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Wellington “waste catchment” trial: An investigation into a new model for waste monitoring

1 Introduction

2 Identifying the Wellington waste catchment

3 Waste facilities in Wellington region

4 Analysis of landfill data 2003–2005

5 MfE source surveys

6 Effect of pricing on landfill tonnages

7 Evaluation of the waste catchment model

Appendix 1 – Special wastes – by landfill

Appendix 2 – Letter to waste operators

5 MfE source surveys

5.1 Methodology

As an adjunct to the catchment study, MfE organised for a waste source survey to be undertaken at four of the Wellington region landfills. The survey at Wainuiomata landfill was not completed in time for preparation of this report.

For each landfill survey, a surveyor was engaged for eight hours per day over a seven day period. The surveyor asked each vehicle driver questions regarding the geographical source of the waste and whether the waste had been generated by commercial or domestic activity. The vehicle licence number and, where possible, the net load weight were recorded for each vehicle. These data were entered onto a spreadsheet for further analysis.

The complete vehicle records for the survey week were obtained from each landfill weighbridge. Waste Not Consulting matched the MfE source survey records with the weighbridge records. Every vehicle load was classified as “cover material/cleanfill”, “domestic kerbside”, “general”, “special”, or “unweighed vehicle”, using the product codes in the weighbridge record as the basis for the classification.

5.2 Results of MfE source surveys

Combining the MfE source survey results with the weighbridge records provides information on the geographical source and on the domestic or commercial origin of each waste type at each landfill surveyed. This information is presented in the four sections on the following pages, and summarised in Sections 5.2.5 and 5.2.8.

All cover material/cleanfill and special waste are considered to be commercial in origin, and are excluded from that analysis. A very small proportion of cleanfill is domestic in origin, but is rarely classified “cleanfill” by the weighbridge operators. All domestic kerbside refuse is, by definition, domestic in origin and is also excluded from the analysis.

The survey at Spicer landfill was not conducted properly, and the survey results for the domestic/commercial origin are not valid. These have been excluded from the analysis.

At the landfills where greenwaste is separated and processed (Otaihanga and Southern), loads of greenwaste have been excluded from the analysis.

As the Otaihanga landfill does not have a weighbridge, the results were based on the volume of waste recorded. The results for the unweighed vehicles are based on the numbers of vehicles.

5.2.1 Otaihanga landfill

The results of the MfE source survey at Otaihanga landfill are given in Table 5.1 below and in the following figures. The calculations have been based on the volume of waste, as there is no weighbridge at the landfill.

Table 5.1 – Results of source survey at Otaihanga landfill

View results of source survey at Otaihanga landfill (large table).

The geographic source of waste disposed of at Otaihanga landfill is given in the figure below.

All of the cover material/cleanfill and domestic kerbside refuse disposed of at Otaihanga landfill originates in the Kapiti Coast area. A very high proportion, over 97% by weight, of general waste and unweighed vehicle waste also originates in the Kapiti Coast.

Just under a third of the general waste stream is domestic in origin and two-thirds is commercial. Over 80%, by weight, of waste carried by unweighed vehicles is domestic in origin and 20% is commercial.

5.2.2 Silverstream landfill

The results of the MfE source survey at Silverstream landfill are given in Table 5.2 below and in the following figures. The Silverstream survey took place from 28 June – 4 July 2006. For the first three days of the survey there was a substantial price differential between Silverstream and Southern landfills. On 1 July, Southern landfill lowered its gate charge. It is likely that this had an influence on the transport of waste from Wellington to Silverstream in the second half of the survey.

Table 5.2 – Results of source survey at Silverstream landfill

View results of source survey at Silverstream landfill (large table).

The geographic source of waste disposed of at Silverstream landfill is shown in the figure below.

All of the cover material/cleanfill and domestic kerbside refuse disposed of at Silverstream landfill originates in the Hutt area. A high proportion, over 84% by weight, of general waste and unweighed vehicle waste also originates in Hutt CityBruce MiddletonChanged on 12 april 2007. previously read from kapiti coast..

Just over a quarter (27%) of the general waste stream is domestic in origin and three-quarters is commercial. 79%, by weight, of waste carried by unweighed vehicles is domestic in origin and 21% is commercial.

5.2.3 Southern landfill

The results of the MfE source survey at Southern landfill are given in Table 5.3 below and in the following figures.

Table 5.3 – Results of source survey at Southern landfill

View results of source survey at Southern landfill (large table).

The geographic source of waste disposed of at Southern landfill is shown in the figure below.

All of the cover material/cleanfill and domestic kerbside refuse disposed of at Southern landfill originates in the Wellington area. Over 95% by weight, of general waste and 99% of unweighed vehicle waste also originates in the Wellington area.

