Environmental Assessment of Former Landfills

Client: NZTA
Date: 2001-2013

We undertook an environmental investigation at a series of former landfills that were located along with the designation of the proposed Christchurch Southern Motorway (CSM) greenfields section.  Principal objectives of the environmental assessment included characterisation of the landfill waste through interpretation of soil and groundwater sampling data to evaluate the potential risks to human health and the environment during and following the motorway construction works; providing an assessment of effects for a suite of earthworks engineering treatment options; providing options for addressing the excavated landfill waste material and providing technical information to assist in the application of resource consents from regional and territorial authorities.

Our team successfully prepared and presented technical evidence at a joint local and regional authority hearing, and following the gaining of resource consents completed pre-construction baseline groundwater monitoring, during-construction groundwater monitoring and closeout post-construction groundwater monitoring.  Groundwater sampling included assessing trends of typical landfill leachate parameters from pre to post-development.

Key Aspects

  • Test pit contamination assessment
  • Pre-construction, during construction and post-construction groundwater and landfill gas (LFG) monitoring
  • Resource consenting and hearing presentation

Client: NZTA
Date: 2001-2013

A significant component of the investigation also included characterisation of the landfill waste through interpretation of landfill gas monitoring data on a regular basis, over a number of years, at strategically placed monitoring wells.  The data provided a critical evaluation as to the potential risks posed to human health and the environment during and following the motorway construction works.  An important stage of the landfill gas assessment programme, prompted by resource consent trigger concentrations, required invasive monitoring within nearby residential properties using specialist high sensitivity equipment.

Undertaking the landfill gas assessments, particularly within private residential properties, required a quick turnaround (typically same day) on interpreting data and providing to the client, with any necessary mitigation measures.  Included in the overall landfill gas assessment was determining potential risks to underground services, associated conduits and the motorway street lighting poles.

Project Outcomes

  • PDP was able to meet the expectations of NZTA in providing a detailed environmental assessment as part of a specimen design roadway construction project.
  • The technical level of the assessment suitably demonstrates PDP’s capabilities with regard to providing NZTA with a sound approach to undertaking environmental contamination assessments.
  • 100% of the technical environmental site assessment work was carried out by PDP.

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