Lagoon Detention Time Calculator
Facultative lagoons treat by time and sunlight. Enter flow, lagoon size, and BOD load to get detention time and surface organic loading against typical design ranges.
Lagoon Performance
| Item | Value |
|---|
How the calculation works
Formulas
Volume from dimensions: L x W x D (ft3) x 7.48052 = gallons; / 1,000,000 = MG
Detention time (days) = volume (MG) / flow (MGD)
Surface area (acres) = L x W / 43,560
Surface BOD loading = BOD load (lb/day) / area (acres) (lb/acre-day)
Volume from dimensions: L x W x D (ft3) x 7.48052 = gallons; / 1,000,000 = MG
Detention time (days) = volume (MG) / flow (MGD)
Surface area (acres) = L x W / 43,560
Surface BOD loading = BOD load (lb/day) / area (acres) (lb/acre-day)
| Facultative lagoon typical range | Value |
|---|---|
| Surface BOD loading | 20–60 lb/acre-day |
| Detention time | 30–180 days |
| Operating depth | 3–8 ft |
Notes & limitations
Surface organic loading is the controlling design parameter for facultative lagoons (Metcalf & Eddy; Ten State Standards). Cold climates use the low end of the range; warm climates can go higher.
- Sludge accumulation shrinks the effective volume over time — survey sludge depth every few years and subtract it from the design volume.
- Short-circuiting cuts effective detention well below the theoretical value; baffles or proper inlet/outlet placement matter more than the raw number.
- Algae-driven pH swings and effluent TSS are normal for lagoons; this tool does not predict effluent quality.
- Aerated lagoons follow different loading rules — this tool is for facultative (non-aerated) lagoons only.
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