View all publications

S2 Results: 18–24 August 2007

S2.1 Transfer station

The transfer station was surveyed on Saturday 18 August, Sunday 19 August and Friday 24 August. During this period, data on 738 vehicles was collected. The data collected on these days has been used as representative of the entire survey week. The truck that transports waste from the transfer station to the tip face is equipped with on-board load cells, and the weight of each load is recorded manually by the driver. The total weight for the survey week was 421 tonnes.

Green waste disposed of at the separate drop-off point is stockpiled then disposed of at the tip face, and so vehicles disposing of green waste at the drop-off point were included in the survey. The vehicles transferring the green waste are not weighed, but a vehicle count is kept. A nominal weight is then used to determine the weight of green waste transferred and disposed of at the tip face. During the period June to September, a total of 448 tonnes of green waste was transferred, an average of about 26 tonnes per week. The green waste was stockpiled at the transfer station through the winter and all of the accumulated material was transferred in September.

This gives an estimated total of 447 tonnes of waste disposed of at the transfer station during the survey week. During this period, 29 tonnes of road sweepings were recorded as being disposed of at the transfer station. These are classed as a special waste. A figure of 418 tonnes will be used as the basis for all further calculations relating to transfer station general waste tonnages. The calculations for this weekly tonnage of general waste are summarised in Table S2.1.

Table S2.1: Calculation of transfer station general waste to tip face, 18–24 August 2007

Transfer truck transporting waste from transfer station to tip face – weight taken from on-board load cells 421 tonnes
Add green waste transported to tip face – based on average for four-month period estimated from number of vehicle movements 26 tonnes
Total waste from transfer station to tip face 447 tonnes
Less road sweepings classified as special waste – from weighbridge records for survey week 29 tonnes
Total transfer station general waste to tip face 418 tonnes

S2.1.1 Primary composition of transfer station general waste

The primary composition of general waste disposed of at the transfer station is presented in Table S2.2 and Figure S2.1. This analysis excludes road sweepings, which are classified as a special waste. The secondary composition, which includes all 22 categories, is given in Appendix S3.

Table S2.2: Primary composition of transfer station general waste, 18–24 August 2007

Primary category % of total
(± 95% confidence level)
Tonnes/week
Paper 4.9% (±0.7%) 21
Plastics 6.0% (±0.8%) 25
Putrescibles 34.2% (±3.7%) 143
Ferrous metals 6.6% (±1.2%) 28
Non-ferrous metals 0.3% (±0.1%) 1
Glass 1.5% (±0.4%) 6
Textiles 5.3% (±1.2%) 22
Nappies and sanitary 0.6% (±0.1%) 2
Rubble 15.6% (±3.9%) 65
Timber 21.2% (±3.1%) 89
Rubber 3.0% (±1.5%) 13
Potentially hazardous 0.7% (±0.4%) 3
Total 100%   418

Figure S2.1: Primary composition of transfer station waste, 18–24 August 2007

Putrescible material, primarily green waste, was the largest single component of waste being disposed of at the transfer station with 34 per cent of the total. This includes green waste disposed of at both the separate green waste drop-off point and at the residual waste tipping pit. Timber was the second largest component, with 21 per cent of the total. The timber included both fabricated timber, such as furniture, and construction and demolition waste. Rubble was the third largest component, at 16 per cent. This included soil, concrete, bricks, rocks and rubble.

S2.1.2 Transfer station waste, by activity source

Each load of waste being disposed of at the transfer station was assessed as to the activity that had resulted in its generation. Table S2.3 shows the percentage of loads originating from each of the activities, the percentage of total weight, and the tonnes per week. This analysis includes road sweepings, which comprise the special waste category.

