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S4 Results: 21–27 February 2008

S4.1 Transfer station

The transfer station was surveyed on Friday 22 February, Saturday 23 February and Sunday 24 February 2008. During this period, data on 811 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 of material transferred from the transfer station to the landfill tip face for the survey week was 500 tonnes.

Green waste that is disposed of at the separate drop-off point at the transfer station 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 December to February a total of 1294 tonnes of green waste was transferred, an average of about 100 tonnes per week.

This gives an estimated total of 600 tonnes of waste disposed of at the transfer station during the survey week. During this period, 32 tonnes of road sweepings were recorded as being disposed of at the transfer station. These are classed as a special waste, and are not included in the calculations relating to general waste. A figure of 568 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 S4.1.

Table S4.1: Calculation of transfer station general waste to tip face, 21–27 February 2008

Table S4.2:Primary composition of transfer station general waste, 21–27 February 2008

Transfer truck transporting waste from transfer station to tip face – weight taken from on-board load cells 500
Add green waste transported to tip face – based on average for three-month period estimated from number of vehicle movements 100
Total waste from transfer station to tip face 600
Less road sweepings classified as special waste – from weighbridge records for survey week 32
Total transfer station general waste to tip face 568

S4.1.1 Primary composition of transfer station general waste

The primary composition of general waste disposed of at the transfer station is presented in Table S4.2 and Figure S4.1. This analysis excludes road sweepings, which are classified as a special waste. The secondary composition, which includes all 22 categories, is given in Appendix S11.

Table S4.2: Primary composition of transfer station general waste, 21–27 February 2008

Primary category % of total
(±95% confidence level)
Tonnes/week
Paper 4.5% (±0.7%) 25
Plastics 4.6% (±0.5%) 26
Putrescibles 43.1% (±4.0%) 245
Ferrous metals 6.5% (±1.0%) 37
Non-ferrous metals 0.4% (±0.1%) 2
Glass 1.9% (±0.6%) 11
Textiles 4.7% (±1.2%) 27
Nappies and sanitary 0.9% (±0.2%) 5
Rubble 10.2% (±2.3%) 58
Timber 20.2% (±2.6%) 115
Rubber 2.5% (±1.5%) 14
Potentially hazardous 0.4% (±0.2%) 2
Total 100%   568

Figure S4.1: Primary composition of transfer station waste, 21–27 February 2008

Putrescible material, primarily green waste, was the largest single component of waste being disposed of at the transfer station, comprising 43 per cent of the total. This includes green waste disposed of at both the separate green waste drop-off point and to the residual waste tipping pit. Timber was the second largest component, with 20 per cent of the total. The timber included both fabricated timber, such as furniture, and C&D waste. Rubble was the third largest component, comprising 10 per cent. This included soil, concrete, bricks, rocks and rubble.

S4.1.2 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 S4.3 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 S4.3: Activity source of transfer station waste, 21–27 February 2008

Activity source No. of loads surveyed % of loads % of weight Tonnes/week
Construction and demolition 89 11% 14% 83
Industrial/commercial/institutional 45 6% 7% 41
Kerbside collections 0 0% 0% 0
Landscaping and earthworks 274 34% 39% 235
Residential 390 48% 35% 208
Special 13 2% 5% 32
Transfer station 0 0% 0% 0
Total 811 100% 100% 599

Residential activity was responsible for generating the highest proportion of loads – 48 per cent of the total number of loads, and 35 per cent by weight. Landscaping loads comprised 34 per cent of the total number of loads and 39 per cent of the total weight. C&D, with 11 per cent of loads, contributed 14 per cent of the total weight. Special waste (road sweepings) represented 2 per cent of loads but accounted for 5 per cent of the total weight.

S4.1.3 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 S4.4. The secondary composition is presented in Appendix S11.

