Tracing sewage-contaminated sediments in Hamilton Harbour using selected geochemical indicators

Natural tracers in bottom sediments around the outfall of the Burlington Skyway Sewage Treatment Plant (STP) were analyzed to investigate the pathways of fine contaminated sediments associated with the outfall. The properties examined were: coprostanol and isotope ratios of nitrogen and carbon. The spatial distribution pattern for all the tracers was characterized by extreme values in the vicinity of the outfall, with a systematic decrease with distance. The STP outfall is clearly the source for coprostanol as well as for light ¹⁵N and heavy ¹³C. The distribution pattern for coprostanol and δ ¹⁵N showed the most consistent transport patterns, while δ ¹³C patterns were different and might be contaminated by terrestrial carbon from sources other than the STP. Interpretation of the net transport patterns from coprostanol and δ ¹⁵N indicates a primary transport trend southward, with a secondary trend northward, curving westward. The net transport patterns inferred from the tracer indicators are compatible with models of two-dimensional circulation of a buoyant effluent plume, under the effect of the prevailing wind-driven current regime.