High Resolution Seismic Survey in a Contaminated Esker Area, Chateauguay River Watershed, Quebec

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A high-resolution seismic reflection survey was carried out in the Chateauguay River watershed in Quebec, Canada. The seismic profiles extend across a buried valley filled with till and marine clays with the objective of defining the spatial extent of stratified materials associated with the buried portion of the Mercier esker. The acquired knowledge provides insight into the various sedimentary processes of importance for groundwater management at the Mercier esker site, the largest contaminated site in Quebec. Notably, the discontinuity of the till layer underneath the Mercier esker is an important flow path for contamination. Following the initial field tests, four seismic lines ranging from 800 to 2100 m in length were chosen. At all four sites, the depth to bedrock was greater than 20 m and saturated marine clays were present at the surface. High frequency reflection signals provided excellent vertical resolution, allowing precise reconstruction of the underground stratigraphic details. Locally, in the absence of borehole logs, it was difficult to assess the exact nature of the high-velocity sediments (till or gravel) found in humps observed in the seismic survey. In regard to the success of the stratigraphic section where borehole logs are available, it is recommended that a refined grid of seismic lines be surveyed close to the contaminated area.