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G5 Results: 25–31 May 2008

G5.1 Transfer pit in the resource recovery area

The transfer pit in the resource recovery area was surveyed on Sunday 25 May, Friday 30 May and Saturday 31 May 2008. Only residual waste disposed of into the transfer pit was included in the survey. During this period, data on 318 vehicle loads was collected. The data collected on these days has been used as representative of the entire survey week.

Weighbridge records for the period 25–31 May indicate that 149 tonnes of residual waste were transported from the transfer pit to the disposal face during the survey week. This number will be used as the basis for all further calculations relating to transfer pit tonnages.

G5.1.1 Primary composition of transfer pit waste

The primary composition of waste disposed of to the transfer pit is presented in Table G5.1 and Figure G5.1. The secondary composition, which includes all 22 categories, is given in Appendix G12.

Table G5.1: Primary composition of transfer pit waste, 25–31 May 2008

Primary category % of total
(± 95% confidence level)
Tonnes/week
Paper 11.1% (±1.7%) 17
Plastics 7.7% (±1.1%) 12
Putrescibles 8.9% (±2.2%) 13
Ferrous metals 7.1% (±1.6%) 11
Non-ferrous metals 0.4% (±0.2%) 1
Glass 3.9% (±2.2%) 6
Textiles 14.5% (±4.6%) 22
Nappies and sanitary 0.9% (±0.3%) 1
Rubble 12.0% (±4.1%) 18
Timber 31.9% (±5.8%) 48
Rubber 1.1% (±0.5%) 2
Potentially hazardous 0.4% (±0.1%) 1
Total 100%   149

Timber was the largest single component of waste being disposed of at the transfer pit, comprising over 30 per cent of the total. The timber included both fabricated timber, such as furniture, and C&D waste. Textiles, primarily carpet and underlay, were the second largest component, at 14% of the total.

Figure G5.1: Primary composition of transfer pit waste, 25–31 May 2008

G5.1.2 Transfer pit waste, by activity source

Each load of waste being disposed of at the transfer pit was assessed as to the activity that had resulted in its generation. Table G5.2 shows the percentage of loads originating from each of the activities, the percentage of total weight, and the tonnes per week.

Table G5.2: Activity source of transfer pit waste, 25–31 May 2008

Activity source No. of loads surveyed % of loads % of weight Tonnes/week
Construction and demolition 62 19% 31% 47
Industrial/commercial/institutional 57 18% 20% 31
Kerbside collections 0 0% 0% 0
Landscaping and earthworks 14 4% 5% 7
Residential 185 58% 44% 65
Special 0 0% 0% 0
Transfer station 0 0% 0% 0
Total 318 100% 100% 149

Residential activity was responsible for generating the highest proportion of loads – nearly 60 per cent of the total – although the loads accounted for only 44 per cent of the total weight. C&D and ICI loads each comprised 18 to 19 per cent of the total, but C&D loads comprised 31 per cent of the total weight. No loads of kerbside collections, special waste or transfer station waste were disposed of during the survey period. These types of loads are disposed of at the disposal face.

G5.1.3 Primary composition of transfer pit waste, by activity source

The primary composition of the four activity sources of waste at the transfer pit is shown in Table G5.3. The secondary composition is shown in Appendix G12.

Table G5.3: Primary composition of transfer pit waste, by activity source, 25–31 May 2008

Primary category C&D ICI Landscaping Residential
Paper 4.7% 19.0% 2.9% 12.8%
Plastics 3.0% 12.9% 2.1% 9.3%
Putrescibles 2.5% 4.5% 55.5% 10.8%
Ferrous metals 3.7% 5.8% 1.9% 10.6%
Non-ferrous metals 0.2% 0.5% 0.0% 0.6%
Glass 0.2% 8.9% 1.6% 4.4%
Textiles 7.0% 23.1% 0.1% 17.4%
Nappies and sanitary 0.1% 1.9% 0.2% 1.2%
Rubble 25.6% 1.9% 23.9% 5.7%
Timber 52.5% 20.4% 9.6% 24.7%
Rubber 0.4% 0.7% 2.0% 1.7%
Potentially hazardous 0.2% 0.5% 0.1% 0.6%

C&D waste was primarily composed of timber and rubble (78 per cent combined). ICI waste was more heterogeneous. Textiles, primarily used clothing and carpets, was the largest single component of ICI waste, with 23 per cent of the total; timber was the second largest component with 20 per cent. Landscaping waste was 55 per cent green waste, with rubble (mainly soil) comprising 24 per cent. The largest component of residential waste was timber (25 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 and landscaping).

