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Appendix E: Typical Example - District Landfill Site
The following illustrates the use of the model for a hypothetical district landfill.
The site is a proposed Greenfields development of a 50,000 tonnes per annum landfill which, for the purpose of this example, will take four years to investigate and obtain consents (the pre-development period). The District Council would prefer the site to operate for at least 20 years. The resource consents will generally be granted for a period not exceeding 35 years. The aftercare period is 30 years.
The project commenced on 1 January 2002 and the target date for commencement of operation is 1 January 2006.
The proposed landfill incorporates several different liner types, and these are outlined below.
This example is used to calculate the required per tonne indicative base cost of disposal (IBC) to cover all costs of the landfill project, including pre-development, development, operation, closure and aftercare.
Furthermore, the District Council wishes to assess the impact on the IBC of reducing waste to landfill. This will enable the council to set realistic waste reduction targets for implementing the district's Waste Strategy. The District Council also wishes to allow for a 1.5% per annum waste growth rate, which will account for long-term demographic projections and per capita waste generation trends.
Finally, the District Council wishes to assess the impact on the IBC of the timing of cell construction (i.e. cell construction staged in equal annual amounts versus cell construction completed in a single year).
Table E1 shows the waste reduction scenarios that have been modelled.
Table E1: Waste reduction scenarios for a hypothetical district landfill
| Scenario | Target waste reduction (% over life of facility) |
|---|---|
|
1 |
0 |
|
2 |
10 |
|
3 |
20 |
|
4 |
30 |
|
5 |
50 |
The model input worksheets (General Input, Geometric Input,and Cost Input) have been included below as have the Project Summary Output and Cashflow Chart Output for the 0% per annum reduction (Scenario 1 with construction staged in equal annual amounts).
Tables E2 and E3 summarise the IBC ($/tonne excluding GST) for the waste reduction scenarios.
Table E2: IBCs for hypothetical district landfill (Cell Construction Staged in Equal Annual Amounts)
Table E3: IBCs for hypothetical district landfill (Cell Construction Completed in Single Year)
Liner Inputs used in the Typical Example
Most of the proposed landfill is to have a liner consisting of 600 mm thickness of compacted clay (with permeability less than 1 x 10-9), a 1.5 mm thick textured HDPE FML, a 1000 g/m2 non-woven geotextile liner protection layer and a 300 mm thick 40/20 aggregate leachate collection layer. In parts of cells 1, 2, 5 and 7, the final placed depth of waste is lower and the thickness of the liner protection layer can be reduced to 600 g/m2. In cells 3 and 4, there are steep sidewalls. The liner on these sidewalls is to consist of a GCL, a 1.5 mm thick textured HDPE FML, and a 200 mm thick protection layer of silts and clays. Note that there is no compacted clay component and no leachate collection layer proposed for the sidewall liner. The costs to be used for the various liner components are shown in Table E4.
Table E4: Costs of liner components for liner types used in Typical Example
|
Compacted clay liner (cut, on-site borrow or stockpile to fill) |
$5.50/m3 |
|
Subgrade preparation: Beneath compacted clay liner Beneath GCL |
$1.00/m3 $1.95/m3 |
|
Synthetic liner: 1.5 mm thick textured HDPE FML GCL |
$15.50/m2 $16.70/m2 |
|
Liner protection layer: 1000 g/m2 non-woven geotextile 600 g/m2 non-woven geotextile 200 mm thick silt & clay layer |
$9.20/m2 $7.10/m2 $2.60/m2 |
|
Leachate Collection layer: 300 mm thick 40/20 aggregate |
$12.50/m2 |
Refer to the Model Input worksheets (Geometric Input and Cost Input) included for this typical example to see how the data has been input to the model.
