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End-of-Life Tyre Management: Storage Options

1 Introduction

2. Research Methodology

3. End-of-life Tyre Properties

4. Overview of Potential Impacts of Tyre Storage

5. Potential Environmental Impacts of Tyre Leachate

6. Potential Environmental Impact of Uncontrolled Tyre Fires

7. Potential Financial Risks Associated with Tyre Storage

8. Review of Best Practice on Tyre Storage

9. Conclusions

Appendix A: References

8. Review of Best Practice on Tyre Storage

8.1 Introduction and Definitions

The main focus of this section is on current best practice of short to medium term tyre storage. The following definitions were developed for the purpose of reading this report:

• end-of-life tyre: a used tyre that is not reused for its originally intended purpose and is not retreaded. End-of-life tyres will be referred to as 'tyres'
• temporary storage: short to medium term storage of end-of-life tyres with an intent of future reuse or reprocessing. The most common form of temporary storage for large volumes of tyres is in outdoor tyre stockpiles that are typically uncovered
• disposal: permanent disposal of end-of-life tyres. Disposal options for end-of-life tyres include a sanitary landfill (that receives other solid waste) and a tyre monofill [Centre for Advanced Engineering (2000)"Landfill Guidelines".]
• tyre monofill: essentially a sanitary landfill, or portion of a landfill, that receives only end-of-life tyres. The landfill has an appropriate liner, cover, leachate collection system and monitoring system. [Ibid.]

This section outlines best practice with regard to establishing and operating a new storage facility, rather than best practice for existing tyre storage sites. Existing tyre storage sites could be assessed by constructing a site model and comparing the existing site model to best practice standards. Existing sites could be classed as high, moderate or low risk, with high risk sites requiring intensive ongoing monitoring and low risk sites requiring ongoing monitoring considered to be best practice for new tyre storage facilities.

8.2 Legal Matters

Rules for the management of end-of-life tyres are obligatory in a number of countries. In the United States end-of-life tyres are managed primarily at state level, with about 48 states having laws or regulations specifically dealing with the management of end-of-life tyres. In the United Kingdom end-of-life tyres are managed primarily under the provisions of the Environmental Protection Act 1990. A detailed review of legislation or compliance monitoring was not included in this investigation.

8.3 Collection and Transport of Tyres

In the United Kingdom and in most states of the United States, end-of-life tyres must be collected and hauled by approved companies and can only be deposited at approved facilities for disposal or reprocessing. At least in the United States, there is a manifest system that must be completed to allow state regulatory authorities to track the movement of end-of-life tyres. A detailed review of the collection and transport of tyres was not included in this investigation.

8.4 Temporary Storage of Tyres

8.4.1 Information sources

End-of-life tyres can be stored temporarily in outdoor tyre stockpiles. The majority of technical information obtained during this study that specifically addresses the design and operation of tyre stockpiles refers to guidelines published by IAFC, STMC and NFPA in the United States. There is a guideline produced by the United Kingdom Environmental Agency; however this has not been obtained.

The Basel Convention [Ibid.] recommends that tyres should only be stored in stockpiles temporarily, prior to reprocessing. While the Basel Convention does not give a time frame for storage, tyre facilities in the United States are only allowed to store the number of tyres that they can process within a month (30 days). [Personal communication2, Michael Playdon, Columbus McKinnon, February 2004.] However there is a continual flux of tyres through the facilities, so the guidelines from the United States should go some way to minimising environmental impacts of tyre storage.

8.4.2 Design of a facility

Issues to consider during design and operation of an above ground tyre stockpile storage facility, based on literature reviewed during this study, include:

• site selection
• fire prevention and minimisation of fire spread, eg, prevent ignition and spread of a fire by setting a minimum distance between daily cells
• minimise leachate production, eg by covering tyre pile
• minimise leachate contamination into soil and groundwater, eg, by having a compacted clay surface
• minimise vermin and insects breeding in monofill.

Table 8.1 compares the best practice for the design of tyre stockpile facilities given in guidelines published by IAFC, STMC and NFPA with that recommended by a practitioner with 20 years' experience in the tyre reprocessing industry.

