Leachate leaking from landfills

The 2001 Ministry for the Environment (MfE) document “A Guideline for the Management of Closing and Closed Landfills in New Zealand” (Guideline) was published by MfE in 2001. It was prepared as a direct result of MfE’s 1998/99 National Landfill Census (98/99 Landfill Census), which covered both open and closed municipal landfills, dedicated landfills and cleanfills, and sought to establish the current state of landfill management practice in New Zealand at that time.

Importantly it recognised (in Clause 1.1.1) that “Until the 1980s most New Zealand landfills were no more than tip/dump sites, which were often poorly sited, designed and managed”.

None of these tips/dumps were lined or had leachate/landfill gas management systems. It was only since the introduction of the RMA in 1991 that disposal sites were required to retrospectively seek resource consents in order to continue operating.

Clearly these retrospective consents were not able to require liners to be constructed under historical waste and so these dumps/tips (subsequently referred to as landfills) would continue to leak during their operational and post closure life.

All new disposal sites post the introduction of the RMA in 1991 have been required to meet significantly higher engineered standards which were effectively set by the Redvale and Whitford landfills, noting these were consented under the Town and Country Planning Act at the time of the RMA coming into force.

Since then, the 98/99 Landfill Census showed that while there had been some improvement since the earlier 1995 Landfill Census, the standard of landfills and landfill management practice in New Zealand was still not good enough. These results stimulated the development of the Ministry’s Landfill Management Programme, which had a stated set of objectives including:

• all landfills to be consented and compliant with consent conditions
• landfill consent conditions to reflect nationally consistent standards of environmental management
• all landfills to be managed by appropriately trained operators
• closed landfill sites to be monitored and effectively managed.

At the time of the 98/99 Landfill Census, the exact number of closed landfills throughout the country was unknown, but was thought to be well in excess of 1000. A significant percentage (30-35%) of closed landfill sites did not have a closure or aftercare plan, but this was thought to reflect the fact that many of the older sites were closed some years before 1998 when such plans were not identified as necessary for good practice. Additionally, some closed landfills did not have the necessary or appropriate resource consents.

In May 2000, the Centre for Advanced Engineering Landfill Guidelines (funded by the Sustainable Management Fund) was published.

MfE’s Landfill Management Programme at the time set out to develop and implement various guidelines which would make explicit the Ministry’s expectations. One of these (5) Guidelines was the Guide for the Management of Closing and Closed Landfills in New Zealand (Guide).

At the time, the aim of this Guide was to increase awareness of the risks associated with the legacy of old style landfills (tips/dumps) and to outline the best practical methods to manage closed sites effectively, so that adverse environmental effects could be minimised. The Guide applied to landfills that were already closed at that time (1998/99), and to landfills that would be closed within two years of 1998/99, as well as to landfills that at that stage did not yet have aftercare management plans prepared.

WM New Zealand agrees that the effects of leachate generated at old unlined landfills (dumps/tips) are of concern. These sites must continue to be managed and monitored during a full aftercare/post closure period to minimise these effects. At modern engineered landfills, like we are proposing in Wayby, the landfill liner system will be installed under strict independent quality control requirements to contain leachate so it can be removed from the landfill.

For noting, in the past few years, the WasteMINZ Technical Guidelines for Disposal to Land 2016 (revised 2018), have been published, although the document is still in the process of being adopted by MfE. These guidelines are available on WasteMINZ website. These are now considered best practice for modern engineered landfills, and will be followed by WM New Zealand at our proposed facility in Wayby.