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G4 Results: 1–7 March 2008

G4.1 Transfer pit in the resource recovery area

The transfer pit in the resource recovery area was surveyed on Saturday 1 March, Sunday 2 March and Friday 7 March. Only residual waste disposed of into the transfer pit was included in the survey. During this period, data on 284 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 1–7 March indicate that 146 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.

G4.1.1 Primary composition of transfer pit waste

The primary composition of waste disposed of to the transfer pit is presented in Table G4.1 and Figure G4.1. The secondary composition, which includes all 22 categories, is given in Appendix G9.

Table G4.1: Primary composition of transfer pit waste, 1–7 March 2008

Primary category % of total
(± 95% confidence level)
Tonnes/week
Paper 9.4% (±1.6%) 14
Plastics 7.1% (±1.1%) 10
Putrescibles 9.3% (±2.2%) 14
Ferrous metals 7.7% (±2.0%) 11
Non-ferrous metals 0.7% (±0.2%) 1
Glass 5.4% (±3.0%) 8
Textiles 11.6% (±3.6%) 17
Nappies and sanitary 1.0% (±0.4%) 1
Rubble 16.9% (±7.0%) 25
Timber 29.9% (±5.8%) 44
Rubber 0.6% (±0.5%) 1
Potentially hazardous 0.4% (±0.1%) 1
Total 100%   146

Timber is the largest single component of waste being disposed of at the transfer pit, comprising 30 per cent of the total. The timber included both fabricated timber, such as furniture, and C&D waste. Rubble was the second largest constituent, at 17 per cent of the total.

Figure G4.1: Primary composition of transfer pit waste, 1–7 March 2008

G4.1.2 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 G4.2 shows the percentage of loads originating from each of the activities, the percentage of total weight, and the tonnes per week.

Table G4.2: Activity source of transfer pit waste, 1–7 March 2008

Activity source No. of loads surveyed % of loads % of weight Tonnes/week
Construction and demolition 47 17% 26% 38
Industrial/commercial/institutional 45 16% 20% 29
Kerbside collections 0 0% 0% 0
Landscaping and earthworks 14 5% 6% 9
Residential 178 63% 48% 71
Special 0 0% 0% 0
Transfer station 0 0% 0% 0
Total 284 100% 100% 146

Residential activity was responsible for generating the highest proportion of loads, at over 60 per cent of the total, although the loads accounted for less than half of the total weight. C&D and ICI loads each comprised 16 to 17 per cent of the total, but C&D loads comprised 26 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.

G4.1.3 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 G4.3. The secondary composition is shown in Appendix G9.

Table G4.3: Primary composition of transfer pit waste, by activity source, 1–7 March 2008

Primary category

C&D

ICI

Landscaping

Residential

Paper

4.0%

15.6%

1.2%

10.8%

Plastics

3.4%

9.5%

0.8%

8.9%

Putrescibles

1.4%

3.2%

42.0%

12.0%

Ferrous metals

2.4%

9.9%

1.0%

10.5%

Non-ferrous metals

0.3%

0.6%

0.0%

1.0%

Glass

1.0%

13.1%

0.5%

5.3%

Textiles

2.3%

11.4%

0.8%

17.9%

Nappies and sanitary

0.0%

1.4%

0.3%

1.5%

Rubble

42.7%

4.1%

50.4%

4.2%

Timber

42.4%

29.2%

3.1%

26.7%

Rubber

0.0%

1.8%

0.0%

0.6%

Potentially hazardous

0.2%

0.1%

0.0%

0.6%

C&D waste was primarily composed of timber and rubble (85 per cent combined). ICI waste was more heterogeneous, with timber the largest single component at 29 per cent of the total. The timber included both fabricated timber, such as furniture, and ‘timber – multi-material/other’, such as joinery waste. Paper was the second largest component of ICI waste, comprising 16 per cent, mainly packaging. Landscaping waste was 42 per cent green waste, with rubble (mainly soil) comprising 50 per cent. The largest component of residential waste was timber (27 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).

G4.1.4 Transfer pit waste, by vehicle type

For each vehicle load of waste disposed of at the transfer pit, the vehicle type was recorded. Table G4.4 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 G4.4: Transfer pit waste, by vehicle type, 1–7 March 2008

Vehicle type No. of loads surveyed % of loads % of weight Tonnes/week
Cars 90 32% 9% 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 4% 10% 14
Trailers 184 65% 81% 119
Total 284 100% 100% 146

Just under two-thirds of the loads disposed of at the transfer pit were carried by trailers, and these trailer loads accounted for 81 per cent of the total weight. Although cars accounted for 32 per cent of vehicle loads, due to the small size of car loads they accounted for only 9 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.

G4.1.5 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 G4.5. The secondary composition is shown in Appendix G9.

