DESIGN AGENDA FOR KOPU TIMBER WASTE PILE

This project was a site trial of phytoremediation on contaminated land at a former timber industry waste site. 
It started in July 2000, on a 1 hectare piece of land. Ten poplar and willow clone trees, as well as two species of Eucalyptus were trialed. The species Populus deltoides (poplar tree) was chosen as the best candidate for phytoremediation. The poplar tree was planted to 7000 trees per hectare.

CONTEXT OF KOPU TIMBER WASTE PILE

New Zealand has 1.6 million hectares of Pinus radiata plantations for timber production which has been treated with biocides to prevent decay. Historically these were treated with the chemicals pentachlorophenol and boron. Today, copper-chromium-arsenic is used. These treatment sites are now contaminated with the biocides and pose a risk to ground/ surfaces waters through contaminant leaching.

The area studied in this project is a timber-waste pile located in Kopu, New Zealand. For thirty years (1966-1996) the chemically treated sawdust and yard scrapings were dumped 

on this site leaving the soil contaminated. The site is designed to not have any water enter it. However, due to NZ’s heavy rainfall/ climate the small holding pond which was placed to prevent leaching, overflowed and brought high levels of toxic boron to the local streams (Robinson Anderson 2007).

monitoring, maintenance & effectiveness

The trees impact helped reduced the amount of drainage needed of water in summer, when trees are fully leafed and transpiring.The leaching that occurs during the winter months can be irrigated onto the trees in times of drought during the summer, or diverted into the stream when it is at high flow.

The results showed that poplars could control leaching at the site but also reduce the B (Boron) loading by phytoextraction. These trees would be harvested (otherwise most of the B is returned to the sawdust via leaf fall) and used as an organic supplement to trees in orchards that are B deficient.The concentrations of other metals in the leaves are not likely to cause further environmental problems.

The cost of phytoremediation at Kopu is estimated to be $200,000 NZ. This includes a site maintenance plan for five years, site assessment, scientific trails, and chemical analysis. The alternative cost of capping the site was estimated to be over $1.2 million NZ dollars. Capping also requires ongoing costly maintenance (Anderson Robinson 2007). This shows that phytoremediation is an effective and viable alternative for remediation.