Annual Landfill Area for a Population of 50,000: 18-Env-A6 Solid Waste Engineering and Management, December 2013, Q7

Question 7: Annual Landfill Area for a Population of 50,000 (5 marks)

Question text not reproduced: the examination questions are © Engineers and Geoscientists BC. Open the official past paper (linked at the top of this page) to read the question, then follow the worked solution below.

Given. Population $= 50{,}000$; compacted refuse depth $= 4\ \text{m}$ (cover material excluded, as stated).

Find. The annual land area (excluding buffer zone) required to place one year's compacted refuse at this depth.

Approach. Estimate the annual mass of waste generated from an assumed per-capita generation rate, convert to compacted volume using an assumed compacted density, then divide by the stated refuse depth to get area.

Check: neither a generation rate nor a compacted density is given in this question. A per-capita generation rate of 2.0 kg/cap/day is assumed (a typical North American municipal design value, Tchobanoglous). The compacted density is taken as 600 kg/m³, reused from this same paper's own Q15 data ("density of well compacted landfill = 600 kg/m³") for internal consistency rather than inventing a separate figure.

Annual mass of waste generated. $$m = 50{,}000 \times 2.0\ \text{kg/cap/d} \times 365\ \text{d/yr} = 36{,}500{,}000\ \text{kg/yr} = 36{,}500\ \text{t/yr}$$
Annual compacted volume. $$V = \dfrac{m}{\rho_{compacted}} = \dfrac{36{,}500{,}000\ \text{kg/yr}}{600\ \text{kg/m}^3} = 60{,}833\ \text{m}^3/\text{yr}$$
Annual area required (at 4 m refuse depth). $$A = \dfrac{V}{\text{depth}} = \dfrac{60{,}833\ \text{m}^3/\text{yr}}{4\ \text{m}} = 15{,}208\ \text{m}^2/\text{yr} = \boxed{1.52\ \text{ha/yr}}$$

Quantity	Value
Annual waste generated	36,500 t/yr
Annual compacted volume	60,833 m³/yr
Annual area required (excl. buffer, excl. cover)	15,208 m²/yr ≈ 1.52 ha/yr

Topic: Landfill area/capacity sizing from population and generation rate.

Key relations: $m = P \times q \times 365$; $V = m/\rho_{compacted}$; $A = V/\text{depth}$.

Why this works: Landfill footprint sizing is a straightforward mass-to-volume-to-area chain once a generation rate and compacted density are fixed — the annual compacted volume found here is also the denominator of the remaining-life ratio in Q11, and the 600 kg/m³ compacted density is the same value this paper gives in Q15.

Common pitfall: using the as-delivered (loose) density instead of the compacted in-place density, which understates the achievable service life of a given footprint by roughly the compaction ratio (here, 2:1 versus the loose 300 kg/m³ used elsewhere in this paper).

Source: Tchobanoglous, Theisen & Vigil, Integrated Solid Waste Management, Ch. 13 (landfill capacity and area estimation).

Question 7 of 16: Annual Landfill Area for a Population of 50,000

Question 7: Annual Landfill Area for a Population of 50,000 (5 marks)