Table S2.3: Activity source of transfer station waste, 18–24 August 2007

Activity source No. of loads surveyed % of loads % of weight Tonnes/week
Construction and demolition 89 12% 17% 76
Industrial/commercial/institutional 79 11% 10% 45
Kerbside collections 0 0% 0% 0
Landscaping and earthworks 200 27% 30% 132
Residential 359 49% 37% 165
Special 11 1% 7% 29
Transfer station 0 0% 0% 0
Total 738 100% 100% 447

Residential activity was responsible for generating the highest proportion of loads: 49 per cent of the total number of loads, and 37 per cent by weight. Landscaping loads comprised 27 per cent of the total number of loads and 30 per cent of the total weight. Construction and demolition (C&D), with 12 per cent of loads, comprised a proportionately higher share of the total weight, contributing 18 per cent of the total. Special waste (road sweepings) represented 1 per cent of loads but accounted for 7 per cent of the total weight.

S2.1.3 Primary composition of transfer station general waste, by activity source

The primary composition of the four activity sources of waste at the transfer station is shown in Table S2.4. The secondary composition is presented in Appendix S3.

Table S2.4: Primary composition of transfer station general waste, by activity source, 18–24 August 2007

Primary category C&D ICI Landscaping Residential
Paper 1.3% 13.7% 0.3% 7.9%
Plastics 3.0% 13.7% 0.6% 9.6%
Putrescibles 4.0% 10.7% 78.6% 18.9%
Ferrous metals 3.7% 7.6% 0.6% 12.5%
Non-ferrous metals 0.7% 0.5% 0.0% 0.4%
Glass 0.8% 3.5% 0.0% 2.5%
Textiles 3.7% 5.1% 0.2% 10.3%
Nappies and sanitary 0.0% 0.8% 0.0% 1.2%
Rubble 37.3% 2.1% 18.5% 6.9%
Timber 45.1% 16.2% 0.9% 27.8%
Rubber 0.1% 23.6% 0.1% 1.2%
Potentially hazardous 0.2% 2.6% 0.3% 0.7%

C&D waste was primarily composed (82 per cent combined) of timber and rubble. Industrial/ commercial/institutional (ICI) waste was more heterogeneous. Paper and plastic, primarily packaging, each comprised about 14 per cent of the total. Landscaping waste was nearly 80 per cent green waste, with rubble (mainly soil) comprising most of the remainder. The largest component of residential waste was timber (28 per cent), which included both fabricated items and C&D-type timber. Loads classified as residential may include waste from several sources, including C&D.

S2.1.4 Transfer station waste, by vehicle type

For each vehicle load of waste disposed of at the transfer station, the vehicle type was recorded. Table S2.5 shows the percentage of loads transported by each of the vehicle types, the percentage of total weight carried by each vehicle type, and the tonnes per week. Road sweepings are included in the analysis.

Table S2.5: Transfer station waste, by vehicle type, 18–24 August 2007

Vehicle type No. of loads surveyed % of loads % of weight Tonnes/week
Cars 228 31% 10% 45
Compactors 0 0% 0% 0
Front-loader trucks 0 0% 0% 0
Gantry trucks 0 0% 0% 0
Huka trucks 0 0% 0% 0
Other trucks 11 1% 7% 29
Trailers 499 68% 83% 373
Total 738 100% 100% 447

Over two-thirds of the loads disposed of at the transfer station were carried by trailers, and these trailer loads accounted for 83 per cent of the total weight. Although cars accounted for 31 per cent of vehicle loads, due to the small size of car loads they accounted for only 10 per cent of the total weight. A small number of other trucks (road sweeping vehicles, small box trucks) also disposed of waste. None of the four heavy truck types used the transfer station.

S2.1.5 Primary composition of transfer station general waste, by vehicle type

The primary composition of general waste loads carried by the two types of vehicles that disposed of general waste at the transfer station is shown in Table S2.6. The secondary composition is shown in Appendix S3.

