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S3 Results: 23–29 November 2007

S3.1 Transfer station

The transfer station was surveyed on Friday 23 November, Saturday 24 November and Sunday 25 November. During this period, data on 895 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 446 tonnes.

Green waste 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 September to November, a total of 576 tonnes of green waste was transferred, an average of about 48 tonnes per week. The green waste was stockpiled at the transfer station after the September removal (see Section S2.1) and all of the accumulated material was transferred in November.

This gives an estimated total of 494 tonnes of waste disposed of at the transfer station during the survey week. During this period, 28 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 466 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 S3.1.

Table S3.1: Calculation of transfer station general waste to tip face, 23–29 November 2007

Transfer truck transporting waste from transfer station to tip face – weight taken from on-board load cells 446
Add green waste transported to tip face – based on average for three-month period, estimated from number of vehicle movements 48
Total waste from transfer station to tip face 494
Less road sweepings classified as special waste – from weighbridge records for survey week 28
Total transfer station general waste to tip face 466

S3.1.1 Primary composition of transfer station general waste

The primary composition of general waste disposed of at the transfer station is presented in Table S3.2 and Figure S3.1. This analysis excludes road sweepings, which are classified as a special waste. The secondary composition, which includes all 22 categories, is given in Appendix S7.

Table S3.2: Primary composition of transfer station general waste, 23–29 November 2007

Primary category % of total
(±95% confidence level)
Tonnes/week
Paper 5.2% (±0.6%) 24
Plastics 4.9% (±0.5%) 23
Putrescibles 45.9% (±3.7%) 214
Ferrous metals 6.1% (±0.8%) 28
Non-ferrous metals 0.4% (±0.2%) 2
Glass 2.2% (±0.4%) 10
Textiles 5.4% (±1.0%) 25
Nappies and sanitary 1.1% (±0.2%) 5
Rubble 9.9% (±2.3%) 46
Timber 16.4% (±2.0%) 76
Rubber 2.3% (±1.3%) 11
Potentially hazardous 0.4% (±0.1%) 2
Total 100%   466

Figure S3.1: Primary composition of transfer station waste, 23–29 November 2007

Putrescible material, primarily green waste, was the largest single component of waste being disposed of at the transfer station, comprising 46 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 16 per cent of the total. The timber included both fabricated timber, such as furniture, and C&D waste. Rubble was the third largest component, with 10 per cent. This included soil, concrete, bricks, rocks and rubble.

S3.1.2 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 S3.3 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 S3.3: Activity source of transfer station waste, 23–29 November 2007

Activity source No. of loads surveyed % of loads % of weight Tonnes/week
Construction and demolition 81 9% 11% 55
Industrial/commercial/institutional 43 5% 6% 32
Kerbside collections 0 0% 0% 0
Landscaping and earthworks 324 36% 41% 201
Residential 436 49% 36% 178
Special 11 1% 6% 28
Transfer station 0 0% 0% 0
Total 895 100% 100% 494

Residential activity was responsible for generating the highest proportion of loads – 49 per cent of the total number of loads and 36 per cent by weight. Landscaping loads comprised 36 per cent of the total number of loads and 41 per cent of the total weight. C&D, at 9 per cent of loads, comprised a slightly higher share of the total weight (11 per cent). Special waste (road sweepings) represented 1 per cent of loads but accounted for 6 per cent of the total weight.

S3.1.3 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 S3.4. The secondary composition is presented in Appendix S7.

Table S3.4: Primary composition of transfer station general waste, by activity source, 23–29 November 2007

Primary category C&D ICI Landscaping Residential
Paper 2.5% 9.3% 0.8% 10.4%
Plastics 2.3% 7.7% 0.7% 10.0%
Putrescibles 5.2% 7.6% 83.6% 22.6%
Ferrous metals 3.7% 5.7% 0.7% 13.0%
Non-ferrous metals 0.0% 1.8% 0.0% 0.6%
Glass 1.2% 6.5% 0.3% 3.8%
Textiles 3.2% 10.7% 0.7% 10.3%
Nappies and sanitary 0.0% 1.1% 0.1% 2.4%
Rubble 32.6% 5.5% 10.2% 3.4%
Timber 49.0% 14.1% 2.8% 22.0%
Rubber 0.0% 29.5% 0.1% 0.7%
Potentially hazardous 0.3% 0.5% 0.0% 0.7%

C&D waste was primarily composed of timber and rubble (83 per cent combined). Rubber, in the form of shredded tyres, was the largest component of ICI waste with almost 30 per cent of the total. Landscaping waste was over 80 per cent green waste, with rubble (mainly soil) comprising most of the remainder. The largest components of residential waste were timber and putrescibles (mainly green waste), each with about 22 per cent of the total. Loads classified as residential may include waste from several sources, including C&D and landscaping.

