A National Environmental Standard (NESsoil) requires that potential contamination from historical
or recent activities is identified and assessed at the time of development and, if necessary, remediated to make the land safe for human use.
This can be achieved by a simple desktop assessment, or a more comprehensive Preliminary Site Investigation (PSI) and Detailed Site Investigation (DSI) reports. If a DSI identifies soil concentrations above the relevant standards, a Remedial Action Plan (RAP) will identify adequate remediation measures. When everything is completed, a Site Validation Report (SVR) will confirm that the site is now clean and safe for the intended use.
When an asset becomes a legacy
Significant amounts of concrete rubble are generated by the demolition of high buildings or structures in the Christchurch Central Business District. This concrete can be a useful resource for landowners, for instance to stabilise farm tracks.
However, what looks like clean, crushed concrete (and is sold as cleanfill) might have traces of lead, arsenic, cadmium or other heavy metals and, more often than not, asbestos. Even if the demolished building did not contain asbestos – cross-contamination may occur. One positive test result and the asset of several thousand tonnes of crushed concrete becomes a legacy.
Testing for contamination
We take a representative number of stratified targeted samples in a grid pattern across stockpiles and analyse them for the presence of asbestos. If the contamination can be localised, only this part requires remediation or removal. Sometimes the contaminated fines can be separated with a power screen (20mm screen size) and safely encapsulated under a meter of clean soil.
Most contamination we find is local and small-scale and involves arsenic and heavy metals. At Eliot Sinclair, we can screen metal concentrations of large, potentially contaminated areas with an X-ray Field Analyser that provides real time results. This can greatly reduce the area that requires remediation.