AR Water Operator cheat sheet

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

Log inactivation of Giardia by free chlorine typically requires higher CT than virus inactivation at the same conditions; Cryptosporidium is highly chlorine-resistant and usually needs UV or ozone.

Turbidity limits under the Surface Water Treatment Rule: combined filter effluent ≤0.3 NTU in 95% of monthly samples and never >1 NTU.

Conventional treatment sequence: coagulation → flocculation → sedimentation → filtration → disinfection.

Jar test determines optimal coagulant dose and pH by simulating coagulation/flocculation on raw water samples.

Alkalinity and pH affect coagulant performance; alum consumes alkalinity, so low-alkalinity waters may need lime or caustic addition.

Langelier Saturation Index (LSI) = pH − pHs; negative LSI indicates corrosive water, positive indicates scale-forming tendency.

Filter backwash is triggered by head loss setpoint, turbidity breakthrough, or run-time limit, whichever occurs first.

Hardness is reported as mg/L CaCO3 equivalent; 1 grain per gallon = 17.1 mg/L as CaCO3.

Minimum distribution system pressure is typically 20 psi under normal conditions; systems must maintain positive pressure to prevent backflow and contamination.

Chlorine residual goals: detectable free chlorine throughout the system, commonly ≥0.2 mg/L at the extremities; many states require a minimum residual at sample points.

Water hammer is caused by rapid velocity changes; mitigation includes slow valve closure, surge tanks, and air relief valves.

Pipe flow velocity is calculated as v = Q/A; typical design velocities are 2–5 ft/s to limit head loss and erosion.

Hazen-Williams head loss: hf = 4.73 × L × Q^1.852 / (C^1.852 × d^4.87) in US customary units.

Cross-connection control hierarchy: air gap (best) > reduced-pressure zone backflow preventer > double check valve > vacuum breaker.

Storage tank turnover prevents stagnation and loss of residual; tanks should be inspected and cleaned on a defined schedule.

Unidirectional flushing uses high velocity in one direction with valves sequenced to scour sediment from mains.

Total coliform positive sample requires follow-up testing for fecal/E. coli; a positive E. coli result triggers public notification and repeat sampling.

Standard Methods 9222 membrane filtration: sample volume filtered, colonies counted, and result reported as CFU/100 mL.

Nephelometric turbidity is measured in NTU; calibration uses formazin or approved polymer standards at defined ranges.

pH meter calibration uses at least two buffers bracketing the expected sample pH (commonly 7 and 10, or 4 and 7).

DPD colorimetric method measures free and total chlorine; total minus free approximates combined chlorine.

Holding time for chlorine residual is short (often 15 minutes) and must be measured in the field; most bacteriological samples must reach the lab within 6–8 hours (check state rule).

Grab samples represent a single point in time; composite samples are flow- or time-proportioned and used for load calculations.

Reporting limit and method detection limit differ: MDL is statistically derived; the reporting limit is the lowest routinely quantifiable concentration.

Chain-of-custody documentation must accompany samples and record collector, date/time, analyses, and transfers.

Total Coliform Rule: systems collecting ≥40 samples/month may have no more than 5% coliform-positive; smaller systems follow the MCLG of zero with repeat sampling rules.

Stage 2 Disinfectants and Disinfection Byproducts Rule limits: TTHM annual average 80 µg/L and HAA5 60 µg/L (LRAA).

Lead and Copper Rule action levels: 0.015 mg/L lead (90th percentile) and 1.3 mg/L copper; exceedance triggers corrosion control and public education.

Arsenic MCL is 0.010 mg/L (10 ppb); nitrate MCL is 10 mg/L as N; nitrite MCL is 1 mg/L as N.

Consumer Confidence Report (CCR) must be delivered to customers annually by July 1 and include source water, detected contaminants, and compliance information.

Public notification tiers: Tier 1 (immediate, 24 hours) for acute violations; Tier 2 (30 days) and Tier 3 (annual) for less urgent violations.

Total coliform MCL and monitoring requirements derive from the Revised Total Coliform Rule, which emphasizes assessment and corrective action.

Operator certification requirements, continuing education hours, and license renewal periods are set by the state primacy agency.

Chlorine gas is heavier than air; a leaking cylinder should be approached from upwind and only with SCBA - never with a dust mask or cartridge respirator.

Confined space entry requires atmospheric testing for oxygen (19.5–23.5%), flammables, and toxics before entry, plus an attendant and rescue plan.

Sodium hypochlorite and acid must never be mixed; mixing releases chlorine gas.

Lockout/tagout isolates hazardous energy before maintenance on pumps, motors, and valves.

Trenching: protective systems are required for excavations 5 ft or deeper; spoils and equipment kept at least 2 ft from the edge.

Hydrogen sulfide is toxic and heavier than air; its odor is not a reliable warning because it deadens the sense of smell at higher concentrations.

Electrical safety: GFCI protection for portable tools, and lockout before opening panels; water and electricity require strict separation.

Hazard communication requires SDS access for every chemical on site and labeling of secondary containers.

A water system's budget should separate O&M costs from capital improvement costs; rate structures must fund both.

Water loss is estimated as (system input volume − authorized consumption) ÷ system input volume × 100%.

Operator-in-charge responsibilities include recordkeeping, reporting to the primacy agency, and ensuring certified operators are on staff.

Records such as bacteriological results, chemical analyses, and operation reports must be retained per state rule (commonly 3–5 years, longer for some).

A sanitary survey is a primacy agency inspection of source, treatment, distribution, and management; significant deficiencies require corrective action.

Cost per 1,000 gallons = total cost ÷ (volume in gallons ÷ 1,000), useful for comparing treatment options and rate setting.

Emergency response plans should identify critical customers, alternate water sources, and mutual aid agreements.

Cross-connection control program administration includes device inventory, annual testing, and record retention.