Table G4.5: Primary composition of transfer pit waste, by vehicle type, 1–7 March 2008

Primary category Car Other truck Trailer
Paper 26.3% 5.5% 7.9%
Plastics 15.9% 6.9% 6.1%
Putrescibles 22.0% 1.5% 8.7%
Ferrous metals 4.6% 14.4% 7.3%
Non-ferrous metals 0.5% 0.7% 0.7%
Glass 5.4% 1.8% 5.9%

Textiles

7.0%

17.9%

11.3%

Nappies and sanitary

4.0%

0.1%

0.8%

Rubble

2.5%

7.9%

19.6%

Timber

11.0%

43.0%

30.6%

Rubber

0.3%

0.2%

0.7%

Potentially hazardous

0.4%

0.3%

0.3%

G4.2 Disposal face

The disposal face was surveyed from Monday 3 March to Thursday 6 March 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 G4.3.

The data collected in the survey from the 153 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 624 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. Cover material is included in the overall waste stream analysed in Section G4.3.

G4.2.1 Primary composition of general waste to disposal face

The primary composition of general waste disposed of at the disposal face is presented in Table G4.6 and Figure G4.2. The secondary composition, which includes all 22 categories, is given in Appendix G10.

Table G4.6: Primary composition of general waste to disposal face, 1–7 March 2008

Primary category % of total
(± 95% confidence level)
Tonnes/week
Paper 4.2% (±2.1%) 26
Plastics 3.8% (±1.7%) 24
Putrescibles 22.5% (±7.9%) 140
Ferrous metals 3.4% (±1.0%) 21
Non-ferrous metals 0.6% (±0.6%) 4
Glass 3.6% (±2.6%) 23
Textiles 2.6% (±0.9%) 16
Nappies and sanitary 0.5% (±0.5%) 3
Rubble 44.1% (±12.8%) 275
Timber 12.7% (±3.0%) 79
Rubber 1.8% (±1.9%) 11
Potentially hazardous 0.3% (±0.3%) 2
Total 100%   624

Rubble was the largest single component of general waste being disposed of at the disposal face, with 44 per cent of the total. Rubble comprised a substantial proportion of both C&D waste and landscaping waste.

Figure G4.2: Primary composition of general waste to disposal face, 1–7 March 2008

G4.2.2 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 G4.7 shows the percentage of loads originating from each of the activities, the percentage of total weight, and the tonnes per week.

Table G4.7: Activity source of general waste to disposal face, 1–7 March 2008

Activity source No. of loads surveyed % of loads % of weight Tonnes/week
Construction and demolition 38 25% 26% 163
Industrial/commercial/institutional 32 21% 19% 120
Kerbside collections 0 0% 0% 0
Landscaping and earthworks 52 34% 45% 283
Residential 31 20% 9% 58
Special 0 0% 0% 0
Transfer station 0 0% 0% 0
Total 153 100% 100% 624

Landscaping and earthworks activity generated the highest number of loads (34 per cent) and the highest percentage of the total weight of general waste (45 per cent) discharged at the disposal face. C&D loads represented the second largest activity source, with 26 per cent of the total weight. ICI activity generated about 20 per cent of loads and a similar percentage of the total weight. By definition, kerbside collections, special waste and transfer station waste are not included in general waste.

G4.2.3 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 G4.8. The secondary composition is shown in Appendix G10.

Table G4.8: Primary composition of general waste to disposal face, by activity source, 1–7 March 2008

Primary category C&D ICI Landscaping Residential
Paper 0.9% 17.1% 0.2% 5.9%
Plastics 1.0% 14.4% 0.5% 5.5%
Putrescibles 3.5% 13.4% 38.9% 14.6%
Ferrous metals 3.3% 4.8% 0.7% 13.7%
Non-ferrous metals 0.8% 1.8% 0.0% 0.7%
Glass 0.3% 16.5% 0.1% 3.8%
Textiles 1.2% 4.0% 0.3% 15.0%
Nappies and sanitary 0.0% 2.5% 0.0% 0.1%
Rubble 61.4% 8.0% 57.0% 7.9%
Timber 27.6% 7.6% 2.4% 31.4%
Rubber 0.0% 8.8% 0.0% 0.6%
Potentially hazardous 0.1% 1.2% 0.0% 0.8%

C&D waste was primarily composed of ‘rubble – multi-material/other’ and timber (89 per cent combined). ICI waste was more heterogeneous. Paper was the largest single component, with 17 per cent of the total. Glass, mostly from a recycling processor, was the second largest component, with 16 per cent of the total. Landscaping waste was nearly 60 per cent rubble, with green waste comprising 39 per cent. The largest component of residential waste was timber (31 per cent), which included both fabricated items and C&D-type timber (residential waste can include waste from several sources, including C&D).

