How do you calculate hydraulic detention time in hours for a clarifier or basin?

Detention Time (hours) = [ Basin Volume (gallons) × 24 hours/day ] ÷ Daily Plant Flow Rate (gallons/day).

What is effective detention time T10 in clearwells?

Effective contact time T10 is the theoretical detention time multiplied by the basin baffling factor (0.10 for unbaffled to 0.70 for superior baffling) under EPA SWTR rules.

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⏱️ Hydraulic Detention Time Calculator

Calculate water retention time in hours, days, and minutes for any basin geometry.

1. Basin Geometry / Input Mode

Length (ft)

Width (ft)

Depth (ft)

2. Plant Inflow / Discharge Rate Throughput volume

Hydraulic Detention Time

2.40 Hours

Equates to 0.100 Days | Total Basin Capacity: 179,532 Gallons

📝 Calculation Steps & Formula

Detention Time (Hours) = Volume (Gallons)Flow Rate (GPD) × 24 hrs/day

Detention Time Exam Concepts & Conversions

Detention time represents the theoretical average amount of time a small particle of water spends inside a specific treatment unit (e.g. flash mix, flocculation basin, sedimentation basin, chlorine contact tank).

⚠️ Key Exam Warning: Conversion Factor 7.48

When calculating tank volume in cubic feet (L × W × D or πr² × D), you must ALWAYS multiply by 7.48 gallons/cubic foot to convert into gallons before dividing by flow!

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⏱️ Hydraulic Detention Time Calculator

Detention Time Exam Concepts & Conversions

📘 Theory & Exam Guide

⚡ Volume & Flow Constants

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