ME Water Operator cheat sheet

CT (contact time) = disinfectant residual concentration (mg/L) × effective contact time (minutes); regulatory CT tables assign credit based on temperature, pH, and disinfectant type.

Log inactivation credit is additive across treatment barriers only when each barrier independently achieves its own required CT; do not sum fractions across processes without the disinfection profile method.

Turbidity limits under the Surface Water Treatment Rule: 0.3 NTU in at least 95% of monthly samples for conventional filtration, with a maximum of 1 NTU at all times.

Required filtered-water turbidity for slow sand and diatomaceous earth filtration is 1 NTU in 95% of monthly measurements; bag/cartridge filtration is 0.3 NTU.

Alkalinity and pH govern coagulation: optimum alum dose typically occurs near pH 6.5–7.5; add lime or caustic to raise alkalinity and pH when raw water is poorly buffered.

Jar tests simulate full-scale coagulation; use rapid mix (1–2 min at 200–300 rpm), flocculation (15–30 min at 20–60 rpm), then settle 30 min and measure turbidity.

Chlorine demand = applied dose − residual after contact time; free chlorine reacts with ammonia to form chloramines, so breakpoint chlorination requires roughly 7.6 mg Cl2 per mg N.

Filter media design: anthracite on sand dual media uses effective size 0.9–1.1 mm (anthracite) and 0.45–0.55 mm (sand), with backwash rates set to achieve 20–25% bed expansion.

Disinfection byproduct control: total trihalomethanes MCL is 0.080 mg/L (LRAA) and haloacetic acids MCL is 0.060 mg/L; precursor removal via enhanced coagulation lowers formation.

Chlorine residual target in distribution: maintain a detectable residual throughout; common state minimum is 0.2 mg/L free chlorine and a maximum of 4.0 mg/L (or 4.0 mg/L total as Cl2).

Minimum pressure rule under the Lead and Copper Rule / state codes: 20 psi at all points under normal conditions and never below 20 psi even during main breaks or fire flow.

Hazen-Williams head loss: h = 10.44 × L × Q^1.85 / (C^1.85 × d^4.87) in US customary units (Q in cfs, d in feet), or use the simplified form with Q in gpm and d in inches.

Water hammer results from rapid velocity change; surge pressure rise (psi) ≈ 0.07 × velocity change (ft/s) for a sudden closure, or use the Joukowsky equation Δp = ρ × a × Δv.

Storage sizing: equalization, fire flow, and emergency reserves are separate components; many states require total storage of at least average day demand plus fire flow for the design period.

Cross-connection control: an air gap is the only truly backflow-proof device; a reduced-pressure zone assembly is required for high-hazard connections, and a double check for low-hazard.

Distribution flushing velocity should reach at least 2.5–3.0 ft/s to scour sediment; calculate the flow needed from pipe diameter (Q ≈ 0.785 × d² × v).

Main break isolation: close valves to limit affected customers, then notify the primacy agency within 24 hours if a boil-water notice is issued per state rules.

Water main disinfection after repair: apply 50–100 mg/L chlorine for at least 30 minutes, flush, then sample for coliform and chlorine residual before returning to service.

Total coliform rule: no more than 5% of routine samples per month may be total-coliform positive for systems collecting 40 or more samples; any E. coli positive is an acute violation requiring public notice within 24 hours.

Stage 2 Disinfectants and Disinfection Byproducts Rule uses locational running annual averages (LRAA) at each monitoring location, not a system-wide average.

Ground Water Rule requires 4-log virus treatment (99.99% inactivation/removal) for systems with a significant deficiency or fecal contamination, or state-approved alternative.

Consumer Confidence Report (CCR) must be delivered by July 1 each year, covering the prior calendar year's monitoring results and detected contaminants.

Lead and Copper Rule: action level is 0.015 mg/L for lead and 1.3 mg/L for copper at the 90th percentile; exceedance triggers corrosion control studies and public education.

Source water protection: delineate the wellhead protection area, inventory potential contaminant sources, and manage them; sanitary surveys assess physical/operational deficiencies every 3–5 years.

Arsenic MCL is 0.010 mg/L; nitrate MCL is 10 mg/L as N (45 mg/L as NO3); fluoride MCL is 4.0 mg/L with a secondary limit of 2.0 mg/L.

Public notification tiers: Tier 1 (acute health risk) within 24 hours; Tier 2 (non-acute) within 30 days; Tier 3 (reporting/monitoring) within 1 year in the CCR.

Radionuclides: combined radium-226/228 MCL is 5 pCi/L and gross alpha MCL is 15 pCi/L; uranium MCL is 30 µg/L.

Confined space entry requires atmospheric testing before and during entry: oxygen 19.5–23.5%, LEL below 10%, H2S below 10 ppm, CO below 35 ppm (or stricter state limits).

Chlorine gas is heavier than air and accumulates in low areas; use a supplied-air respirator (SCBA) for escape from or entry into chlorine atmospheres, never an air-purifying respirator.

Sodium hypochlorite stored above 30°C degrades rapidly and releases oxygen gas; vent storage tanks and never store near acids to avoid chlorine gas release.

Lockout/tagout (29 CFR 1910.147) requires energy isolation, verification of zero energy, and only the person who applied the lock may remove it.

Hazard communication: Safety Data Sheets must be available for every chemical on site; labeling follows the GHS pictogram and signal-word system.

Emergency response plan should address source contamination, loss of pressure, power failure, main breaks, and intentional contamination; test the plan with tabletop exercises annually.

Security measures: control access to treatment plants, lock chemical feed rooms, secure hydrants and storage tanks, and monitor for tampering at entry points and reservoirs.

Boil-water notice requires rolling boil for at least 1 minute (3 minutes above 6,500 ft elevation), then cooling; issue with the primacy agency and rescind only after two consecutive negative coliform samples.

Electrical safety: use ground-fault circuit interruption (GFCI) protection for portable tools in wet areas; maintain at least the required approach distance from energized equipment per NFPA 70E.