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S5 Results: 17–23 May 2008

S5.1 Transfer station

The transfer station was surveyed on Saturday 17 May, Sunday 18 May and Friday 23 May 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 369 tonnes.

Before this survey, green waste collected at the separate drop-off point was stockpiled at the transfer station and transferred intermittently to the tip face. The vehicles transferring the green waste were not weighed, but a vehicle count was kept. A nominal weight could then be used to determine the weight of green waste transferred and disposed of at the tip face. This practice was discontinued before the current survey, and small quantities of green waste were loaded on top of each truckload of transfer station waste going to the tip face. The weight of the green waste is included in the weight of the refuse.

This gives a total of 369 tonnes of waste, including green waste disposed of at the transfer station during the survey week. During this period, 13 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 356 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 S5.1.

Table S5.1: Calculation of transfer station general waste to tip face, 17–23 May 2008

Transfer truck transporting waste from transfer station to tip face – weight taken from on-board load cells 369
Green waste transported to tip face – included in figure above 0
Total waste from transfer station to tip face 369
Less road sweepings classified as special waste – from weighbridge records for survey week 13
Total transfer station general waste to tip face 356

S5.1.1 Primary composition of transfer station general waste

The primary composition of general waste disposed of at the transfer station is presented in Table S5.2 and Figure S5.1. This analysis excludes road sweepings, which are classified as a special waste. The secondary composition, which includes all 22 categories, is given in Appendix S15.

Table S5.2: Primary composition of transfer station general waste, 17–23 May 2008

Primary category % of total
(±95% confidence level)
Tonnes/week
Paper 3.9% (±0.5%) 14
Plastics 4.5% (±0.7%) 16
Putrescibles 43.5% (±4.1%) 155
Ferrous metals 4.9% (±0.8%) 17
Non-ferrous metals 0.3% (±0.1%) 1
Glass 1.8% (±0.4%) 6
Textiles 5.1% (±1.0%) 18
Nappies and sanitary 1.0% (±0.2%) 4
Rubble 8.2% (±2.0%) 29
Timber 19.5% (±2.9%) 69
Rubber 7.0% (±3.0%) 25
Potentially hazardous 0.3% (±0.1%) 1
Total 100%   356

Figure S5.1: Primary composition of transfer station general waste, 17–23 May 2008

Putrescible material, primarily green waste, was the largest single component of waste being disposed of at the transfer station, at 44 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 19 per cent of the total. The timber included both fabricated timber, such as furniture, and C&D waste. Rubble was the third largest component, at 8 per cent. This included soil, concrete, bricks, rocks and rubble. Rubber, 7 per cent of the total, comprised tyres delivered from a single source.

S5.1.2 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 S5.3 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 S5.3: Activity source of transfer station waste, 17–23 May 2008

Activity source No. of loads surveyed % of loads % of weight Tonnes/week
Construction and demolition 68 9% 12% 43
Industrial/commercial/institutional 52 7% 11% 42
Kerbside collections 0 0% 0% 0
Landscaping and earthworks 253 33% 39% 145
Residential 392 51% 34% 126
Special 7 1% 4% 13
Transfer station 0 0% 0% 0
Total 772 100% 100% 369

Residential activity was responsible for generating the highest proportion of loads – 51 per cent of the total number of loads, and 34 per cent by weight. Landscaping loads comprised 33 per cent of the total number of loads and 39 per cent of the total weight. C&D, with 9 per cent of the loads, contributed 12 per cent of the total weight. Special waste (road sweepings) represented 1 per cent of loads and accounted for 4 per cent of the total weight.

S5.1.3 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 S5.4. The secondary composition is presented in Appendix S15.

Table S5.4: Primary composition of transfer station general waste, by activity source, 17–23 May 2008

Primary category C&D ICI Landscaping Residential
Paper 1.5% 4.6% 0.4% 8.5%
Plastics 2.6% 6.6% 0.5% 9.1%
Putrescibles 3.2% 5.1% 84.2% 23.3%
Ferrous metals 4.0% 3.2% 0.5% 10.7%
Non-ferrous metals 0.3% 0.4% 0.0% 0.6%
Glass 1.6% 2.4% 0.3% 3.3%
Textiles 1.6% 3.8% 0.4% 12.0%
Nappies and sanitary 0.1% 0.7% 0.2% 2.4%
Rubble 22.4% 1.0% 9.5% 4.3%
Timber 62.2% 15.4% 4.0% 24.1%
Rubber 0.0% 56.5% 0.0% 0.9%
Potentially hazardous 0.4% 0.2% 0.0% 0.6%

C&D waste was primarily composed of timber and rubble (85 per cent combined). Rubber, in the form of shredded tyres, was the largest component of ICI waste at 56 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 (24 per cent) and putrescibles (mainly green waste), comprising about 23 per cent of the total. Loads classified as residential may include waste from several sources, including C&D and landscaping.

