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Green Island Landfil - G1 Introduction

G1.1 Waste management services in Dunedin

G1.1.1 Regional overview

Dunedin City had a usually resident population of about 120,000 at the time of the March 2006 census.1 The city’s economy has been very buoyant for the past three years, with employment levels at a record high. The local economy is unusually diversified, with health, engineering, transport, tourism, retailing, education and communication all contributing substantially.2

The major waste operators in the Dunedin region are Dunedin City Council, Transpacific Industries Group (NZ) Limited and EnviroWaste Services Limited. In 2006 Transpacific Industries merged with Waste Management NZ Ltd and sought Commerce Commission permission to purchase the South Island assets of EnviroWaste Services Limited. In May 2007 the Commerce Commission declined clearance for Transpacific Industries to purchase Envirowaste’s Dunedin landfill in Fairfield.

In November 2007 the Commission allowed the sale of the EnviroWaste Dunedin assets, providing that Transpacific divested the front-end load bin and private wheelie bin waste collection businesses in Dunedin. EnviroWaste and Waste Management NZ are now the main waste collectors in the residential, commercial and industrial sectors. However, there are several small waste operators in the skip bin market servicing commercial, industrial and residential customers.

Dunedin City Council provides several waste disposal facilities in the region surrounding Dunedin City. These include:

  • Green Island Resource Recovery Centre – 12 km south of Dunedin city centre (this facility includes a public-access transfer pit, a reusable goods shop and the landfill)

  • Middlemarch Transfer Station – 80 km northwest, transported to Green Island

  • Sawyers Bay Landfill – 12 km north

  • Waikouaiti Landfill – 40 km north.

The Green Island facility is used primarily for small loads transported by residents and businesses, council waste streams (such as the domestic kerbside bagged refuse collection), small-scale waste operators, and for cleanfill disposal. A small number of loads from Transpacific Industries Group are disposed of at the facility after-hours and on weekends.

Transpacific Industries Group operates a landfill at Fairfield, 12 km south of Dunedin city centre, and a refuse transfer station at Wickliffe, in the city centre. Waste from the refuse transfer station is transported to the Fairfield landfill. A high proportion of refuse collected by both Envirowaste Services and Waste Management is disposed of at the Fairfield landfill.

Clutha District Council provides refuse transfer stations at:

  • Taieri Mouth – 35 km south of Dunedin city centre

  • Milton – 55 km south.

Waste from the refuse transfer stations is transported to Mt Cooee Landfill, near Balclutha, 80 km south of Dunedin.

G1.1.2 Waste services for the residential sector

Through contracted service providers, Dunedin City Council offers weekly kerbside collections of both bagged refuse and recyclables to residents. The domestic refuse collection is based on a user-pays bag system, with the cost of collection and disposal covered by the sale of the official refuse bags. The maximum set-out weight of a bag is 20 kg, and residents are permitted to set out any number of bags.

The weekly council kerbside recycling collection is based on 45-litre plastic crates, which are provided to every household. Households of five or more occupants may request a 70-litre crate. The following materials are accepted by the collection:

  • aluminium cans

  • cardboard and plastic milk cartons

  • glass bottles and jars

  • steel food cans

  • plastic bottles #1 and #2 only.

A weekly kerbside collection of paper and cardboard, either bundled or bagged, is provided by the council.

Commercial waste operators also offer user-pays weekly kerbside refuse collections to urban residents, based on wheelie bins. There is no data on the uptake of the services, but anecdotal evidence indicates that the private services have captured a significant proportion of the market. Commercial operators also offer gantry skip bin services3 to householders for occasional disposal of large quantities of waste. Different sizes of bins are available, with specific bins being provided for dense materials such as hard fill and soil.

There are a number of garden operators that remove green waste from residential properties and transport it for disposal.

Householders in Dunedin City have ready access to two refuse transfer stations: the Green Island Resource Recovery Centre to the south of the city, and the Transpacific Industries Transfer Station in the central city. There is no data available on the geographic distribution of the users of these facilities.

G1.1.3 Waste services for the commercial sector

In the commercial area of Dunedin City the council provides a daily collection of refuse. For this refuse collection businesses use the official council refuse bag. A twice-weekly collection of cardboard is provided by a private operator. Cardboard is collected from the kerbside on Monday and Thursday nights.

Commercial waste operators provide services for most other commercial organisations in the region. Depending on the volume of waste generated, wheelie bins, gantry bins and front-loader bins are available. Some businesses transport their own waste to one of the disposal facilities using their own transport equipment.

A number of general transport operators provide waste disposal services to the construction, demolition and infrastructure sectors.

There is no data available on the volumes or sources of waste being disposed of at the Transpacific landfill at Fairfield or its central city transfer station. It is, however, apparent that a substantial proportion of industrial, commercial and institutional waste is disposed of at those facilities because Envirowaste and Waste Management dominate the collection market, and they dispose of very little waste at the council-owned Green Island facility.

