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

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

Assumptions

• Organic loading rates are based on climate zone averages: 15-20 lbs BOD/acre/day for cold climates, 25-35 lbs/acre/day for moderate climates, up to 50 lbs/acre/day for warm climates
• Influent BOD and TSS are user-entered and assumed constant (no seasonal or diurnal variation applied)
• Lagoon operating depth follows standard ranges: 3-5 feet for facultative, 8-15 feet for aerated
• Side slope ratios are user-selectable and default to 3:1 horizontal to vertical per typical state design standards
• Multi-cell configurations assume equal cell sizing with series flow for improved treatment performance
• Earthwork volume is estimated from prismoidal formula using top and bottom dimensions with the selected side slope
• Evaporation and seepage losses are not included in the hydraulic detention time calculation

Limitations

• Does not model algae growth, DO profiles, or seasonal treatment performance — lagoon effluent quality varies significantly with temperature and sunlight
• Wind-induced mixing effects and thermal stratification in deep lagoons are not modeled
• Does not evaluate liner requirements (clay, HDPE, GCL) based on site soil permeability and groundwater protection standards
• Odor potential from overloaded primary cells or anaerobic conditions is not assessed
• Does not account for sludge accumulation over time, which reduces effective volume and treatment capacity
• Setback distances from residences, wells, and property lines are jurisdiction-specific and not calculated here

References

• EPA 625/1-83-015 — Design Manual: Municipal Wastewater Stabilization Ponds (lagoon design methodology)
• Ten States Standards — Recommended Standards for Sewage Works (lagoon design criteria by climate zone)
• WEF Manual of Practice FD-16 — Natural Systems for Wastewater Treatment (lagoon and constructed wetland design)
• Crites, Middlebrooks & Reed — Natural Wastewater Treatment Systems, 2nd Edition (lagoon performance and design)
• USDA-NRCS — Agricultural Waste Management Field Handbook (lagoon sizing for agricultural applications)
• State design standards vary — refer to your state environmental agency's Design Standards for Wastewater Lagoon Systems

Frequently Asked Questions