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Frequently asked questions (FAQ's)

Frequently asked questions (FAQ's)

Updated 17 March 2017 10:25am

Are T and T landfills allowed to discharge to the Owhiro Stream?

Yes, but only if they meet their consent conditions. The consent sets limits on contaminants to ensure the stream environment impact is minimised to an acceptable level.

What is the adaptive management framework under T&T Landfill Limited discharge consent?

T&T Landfill Limited have a suite of resource consents for the operation of the landfill. One of these consents is a discharge permit which allows T&T Landfill Limited to discharge contaminants including sediment-laden stormwater, leachate from the site to tributaries of the Owhiro Stream. The discharge is subject to a number of resource consent conditions which T&T Landfill Limited needs to comply with to manage the effects of the discharge on Owhiro Stream and its tributaries. In particular, the resource consent sets out discharge quality limits and an adaptive management framework. Under their consent conditions T&T Landfill Limited is required to:

  • Undertake quarterly groundwater and surface water quality monitoring and get these samples analysed for a range of parameters;
  • Do a comparison of the quarterly water quality sample results with the limits set out in the consent conditions and with Australia and New Zealand Guidelines for Fresh and Marine Water Quality Guidelines (ANZECC Guidelines);
  • If the consent limit for any parameter is exceeded, and where that parameter also exceeds the latest ANZECC Guideline, a further round of sampling must be undertaken within 1 month of the exceedance being detected.
  • If the results of the second round of sampling show an increase in the level of any one contaminant, T&T Landfill Limited must engage an independent ecologist to provide an assessment of the ecological effects of the discharges from the site. The assessment must include (amongst other things) an assessment of whether the treatment methodology for the discharge is the best practicable option and recommendations on methods that could be used to further treat the discharge.
  • The recommendations from the ecological assessment which are approved by GWRC must then be implemented by T&T Landfills within the timeframe specified by GWRC.

Have T and T Landfills met all their consent requirements?

No, T and T are currently not complying with their consent, and GWRC already has taken enforcement action in the form of an Abatement Notice.

What requirements of the consent have T and T Landfills not met?

There are two interlinked matters that T and T have not met for the consents they hold for the site:

  1. A wetland to capture and treat leachate in place of the current stilling basin has not been constructed (due to the need to divert clean stormwater around the site and out of the wetland area)
  2. A clean stormwater diversion system has not been constructed yet

T and T landfill currently have a resource consent application with GWRC awaiting approval for the stormwater diversion system. T and T have been working with WCC property team who own the lower part of the site to resolve issues relating to the design of the system.

Why don't you close them down until they comply?

GWRC does not have the power to close sites under the Resource Management Act. Our first response to incidents such as this is always to work with the consent holder to address and reduce the environmental effects. Secondly we investigate to determine the seriousness of any non-compliance and whether enforcement action is required. 

What sort of landfill is T and T?

T and T is a construction and demolition waste landfill, and cannot accept any hazardous or household waste for disposal. However, the site has operated for a number of years (since the 1960's) and the nature of the waste in the first stages of the landfill is known to contain material that would not be allowed today.

Has there always been a landfill there? 

Here is a brief history of landfilling at the site (source 2006 GWRC report to Hearing Committee):

“While historical information for the area is scarce, it is believed that the large gully that is subject to the filling activity has had some form of landfill or dumping since the 1960’s. Some form of informal agreement between WCC and the operators at the time is believed to have existed to allow the site to run as a landfill with minimal waste acceptance protocols in place. Between 1991 and 1995, a company known as Ace Demolition Limited, took over the site, operating it as a construction and demolition landfill – permitting concrete, reinforced steel and the like to be placed within the landfill. The applicant (T and T Landfills) took over the site in 1995 and has operated the site as a construction and demolition landfill until the present date.”

Is it safe to use the water from the stream to water plants?

The results of testing the stream for iron, manganese and zinc have shown that the levels of these do not pose a health risk when used for watering plants.  However, we are waiting on the results of further testing of Owhiro Stream to make sure there are no other contaminants of concern. As a precautionary approach we recommend using an alternative water source until these results are back, for example, rain water or tap water.

