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G3 Results: 1–7 December 2007

G3.1 Transfer pit in the resource recovery area

The transfer pit in the resource recovery area was surveyed on Saturday 1 December, Sunday 2 December and Friday 7 December. Only residual waste disposed of into the transfer pit was included in the survey. During this period, data on 429 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 December indicate that 215 tonnes of residual waste were transported from the transfer pit to the disposal face10 during the week. This number will be used as the basis for all further calculations relating to transfer pit tonnages.

G3.1.1 Primary composition of transfer pit waste

The primary composition of waste disposed of to the transfer pit is presented in Table G3.1 and Figure G3.1. The secondary composition, which includes all 22 categories, is given in Appendix G6.

Table G3.1: Primary composition of transfer pit waste, 1–7 December 2007

Primary category % of total
(± 95% confidence level)
Tonnes/week
Paper 7.7% (±1.1%) 17
Plastics 5.6% (±0.8%) 12
Putrescibles 16.4% (±2.8%) 35
Ferrous metals 8.8% (±1.8%) 19
Non-ferrous metals 0.4% (±0.1%) 1
Glass 3.3% (±1.2%) 7
Textiles 10.4% (±3.1%) 22
Nappies and sanitary 0.8% (±0.2%) 2
Rubble 11.9% (±3.6%) 26
Timber 33.0% (±5.1%) 71
Rubber 1.2% (±0.7%) 3
Potentially hazardous 0.4% (±0.1%) 1
Total 100%   215

Timber is the largest single component of waste being disposed of at the transfer pit, comprising 33 per cent of the total. The timber included both fabricated timber, such as furniture, and C&D waste. Putrescible material was the second largest component, at 16 per cent. This was primarily green waste and food waste in domestic refuse bags.

Figure G3.1: Primary composition of transfer pit waste, 1–7 December 2007

G3.1.2 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 G3.2 shows the percentage of loads originating from each of the activities, the percentage of total weight, and the tonnes per week.

Table G3.2: Activity source of transfer pit waste, 1–7 December 2007

Activity source No. of loads surveyed % of loads % of weight Tonnes/week
Construction and demolition 69 16% 26% 56
Industrial/commercial/institutional 42 10% 13% 28
Kerbside collections 0 0% 0% 0
Landscaping and earthworks 60 14% 15% 33
Residential 258 60% 45% 97
Special 0 0% 0% 0
Transfer station 0 0% 0% 0
Total 429 100% 100% 215

Residential activity was responsible for generating the highest proportion of loads – over 60 per cent of the total – although the loads accounted for less than half of the total weight. C&D, ICI and landscaping loads all comprised similar proportions of the total (between 10 and 16 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.

G3.1.3 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 G3.3. The secondary composition is shown in Appendix G6.

Table G3.3: Primary composition of transfer pit waste, by activity source, 1–7 December 2007

Primary category C&D ICI Landscaping Residential
Paper 2.8% 13.7% 2.7% 10.5%
Plastics 2.4% 8.1% 2.2% 7.8%
Putrescibles 2.7% 7.6% 59.6% 12.1%
Ferrous metals 4.6% 9.2% 1.7% 13.6%
Non-ferrous metals 0.1% 0.4% 0.0% 0.7%
Glass 1.6% 5.5% 0.8% 4.5%
Textiles 0.4% 18.9% 1.6% 16.7%
Nappies and sanitary 0.0% 0.8% 0.2% 1.5%
Rubble 25.1% 2.5% 20.8% 3.9%
Timber 59.9% 29.2% 9.3% 26.6%
Rubber 0.0% 3.3% 0.9% 1.4%
Potentially hazardous 0.2% 0.7% 0.1% 0.6%

C&D waste was primarily (85 per cent) composed of timber and rubble. 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. Textiles was the second largest component of ICI waste, and included several large loads of used carpets and underlay. Landscaping waste was 60 per cent green waste, with rubble (mainly soil) comprising another 21 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).

G3.1.4 Transfer pit waste, by vehicle type

For each vehicle load of waste disposed of at the transfer pit, the vehicle type was recorded. Table G3.4 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 G3.4: Transfer pit waste, by vehicle type, 1–7 December 2007

Vehicle type No. of loads surveyed % of loads % of weight Tonnes/week
Cars 141 33% 10% 21
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 6 1% 4% 8
Trailers 282 66% 86% 186
Total 429 100% 100% 215

Two-thirds of the loads disposed of at the transfer pit were carried by trailers, and these trailer loads accounted for 86 per cent of the total weight. Although cars accounted for 33 per cent of vehicle loads, due to the small size of car loads they accounted for only 10 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.

