6.2.2. Groundwater Monitoring at the 317/319 Area

Eleven active monitoring wells (some of which are clustered or nested) are installed at the locations shown in Figure 6.2. Well data are listed in Table 6.11. The wide range in water level elevations shown in Table 6.11 is not unusual and is due to the fact that some of the wells are screened at different depths in different saturated zones. This variation in water level also may be indicative of "perched" (i.e., discontinuous) groundwater conditions within the glacial till. Samples are collected quarterly following EPA sampling protocols listed in the RCRA Ground-Water Monitoring Technical Enforcement Guidance Document (September 1986).³³

Groundwater monitoring in the 317/319 Area has been conducted since 1986. Wells 319011, 317021, and 319031, were installed in September 1986; 317061 in August 1987; 317091 in July 1988; 317101 and 317111 in September 1988; and wells 319032 and 317052 were installed in June 1989. These wells were all completed in the glacial till. In addition, wells 317121D and 319131D were installed in November 1989 and reach the dolomite aquifer at about 25 m (80 ft) below the surface. Well 319071, which was dry, was sealed in September 1995 in accordance with state and county well code regulations. Well 317081 was damaged and removed during 1995.

Wells 317101 and 317111 are upgradient of the 317 storage area, and well 319011 is upgradient of the 319 landfill area. A sand lens present at 5 to 8 m (15 to 25 ft) was recently discovered and wells 317052 and 319032 were placed at this depth. This layer is also intercepted by wells 317091 and 317101.

In addition to wells in this area, two manholes associated with the vault sewer system were monitored on a monthly basis. The location of the manholes is shown in Figure 6.1.

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