Contaminated Sites in Dunedin (2011)

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The objective is to examine the legislative control guidelines and standards affecting treatment of contaminated sites in New Zealand using the Dunedin Gasworks as an example of a contaminated site.

The old Dunedin gasworks site was chosen as our example as it is currently being remediated for a new Countdown Supermarket with some of the excavated soil destined for landfill.

In addressing the objective we will look at the relevant sections of the Resource Management Act and The Otago Regional Council Rules around Contaminated sites. We will critically evaluate the Landfill Classification and Waste Acceptance criteria, the proposed National Environmental Standard for Contamainted soil and compare and contrast the heavy metal values common to each. We will also assess the disposal techniques available to Landfill Operators to ensure that waste entering their facilities are acceptable for landfilling.


In Otago there are 140 confirmed, managed, remediated or not contaminated (after investigation) sites across Otago, including:

  • 33 confirmed contaminated sites.
  • 35 managed sites.
  • 15 remediated.
  • 6 remediated/managed.
  • 51 not contaminated.
Cars dumped on a site without leachate control. This photo was taken July 2011 and demonstrates that activities which created contaminated sites are still being undertaken.

Sites still contaminated are:

  • Andersons Bay Gasworks, Andersons Bay Rd, Dunedin.
  • Oamaru Gasworks, Humber St, Oamaru.
  • Finegand Freezing Works landfill, Owaka Highway, Balclutha.
  • Craigpine Timber Treatment waste disposal area, Northland St, Ranfurly.
  • Wingatui closed landfill, Gladstone Rd North, Mosgiel.
  • Orokonui Holiday and Recreation Park, Orokonui Rd, Waitati.
  • AgResearch Invermay, Puddle Alley, Mosgiel.
  • North Taieri landfill, Milners Rd, Mosgiel.
  • North Taieri recycling centre, Milners Rd, Mosgiel.
  • Humber St Gasworks waste site, Humber St, Oamaru.
    Leachate oozing from a contaminated site.
  • Threepwood Farm Ltd, Lake Hayes, Queenstown.
  • Shell Dunedin depot, Wickliffe St, Dunedin.
  • Kakapuaka Garage/Scrap Metal, Kakapuaka Rd, Balclutha.
  • Balclutha Motors, Elizabeth St, Balclutha.
  • Wylies Garage Ltd, Northumberland St, Tapanui.
  • Omakau Autos, Wilson St, Omakau.
  • Lauder Service Station, Lauder-Omakau Rd, Lauder.
  • BP Concord, Corstorphine Rd, Dunedin.
  • Coronation Hall, Gordon Rd, Mosgiel.
  • Shell Fairfield, Main Rd, Fairfield.
  • BP Regent, George St, Dunedin
  • Gardens Service Centre Mobil, Cumberland St, Dunedin.
  • Mobil Mosgiel, Factory Rd, Mosgiel.
  • BP Hiway Autocentre, Usk St, Oamaru.
  • Lengs Motors /BP Palmerston, Ronaldsay St, Palmerston.
  • Glendermid Leathers, State Highway 88, Sawyers Bay.
  • W E Perrin Ltd, Royal Tce, Owaka.
  • Arrowtown oxidation ponds, Centennial Ave, Arrowtown.
  • Toko Timber Treatments, Springfield Rd, Milton.
  • Blue Mountain Lumber, Pomahaka Rd, Tapanui.
  • Barrow Box, Cameron Rd, Tapanui.
  • Waihemo Timber Co Ltd, Burraness St, Palmerston.
  • 57 Selwyn St, Northeast Valley. <ref>Morris, C. (2009) 'ORC identifies Otago's contaminated sites', Otago Daily Times, 17 October.</ref>

Contaminated sites are predominantly covered by the Resource Management Act 1991. The effects based decentralised nature of the RMA has lead to divergent approaches towards hazardous waste management in New Zealand. In handling contaminated wastes, other legislation also applies such as the Health and Safety Act 1991. The transport of hazardous substances from contaminated sites is governed by the Land Transport Act 1998. The Health Act 1956 also applies if contaminated sites are having an impact on human health.

The purpose of the RMA is to promote the sustainable management of natural and physical resources. The various relevant sections are summarised below.

  • Section 5 (2) defines sustainable management as managing the use, development and protection of these resources while safeguarding the life supporting capacity of air, water, soil and ecosystems and avoiding, remedying or mitigating any adverse effects of activities on the environment.
  • Section 6 adresses matters of National importance.
  • Section 7 deals with the efficient use and development of natural and physical resources and the intrinsic value of ecosystems.
  • Section 8 requires the principals of the Treaty of Waitangi to be taken into account.

The implementation of the RMA generally rests with Local Government. Section 30 and 31 describe the functions of Regional Councils and the Territorial Local Authorities (TLA) respectively. In considering a contaminated site, Regional Councils are responsible for controlling the discharge of contaminants to the environment (Section 15) while TLAs have the responsibility for land use matters.

In practice what this means is that if an owner of a site that is known to be contaminated wants to disturb the contaminated land they will be required to get a Resource Consent unless a plan specifically permits this activity. A Land Use Consent will also be required from the TLA. This decentralised approach has resulted in significant variation between sites, for example different rules were applied in the treatment of gasworks sites in Auckland in comparison with Dunedin <ref>New Zealand Institute of Building (2011) Progressive building: the magazine of The New Zealand Institute of Building, Vol 87, pp 30-39.</ref>. In Auckland, as the old Gasworks site was being disturbed, they were required to capture and treat all gasworks fumes being generated from the site before discharging them into atmosphere. This resulted in the establishment of the largest tent structure ever erected in New Zealand, where as the Dunedin site excavation is exposed to open air with no discharge controls.

There have also been many guidance documents written by the Ministry for the Environmentfor significant hazardous waste steams. These include: the assessment and management of Gasworks sites, petroleum waste sites, timber treatment etc. As a further recent development to managing the disposal of contaminated site waste, a Proposed National Environmental Standard for soils has been published (2010). A critical examination of the impact this standard in relation to New Zeland Hazardous Waste Guideline:Module 2 Landfill Waste Acceptance Criteria and Landfill Classification is put forward.

