What is the typical detention time for lagoon or small pond wastewater systems?

• A. 50 days
• B. 150+ days
• C. 100 days
• D. 200 days

Answer: (B)

Detention time, or hydraulic retention time, is the average time wastewater stays in the lagoon. Lagoon systems rely on slow biological processes, settling, and sunlight to stabilize waste, and in cold climates like Wisconsin this takes a relatively long period. Because of that, lagoons and small ponds are designed for a long residence time—around five months or more—roughly 150 days or longer. Shorter times wouldn’t give enough time for stabilization and pollutant reduction, while a time like 200 days is longer than typical practice. So the common expectation is about 150 days or more.