G3.1.5 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 G3.5. The secondary composition is shown in Appendix G6.

Table G3.5: Primary composition of transfer pit waste, by vehicle type, 1–7 December 2007

Primary category Car Other truck Trailer
Paper 18.7% 7.6% 6.5%
Plastics 10.8% 8.3% 4.9%
Putrescibles 29.4% 6.7% 15.3%
Ferrous metals 5.5% 15.1% 9.0%
Non-ferrous metals 0.8% 0.7% 0.4%
Glass 5.8% 4.5% 3.0%
Textiles 8.2% 16.4% 10.4%
Nappies and sanitary 3.7% 0.0% 0.5%
Rubble 4.1% 2.9% 13.1%
Timber 11.3% 35.7% 35.4%
Rubber 1.2% 1.8% 1.2%

Potentially hazardous

0.5%

0.5%

0.4%

G3.2 Disposal face

The disposal face was surveyed from Monday 3 December to Thursday 6 December 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 G3.3.

The data collected in the survey from the 136 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 401 tonnes of general waste were disposed of at the disposal face. A greater quantity of cover material (based on the weighbridge product names in Appendix G2) than general waste was also disposed of at the disposal face during the survey, but these loads have been excluded from this analysis. Cover material is included in the analysis of the overall waste stream to landfill in Section G3.3.

G3.2.1 Primary composition of general waste to disposal face

The primary composition of general waste disposed of at the disposal face is presented in Table G3.6 and Figure G3.2. The secondary composition, which includes all 22 categories, is given in Appendix G7.

Table G3.6: Primary composition of general waste to disposal face, 1–7 December 2007

Primary category % of total
(± 95% confidence level)
Tonnes/week
Paper 8.7% (±4.0%) 35
Plastics 5.5% (±2.4%) 22
Putrescibles 14.1% (±4.1%) 57
Ferrous metals 3.3% (±1.1%) 13
Non-ferrous metals 0.4% (±0.2%) 2

Glass

7.6%

(±5.4%)

30

Textiles

2.5%

(±1.1%)

10

Nappies and sanitary

0.8%

(±0.6%)

3

Rubble

39.3%

(±12.7%)

158

Timber

15.8%

(±5.0%)

63

Rubber

1.7%

(±1.6%)

7

Potentially hazardous

0.3%

(±0.2%)

1

Total

100%

 

401

Rubble is the largest single component of general waste being disposed of at the disposal face, with 39 per cent of the total. Rubble comprised a substantial proportion of both C&D waste and landscaping waste.

Figure G3.2: Primary composition of general waste to disposal face, 1–7 December 2007

G3.2.2 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 G3.7 shows the percentage of loads originating from each of the activities, the percentage of total weight, and the tonnes per week.

Table G3.7: Activity source of general waste to disposal face, 1–7 December 2007

Activity source No. of loads surveyed % of loads % of weight Tonnes/week
Construction and demolition 34 25% 26% 103
Industrial/commercial/institutional 43 32% 40% 161
Kerbside collections 0 0% 0% 0
Landscaping and earthworks 37 27% 27% 107
Residential 22 16% 8% 31
Special 0 0% 0% 0
Transfer station 0 0% 0% 0
Total 136 100% 100% 401

ICI activity generated the highest number of loads and the highest percentage of the total weight. C&D and landscaping generated similar proportions of the loads of general waste to the disposal face (25 to 27 per cent) and a similar proportion of the total weight. Residential activity generated 16 per cent of the loads, which accounted for 8 per cent of the total weight. By definition the other three activity sources are not included in the general waste stream.

G3.2.3 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 G3.8. The secondary composition is shown in Appendix G7.

