Assessment of sediment and porewater after one year of subaqueous capping of contaminated sediments in Hamilton Harbour, Canada

Abstract

In this manuscript, we present data from a demonstration in situ capping site (100 m × 100 m) in Hamilton Harbour, Lake Ontario, Canada. A layer of clean medium to coarse sand with the average thickness of 35 cm was placed at the site in the summer of 1995. Concentration of Zn, Cr, and Cd in the original sediments reached values over 6000, 300 and 15 μg/g, respectively. The predicted consolidation of the uppermost one meter of sediment was about 14 cm, which was in good agreement with values obtained from comparisons of moisture content values of pre-capping and post-capping cores. A thin layer of fresh moderately contaminated sediments has started to develop on the top of the cap. In general, the concentrations of elements were greater in porewater than in the overlying water, e.g., the concentration of Fe and soluble reactive phosphorus were 1000 times, and those of Mn 100 times greater. There was a significant reduction in the vertical fluxes of all the trace elements after the capping of the contaminated sediments.

Role of sand capping in phosphorus release from sediment

“…Contaminated sediment containing nutrients, metals, PCBs, and PAHs was isolated from overlying water by deploying a capping layer on top of the sediment (Azcue et al, 1998;Palermo, 1998;Jacobs et al, 1999;Mohan et al, 2000;Berg et al, 2004). Capping consists in the placement of a layer of capping materials evenly spread over the contaminated sediment.…”

“…Sand (Azcue et al, 1998), zeolite (Jacobs et al, 1999) and calcite (Berg et al, 2004) have been proposed as capping and additive materials to date. Other chemicals may be used as reinforce capping materials to attenuate the contaminant loading induced by the sediment.…”

Predicting the response of Hamilton Harbour to the nutrient loading reductions: A modeling analysis of the “ecological unknowns”

“…Similarly, while Mayer and Manning (1990) reported quite high phosphorus concentrations in solids collected from the sediment-water interface (N3500 mg kg − 1 ) as well as unusually high non-apatite inorganic phosphorus levels in the areas adjacent to the municipal discharges, they concluded that there is sufficient ferric iron in the system to alleviate the impact of the high inputs of P. The same study also speculated that the retention of phosphorus in the sediments may be attributed to the ferric iron reduction, which subsequently leads to the formation of an insoluble "Fe + 2 -other metal-P" complex (Mayer and Manning, 1990). Further, Azcue et al (1998) reported upward diffusion PO 4 fluxes into the overlying water column at the level of 1.7 mg m 2 day − 1 , which were very close to the lower value examined herein.…”

In situ removal of copper from sediments by a galvanic cell

“…In situ methods include capping, solidification/stabilization, chemical treatment, biological treatment and so on (EPA, 1993). Capping covers contaminated sediments with cleaner sediments with or without lateral walls (Azcue et al, 1998;St} uben et al, 1998). It consumes much clean sediment and pollutants are not removed from the site.…”