Wellington Scoop

More pollution from sediment and erosion in Owhiro Stream and Owhiro Bay

News from Wellington Regional Council
There is discolouration in the Owhiro Stream and a sediment plume in Owhiro Bay from rain in the last 24 hours.

This rain has mobilised sediment which has been disturbed during the construction of the stormwater diversion channels at T&T landfill.

We have been on site and are working with the landfill operators and their contractors and consultants to ensure that erosion and sediment control measures are in place to minimise the release of sediment into the stream.

A discharge of sediment from the site during the early phase of construction was expected as there are limited options to manage the release of sediment from within the diversion channels themselves. We expect the release of sediment from the site to continue to decrease as the works progress and as additional sediment treatment measures are put in place.

Wellington.Scoop – May 8
A report commissioned by the Wellington Regional Council describes how the T&T Landfill is causing “significant adverse effects” on water clarity and colour and on aquatic life in the Owhiro Stream. It recommends urgent action.

It says a number of clear spikes in the concentrations of contaminants were measured in January and August 2012, June 2013 and October 2016.

The report states:

The November 2016 event led to greater effects than the normal ongoing/background effects. However, this does not appear to have been a unique event, similar conditions having been reported in 2012. It is also possible that the June 2013 and October 2016 spikes in contaminants were the result of similar events.

On the basis of the above conclusions, we can only recommend that some urgency be given to implementing mitigation measures, including:

diversion of the tributaries around the landfill to reduce as much as practicable, the amount of water circulating under and through the fill area. We understand that surface diversion channels are being considered. We recommend that their design incorporates input from a water quality scientist/ecologist to ensure that the diversion channels do not prevent fish passage and do not lead to other effects (for example, some shading should be provided to avoid significant increases in temperature);

capture and treatment of the remainder of the leachate at the toe of the landfill. We understand that a wetland treatment is being considered. As with all wetland treatment systems, adequate design of the wetland will be critical to treatment efficiency, particularly given the physical constraints of the site (only a very small wetland will be able to be constructed). We also note that
wetland treatment is not generally considered efficient for removal of ammoniacal nitrogen, and additional treatment may be required if elevated ammoniacal nitrogen are recorded again in the future.

With regards to ongoing monitoring, we make the following recommendations:

It appears that events similar to that of November 2016 have already occurred in the past following heavy rainfall, leading to “spikes” in contaminant concentrations being discharged to the Owhiro Stream. The frequency of the current water quality monitoring regime (every three months) means that short- to medium-term spikes may not be identified. It would seem appropriate to undertake systematic water quality sampling in the 2-4 week period following heavy rainfall. Site inspections may also help identify any water ponding areas;

There does not appear to be any data on the presence or abundance of organic micro-contaminants in the Owhiro Stream. Given the unknown nature of the waste underlying the T&T clean fill operation, some analyses of SVOC/VOCs in sediment at various points down the catchment would be useful to provide some base information on the presence of these contaminants in the catchment.

The report in full

April 11: Five reports of pollution in stream
April 28: Mitigation measures being reviewed

Sewage smell from Owhiro landfill

1 comment:

  1. William, 8. May 2017, 16:52

    It is time for the EPA or MOE to issue a compliance order. If nothing has been done following previous occasions, there needs to be some ‘encouragement’ to enforce urgent action.