Math, Calculations, and Recordkeeping
What the candidate must know
Operator math covers flow, volume, detention time, loading rates, dosage, and chemical feed. Recordkeeping supports compliance and process control. Candidates should be comfortable with unit conversions and dimensional analysis.
Concepts to master
- Flow: Q = V/t and conversions (gpm, MGD, cfs).
- Volume of tanks: rectangular and cylindrical.
- Detention time: t = V/Q (watch units).
- Loading: hydraulic and organic loading rates.
- Chemical dose: pounds = mg/L × MGD × 8.34.
- Filter and clarifier surface loading rates (gpm/ft²).
- Recordkeeping: daily logs, calibration records, and retention.
Traps in questions
Unit mismatches are the biggest trap - mixing gallons and cubic feet, or minutes and days. Another is forgetting the 8.34 lb/gal factor for water. Always check that units cancel.
Worked example / rule of thumb
A tank holds 500,000 gallons and flow is 1.0 MGD. Detention time = 0.5 MG ÷ 1.0 MGD = 0.5 day = 12 hours. For chemical feed: to dose 2 mg/L at 1.5 MGD, pounds = 2 × 1.5 × 8.34 = 25.0 lb/day.