Presenter:  Alex Davies-Colley, Tonkin & Taylor

Presentation title: Metals screening in painted concrete – informing decisions around onsite reuse vs. offsite disposal

Our client is redeveloping an estate which includes numerous concrete block buildings that are over 50 years old. These buildings are known to have been historically coated with lead based paints (commonly used to speed up drying and increase the paint lifespan) before they were phased out in the 1970s in New Zealand. As part of wider services, our specific task involved the assessment of painted concrete blocks with regards to suitability for onsite re-use as part of redevelopment works. Preliminary laboratory testing (including assessment of lead leachability under acidic conditions) returned high lead concentrations and suggested that a considerable volume of demolition debris may require disposal to landfill. The preliminary results implied that a much more intensive sampling programme was required to better assess the fate of large quantities of concrete blocks for cost saving purposes. Paint shop lead test kits were trialled but returned unreliable results, inconsistent with laboratory data. A field XRF (X-ray fluorescence) unit, capable of detecting a wide range of metals, was able to process all on-site buildings and collect over 600 insitu, real-time readings across all concrete block buildings at the site. XRF results indicated variable lead concentrations between (and within) individual buildings and identified other elevated metal contaminants including arsenic and zinc.  Together with laboratory data, XRF results enabled differentiation of individual buildings (and/or areas) based on contaminant concentrations. The XRF was able to provide large amounts of data (albeit only semi-quantitative) rapidly allowing onsite decisions with potential significant waste minimisation and cost saving implications.

Event: WasteMINZ Conference 2013

Date: Tuesday 22 October 2013