Table S2.6: Primary composition of transfer station general waste, by vehicle type, 18–24 August 2007

Primary category Car Trailer
Paper 14.1% 3.8%
Plastics 11.7% 5.2%
Putrescibles 34.9% 33.9%
Ferrous metals 4.3% 6.9%
Non-ferrous metals 0.5% 0.3%
Glass 2.0% 1.5%
Textiles 4.7% 5.4%
Nappies and sanitary 2.3% 0.4%
Rubble 6.5% 16.5%
Timber 17.1% 21.5%
Rubber 0.2% 3.3%
Potentially hazardous 1.7% 1.3%

S2.2 Tip face

The tip face was surveyed from Monday 20 August to Thursday 23 August 2007. Only vehicles disposing of waste directly to the tip face were included. Vehicles disposing of special waste such as asbestos to a separate disposal area were not included, but are included in the overall waste stream in Section S2.3.

The data that was collected in the survey from the 241 vehicles carrying general waste was used to determine the composition of the general waste to the tip face. General waste includes waste from the following activity sources: C&D, ICI, landscaping and earthworks, and residential. General waste does not include waste from kerbside collections, the transfer station, special waste or cover material.

Weighbridge records for the survey week were analysed, and it was determined that 976 tonnes of general waste were disposed of at the tip face. Both cover materials and special waste were also disposed of at the tip face, but these have been excluded from this analysis. Cover material and special waste are included in the analysis of the overall waste stream to landfill in Section S2.3.

S2.2.1 Primary composition of general waste to tip face

The primary composition of general waste disposed of at the tip face is presented in Table S2.7 and Figure S2.2. The secondary composition, which includes all 22 categories, is given in Appendix S4.

Table S2.7: Primary composition of general waste to tip face, 18–24 August 2007

Primary category % of total
(±95% confidence level)
Tonnes/week
Paper 10.2% (±2.0%) 100
Plastics 18.5% (±0.5%) 181
Putrescibles 20.0% (±4.1%) 195
Ferrous metals 6.1% (±4.4%) 59
Non-ferrous metals 1.1% (±3.4%) 11
Glass 6.1% (±1.0%) 60
Textiles 6.0% (±0.7%) 59
Nappies and sanitary 3.2% (±4.5%) 32
Rubble 6.1% (±0.7%) 60
Timber 17.4% (±0.5%) 169
Rubber 2.4% (±1.0%) 23
Potentially hazardous 2.9% (±0.4%) 28
Total 100%   976

Plastics, putrescibles and timber all comprised similar proportions of the general waste disposed of at the tip face – from 17 to 20 per cent.

Figure S2.2: Primary composition of general waste to tip face, 18–24 August 2007

S2.2.2 General waste to tip face, by activity source

Each load of general waste being disposed of at the tip face was assessed as to the activity that had resulted in its generation. Table S2.8 shows the percentage of loads originating from each of the activities, the percentage of total weight, and the tonnes per week.

Table S2.8: Activity source of general waste to tip face, 18–24 August 2007

Activity source No. of loads surveyed % of loads % of weight Tonnes/week
Construction and demolition 42 17% 9% 90
Industrial/commercial/institutional 168 70% 87% 847
Kerbside collections 0 0% 0% 0
Landscaping and earthworks 14 6% 2% 16
Residential 17 7% 2% 23
Special 0 0% 0% 0
Transfer station 0 0% 0% 0
Total 241 100% 100% 976

ICI activity generated a high proportion of general waste disposed of to the tip face – 70 per cent of all loads and 87 per cent by weight. Kerbside collections, special waste and transfer station waste are not considered to be general waste.

S2.2.3 Primary composition of general waste to tip face, by activity source

The primary composition of the four activity sources of waste disposed of at the tip face is shown in Table S2.9. The secondary composition is shown in Appendix S4.