In general, stream water would not be recommended for watering vegetables during and for 48 hours following heavy rain, as urban streams can be contaminated by run-off from surrounding land.

What did the soil testing find?

Testing of the community garden soil was done on 8th December 2016 and involved mixing samples from 4 different sites in the garden. The soil was tested for arsenic, chromium, copper, iron, lead, manganese, zinc and pH.  All of the levels, except for arsenic, were below concentrations with a potential risk to human health. The levels of arsenic were slightly elevated above the guidelines recommended for soil used for home grown vegetables and fruits (22mg/kg versus the recommended <17mg/kg).

What are T and T doing to stop this discharge?

 On 7th December 2016 GWRC met with the landfill operator, their planning consultant and engineer to discuss any immediate actions that can be taken onsite to avoid, remedy or mitigate the effects of this discharge. T and T advised they will:

  • Enlarge the wetland/ stilling basin onsite to increase its volume and therefore detention time. This wetland/ stilling basin receives all water that flows through the site and the engineer was confident that this would increase treatment.
  • Begin works to divert clean water in the gully systems upstream of the landfill around the active landfill area before it enters the stream. This will reduce the amount of water leaching through the landfill.
  • Remove dead vegetation from a gully which may be decaying and causing deoxygenation which could result in higher contaminant concentrations. 

What has been the impact on stream and fish life?

It’s clear from our inspections of the stream that there is a visible ‘iron/manganese flocculant’ in the bed of the stream, and this is still clear on the Owhiro Bay beach. While this is ‘visually’ concerning, we are seeking advice from our GWRC Science Team as to what ecological assessment of the stream life needs to be done.  We will also seek their view on the causes of the ‘foam’ which was present in the stream during rain.

What impacts did the discharge likely cause? 

GWRC Environmental Science advised that the discharge from the landfill may have had the following impacts on stream ecology - however, what is to early to say at this stage is the severity of these impacts (more on this below):

  • Physical disturbance due to smothering from high suspended sediments and iron/manganese flocculant
  • Toxicity associated with high metal loads both in dissolved and total phase
  • Reduced light penetration thus impacting on aquatic plant life
  • Potential reduction in oxygen availability in the stream
  • Clogging of gills of resident aquatic biota (invertebrates/crustaceans as well as fish),
  • Probable toxicity from ammoniacal-N and reduced dissolved oxygen availability
  • Ongoing aesthetic impacts of deposited orange precipitate

We appreciated that these effects do raise concern, and that is why this initial 'screening' of the water quality samples have highlighted the need for a more intensive ecological assessment of the stream environment, to understand the degree of any impact from this discharge event in late November.

What is the source of the foam?

Foam forms when the water contains higher concentrations of dissolved organic matter (DOM) – such as from decaying matter washing downstream as well as that potentially mixed from the landfill.  It can be naturally occurring.  In this case, it is probably a combination of both naturally occurring DOM washing rapidly downstream from the surrounding catchment, mixed in with an unknown concentration of organic based chemical leachate from the landfill that has been flushed out of this system.  It is unlikely that the foam is purely landfill based contaminant leachate, and will contain a high amount of DOM washed down from the catchment.

What is the source of the red deposits on the stream bed?

This is largely due to deposited iron/manganese flocculant, sourced from the landfill leachate. This type of orange coloured precipitate occurs when reduced groundwater (i.e. low oxygen, but containing elevated concentrations of dissolved iron & manganese) then enters surface water and comes into contact with oxygen.  The iron & manganese then become oxidised in the surface water which forms the orange/rust coloured precipitate/floc that is then deposited as a fine layer in the stream bed.  

What are the Guideline levels for arsenic in soil?

