In urban catchments, storm water and other run-off drains away across impermeable surfaces, many of which are made of concrete. Recent research has shown that the leaching of chemicals from concrete can significantly alter the composition of draining water. In an Australian experiment in which 20 litres of rainwater were circulated through a concrete pipe for 100 minutes, the electrical conductivity of the water doubled, its pH increased from 4.8 to 7.9, calcium concentrations increased seven times and bicarbonate increased 34-fold. The apparent effects of concrete leaching are detectable at much larger scales. For example, sampling in the area of Sydney, Australia showed that reference streams in catchments covered by natural vegetation were acidic, dilute, and poorly buffered, while urban streams tended to be more neutral, less dilute and moderately buffered, with higher levels of calcium and bicarbonate ions. Because the ionic composition of water can have a strong influence on the structure of freshwater communities, the implications of concrete leaching should be considered when developing water-sensitive urban designs.
Reference: Wright, I.A., Davies, P.J., Findlay, S.J. & Jonasson, O.J. 2011. A new type of water pollution: concrete drainage infrastructure and geochemical contamination of urban waters. Marine and Freshwater Research 62, 1355–1361. http://www.publish.csiro.au/?act=view_file&file_id=MF10296.pdf
Freshwater Research News 
Posted on January 5, 2013