Required Landfill Area: 18-Env-A6 Solid Waste Engineering and Management, December 2016, Q7

Question 7: Required Landfill Area (3 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	30,000 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 this three-mark, no-calculator question is answered on a per-year-of-operation basis (a standard framing for this classic problem type): 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 to obtain the annual land area consumed.

Daily and annual waste mass. $W_{day} = 30{,}000 \times 3 = 90{,}000\ \text{kg/day}$; $W_{yr} = 90{,}000 \times 365 = 32{,}850{,}000\ \text{kg/yr}$.
Annual compacted (in-place) volume. $V_{yr} = \dfrac{W_{yr}}{\rho} = \dfrac{32{,}850{,}000\ \text{kg/yr}}{500\ \text{kg/m}^3} = 65{,}700\ \text{m}^3/\text{yr}$.
Annual land area, dividing by the compacted depth. $A_{yr} = \dfrac{V_{yr}}{d} = \dfrac{65{,}700\ \text{m}^3/\text{yr}}{8\ \text{m}} = \boxed{8{,}213\ \text{m}^2/\text{yr}\ (\approx 0.82\ \text{ha/yr})}$.

Check

The exam gives no service life, so the boxed figure is deliberately expressed as an annual land-consumption rate rather than a single total area: a review engineer or planner then simply multiplies by the intended operating life (e.g. ×20 for a 20-year landfill → ≈16.4 ha, excluding buffer, access roads, leachate/gas infrastructure and daily-cover soil volume, all of which enlarge the true footprint further).

Quantity	Result
Annual compacted waste volume	65,700 m³/yr
Required landfill area (excl. buffer)	8,213 m²/yr (≈0.82 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 same logic used to check remaining capacity in Question 9.

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, Ch. 13 (landfill area and capacity estimation).

Question 7 of 20: Required Landfill Area

Question 7: Required Landfill Area (3 marks)