S3.1.4 Transfer station waste, by vehicle type

For each vehicle load of waste disposed of at the transfer station, the vehicle type was recorded. Table S3.5 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 S3.5: Transfer station waste, by vehicle type, 23–29 November 2007

Vehicle type No. of loads surveyed % of loads % of weight Tonnes/week
Cars 257 29% 12% 58
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 13 1% 6% 30
Trailers 625 70% 82% 406
Total 895 100% 100% 494

Seventy per cent of the loads disposed of at the transfer station were carried by trailers, and these trailer loads accounted for 82 per cent of the total weight. Although cars accounted for 29 per cent of vehicle loads, due to the small size of car loads they accounted for only 12 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.

S3.1.5 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 S3.6. The secondary composition is shown in Appendix S7.

Table S3.6: Primary composition of transfer station general waste, by vehicle type, 23–29 November 2007

Primary category

Car

Other trucks

Trailer

Paper

11.3%

6.1%

4.4%

Plastics

7.7%

14.5%

4.5%

Putrescibles

44.1%

0.9%

46.3%

Ferrous metals

6.5%

19.3%

6.0%

Non-ferrous metals

0.3%

0.9%

0.4%

Glass

2.8%

4.4%

2.1%

Textiles

6.0%

12.3%

5.2%

Nappies and sanitary

2.8%

0.0%

0.8%

Rubble

3.0%

5.3%

10.9%

Timber

14.7%

34.6%

16.5%

Rubber

0.3%

0.9%

2.6%

Potentially hazardous

0.5%

0.9%

0.3%

S3.2 Tip face

The tip face was surveyed from Monday 26 November to Thursday 29 November 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 in the survey, but are included in the overall waste stream in Section S3.3.

The data that was collected in the survey from the 227 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 837 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 S3.3.

S3.2.1 Primary composition of general waste to tip face

The primary composition of general waste disposed of at the tip face is presented in Table S3.7 and Figure S3.2. The secondary composition, which includes all 22 categories, is given in Appendix S8.

Table S3.7: Primary composition of general waste to tip face, 23–29 November 2007

Primary category

% of total
(±95% confidence level)

Tonnes/week

Paper

11.3%

(±2.4%)

94

Plastics

16.3%

(±4.6%)

137

Putrescibles

23.7%

(±5.8%)

198

Ferrous metals

6.3%

(±1.2%)

53

Non-ferrous metals

0.6%

(±0.1%)

5

Glass

6.5%

(±1.9%)

55

Textiles

6.0%

(±2.0%)

50

Nappies and sanitary

3.2%

(±0.8%)

26

Rubble

5.6%

(±2.4%)

47

Timber

17.6%

(±3.1%)

147

Rubber

1.2%

(±1.1%)

10

Potentially hazardous

1.7%

(±1.0%)

14

Total

100%

  837

Putrescible material was the largest component of the general waste disposed of at the tip face, comprising 24 per cent of the total. Timber was the second largest component, with 18 per cent of the total.

Figure S3.2: Primary composition of general waste to tip face, 23–29 November 2007

S3.2.2 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 S3.8 shows the percentage of loads originating from each of the activities, the percentage of total weight and the tonnes per week.

Table S3.8: Activity source of general waste to tip face, 23–29 November 2007

Activity source No. of loads surveyed % of loads % of weight Tonnes/week
Construction and demolition 46 20% 11% 89
Industrial/commercial/institutional 129 57% 80% 668
Kerbside collections 0 0% 0% 0
Landscaping and earthworks 26 11% 5% 42
Residential 26 11% 4% 37
Special 0 0% 0% 0
Transfer station 0 0% 0% 0
Total 227 100% 100% 837

ICI activity generated the majority of general waste disposed of to the tip face – 57 per cent of all loads and 80 per cent by weight. Kerbside collections, special waste and transfer station waste are not considered to be general waste.

S3.2.3 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 S3.9. The secondary composition is shown in Appendix S8.