Table S2.9: Primary composition of general waste to tip face, by activity source,
18–24 August 2007

Primary category C&D ICI Landscaping Residential
Paper 3.6% 11.2% 0.0% 6.1%
Plastics 3.8% 20.6% 0.1% 11.9%
Putrescibles 1.0% 21.2% 77.7% 9.7%
Ferrous metals 7.2% 5.7% 1.1% 17.5%
Non-ferrous metals 0.2% 1.2% 0.0% 0.8%
Glass 1.9% 6.8% 0.0% 3.8%
Textiles 0.7% 6.5% 0.4% 12.0%
Nappies and sanitary 0.1% 3.7% 0.0% 0.8%
Rubble 23.3% 4.1% 14.3% 7.5%
Timber 57.1% 13.0% 6.4% 28.4%
Rubber 0.4% 2.7% 0.0% 0.7%
Potentially hazardous 0.7% 3.2% 0.0% 0.8%

C&D waste was primarily (80 per cent) composed of rubble and timber. ICI waste was more heterogeneous, with putrescibles and plastics comprising similar proportions of the total at approximately 21 per cent. A significant proportion of the plastics was waste from the kerbside recycling processor. Landscaping waste was over three-quarters green waste, with rubble (mainly soil) comprising 14 per cent. The largest component of residential waste was timber (28 per cent), which included both fabricated items and C&D-type timber (residential waste can include waste from several sources, including C&D).

S2.2.4 General waste to tip face, by vehicle type

For each vehicle load of waste disposed of at the tip face, the vehicle type was recorded. Table S2.10 shows the percentage of loads transported by each of the vehicle types, the percentage of total weight carried by each vehicle type, and the tonnes per week. Vehicles carrying kerbside collections, special waste and transfer station waste are not included in the analysis.

Table S2.10: General waste to tip face, by vehicle type, 18–24 August 2007

Vehicle type No. of loads surveyed % of loads % of weight Tonnes/week
Cars 0 0% 0% 0
Compactors 8 3% 4% 37
Front-loader trucks 50 21% 52% 506
Gantry trucks 90 37% 17% 170
Huka trucks 20 8% 12% 115
Other trucks 73 30% 15% 147
Trailers 0 0% 0% 0
Total 241 100% 100% 976

The highest proportions of loads were transported by gantry trucks4 and other trucks, carrying 37 per cent and 30 per cent respectively. Front-loader trucks accounted for 21 per cent of vehicle movements, but 52 per cent of the total weight.

S2.2.5 Primary composition of general waste to tip face, by vehicle type

The primary composition of loads carried by the five types of vehicles that disposed of general waste at the tip face is shown in Table S2.11. The secondary composition is presented in Appendix S4.

Table S2.11: Primary composition of general waste to tip face, by vehicle type, 18–24 August 2007

Primary category Compactor Front-loader truck Gantry truck Huka truck Other truck
Paper 14.0% 14.3% 7.8% 4.5% 2.6%
Plastics 15.8% 19.7% 12.3% 28.7% 14.6%
Putrescibles 27.3% 29.2% 8.4% 7.7% 9.7%
Ferrous metals 4.1% 4.9% 8.8% 7.5% 6.3%
Non-ferrous metals 0.9% 0.9% 0.3% 3.8% 0.5%
Glass 5.8% 6.6% 2.2% 15.5% 2.0%
Textiles 5.4% 5.4% 4.9% 1.2% 13.4%
Nappies and sanitary 5.2% 5.2% 0.8% 0.9% 0.5%
Rubble 2.4% 2.9% 13.6% 13.9% 3.3%
Timber 5.4% 8.9% 30.0% 15.8% 36.0%
Rubber 12.8% 1.0% 0.4% 0.2% 8.4%
Potentially hazardous 0.9% 1.0% 10.5% 0.4% 2.8%

S2.3 Overall waste to landfill

The composition of the overall waste stream being disposed of at the Silverstream Landfill tip face was determined by combining information from the weighbridge records with the survey results and information provided by landfill management. The product name field of the weighbridge records has been used to categorise all materials being disposed of at the tip face into one of the following four types: cover material, kerbside collections, general or special. The product name field classifications are given in Appendix S2.

S2.3.1 Source of overall waste to landfill, including cover material

Cover material at Silverstream Landfill includes spoil generated within the facility (which is not weighed and not included in this analysis) and sawdust from a local sawmill. Weighbridge data for the survey week shows that 2360 tonnes of material were disposed of at Silverstream Landfill. The proportions of the different waste types are shown in Table S2.12 and Figure S2.3.

