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3 <br /> • 4 0 FIRST RIVERBANK AQUIFER <br /> Isopach, potentiometric, and isocontour maps have been prepared and submitted for the <br /> first Riverbank aquifer in previous reports The geometry of this sand body is well- <br /> controlled because all existing borings penetrated it It trends east-west through the site, <br /> but may turnsouthward beyond the area of investigation Groundwater in GT-6 and CPT- <br /> 3 is impacted, and it is evident that additional data points are needed to delineate,the <br /> eastern extent of contamination Figure 4 shows three proposed wells for this purpose <br /> (GT-16, GT-20, and GT-21) Both GT-20 and GT-21 will probably be completed only in <br /> this aquifer, unless data from other wells indicate that dual completion in the 2nd or 3`d <br /> Riverbank aquifers is needed to delineate the groundwater impact in those aquifers <br /> Similarly, because diesel was di-tected at a concentration of 140 ppb in CPT-2, a well is Q� <br /> needed to the north, nearer the Gillies domestic well(G-1) This well will be screened dts � ' ,-� <br /> only in the I" Riverbank aquifer, but will be clustered with nested well GT-12 (screened <br /> in the 2nd and 3`d aquifers, as descnbed in sections 2 0 and 3 0) <br /> Additional data points are required to define the extent of contamination south of GT-I <br /> and GT-6 and west of GT-2 and GT-7 Wells GT-13, GT-17, and GT-19 will fulfill this <br /> purpose GT4 3 will be a nested well with a second completion in the 3`d Riverbank , <br /> aquifer, and GT-17 will be nested with a well in the 2nd aquifer, but GT-19 will likely be <br /> completed only in the 151 aquifer In total, 8 additional wells are proposed to meet the <br /> • request of EHD for complete delineation of the extent of contamination in this aquifer <br /> 5 0 SUMMARY <br /> In order to satisfy the requirements imposed in EHD's June 17, 2004 letter, Upgradient <br /> Environmental proposes to drill ten new borings and install nested monitoring wells The <br /> first four wells (GT-12 through GT-15) will be installed in the 3`d Riverbank aquifer <br /> Three of these will also be screened within the 2nd Riverbank aquifer, and the other will <br /> be screened in the I"Riverbank aquifer Soil and water samples will be collected to <br /> determine whether the four wells in the 3`d aquifer are adequate to delineate the extent of <br /> impact in this aquifer If so, the next three borings (GT-16 through GT-18)will be drilled <br /> through the 2nd Riverbank aquifer, and nested wells will be constructed in the 2"d and 1 st <br /> aquifers After the results from these wells have been analyzed, the westernmost well <br /> (GT-19) and the two easternmost wells (GT-20 and GT-21)will be drilled These will be <br /> completed only in the first aquifer, unless data from the previous wells indicate that these <br /> wells should also be screened in the 2nd or 3`d aquifers In total, 18 new wells (8 in the ls1 <br /> aquifer, 6 in the second aquifer, and 4 in the 3`d aquifer) are proposed <br />