Contaminated Land Management

The need to understand and investigate potentially contaminated land in order to satisfy the requirements of the National Environmental Standard (NES) is becoming more important. The increasing demand of developable land necessitates the subdivision of former agricultural and industrial sites, where historical activities has negatively impacted the environment. Where this is left undetected or not fully investigated, any subsequent discovery of contamination can cause significant delays to the construction programme when retrospective Resource Consent is needed to to prove the site is safe or what mitigation is required. GCL has the in-house capability to carry out contaminated land studies in order to facilitate site development and meet the Regulatory Authorities requirements as well as those of the NES, following the guidelines set by the Ministry for the Environment.

• Site walkovers and desktop studies

  Increasingly part of the geotechnical investigations, GCL is cognisant of a site’s history and identifying tell-tale signs during the initial site reconnaissance. This can often be an early warning to a perspective buyer or developer that there may be environmental constraints or issues associated with a site.

• Preliminary Site Investigations (PSIs)

  The first formal investigation of a site in terms of potential contamination is the PSI, which has the purpose of identifying if the site has been subject to potentially contaminating activities or indeed has been impacted as such from neighbouring properties. The foremost objective is to ascertain if ‘Hazardous Industries or Activities List’ (HAIL) have been undertaken on the site. This is determined through orderly investigation including but not restricted to:

  • Review of the site history from aerial photography, archives and library images
  • A search of Title information to prove site ownership over time
  • Interrogation of the Council property files
  • Determine any likely environmental constraints or impact on the site
  • Develop a Conceptual Site Model
  • Identify risks to current and future land users and environmental receptors
  • Recommend further investigation, mitigation or management of any perceived environmental risks

• Detailed Site Investigations (DSIs)

  Where a PSI has identified the site has or is likely to have been impacted by HAIL activity, then an intrusive investigation with soil sampling and testing is required to determine the level of residual contamination on site. The DSI involves the following:

  • Appropriately targeted site investigation (boreholes, hand augers, test pits etc) for collection of representative soil samples
  • Laboratory analysis
  • Comparison of results against appropriate guidelines
  • Re-evaluation of the risk assessment developed in the PSI
  • Recommendations for further work, e.g. remedial and mitigation works

• Site Management Plans (SMP)

Where site contamination is marginal or can be easily managed on site through specified earthworks, testing and certification, a Site Management Plan is required in order to formally manage the risk. The SMP is a document designed to assist in managing and minimising the risks to human health and the environment through formalised steps and procedures to handling the contaminated soils and groundwater during site development and construction.