Table S2.12: Waste types to landfill, including cover material, 18–24 August 2007

Waste type % of weight Tonnes/week
Cover material 5% 111
General 41% 976
Kerbside collections 17% 391
Special 20% 464
Transfer station 18% 418
Total 100% 2360

Figure S2.3: Waste types to landfill, including cover material, 18–24 August 2007

General waste disposed of directly at the tip face accounted for 41 per cent of the total amount of the waste. Kerbside collections, special waste and general waste from the transfer station comprised similar proportions of the waste stream – between 17 and 20 per cent.

S2.3.2 Primary composition of overall waste to landfill, including cover material

The primary composition of the overall waste to landfill is calculated by combining the compositions of the five different waste types in the proportions shown in the previous section. The compositions of the five different waste types have been determined as follows:

  • cover material – assumed to all be ‘timber – multi-material/other’ because it was composed entirely of sawdust

  • kerbside collection – assumed to be the composition given in Appendix S1, which is based on the results of the previous audits of domestic kerbside refuse undertaken by Waste Not Consulting

  • general waste – as determined from survey results and shown in Section S2.2.1

  • special:

  • it is assumed that all of the product names listed in Appendix S2 as being special waste and the road sweepings discharged at the transfer station are ‘potentially hazardous’

  • meat-processing waste enters the facility under the general refuse product name, and has been identified by the customer name in the weighbridge records

  • meat-processing waste is classified as ‘putrescibles – multi-material/other’

  • the assumed composition of special waste is shown in Appendix S1

  • transfer station – as determined from surveys results and shown in Section S2.1.1.

  • transfer station – as determined from surveys results and shown in Section S2.1.1.

The primary composition of the overall waste stream disposed of at Silverstream Landfill, including cover, is presented in Table S2.13 and Figure S2.4. The secondary composition is given in Appendix S5.

Table S2.13: Primary composition of overall waste, including cover, 18–24 August 2007

Primary category % of total Tonnes/week
Paper 7.5% 177
Plastics 11.1% 262
Putrescibles 22.4% 528
Ferrous metals 4.1% 97
Non-ferrous metals 0.6% 14
Glass 3.5% 83
Textiles 3.8% 89
Nappies and sanitary 3.1% 72
Rubble 5.6% 132
Timber 15.7% 371
Rubber 1.5% 36
Potentially hazardous 21.1% 498
Total 100% 2360

Figure S2.4: Primary composition of overall waste, including cover, 18–24 August 2007

Putrescible materials were the largest component of the overall waste stream. These materials included both green waste from the transfer station and food waste from ICI activity. Potentially hazardous materials were the second largest component of the overall waste stream. A high proportion of these materials were biosolids and milliscreenings from a wastewater treatment plant, and industrial by-products from chemical and manufacturing industries.

S2.3.3 Source of overall waste to landfill, excluding cover material

Cover material at Silverstream Landfill includes spoil generated within the facility (which is not weighed) and sawdust from a local sawmill. Both types are excluded from this analysis. Weighbridge data for the survey week shows that 2249 tonnes of material were disposed of at Silverstream Landfill. The proportions of the different waste types are shown in Table S2.14 and Figure S2.5.

Table S2.14: Waste types to landfill, excluding cover, 18–24 August 2007

Waste type % of weight Tonnes/week
Cover material 0% 0
General 43% 976
Kerbside collections 17% 391
Special 21% 464
Transfer station 19% 418
Total 100% 2249

Figure S2.5: Waste types to landfill, excluding cover, 18–24 August 2007

General waste disposed of directly at the tip face accounted for 43 per cent of the total amount of the waste. Kerbside collections, special waste and general waste from the transfer station comprised similar proportions of the waste stream – between 17 and 21 per cent.

