Installation Restoration Program. Phase 2: Stage 1 Problem Confirmation Study, Duluth International Airport, Duluth, Minnesota

摘要

The following are among the study's key conclusions: (1) Groundwater occurs under shallow water table conditions in and around all sites investigated. Lateral groundwater gradients typically average about 0.02. While the hydraulic driving force for groundwater contaminant migration is fairly large, the actual rate of movement of groundwater is slow due to the presence of low-permeability glacial till. (2) Regional water table flow is generally northerly. Locally, however, this regional gradient is modified by surface drainageways which intercept the upper few feet of water table flow. Discharge of shallow groundwater to these surface drainageways creates a potential for off-base migration of contaminants. (3) Such migration of contaminants is demonstrated by detection of solvent compounds in the surface drainageway adjacent to the DPDO Storage Area C and by observation of oily discharges in surface drainageways adjacent to the Fuel Storage Area. (4) Part-per-billion level concentrations of the pesticide DDD were found in the bottom sediments of the GMSDA (Goose Missile Site Disposal Area) but off-site migration appears to be negligible. A non-pesticide compound, tentatively identified as PCB, was detected in GMSDA sediments in the same general distribution as the pesticide.