The Resource Management Act 1991

Ongoing environmental monitoring of a creek. The creek is in very poor health with an approximate average pH of 5. The creek recieves a discharge from a contaminated site.

The RMA is the core piece of environmental legislation for controlling the effects of contaminated land on the environment and people. The Resource Management Act defines contaminated land. The full definition of contaminated land is specified under section 2 of the Resource Management Act being:

contaminated land means land that has a hazardous substance in or on it that - (a) has significant adverse effects on the environment; or (b) is reasonably likely to have significant adverse effects on the environment.

The Ministry for the Environment is responsible for administering the Resource Management Act (RMA) 1991. Local government (regional councils, city and district councils) are responsible for the day-to-day management of contaminated land and have specific functions under the RMA. Local government is in charge of controlling the effects of contaminated land, and also for controlling activities that cause land to become contaminated. Sections 30 and 31 of the RMA give local government the following functions:

  • Regional Councils – “the investigation of land for the purposes of identifying and monitoring contaminated land”
  • District and City Councils – “the prevention or mitigation of any adverse effects of the development, subdivision, or use of contaminated land”.

These functions generally mean that Regional Councils work to identify and monitor the environmental effects of land that is contaminated within their region. District and City Councils are responsible for checking, before approving a subdivision, development or change of land use, that health guideline levels are not exceeded for any contaminants present. In addition to the RMA functions, local authorities also have responsibilities under other Acts to provide information about the presence of hazardous substances on land.

The Otago Regional Council Regional Plan: Waste Policy and Rules Around Contaminated Sites

Aerial of the Closed North Taieri Landfill. This Landfill sits on a Ground water protection zone A. The Landfill closed in 1990, a move strongly opposed by the Mosgiel Community. The ongoing monitoring of this site is significant, and concerns exist on the landfills impact on groundwater. The remediation solutions are almost prohibitively expensive.

Regional Council Plan: Waste policy and rules around contaminated sites

In the Regional Plan: Wasteof Otago 1997, contaminated sites are defined as “a site at which hazardous substances occur at concentrations above background levels and where assessment indicates it poses, or likely to pose an immediate or long term hazard to human health or the environment” <ref>Otago Regional Council (1997) 'Regional Plan: Waste For Otago', Chapter 5 Contaminated Sites, pg 48.</ref>. Contaminated sites in New Zealand are largely underestimated when it comes to the potential impacts they could have on peoples health and the environment. They can cause a number of detrimental environmental effects, such as loss of vegetation and habitat, threats to surface and ground water and ecosystems. These effects can have significant economic and social impacts. New developments such as residential, commercial, industrial and agricultural sites which occur in the Otago region are required to be assessed for potential adverse effects they could have on the the environment, prior to any construction.

The significant variety of highly toxic organic compounds that were commonly used in New Zealand. Illustrated are the organochloring chemicals of Lindane, 245T and Dioxan. These are mutagenic compounds meaning the are passed on from plants to animals. They can cause birth defects and other serious health issues in humans and to other species present in the environement.


5.2 Issues. In the Otago region, large numbers of contaminated sites are currently unidentified. This is because the past records of the storage, use, and disposal of contaminants were poorly managed because it was generally thought that the products that were being handled and used were safe eg. the use of DDT which was commonly used in 1950s. This becomes problematic when new developments are being carried out. With lack of records, it is difficult to judge whether or not it is appropriate to carry out development on particular sites. Also, depending on the types of the contaminant(s), the environmental impacts that the contaminant(s) pose are different for each site. Contaminants are capable of not only harming human health, animals, plants, water and land quality, but also integrity of building and service structures as well. Moreover, some contaminants can be threat to adjoining areas of the contaminated sites.


5.3 Objectives. The objectives of the regional plan for the contaminated sites are “to avoid, remedy or mitigate any adverse effects of contaminated sites” and “to avoid further site contamination”. When a contaminated site is identified, any effects on the environment should be avoided, remedied, or mitigated. The objective is to improve handling and disposal of hazardous substances and hazardous wastes, and to manage the on-going industrial, agricultural and commercial activities, so that site contamination is less likely to occur.


5.4 Policies. Policies for the contaminated sites are stated in the Regional Plan: Waste 1997.

The policy 5.4.1 states that “To recognize and provide for the relationship Kai Tahu have with Otago’s natural and physical resources through:

a)Carrying out investigations of, and works to remedy and mitigate, contaminated sites in a manner which takes into account Kai Tahu cultural values.

b)Protecting waahi tapu and waahi taoka, and access to them by Kai Tahu, from the effects of contamination.

c)Acknowledging that future generations will inherit the results of work carried out to remedy or mitigate contaminated sites.

d)Maintaining consultation with Kai Tahu on issues relating to site contamination”.

This policy aims to value the relationship between Kai Tahu and to protect and enhance the sites and resources important to them.

5.4.2 states “To locate and investigate contaminated sites in Otago”, seeks to detect existing contaminated sites and their sources in the Otago region, and to investigate their past histories.

5.4.3 states “To contain contaminated sites and rehabilitate them to the extent that is practicable having regard to the use to which the land is to be put”. This policy explains the necessity to determine restriction of contaminants and risks posed in the contaminated sites. In agreement with the policy, any persons operating activities within the contaminated sites must prioritize the management of contaminants to control adverse effects to the air and water. The risks of the contaminants, rehabilitation of the contaminated sites, and practicality of rehabilitation needed to be considered. The local authority or a consent authority can apply to the Environmental Court for an enforcement order if they are not satisfied with the methods taken to contain and rehabilitate contaminated sites.

