As part of the Auckland regions work to improve industrial sites, Papakura Timber Processors was asked to apply for an Industrial or Trade Activity Consent. This process, coupled with early site design advantages, has made Papakura Timber a leader in the timber industry in the area of pollution prevention.
The key elements of this approach include:
- The decision early in the development of the site to concrete key areas of the yard, enabling stormwater collection and soil protection.
- The decision in 2008 to install a significant stormwater recovery and treatment plant, as described further below.
- The uptake of and the improvements gained from the use of an Environmental Management Plan process.
The Stormwater Treatment Plant
The layout of the 2ha site and the concreted access and storage surfaces mean that about 80% of the site’s stormwater from industrial activity areas is discharged at one stormwater manhole, to the adjacent Papakura Stream. Timber industry stormwater typically has elevated levels of the heavy metals that are used in the timber treatment process – various forms of Copper, Chromium and Arsenic predominantly.
The site, as with many timber industry sites, is also a significant user of water in its various waterborne timber treatment processes. A minimum of 50m3 of water is used per work day, and sometimes much more. The stormwater treatment solution was designed around the collection and storage of the stormwater, which is low in suspended solids due the concreted work areas, for reuse as the plant make-up water. The site can store about 400 m3 of water. If there is inadequate stored rainwater the site has a consent for a limited surface water take from the adjacent stream.
In sustained rainfall, the stormwater that is surplus to the site’s storage capacity is discharged via a Sand and Peat Filter to the stormwater network and on to the stream. This storage/reuse, coupled with the tail end treatment, deals with the ‘Water Quality Volume’ – a volume identified by the Auckland Council as containing the highest levels of contaminants generally. This enable a good first flush volume of rainfall to be collected. Very high storm flows bypass the system entirely, with a direct discharge from the flushed site to the network.
The Papakura Timber site is able to recycle millions of litres of contaminated stormwater each year. In broad terms, it is not uncommon in the industry for there to be 50 grams of ‘timber treatment heavy metals’ lost into the natural environment from a 1 hectare site in 10mm of rainfall runoff (equating to 100 m3 of runoff). Being able to capture much of this rainfall for reuse, thereby putting the heavy metals into the timber, is a substantial environmental gain, year in and year out. This BPO (Best Practicable Option) approach substantially reduces the contaminant load in the natural environment.This environmental solution also saves a huge water bill.
Environmental Management Plan approach
All industrial sites are busy getting on with what they do best. In IWS’s experience, industry generally has not fully recognised the risk and the responsibility of being linked to the natural environment by a ‘stormwater pipe’. New Zealand has a significant natural resource to protect out there, even in an urban area. The health of the natural environment is closely linked to the health of its human population. As a requirement of the Auckland Air, Land and Water Plan initially, Papakura Timber has operated an Environmental Management Plan (EMP) for some years. An EMP assists with the ‘avoid, remedy and mitigate’ objectives of the Resource Management Act.
The Papakura Timber EMP strives to deal with the small day-to-day environmental issues that need checking, solving and recording. It has also resulted in upgrades to equipment and structures to reduce the environmental risk. This document is only useful if it is ‘live’ and the Papakura Timber EMP is becoming more valuable and effective each year, further protecting the local natural environment.
Permission for this case study was given by Tom Logan, retired owner of Papakura Timber Processors.