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G2 Results: 6–12 August 2007

G2.1 Transfer pit in the resource recovery area

The transfer pit in the resource recovery area was surveyed on Friday 10 August, Saturday 11 August and Sunday 12 August. Only residual waste disposed of into the transfer pit was included in the survey. During this period, data on 412 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 6–12 August indicate that 224 tonnes of residual waste were transported from the transfer pit to the disposal face7 during the week. This number will be used as the basis for all further calculations relating to transfer pit tonnages.

G2.1.1 Primary composition of transfer pit waste

The primary composition of waste disposed of to the transfer pit is presented in Table G2.1 and Figure G2.1. The secondary composition, which includes all 22 categories, is given in Appendix G3.

Table G2.1: Primary composition of transfer pit waste, 6–12 August 2007

Primary category % of total
(± 95% confidence level)
Tonnes/week
Paper 7.5% (±1.2%) 17
Plastics 5.7% (±0.9%) 13
Putrescibles 11.8% (±2.4%) 26
Ferrous metals 9.2% (±1.7%) 21
Non-ferrous metals 0.3% (±0.1%) 1
Glass 2.9% (±0.9%) 7
Textiles 12.3% (±2.9%) 28
Nappies and sanitary 0.5% (±0.2%) 1
Rubble 14.7% (±4.8%) 33
Timber 33.6% (±5.2%) 75
Rubber 0.9% (±0.6%) 2
Potentially hazardous 0.4% (±0.2%) 1
Total 100%   224

Timber is the largest single component of waste being disposed of at the transfer pit, comprising 34 per cent of the total. The timber included both fabricated timber, such as furniture, and construction and demolition waste. Rubble was the second largest component, at 15 per cent. This included soil, concrete, bricks, rocks and rubble.

Figure G2.1: Primary composition of transfer pit waste, 6–12 August 2007

G2.1.2 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 G2.2 shows the percentage of loads originating from each of the activities, the percentage of total weight, and the tonnes per week.

Table G2.2: Activity source of transfer pit waste, 6–12 August 2007

Activity source No. of loads surveyed % of loads % of weight Tonnes/week
Construction and demolition 60 15% 26% 59
Industrial/commercial/institutional 45 11% 11% 26
Kerbside collections 0 0% 0% 0
Landscaping and earthworks 39 9% 9% 21
Residential 268 65% 53% 118
Special 0 0% 0% 0
Transfer station 0 0% 0% 0
Total 412 100% 100% 224

Residential activity was responsible for generating the highest proportion of loads – nearly two-thirds of the total. Construction and demolition (C&D), industrial/commercial/institutional (ICI) and landscaping loads all comprised similar proportions of the total (between 9 and 15 per cent), but C&D loads comprised a proportionally higher share 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.

G2.1.3 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 G2.3. The secondary composition is shown in Appendix G3.

Table G2.3: Primary composition of transfer pit waste, by activity source, 6–12 August 2007

Primary category C&D ICI Landscaping Residential
Paper 2.3% 25.3% 1.4% 7.4%
Plastics 1.1% 14.2% 1.0% 7.1%
Putrescibles 1.0% 5.1% 55.1% 10.9%
Ferrous metals 3.7% 12.6% 0.3% 12.9%
Non-ferrous metals 0.1% 0.2% 0.5% 0.4%
Glass 1.5% 4.3% 0.4% 3.8%
Textiles 3.2% 9.9% 0.6% 19.5%
Nappies and sanitary 0.0% 0.6% 0.4% 0.8%
Rubble 29.6% 5.9% 32.6% 6.0%
Timber 57.1% 18.9% 7.8% 29.7%
Rubber 0.3% 2.5% 0.0% 1.1%
Potentially hazardous 0.2% 0.7% 0.1% 0.5%

C&D waste was primarily composed of timber (86 per cent), both multi-material/other and rubble. ICI waste was more heterogeneous, with paper (mostly cardboard packaging) the largest single component at 25 per cent of the total. Landscaping waste was over half green waste, with rubble (mainly soil) comprising another third. The largest component of residential waste was timber (30 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).

G2.1.4 Transfer pit waste, by vehicle type

For each vehicle load of waste disposed of at the transfer pit, the vehicle type was recorded. Table G2.4 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 G2.4: Transfer pit waste, by vehicle type, 6–12 August 2007

Vehicle type No. of loads surveyed % of loads % of weight Tonnes/week
Cars 92 22% 6% 14
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 10 2% 5% 11
Trailers 310 75% 89% 199
Total 412 100% 100% 224

Three-quarters of the loads disposed of at the transfer pit were carried by trailers, and these trailer loads accounted for 89 per cent of the total weight. Although cars accounted for 22 per cent of vehicle loads, due to the small size of car loads they accounted for only 6 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.