5.4.4 states “To apply the Australia and New Zealand Conservation Council (ANZECC) ‘Guidelines for the Assessment and Management of Contaminated Sites’ (January 1992) as a guide to determine the most appropriate course of action for a particular contaminated site”. This guideline provides a clear decision making process to determine if any remediation works are required. The Ministry of Environment also provide various specific industries which create contamination. For example gasworks contaminated sites, timber treatment, petroleum hydrocarbons, dioxins etc.

5.4.5 of the Regional Plan: Waste states that “To prepare and maintain a register outlining details of sites which are contaminated”. This policy promotes Otago Regional Council to maintain the records of the contaminated sites, and make them available to territorial authorities and the public.

Contaminated Sites Methods

5.5 Methods. In order to achieve the objectives and implement the policies, the Otago Regional Council is required to take certain methodologies to address how to manage indentified contaminated sites.

In accordance with 5.5.1, contaminated sites in Otago are identified by carrying out investigations and responding to information supplied by the public.

5.5.2 describes which steps are to be taken when a contaminated site has been located. These steps are described as follows:

  1. Any persons exercising any activities need to consult with the land owner and occupier.
  2. The contaminated site where activities are being carried out needs to be investigated prior to any activities being undertaken.
  3. The use of the ANZECC "Guidelines for the Assessment and Management of Contaminated Sites" (January 1992) should be encouraged for determination of actions which are to be taken. While assessing contaminated sites, assessors should refer to the "[1] National Rapid Hazard Assessment for Contaminated Sites guideline".
  4. The Otago Regional Council is responsible for encouraging the landowner or occupier of the contaminated sites to conduct remediation or mitigation for any adverse effects on the environment. Furthermore, pursuant to Section 314 of the Resource Management Act, Otago Regional Council is permitted to apply enforcement order where no actions are taken.
  5. Resource consents must be issued where contaminants are being discharged into water, land, or air, and emanated from the contaminated sites. Disturbance of the sites caused by the activities which could possibly affect the environment adversely is also subject to the resource consent issue.
  6. Any contaminated sites which are considered to be appropriate, should be included in the Otago Regional Contaminated Sites Register.
  7. Contaminated sites which are registered on the Otago Regional Contaminated Sites Register should be removed if the adverse effects on the environment induced by the contaminants are deemed to be ceased.
The NZ Fire Service handling a drum of unknown substance illegally dumped in a suburb in Dunedin. Fortunately the drum remained intact and the soil did not become contaminated.

5.5.3 lists the information to be compiled and maintained in the Otago Regional Contaminated Sites Register. The information that needs to be included are “the location and legal description of the site, the nature and extent of contamination, any work carried out, or to be carried out, to remedy or mitigate any adverse environmental effects, any conditions imposed on resource consents relating to work being carried out on the site, details of monitoring to be undertaken, any restrictions applying to the use of the land, and any other information the Otago Regional Council considers relevant”. Copies of the Register are passed onto territorial authorities for this express purpose.

5.5.4 seeks ways to carry out activities without land use consents. Territorial authorities are encouraged to develop resource management techniques which allow them to carry out activities without obtaining the land use consent at contaminated sites where remediation and mitigation are practicable.

5.5.5 promotes resource management which enables the land owners to avoid, remedy, and mitigate threats on environment.

5.5.6 encourages the adoption of codes of practice. Installing the codes of practice in various activities could lead to the reduction in the number of contaminated sites.

5.5.7 concerns consultation with Manawhenua where activities are being practiced. The Otago Regional Council is obliged to provide information on sites that could potentially be contaminated.


5.6 Rule. For the Otago region there are essentially five rules for contaminated sites a synoposis of which follows. A breach in any of these rules will require the owner to obtain a Resource Consent.

  1. If land is going to be disturbed
  2. If there is any discharge of hazardous wastes into water
  3. If there is any discharge of hazardous wastes into, or onto land in circumstances that may result in hazardous wastes entering water
  4. If the owner intends to deposit of any hazardous wastes in, on, or under land
  5. If the discharge of harzardous wastes into air at, or from the contaminated sites or activities that are to be carried out on

Essentially if the land owner is going to interfere with a contaminated site, it is going to be a discretionary activity, and a resource consent will be required.

Ultimate Otago Regional Council Objectives

5.7 Results. The environmental outcomes which should be achieved through the regional plan are stated. These outcomes are to locate and assess the hazard to the environment in the contaminated sites, protect the environment in an immediate and long-term manner and ensure that no extra contaminated sites are created.

Proposed National Environmental Standard (NES) - For Assessing and Managing Contaminants in Soil 2010

New Zealand has been a relatively late player on the world stage when it comes to managing soil contamination; the issue of soil contamination was not specifically targeted until 2005 when the RMA was amended. This required local councils to develop their own criteria to deal with soil contamination. With many different soil guideline values (SGVs) set by local, regional and central governments it makes it difficult to determine which one to use. Consequently a National Environmental Standard (NES) is being proposed by the Ministry for the Environment. It is intended that this proposed NES will provide a more integrated and collaborative approach to the management of soil contamination in New Zealand. <ref>Ministry for the Environment (2010), 'Proposed National Environmental Standard for Contaminated Soils Discussion Document', Ministry for the Environment, Wellington (Downloaded 12th August, 2011)</ref>

Objectives of the Proposed National Environmental Standard

The Ministry for Environment has set a number of goals which they wish to achieve by developing a NES, these include:

  • Planning controls that will be suitable for all district and city councils for assessing and managing contaminants in soil.
  • Providing a set of chemical-specific soil contaminant thresholds that will provide an acceptable level of protection for human health and the environment on a national level, regardless of the land-use.
  • Ensuring that land affected by contaminants in soil is appropriately identified and assessed at the time of being developed and if necessary remediated, or the contaminants contained, to make the land safe for human use.

Current Procedures for Management of Soil Contamination

Analysis of the current techniques of managing contaminated sites by the ministry for the envirmonment, in developing these standards found that were a number of inadequecies. The propsed NES recomendeds a simple three step process for determining whether or not land is safe for human use. This involves:

  1. Identifying whether or not the land specified is affected or potentially affected (concentration of a particular toxin could accumulate over time) by contaminants in the soil.
  2. Assessing whether or not the contaminants in the soil could have an adverse effect by using the appropriate soil guideline values.
  3. Whether or not the remediation of the contaminated soil is required and to minimise the risks of adverse effects occurring.

