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4.0 FIRST RIVERBANK AQUIFER Isopach,potentiometric, and isocontour maps have been prepared and submitted for the first Riverbank aquifer in previous reports. The geometry of this sand body is well- controlled because all existing borings penetrated it. It trends east-west through the site, but may turn southward beyond the area of investigation. Groundwater in GT-6 and CPT- 3 is impacted, and it is evident that additional data points are needed to delineate-the eastern extent of contamination. Figure 4 shows three proposed wells for this purpose (GT-16, GT-20, and GT-21). Both GT-20 and GT-21 will probably be completed only in this aquifer, unless data from other wells indicate that dual completion ip the 2nd or 3`d Riverbank aquifers is needed to delineate the groundwater impact in those aquifers. Similarly, because diesel was detected at a concentration of 140 ppb in CPT-2, a well is +� needed to the north, nearer•the Gillies domestic well,(G-1). This well will be screened only in the lst Riverbank aquifer, but will be clustered with nested well GT-12 (screened 00�°{5`'�� G in the 2nd and 3`d aquifers, as described in sections 2.0 and 3.0). 1 Additional data points are required to define the extent of contamination south of GT-1 and GT-6 and west of GT-2 and GT-7. Wells GT-13, GT-17, and GT-19 will fulfill this purpose. GT-13 will be a nested well with a second completion in the 3`d Riverbank aquifer,and GT-17 will be nested with a well in the 2nd aquifer, but GT-19 will likely be completed only in the 1st aquifer. In total, 8 additional wells are proposed to meet the request of EHD for complete delineation of the extent of contamination in this aquifer. 5.0 SUMMARY In order to satisfy the requirements imposed in EHD's June 17, 2004 letter, Upgradient Environmental proposes to drill ten new borings and install nested monitoring wells. The first four wells(GT-12 through GT-15)will be installed in the 3`d Riverbank aquifer. Three of these will also be screened within the 2nd Riverbank aquifer, and the other will be screened in the 15`Riverbank aquifer. Soil,and water samples will be collected to determine whether the four wells in the 3`d aquifer are adequate to delineate the extent of impact in this aquifer. If so, the next three borings (GT-16 through GT-18)will be drilled through the 2"d Riverbank aquifer, and nested wells will be constructed in the 2"d and 1 st aquifers. After the results from these wells have been analyzed, the westernmost well (GT-19) and the two easternmost wells (GT-20 and GT-21)will be drilled. These will be completed only in the first aquifer, unless data from the previous wells indicate that these wells should also be screened in the 2"d or 3`d aquifers. In total, 18 new wells(8 in the 0 aquifer, 6 in the second aquifer, and 4 in the 3`d aquifer) are proposed.