G2.1.5 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 presented in Table G2.5. The secondary composition is shown in Appendix G3.

Table G2.5: Primary composition of transfer pit waste, by vehicle type, 6–12 August 2007

Primary category Car Other truck Trailer
Paper 16.9% 4.2% 7.1%
Plastics 12.0% 7.3% 5.2%
Putrescibles 26.0% 2.8% 11.3%
Ferrous metals 8.8% 17.6% 8.8%
Non-ferrous metals 0.4% 0.3% 0.3%
Glass 5.1% 8.4% 2.5%
Textiles 8.7% 10.6% 12.7%
Nappies and sanitary 2.3% 0.0% 0.4%
Rubble 1.0% 19.7% 15.4%
Timber 15.4% 28.8% 35.1%
Rubber 1.3% 0.0% 0.9%

Potentially hazardous

2.0%

0.3%

0.3%

G2.2 Disposal face

The disposal face was surveyed from Monday 6 August to Thursday 9 August 2007. 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 G2.3.

The data collected in the survey from the 119 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), special waste, or cover material and cleanfill classified as such at the weighbridge. Included as general waste is 29 tonnes of 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 353 tonnes of general waste were disposed of at the disposal face. Considerable quantities of cover material were also disposed of at the disposal face, but these have been excluded from this analysis. Cover material is included in the analysis of the overall waste stream to landfill in Section G2.3.

G2.2.1 Primary composition of general waste to disposal face

The primary composition of general waste disposed of at the disposal face is presented in Table G2.6 and Figure G2.2. The secondary composition, which includes all 22 categories, is given in Appendix G4.

Table G2.6: Primary composition of general waste to disposal face, 6–12 August 2007

Primary category % of total
(± 95% confidence level)
Tonnes/week
Paper 7.4% (±3.8%) 26
Plastics 8.4% (±3.7%) 30
Putrescibles 15.2% (±6.5%) 53
Ferrous metals 4.1% (±1.3%) 15
Non-ferrous metals 0.3% (±0.1%) 1
Glass 7.0% (±4.0%) 25
Textiles 3.7% (±1.7%) 13
Nappies and sanitary 1.0% (±0.8%) 3
Rubble 37.9% (±13.7%) 134
Timber 14.5% (±3.3%) 51
Rubber 0.2% (±0.2%) 1
Potentially hazardous 0.4% (±0.1%) 1
Total 100%   353

Rubble is the largest single component of general waste being disposed of at the disposal face, with 38 per cent of the total. Rubble comprised a substantial proportion of C&D waste and landscaping waste.

Figure G2.2: Primary composition of general waste to disposal face, 6–12 August 2007

G2.2.2 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 G2.7 shows the percentage of loads originating from each of the activities, the percentage of total weight, and the tonnes per week.

Table G2.7: Activity source of general waste to disposal face, 6–12 August 2007

Activity source No. of loads surveyed % of loads % of weight Tonnes/week
Construction and demolition 44 37% 40% 142
Industrial/commercial/institutional 43 36% 39% 137
Kerbside collections 0 0% 0% 0
Landscaping and earthworks 18 15% 14% 51
Residential 14 12% 7% 23
Special 0 0% 0% 0
Transfer station 0 0% 0% 0
Total 119 100% 100% 353

C&D and ICI activity generated similar proportions of the loads of general waste to the disposal face, at approximately 36 per cent. By weight, C&D represented a greater proportion of the total, with 40 per cent. Landscaping loads comprised 15 per cent of the total number of loads and 14 per cent of the total weight. By definition three of the activity sources are not included in the general waste stream.

G2.2.3 Primary composition of general waste to disposal face, by activity source

The primary composition of the four activity sources of waste disposed of at the disposal face is shown in Table G2.8. The secondary composition is shown in Appendix G4.

Table G2.8: Primary composition of general waste to disposal face, by activity source, 6–12 August 2007

Primary category C&D ICI Landscaping Residential
Paper 1.0% 17.2% 0.2% 3.9%
Plastics 1.3% 19.6% 0.3% 3.7%
Putrescibles 0.6% 15.4% 53.4% 18.5%
Ferrous metals 3.2% 5.2% 0.0% 12.3%
Non-ferrous metals 0.1% 0.6% 0.0% 0.5%
Glass 0.2% 15.8% 4.6% 2.1%
Textiles 2.1% 5.5% 0.1% 10.2%
Nappies and sanitary 0.0% 2.5% 0.0% 0.1%
Rubble 69.0% 8.3% 39.8% 17.5%
Timber 22.2% 8.8% 1.5% 30.2%

Rubber

0.1%

0.4%

0.0%

0.3%

Potentially hazardous

0.2%

0.7%

0.0%

0.5%

C&D waste was primarily (69%) composed of ‘rubble – multi-material/other’ and timber. ICI waste was more heterogeneous. Plastics was the largest single component, with 20 per cent of the total. A significant proportion of the plastics was waste from the kerbside recycling process. Landscaping waste was over half green waste, with rubble (mainly soil) comprising nearly 40 per cent. The largest component of residential waste was timber (30 per cent), which included both fabricated items and C&D-type timber (residential waste can include waste from several sources, including C&D).

