CT Water Operator cheat sheet

CT (contact time) = disinfectant residual concentration (mg/L) × contact time (minutes); required CT depends on disinfectant, pH, temperature, and target pathogen.

Log removal = log10(influent concentration / effluent concentration); 2-log = 99% removal, 3-log = 99.9%, 4-log = 99.99%.

Surface loading rate (gpm/ft²) = flow (gpm) / surface area (ft²); typical clarifier rates: 0.5–1.0 gpm/ft².

Filtration rate (gpm/ft²) = flow (gpm) / filter area (ft²); rapid sand filters typically 2–5 gpm/ft².

Backwash rate must expand filter bed 15–25%; backwash flow (gpm) = rate (gpm/ft²) × filter area (ft²).

Detention time (hours) = volume (gal) / flow (gal/hr) or volume (ft³) / flow (ft³/hr).

Chlorine demand = chlorine dose (mg/L) − chlorine residual (mg/L).

Jar test determines optimal coagulant dose and pH by simulating coagulation/flocculation/sedimentation.

Langelier Saturation Index (LSI) predicts calcium carbonate scaling (positive) or corrosion (negative); target near 0.

Minimum distribution system pressure: 20 psi under normal conditions; 20 psi during fire flow; never below 20 psi.

Required fire flow: determined by ISO or local fire code; typical 500–3,500 gpm for 2–4 hours.

Head loss in pipe: Hazen-Williams equation h_f = 10.44 L Q^1.85 / (C^1.85 d^4.87) in SI; use consistent units.

Water hammer pressure surge = 0.07 × velocity change (ft/s) × wave speed (ft/s) for instantaneous closure.

Storage volume: equalization + fire flow + emergency reserve; typical total 1.5–2.0 times average day demand.

Pipe velocity: 2–5 ft/s typical; <1 ft/s causes sedimentation; >10 ft/s causes excessive head loss and erosion.

Chlorine residual maintenance: ≥0.2 mg/L in distribution system; detectable at all points.

Cross-connection control: backflow prevention by air gap (preferred) or reduced pressure zone (RPZ) assembly.

Distribution system flushing: minimum 2.5 ft/s velocity to scour biofilm and sediment.

Turbidity: nephelometric method (NTU); treatment technique requires ≤0.3 NTU in 95% of monthly samples for conventional filtration; max 1 NTU.

pH: electrometric method; typical range 6.5–8.5; affects coagulation, disinfection, corrosion.

Chlorine residual: DPD colorimetric or amperometric titration; free chlorine measured after 2 min, total after 2 min with KI.

Total coliform: presence/absence (P/A) method; positive triggers repeat sampling and investigation.

Heterotrophic plate count (HPC): pour plate method; <500 CFU/mL indicates adequate treatment.

Fluoride: ion-selective electrode or colorimetric; optimal 0.7–1.2 mg/L; MCL 4.0 mg/L.

Nitrate: ion chromatography or cadmium reduction; MCL 10 mg/L as N.

Lead and copper: 90th percentile action levels: Pb 0.015 mg/L, Cu 1.3 mg/L.

Disinfection byproducts: TTHM MCL 0.080 mg/L; HAA5 MCL 0.060 mg/L (LRAA).

Total coliform rule: no more than 5% of samples positive for systems >40 samples/month; any positive requires repeat within 24 hours.

Surface Water Treatment Rule: 99.9% (3-log) Giardia and 99.99% (4-log) virus removal/inactivation.

Stage 2 Disinfectants/Disinfection Byproducts Rule: locational running annual average (LRAA) for TTHM and HAA5.

Lead and Copper Rule: action levels Pb 0.015 mg/L, Cu 1.3 mg/L; 90th percentile; corrosion control treatment.

Arsenic MCL: 0.010 mg/L (10 ppb).

Consumer Confidence Report (CCR) due by July 1 annually; includes source water, detected contaminants, health effects.

Public notification: Tier 1 (immediate, 24 hours) for MCL violations; Tier 2 (30 days) for monitoring/reporting; Tier 3 (annual) for other violations.

Operator certification: state-issued; minimum requirements include experience and exam; continuing education for renewal.

Cross-connection control: state plumbing code requires containment and isolation backflow prevention.

Confined space entry: permit required; test atmosphere for O2 (19.5–23.5%), LEL (<10%), H2S (<10 ppm), CO (<35 ppm) before entry.

Chlorine gas: IDLH 10 ppm; use supplied-air respirator; evacuate if smell detected; never enter without SCBA.

Ammonia: IDLH 300 ppm; corrosive to eyes and respiratory tract; use appropriate PPE.

Chemical storage: acids and bases stored separately; chlorine and ammonia never stored together (forms toxic chloramines).

Lockout/tagout (LOTO): isolate energy sources before maintenance; verify zero energy.

Electrical safety: GFCI required in wet locations; avoid water near electrical panels.

Fall protection: required at 4 feet (general industry) or 6 feet (construction); guardrails, harness, lanyards.

Hazard communication: SDS (Safety Data Sheet) available for all chemicals; labeling per GHS.

Excavation: protective system required for trenches ≥5 ft deep; ladder every 25 ft of lateral travel.

Recordkeeping: maintain operational records for at least 3 years; some (e.g., lead/copper) for 12 years.

Budget: O&M (operations and maintenance) vs. capital improvement plan (CIP); rate structure covers full cost of service.

Asset management: inventory, condition assessment, level of service, criticality, life-cycle costing.

Emergency response plan (ERP): required for community water systems; includes vulnerability assessment and response procedures.

Operator certification: state primacy agency administers exams; reciprocity may be available.

Public relations: consumer confidence report, public notification, media relations.

Work orders: track labor, materials, and equipment for maintenance and repairs.

Safety program: written safety manual, training, incident reporting, OSHA compliance.

Water loss control: audit, leak detection, repair; target non-revenue water <10%.