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ABC Wastewater Collection Class II study materials
ABC Wastewater Collection Class II study resources

ABC Wastewater Collection Class II: Math and Calculations

ABC Wastewater Collection Class II · Work through your exam, one topic at a time.

All guide sections

Math and Calculations

What the exam expects

Math questions reward method over memorization. Set up the problem, track units, and sanity-check the answer. Most collection-system math involves flow, volume, velocity, detention time, loading, and cost.

Concepts to master

  • Flow conversions: gpm, mgd, cfs, liters.
  • Volume = area × length; detention time = volume ÷ flow.
  • Velocity = distance ÷ time; Q = A × V.
  • Loading: lbs = concentration (mg/L) × volume (MG) × 8.34.
  • Detention time in wet wells and force mains.
  • Cost and dosage problems.

Traps

Unit mismatches are the biggest trap: mixing mgd with gpm, or hours with minutes. Convert first, then calculate. Also watch for questions that give diameter in inches but ask for area in square feet.

Worked example

A wet well holds 5,000 gallons. Inflow is 50 gpm. Detention time = 5,000 ÷ 50 = 100 minutes ≈ 1.67 hours. If the pump runs at 200 gpm, net drawdown rate is 150 gpm and cycle time = 5,000 ÷ 150 ≈ 33 minutes.