G4.2.4 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 G4.9 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 G4.9: General waste to disposal face, by vehicle type, 1–7 March 2008

Vehicle type No. of vehicles surveyed % of loads % of weight Tonnes/week
Cars 0 0% 0% 0
Compactors 2 1% 1% 4
Front-loader trucks 3 2% 6% 38
Gantry trucks 72 47% 41% 257
Huka trucks 0 0% 0% 0
Other trucks 72 47% 52% 321
Trailers 4 3% 1% 3
Total 153 100% 100% 624

No cars disposed of waste at the disposal face, and the only huka truck was transporting the transfer trailer from the transfer pit. Gantry trucks and other trucks each accounted for 47 per cent of general waste loads discharged at the disposal face, but other trucks accounted for 52 per cent of the total weight, compared to 41 per cent for gantry trucks.

G4.2.5 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 G4.10. The secondary composition is shown in Appendix G10.

Table G4.10: Primary composition of general waste to disposal face, by vehicle type, 1–7 March 2008

Primary category Compactor Front-loader truck Gantry truck Other truck Trailer
Paper 27.7% 22.2% 5.5% 0.5% 13.1%
Plastics 14.9% 18.9% 5.0% 0.8% 6.5%
Putrescibles 11.9% 22.0% 8.4% 34.0% 13.2%
Ferrous metals 5.0% 6.4% 6.1% 0.8% 5.5%
Non-ferrous metals 3.0% 1.0% 0.3% 0.8% 0.6%
Glass 25.7% 2.6% 7.9% 0.1% 2.0%
Textiles 3.0% 8.6% 4.3% 0.5% 1.4%
Nappies and sanitary 3.0% 7.0% 0.1% 0.0% 3.6%
Rubble 1.0% 1.5% 39.7% 53.7% 10.9%
Timber 3.0% 7.5% 22.2% 5.5% 42.2%
Rubber 1.0% 1.1% 0.2% 3.1% 0.4%
Potentially hazardous 1.0% 1.2% 0.3% 0.2% 0.6%

G4.3 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.

G4.3.1 Source of overall waste to landfill, including cover material

Weighbridge data for the survey week shows that 1833 tonnes of material were disposed of at Green Island Landfill. The proportions of the different waste types are shown in Table G4.11 and Figure G4.3.

Table G4.11: Waste types to landfill, including cover, 1–7 March 2008

Waste type % of weight Tonnes/week
Cover material 24% 444
General 34% 624
Kerbside collections 8% 151
Special 26% 467
Transfer station 8% 146
Total 100% 1833

Figure G4.3: Waste types to landfill, including cover, 1–7 March 2008

General waste was the largest category of waste discharged during the survey period, comprising 34 per cent of the total. Special waste was the second largest category, with 26 per cent of the total.

G4.3.2 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 G4.2.1

  • 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 the surveys results and shown in Section G4.1.1.

  • transfer pit – as determined from the surveys results and shown in Section G4.1.1.

The primary composition of the overall waste stream to Green Island Landfill is presented in Table G4.12 and Figure G4.4. The secondary composition is given in Appendix G11.

Table G4.12: Primary composition of overall waste, including cover, 1–7 March 2008

Primary category % of total Tonnes/week
Paper 3.4% 61
Plastics 3.0% 54
Putrescibles 20.0% 366
Ferrous metals 2.2% 40
Non-ferrous metals 0.3% 6
Glass 2.2% 41
Textiles 2.0% 36
Nappies and sanitary 0.8% 14
Rubble 47.9% 877
Timber 6.7% 124
Rubber 0.7% 12
Potentially hazardous 10.9% 200
Total 100% 1833

Figure G4.4: Primary composition of overall waste, including cover, 1–7 March 2008

Rubble, primarily material intended for use as capping, comprised nearly 50 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 20 per cent of the total. Potentially hazardous materials, primarily sewage sludge, made up 11 per cent of the total.

G4.3.3 Source of overall waste to landfill, excluding cover material

If cover materials are excluded, weighbridge data for the survey week shows that 1389 tonnes of material were disposed of at Green Island Landfill. The proportions of the different waste types are shown in Table G4.13 and Figure G4.5.

Table G4.13: Waste types to landfill, excluding cover, 1–7 March 2008

Waste type % of weight Tonnes/week
Cover material 0% 0
General 45% 624
Kerbside collections 11% 151
Special 34% 467
Transfer station 11% 146
Total 100% 1389

Figure G4.5: Waste types to landfill, excluding cover material, 1–7 March 2008

G4.3.4 Primary composition of overall waste to landfill, excluding cover material

If the calculations described in Section G4.3.2 are undertaken with cover material excluded, the primary composition of the remaining waste types combined is as shown in Table G4.14 and Figure G4.6. The secondary composition is given in Appendix G11.