Although this seems like a straight forward process, many regional and local councils lack suitable controls and technical skills to ensure that this process will be followed through at critical stages. These include land affected by contaminants in soil that has already been developed, subdivided or has had its land use changed.

When contaminated sites are not well managed the result can be harmful to human health. Under section 31(b) (iia) of the RMA territorial authorities such as local and district councils are responsible for the prevention or mitigation of any adverse effects of development, subdivision, or the use of contaminated land. Many of these authorities fail to meet the requirements of section 31 under the RMA 1991.

Table 1: Number of district plans that have no specific information regarding contaminated land <ref>Ministry for the Environment (2010) 'Proposed National Environmental Standard for Assessing and Managing Contaminants in Soil', Ministry for the Environment: Wellington. (Downloaded 12th August, 2011)</ref>.

NES-table 1.jpg

The major shortcomings of District plans is they lack specific mention of the management of contaminated land. This leads to a greater chance of the contamination being missed, especially at the when identifying and assessing contaminated soils.

Responsibility for Implementation

All of New Zealand’s territorial (district and city) councils will be responsible for the implementation of the RMA under section 31(1) (B) (iia). This allows them to control any actual or potential effects from the use, development, subdivision and the use of contaminated land, also to prevent or mitigate any adverse effects of the development, subdivision or the use of contaminated land.


The NES allows for a shortening of the decision-making process which will give the owner a greater range of options for the disposal of contaminated soils. This “stream-lined” process is unrealistic because the less time spent assessing the impact of soil contaminates on a particular site, the greater the chance of an error occurring when a final decision is made. In our opinion, the costs and benefits in the proposed NES are also quite vague. In section 5.1.6 of the discussion document produced by MfE they mention that there is the potential for improved environmental outcomes as a result of this proposed NES. No information or facts have been provided to indicate research has been undertaken to come to this conclusion. Indeed, when comparing the guideline values to that of the Landfill Acceptance Criteria and the New Zealand Drinking Water Standards 2005 for the maximum acceptable values for the protection of human health there is a vast difference between all three. The values chosen need to be robust and align with other standards and guidelines. In our opinion the values appear to be overstated and this may lead to a potential environmental deterioration.

The Landfill Guidelines

Hazardous Waste Guidelines: Landfill Acceptance Criteria and Landfill Classification Published by the Ministry for the Environment in May 2004<ref> Ministry for the Environment (2004) 'Module 2: Hazardous Waste Guidelines, Landfill Acceptance Criteria', Ministry for the Environment, Wellington (Downloaded 15th August, 2011)</ref>

Guideline Aim

The aim of these guidelines is to offer a nationally consistent approach to the disposal of waste to landfills.

  • These guidelines point out that current New Zealand approaches to the landfill disposal of hazardous wastes were out of alignment with international best practice. The Ministry for the Environment believes that policy instruments for controlling hazardous waste disposal should be adopted at a national level as opposed to being developed locally. The reasons for their development is that there were significant inconsistencies and variance in accepting contaminated wastes to landfill across the country. The guideline provides waste generators and the waste management industry with both certainty and a level playing field for the acceptance of wastes to landfills.

New Zealand Landfill Definitions

The Landfill Guidelines only specify two classes of landfill. Either landfills are a Class A - being fully lined, constructed and located to the specifications of the US EPA Subtitle D requirements, or they were considered to be a Class B - where the criteria is not as stringent. Even some lined, well sited facilities are considered Class B sites. There are only two landfills that are categorized as Class A in the South Island, being in Christchurch and Invercargill. The engineering of these Class A sites is specifically designed to mitigate, to an almost negligible level, the possibility of a leachate escape and consequential threat to the environment. Class B Landfills sites are the remainder of landfills in the South Island that do not meet such stringent criteria. For example the Green Island Landfill is classified as a Class B site. It essentially an unlined landfill sited in an estuary, however, it does have a retro-engineered leachate collection system, an extensive monitoring programme and adheres to a strict waste acceptance criteria. Its effect on the estuary and adjacent Kaikorai stream has remained negligible since monitoring began some 15 years ago. The New Zeland Hazardous Waste Guideline:Module 2 Landfill Waste Acceptance Criteria and Landfill Classification is the overarching document for the acceptance of contaminated waste to landfills in New Zealand. Prior to the relatively recent introduction of the Landfill Acceptance Criteria there were no national guidelines or standards for the acceptance of contaminated waste material to landfills. Dunedin, like many other centres, felt the need to have some sort of acceptance criteria for their landfill facilities and as a consequence criteria was adopted from other countries. Dunedin Landfills main acceptance criteria was primarily based on Western Australian Landfill Acceptance Criteria (1996)for a class III putrescible landfill. The over arching conditions for operation were the Otago Regional Council Discharge Consent Conditions for the landfill and in Dunedin's case (a condition that still prevails today) there is only a requirement to monitor discharges. No leachate indicator limits are specified.

In our opinion there remains a strong case in New Zealand for a B+ or A- landfill class. It is worth considering that the same rules apply to a Class B site that has no management or leachate protection systems in place.

Waste Acceptance Criteria

The Landfill Classification Guideline provides a method for determining if contaminated wastes are acceptable for disposal to landfill. Under the guidelines, a Class A Landfill can accept a greater range of wastes due to it's more stringent environmental protection systems in a Class B site.

There are two types of tests undertaken to determine whether waste can be accepted to either class of landfill. These tests are:

  1. The material screening test, called the Total Concentration test. This test looks at the amount of contaminat per kilogram of material. It is measured in milligrams per kilogram.
  2. The leachability test. This test is called the Toxic Characteristic Procedure Test (TCLP). It is perhaps the most important test as it looks at the how readily leachable the material is. The units of this test are in milligrams per litre. The TCLP test is the more important test as it determines if the material will leach and consequently form part of the landfill leachate.

