FE Environmental Practice Question Solution included after investigation
CASE E-078 · FE

The Landfill That Produced 12,000 m³ of Leachate, Not 22,000

Precipitation minus evapotranspiration was not enough. Runoff and storage change reduced the annual leachate estimate to 12,000 m³.

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Case E-078 engineering failure visual
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Case Brief

SAME PRINCIPLES. HIGHER STANDARDS.
PROBLEM STATEMENT

A 4.0 ha landfill receives 1.00 m/yr of precipitation. Annual evapotranspiration is 0.45 m, surface runoff is 0.20 m, and water stored in the cover/soil profile increases by 0.05 m over the year. Assume the remaining water becomes leachate. A note uses only P-ET and reports 22,000 m³/yr. Determine the correct annual leachate volume.

Solid Hazardous Waste Environmental Design Verification Root Cause Analysis Safe Correction
E-078
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CASE CLOSED · ENGINEERING VERDICT

What actually failed — and what should change.

What failed

The water balance stopped after subtracting evapotranspiration.

What was missed

Runoff and water retained in storage.

Corrected model

For the stated balance, use leachate=P-ET-runoff-ΔS, then multiply depth by area.

QUICK ANSWER

Using L=P-ET-runoff-ΔS gives L=1.00-0.45-0.20-0.05=0.30 m/yr. Over 4 ha (40,000 m²), annual leachate is 0.30×40,000=12,000 m³/yr.

ENGINEERING TAKEAWAY

For the stated simplified balance, leachate depth=P-ET-runoff-ΔS, with a positive storage increase reducing drainage.

CASE QUESTIONS

Questions this case should settle.

How do you convert leachate depth to volume?

Multiply the net leachate depth by the landfill plan area using consistent units.

Does a positive storage change increase or decrease leachate in this balance?

It decreases leachate because more water remains stored in the cover or soil profile.

NEXT FE PRACTICE QUESTION

The Mixed Waste Batch That Was 5.67%, Not 4.5%

Solid Hazardous Waste · 5–10 min

Continue Practice →
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