Water Treatment Operator Class I cheat sheet

Groundwater typically shows higher hardness, iron, manganese, and dissolved solids; surface water shows more variable turbidity, color, TOC, and microbial load.

Turbidity is reported in NTU and measured by nephelometry; it is a surrogate for particle and pathogen removal, not a direct pathogen count.

Total hardness (mg/L as CaCO3) = carbonate hardness + noncarbonate hardness; carbonate hardness equals alkalinity when alkalinity is less than total hardness.

Convert an ion to CaCO3 equivalent: mg/L as CaCO3 = mg/L ion x (50 / equivalent weight of the ion).

LSI = pH minus pHs; a positive LSI indicates calcium carbonate scaling tendency, a negative LSI indicates corrosive tendency.

Waters with alkalinity below about 50 mg/L as CaCO3 may not buffer alum or ferric coagulation and require lime, caustic, or soda ash addition.

TOC and UV254 are DBP-precursor indicators; higher TOC and higher UV254 mean greater coagulant demand and greater THM/HAA formation potential.

Under the Surface Water Treatment Rule, conventional filtration must achieve at least 3-log Giardia and 4-log virus inactivation/removal combined.

Common coagulants are alum, ferric chloride, ferric sulfate, polyaluminum chloride, and cationic polymers; each has its own optimum pH and alkalinity demand.

Alkalinity consumption: 1 mg/L of alum consumes roughly 0.45-0.5 mg/L of alkalinity as CaCO3; 1 mg/L of ferric chloride consumes about 0.9 mg/L.

Optimum coagulation pH is typically 6.0-7.0 for alum; ferric salts work over a wider range, roughly 4.5-7.5.

Rapid mix design: velocity gradient of 300-1000 per second for 10-60 seconds; flocculation: tapered G of 10-75 per second for 15-45 minutes.

Surface overflow rate (gpm/ft2) = flow (gpm) / clarifier surface area (ft2); particles with settling velocity greater than the overflow rate are removed.

Conventional sedimentation basins are designed for overflow rates of about 0.3-1.0 gpm/ft2 and detention times of 2-4 hours.

A zeta potential near zero indicates charge neutralization and good destabilization; a strongly negative zeta potential indicates underdosing.

Jar test rules: identical rapid mix, flocculation, and settling times in all jars; vary only coagulant dose and pH; select the lowest settled turbidity.

Sludge production rises with coagulant dose and raw water turbidity, so solids handling must be sized for the highest expected raw turbidity.

Conventional rapid-rate filters are designed for about 2-6 gpm/ft2; dual-media anthracite-over-sand beds commonly run at 3-5 gpm/ft2.

Slow sand filters run at 0.1-0.4 gpm/ft2 and rely on the schmutzdecke biological layer; they are cleaned by scraping, not backwashing.

Backwash at 15-20 gpm/ft2 for 10-15 minutes to reach 20-50 percent bed expansion; poor expansion leaves mudballs and media cracks.

L/d ratio = media depth / effective size; values of at least 1000 are needed to prevent turbidity breakthrough.

Uniformity coefficient = d60 / d10; values of 1.3-1.5 give even backwashing and limit media stratification.

End a filter run on whichever occurs first: turbidity breakthrough at the state limit (often 0.3 NTU), maximum head loss, or maximum run time.

Combined filter effluent must be 0.3 NTU or less in at least 95 percent of monthly samples and must never exceed 1 NTU for conventional filtration.

Filter-to-waste or a slow start after backwash prevents the post-backwash turbidity spike from reaching the clearwell.

Typical media: anthracite effective size about 0.9-1.1 mm, sand about 0.45-0.55 mm, with garnet used in the bottom support layer.

CT = disinfectant residual (mg/L) x contact time (min); the required CT depends on disinfectant type, pH, temperature, and the log credit needed.

Free chlorine is a stronger biocide than chloramine; chloramines maintain a distribution residual while lowering THM and HAA formation.

Breakpoint chlorination: at the breakpoint all ammonia is oxidized; beyond it, free chlorine residual rises roughly 1:1 with additional dose.

Stage 2 DBPR MCLs are TTHM 80 ug/L and HAA5 60 ug/L, both evaluated as locational running annual averages.

THM formation increases with higher pH, temperature, contact time, and TOC; HAA formation is favored at lower pH.

Enhanced coagulation removes TOC; the required removal percentage depends on raw TOC and raw alkalinity under the D/DBP Rule.