If the concentration is below screening level, there is no need to test for TCLP. However, if it exceeds the limit then a TCLP test is recommended to be undertaken. If the results exceed the TCLP limits then the disposer of the contaminated material must devise a methodology of treatment to ensure that the material is immobilized so that leachability of the material meets the TCLP criteria for the respective landfill class.

A waste may fail the total concentration levels specified in the guidelines but pass the leachability test. For example a lump of copper in a kilogram of material may fail the total concentration test, however, the same lump will pass the leachability test as copper is a relatively stable metal and does not readily dissolve (leach).

Liquid Waste is also not recommended for disposal to landfill. This is because liquid contributes directly to leachate. Liquid waste is defined as a solid’s content of at least 20% and liberate no free liquids when transported or no free liquids when tested in accordance with the US EPA Paint Filter Liquids test and liberate no free liquids when transported <ref>Ministry for the Environment, (2004) 'Module 2: Hazardous Waste Guidelines Landfill Acceptance Criteria', Ministry for the Environment, Wellington (Downloaded 15th August, 2011)</ref>. The reality is much liquid waste is still disposed of to landfill, especially if it cannot go to a waste water treatment plant facility.

There is generally a six step process to follow in the waste acceptance decision making process. These are:

  1. Is the waste included in the list of prohibited wastes?
  2. Is the Waste a Solid?
  3. Does the Waste comply with the cleanfill definition?
  4. Is the waste asterisked in the NZ waste list?
  5. Test for Total concentration of contaminants in waste and/or test for concentration of contaminants using TCLP test.
  6. Treatment.

The following flow diagram indicates the Waste Acceptance Decision-making process.

Caption text <ref>Ministry for the Environment (2004) 'Module 2: Hazardous Waste Guidelines, Landfill Acceptance Criteria', Ministry for the Environment, Wellington (Downloaded September 28th, 2011) </ref>

The treatment options include:

  • Micro encapsulation – Generally this involves mixing cement through the material so that the material become bound in a cement matrix.
  • Macro encapsulation – Essentially this is effectively entombing the material in a concrete.
  • Chemical neutralization - For example mixing acids with alkaline agents (acid + lime).
  • Bio-remediation - This process essentially composts the waste. It is very useful for Hydrocarbon contaminated soils. While it is a relatively cheap process it is considerably time consuming.

Many intractable chemicals such as persistent organo-chlorine products being 245 T, DDT, Lindane and PCPs cannot be disposed in New Zealand and require export to a facility that has a Plasma Incinerator. A Plasma Incinerator burns at 3000 degress celcius which is hot enough to break the strong organo-chlorine chemical bonds and rendering the chemical safe.

A Comparison Between the Landfill Guidelines and the Proposed NES Soils

We will be comparing the landfill guidelines with the Proposed National Environmantal Standard for Assessing and Managing Contaminants in Soils.

Currently, throughout New Zealand there are inconsistencies in which the way landfills are being managed, this is due to widely differing consent conditions imposed by Regional Councils. These inconsistencies on an international scale are not considered to be best practice for hazardous waste and landfill management and consequently the NES for Contaminated Soils was proposed. When comparing the acceptance criteria for various “cleanfill” sites a significant disparity exists with what the NES considers acceptable for fill to that specified in the Landfill Guidelines. This ambiguity has imposed large and unnecessary costs those wishing to dispose of contaminated materials and hazardous waste as they are being directed to landfills where as the NES allows for the same material to potentially be used on local cleanfill sites.

Proposed National environmental standard: for assessing and managing contaminants in the soil

New Zealand has less prescriptive legislation around managing contaminated in comparison to other countries. In 2005 the RMA was amended to account for contaminated land and control was assigned to local authorities allowing specific land legislations to be regulated throughout New Zealand under the RMA 1991. The soil guideline values (SGVs) are now part of a National Environmental Standard (NES) framework<ref>Ministry for the Environment (2010) 'Proposed National Environmental Standard for Contaminated Soils Discussion Document', Ministry for the Environment, Wellington (Downloaded 13th August, 2011)</ref>.

Land identified as having contamination must be assessed to see if a risk is posed and apply any conditions appropriate to make the land safe for its designated risk. The NES, in collaboration with regional and city/district councils, as proposed by this standard will prioritise contaminated land to be assessed and appraised in full especially when the land changes in its designated land use for example changing from rural to urban.

The NES outlines controls appropriate to district and city council plans for contaminants in soil and defining specific chemical contaminant thresholds for soils designed for the protection for human health. These contaminant levels range considerably depending on land-uses, for example industrial land has a different permitted maximum values to land intended for residential use. These proposed ranges are designed to address significant gaps in how soil contamination is managed.

One of the issues with this proposal is that past use of hazardous substances in industry, agriculture and horticulture has left soils contaminated throughout New Zealand contaminated before legislation for correct management of such chemicals was set in place. The objective of the proposed standard is to ensure that land affected by contaminants in soil are appropriately identified and assessed and if necessary the land remediated, or the contaminant contained, so that the land becomes safe for human use. In order to meet this objective, an option has been proposed as a National Environmental Standard to assess health effects from exposure to contaminants in soil.

The proposed NES has only identified a relatively small number of contaminatss that are considered to be a high priority and need addressing. For example the proposed NES has only 7 metals and 5 organic compounds listed, however, there remains a great many more indicators which are not mentioned that are harmful to health of humans and other species. In our opinion it is also considered that the human health impact is to narrow as there are many other species (both plant and animals) in the environment that can be effected at different levels than what humans can tollerate.

Soil Guideline Values (SGVs)

If this standard is implemented the soil guideline values in the tables below (6-8) and the method for deriving the site specific soil guideline values will be become a National Environment Standard. SGV are threshold concentrations for 12 contaminants in the soil that are calculated for five generic land-use exposure scenarios at which the exposure is judged to be acceptable because adverse effects on human health for most people are likely to be no more than minor.