G5.1.4 Transfer pit waste, by vehicle type

For each vehicle load of waste disposed of at the transfer pit, the vehicle type was recorded. Table G5.4 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.

Table G5.4: Transfer pit waste, by vehicle type, 25–31 May 2008

Vehicle type No. of loads surveyed % of loads % of weight Tonnes/week
Cars 108 34% 12% 18
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 8 3% 4% 6
Trailers 202 64% 84% 125
Total 318 100% 100% 149

Almost two-thirds of the loads disposed of at the transfer pit were carried by trailers. These trailer loads accounted for 84 per cent of the total weight. Although cars accounted for 34 per cent of vehicle loads, due to the small size of car loads they accounted for only 12 per cent of the total weight. A small number of other trucks (small tip trucks or box trucks) also disposed of waste. None of the four heavy truck types used the transfer pit during the survey period.

G5.1.5 Primary composition of transfer pit waste, by vehicle type

The primary composition of loads carried by the three types of vehicles that disposed of waste at the transfer pit is shown in Table G5.5. The secondary composition is shown in Appendix G12.

Table G5.5: Primary composition of transfer pit waste, by vehicle type, 25–31 May 2008

Primary category Car Other truck Trailer
Paper 20.1% 13.7% 9.7%
Plastics 13.5% 6.3% 7.0%
Putrescibles 20.7% 0.2% 7.7%
Ferrous metals 6.8% 8.1% 7.1%
Non-ferrous metals 0.5% 0.2% 0.4%
Glass 4.1% 2.6% 3.9%
Textiles 14.9% 40.9% 13.1%
Nappies and sanitary 3.1% 0.0% 0.7%
Rubble 3.2% 2.0% 13.8%
Timber 11.6% 21.8% 35.3%
Rubber 0.9% 3.1% 1.0%
Potentially hazardous 0.5% 1.2% 0.4%

G5.2 Disposal face

The disposal face was surveyed from Monday 26 May to Thursday 29 May 2008. Only vehicles disposing of waste directly to the disposal face were included. Vehicles disposing of waste at the sludge sump, mixing pit, asbestos pit or cover stockpile were not included, but are included in the overall waste stream in Section G5.3.

The data collected in the survey from the 120 vehicles carrying general waste was used to determine the composition of the general waste to the disposal face. General waste includes waste from the following activity sources: construction and demolition (C&D), industrial/ commercial/institutional (ICI), landscaping and earthworks, and residential. General waste does not include waste from kerbside collections, transfer stations (including the transfer pit) or special waste. Included as general waste is waste from the kerbside recycling processing facility that is classified at the weighbridge as ‘Refuse col DCC contract – Envirowaste’.

Weighbridge records for the survey week were analysed, and it was determined that 998 tonnes of general waste were disposed of at the disposal face. A quantity of cover material (based on the weighbridge product names in Appendix G2) was also disposed of at the disposal face during the survey, but these loads are excluded from this analysis.

G5.2.1 Primary composition of general waste to disposal face

The primary composition of general waste disposed of at the disposal face is presented in Table G5.6 and Figure G5.2. The secondary composition, which includes all 22 categories, is given in Appendix G13.

Table G5.6: Primary composition of general waste to disposal face, 25–31 May 2008

Primary category % of total
(± 95% confidence level)
Tonnes/week
Paper 3.0% (±1.6%) 30
Plastics 3.3% (±2.1%) 32
Putrescibles 7.7% (±4.2%) 76
Ferrous metals 1.4% (±0.5%) 14
Non-ferrous metals 0.2% (±0.1%) 2
Glass 3.1% (±2.8%) 30
Textiles 1.1% (±0.8%) 11
Nappies and sanitary 0.2% (±0.2%) 2
Rubble 72.6% (±20.1%) 725
Timber 7.3% (±2.9%) 72
Rubber 0.1% (±0.1%) 1
Potentially hazardous 0.1% (±0.1%) 1
Total 100%   998

Rubble was the largest single component of general waste being disposed of at the disposal face, with 73 per cent of the total. Rubble comprised a substantial proportion of both C&D waste and landscaping and earthworks waste. Most of the rubble was contained in loads classified as ‘Clean (Dry)’ by the weighbridge.