UV disinfection dose is expressed in mJ/cm2 and leaves no residual, so a chemical secondary disinfectant is still required in distribution.

Maintain a detectable free chlorine residual throughout distribution, typically at least 0.2 mg/L at the farthest points per state rule.

Chlorine demand = dose applied minus residual remaining; demand must be satisfied before any measurable residual persists.

Affinity laws for a constant impeller diameter: flow varies with speed, head with speed squared, and brake horsepower with speed cubed.

The operating point is the intersection of the pump curve and the system curve; speed changes or valve throttling move that point.

Brake horsepower = (gpm x head in ft x specific gravity) / (3960 x efficiency expressed as a decimal).

NPSH available must exceed NPSH required at all flow rates to prevent cavitation, which causes noise, vibration, and impeller pitting.

1 psi = 2.31 ft of water head, so a 100-ft head equals about 43.3 psi.

Minimum distribution pressure is commonly 20 psi under all conditions; normal service pressure is about 35-80 psi with a 150 psi typical maximum.

Storage must provide equalization, fire flow, and emergency reserve; many states require total storage equal to maximum-day demand plus fire flow.

Dead-end mains promote stagnation, low residual, and biofilm; looped grids plus routine flushing control these conditions.

Water hammer from rapid valve closure or pump trip is controlled with slow-closing valves, surge tanks, air chambers, and flywheels.

Calibrate nephelometric turbidimeters with formazin or approved polymer standards and verify with a secondary standard each day of use.

Free and total chlorine residual are measured by DPD colorimetry or amperometric titration; DPD is the standard field method.

pH meters need two-point calibration using buffers that bracket the sample, typically 4.0, 7.0, and 10.0.

Holding times: chlorine residual and pH 15 minutes; turbidity 48 hours; nitrate 48 hours; coliform samples 8 hours (up to 30 hours with refrigeration in transit).

Revised Total Coliform Rule: a total-coliform-positive routine sample triggers repeat sampling within 24 hours and may require a Level 1 or Level 2 assessment.

Individual filter and combined filter effluent turbidity must be recorded at least every 15 minutes to establish compliance with the SWTR.

Quality control checks include method blanks, duplicates, matrix spikes, and continuing calibration verification; blanks should read near zero.

Trend coagulant dose, filtered turbidity, and chlorine residual on control charts and investigate shifts before they become exceedances.

Feed rate (lb/day) = mg/L x MGD x 8.34; rearranged, dose (mg/L) = lb/day / (MGD x 8.34).

Detention time = volume / flow; keep units consistent so gal / gpm gives minutes and ft3 / cfs gives seconds.

Surface loading rate (gpm/ft2) = flow (gpm) / area (ft2); weir loading (gpm/ft) = flow (gpm) / weir length (ft).

Conversions: 1 ft3 = 7.48 gal; 1 MGD = 694.4 gpm = 1.547 cfs; 1 cfs = 448.8 gpm.

Cylinder volume = 0.785 x D2 x H; rectangular basin volume = L x W x H.

Head (ft) = psi x 2.31; psi = ft of head / 2.31.

Percent removal = [(influent concentration - effluent concentration) / influent concentration] x 100.

Hypochlorite feed (lb/day) = gpd x 8.34 x (percent strength / 100).

CT = residual (mg/L) x contact time (min), where contact time = basin volume (gal) / flow (gpm) with consistent time units.

Permit-required confined space entry requires atmospheric testing (O2 19.5-23.5 percent, LEL under 10 percent, H2S under 10 ppm, CO under 35 ppm), a permit, an attendant, and rescue provisions.

Chlorine gas is heavier than air with an IDLH of 10 ppm; use supplied-air respiratory protection, keep cylinders away from heat, and evacuate upwind.

An SDS must be available for every hazardous chemical, and eyewash stations and safety showers must be within about 10 seconds of travel.

Lockout/tagout is required before servicing pumps, mixers, or chemical feeders; verify zero energy before work begins.

Public notice tiers: Tier 1 within 24 hours (immediate risk, such as an E. coli MCL), Tier 2 within 30 days, Tier 3 within 90 days.

Community water systems must deliver the annual Consumer Confidence Report to customers by July 1 covering the previous calendar year.

Retain turbidity and filter operating records at least 3 years, microbiological records at least 5 years, and chemical analysis records at least 10 years.

Operator certification requires passing the state exam and earning continuing education credits for renewal, commonly on a 2- or 3-year cycle.

Falsifying a monitoring report is a criminal violation; report MCL and monitoring violations to the primacy agency within the regulation's deadline.