Table G3.8: Primary composition of general waste to disposal face, by activity source, 1–7 December 2007

Primary category C&D ICI Landscaping Residential
Paper 0.6% 20.1% 0.3% 4.9%
Plastics 1.7% 11.8% 0.2% 2.9%
Putrescibles 2.7% 10.0% 29.3% 20.5%
Ferrous metals 3.5% 3.5% 0.2% 12.9%
Non-ferrous metals 0.1% 0.8% 0.0% 0.8%
Glass 0.1% 18.6% 0.0% 1.3%
Textiles 0.5% 3.8% 0.1% 10.1%
Nappies and sanitary 0.0% 2.0% 0.0% 0.2%
Rubble 57.0% 14.0% 68.8% 10.7%
Timber 33.7% 10.7% 0.9% 34.6%
Rubber 0.0% 4.1% 0.0% 0.5%
Potentially hazardous 0.1% 0.5% 0.0% 0.6%

C&D waste was primarily (90 per cent) composed of ‘rubble – multi-material/other’ and timber. ICI waste was more heterogeneous. Paper was the largest single component, with 20 per cent of the total. A significant proportion of the paper was waste from the kerbside recycling process. Landscaping waste was nearly 70 per cent soil, with green waste comprising 29 per cent. The largest component of residential waste was timber (35 per cent), which included both fabricated items and C&D-type timber.

G3.2.4 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 G3.9 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 G3.9: General waste to disposal face, by vehicle type, 1–7 December 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% 10% 40
Gantry trucks 72 53% 50% 200
Huka trucks 0 0% 0% 0
Other trucks 55 40% 40% 159
Trailers 4 3% 1% 3
Total 136 100% 100% 401

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, which accounted for 50 per cent of the total weight. Other trucks, primarily tip trucks, accounted for 40 per cent of vehicle loads and 40 per cent of the total weight.

G3.2.5 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 G3.10. The secondary composition is shown in Appendix G7.

Table G3.10: Primary composition of general waste to disposal face, by vehicle type,
1–7 December 2007

Primary category Front-loader truck Gantry truck Other truck Trailer
Paper 18.4% 12.9% 1.0% 5.5%
Plastics 18.4% 5.6% 2.1% 7.0%
Putrescibles 23.2% 13.1% 12.5% 45.0%
Ferrous metals 5.6% 3.7% 1.8% 31.5%
Non-ferrous metals 1.1% 0.6% 0.1% 0.5%
Glass 6.9% 13.7% 0.2% 1.5%
Textiles 8.0% 1.9% 1.7% 2.0%
Nappies and sanitary 6.0% 0.1% 0.4% 5.0%
Rubble 3.2% 28.0% 63.4% 0.5%
Timber 7.1% 20.2% 12.7% 0.5%

Rubber

1.1%

0.1%

3.9%

0.5%

Potentially hazardous

1.1%

0.2%

0.2%

0.5%

G3.3 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.

G3.3.1 Source of overall waste to landfill, including cover material

Weighbridge data for the survey week shows that 3517 tonnes of material were disposed of at Green Island Landfill. The proportions of the different waste types are shown in Table G3.11 and Figure G3.3.

Table G3.11: Waste types to landfill, including cover, 1–7 December 2007

Waste type % of weight Tonnes/week
Cover material 70% 2462
General 11% 401
Kerbside collections 4% 143
Special 8% 295
Transfer station 6% 216
Total 100% 3517

Figure G3.3: Waste types to landfill, including cover material, 1–7 December 2007

70 per cent 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 4 and 11 per cent of the total.

G3.3.2 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 G3.2.1

  • 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 the surveys results and shown in Section G3.1.1.

  • transfer pit – as determined from the surveys results and shown in Section G3.1.1.

The primary composition of the overall waste stream to Green Island Landfill is presented in Table G3.12 and Figure G3.4. The secondary composition is given in Appendix G8.

Table G3.12: Primary composition of overall waste, including cover, 1–7 December 2007

Primary category % of total Tonnes/week
Paper 2.1% 72
Plastics 1.5% 53
Putrescibles 7.5% 263
Ferrous metals 1.1% 39
Non-ferrous metals 0.1% 4
Glass 1.3% 47
Textiles 1.0% 35
Nappies and sanitary 0.4% 14
Rubble 77.2% 2716
Timber 3.9% 135
Rubber 0.3% 9
Potentially hazardous 3.6% 128

Total

100%

3517

Figure G3.4: Primary composition of overall waste, including cover, 1–7 December 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 categories of material comprised 7 per cent or less each, of the total.