Table G4.14: Primary composition of overall waste, excluding cover, 1–7 March 2008

Primary category % of total Tonnes/week
Paper 4.4% 61
Plastics 3.9% 54
Putrescibles 26.4% 366
Ferrous metals 2.9% 40
Non-ferrous metals 0.4% 6
Glass 3.0% 41
Textiles 2.6% 36
Nappies and sanitary 1.0% 14
Rubble 31.2% 433
Timber 8.9% 124
Rubber 0.9% 12
Potentially hazardous 14.4% 200
Total 100% 1389

Figure G4.6: Primary composition of overall waste, excluding cover, 1–7 March 2008

G4.4 Discussion and analysis

G4.4.1 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 G4.15.

Table G4.15: C&D waste to landfill, 1–7 March 2008

Activity source Waste to transfer pit General waste to disposal face
Construction and demolition 38 tonnes
(Table G4.2)
163 tonnes
(Table G4.7)
Total C&D waste to landfill – 201 tonnes (from above)
Overall waste to landfill, including cover – 1833 tonnes (Table G4.11)
C&D waste as proportion of overall waste to landfill, including cover – 11.0%
Overall waste to landfill, excluding cover – 1389 tonnes (Table G4.13)
C&D waste as proportion of overall waste to landfill, excluding cover – 14.5%

Table G4.15 shows that C&D waste comprised 11.0 per cent of the overall waste to landfill, if cover is included. If cover is excluded, C&D waste comprised 14.5 per cent of waste, by weight.

G4.4.2 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 1–7 March 2008 survey period, are discussed below.

G4.4.2.1 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 was the absence of disposal charges for cover material (see 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 survey period. 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. This resulted in a 48 per cent decrease in the overall waste stream being disposed of at the facility.

G4.4.2.2 Increase in general waste to disposal face

This change to gate charges has also resulted in an increase in general waste discharged at the disposal face. The quantity of general waste is calculated by analysing the product names in the weighbridge records and assigning a designation of special, general or cover material to each product name (see Appendix G2).

The designation of each product name was determined during the analysis of the first survey, and has been done consistently for the second and third surveys. During the first survey waste loads identified by the weighbridge as ‘Clean (Dry)’ and ‘Veg to shredder’ were classified as general waste because many loads contained significant quantities of waste materials other than rubble and vegetation.

Between the second and third surveys, after the introduction of gate charges for cover material, the quantity of waste materials identified by the weighbridge as being ‘Clean (Dry)’ and ‘Veg to shredder’ increased from 66 tonnes for the survey week to 348 tonnes, resulting in a concomitant change in the quantity of general waste, as defined for the surveys. A high proportion of this waste was assessed by the surveyor as originating from landscaping and earthworks activity, and the total for that activity increased substantially for the third survey.

This increase in waste material categorised as ‘Clean (Dry)’ and ‘Veg to shredder’ is more likely to be the result of the weighbridge operators classifying loads differently after the introduction of charges for cover material rather than an actual change in the waste stream.

G4.4.2.3 University term

The 1–7 March 2008 surveys occurred shortly after the start of the first semester at the University of Otago.15 As approximately 20,000 students are enrolled at the University (out of an overall population in Dunedin of 120,000)16 it is expected that waste volumes would be higher during university semesters, when more students are resident in Dunedin.

G4.4.2.4 Weather before and during the survey period

February rainfall was 50 per cent or less of normal in coastal Otago. As a result, severe soil moisture deficits persisted in Otago and Southland.17 This is likely to have slowed vegetation growth, and to have resulted in less green waste disposal than normal at this time of year.

On Saturday 1 March and Sunday 2 March the weather was cold, with persistent, heavy rain. This weather is likely to be associated with the lower number of vehicles discharging waste at the transfer pit compared to the previous surveys.

G4.4.2.5 Economic conditions

Economic activity showed generally favourable indicators in Otago, with the region experiencing a 2.8 per cent growth in the year to December 2007. The National Bank’s Regional Trends18 for February 2008 reads as follows:

Real estate figures for Otago recorded an improvement in December. The number of farm sales increased 23 percent, house sales increased 13 percent and lifestyle blocks rose 7 percent. The number of commercial construction consents increased 17 percent, three times the 5.4 percent rise recorded nationally. Employment rose 2.3 percent – double the 1.1 percent rise measured over the entire country. Labour market weakness was measured in a 7.9 percent drop in newspaper job advertising. Also weaker was a 3.1 percent drop in accommodation guest nights, and occupancy rates falling sharper than the national decline. Retail trade weakened 2.5 percent, contrasting a 0.3 percent rise nationwide.

The increase in commercial construction consents should result in an increase in C&D waste over the medium term, while the decrease in guest nights and the retail trade should result in reduced waste. The overall effects of these economic factors on waste disposal can not be estimated.

16 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