S5.1.4 Transfer station waste, by vehicle type

For each vehicle load of waste disposed of at the transfer station, the vehicle type was recorded. Table S5.5 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 S5.5: Transfer station waste, by vehicle type, 17–23 May 2008

Vehicle type No. of loads surveyed % of loads % of weight Tonnes/week
Cars 208 27% 10% 36
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 35 4% 12% 43
Trailers 529 69% 79% 290
Total 772 100% 100% 369

Nearly 70 per cent of the loads disposed of at the transfer station were carried by trailers, and these trailer loads accounted for 79 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 10 per cent of total weight. A smaller 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.

S5.1.5 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 S5.6. The secondary composition is shown in Appendix S15.

Table S5.6: Primary composition of transfer station general waste, by vehicle type, 17–23 May 2008

Primary category Car Other trucks Trailer
Paper 9.2% 2.7% 3.4%
Plastics 8.0% 3.4% 4.2%
Putrescibles 50.2% 12.6% 45.7%
Ferrous metals 3.7% 4.4% 5.1%
Non-ferrous metals 0.4% 0.3% 0.3%
Glass 3.1% 1.5% 1.6%
Textiles 5.0% 2.4% 5.3%
Nappies and sanitary 3.4% 0.9% 0.7%
Rubble 2.2% 0.9% 9.7%
Timber 14.4% 5.6% 21.5%
Rubber 0.3% 65.1% 2.2%
Potentially hazardous 0.4% 0.2% 0.3%

S5.2 Tip face

The tip face was surveyed from Monday 19 May to Thursday 22 May 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 S5.3.

The data that was collected in the survey from the 177 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 741 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 S5.3.

S5.2.1 Primary composition of general waste to tip face

The primary composition of general waste disposed of at the tip face is presented in Table S5.7 and Figure S5.2. The secondary composition, which includes all 22 categories, is given in Appendix S16.

Table S5.7: Primary composition of general waste to tip face, 17–23 May 2008

Primary category % of total
(±95% confidence level)
Tonnes/week
Paper 10.9% (±2.3%) 81
Plastics 13.0% (±3.2%) 96
Putrescibles 24.4% (±5.4%) 181
Ferrous metals 5.0% (±0.9%) 37
Non-ferrous metals 0.7% (±0.2%) 5
Glass 4.8% (±1.2%) 35
Textiles 5.4% (±1.5%) 40
Nappies and sanitary 3.7% (±1.0%) 27
Rubble 7.5% (±3.3%) 55
Timber 20.3% (±5.1%) 150
Rubber 1.2% (±0.9%) 9
Potentially hazardous 3.1% (±2.2%) 23
Total 100%   741

Putrescible material was the largest component of the general waste disposed of at the tip face, comprising 24 per cent of the total. Timber comprised 20 per cent of the total, much of which was from timber processing and joinery manufacture.

Figure S5.2: Primary composition of general waste to tip face, 17–23 May 2008

S5.2.2 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 S5.8 shows the percentage of loads originating from each of the activities, the percentage of total weight and the tonnes per week.

Table S5.8: Activity source of general waste to tip face, 17–23 May 2008

Activity source No. of loads surveyed % of loads % of weight Tonnes/week
Construction and demolition 26 15% 9% 66
Industrial/commercial/institutional 103 58% 79% 583
Kerbside collections 0 0% 0% 0
Landscaping and earthworks 28 16% 8% 59
Residential 20 11% 5% 34
Special 0 0% 0% 0
Transfer station 0 0% 0% 0
Total 177 100% 100% 741

ICI activity generated the majority of general waste disposed of to the tip face – 58 per cent of all loads and 79 per cent by weight. Kerbside collections, special waste and transfer station waste are not classified as general waste.

S5.2.3 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 S5.9. The secondary composition is shown in Appendix S16.