Table 8.1: Comparison of best practice for the design of tyre stockpile facilities

View comparison of best practice for the design of tyre stockpile facilities (large table)

The guidelines summarised in Table 8.1 are the same as those recommended by Hamilton Fire Service [Berryman M. (2002)"Recommendations for the Storage of Used Vehicle Tyres". Hamilton Fire District Recommendations.] and are similar to those in the Basel Convention [Basel Convention Working Group (1999)"Basel Convention Technical Guidelines on the Identification and Management of Used Tyres". Basel Convention on the control of transboundary movements on hazardous wastes and their disposal. Document No. 10.] and those produced by the South Australian Environmental Protection Agency. [South Australian Environmental Protection Agency (July 2003)"EPA Guidelines: Waste Tyres".] However, the Basel Convention recommends that the maximum width of a tyre pile is 6m and the South Australian guidelines highlight the importance of not locating tyre storage sites near groundwater recharge points.

In addition to the IAFC, STMC and NFPA guidelines given in Table 8.1, the NFPA also recommends minimum separation distances between adjacent tyre piles based on the size of the exposed face and the tyre pile height. These are outlined in Table 8.2. These distances are also recommended between tyre piles and buildings; however soil bunds of one and a half the height of the tyre piles can be used.

Table 8.2: Minimum exposure separation distances [National Fire Protection Association (2003)"Standard No 230: Standard for the Fire Protection of Storage".]

8.4.3 Facility management issues

Issues to consider during management and operation of an outdoor tyre stockpile storage facility, based on literature reviewed during this study, include:

• minimisation of environmental risk by routine operation, eg due to tyre leachate
• minimisation of risk of tyre fire starting
• minimisation of environmental impacts caused by a tyre fire.

Little information was found regarding the management and day-to-day operation of an outdoor tyre storage facility. However the following practices were noted by Mr Playdon: [Personal communication2, Michael Playdon, Columbus McKinnon, February 2004.]

• monitoring is not carried out, unless the site is in an environmentally sensitive area
• the United States tyre manifest documents record the numbers of tyres that are received and removed from a tyre storage facility, and hence the number of tyres stored at a facility can be calculated at any given time.

8.5 Tyre Monofills

8.5.1 Information sources

End-of-life tyres can be disposed of within tyre monofills, which can be located above ground, below ground, or partly below ground. Tyre monofills are essentially landfills, or portions of a landfill, that receive only end-of-life tyres.

Little technical information that specifically addresses the design and operation of tyre monofills was sourced during this review. No technical information was available from Canadian, Australian or United Kingdom sources. This may be a reflection on the banning of landfilling of tyres in Canada and the United Kingdom.

Information was obtained from current waste management regulations contained in the California Code of Regulations (administered by the California Integrated Waste Management Board, CIWMB) and in the Ohio Administrative Rules (administered by the Ohio Branch of the Environmental Protection Agency, Ohio EPA). This information suggests tyre monofills are constructed and operated as sanitary landfills with a liner and leachate collection system.

The Basel Convention document does contain information about landfilling. However, the majority of this information appears to be sourced from "Annex F: Guidelines for Outdoor Storage of Scrap Tires" contained within the document NFPA 231D: Standard for Storage of Rubber Tires (1998). Annex F was developed to aid in the prevention and management of fire incidents that occur in whole, baled or processed end-of-life tyre stockpiles, rather than for tyre monofills. Accordingly, this information is outlined in Section 8.4 of this report.

8.5.2 Design of a monofill facility

The components of a tyre monofill, based on the Centre for Advanced Engineering (CAE) Landfill Guidelines, [Centre for Advanced Engineering (2000)"Landfill Guidelines".] include a liner system, daily cover and intermediate cover, final cap system, leachate collection system, stormwater collection system and a monitoring system.

Issues to consider during design and operation of a tyre monofill, based on literature reviewed during this study, include:

• site selection
• fire prevention and minimisation of fire spread:
  • limit potential for internal heating by setting a minimum size limit to tyre chips, for example
  • prevent ignition and spread of a fire by setting a minimum distance between daily cells, for example
• minimisation of leachate production by having adequate cover
• minimisation of contamination of soil and groundwater at the site and in the surrounding area
• minimisation of vermin and insects breeding.

Table 8.3 compares the best practice for the design of tyre monofill facilities outlined in the Basel Convention as well as in regulations administered by CIWMB and Ohio EPA.