Table S4.4: Primary composition of transfer station general waste, by activity source, 21–27 February 2008

Table S4.5:Transfer station waste, by vehicle type, 21–27 February 2008

Primary category C&D ICI Landscaping Residential
Paper 1.4% 9.4% 0.3% 9.5%
Plastics 2.2% 7.7% 0.5% 9.5%
Putrescibles 2.7% 7.6% 84.4% 19.5%
Ferrous metals 6.5% 5.3% 0.6% 13.5%
Non-ferrous metals 0.2% 1.1% 0.0% 0.7%
Glass 0.9% 7.6% 0.2% 3.1%
Textiles 2.2% 12.3% 0.5% 9.0%
Nappies and sanitary 0.0% 1.4% 0.1% 2.2%
Rubble 26.3% 3.9% 10.3% 4.9%
Timber 57.3% 11.3% 3.1% 26.3%
Rubber 0.0% 30.8% 0.0% 0.8%
Potentially hazardous 0.2% 1.5% 0.0% 0.8%

C&D waste was primarily composed of timber and rubble (84 per cent combined). Rubber, in the form of shredded tyres, was the largest component of ICI waste, comprising almost 31 per cent of the total. Landscaping waste was over 84 per cent green waste, with rubble (mainly soil) comprising most of the remainder. The largest components of residential waste were timber (26 per cent) and putrescibles (mainly green waste), with about 20 per cent of the total. Loads classified as residential may include waste from several sources, including C&D and landscaping.

S4.1.4 Transfer station waste, by vehicle type

For each vehicle load of waste disposed of at the transfer station, the vehicle type was recorded. Table S4.5 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 S4.5: Transfer station waste, by vehicle type, 21–27 February 2008

Vehicle type No. of loads surveyed % of loads % of weight Tonnes/week
Cars 223 27% 11% 65
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 16 2% 6% 35
Trailers 572 71% 83% 500
Total 811 100% 100% 599

Over 70 per cent 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 27 per cent of vehicle loads, due to the small size of car loads they accounted for only 11 per cent of 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.

S4.1.5 Primary composition of transfer station general waste, by vehicle type

The primary composition of general waste loads carried by the three types of vehicles that disposed of general waste at the transfer station is shown in Table S4.6. The secondary composition is shown in Appendix S11.

Table S4.6: Primary composition of transfer station general waste, by vehicle type, 21–27 February 2008

Primary category Car Other trucks Trailer
Paper 9.7% 0.8% 3.8%
Plastics 7.2% 1.0% 4.3%
Putrescibles 47.4% 58.7% 42.4%
Ferrous metals 6.0% 7.2% 6.6%
Non-ferrous metals 0.7% 0.1% 0.3%
Glass 1.6% 0.2% 1.9%
Textiles 4.4% 24.2% 4.6%
Nappies and sanitary 2.7% 0.7% 0.7%
Rubble 4.0% 0.1% 11.1%
Timber 15.6% 6.9% 20.9%
Rubber 0.1% 0.1% 2.9%
Potentially hazardous 0.6% 0.1% 0.4%

S4.2 Tip face

The tip face was surveyed on Thursday 21 February and from Monday 25 February to Wednesday 27 February 2008. 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 in the survey, but are included in the overall waste stream in Section S4.3.

The data that was collected in the survey from the 211 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 802 tonnes of general waste were disposed of at the tip face. Both cover material 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 S4.3.

S4.2.1 Primary composition of general waste to tip face

The primary composition of general waste disposed of at the tip face is presented in Table S4.7 and Figure S4.2. The secondary composition, which includes all 22 categories, is given in Appendix S12.