Table S5.9: Primary composition of general waste to tip face, by activity source, 17–23 May 2008

Primary category C&D ICI Landscaping Residential
Paper 5.0% 12.8% 0.5% 7.4%
Plastics 5.1% 15.3% 0.5% 11.0%
Putrescibles 4.4% 24.6% 53.4% 9.9%
Ferrous metals 3.1% 5.1% 0.1% 15.5%
Non-ferrous metals 0.1% 0.8% 0.0% 0.8%
Glass 0.4% 5.7% 0.3% 3.8%
Textiles 0.6% 6.1% 0.1% 11.6%
Nappies and sanitary 0.0% 4.7% 0.1% 0.0%
Rubble 21.3% 2.7% 39.1% 8.8%
Timber 54.9% 17.4% 5.9% 28.6%
Rubber 5.2% 0.9% 0.0% 1.0%
Potentially hazardous 0.1% 3.9% 0.0% 1.6%

C&D waste was primarily composed of timber (55 per cent) and rubble (21 per cent). ICI waste was more heterogeneous, with putrescibles (25 per cent) and timber (17 per cent) being the two largest components. Landscaping waste was 53 per cent green waste and 39 per cent rubble. The largest component of residential waste was timber (29 per cent), which included both fabricated items and C&D-type timber (residential waste can include waste from several sources, including C&D).

S5.2.4 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 S5.10 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 S5.10: General waste to tip face, by vehicle type, 17–23 May February 2008

Vehicle type No. of loads surveyed % of loads % of weight Tonnes/week
Cars 0 0% 0% 0
Compactors 0 0% 0% 0
Front-loader trucks 32 18% 50% 371
Gantry trucks 69 39% 24% 180
Huka trucks 14 8% 10% 75
Other trucks 62 35% 16% 115
Trailers 0 0% 0% 0
Total 177 100% 100% 741

The highest proportions of loads were transported by gantry trucks and other trucks, carrying 39 per cent and 35 per cent respectively. Front-loader trucks accounted for 18 per cent of vehicle movements but 50 per cent of the total weight.

S5.2.5 Primary composition of general waste to tip face, by vehicle type

The primary composition of loads carried by the four main types of vehicles that disposed of general waste at the tip face is shown in Table S5.11. The secondary composition is presented in Appendix S16.

Table S5.11: Primary composition of general waste to tip face, by vehicle type, 17–23 May 2008

Primary category Front-loader truck Gantry truck Huka truck Other truck
Paper 13.8% 9.2% 12.2% 3.4%
Plastics 15.7% 9.0% 23.3% 4.0%
Putrescibles 31.0% 17.7% 17.2% 18.3%
Ferrous metals 4.9% 5.5% 3.8% 5.2%
Non-ferrous metals 1.0% 0.5% 0.6% 0.2%
Glass 7.2% 2.3% 4.3% 1.1%
Textiles 5.9% 3.5% 4.5% 7.3%
Nappies and sanitary 5.9% 1.3% 3.7% 0.3%
Rubble 3.1% 15.6% 2.4% 12.3%
Timber 9.7% 24.6% 21.8% 46.9%
Rubber 1.0% 0.4% 5.0% 0.9%
Potentially hazardous 1.0% 10.3% 1.2% 0.2%

S5.3 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.

S5.3.1 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 2107 tonnes of material were disposed of at Silverstream Landfill. The proportions of the different waste types are shown in Table S5.12 and Figure S5.3.

Table S5.12: Waste types to landfill, including cover material, 17–23 May 2008

Waste type % of weight Tonnes/week
Cover material 6% 127
General 33% 697
Kerbside collections 18% 386
Special 26% 542
Transfer station 17% 356
Total 100% 2107

Figure S5.3: Waste types to landfill, including cover material, 17–23 May 2008

General waste was the largest component of the overall waste stream, comprising 33 per cent of the total. Special waste was the second largest component, with 26 per cent of the total.

S5.3.2 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 S5.2.1

  • 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 surveys results and shown in Section S5.1.1.

  • transfer station – as determined from surveys results and shown in Section S5.1.1.

The primary composition of the overall waste stream disposed of at Silverstream Landfill, including cover material, is presented in Table S5.13 and Figure S5.4. The secondary composition is given in Appendix S17.