S2.3.4 Primary composition of overall waste to landfill, excluding cover material

If the calculations described in Section S2.3.2 are undertaken with cover material excluded, the primary composition of the remaining waste types combined is as shown in Table S2.15 and Figure S2.6. The secondary composition is given in Appendix S6.

Table S2.15: Primary composition of overall waste, excluding cover, 18–24 August 2007

Primary category % of total Tonnes/week
Paper 7.9% 177
Plastics 11.7% 262
Putrescibles 23.5% 528
Ferrous metals 4.3% 97
Non-ferrous metals 0.6% 14
Glass 3.7% 83
Textiles 4.0% 89
Nappies and sanitary 3.2% 72
Rubble 5.9% 132
Timber 11.6% 260
Rubber 1.6% 36
Potentially hazardous 22.1% 498
Total 100% 2249

Figure S2.6: Primary composition of overall waste, excluding cover, 18–24 August 2007

Putrescible materials were the largest component of the overall waste stream, comprising nearly a quarter of the total. These materials included both green waste from the transfer station and food waste from ICI activity. Potentially hazardous materials were the second largest component of the overall waste stream. A high proportion of these materials was biosolids and milliscreenings from a wastewater treatment plant, and industrial by-products from chemical and manufacturing industries.

S2.4 Discussion and analysis

S2.4.1 C&D waste

Loads of waste generated by C&D activity (see Section 2.6 for the taxonomy of C&D waste) were identified during the surveys of waste to the transfer station and the general waste to the tip face. None of the other waste streams (kerbside collections, cover material and special) contained C&D waste. The quantities of C&D waste in these two waste streams are shown in Table S2.16.

Table S2.16: C&D waste to landfill, 18–24 August 2007

Activity source Waste to transfer station General waste to tip face
Construction and demolition 76 tonnes
(Table S2.3)
90 tonnes
(Table S2.8)
Total C&D waste to landfill – 166 tonnes (from above)
Overall waste to landfill –– 2360 tonnes (Table S2.12)
C&D waste as proportion of overall waste to landfill – 7%

Table S2.16 shows that C&D waste comprised 7 per cent of the overall waste to landfill. Because cover material represents a relatively small proportion of the overall waste, the proportion of the C&D waste is the same with cover material included and excluded.

S2.4.2 Organic waste

The New Zealand Waste Strategy contains several targets relating to organic waste. The first of these is: “By December 2003, all territorial local authorities will have instituted a measurement programme to identify existing organic waste quantities, and set local targets for diversion from disposal”. Although the Strategy does not provide a definition for ‘organic waste’, the following description is included in its Glossary: “Organic waste includes garden and kitchen waste, food process wastes, and sewage sludge”.

Based on the preceding description, Table S2.17 on the following page shows the quantity of organic waste landfilled during the survey period.

Table S2.17: Organic waste to landfill, 18–24 August 2007

Material Tonnes/week Data source
Kitchen waste 295 Appendix S5
Green waste 189 Appendix S5
Meat-processing waste 28 Weighbridge records
Sewage pellets 83 Weighbridge records
Total 595  

A total of 595 tonnes of organic waste was disposed of during the survey week.

S2.4.3 Factors affecting waste generation and disposal during survey period

A range of factors affect the quantity and composition of waste disposed of at any individual disposal facility. Some of the factors considered to have the potential to be most relevant to the waste disposed of during the 18–24 August 2007 survey period are discussed below.

S2.4.3.1 Weather before and during the survey period

There were no unusual weather events in the Wellington region in the weeks preceding the audit. July temperatures were slightly below normal, rainfall was above normal, and sunshine hours were below normal. August sunshine hours were well above normal.

S2.4.3.2 Economic conditions

In the quarter to June 2007 consumer confidence dropped in Wellington, mirroring the trend recorded in most regions, but Wellington’s fall was the smallest across the regions. Wellington recorded the second strongest rise in both building permit types. Residential dwelling approvals rose 22 per cent and commercial consents lifted 3.4 per cent.5 Increased consumer confidence and construction could be expected to result in an increase in waste generation in the region.

4 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.