Just under a third (32%) of the general waste stream is domestic in origin and two-thirds is commercial. 69%, by weight, of waste carried by unweighed vehicles is domestic in origin and 31% is commercial.

5.2.4 Spicer landfill

The results of the MfE source survey at Spicer landfill are given in Table 5.4 below and in the following figures. Due to an error in the surveying, information on the domestic/commercial origin is not available.

Table 5.4 – Results of source survey at Spicer landfill

View results of source survey at Spicer landfill (large table).

The geographic source of waste disposed of at Spicer landfill is shown in the figure below.

A large proportion (81%) of cover material/cleanfill disposed of at Spicer landfill originates in the Wellington area. The rest comes from Porirua. All of the domestic kerbside refuse originates in the Porirua area.

Two-thirds of general waste originates in Wellington, the remainder in Porirua. Nearly 90% of special wastes originate in Porirua, the remainder from Wellington.

Slightly more than half the waste from unweighed vehicles comes from Wellington and the rest from Porirua.

5.2.5 Summary of findings on geographic source

By combining the data from the four source surveys, the geographic source of all of the waste disposed of within the Wellington catchment can be determined. The table below contains the tonnage data from all of the landfills surveyed, broken down by geographical source. The tonnages have been taken from the weighbridge totals for the week surveyed, with the survey results being extrapolated up to that total.

The 6631 tonnes of waste during the combined survey weeks represents approximately 80% of the average weekly waste disposed of at the four landfills during 2005. The quantity of cover material/cleanfill during the survey weeks is about 50% of the average during the previous year, possibly due to the surveys being conducted during winter, when large-scale earthworks are generally not undertaken.

Table 5.5 – Geographical source of waste during survey periods – by tonne

Of the 6631 tonnes of waste material, only nine tonnes were recorded as coming from outside the catchment area of Wellington, Porirua, Hutt, and the Kapiti Coast (recognising that the exact boundary of the catchment along the Kapiti Coast has not been defined). The nine tonnes comprised two commercial loads at Spicer landfill (recorded as being partially from the Horowhenua district), four commercial loads and two unweighed vehicle loads at Otaihanga (also from the Horowhenua district), and eight unweighed vehicle loads at Silverstream landfill from Wairarapa district.

The tonnage data in Table 5.5 above is given as percentages in Table 5.6 below.

Table 5.6 – Geographical source of waste during survey periods – by percentage

Overall, the survey results showed 99.86% of the waste, by weight, disposed of at the landfills in the Wellington catchment originated within the catchment.

The absence of data from Wainuiomata landfill is not considered to have any effect on the results. The Wainuiomata landfill is geographically isolated, and any waste loads originating from outside of the catchment area would need to travel by either Otaihanga or Silverstream landfill before reaching Wainuiomata. It is considered highly unlikely that a significant quantity of refuse from outside the catchment is being disposed of at Wainuiomata landfill.

5.2.6 Comparison of survey results to population data

As waste generation is related to population, the results of the MfE source survey can be compared to population data for the Wellington region to assess the results of the survey. In Table 5.7 below, the population data from the provisional 2006 census are compared to the geographic source survey. As the survey was not undertaken at Wainuiomata landfill, for the calculations 80% of one week’s average waste generation for the landfill has been added to the total tonnage and it has been assumed that all of this waste was generated in the Hutt area (for the other landfills, the total tonnage during the survey weeks was about 80% of the average annual weekly total).

For the final column, cover material/cleanfill and special wastes have been removed from the calculations.

Table 5.7 – Comparison to % of waste generated to % of population

View comparison to % of waste generated to % of population (large table).

The total quantity of all waste categories generated in each area, as measured by the MfE source survey, closely matches each area’s proportion of the population. When cover material/cleanfill and special wastes are excluded, the proportion of domestic kerbside, general, and unweighed vehicle waste generated in each area matches even more closely the proportion of population in the area. Lower and Upper Hutt generate slightly more waste per person than the average, and Kapiti generates less. This is possibly related to the differing amount of commercial and industrial activity in each area, but could also be sampling error, recording error, or misreporting by vehicle drivers.

5.2.7 Per capita waste generation

Using the data from Table 5.5 above, per capita waste generation figures can be derived. Table 5.8 below shows the per capita generation of all waste classifications for each area. The total landfill tonnage figure for 2005 from Table 4.1 is used for the calculations.

Table 5.8 – Per capita waste generation – all waste types

View per capita waste generation – all waste types (large table).