Table S5.13: Primary composition of overall waste, including cover, 17–23 May 2008

Primary category % of total Tonnes/week
Paper 7% 146
Plastics 8% 162
Putrescibles 29% 603
Ferrous metals 3% 62
Non-ferrous metals 0.4% 8
Glass 3% 56
Textiles 3% 64
Nappies and sanitary 3% 67
Rubble 4% 89
Timber 16% 339
Rubber 2% 34
Potentially hazardous 23% 477
Total 100% 2107

Figure S5.4: Primary composition of overall waste, including cover material, 17–23 May 2008

Putrescible materials was the largest component of the overall waste stream at 29 per cent of the total. Putrescible materials included green waste from the transfer station, meat-processing waste, food waste from other ICI activity, and food waste from kerbside collections.

S5.3.3 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 1981 tonnes of material were disposed of at the landfill. The proportions of the different waste types are shown in Table S5.14 and Figure S5.5.

Table S5.14: Waste types to landfill, excluding cover material, 17–23 May 2008

Waste type % of weight Tonnes/week
Cover material 0% 0
General 35% 697
Kerbside collections 19% 386
Special 27% 542
Transfer station 18% 356
Total 100% 1981

Figure S5.5: Waste types to landfill, excluding cover material, 17–23 May 2008

General waste disposed of directly at the tip face accounted for 35 per cent of the total amount of the waste, excluding cover material. Special waste accounted for 27 per cent of the total.

S5.3.4 Primary composition of overall waste to landfill, excluding cover material

If the calculations described in Section S5.3.2 are undertaken with cover material excluded, the primary composition of the remaining waste types combined is as shown in Table S5.15 and Figure S5.6. The secondary composition is given in Appendix S18.

Table S5.15: Primary composition of overall waste, excluding cover, 17–23 May 2008

Primary category % of total Tonnes/week
Paper 7% 146
Plastics 8% 162
Putrescibles 30% 603
Ferrous metals 3% 62
Non-ferrous metals 0.4% 8
Glass 3% 56
Textiles 3% 64
Nappies and sanitary 3% 67
Rubble 4% 89
Timber 11% 213
Rubber 2% 34
Potentially hazardous 24% 477
Total 100% 1981

Figure S5.6: Primary composition of overall waste, excluding cover material, 17–23 May 2008

Putrescible material was the largest component of the overall waste stream, at 30 per cent of the overall waste stream, excluding cover material.

S5.4 Discussion and analysis

S5.4.1 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 S5.16.

Table S5.16: C&D waste to landfill, 17–23 May 2008

Activity source Waste to transfer station General waste to tip face
Construction and demolition 43 tonnes
(Table S5.3)
66 tonnes
(Table S5.8)
Total C&D waste to landfill – 109 tonnes (from above)
Overall waste to landfill – 2107 tonnes (Table S5.12)
C&D waste as proportion of overall waste to landfill – 5.2%

Table S5.16 shows that C&D waste comprised 5.2 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.

S5.4.2 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 S5.17 shows the quantity of organic waste landfilled during the survey period.

Table S5.17: Organic waste to landfill, 17–23 May 2008

Material Tonnes/week Data source
Kitchen waste 258 Appendix S17
Green waste 217 Appendix S17
Meat-processing waste 91 Weighbridge records
Sewage pellets 73 Weighbridge records
Total 639  

A total of 639 tonnes of organic waste was disposed of during the survey week.

S5.4.3 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 17–23 May 2008 survey period are discussed below.

Between the third and fourth surveys, general waste disposed of at the tip face decreased by 8 per cent. Overall, there was a 24 per cent decrease in general waste disposed of at the tip face between the first and fourth 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 decrease 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 decreased to 90 tonnes per week during the fourth survey. This may be due to seasonal variations in meat-processing activity.

The general waste disposed of at the transfer station decreased 19 per cent between the third and fourth surveys. The decrease in general waste may be due to seasonal differences in green waste generation and disposal, as the decrease in general waste was associated with a 19 per cent decrease in green waste.

S5.4.3.1 Weather before and during the survey period

In April 2008 rainfall was double the normal average in the Wellington region but sunshine hours were also above average.9 There were no unusual weather events preceding or during the survey.

S5.4.3.2 Economic conditions

In the quarter to March 2008 most economic indicators weakened in the Wellington region. House sales, the labour market and consumer confidence all decreased. However, retail trade remained firm, recording a 2.4 per cent increase, compared to a 1.2 per cent decrease nationally.10 No assumptions can be made regarding any effects these economic conditions may have had on waste disposal in the May survey.