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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

4 Analysis of landfill data 2003–2005

4.1 Methodology

As all of the landfills in the Wellington catchment are owned by local district authorities, an initial request for historical landfill data was made to the relevant council officers. A summary of all data from the three calendar years 2003–2005 was requested. After the landfill data were received, several requests for further information and clarification were made to the officers.

A significant proportion of the domestic kerbside refuse is collected by commercial waste operators, rather than by councils, and this refuse is not separately identified in the landfill weighbridge records. To gather data on commercial domestic kerbside refuse collections, a letter requesting tonnage data was sent to all identified commercial operators. The purpose of the letter was twofold:

1. to complete the dataset on the total quantity of domestic kerbside refuse collected in the region
2. to gauge the reaction of the commercial waste operators to a request to voluntarily supply this information.

A copy of the letter sent to the commercial waste operators is included in Appendix 2.

Analysis of all of the weighbridge records showed that there were enough similarities in the waste categories to allow the following five classifications to be differentiated from each dataset:

1. Cover material and cleanfill

2. Domestic kerbside collection

3. General waste

4. Special waste

5. Unweighed vehicles.

Although the precise parameter for each may vary slightly from landfill to landfill, as long as each landfill is consistent from year to year, the system of waste classification would be appropriate for waste catchment monitoring over time.

Section 4.2 contains a summary of the analysis of weighbridge records for the years 2003–2005. Further analysis of each waste classification is presented in the sections that follow. Each section is ended by a discussion of the results and their relation to the use of the waste catchment concept for long-term solid waste monitoring.

4.2 Summary of weighbridge data 2003–2005

Table 4.1 below combines the historical data from the six landfills for each of the individual waste classifications. As will be discussed in subsequent sections, the general waste stream and the domestic kerbside refuse collection are inter-related, in that a significant proportion of private domestic collections are classified by landfill weighbridges as general refuse. Similarly, the waste carried by unweighed vehicles does not represent a separate waste stream to the general refuse stream. For these reasons, a subtotal of domestic kerbside refuse, general waste, and unweighed vehicles is included in the table.

Table 4.1 – Summary of Wellington catchment weighbridge data 2003–2005

The total tonnage of waste to landfill shows, over the short period analysed, a marked degree of volatility, increasing 12% between 2003 and 2004, and then decreasing by 12% between 2004 and 2005.

This volatility is primarily the result of volatility in the quantity of cover material/cleanfill being disposed of to landfill. Cover material/cleanfill increases 26% between 2003 and 2004, then decreases 31% between 2004 and 2005.

The domestic kerbside refuse, unweighed vehicles, and general waste streams are much more regular, varying a maximum of less than 5% from year to year. Combined, these waste streams increased 3.7% between 2003 and 2004, then decreased 0.5% between 2004 and 2005.

4.3 Analysis of weighbridge data – by waste classifications

4.3.1 Cover material and cleanfill

Each of the landfill weighbridges in the Wellington catchment uses classifications to identify cleanfill and/or cover materials. Some of these classifications relate to specific customers, and others are used for charging purposes, as cleanfill disposal is generally charged at a lower rate than other materials.

The classifications from each landfill that were included in this analysis as “cover material and cleanfill” are as follows:

• Northern and Southern landfills – “cleanfill” (various rates and attributed to various customers), “imported cover”

• Otaihanga landfill – “clean fill”

• Silverstream landfill – “sawdust no charge” (used as a cover material)

• Spicer landfill – “cleanfill” and “concrete and demolition/roading material/cover”

• Wainuiomata – “sawdust no charge” (used as a cover material).

Not all cleanfill that is weighed into the landfills is disposed of at the tip face. An unknown proportion is used for construction purposes on the site, such as road building and bund construction.

The historical weighbridge data for cover material and cleanfill for each of the landfills in the Wellington catchment is presented in the table below.

Table 4.2 – Cover material and cleanfill tonnages 2003–2005

The quantity of cover material and cleanfill disposed of varies considerably from year to year. The total for 2004 is 26% greater than that for 2003, while the total for 2005 is 13% less than that for 2003.

There are several plausible factors involved in the annual variation of the quantity of cover material and cleanfill disposed of at landfills in the Wellington catchment. Cleanfill generation is often associated with construction projects, and the quantity of cleanfill generated will vary considerably from project to project. The number, type, and size of construction projects can vary from year to year, resulting in greater annual variation than for other types of waste.