SGV’s perform two functions these are Health Based trigger values representing human health threshold and remediation targets representing maximum concentrations of contaminants at or beneath which land is considered safe for human use. SGV’s do not necessarily protect the natural environment such as soil, invertebrates and plants. The relationship between human health risk thresholds (SGV(health)) and effect thresholds as defined under the RMA are shown in Figure 6 below.

Compaison of Contaminats

In the proposed NES the overall numbers are significantly higher relative to the Landfill Acceptance criteria. The measures are in milligrams per kilogram. The proposed NES does not address solubility (leachability)of the material. In our opinion the solubility is the most important measure of whether contamination will have an effect on the environment. For example if Chromium 6 was deposited onto industrial land and the land was adjacent to a stream where people took in water it is quite possible that the chromium may well leach and mobilise into the stream potentially altering the water quality beyond what is considered safe for drinking (New Zealand Drinking Water Standards, 2005) the Cr limit in the Drinking water standard is 0.004 mg/l where as the Proposed NES for industrial fill 5200 mg/kg when compared to the landfill acceptance criteria of 10 mg/kg or 0.5 mg/l examplifies the issue and raises significant concerns about the validility of the limits.

Inorganic Contaminants

Table of waste accepatance values for the proposed NES vs the landfill Acceptance Criteria Values vs the Maximum Acceptable Values for the protection of Human Health listed in the NZ Drinking Water Standard 2005

(Organic contaminants couldn’t be compared as they are not listed in the Landfill Acceptance Criteria Guideline)

The Dunedin Gasworks history and remediation

Dunedin Gasworks circa late 1800's


The Dunedin Gasworks site was selected as an example of a large scale remediation of a contaminated site. In examining such a site an assessment needs to be made which assesses the processes that occurred on the site and the degree of contamination. Contamination at gas work sites differ depending on the process and the residue variations in conjunction with the waste management practices that occurred both on and off site. The recovery of by-products influences the type of contaminants and waste products that may be found at gas works sites. Typical Contaminates found at gas works sites include:

• Organics contaminants, such as coal, oil tar, tar/water/oil emulsions and hydrocarbons sludges

• Inorganic material, such as, coke, ash, lime wastes and ammonium sulphate

• Coal particles underground at coal storage areas

• Leaks from coal-gas

• From other raw material used which may have occasionally have contributed to land contamination

• From common industry operations, such as spillages of fuel oils or paints or dumping land acid batteries.

Gasworks Industry General Overview

“Coal fuelled the nineteenth century, steam powered it, but gas illuminated it” <ref>Pollard, J.S. (1987) 'Requiem for a Gasworks',: University of Canterbury Publishing, Christchurch.</ref>. Gasworks began life in the early 1790’s in Great Britain. Invented by William Murdoch a Scottish Engineer and inventor, he was the first person to substitute oil with coal gas based lighting. Gas supply was the first source of energy to light street lamps. Before electricity, the flammable gas created from gas works illuminated New Zealand’s cities and towns. To do this, companies had to adapt the existing kerosene lamps to gas. Lamps were converted by running a soft leaden gas pipe up the light standard to feed the burner placed within the lantern. By the 1860s many towns and cities had some form of gas street lighting, installed at strategic areas, such as large intersections, and bridge entrances. By 1876 Christchurch lead New Zealand’s production with, "boasting 152 gas lamps". Although far superior to previous lighting, their illumination and extent was still limited. Early systems required lamp lighters, although pilot lights were soon introduced, which lit the lamp when the gas was turned on centrally. Their use was not continuous with the Wellington City Council adopting a policy of only using the gas lights on moonless nights only and then no later than twelve o’ clock.
Manual lighting of a gas lantern. The making of the gas industry

From 1805 gasworks produced lighting for industrial factories, and residential housing from 1845. From there Gasworks sites in New Zealand became a prominent source of heating, lighting, and cooking. Gas made from coal, oil and coke was distributed throughout New Zealand up until the late 1980’s. During this time 54 sites existed throughout the country. As electrical power became main stream, the need for clean efficient energy grew at an exponential rate. Gasworks in New Zealand was eventually made redundant leaving behind factories and contaminated land. The last operation to close was the Hastings plant in 1988 with the Dunedin plant closing in 1986. Large plants existed throughout New Zealand including Taranaki, Auckland, Christchurch and Dunedin with the remains of these gasworks often seen throughout the country in the form of old factories. "For more than a century the coal gas makers knew their sacred mission in life was to bring the blessings of their light into the daily lives of all. Some, to the detriment of their industry, never really realised that their own peculiar technology of making gas from coal could come to an end, but end it did, and thereafter gas ceased to have exclusive connotations” <ref>Pollard, J.S. (1987) 'Requiem for a Gasworks', University of Canterbury Publishing, Christchurch.</ref>.

The gas production process produced volatile by products which are harmful to the environment and human health. Underground structures containing hazardous by-products exist along with land contaminated with a variety of different products produced from the burning of coal and the gas production. To assist owners of such facilites the Ministry for the Environment, produced guidelines for Assessing and Managing Contaminated Gasworks Sites in New Zealand (1997) This document assists in systematically addressing the legacy of the contamination and provides guidance for the remediation processes.<ref> Ministry for the Environment (1997) 'Guidelines for Assessing and Managing Contaminated Gasworks Sites in New Zealand', Ministry for the Environment, Wellington (Downloaded 25th August 2011)</ref>

Dunedin Gasworks History

Dunedin Gasworks circa 1980

The Dunedin Gas light and Coke Company was formed in 1862 with the intention to erect a small plant to supply some 50 street lights. However the original scope of the project required to be expanded as Dunedin was undergoing a massive period of growth due to the discovery of gold in Central Otago. Instead of 50 street lights the company provided gas to 150 lanterns. Gas was generally used solely for this purpose as domestic consumers considered expensive and generally retained candles and oil lamps. The plant was taken over by the City in 1876. In 1881 a private gas company was formed competing directly with the Council gas company ironically winning a key Council contract to supply the boroughs of Caversham, Mornington and Roslyn.

