculated elevation in GT-18A is —3147 feet, which is 3 5 feet too shallow This is due to the fact that the measured depth to groundwater in GT-18A was only 59 00 feet (Table 2) This anomalous result suggests a problem with this well, wluch is discussed further below Static water levels in the 3`d Riverbank aquifer are slightly higher than those in the 2'td Riverbank aquifer The difference is generally 0 3 to 0 5 feet in individual wells, and is fairly consistent throughout all the wells, giving the piezometric surface a similar eastward slope (Figure 12) Figuie 12 also shows that the bend in the elevation contours increases from the 2`td to the 3`d aquifer and shifts northward due to Iow static water levels in both GT-13 and GT-14 Hence, it is interesting to note that there is a slight progressive rise in the piezometric surface progressing downward from the 1St to the 3`d Riverbank The data for GT-18B were not used in making Figure 12, because the calculated elevation is nearly 3 feet too deep (in contrast to GT-18A, where the elevation was 3 5 feet too shallow) These anomalies suggest that the well was damaged during construction when the percussion hammer was left in the borehole and cemented in place The cement grout may have damaged the filter pack of the native soil surrounding the borehole On April 14, V&W Drilling was dispatched to the site to surge the well and attempt to improve the sand pack to determine whether this would allow the static water levels in both aquifer zones to equilibrate with the piezometric surfaces Water depths in GT-18A, GT-1813, and GT-12A were momtored again on April 29 and were within a few inches of each other, implying that the static water level had equilibrated in the three wells GT-18A was then purged of approximately 1 5 gallons of water, lowetmg the water level by more than a foot The recovery rate was then monitored, and the well recovered at a rate of 3-5 seconds per inch, which is satisfactory Hence, it appears that the development work performed by V&W Drilling on April 14 was successful 7