Table S3.9: Primary composition of general waste to tip face, by activity source, 23–29 November 2007

Primary category C&D ICI Landscaping Residential
Paper 3.9% 13.3% 0.5% 5.5%
Plastics 3.8% 19.4% 1.5% 8.5%
Putrescibles 2.9% 23.9% 72.2% 14.9%
Ferrous metals 8.4% 5.7% 1.2% 18.1%
Non-ferrous metals 0.1% 0.7% 0.0% 0.7%
Glass 1.4% 7.8% 0.1% 3.4%
Textiles 2.3% 6.5% 0.4% 11.8%
Nappies and sanitary 0.0% 4.0% 0.0% 0.2%
Rubble 13.8% 3.4% 20.6% 9.0%
Timber 62.6% 11.9% 3.3% 26.6%
Rubber 0.4% 1.4% 0.0% 0.7%
Potentially hazardous 0.4% 2.1% 0.0% 0.8%

C&D waste was primarily composed of timber (63 per cent) and rubble (14 per cent). ICI waste was more heterogeneous, with putrescibles (24 per cent) and plastics (19 per cent) being the two largest components. Large quantities of the plastics were waste from the kerbside recycling processor. Landscaping waste was almost three-quarters green waste, with rubble (mainly soil) comprising 20 per cent. The largest component of residential waste was timber (27 per cent), which included both fabricated items and C&D-type timber (residential waste can include waste from several sources, including C&D).

S3.2.4 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 S3.10 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 S3.10: General waste to tip face, by vehicle type, 23–29 November 2007

Vehicle type No. of loads surveyed % of loads % of weight Tonnes/week
Cars 0 0% 0% 0
Compactors 10 4% 5% 38
Front-loader trucks 43 19% 48% 404
Gantry trucks 97 43% 23% 195
Huka trucks 10 4% 5% 45
Other trucks 67 30% 19% 156
Trailers 0 0% 0% 0
Total 227 100% 100% 837

The highest proportions of loads were transported by gantry trucks and other trucks, carrying 43 per cent and 30 per cent respectively. Front-loader trucks accounted for 19 per cent of vehicle movements but 48 per cent of the total weight.

S3.2.5 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 S3.11. The secondary composition is presented in Appendix S8.

Table S3.11: Primary composition of general waste to tip face, by vehicle type, 23–29 November 2007

Primary category Compactor Front-loader truck Gantry truck Huka truck Other truck
Paper 13.4% 15.8% 6.4% 12.4% 3.8%
Plastics 14.3% 24.0% 6.3% 35.9% 3.9%
Putrescibles 39.8% 26.4% 15.0% 15.2% 21.9%
Ferrous metals 4.3% 4.3% 8.2% 4.0% 11.0%
Non-ferrous metals 1.1% 0.8% 0.3% 0.5% 0.3%
Glass 7.9% 7.5% 8.5% 5.2% 1.5%
Textiles 4.8% 5.0% 3.4% 3.0% 13.1%
Nappies and sanitary 4.8% 5.0% 0.7% 3.0% 0.2%
Rubble 2.4% 2.5% 12.5% 1.5% 8.2%
Timber 5.6% 7.2% 32.8% 18.3% 32.4%
Rubber 0.9% 0.8% 0.5% 0.5% 3.4%
Potentially hazardous 0.9% 0.8% 5.4% 0.5% 0.3%

S3.3 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.

S3.3.1 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 2254 tonnes of material were disposed of at the landfill. The proportions of the different waste types are shown in Table S3.12 and Figure S3.3.

Table S3.12: Waste types to landfill, including cover, 23–29 November 2007

Waste type % of weight Tonnes/week
Cover material 3% 75
General 37% 837
Kerbside collections 19% 432
Special 19% 435
Transfer station 21% 466
Total 100% 2245

Figure S3.3: Waste types to landfill, including cover, 23–29 November 2007

General waste disposed of directly at the tip face accounted for 37 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 19 and 21 per cent.

S3.3.2 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 S3.2.1

  • 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 survey results and shown in Section S3.1.1.

  • transfer station – as determined from survey results and shown in Section S3.1.1.

The primary composition of the overall waste stream disposed of at Silverstream Landfill, including cover material, is presented in Table S3.13 and Figure S3.4. The secondary composition is given in Appendix S9.

