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Lagoon Sizing Calculator - Facultative & Aerated Lagoon Design with Climate Loading Rates

Size wastewater lagoons based on BOD loading, climate zone & detention time requirements

Size facultative and aerated wastewater lagoons based on organic loading rate, climate zone, and detention time. Enter flow rate, influent BOD, and climate data to get required surface area, volume, detention time, and earthwork estimates. Includes design standard compliance checks for organic loading, detention time, and depth.

Pro Tip: The number one mistake in lagoon sizing is using warm-weather loading rates in a cold climate. A facultative lagoon designed at 35 lbs BOD/acre/day works fine in Texas but fails in Minnesota where the design rate is 15-20 lbs/acre/day. Biological activity drops roughly 50% for every 18°F decrease in water temperature.

Calculate detention time for existing lagoons

Detention Time Calculator →

Estimate sludge accumulation in lagoons

Sludge Production Calculator →

Check chemical dosing for lagoon effluent

Chemical Dosing Calculator →
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Lagoon & Stabilization Pond Sizing Calculator
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How It Works

  1. Enter Design Parameters

    Input flow rate, influent BOD concentration, and effluent BOD target. For small communities, flow can be estimated from population at 80-120 GPD per person.

  2. Select Lagoon Type and Climate

    Choose facultative, aerated, or storage lagoon. Select your climate zone or enter design winter temperature. The calculator adjusts organic loading rates for temperature.

  3. Configure Cell Layout

    Set number of cells, operating depth, freeboard, and side slope ratio. Multi-cell systems (2-3 cells in series) perform better than single-cell designs.

  4. Review Design Results

    Get required surface area in acres, volume in acre-feet, actual detention time, loading rate compliance, approximate cell dimensions, and earthwork volume.

Built For

  • Small towns designing new lagoon wastewater systems
  • Engineers evaluating lagoon expansion for population growth
  • Operators checking if existing lagoons are overloaded
  • Rural communities comparing lagoon vs. mechanical treatment costs
  • State regulators reviewing lagoon design submittals

Frequently Asked Questions

Calculate BOD loading in lbs/day: Flow (MGD) × BOD (mg/L) × 8.34. Divide by the allowable organic loading rate for your climate (15-35 lbs BOD/acre/day for facultative lagoons). The result is required surface area in acres. Multiply by operating depth to get volume, then check that detention time meets your state minimum (typically 45-120 days).
Facultative lagoons rely on natural processes: algae produce oxygen in the top layer while the bottom is anaerobic. They need large surface area (3-6 feet deep) but low energy. Aerated lagoons use mechanical aerators to supply oxygen, allowing deeper basins (8-15 feet) and smaller footprints with higher loading rates. Aerated lagoons cost more to operate but need less land.
At 100 GPD/person, flow is 50,000 GPD (0.05 MGD). At 200 mg/L influent BOD, loading is 83.4 lbs/day. In a moderate climate at 25 lbs/acre/day, you need about 3.3 acres of lagoon surface. Add berms, access roads, and buffer zones and you need roughly 8-12 acres total land area.
Disclaimer: This calculator provides preliminary sizing estimates. Actual lagoon design must comply with your state design standards, which vary significantly by jurisdiction. Factors including groundwater protection, soil permeability, setback distances, and wildlife impact must be evaluated by a licensed professional engineer.

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