Figure G5.2: Primary composition of general waste to disposal face, 25–31 May 2008

G5.2.2 General waste to disposal face, by activity source

Each load of general waste being disposed of at the disposal face was assessed as to the activity that had resulted in its generation. Table G5.7 shows the percentage of loads originating from each of the activities, the percentage of total weight, and the tonnes per week.

Table G5.7: Activity source of general waste to disposal face, 25–31 May 2008

Activity source No. of loads surveyed % of loads % of weight Tonnes/week
Construction and demolition 36 30% 23% 230
Industrial/commercial/institutional 26 22% 17% 171
Kerbside collections 0 0% 0% 0
Landscaping and earthworks 49 41% 57% 571
Residential 9 8% 3% 26
Special 0 0% 0% 0
Transfer station 0 0% 0% 0
Total 120 100% 100% 998

Landscaping and earthworks activity generated the highest number of loads (41 per cent) and the highest percentage of the total weight of general waste (57 per cent) discharged at the disposal face. C&D loads represented the second largest activity source, with 23 per cent of the total weight. ICI activity generated about 22 per cent of loads and 17 per cent of the total weight. By definition, kerbside collections, special waste and transfer station waste are not included in general waste.

G5.2.3 Primary composition of general waste to disposal face, by activity source

The primary composition of the four activity sources of general waste disposed of at the disposal face is shown in Table G5.8. The secondary composition is shown in Appendix G13.

Table G5.8: Primary composition of general waste to disposal face, by activity source, 25–31 May 2008

Primary category C&D ICI Landscaping Residential
Paper 0.7% 15.5% 0.0% 5.0%
Plastics 0.6% 17.6% 0.0% 3.6%
Putrescibles 2.2% 7.6% 9.4% 17.4%
Ferrous metals 1.6% 3.3% 0.1% 15.7%
Non-ferrous metals 0.1% 0.9% 0.0% 0.6%
Glass 0.0% 17.5% 0.0% 1.9%
Textiles 0.9% 3.8% 0.0% 10.9%
Nappies and sanitary 0.0% 1.1% 0.0% 0.0%
Rubble 75.8% 20.6% 90.0% 6.5%
Timber 17.8% 11.7% 0.4% 35.2%
Rubber 0.2% 0.2% 0.0% 2.2%
Potentially hazardous 0.2% 0.3% 0.0% 0.9%

C&D waste was primarily composed of rubble and timber (96 per cent combined). ICI waste was more heterogeneous, with paper, plastics, glass and rubble all comprising between 15 and 21 per cent of the total. Landscaping waste was nearly 90 per cent rubble, with green waste comprising only 9 per cent. The largest component of residential waste was timber (35 per cent), which included both fabricated items and C&D-type timber (residential waste can include waste from several sources, including C&D).

G5.2.4 General waste to disposal face, by vehicle type

For each vehicle load of waste disposed of at the disposal face, the vehicle type was recorded. Table G5.9 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.

Table G5.9: General waste to disposal face, by vehicle type, 25–31 May 2008

Vehicle type No. of vehicles surveyed % of loads % of weight Tonnes/week
Cars 0 0% 0% 0
Compactors 3 3% 1% 8
Front-loader trucks 2 2% 3% 28
Gantry trucks 44 37% 31% 310
Huka trucks 1 1% 2% 19
Other trucks 66 55% 63% 628
Trailers 4 3% 1% 6
Total 120 100% 100% 998

No cars disposed of waste at the disposal face, and the only huka truck was transporting the transfer trailer from the transfer pit. Other trucks accounted for 55 per cent of general waste loads discharged at the disposal face and 63 per cent of the total weight. Gantry trucks accounted for 37 per cent of loads and 31 per cent of the total weight.

G5.2.5 Primary composition of general waste to disposal face, by vehicle type

The primary composition of loads carried by the five types of vehicles that disposed of general waste at the disposal face is shown in Table G5.10. The secondary composition is shown in Appendix G13.