The level of arsenic in soil is slightly higher than recommended for growing home produce. In New Zealand the primary source of information on soil contaminants is the National Environmental Standard for Assessing and Managing Contaminants in Soil to Protect Human Health. These National Environmental Standards (NES) include an indication of the maximum concentration of substances in soil to protect human health. The recommended maximum concentration varies depending on what the land is used for – for example, lower levels are recommended for a lifestyle block (where it’s assumed 25% of produce will be consumed from the land) and much higher for commercial or industrial land or sports fields. The guidelines recommend arsenic levels of 17 and 20mg/kg when 25% and 10% of produce is consumed from home gardens, respectively.  This level is considered to be conservative with a high safety factor to protect against potential health effects.

What should I do to minimise my exposure to arsenic in soil? 

We are all exposed to a background level of arsenic from the environment (via food, water, soil and dust) and swallowing small amounts of arsenic every day for a long time does not lead to obvious health effects. The main way that we are exposed to arsenic from a garden is via swallowing small amounts of soil contaminated with arsenic.  We should aim to lower the amount of arsenic we are exposed to from the soil by following these simple steps:

  • Washing all produce thoroughly before consuming. We also recommend peeling root vegetables before consuming.
  • Using gloves when gardening and washing hands carefully when finished
  • Removing shoes that have been used in the soil before entering the house

The Ministry of Health have a booklet ‘Arsenic and Health’, which is a great source of additional information and advice and can be accessed online:

The information in this pamphlet also covers situations where the level of arsenic is much higher than the level found from the soil sampling in Owhiro Community Garden.

Is it safe to eat vegetables in soil with slightly elevated arsenic levels?

The main way that arsenic enters the body from home gardens is via swallowing contaminated soil. The guideline level assumes that 100% of the arsenic in the soil we swallow will be absorbed by the body.  We know that the actual amount the body can absorb is a lot lower (around 70%) and so the level is set with a high safety factor. People can swallow small amounts of arsenic every day for a long time without any obvious health effects.

Although plants can absorb arsenic from soil, the levels absorbed will be much lower than what is found in the soil.  It is more important to remove soil and dust from the surfaces of vegetables and fruits.

We do not believe that the current level of arsenic is high enough to stop using the garden. However, it is important to take steps to reduce the amount of soil that might be swallowed, for example, dirt on unwashed vegetables or transferred from hands to mouth, while in the garden.  This includes ensuring vegetables are washed to remove any dirt from the roots and surfaces.  We also recommend that root vegetables are peeled before eating.

Eating fresh fruit and vegetables is important for good health, as is participating in the community garden.  The benefits of these activities for improving health are greater than any potential risk from arsenic in the soil. 

Is it safe to garden at the site?

We are exposed to small amounts of arsenic from the environment over our lifetime and when we are aware of a potential source, the aim is to reduce the amount of exposure.  Some simple steps can be taken to reduce the amount of arsenic exposure from gardening by limiting the amount of soil that could be swallowed.  This includes using gloves for gardening, washing hands after gardening and before eating, removing shoes used in the garden before entering the house.  The good thing about following this advice is it also helps protect against other illnesses that can be associated with gardening, for example, legionella and other bacteria.  Wearing a mask while gardening is also recommended to prevent breathing in legionella bacteria from soil and compost.

Is it safe for children to play in the garden? 

Young children tend to have more exposure to soil due to their higher level of hand to mouth activity.  It will be important to, as much as practicable, minimise the amount of soil swallowed by children by discouraging children from putting soil in their mouths, washing children’s hands frequently and washing children’s outdoor toys frequently to remove soil and dust.

The arsenic level detected in the garden is acceptable for soil used in parks and recreational areas, but above the guideline recommended for eating home grown produce. It will be important to limit as much as practicable the amount of soil swallowed by children while taking part in gardening activities.

Is it safe to swim in Owhiro Bay? 

The levels of contaminants sampled from Owhiro Stream are not of concern for swimming in Owhiro Bay.  However, at times the water in Owhiro Bay is not suitable for swimming, usually during and within 48 hours after heavy rainfall.  The water quality of Owhiro Bay is monitored weekly during the summer season.  See for information about the water quality at this site and any warnings that are in place.

In general, urban streams are not recommended for recreational use such as swimming or paddling as the water quality can be unsuitable at times.  If there is contact with the stream water we recommend that people follow good washing hands practice after activity in or with the stream.