Annual Landfill Area for a Population of 50,000: 18-Env-A6 Solid Waste Engineering and Management, December 2017, Q2

Question 2: 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 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 obtain 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 500 kg/m³ — reused from this same paper's own Question 4 (compacted specific weight of solid waste in the landfill) for internal consistency rather than inventing a separate figure, since both questions describe an ordinary (“normally compacted”) municipal cell.

Daily and annual waste mass. $W_{day} = 50{,}000 \times 2.0 = 100{,}000\ \text{kg/day}$; $W_{yr} = 100{,}000 \times 365 = 36{,}500{,}000\ \text{kg/yr} = 36{,}500\ \text{t/yr}$.
Annual compacted (in-place) volume. $V_{yr} = \dfrac{W_{yr}}{\rho_{compacted}} = \dfrac{36{,}500{,}000\ \text{kg/yr}}{500\ \text{kg/m}^3} = 73{,}000\ \text{m}^3/\text{yr}$.
Annual land area, dividing by the compacted depth. $A_{yr} = \dfrac{V_{yr}}{d} = \dfrac{73{,}000\ \text{m}^3/\text{yr}}{4\ \text{m}} = \boxed{18{,}250\ \text{m}^2/\text{yr}\ (\approx 1.83\ \text{ha/yr})}$.

Quantity	Result
Annual waste generated	36,500 t/yr
Annual compacted volume	73,000 m³/yr
Annual area required (excl. buffer, excl. cover)	18,250 m²/yr ≈ 1.83 ha/yr

Topic: Landfill area/capacity sizing from population, generation rate and compacted density

Key relations: $A_{yr} = \dfrac{(\text{population})(\text{generation rate})(365)}{\rho_{compacted}\, d}$

Why this works: Landfill footprint sizing is a straightforward mass→volume→area chain once a generation rate and compacted density are fixed — the same chain (population → mass → compacted volume) reappears in Question 4 with a given rather than assumed generation rate and density, letting the two answers be checked against each other for consistency.

Common pitfall: Using the as-delivered (loose, uncompacted) density instead of the in-place compacted density, which overstates the annual area by roughly the compaction ratio (typically 2:1 or more); forgetting to annualize the daily generation rate before dividing by depth.

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

Question 2 of 18: Annual Landfill Area for a Population of 50,000

Question 2: Annual Landfill Area for a Population of 50,000 (5 marks)