As well as landfills, cleanfill may also be disposed of at cleanfill sites, for which there are no data available. As cleanfill sites are not regulated as stringently as landfills, the gate charge at cleanfill sites is usually lower than at landfills. The annual variation in tonnages disposed of at landfills may be due to a variation in the market share of the landfills compared to the cleanfills, with a higher proportion being disposed of at landfills in some years than in others, depending on gate charges.

Discussion and recommendations

The separation of the cover material/cleanfill classification of waste from the other waste classifications is, perhaps, the single most important step in understanding waste flows within a catchment over time. Due to its magnitude (about 30% of the Wellington catchment waste), variability over time, and the availability of alternative disposal pathways, cover material/cleanfill data obfuscate all combined waste data, and make the data worthless for monitoring waste data at the level of precision needed for assessing the effects of government policy.

The separation of cover material/cleanfill data is also of importance as the Government has set specific targets for the reduction of construction and demolition (C&D) wastes in the NZWS, and cleanfill comprises a significant proportion of C&D wastes. The type of data generated during this research is not sufficient for monitoring C&D waste. Significant quantities of C&D waste are disposed of at cleanfill sites and at landfills as “general” waste. These materials could be quantified using visual assessment surveys at the facilities. Conversely, while a significant proportion of cleanfill is composed of C&D waste, an indeterminate quantity is derived from infrastructure work.

It is recognised that the inclusion of cover material as a waste is a potentially contentious decision. However, it is not possible, in most instances, to use weighbridge records to distinguish between cleanfill that is needed for cover material and that which is not.

This research has been unable to address the issue of disposal of non-cleanfill material at cleanfill sites. Compared to the overall waste being disposed of to landfill, it is not likely to be significant, but further research is needed for this to be determined.

Domestic kerbside refuse collection

Council domestic kerbside collections are clearly delineated in the weighbridge data summaries from Spicer and Wainuiomata landfills. In the initial summary of data from Northern and Southern landfills, the council domestic kerbside collection tonnage was included in the “general” classification. A separate record of council domestic kerbside collection tonnages was made available by the weighbridge administrator. At Otaihanga landfill, the Council collection is included in a “compactor” classification, which also includes waste from the Otaki transfer station.

At Silverstream landfill, a “Refuse collections” category includes vehicles that simultaneously collect the bagged Council collection and private wheelie bins, so it is not possible to identify the Council collection.

An unknown quantity of domestic kerbside refuse is collected by private waste operators. This waste is classified as “general” waste in all of the weighbridge records, and cannot be separated out from the data summaries provided. A letter was sent to each of the waste operators requesting tonnage data on domestic kerbside refuse, but no replies were received (a copy of the letter is in Appendix 2).

In a 2005 report to MfE (Desktop Survey of Packaging Waste to Landfill), Waste Not Consulting, by using data from a range of local authorities, calculated an average disposal rate for domestic kerbside refuse of 167 kg/person/annum. Combining this figure with the provisional results of the 2006 census, Table 4.3 below compares the expected total (council and private collections) tonnage of domestic kerbside refuse with the 2005 tonnage of domestic kerbside refuse collected by the councils in the region.

Table 4.3 – Analysis of domestic kerbside refuse tonnages

The weighbridge data for domestic kerbside refuse collection represent a high proportion of the estimated quantity generated in Kapiti Coast District and in Hutt City (around 85%), but a much smaller proportion of the market in Porirua and Wellington (less than 40%). In Hutt City, the proportion is high because the data include vehicles that transport both the Council bagged collection and a private wheelie bin service. Several small private operators collect the remainder of the refuse generated. In Wellington and Porirua, the data indicate that the council collections comprise less than a 40% share of the domestic kerbside refuse collection market.

These factors must be taken into consideration when assessing the historic weighbridge records for domestic kerbside refuse. Data from 2003–2005 for each landfill are presented in the table below.

Table 4.4 – Domestic kerbside refuse tonnages 2003–2005

The combined data for all landfills shows a 4% increase in domestic kerbside refuse disposal between 2003 and 2004, followed by a decrease in 2005 to 1.1% below the 2003 figure.