Table G5.10: Primary composition of general waste to disposal face, by vehicle type, 25–31 May 2008

Primary category Compactor Front-loader truck Gantry truck Other truck Trailer
Paper 28.6% 15.8% 6.6% 0.2% 5.0%
Plastics 17.2% 13.2% 7.1% 0.1% 4.6%
Putrescibles 19.6% 23.0% 3.7% 8.9% 16.2%
Ferrous metals 4.7% 5.3% 3.3% 0.2% 3.0%
Non-ferrous metals 3.4% 1.1% 0.3% 0.0% 0.2%
Glass 12.6% 5.8% 4.9% 0.0% 1.3%
Textiles 3.4% 7.4% 1.7% 0.6% 1.1%
Nappies and sanitary 3.4% 4.7% 0.1% 0.0% 1.1%
Rubble 1.1% 4.2% 58.4% 86.3% 16.0%
Timber 3.4% 17.4% 13.5% 3.6% 50.8%
Rubber 1.1% 1.1% 0.2% 0.1% 0.2%
Potentially hazardous 1.1% 1.1% 0.2% 0.0% 0.4%

G5.3 Overall waste to landfill

The composition of the overall waste stream being disposed of at Green Island Landfill was determined by combining information from the weighbridge records with the survey results. The product name field of the weighbridge records was used to categorise all materials entering the facility as being one of the following five types: cover material, kerbside collections, general waste, special waste, or transfer station. The product name field classifications are given in Appendix G2.

G5.3.1 Source of overall waste to landfill, including cover material

Weighbridge data for the survey week shows that 1895 tonnes of material were disposed of at Green Island Landfill. The proportions of the different waste types are shown in Table G5.11 and Figure G5.3.

Table G5.11: Waste types to landfill, including cover, 25–31 May 2008

Waste type

% of weight

Tonnes/week

Cover material

17%

324

General

53%

998

Kerbside collections

10%

183

Special

13%

241

Transfer station

8%

149

Total

100%

1895

Figure G5.3: Waste types to landfill, including cover, 25–31 May 2008

General waste was the largest category of waste discharged during the survey period, comprising 53 per cent of the total. Cover material was the second largest category, with 17 per cent of the total.

G5.3.2 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 – presumed to all be ‘rubble – multi-material/other’

  • kerbside collection – estimated to be the composition given in Appendix G1, which is based on the results of the previous audits at Green Island Landfill, with some minor adjustments for what appear to be anomalies in those results

  • general waste – as determined from survey results and shown in Section G5.2.1

  • special – calculated to be the composition given in Appendix G1, based on the following assumptions relating to product names in the weighbridge records:

  • sewage sludge, sumps and asbestos are ‘potentially hazardous’

  • woolscour/tannery/fellmongery waste are ‘putrescibles – multi-material/other’

  • foundry sands were from ferrous metal production so were not hazardous and are ‘rubble – multi-material/other’

  • transfer pit – as determined from surveys results and shown in Section G5.1.1.

  • transfer pit – as determined from surveys results and shown in Section G5.1.1.

The primary composition of the overall waste stream to Green Island Landfill is presented in Table G5.12 and Figure G5.4. The secondary composition is given in Appendix G14.

Table G5.12: Primary composition of overall waste, including cover, 25–31 May 2008

Primary category % of total Tonnes/week
Paper 3.8% 72
Plastics 3.6% 69
Putrescibles 15.5% 293
Ferrous metals 1.8% 33
Non-ferrous metals 0.2% 4
Glass 2.6% 49
Textiles 1.9% 37
Nappies and sanitary 0.8% 15
Rubble 57.9% 1098
Timber 6.4% 121
Rubber 0.2% 3
Potentially hazardous 5.3% 101
Total 100% 1895

Figure G5.4: Primary composition of overall waste, including cover, 25–31 May 2008

Rubble comprised 58 per cent of all material discharged at the landfill. Putrescible materials, which include food waste, green waste and special waste such as woolscour and fellmongery waste, comprised a further 15 per cent of the total.

G5.3.3 Source of overall waste to landfill, excluding cover material

If cover materials are excluded, weighbridge data for the survey week shows that 1571 tonnes of material were disposed of at Green Island Landfill. The proportions of the different waste types are shown in Table G5.13 and Figure G5.5.