Table S3.13: Primary composition of overall waste, including cover, 23–29 November 2007

Primary category % of total Tonnes/week
Paper 8.1% 181
Plastics 9.9% 222
Putrescibles 32.2% 723
Ferrous metals 4.1% 93
Non-ferrous metals 0.4% 10
Glass 3.7% 83
Textiles 3.7% 84
Nappies and sanitary 3.3% 74
Rubble 4.5% 101
Timber 13.4% 300
Rubber 0.9% 21
Potentially hazardous 15.8% 354
Total 100% 2245

Figure S3.4: Primary composition of overall waste, including cover material, 23–29 November 2007

Putrescible materials were the largest component of the overall waste stream. Putrescible materials included green waste from the transfer station, meat-processing waste, food waste from other ICI activities, and food waste from kerbside collections. Potentially hazardous materials were the second largest component with 16 per cent of the total. A high proportion of these materials were biosolids and milliscreenings from a wastewater treatment plant, and industrial by-products from chemical and manufacturing industries.

S3.3.3 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 2170 tonnes of material were disposed of at Silverstream Landfill. The proportions of the different waste types are shown in Table S3.14 and Figure S3.5.

Table S3.14: Waste types to landfill, excluding cover material, 23–29 November 2007

Waste type % of weight Tonnes/week
Cover material 0% 0
General 39% 837
Kerbside collections 20% 432
Special 20% 435
Transfer station 21% 466
Total 100% 2170

Figure S3.5: Waste types to landfill, excluding cover, 23–29 November 2007

General waste disposed of directly at the tip face accounted for 39 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 20 and 21 per cent.

S3.3.4 Primary composition of overall waste to landfill, excluding cover material

If the calculations described in Section S3.3.2 are undertaken with cover material excluded, the primary composition of the remaining waste types combined is as shown in Table S3.15 and Figure S3.6. The secondary composition is given in Appendix S10.

Table S3.15: Primary composition of overall waste, excluding cover, 23–29 November 2007

Primary category % of total Tonnes/week
Paper 8.3% 181
Plastics 10.2% 222
Putrescibles 33.3% 723
Ferrous metals 4.3% 93
Non-ferrous metals 0.4% 10
Glass 3.8% 83
Textiles 3.9% 84
Nappies and sanitary 3.4% 74
Rubble 4.7% 101
Timber 10.4% 225
Rubber 1.0% 21
Potentially hazardous 16.3% 354
Total 100% 2170

Figure S3.6: Primary composition of overall waste, excluding cover, 23–29 November 2007

Putrescible materials were the largest component of the overall waste stream, comprising over 33 per cent of the total. They included green waste from the transfer station, meat-processing waste, food waste from other ICI activities, and food waste from kerbside collections. Potentially hazardous materials were the second largest component of the overall waste stream, with 16 per cent of the total. A high proportion of these materials were biosolids and milliscreenings from a wastewater treatment plant, and industrial by-products from chemical and manufacturing industries.

S3.4 Discussion and analysis

S3.4.1 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) contained C&D waste. The quantities of C&D waste in these two waste streams are shown in Table S3.16.

Table S3.16: C&D waste to landfill, 23–29 November 2007

Activity source Waste to transfer station General waste to tip face
Construction and demolition 55 tonnes
(Table S3.3)
89 tonnes
(Table S3.8)
Total C&D waste to landfill – 144 tonnes (from above)
Overall waste to landfill –– 2245 tonnes (Table S3.12)
C&D waste as proportion of overall waste to landfill – 6%

Table S3.16 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.

S3.4.2 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 S3.17 shows the quantity of organic waste landfilled during the survey period.

Table S3.17: Organic waste to landfill, 23–29 November 2007

Material Tonnes/week Data source
Kitchen waste 293 Appendix S9
Green waste 272 Appendix S9
Meat-processing waste 101 Weighbridge records
Sewage pellets 85 Weighbridge records
Total 751  

Table S3.17 shows that a total of 751 tonnes of organic waste was disposed of during the survey week.

S3.4.3 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 23–29 November 2007 survey period are discussed below.

General waste disposed of at the tip face decreased by approximately 140 (15 per cent) between the first and second surveys of this series. This decrease is almost entirely due to a 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 survey. 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. This included a substantial increase in the quantity of green waste being disposed of. This is likely due to seasonal differences in green waste generation and disposal.

S3.4.3.1 Weather events before and during the survey period

November 2007 was extremely dry in many regions of New Zealand, with below normal rainfall and significant soil moisture deficits in the Wellington region.

S3.4.3.2 Economic conditions

In the quarter to September 2007 year-on-year growth in the Wellington region was 2.1 per cent. Building consents declined, with commercial construction consents falling 9.4 per cent.6 Consumer confidence increased during the quarter, but business confidence fell short of the national benchmark.