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Paul Hanly, 06/10/05, reader opinion to MDN article 06/10/05

Although it might be rare for undisturbed residential land to have dioxin contaminated soil under a clean top 6", it has been shown that where land has been reclaimed from bays, rivers or swamps and chemical wastes were used in fill (even in municipal tips) the top layer can be clean and the soil contaminated at depth, with possible/likely impacts on groundwater, and risks if the soil is disturbed during gardening or landscaping.

Near the former Union Carbide plant at Rhodes, on Homebush Bay, Sydney, Australia some soil in a local school was contaminated to 300 ppt because Union Carbide had provided plantings and the soil that was used came from the land the factory was on. Residential blocks that have been leveled by importing soil from off site could be at risk if the soil was imported from a contaminated site.

In Rivers and Bays, the contamination to a depth of 20" or 0.5 m is critical as that is the likely range of the benthic organism eaten by fish which then flows up the food chain to humans. At Homebush Bay the top 20" (0.5 Metre)of the most dioxin contaminated sediments will be removed, treated and replaced with clean material (VENM - virgin excavated natural material). Sedimentation and scouring from water flows and wave action can cover and uncover dioxin contaminated sediments, hence the need to sample through the full range of the benthos ( eg worms.)

For more information see www.rhodesnsw.org


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