In 1906 a major upgrade programme took place at the City Works. A new retort House was construted and a large 1,000,000 ft gas holder was constructed. This holder was later dismantled due to unstable ground and moved in to Wilki Street in 1927 where operated until the site was eventually closed. The holder was demolished in 2000.

Further improvements were made to the works in 1927 when a Glover West Vertical Retort House was built and new exhausting and pumping machinery was installed. The surviving Bryan Donkin Booster was installed at this time.

In 1962 a Woodall Duckham Vertical Retort House was build to replace the Glover West plant and the old horizontal retorts were removed. These vertical plants were more efficient at producing gas from a given weight of coal however they were more demanding of coal quality. Coal supplied from the West coast was typically used. By the mid 1980s the coal plant was reaching the end of its useful life and the cost of a refit could not be justified as gas use in the city was declining. The City Council resolved to convert to LPG and in the Woodall Duckham Vertical Retort House was finally closed down in June 1987. Dunedin was the first and last place in New Zealand where coal gas was manufactured. Due to its structural integrity, the Vertical Retort House was demolished in 1989, and with its destruction saw the demise of the last remaining coal carbonisation plant in New Zealand.

As part of the extracting gas from coal coke was produced. Coke was used in part to heat the retorts, some was sold domestically as a solid fuel and some was used to produce water gas.

Gas was also made from oil. Gas to oil plants were popular in the 1960s . They were a substantially cleaner plant to operate and had no disposal issues like the use of coal. They also had the capacity to supply the entire city. Dunedin had a number of these plants however the oil shocks of 1973 meant these plants became uneconomic to operate and coal was used throughout this period.

Site layouts

Figure 1: Layout for a gasworks

Many gasworks sites were located near ports, rivers and railways, as this was how the coal feedstock was delivered. They were also generally laid out in a similar way. Figure 1 shows the common layout for a gasworks. <ref>Ministry for the Environment (1997) 'Guidelines for Assessing and Managing Contaminated Gasworks Sites in New Zealand', Ministry for the Environment, Wellington, pg 8 (Downloaded 25th August 2011).</ref>

Contaminants of primary concern

Contaminants found at gas works sites that are of primary concern:

• Polycyclic aromatic hydrocarbons (PAHs) in tar dominates surface soil Benzene toluene, ethylbenzene, xylene (BTEX) contaminates ground water and soil. Tar still exists at the Countdown site (approximately 1,000,000 litres quantities stored underground in a double line brick tank from the old gasworks operation)

• Phenolics contaminates groundwater

• Inorganics, such as cyanide, sulphate and ammonia contaminate groundwater

• Heavy metals found in soils

These contaminates are all a risk to human health and are highly toxic even in minute quantities. Health and safety precautions on site are:

Personal Protective Equipment

Under the Health and Safety Act 1992 there is a requirement of employers to take all practicle steps to ensure the safety of employees.
Typical array of personal protective equipment

After the principal has highlighted the hazards to the contractor a risk assessment is prepared so that all parties understand what mitigating measures will be carried out to either, eliminate, isolate or minimise the hazards to all employees and visitors that enter the site. The overall management of such requires a designated clean and dirty areas. Showers and access to handwashing facilites is critical to a decontamination process after working with this material. The personal protective equipment staff are required to wear when disturbing the contaminated material include:

  • Charcoal filter respiratory protection.
  • Disposal vapour proof overalls
  • Gumboots, chemical resistant gloves and hard hats.
  • Extensive staff training.
  • Personal meters that are sensitive to Poly Aromatic Hydrocarbons discharges.

Discharge Management

The solvent glued sewerage pipes and the concrete dam preventing the trench acting like a drainage channel for contaminats leaching off site
The green substance in this image is a deposit of Cyanide and ash from the coal gas process

When disturbing such sites there are a number of specific consent requirements to ensure that the discharges are managed and controlled as best as practicably possible so that the environmental discharges are limited. These discharges are normally stated in a site risk assessment and operations plan developed by the Contractor and site owner. Some of the key steps for this site include:

  • Capturing all stormwater
  • Controlling all odour discharges where possible. The use of odour control machines, spreading lime and covering excavations is most important in achieving this objective
  • Specific glued joints on pipes. The acid tars attack and degrade more commonly used rubber ring jointed pipes
  • Prevention of drainage trenches becoming conduits for the offsite migration of contamination by constructing concrete dams in the trench
  • Protection of steel foundations by encasing the foundations in concrete
  • Designated Clean and Dirty areas for excavated materials
  • Covering of all contaminated excavated soils

Patterns of contamination at gasworks sites

Historical records and fortunately in Dunedin’s case interviewing old workers to explain how the site layout helps to identify the nature and location of contamination. Site inspections provide further information on the location of contamination. For example, features of significance may include chemical or other unusual odours, discoloured or poor quality surface waters.
The excavated contaminated material. This material will be treated to the acceptable limits for a Class B landfill and then disposed.

Contaminants can be found around gas works sites as follows:

  • Chemicals migrating through high permeability soil, contaminates soil and groundwater
  • Tars solidified into rocky masses at the soil surface
  • Tar ponds and tar pits unlined and being filled with soil, rubble or ash, so there is contaminants beneath the pond
  • Spills and leaks at tar handling areas, contaminates soil
  • Waste materials from the site being used as fill
  • Purifier wastes often disposed off site and used for roading base and fill along river banks
  • Sulphates, cyanides and ammonia are found in groundwater at gas works sites, reflecting their mobility in the soil environment.

Free tars may accumulate in stratigraphic traps in the ground resulting in lateral migration, causing contamination over considerable areas.