G2.2.4 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 G2.9 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 G2.9: General waste to disposal face, by vehicle type, 6–12 August 2007

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 5 4% 13% 46
Gantry trucks 62 52% 54% 191
Huka trucks 0 0% 0% 0
Other trucks 44 37% 32% 111
Trailers 8 7% 1% 4
Total 119 100% 100% 353

No cars disposed of waste at the disposal face. All compactors were carrying kerbside collections, and the only huka truck was transporting the transfer trailer from the transfer pit. Over half of the loads of general waste disposed of at the disposal face were carried by gantry trucks. These truck loads accounted for 54 percent of the total weight. Other trucks (primarily tip trucks) accounted for 37 per cent of vehicle loads and 32 per cent of the total weight.

G2.2.5 Primary composition of general waste to disposal face, by vehicle type

The primary composition of loads carried by the four types of vehicles that disposed of general waste at the disposal face is shown in Table G2.10. The secondary composition is shown in Appendix G4.

Table G2.10: Primary composition of general waste to disposal face, by vehicle type,
6–12 August 2007

Primary category Front-loader truck Gantry truck Other truck Trailer
Paper 26.7% 6.1% 0.8% 10.1%
Plastics 16.3% 10.6% 0.8% 8.9%
Putrescibles 23.3% 7.5% 28.1% 32.9%
Ferrous metals 5.9% 4.7% 2.2% 4.6%
Non-ferrous metals 1.0% 0.3% 0.0% 0.6%
Glass 5.9% 9.9% 2.2% 4.7%
Textiles 5.2% 3.0% 3.9% 4.0%
Nappies and sanitary 6.1% 0.2% 0.1% 3.1%
Rubble 2.2% 40.3% 48.7% 1.7%
Timber 5.3% 16.9% 13.0% 28.2%
Rubber 0.9% 0.1% 0.1% 0.5%
Potentially hazardous 1.1% 0.3% 0.1% 0.7%

G2.3 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.

G2.3.1 Source of overall waste to landfill, including cover material

Weighbridge data for the survey week shows that 3293 tonnes of material were disposed of at Green Island Landfill. The proportions of the different waste types are shown in Table G2.11 and Figure G2.3.

Table G2.11: Waste types to landfill, including cover, 6–12 August 2007

Waste type % of weight Tonnes/week
Cover material 73% 2409
General 11% 353
Kerbside collections 5% 150
Special 5% 156
Transfer station 7% 226
Total 100% 3293

Figure G2.3: Waste types to landfill, including cover, 6–12 August 2007

Nearly three-quarters of the material being disposed of at Green Island Landfill was cover material. Most of this material was being stockpiled in preparation for capping closed landfill cells. The other four waste types comprised between 5 and 11 per cent of the total.

G2.3.2 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 G2.2.1

  • 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 constitute ‘rubble – multi-material/other’

  • transfer pit – as determined from survey results and shown in Section G2.1.1.

  • transfer pit – as determined from survey results and shown in Section G2.1.1.

The primary composition of the overall waste stream to Green Island Landfill is presented in Table G2.12 and Figure G2.4. The secondary composition is given in Appendix G5.

Table G2.12: Primary composition of overall waste, including cover, 6–12 August 2007

Primary category % of total Tonnes/week
Paper 2.0% 65
Plastics 1.9% 63
Putrescibles 5.4% 177
Ferrous metals 1.3% 43
Non-ferrous metals 0.1% 3
Glass 1.3% 42
Textiles 1.3% 44
Nappies and sanitary 0.4% 14
Rubble 79.1% 2606
Timber 3.9% 128
Rubber 0.1% 3
Potentially hazardous 3.2% 106
Total 100% 3293

Figure G2.4: Primary composition of overall waste, including cover, 6–12 August 2007

Rubble, primarily material disposed of at no charge for use as capping, comprised nearly 80 per cent of all material disposed of at the landfill. All other materials comprised 6 per cent or less each, of the total.

G2.3.3 Source of overall waste to landfill, excluding cover material

If cover materials are excluded, weighbridge data for the survey week shows that 884 tonnes of material were disposed of at Green Island Landfill. The proportions of the different waste types are shown in Table G2.13 and Figure G2.5.