Table G5.13: Waste types to landfill, excluding cover, 25–31 May 2008

Waste type % of weight Tonnes/week
Cover material 0% 0
General 63% 998
Kerbside collections 12% 183
Special 15% 241
Transfer station 9% 149
Total 100% 1571

Figure G5.5: Waste types to landfill, excluding cover material, 25–31 May 2008

G5.3.4 Primary composition of overall waste to landfill, excluding cover material

If the calculations described in Section G5.3.2 are undertaken with cover material excluded, the primary composition of the remaining waste types combined is as shown in Table G5.14 and Figure G5.6. The secondary composition is given in Appendix G14.

Table G5.14: Primary composition of overall waste, excluding cover, 25–31 May 2008

Primary category % of total Tonnes/week
Paper 4.6% 72
Plastics 4.4% 69
Putrescibles 18.7% 293
Ferrous metals 2.1% 33
Non-ferrous metals 0.3% 4
Glass 3.1% 49
Textiles 2.3% 37
Nappies and sanitary 1.0% 15
Rubble 49.2% 774
Timber 7.7% 121
Rubber 0.2% 3
Potentially hazardous 6.4% 101
Total 100% 1571

Figure G5.6: Primary composition of overall waste, excluding cover, 25–31 May 2008

G5.4 Discussion and analysis

G5.4.1 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 pit and the general waste to the disposal 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 G5.15.

Table G5.15: C&D waste to landfill, 25–31 May 2008

Activity source Waste to transfer pit General waste to disposal face
Construction and demolition 47 tonnes
(Table G5.2)
230 tonnes
(Table G5.7)
Total C&D waste to landfill – 277 tonnes (from above)
Overall waste to landfill, including cover – 1895 tonnes (Table G5.11)
C&D waste as proportion of overall waste to landfill, including cover – 12%
Overall waste to landfill, excluding cover –1571 tonnes (Table G5.13)
C&D waste as proportion of overall waste to landfill, excluding cover –18%

Table G5.15 shows that C&D waste comprised 12 per cent of the overall waste to landfill, if cover is included. If cover is excluded, C&D waste comprised 18 per cent of waste, by weight.

G5.4.2 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 be most relevant to the waste disposed of during the 25–31 May 2008 survey period are discussed below.

G5.4.2.1 Gate charge for cover materials

In the analysis of the first two surveys at Green Island Landfill, it was suggested that a major factor affecting the quantity and type of waste being disposed of at the landfill was the absence of disposal charges for cover material (Table G1.1). It was suggested that if disposal charges similar to those for general waste were imposed, it was likely that the overall quantity of waste disposed of at the facility would decrease significantly.

This hypothesis has been supported by the change in waste disposal during the third and fourth survey periods. Between the second and third surveys, free disposal of cover material ceased and material previously disposed of as cover was reclassified and disposal charges were incurred. Between the second and third surveys the quantity of cover material discharged during the survey week decreased from 2462 tonnes to 444 tonnes. The quantity of cover material decreased again, to 324 tonnes, during the fourth survey period.

G5.4.2.2 University term

The 25–31 May 2008 surveys were towards the end of the first semester at the University of Otago.19 Because approximately 20,000 students are enrolled at the University (out of an overall population in Dunedin of 120,000)20 it is expected that waste volumes would be higher during university semesters, when more students are resident in Dunedin.

G5.4.2.3 Weather before and during the survey period

April rainfall was well below normal in Otago, with significant soil moisture deficits persisting throughout the region.21 This is likely to have slowed vegetation growth, and resulted in less green waste disposal than normal at this time of year. There were no significant weather events during the survey period that would have affected normal vehicle traffic at the landfill.

G5.4.2.4 Economic conditions

Economic activity slowed in the March quarter in Otago. Major plant closures, including the PPCS meat-processing plant and the Fisher and Paykel appliance manufacturing factory, were announced in the months before the survey. The National Bank’s Regional Trends22 for May 2008 reads as follows:

Otago recorded the (nation’s) largest fall in retail sales, dropping 2.1% from three months earlier. Employment also suffered a large decline, falling 3.9% in the quarter. The number of residential building approvals lifted 5.8% and contrasts a decline nationally, but commercial building consents eased 6.3% (compared to a 1.5% decline recorded nationally).

The increase in residential construction consents should result in an increase in construction and demolition waste over the medium term, while the decrease in retail trade could be expected to result in reduced waste. The overall effects of these economic factors on waste disposal can not be estimated.

20 The 2006 census was undertaken during the first semester at University of Otago. http://www.stats.govt.nz/census/2006-census-information-about-data/introduction-the-census/default.htm