Table 8.3: Comparison of published best practice for monofill design

View comparison of published best practice for monofill design (large table)

Previous MWH work [MWH New Zealand Ltd (June 2003)"Development of a Regional Waste Recovery / Processing Sector". A report prepared for the Wellington City Council, Ministry for the Environment and Ministry of Economic Development.] reported monofills in the United States have been designed using 0.9 m recompacted liners and 1.5 m soil caps, however it noted that this design does not address the issue of fire. This work also reported tyres could be evenly distributed along the base of a landfill cell, however it noted shredded or quartered tyres would leave exposed 'band wire' which has the potential to damage liner systems. It also noted that the issue of differential settlement from waste compaction should be considered when placing whole tyres in one area.

8.5.3 Facility management issues

Issues to consider during management and operation of a tyre monofill, based on literature reviewed during this study, include:

• minimisation of environmental risk in routine operations, eg from tyre leachate
• minimisation of risk of tyre fire starting
• minimisation of environmental impacts caused by a tyre fire.

Table 8.4 provides an overview of best practice for the management of tyre monofill facilities outlined in regulations administered by CIWMB and Ohio EPA.

Table 8.4: Comparison of published best practice for management of monofill facilities

8.6 Future Reprocessing of End-of-life Tyres

8.6.1 Reprocessing options for tyres

New Zealand currently generates approximately 4 million end-of-life tyres each year, which equates to approximately 36,000 tonnes per annum. [MWH New Zealand Ltd (June 2003)"Development of a Regional Waste Recovery / Processing Sector". A report prepared for the Wellington City Council, Ministry for the Environment and Ministry of Economic Development.] These tyres are currently landfilled, used as silage cover weights in the agricultural industry, recycled, stockpiled or dumped. There is little information available on respective quantities.

Current reprocessing options used internationally and described in previous MWH work, [Ibid.] include:

• Feedstock production: tyre shredding, tyre crumbing plant
• Recycling: rubberised asphalt concrete, civil engineering applications, playground mats, flooring
• Energy recovery: cement kilns, pyrolysis, gasification, polymerisation.

8.6.2 Compatibility of tyre storage methods with reprocessing options

It is important that the storage of tyres in New Zealand is compatible with current and potential reprocessing options. Table 8.5 outlines the suitability of tyres stored above ground in outdoor stockpiles and buried in tyre monofills for various reprocessing options. It should be noted that it would be more expensive to remove tyres from monofills than from stockpiles, making all reprocessing options more economically viable if tyres are stored in stockpiles.

Table 8.5: Comparison of the suitability of end-of-life tyres in monofills and stockpiles for various reprocessing options [Personal communication2. Michael Playdon, Columbus McKinnon, February 2004.] , [MWH New Zealand Ltd (June 2003)"Development of a Regional Waste Recovery / Processing Sector". A report prepared for the Wellington City Council, Ministry for the Environment and Ministry of Economic Development.] , [Personal communication3, Timothy Scott, Matta Products Ltd, February 2004.]

From Table 8.5 it appears there are more issues associated with reprocessing tyres from monofills (eg dirt contamination rendering tyres unsuitable for shredding). No tyre monofills have been identified as being 'mined' to date. However, it may be possible to reuse tyres from monofills if:

• tyre monofill design is altered to have clean linings etc to minimise dirt and contamination. However, this design would have to be carefully analysed to ensure the risk of fire is minimised
• an inexpensive way can be developed to remove tyres from a monofill and clean them. However, the tyres would still be unsuitable for crumbing as it is unlikely the cleaning procedure would be able to remove small soil fines from the tyres
• tyres are shredded to a suitable size for reuse prior to being placed in a monofill.

8.7 Future Disposal

In the event that further reprocessing options are not implemented in New Zealand, end-of-life tyres must be disposed of in an environmentally acceptable manner.

Tyres from temporary outdoor tyre stockpiles will need to be removed and transported to a suitable disposal site, which is monitored for tyre leachate and is appropriately managed to minimise the risk of fire. The temporary tyre storage site may also require remedial work, such as the removal of the top layer of soil if it is contaminated.