Table G2.13: Waste types to landfill, excluding cover, 6–12 August 2007

Waste type % of weight Tonnes/week
Cover material 0% 0
General 40% 353
Kerbside collections 17% 150
Special 18% 156
Transfer station 26% 226
Total 100% 884

Figure G2.5: Waste types to landfill, excluding cover material, 6–12 August 2007

G2.3.4 Primary composition of overall waste to landfill, excluding cover material

If the calculations described in Section G2.3.2 are undertaken with cover material excluded, the primary composition of the remaining waste types combined is as shown in Table G2.14 and Figure G2.6. The secondary composition is given in Appendix G5.

Table G2.14: Primary composition of overall waste, excluding cover, 6–12 August 2007

Primary category % of total Tonnes/week
Paper 7.3% 65
Plastics 7.1% 63
Putrescibles 20.1% 177
Ferrous metals 4.8% 43
Non-ferrous metals 0.4% 3
Glass 4.7% 42
Textiles 5.0% 44
Nappies and sanitary 1.6% 14
Rubble 22.3% 197
Timber 14.5% 128
Rubber 0.3% 3
Potentially hazardous 12.0% 106
Total 100% 884

Figure G2.6: Primary composition of overall waste, excluding cover, 6–12 August 2007

G2.4 Discussion and analysis

G2.4.1 C&D waste

Loads of waste generated by C&D (see Section 2.6 for the taxonomy of C&D waste) were identified during the surveys of waste to the transfer pit and 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 G2.15.

Table G2.15: C&D waste to landfill, 6–12 August 2007

Activity source Waste to transfer pit General waste to disposal face
Construction and demolition 59 tonnes
(Table G2.2)
142 tonnes
(Table G2.7)
Total C&D waste to landfill – 201 tonnes (from above)
Overall waste to landfill, including cover – 3293 tonnes (Table G2.11)
C&D waste as proportion of overall waste to landfill, including cover – 6.1%
Overall waste to landfill, excluding cover – 884 tonnes (Table G2.13)
C&D waste as proportion of overall waste to landfill, excluding cover – 22.7%%

Table G2.15 shows that C&D waste comprised 6 per cent of the overall waste to landfill, if cover is included. If cover is excluded, C&D waste comprised over 23 per cent of waste, by weight.

G2.4.2 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 6–12 August 2007 survey period, are discussed below.

G2.4.2.1 Gate charge for cover materials

A major factor affecting the quantity and type of waste currently being disposed of at Green Island Landfill is the absence of disposal charges for cover material (see Table G1.1). If disposal charges similar to those for general waste were imposed, it is likely that the overall quantity of waste disposed of at the facility would decrease significantly.

G2.4.2.2 University term

The 6–12 August 2007 surveys occurred during the second semester at the University of Otago.8 As approximately 20,000 students are enrolled at the University (out of an overall population in Dunedin of 120,000)9 it is expected that waste volumes would be higher during university semesters, when more students are resident in Dunedin.

G2.4.2.3 Weather before and during the survey period

Heavy rain in South Canterbury and Otago at the end of July caused flood damage in many parts of the region, with flooding reported in flat areas of Dunedin, including Mosgiel and parts of South Dunedin. It could be expected that a proportion of residential waste disposed of at Green Island during the survey period was due to flood damage, although there was no anecdotal evidence of this. The worst damage occurred in Milton, south of Dunedin, which has its own landfill.

G2.4.2.4 Economic conditions

The Otago economy was very buoyant during the March 2007 quarter according to Otago Outlook June 2007 published by Otago Regional Council. The following are relevant excerpts from the report.

The Otago economy began the year with a bang in the March quarter. A sharp lift in non-residential building activity, a busy period at Port Otago, and a rebound in commercial vehicle sales were the main contributors to a 10.7% jump in the region’s Business Environment Index.

Tourism activity in Otago was strong in the March quarter. The number of guest nights purchased in the region over the March quarter was up 4.4% on the same period last year.

Retail activity in Otago rebounded strongly during the March quarter. The nominal value of retail sales (excluding vehicles) was up 9.7% on the March quarter 2006 – the largest annual gain since the September quarter of 2005 and a marked improvement on the 4.1% growth averaged last year.

Residential construction in Otago was steady rather than spectacular during the March quarter. The 364 residential building consents (including apartments) issued represented a 2.0% increase on the March quarter last year.

The March quarter was a strong period for non-residential consent issuance in the Otago region. A number of visitor accommodation projects in the Queenstown–Lakes district and two large-scale commercial building alterations in Dunedin City lifted the value on non-residential consents 31% ahead of the March quarter last year.

Increased economic activity in all of the sectors mentioned – construction, retail and tourism – could be expected to result in an increase in waste generation in the region.

7 Weighbridge product name: ‘Domestic solid waste – transfer trailer’.

9 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