On average, 1.16 tonnes of waste were disposed of to landfill for each person in the Wellington catchment in 2005. The rate by local authority varies markedly, from 0.755 tonnes per person in Kapiti Coast District to 1.322 tonnes per person in Wellington City.

The table below presents the 2005 waste data for the combined domestic kerbside, general, and unweighed vehicle waste categories, by local authority.

Table 5.9 – Per capita waste generation – domestic kerbside, general, unweighed vehicles wastes

On average, 0.67 tonnes of domestic kerbside, general, and unweighed vehicle waste were disposed of to landfill for each person in the Wellington catchment in 2005. The rate by local authority varies from 0.443 in Kapiti Coast District to 0.737 tonnes in Lower and Upper Hutt.

For all waste combined, Wellington produces the highest amount per capita, which is related to the quantity of cleanfill and special wastes disposed of at Southern landfill. The higher generation rate of residential, commercial, and industrial waste (the domestic kerbside, general, and unweighed vehicle waste classifications combined) in Upper and Lower Hutt is likely related to the large manufacturing base in the city.

Discussion and recommendations

Unless misreporting of geographic source by vehicle drivers was widespread, the strong correlation between population and waste tonnages indicates that the MfE source surveys have produced credible results. The possibility of deliberate misreporting must be recognised, however, particularly from commercial waste operators who might think it in their own best interest to lead landfill operators to believe that waste is of local origin.

The results indicate that the Wellington waste catchment is virtually self-contained with regards to waste generation and disposal. This is assuming that as little waste is transported out of the catchment as comes in, which would require source surveys at disposal facilities in Horowhenua and Wairarapa to determine. It is not considered likely that significant quantities of waste are currently being transported out of the catchment. In the opinion of Peter Ruddock, Waste Minimisation Officer, Waste Management Wairarapa, “We don't get any area leakage in or out of here due to our geographic isolation from the other councils”. ⁵

A potential “leakage” of waste out of the catchment is from Waste Management NZ Ltd transporting waste to its joint venture operation Bonny Glen landfill, north of Marton. Anecdotally, the company has indicated to council officers that this would be a possibility if disposal charges in the Wellington region become too high. The 150 km distance (between Porirua and Marton) would be a significant financial disincentive to this transport of waste out of the catchment.

5.2.8 Summary of findings on domestic/commercial source

During the MfE source survey, each vehicle driver was asked if the waste being transported was of either “domestic” or “commercial” origin. No definitions for the terms were provided to the vehicle drivers, so their interpretation was left to each driver.

Although all vehicle drivers were asked this question, the response is only relevant for loads of “general” waste or “unweighed vehicle” loads. All “domestic kerbside collection” loads are domestic in origin, and all “cover material/cleanfill” and “special waste” loads have been deemed to be commercial in origin.

Table 5.10 –Source of waste during MfE source survey periods

By combining the results of the MfE source survey with the summary of 2005 weighbridge data in Section 4.3, an estimate can be made of the source of the entire waste stream. The results are presented in Table 5.11 on the following page.

Table 5.11 – Domestic/commercial source of waste - 2005

View domestic/commercial source of waste - 2005 (large table).

Based on the MfE source survey results and the underlying assumptions regarding the source of the cover material/cleanfill, domestic kerbside refuse, and special classifications of waste, 28.5% of all landfill waste in the Wellington catchment is domestic in origin, and 71.5% is commercial in origin.

Discussion and recommendations

The domestic/commercial distinction in classifying refuse loads originated in the 1992 Waste Analysis Protocol and was carried through into the 2002 Solid Waste Analysis Protocol. In these documents the terms “residential” and “business” are used.

The terms are not defined in either document, and were not defined in the instructions given to the surveyors undertaking the MfE source survey. During the source survey, respondents were not given definitions for the terms. Without a specific meaning being applied to the terms, some types of waste are difficult to classify, such as waste generated by commercial landscaping firms servicing residential properties, or commercial builders working on residential properties. As a result of the indeterminate meaning for the terms, the results of the source survey must be considered of an indicative nature only.

The terms “domestic” and “commercial” can only be meaningfully applied to the general waste stream. While some special wastes, such as abattoir waste, are clearly commercial in origin, others, such as sewage sludge, are generated by both commercial and residential activities. Similarly, classifying cleanfill as either commercial or residential is of little value, particularly as a significant proportion of cleanfill is generated by infrastructural activity.

Despite these shortcomings, there is still value in gathering data on the commercial/residential split in waste generation. The distinction is easily comprehended by the public, and forms an important part of the information released for public education purposes. To be able to say, for example, that “70% of waste is generated by the commercial sector” is useful in terms of raising the sector’s awareness of waste issues.

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