Table S4.7: Primary composition of general waste to tip face, 21–27 February 2008

Primary category % of total
(±95% confidence level)
Tonnes/week
Paper 10.1% (±2.2%) 81
Plastics 15.2% (±3.8%) 122
Putrescibles 23.2% (±4.9%) 187
Ferrous metals 5.8% (±1.2%) 46
Non-ferrous metals 0.7% (±0.2%) 5
Glass 14.3% (±6.9%) 115
Textiles 6.8% (±2.0%) 54
Nappies and sanitary 3.4% (±0.9%) 27
Rubble 3.4% (±1.0%) 27
Timber 14.6% (±3.8%) 117
Rubber 0.9% (±0.4%) 7
Potentially hazardous 1.6% (±1.0%) 13
Total 100%   802

Putrescible material was the largest component of the general waste disposed of at the tip face, comprising 23 per cent of the total. Timber, plastics and glass all formed similar proportions of the waste stream, at about 14–15 per cent. The higher-than-normal proportions of plastics and glass are partly due to large quantities of waste from a recycling processor.

Figure S4.2: Primary composition of general waste to tip face, 21–27 February 2008

S4.2.2 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 S4.8 shows the percentage of loads originating from each of the activities, the percentage of total weight and the tonnes per week.

Table S4.8: Activity source of general waste to tip face, 21–27 February 2008

Activity source No. of loads surveyed % of loads % of weight Tonnes/week
Construction and demolition 10 5% 3% 22
Industrial/commercial/institutional 134 64% 87% 698
Kerbside collections 0 0% 0% 0
Landscaping and earthworks 27 13% 4% 34
Residential 40 19% 6% 48
Special 0 0% 0% 0
Transfer station 0 0% 0% 0
Total 211 100% 100% 802

ICI activity generated the majority of general waste disposed of to the tip face – 64 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.

S4.2.3 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 S4.9. The secondary composition is shown in Appendix S12.

Table S4.9: Primary composition of general waste to tip face, by activity source, 21–27 February 2008

Table S4.10:General waste to tip face, by vehicle type, 21–27 February 2008

Primary category C&D ICI Landscaping Residential
Paper 3.0% 10.9% 2.9% 7.1%
Plastics 4.8% 16.4% 1.3% 12.4%
Putrescibles 8.1% 21.5% 84.9% 12.8%
Ferrous metals 7.0% 5.0% 0.7% 20.2%
Non-ferrous metals 0.2% 0.7% 0.0% 0.9%
Glass 1.0% 16.2% 0.0% 3.8%
Textiles 1.0% 6.9% 0.7% 11.8%
Nappies and sanitary 0.2% 3.8% 0.1% 0.7%
Rubble 33.6% 2.3% 2.7% 4.8%
Timber 40.6% 13.8% 2.3% 23.6%
Rubber 0.1% 0.8% 4.3% 0.8%
Potentially hazardous 0.5% 1.7% 0.0% 1.3%

C&D waste was primarily composed of timber (41 per cent) and rubble (34 per cent). ICI waste was more heterogeneous, with putrescibles (22 per cent) and plastics (16 per cent) the two largest components. Large quantities of the plastic and glass were waste from a recycling processor. Landscaping waste was 85 per cent green waste. The largest component of residential waste was timber (24 per cent), which included both fabricated items and C&D-type timber (residential waste can include waste from several sources, including C&D).

S4.2.4 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 S4.10 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 S4.10: General waste to tip face, by vehicle type, 21–27 February 2008

Vehicle type No. of loads surveyed % of loads % of weight Tonnes/week
Cars 0 0% 0% 0
Compactors 11 5% 3% 24
Front-loader trucks 34 16% 49% 395
Gantry trucks 80 38% 18% 143
Huka trucks 21 10% 18% 141
Other trucks 62 29% 12% 95
Trailers 3 1% 0% 4
Total 211 100% 100% 802

The highest proportions of loads were transported by gantry trucks and other trucks, carrying 38 per cent and 29 per cent respectively. Front-loader trucks accounted for 16 per cent of vehicle movements but 49 per cent of the total weight.

S4.2.5 Primary composition of general waste to tip face, by vehicle type

The primary composition of loads carried by the five main types of vehicles that disposed of general waste at the tip face is shown in Table S4.11. The secondary composition is presented in Appendix S12.