G3.3.3 Source of overall waste to landfill, excluding cover material

If cover materials are excluded, weighbridge data for the survey week shows that 1055 tonnes of material were disposed of at Green Island Landfill. The proportions of the different waste types are shown in Table G3.13 and Figure G3.5.

Table G3.13: Waste types to landfill, excluding cover, 1–7 December 2007

Waste type % of weight Tonnes/week
Cover material 0% 0
General 38% 401
Kerbside collections 14% 143
Special 28% 295
Transfer station 21% 216
Total 100% 1055

Figure G3.5: Waste types to landfill, excluding cover material, 1–7 December 2007

G3.3.4 Primary composition of overall waste to landfill, excluding cover material

If the calculations described in Section G3.3.2 are undertaken with cover material excluded, the primary composition of the remaining waste types combined is as shown in Table G3.14 and Figure G3.6. The secondary composition is given in Appendix G8.

Table G3.14: Primary composition of overall waste, excluding cover, 1–7 December 2007

Primary category % of total Tonnes/week
Paper 6.8% 72
Plastics 5.0% 53
Putrescibles 24.9% 263
Ferrous metals 3.7% 39
Non-ferrous metals 0.4% 4
Glass 4.5% 47
Textiles 3.3% 35
Nappies and sanitary 1.4% 14
Rubble 24.0% 254
Timber 12.8% 135
Rubber 0.9% 9
Potentially hazardous 12.1% 128
Total 100% 1055

Figure G3.6: Primary composition of overall waste, excluding cover, 1–7 December 2007

G3.4 Discussion and analysis

G3.4.1 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 G3.15.

Table G3.15: C&D waste to landfill, 1–7 December 2007

Activity source Waste to transfer pit General waste to disposal face
Construction and demolition 56 tonnes
(Table G3.2)
103 tonnes
(Table G3.7)
Total C&D waste to landfill – 159 tonnes (from above)
Overall waste to landfill, including cover – 3517 tonnes (Table G3.11)
C&D waste as proportion of overall waste to landfill, including cover – 4.5%
Overall waste to landfill, excluding cover – 1055 tonnes (Table G3.13)
C&D waste as proportion of overall waste to landfill, excluding cover – 15.1%

Table G3.15 shows that C&D waste comprised 4.5 per cent of the overall waste to landfill, if cover is included. If cover is excluded, C&D waste comprised over 15.1 per cent of waste, by weight.

G3.4.2 Factors affecting waste generation and disposal during the 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 December 2007 survey period, are discussed below.

G3.4.2.1 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.

G3.4.2.2 University term

The 1–7 December 2007 surveys occurred after completion of the second semester at the University of Otago.11 As approximately 20,000 students are enrolled at the University (out of an overall population in Dunedin of 120,000)12 it is expected that waste volumes would be lower between university semesters, when fewer students are resident in Dunedin. Significant quantities of waste at the transfer pit appeared to be from young people disposing of furniture and personal effects.

G3.4.2.3 Weather before and during the survey period

The weather during the survey period was mainly fine and warm, with a few scattered showers on the weekend. November 2007 was extremely dry in many regions, especially in the South Island, with totals of less than 10 mm throughout much of Nelson, Marlborough and Central Otago. The second half of November was very dry and very warm, with little rainfall in many areas.13 The soil moisture deficits may have resulted in changes to stock management. A considerably greater amount of wool scour was disposed of at Green Island during the December 2007 compared to the August 2007 survey, but this is likely to be a seasonal variation rather than directly attributable to specific weather conditions.

G3.4.2.4 Economic conditions

Economic activity showed generally favourable indicators in Otago during the September 2007 quarter, the most recent quarter for which information is available.

Otago recorded the largest increase in the number of residential dwelling approvals issued in September (up 5.5 percent), contrasting a 6.8 percent fall nationally. Farm indicators strengthened. New tractor registrations increased 19 percent in the three months to September; and rural real estate sales increased, underpinned by a 29 percent lift in the number of large farm sales. Residential real estate sales dropped (down 15 percent) but the decline wasn’t as extreme as the nationwide decline (-19 percent). Retail sales lifted 1.4 percent, compared to a modest 0.2 percent rise nationally. Business confidence was below the national benchmark but consumers were marginally more optimistic than their nationwide counterparts.14

The overall effect of this level and type of economic activity on waste generation can not be determined.

10 Weighbridge product name: Domestic solid waste – transfer trailer.

12 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