Estimating Required Site Area

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Before attempting to identify potential landfill sites, planners must estimate the area requirement of the landfill. Landfill sizing is a function of:

Landfill life (typically five to twenty-five years) Population served

Waste production per person per day Extent of waste diversity Shape and height of the landfill Landfill area used for buffer zone, offices, roads, scalehouse, and optional facilities such as MRF, tire disposal and storage, composting, and convenience center

A number of formulas can help determine the acreage required for waste disposal (Tchobanoglous, Theissen, and Vigil 1993; Noble 1992). The total annual waste produced by the population to be served by the landfill for each year of the expected landfill's life is estimated as:

where:

Vip = annual in-place waste volume (cu y®/yr) P = population served by landfill in a given year Wg = waste generation in a given year (lb/person/d) f = fraction of waste stream diverted in a given year Cd = specific density of the waste (lb/cu yd)

Population predictions for the years of expected landfill operation can usually be obtained from local government agencies. The total amount of waste generated in a community per person can be developed from waste characterization studies. State or national data can be used if no other data are available. Data on recycling trends should be gathered locally.

As landfilling costs increase, larger and heavier compactors are becoming more common, resulting in higher compaction. Compaction densities achieved in landfills vary from around 800 to as high as 1400 lb/cu yd depending on the type of compaction equipment used. Values of 1000 to 1200 lb/cu yd are often used as estimates.

Cover material adds to the amount of material placed in the landfill, reducing the landfill's effective volume. Typical waste-to-cover-soil-volume ratios are in the range of 4:1 to 10:1. A value of 5:1 or 4:1 is often assumed, in dicating that for every 4 or 5 cu yd of waste, 1 cu yd of cover soil is deposited. In a 5:1 ratio, the cover-soil-to-waste ratio is 1 divided by 5, or 0.2. Incorporating waste and cover soil, the annual in-place waste and soil volume is:

where:

Vap = annual in-place waste and soil volume, including waste and cover soil (cu yd/yr) CR = cover-soil-to-waste ratio

Sometimes planners assume that all of the cover soil will come from the landfill excavation. In this case, all of the soil material excavated from the landfill ends up in the landfill. With this assumption, planners can estimate the area using the assumed shape and height of the landfill above ground level and the sum of the annual in-place waste volume the landfill expects to receive. Height regulations are generally included in state or local landfill regulations and vary from place to place.

The simplest shape that can be assumed is the cube. A more realistic shape is the flat-topped pyramid. Both shapes are shown in Figure 10.13.1. The volume of the cubic landfill is V = (H)(B2), where H = the height and B = the length of the base. Thus, area = B2 = V/H. The volume of the flat-topped pyramid landfill, with a square base and 3:1 side slopes, is:

where a 3:1 side slope means that for every 3 ft horizontal run, the slope rises 1 ft. Solving for B with the quadratic equation gives:

V4HVip - 12H4

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