Council to receive report on closed landfills in Southland

A risk assessment report into identified closed landfills will enable Southland District Council to formulate a plan for their ongoing protection.

In Council’s 2021-2031 long term plan $500,000 was allocated to investigation of all landfills and to action any recommendations. This was split $150,000 in 2021/2022 and $350,000 in 2023/2024.

Strategic manager water and waste Mike Bourke said a review of all closed landfill sites was done by e3 Scientific in 2022 and a subsequent report will be tabled at next week’s Council meeting.

“This investigation has provided Council with a comprehensive review of all sites and the information allows us to put the right steps in place to manage these into the future,” he said.

Of the 62 landfills previously identified, eight were subsequently found to be private with another four not considered to have landfill material deposited.

56 separate Selected Land Use Register (SLUS) sites, including some landfills split into multiple SLUS records, were investigated. A number of sites were considered low risk and capable of being managed through a simplified site management plan, including five sites which no longer required on-going, proactive site management.

A total of 17 sites were considered to present a possible risk due to leachate impacting surface water or groundwater quality, or due to potential exposure to erosion/flooding. For these sites, it was recommended detailed site management plans be prepared to act as a guide for additional investigation and assessment.

After reviewing the e3 Scientific investigation, SDC staff created a risk register based on likelihood of failure, consequences of failure and ability to mitigate risk and 17 sites were identified as requiring further works.

Closed landfill management plans were created for the 17 sites, containing considerably more detail than the original report. The two main recommendations were surface water/groundwater sampling for leachate contaminants and assessment of at-risk sites by a coastal engineer for stability and protection options.

The first round of water sampling on some sites has been undertaken with results being processed currently. Other sites are due for their first round of sampling in coming weeks when weather permits.

The Colac Bay landfill was included with further water sampling recommended to confirm presence and concentrations of leachate indicators upstream and downstream of the site. The first round of sampling is scheduled for the coming weeks. Erosion of the coastline will continue to be monitored, however the distance from the coast to landfill compared to other sites around the district does not make this site an immediate risk requiring reactive works.

“The Colac Bay site has been assessed three times in the past and has been listed as low risk, although beach erosion is still occurring but a long way off yet. It is considered that the site may be vulnerable in the long term, but current risk is low,” Mr Bourke said.

e2 Environmental were engaged to undertake coastal engineering assessment of sites at Otautau, Bayswater, Wreys Bush, Thornbury and Riverton Rocks. The subsequent erosion protection for landfills report gave protect in place vs removal considerations, the works likely required, high level costs and approximate timelines for this to occur.

Based on e2 Environmental recommendations, protection/removal works at Otautau, Bayswater, Wreys Bush, Thornbury and Riverton Rocks have been added into the 2024 -2034 long term plan with an estimated cost of $12 million. These works are planned to be completed within the next 15- 20 years.

The Bluecliffs Beach Road dump site, near Tuatapere, was not included in the report as Council was not aware of its existence until recently.

Historically, waste disposal in Southland was decentralised and most townships had one or more local tip sites that fitted their community needs. These landfills by today’s standards were poorly designed, managed and located in marginal areas, typically empty gravel pits or the like.

When the Resource Management Act 1991 came into effect, resource consents became required to control environmental impacts of these activities. As a result, these localised sites were closed rather than gain consent.

Southland District Council is responsible for any works required going forward due to being the successor of the local authority who operated or allowed the landfill, or the current landowner of the site.