Table S4.11: Primary composition of general waste to tip face, by vehicle type, 21–27 February 2008

Primary category Compactor Front-loader truck Gantry truck Huka truck Other truck
Paper 12.7% 14.0% 6.5% 5.5% 5.5%
Plastics 15.1% 19.1% 11.9% 14.3% 5.8%
Putrescibles 40.6% 28.7% 18.4% 8.7% 24.5%
Ferrous metals 4.1% 5.1% 11.5% 1.2% 7.3%
Non-ferrous metals 1.0% 0.9% 0.4% 0.2% 0.5%
Glass 5.2% 6.5% 4.4% 55.3% 3.8%
Textiles 5.1% 6.0% 9.5% 1.8% 13.6%
Nappies and sanitary 7.8% 5.3% 1.0% 1.4% 0.6%
Rubble 2.1% 3.0% 7.7% 0.7% 2.8%
Timber 4.3% 9.5% 22.0% 9.3% 35.0%
Rubber 1.0% 0.9% 1.1% 1.3% 0.3%
Potentially hazardous 1.0% 0.9% 5.7% 0.2% 0.3%

S4.3 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.

S4.3.1 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 5011 tonnes of material were disposed of at the landfill. The proportions of the different waste types are shown in Table S4.12 and Figure S4.3.

Table S4.12: Waste types to landfill, including cover material, 21–27 February 2008

Waste type % of weight Tonnes/week
Cover material 3% 138
General 16% 802
Kerbside collections 8% 411
Special 62% 3091
Transfer station 11% 568
Total 100% 5011

Figure S4.3: Waste types to landfill, including cover material, 21–27 February 2008

Special waste, predominantly from a research facility, was the largest component of the overall waste stream, comprising 62 per cent of the total. General waste disposed of at the tip face was the second largest component, with 16 per cent of the total.

S4.3.2 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 previous audits of domestic kerbside refuse undertaken by Waste Not Consulting

  • general waste – as determined from survey results and shown in Section S4.2.1

  • special:

  • it is assumed that all of the product names listed in Appendix S2 as being special waste 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 survey results and shown in Section S4.1.1.

  • transfer station – as determined from survey results and shown in Section S4.1.1.

The primary composition of the overall waste stream disposed of at Silverstream Landfill, including cover material, is presented in Table S4.13 and Figure S4.4. The secondary composition is given in Appendix S13.

Table S4.13: Primary composition of overall waste, including cover, 21–27 February 2008

Primary category % of total Tonnes/week
Paper 3% 166
Plastics 4% 207
Putrescibles 15% 732
Ferrous metals 2% 95
Non-ferrous metals 0.2% 10
Glass 3% 143
Textiles 2% 90
Nappies and sanitary 1% 73
Rubble 2% 93
Timber 7% 372
Rubber 0.4% 22
Potentially hazardous 60% 3010
Total 100% 5011

Figure S4.4: Primary composition of overall waste, including cover material, 21–27 February 2008

Potentially hazardous materials, predominantly spoil from a research facility, were the largest component of the overall waste stream and comprised 60 per cent of the total. Putrescible materials, which included green waste from the transfer station, meat-processing waste, food waste from other ICI activities, and food waste from kerbside collections, were the second largest component, comprising 15 per cent of the total.

S4.3.3 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 materials are excluded from this analysis. Weighbridge data for the survey week shows that 4873 tonnes of material were disposed of at Silverstream Landfill. The proportions of the different waste types are shown in Table S4.14 and Figure S4.5.

Table S4.14: Waste types to landfill, excluding cover material, 21–27 February 2008

Waste type % of weight Tonnes/week
Cover material 0% 0
General 16% 802
Kerbside collections 8% 411
Special 63% 3091
Transfer station 12% 568
Total 100% 4873

Figure S4.5: Waste types to landfill, excluding cover material, 21–27 February 2008

Special waste, predominantly spoil from a research facility, comprised 63 per cent of the overall waste stream, when cover material is excluded. The spoil from the research facility was discharged and stockpiled at a separate area, removed from the main tip face. General waste disposed of directly at the tip face accounted for 16 per cent of the total amount of the waste. General waste from the transfer station accounted for 12 per cent of the total.

