Geophysical Mapping of a Shallow Contaminant Plume in Thin Glacial Till, Northeast Newfoundland: Part II Interpretation of New Data

Abstract

Geophysical techniques have been used to detect the presence and map the lateral extent of a groundwater contaminant plume in a region of thin glacial till overburden at a domestic waste disposal site in Newfoundland. This site is typified by waste cells which have significant quantities of material above the water table. An earlier investigation documented the use of various electromagnetic methods to detect the presence of a contaminant plume in the groundwater and to determine the bedrock topography which constrains the flow of the plume. The earlier study demonstrated the correlation of the electromagnetic signatures of the plume with the presence of chloride ions in the groundwater as detected at water monitoring wells in the study area. The present study provides additional information on geophysical techniques which work in this environment. The geophysical methods presented are (i) the inversion of terrain conductivity data acquired using four different coil positions relative to the ground at two elevations and two coil orientations, (ii) the results from DC resistivity sounding and profiling, and (iii) imaging of selected profiles using Ground Probing Radar. The results corroborate the depth to bedrock derived from the previous investigation. In addition, the water table depth and the location and intensity of the contaminant concentration in the subsurface have been resolved and mapped. This enables the plume configuration to be understood, and suggests a strategy for easy monitoring of the advance of the plume front.