Volume of contaminated sediment

The volume of contaminated deposits was evaluated for both the Louise Basin and the Saint-Charles River estuary. Intervention strategies could not be formulated without this information, which impacts not only cost, byt also the choice of technology to be used.

The volume of contaminated sediment was calculated based on information gathered by Environment Canada since 1989 and on information gleaned from Port of Québec Corporation publications.

The approach consisted in using computer software to trace the surface and bottom planes of contaminated sediment, which were subtracted to calculate the volume of deposits. The surface plane of contaminated sediment was delineated by the bathymetric plane and the bottom plane, by the natural riverbed, which was determined by drilling carried out in 1991 coupled with previously compiled data. Nearly all sediment samples taken from surface deposits to depth of 10 cm above the original bottom showed contamination over the Toxic Effect Level (TEL), which leads us to believe that the entire volume of deposits is contaminated.

This initial assessment allowed us to estimate the volume of contaminated sediment in the two areas under study at 4.8 million cubic metres, although the margin of error is relatively high given the limited number of drillings carried out. This volume had to be revalued at a later stage to obtain more precise information.