UNDERSTANDING GROUNDWATER/SURFACE-WATER INTERACTIONS A KEY FACTOR IN DELINEATING CONTAMINANT PLUMES AND SELECTING REMEDIAL ACTIONS AT THE MASSACHUSETTS MILITARY RESERVATION, CAPE COD, MA (Invited Presentation)

More than 20 contaminant plumes originate on the Massachusetts Military Reservation (MMR) on Cape Cod and extend 1–7 km from the reservation toward the coast. The plumes, which are in a 40- to 100-m-thick unconfined glacial drift aquifer, intersect and discharge into or pass beneath kettle ponds, streams, and cranberry bogs. The delineation of the plume paths and selection of actions to remediate the plumes have required an understanding of groundwater-flow paths near the water bodies. A variety of field methods, including seepage meters, shallow push points, diffusion samplers, and stable-isotope analysis, have been used to investigate groundwater flow in these areas. Results show that the plumes penetrate deeper into the aquifer than originally thought, especially near the kettle ponds. In one case, a plume passes beneath two large ponds that both are about 0.8 km across and 20 m deep along a flow path that is at least 3 km long. Other plumes discharge in complex patterns to streams and bogs, including a plume that passes beneath and partly discharges to a 2-km-long complex of cranberry bogs. Extensive sampling for plume contaminants by direct-push profiling to depths of 30 m near the bogs and by diffusion and push-point sampling in the bog complex’s drainage ditches was used to characterize the plume’s path. Remedial actions at the MMR have had to account for groundwater/surface-water interactions and have included the capture of the contaminated groundwater by pumping and the placement of reactive barriers near where the plumes intersect the shore of the surface-water bodies.