These figures could be indicative of changes in domestic kerbside refuse generation by households during this time period. However, as it has been estimated that these figures include only about 60% of the total amount of domestic kerbside refuse that is generated in the region, it cannot be assumed that these changes are not related to variations in the market share held by council collections compared to the private waste operators.

Discussion and recommendations

Without reliable data on domestic kerbside refuse disposal from the private waste operators, currently there is limited value in the data on council domestic kerbside refuse collections. However, as licensing of waste operators by local authorities and the reporting of waste tonnages as a condition of licensing becomes more widespread, the required data are likely to be provided more readily by the waste operators. At 167/kg/person/annum, domestic kerbside refuse comprises about a quarter of the combined domestic kerbside/general/unweighed vehicle waste stream. As such, it is worthwhile separating the data to obtain a better understanding of changes in that waste stream.

In addition, reduction of the domestic kerbside refuse is a priority for many local authorities. It is the waste stream householders are most familiar with, and it is one of the few for which local authorities are able to provide effective waste minimisation measures. Establishing a national waste monitoring programme based on waste catchments would, in time, provide data on domestic kerbside refuse that would be beneficial to local authorities.

4.3.3 General waste

Five of the six landfills studied used “general waste” as a weighbridge category. The Otaihanga landfill data that were provided included a “cubic metre standard rate” category, which fulfils the same function. The Otaihanga data were converted from volume to weight data for the analysis.

Table 4.5 – General refuse tonnages 2003–2005

The data indicate that general refuse tonnages rose 4.3% between 2003 and 2004, and then a further 1.6% in 2005.

Within this overall pattern of relative stability, there is considerable change at the individual landfills. With the closure of Northern landfill imminent, in September 2004 Wellington City Council altered gate charges at Northern and Southern landfills to increase the differential between the two (from Southern costing $15.50/tonne more than Northern to $29.30/tonne more) to encourage more waste to be disposed of at Northern. The combined tonnages are shown in the table below.

Table 4.6 – General refuse tonnages 2003–2005 Northern and Southern combined

The combined tonnage at Northern and Southern decreases 7% between 2003 and 2004, and then a further 3% between 2004 and 2005. There is much less volatility when the two landfills are examined as a single functional unit rather than as individual facilities.

Discussion and recommendations

General waste is the largest single waste strata, comprising nearly 40% of all waste to landfill in the Wellington catchment. As the name implies, “general” waste comprises waste from a wide range of sources. It includes industrial, commercial, and institutional waste as well as residential and domestic kerbside refuse carried by commercial waste operators. Other landfill and transfer station studies by Waste Not Consulting (in 2005 “Waste Composition and Construction Waste Data” report to MfE) indicate that C&D waste commonly comprises approximately 30% of the general waste stream.

“Waste minimisation” is one of the three priority waste areas in the NZWS. While the targets for waste minimisation in the NZWS address capacity-building, rather than specific waste streams, it is the general waste stream that will be most significantly affected by businesses and local authorities meeting the targets. Monitoring the general waste stream is crucial to determining the success of waste minimisation initiatives related to these targets.

The three specific waste streams identified in the NZWS in relation to waste minimisation are organic wastes, special wastes, and C&D waste. A significant proportion of these waste streams, as described in the NZWS, would be classified as “general” waste in the classification system used in this report. A more detailed understanding of the general waste stream than is provided in this report is needed to monitor the NZWS targets for these specific waste streams.

A framework for achieving this more detailed understanding is outlined in the 2005 “Waste Composition and Construction Waste Data” report to MfE. The framework involves surveys based on both visual assessment of loads (including classification into specific waste types such as “residential”, “commercial”, and “C&D”) and SWAP sort and weigh audits for minor waste components, such as e-waste.

The general waste stream may be more closely tied to economic activity and conditions than the other waste classifications. While some waste streams, such as domestic kerbside refuse and sewage sludge, are likely to be generated at substantially the same rate regardless of economic activity, the commercial, industrial, and C&D component of the general waste stream may be more closely tied. Further research, using an appropriate indicator of economic activity, such as GDP per capita, would establish any underlying relationship.

4.3.4 Special wastes

While there is no specific legal definition for “special wastes”, the NZWS defines “special waste” as “…wastes that cause particular management and/or disposal problems and need special care. Examples include used oil, tyres, end-of-life vehicles, batteries and electronic goods”.