Like all contaminated sites the treatment and/or containment of these wastes relative to requirements specified by the consent conditions defines their ultimate destination. Consent conditions, typically the material must go to an approved landfill and must meet the landfill acceptance criteria. The onus is on the owner of the owner of the contaminated material to prove its acceptability for the landfill operator. In the case of the Dunedin Gasworks the treatment has included the following:

  • Insitu containment through the specific specialist foundation engineering design
  • Removal to stockpile for blending with uncontaminated materials
  • Lime is added to help to dry the material and to suppress odours.
  • Statistically robust sampling of the mixed stockpile

Testing is then undertaken using the Toxic Characteristic Procedure test (TCLP Test), a test that measures leachability of the substance. The TCLP test is undertaken initially on the material without treatment to see how it leaches relative to the acceptance criteria of the landfill. If the results fail to meet the landfill acceptance criteria (LINK) for the class of landfill, cement is then added at various percentages to determine, through trial and error, how much cement is required to be added to the contaminant. Typically five different percentages of cement are trialed being 5%, 10%, 15%, 20% and 30% by weight. Using the same TCLP test the results of each percentage are compared with the acceptance criteria. The percentage that meets the criteria is then used as the treatment design.

The conversion of the Dunedin Hillside Road Gasworks site to a new Countdown Supermarket.


Contaminants are a problem when the hazardous substances are at a concentration and a place where they have, or are reasonably likely to have, an adverse effect on human health and the environment. Contaminants are a greater problem in environments where food is grown or in close proximity to buildings, people, water bodies and important habitats. Contamination is not always limited to a specific site. Hazardous substances may seep through the soil into groundwater, or be carried to nearby land and waterways in rainwater and attached to dust. Hazardous gases can also pollute our air. Our focus has been on the technical documents around treatment and disposal of contaminated sites with a particular emphasis on the limits for disposal.

For landfills the New Zealand Hazardous Waste Guideline: Module 2 Landfill Waste Acceptance Criteria and Landfill Classification defines the landfill type (either a Class A or B) and the acceptable levels of contamination for each of the respective classes. These levels have until recently been the chief guidance document for landfills when accepting contaminated wastes to landfill. The two issues with this document are as follows:

  1. There are only two classes of landfill based that the Guideline proposes. If any one of the Landfill criteria is breached then the landfill is a class B site. A Class B site can range from being a unlined landfill located next to a waterway with limited monitoring to a fully lined site but perhaps not ideally located or designed. This is a real failing of this guideline and a strong argument for a B+ or A- criteria.
  2. The limits defined in the criteria are conservative. The concentration levels (mg/kg) are low relative to drinking water standards. Landfills, essentially are known contaminated sites and in terms of the concentrations of contaminants permitted in our opinion should significantly greater that what is listed in the standard. The key test is the leachability (TCLP) test. The numbers in the standard numbers have been defined relative to the numbers listed in the New Zealand Drinking water Standard. It is considered that these numbers should be the standard test for waste acceptance to landfill. It is our opinion that the indicator levels should be agreed with the Regional Authority based on the protection systems of the landfill. Green Island for example has a retro-engineered leachate collection system, a comprehensive and detailed management and operations plan and monitoring programme that despite being unlined and cited next to an estuary provides a excellent level of assurance that the leachate is not leaking into the environment.

The Government is also considering introducing a NES for contaminated soils. The purpose of this document is to provide owners and receivers of contaminated material a range of indicators levels acceptable for disposal, depending on the class of land, the material is destined. In theory, this is an excellent approach, as currently there are no national definition levels for what is cleanfill and therefore considered acceptable for cleanfill landfills. The problem with this approach is that levels prescribed in the proposed NES relative to the Landfill Guidelines are significantly higher and in many of the cases several times higher. We consider that major failing of the standard is that it does not address how leachable the indicators are. This failing is a significant issue as the concentration levels (mg/kg) are many hundreds of times greater than drinking water standards measured in mg/l (For example, Chromium VI listed in the proposed NES for disposal to an industrial site is 104,000 times greater than the NZ Drinking Water MGV (Maximum Guideline Value)). The issue is that cleanfill sites have no contaminant measures. What is also possible is that land use over time may change and what is potentially “acceptable” for an industrial site may not be acceptable for residential fill. In our opinion the values of this proposed standard need review. In looking at a current contaminated site remediation, using our example of the Dunedin Gasworks, the management of the contaminated fill directly has used the standards and guidelines detailed above. The treatment options for this site have been:

a) On-site containment – all areas on the site are sealed and the material confined and contained on site. This is considered to be acceptable, cost effective and suitable remediation methodology for this site. This approach minimizes the treatment and disposal costs which are significant (DCC landfill fees are $219/ tonne inc GST)

b) All excavated material that has clear contamination is stockpiled contaminated fill, blending with as a treatment option statistically robustly sampled. The sample is tested using the TCLP test to ensure that the material meets the landfill acceptance criteria for a Class B landfill. If the material fails the TCLP test it is then treated using a defined percentage cements and limes to ensure that it meets the acceptance criteria, then landfilled. The disposal site within the landfill is normally in a central place within the landfill site so that if leaching does occur the attenuation process of leachable material is significant i.e the leachate has time (years) to mix with other leachates before discharging into the leachate collection system.

The practical treatment of contaminated sites is a costly time consuming process. Land that has been contaminated is often left abandoned and in a derelict state because the owner of the land has the responsibility to remediate the site. The owner frequently cannot afford, in the vast majority of cases the prohibitively expensive remediation cost. For owners, there are Government funds available to assist where remediation is required for environmental reasons, but again, access to it is expensive and time consuming.

In general contaminated sites in New Zealand are being managed (monitored). Many of the current guidelines have a number of inconsistencies and there are significantly different approaches to this issue amongst local and regional authorities. In our opinion there needs to be a national collaborative and consistent approach towards contaminated land management. A review of the waste acceptance criteria particulaly around landfill classes, and waste acceptance is required. The proposed NES need further review, particularly around leachability testing. There needs to be a national definition of "cleanfill".


Russell Lund. Managing Director, Lund South Ltd. For the informative tour of the Countdown Construction site.

Gasworks Museum staff

DELTA Utility Services Ltd. For the use of the photographs