Required Landfill Area for a Community of 31,000: 18-Env-A6 Solid Waste Engineering and Management, December 2017, Q4

Question 4: Required Landfill Area for a Community of 31,000 (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.

Quantity	Value
Population served	31,000 persons
Generation rate	3 kg/capita·day
Compacted specific weight in landfill	500 kg/m³
Average compacted depth of refuse	8 m

Find. The landfill footprint area (excluding any buffer zone) required to accommodate the community's waste.

Approach. No design/service life is stated, so — consistent with the same no-life-given framing used in Question 2 — this is answered as an annual land-consumption rate: convert the daily generation rate to an annual mass, convert to an annual placed volume via the compacted specific weight, then divide by the compacted depth.

Daily and annual waste mass. $W_{day} = 31{,}000 \times 3 = 93{,}000\ \text{kg/day}$; $W_{yr} = 93{,}000 \times 365 = 33{,}945{,}000\ \text{kg/yr}$.
Annual compacted (in-place) volume. $V_{yr} = \dfrac{W_{yr}}{\rho} = \dfrac{33{,}945{,}000\ \text{kg/yr}}{500\ \text{kg/m}^3} = 67{,}890\ \text{m}^3/\text{yr}$.
Annual land area, dividing by the compacted depth. $A_{yr} = \dfrac{V_{yr}}{d} = \dfrac{67{,}890\ \text{m}^3/\text{yr}}{8\ \text{m}} = \boxed{8{,}486\ \text{m}^2/\text{yr}\ (\approx 0.85\ \text{ha/yr})}$.

Check

As in Question 2, no operating/design life is stated, so the boxed figure is an annual land-consumption rate; multiplying by an intended operating life (e.g. ×20 for a 20-year landfill → ≈17.0 ha) gives the total footprint, excluding buffer zone, access roads, leachate/gas infrastructure and daily-cover soil volume.

Quantity	Result
Annual compacted waste volume	67,890 m³/yr
Required landfill area (excl. buffer)	8,486 m²/yr (≈ 0.85 ha/yr)

Topic: Landfill area sizing from generation rate, compacted density and cell depth

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

Why this works: Landfill footprint is set by the volume of waste that must be placed each year, which is a direct chain of unit conversions from population and per-capita generation through compacted density to compacted depth — the identical logic used in Question 2, but here with a fully specified (rather than assumed) generation rate and density, giving an internally consistent pair of answers within the paper.

Common pitfall: Forgetting to annualize the daily generation rate (using $W_{day}$ directly against a whole-community area), or dividing by depth before dividing by density, which silently changes the units of the intermediate result.

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

Question 4 of 18: Required Landfill Area for a Community of 31,000

Question 4: Required Landfill Area for a Community of 31,000 (5 marks)