G1.1.4 Special waste

Special waste generated in the region include 11,000 tonnes annually of wastewater treatment sludges and milliscreenings4 from council treatment plants, and 9000 tonnes annually of industrial sludges.5 Of these sludges, approximately 4000 tonnes are incinerated at Tahuna Wastewater Treatment Plant, and the remainder are landfilled at Green Island Landfill.

G1.1.5 Green Island Resource Recovery Centre

The council-owned Green Island Resource Recovery Centre (Green Island) is situated 12 km south of Dunedin city centre, close to State Highway 1 South. Green Island is operated under contract by Delta Utility Services Ltd, a 100 per cent-owned subsidiary within the Dunedin City Council group of companies. The posted disposal charges for the facility in August 2007 are shown in Table G1.1.

Table G1.1: Disposal charges, August 2007

 

General waste

Recyclable and vegetation
(50% of load)

Small vehicle charges    
Refuse bag $2.00 per bag Not applicable
Cars $12.00 $6.00
Station wagons $20.00 $10.00
Cars and trailers (single axle), vans and utes $30.00 $15.00
Cover Free  
Cleanfill $10.00 Not applicable
Demolition (excluding wood and steel) $15.00 Not applicable
Vehicle bodies $45.00 Not applicable
Oil under 10 litres Free Not applicable
Oil over 10 litres $1.00 per litre Not applicable
Car tyres – each $2.50 Not applicable
Whiteware and scrap metal   Depending on volume
Large vehicle charges (include double/tandem trailers) Charges
General solid waste $81.00 per tonne (minimum $40)
General solid waste if 50 % of load is recycle and/or vegetation $50.00 per tonne (minimum $25)
Cover Free
Special/hazardous waste, sludges and liquids
(solid contents at least 20%)
$115.00 per tonne (minimum $50)
Special/hazardous waste, sludges and liquids
(solid contents less than 20%)
$140.00 per tonne (minimum $50)
Cleanfill (dry) $5.00 per tonne (minimum $12)
Cleanfill (wet or slip) $12.00 per tonne (minimum $12)
Demolition (excluding wood and steel) $12.00 per tonne (minimum $12)
Foundry sands $12.00 per tonne (minimum $12)
Contaminated soil (low-level) $12.00 per tonne (minimum $12)
Tyres $250.00 per tonne

Disposal charges were altered before the March 2008 audit, the only change being the elimination of free disposal for cover material.

The following descriptions of the different materials have been taken from the council website.

  • Special/ hazardous waste, sludges and liquids – special waste is any waste which, by its “physical or chemical properties, requires special handling”. Special/hazardous waste, sludges and liquids are acceptable only at the Green Island facility provided they are suitable for landfill disposal.

  • Demolitionmaterial – concrete, bricks, roading material, concrete pipes and earthenware pipes. The maximum acceptable size for demolition material is 1 metre in any direction. Material is to be clean (no asbestos, no rubbish, no individual steel pieces included) and contain less than 10 per cent organic material (eg, vegetation, wood). Reinforcing steel protruding from the concrete pieces must be less than 500 mm in length.

  • Cover – clay, sand and soil that is free of contaminants and other deleterious matter.

  • Cleanfill – a natural material such as clay, soil and rock, and other materials such as concrete, brick or demolition products that are free of combustible or organic materials and are therefore not subject to biological or chemical breakdown.

The Green Island Resource Recovery Centre incorporates several disposal points and undertakes a range of resource recovery activities, which are outlined in the following sections.

G1.1.5.1 Weighbridge

All vehicles entering the facility must pass through the weighbridge. All commercial vehicles are weighed. Small domestic vehicle loads are not weighed, but are charged a flat fee, as shown in Table G1.1. Large vehicles are weighed when entering and leaving the facility.

G1.1.5.2 Resource recovery area

The resource recovery area (RRA) is immediately adjacent to the weighbridge. Small quantities of residual refuse, recyclables and reusable goods are disposed of in the RRA by the general public. The RRA includes a reuse shop and separate drop-off points for the following materials:

  • residual waste (into transfer pit)

  • glass bottles

  • plastic bottles

  • cardboard

  • newspapers

  • branches

  • other green waste

  • bricks, concrete, gravels

  • scrap metals

  • computer equipment

  • plastic farm chemical containers

  • oil

  • batteries

  • toxic chemicals

  • gas bottles

  • reusable goods.

The disposal pathways for the different materials accepted at the RRA are shown in Table G1.2.

Table G1.2: Disposal pathways for materials from the public-access resource recovery area

Material Disposal pathway
Residual waste Transported from transfer pit to disposal face by transfer trailer
Glass bottles Removed from site by contractor
Plastic bottles Removed from site by contractor
Cardboard Removed from site by contractor
Newspapers Removed from site by contractor
Branches Shredded, windrow composted, removed from site
Other green waste Transported to disposal face, disposed of as waste
Bricks, concrete, gravels Transported to disposal face, used as cover material
Scrap metals Removed from site by contractor
Computer equipment Removed from site by contractor
Plastic farm chemical containers Removed from site by contractor
Oil Removed from site by contractor
Batteries Removed from site by contractor
Toxic chemicals Removed from site by contractor
Gas bottles Removed from site by contractor
Reusable goods Some sold to public, remainder go to disposal face

The separate drop-off points for branches and other green waste were established primarily to facilitate the separation of lawn clippings. Lawn clippings can be a compost contaminant if chlopyralid, which is used for broadleaf weed control in lawns, is present, so the other green waste is disposed of as residual waste. However, substantial amounts of green waste other than lawn clippings are also disposed of at the other green waste drop-off point.