These criteria did not form the basis for classifying “special wastes” for this project. “Special wastes” have been labelled as such when analysing the weighbridge records on the basis of being significant, identifiable waste streams, usually from a single generator. Although many of the waste streams that have been classified as “special wastes” do require particular management techniques due to environmental considerations, this was not an over-riding consideration.

Examples of “special wastes” are lead slag from GNB Battery Technologies, a battery recycler, sewage sludge from wastewater treatment plants in the region, contaminated soils, Taylor Preston abattoir waste, and slip waste, from the cleanup after the 2004 floods in the Hutt Valley. A complete list of the weighbridge categories that have been classified as “special waste” is contained in Appendix 1.

The historical weighbridge data for special wastes for each of the landfills in the Wellington catchment is presented in the table below. No special wastes were identified at either Northern landfill or Otaihanga landfill.

Table 4.7 – Special wastes 2003–2005

While some of the special wastes listed in Appendix 1 are constant over time, such as sewage sludges, others are from one-off events, such as the 11,563 tonnes of slip waste disposed of at Silverstream landfill in 2004.⁴ Still others, particularly industrial waste streams, vary markedly from year to year.

Despite these differing profiles, the total tonnage of special wastes is relatively consistent over the period analysed. There is an 11% increase between 2003 and 2004, due largely to the slip waste disposed of at Silverstream. The tonnage remains constant from 2004 to 2005. The absence of the slip waste at Silverstream in 2004 is balanced by a large amount of contaminated soil disposed of at Southern landfill in 2005.

Discussion and recommendations

Composed as it is of waste from a relatively small number of waste generators, the special wastes classification would be expected to exhibit a higher degree of volatility than waste streams arising from a large number of generators, such as general waste. For this reason it is important that these individual waste streams be considered separately in order that underlying patterns in the other classifications can be more readily discerned.

The number and types of waste streams that were classified as “special wastes” varied markedly from landfill to landfill. This was primarily due to the level of detail of the weighbridge records that were supplied by the landfill operator for this project. For the most part, “special wastes” could not be separated from other waste streams at landfills that supplied records at a more general level. It is recommended that, in future, landfill records at the most detailed level possible be used for catchment analysis.

4.3.5 Unweighed vehicles

All of the landfills in the Wellington catchment use a range of weighbridge categories to classify smaller vehicle loads entering the facilities. These commonly include combinations of categories for cars, utilities, vans, trailers of different sizes, and different types of materials, such as greenwaste.

These categories are commonly used as the basis for disposal charges, as at most facilities small loads are not weighed, and are charged at a flat fee based on load type rather than on a tonnage basis. Southern landfill is the exception, and all vehicle loads are now weighed. Most disposal facilities use an average load weight (or volume at Otaihanga landfill) for each classification to calculate disposal tonnages.

Table 4.8 – Unweighed vehicles 2003–2005

The tonnage carried by unweighed vehicles increased 2% between 2003 and 2004, then decreased 4% between 2004 and 2005. The MfE source survey shows that the majority of this waste is residential in origin (see Section 5.2.8). Changes in the tonnage figures from year to year do not necessarily relate to actual changes in waste generation or disposal. These figures are measuring the transport of relatively small quantities of waste in small vehicles that are not weighed at weighbridges and, as such, these figures are actually measuring the preferred means of transport of small quantities of waste. The quantity of waste transported in small loads depends on factors such as the rate of trailer ownership and the propensity of individuals or organisations to transport their own waste rather than have it done by a commercial waste operator.

Discussion and recommendations

Waste transported to landfill in small quantities in unweighed vehicles represents approximately 10% of all waste to landfill in the Wellington catchment. It is composed of residential waste transported by householders and commercial waste from small waste generators. Very little, if any, is carried by commercial waste operators.

Statistically separating waste transported by unweighed vehicles from other waste streams is potentially useful because many local authorities are attempting to reduce this waste through the introduction of separate disposal areas at transfer stations for different materials. Small loads, transported by the waste generator, are more likely to use these facilities than commercial waste operators, hauling large, heterogeneous loads. The effectiveness of these waste minimisation measures can best be judged by monitoring waste from unweighed vehicles and the quantities of materials recovered.

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