Laserfiche WebLink
2 .4 Groundwater Monitoring <br /> To ensure that the construction and operation of the IR- l4 containment facility does not adversely <br /> affect local groundwater, a comprehensive groundwater monitoring program will be a key element of site <br /> management. At present, data characterizing soil and groundwater conditions on site are limited . More <br /> detailed information characterizing on-site soil conditions — to be obtained through comprehensive <br /> subsurface investigation during the final design phase — is required to assess the site ' s potential to impact <br /> local groundwater. Additional sediment data will be derived from core borings taken in channel shoals before <br /> each scheduled maintenance operation . As discussed in Section 2 . 1 , excavation depth wil l be limited as much <br /> as practical . Nevertheless, containment basin construction will still require excavation below the apparent <br /> seasonal high water table . Material dredged from the ICWW will be discharged into the IR- 14 containment <br /> basin as a slurry containing approximately 20% marine sediments and 80% saline water. Hydrostatic <br /> pressure could potentially force saline water from the basin into the local shallow aquifer. However, two <br /> factors limit the off-site movement of saline water. First, a system of perimeter ditches (discussed in Section <br /> 2 . 3 . 6) surrounding the containment basin will interdict the horizontal migration of basin seepage . Second , <br /> ponded saline water should remain in the basin for relatively short periods (about 8 to 12 weeks) only once <br /> every 5 to 10 years . Thus, the contamination of off-site groundwater by saline water seepage from the basin <br /> appears unlikely . <br /> Notwithstanding the above, an on- site groundwater monitoring program will be implemented to <br /> detect any changes in local groundwater chemistry due to site operations . The program will begin before <br /> facility construction and will remain in place throughout the life of the site . Preconstruction groundwater <br /> monitoring activities are discussed below . <br /> Implementation of the groundwater monitoring program requires the installation of shallow test <br /> wells before site construction activities begin . Initially, three pairs of wells — one pair each on the <br /> containment basin ' s north, west, and south sides -- will be sunk within the buffer area . Each pair will consist <br /> of one shallow well (to 8 ft below soil surface) and one deeper well (to 30 ft below the soil surface) . Samples <br /> from the test wells will be analyzed to document preconstruction groundwater elevations and chloride <br /> concentrations . Analysis of the groundwater samples may also include additional chemical constituents if <br /> present in the sediment to be dredged . Well monitoring data will be used to establish baseline groundwater <br /> 24 <br />