S4.3.4 Primary composition of overall waste to landfill, excluding cover material

If the calculations described in Section S4.3.2 are undertaken with cover material excluded, the primary composition of the remaining waste types combined is as shown in Table S4.15 and Figure S4.6. The secondary composition is given in Appendix S14.

Table S4.15: Primary composition of overall waste, excluding cover, 21–27 February 2008

Primary category % of total Tonnes/week
Paper 3% 166
Plastics 4% 207
Putrescibles 15% 732
Ferrous metals 2% 95
Non-ferrous metals 0% 10
Glass 3% 143
Textiles 2% 90
Nappies and sanitary 1% 73
Rubble 2% 93
Timber 5% 234
Rubber 0% 22
Potentially hazardous 62% 3010
Total 100% 4873

Figure S4.6: Primary composition of overall waste, excluding cover material, 21–27 February 2008

Potentially hazardous materials, predominantly spoil from a research facility, were the largest component of the overall waste stream and comprised 62 per cent of the total. Putrescible materials were the second largest component, with 15 per cent of the total.

S4.4 Discussion and analysis

S4.4.1 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. Although residential waste can contain several kinds of waste, including C&D, and still be classified as residential, none of the other waste streams (kerbside collections, cover material and special waste) contained C&D waste. The quantities of C&D waste in these two waste streams are shown in Table S4.16.

Table S4.16: C&D waste to landfill, 21–27 February 2008

Activity source Waste to transfer station General waste to tip face
Construction and demolition 83 tonnes
(Table S4.3)
22 tonnes
(Table S4.8)
Total C&D waste to landfill – 105 tonnes (from above)
Overall waste to landfill – 5011 tonnes (Table S4.12)
C&D waste as proportion of overall waste to landfill – 6%

Table S4.16 shows that C&D waste comprised 6 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.

S4.4.2 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 S4.17 shows the quantity of organic waste landfilled during the survey period.

Table S4.17: Organic waste to landfill, 21–27 February 2008

Material Tonnes/week Data source
Kitchen waste 290 Appendix S13
Green waste 299 Appendix S13
Meat-processing waste 100 Weighbridge records
Sewage pellets 81 Weighbridge records
Total 770  

Table S4.17 shows that a total of 770 tonnes of organic waste was disposed of during the survey week.

S4.4.3 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 21–27 February 2008 survey period are discussed below.

General waste disposed of at the tip face decreased by approximately 140 tonnes (15 per cent) between the first and second surveys of this series, and a further 35 tonnes (4 per cent) between the second and third surveys. This decrease is associated with a similar-sized decrease in waste transported to the facility by a major waste operator. The reason for this is not known.

The quantity of meat-processing waste being disposed of at the facility increased from 20 tonnes per week during the first survey to over 100 tonnes per week during the second and third surveys. This may be partly due to seasonal variation and partly due to an increase in the numbers of animals sent for processing due to the very dry conditions in pastoral areas.

General waste disposed of at the transfer station increased by about 11 per cent between the first and second surveys and a further 15 per cent between the second and third surveys. These increases included a substantial increase in the amount of green waste. This may be due to seasonal differences in green waste generation and disposal.

The potentially contaminated spoil from a research facility constituted a high proportion of the overall waste stream during the survey period. This material was all classified as potentially hazardous and would have substantially altered the composition of the overall waste stream compared to the previous surveys.

S4.4.3.1 Weather before and during the survey period

In February 2008 rainfall was below normal in Wellington and sunshine hours were above normal.7 During the survey period the weather was hot and sunny.

S4.4.3.2 Economic conditions

In the quarter to December 2007, year-on-year growth in the Wellington region was 3.0 per cent and employment increased 1.3 per cent. Both residential and commercial building consents declined.8 Consumer confidence was the highest in the country during the quarter. No assumptions can be made regarding any effects these economic conditions may have had on waste disposal in the February survey.