Some reusable goods are recovered from the transfer pit for sale at the reuse shop, but most are dropped off directly by the public. Some metals, particularly whiteware, are also recovered from the transfer pit.

G1.1.5.3 Sludge sump, mixing pit and asbestos pit

Sumps and pits are maintained at the facility for the disposal of special waste that requires separate handling, such as sludges and hazardous materials. The sumps and pits are separate to the main disposal face, and are repositioned as required.

G1.1.5.4 Windrow composting

Green waste that is collected at the resource recovery area is intermittently shredded, stockpiled and transported to a separate area of the facility for windrow composting6.

G1.1.5.5 Stockpiling of cover material

Due to emissions of landfill gas from closed cells at the facility, cover material and cleanfill were being stockpiled during the second half of 2007. This material would, in the future, be used for further capping of the leaking cells. To facilitate the stockpiling, disposal charges for cover material were temporarily removed and charges for other suitable materials were reduced. Disposal charges for cover material were introduced in early 2008.

G1.1.5.6 Disposal face

All residual waste materials are disposed of at the disposal face. Due to driver error and other reasons, however, a significant amount of cover material and cleanfill are also disposed of at the disposal face.

G1.2 Data analysis and reporting

Data analysis and reporting are based on the classification and structure of waste flows shown in Figure G1.1. The diagram illustrates the four activity sources (ie, construction and demolition, industrial/commercial/institutional, landscaping and earthworks, and residential) that comprise both the waste being discharged at the transfer pit and the general waste being discharged at the disposal face. The combination of the transfer pit waste, waste from other transfer stations, the general waste to disposal face, the kerbside collections, cover material, and special waste together make up the overall waste to landfill.

Figure G1.1: Waste flows at Green Island Landfill

The diagram illustrates the four activity sources (i.e. C&D, ICI, landscaping and earthworks, and residential) that comprise both the waste being discharged at the transfer pit and the general waste being discharged at the disposal face. The combination of the transfer pit waste, waste from other transfer stations, the general waste to disposal face, the kerbside collections, cover material, and special wastes together make up the overall waste to landfill.

From the data collected directly by the visual survey it was possible to generate information on:

  • the proportion, by number of vehicle loads and by weight, and composition of waste from each activity source for both the transfer station and the disposal face

  • the proportion, by number of vehicle loads and by weight, and composition of waste being carried by each vehicle type for both the transfer pit and the disposal face

  • the tonnage and composition of the general waste stream entering both the transfer pit and the disposal face during the survey period

  • the tonnage and composition of the overall waste stream entering the facility during the survey period.

The data analysis process started with obtaining the complete weighbridge records from the facility for the period of the audit. Initially the weighbridge data was used to obtain the net load weights of the vehicles that were surveyed at the disposal face. These were then used to calculate the weight of the different materials included in each load. After removal of special waste loads, kerbside collections and loads classified as cover material by the weighbridge, this data was amalgamated to provide the composition of the general waste stream disposed of at the disposal face.

The data from the visual survey at the transfer pit, which included estimated load weights, was used to directly determine the composition of waste disposed of at the transfer pit. Based on the classifications of waste loads used by the weighbridge, the weighbridge data for the audit period was then analysed to determine the quantities of specific identifiable waste streams, such as council kerbside collections, cleanfill, cover materials and special waste. The composition of the overall waste stream was calculated by amalgamating the compositions of the separate component waste streams in proportion to their presence in the overall waste stream.

Statistical analysis was undertaken to determine the margins of error for general waste disposed of at the transfer pit and general waste disposed of at the disposal face. By contrast, it was not possible to determine confidence intervals for the overall waste stream, because its composition is based on the weighbridge records.

3 Gantry bins are commonly used for the removal of waste from construction sites, industrial sites or residential properties. Gantry bins are left at the site until removed by a purpose-built vehicle. The most common gantry bins have a capacity of 9 cubic metres, but smaller and larger bins are available.

4 Milliscreenings: fine solid particles, generally inorganic, that are screened from wastewater as part of the initial treatment at a wastewater treatment plant.

5 Dunedin City Council, Resource Recovery and Waste Management Strategy – 2006/07 [2015/16], 2006.

6 Windrow composting: a type of aerobic composting involving piling organic matter or biodegradable waste into long rows (windrows). The windrow can be managed by a windrow turner that turns the compost to improve the oxygen content, mix in or remove moisture, and redistribute material within the pile.