Tyres stored in an appropriately closed tyre monofill should be able to remain in the monofill. However, such a site will still require ongoing post-closure maintenance, monitoring of tyre leachate and appropriate management of the risk of fire. Based on literature and MWH experience in solid waste management, issues that need to be considered include:

• low density of tyres
• compressibility of tyres
• large void space in tyres, which may allow a large volume of water storage within the monofill. There is likely to be a low flow through these void spaces, which increases the risk of water contamination by tyre compounds
• stability of monofill
• ongoing fire risks
• limited future land use options.

The overall costs associated with the final disposal of tyres from temporary outdoor tyre stockpile facilities are likely to be greater than those for final disposal of tyres in monofills.

8.8 Environmental Risk Mitigation

The major environmental risks associated with tyre storage are the risk of tyre fires (which have severe potential environmental impacts) and the risk of tyre leachate contaminating groundwater, surface water and soil. Specific mitigation measures have been addressed previously in both the design and operation of storage facilities (Section 8.4 and Section 8.5), however this section will outline general mitigation measures based on literature reviewed and previous MWH experience in solid waste management.

Risks associated with tyre fires at tyre storage facilities can be mitigated in several ways, including:

• design of the storage facility to minimise the volume of tyres in one area (eg, with fire breaks between above ground piles and minimum allowable daily cover depths on below ground stores)
• operation of the storage facility to minimise risk of fires starting (eg, ensuring all ignition sources are kept beyond a specific distance from the tyres and setting a minimum allowable size on tyre chips in monofills)
• operation of the storage facility to maximise the chances of fires being extinguished quickly, and hence minimise the production of tyre decomposition products (eg, ensuring the site has adequate stockpiles of cover material to smother fires and clear access for fire service vehicles at all times)
• operation of storage facilities to minimise environmental impacts of tyre decomposition products (eg, ensuring there are contingency plans to enable water runoff from fire fighting to be collected).

The risk of tyre leachate contaminating groundwater and soil can be mitigated in several ways, including:

• design of the storage facility to minimise the amount of water runoff from tyre piles (eg, by designing a suitable stormwater collection system, covering tyres to minimise water contact with tyres, installing an adequate cover and liner system)
• monitoring surface water and groundwater levels for evidence of tyre leachate (eg, presence of iron, manganese and organic compounds, see Section 5) and carrying out remedial work if levels are significantly greater than baseline levels. It should be noted that the location and number of monitoring points and frequency of monitoring would be site specific
• removal of top layer of soil from sites when facilities are closed if soil testing results indicate contamination (eg, presence of zinc, cadmium and lead, see Section 5). Contaminated soil would need to be treated or disposed of in a landfill
• appropriate site selection, such as avoiding areas with low permeable soils, flood prone areas and areas near groundwater recharge points. An example of a suitable area would be one located away from surface water bodies on top of relatively impermeable clayey soils.

8.9 Financial Risk Mitigation

The major financial risks associated with tyre storage are related to the landowner, facility owner, costs of managing the facility, contamination, future value of end-of-life tyres and future final disposal costs if reprocessing options do not prove viable.

There are several financial assurance mechanisms, currently used internationally for landfills, [United States Environmental Protection Agency (1995)"Decision-Makers' Guide to Solid Waste Management, Volume II".] that could be used to minimise the major financial risks associated with tyre storage, including:

• operating liability insurances, eg, to cover the costs associated with tyre fires
• bonds, eg, to cover potential costs of final disposal, site monitoring and remedial work
• charges, eg, to cover potential costs of final disposal, site monitoring and remedial work
• trust funds, eg, to cover potential costs of final disposal, site monitoring and remedial work
• letter of credit, eg, to cover potential costs of final disposal, site monitoring and remedial work
• use of multiple mechanisms.

Insurances and bonds appear to be the most commonly used financial assurance mechanisms for tyre storage facilities in the United States.

Other ways to minimise financial risks, based on previous MWH experience in solid waste management, include:

• having a review period for licensing of a tyre storage facility - this allows bonds to be increased at the end of the review to reflect inflation as well as increases in, say, disposal costs
• appropriate site selection with appropriate hydrogeological and geotechnical studies of the site
• limit the time of operation
• limit the size of the facility
• having an appropriate quality assurance system to ensure the end-of-life tyres are suitable for a wide range of reprocessing options.