IN Water/WW Operator cheat sheet

Coagulation (alum, ferric salts, cationic polymer) destabilizes colloidal particles; alum generally performs best near pH 5.5-6.5 for turbidity removal.

Flocculation is gentle tapered mixing (velocity gradient G roughly 10-75 s^-1 for 15-45 minutes) so destabilized particles collide and grow into settleable floc.

Sedimentation sizing: surface overflow rate = flow / surface area; particles whose settling velocity is below the overflow rate carry over in the effluent.

Rapid sand filtration loading is about 2-5 gpm/ft2; backwash runs 15-20 gpm/ft2 with roughly 20-30 percent bed expansion, often with air scour.

CT = disinfectant residual (mg/L) x contact time (minutes); the required CT for free chlorine rises as pH increases and as water temperature falls.

Chlorine demand = applied dose minus residual; finished water typically leaves the plant with a free chlorine residual of at least 0.2 mg/L.

Conventional filtration turbidity limits: combined filter effluent at or below 0.3 NTU in 95 percent of monthly samples and never above 1 NTU.

Lime softening: a first stage near pH 9.5 precipitates calcium carbonate; a second stage near pH 10.5-11 precipitates magnesium hydroxide.

MF and UF membranes remove particles and pathogens; NF and RO remove dissolved ions and are rated by molecular weight cutoff or salt rejection rather than pore size.

Static pressure equals 0.433 psi per foot of elevation; a tank water surface 100 feet above a tap produces about 43.3 psi at that tap.

Hazen-Williams head loss hL = 10.44 L Q^1.852 / (C^1.852 d^4.87) in US units; higher C means smoother pipe, about 130-140 for new cement-lined or PVC main.

A common regulatory minimum is 20 psi anywhere in the system under all flow conditions, while design targets are usually 35-50 psi at customer meters.

A detectable disinfectant residual must be carried throughout the system; many primacy agencies require at least 0.2 mg/L free chlorine at representative points.

Water hammer controls include slow-closing valves, surge tanks, air and vacuum release valves, and pump bypass or flywheel arrangements.

Backflow protection hierarchy: air gap is best, then reduced-pressure principle assembly, then double check valve, then vacuum breaker; only testable assemblies resist backpressure.

Unidirectional flushing targets at least 2.5-3 ft/s to scour sediment; dead-end mains are flushed on a schedule to limit stagnation and biofilm growth.

Leak detection pairs minimum night flow analysis with acoustic correlation; a rising 2-4 a.m. baseline flow indicates unreported leakage.

BOD5 is measured after 5 days of incubation at 20 degrees Celsius; nitrification must be inhibited when only carbonaceous oxygen demand is reported.

Activated sludge F/M = lb BOD applied per day / lb MLVSS under aeration; conventional plants run 0.2-0.5 per day and extended aeration runs below 0.1 per day.

MCRT (SRT) sets the biomass inventory; nitrification generally needs SRT of at least 10 days at 20 degrees C and longer in cold water.

Dissolved oxygen in the aerobic basin is held near 1.5-3.0 mg/L; aeration blowers are normally the plant's largest energy consumer.

RAS returns 50-100 percent of influent flow, WAS controls SRT, and SVI of 80-150 mL/g indicates good settling while values above 200 mL/g indicate filamentous bulking.

Secondary clarifier design values are about 400-800 gpd/ft2 overflow rate and no more than 25-30 lb/day/ft2 solids loading at peak flow.

Nitrification consumes about 7.14 mg alkalinity as CaCO3 and 4.57 mg O2 per mg NH3-N oxidized; denitrification recovers roughly 2.86 mg O2 per mg NO3-N.

Mesophilic anaerobic digestion runs at 35-38 degrees C with a 20-30 day SRT, destroying 40-50 percent of volatile solids and producing biogas of about 60-65 percent methane.

Gravity sewers are designed for a self-cleansing velocity near 2 ft/s, with scour risk above roughly 10-15 ft/s in concrete pipe.

Typical minimum slopes are about 0.40 percent for 8-inch, 0.28 percent for 10-inch, and 0.22 percent for 12-inch pipe, chosen to deliver 2 ft/s at design average flow.

Manning equation: V = (1.486/n) R^(2/3) S^(1/2), with n near 0.013 for new concrete or VCP and 0.015 or higher for old or rough pipe.

Sanitary sewers convey domestic and industrial flow to treatment, storm sewers discharge directly to receiving waters, and combined sewers overflow as CSOs in wet weather.

Force mains need at least 2 ft/s to keep solids suspended, and designers often check the system against a 3-5 ft/s scouring criterion.

I/I reduction uses smoke testing, dye testing, CCTV inspection, and joint or CIPP rehabilitation; excessive I/I is a leading cause of sanitary sewer overflows.

Wet well pump cycling targets a minimum cycle time of about 10-15 minutes; pumps alternate to equalize wear and VFDs soften surge.

Confined space entry atmosphere limits: oxygen 19.5-23.5 percent, LEL below 10 percent, hydrogen sulfide below 10 ppm, carbon monoxide below 35 ppm, monitored continuously.

Hydrogen sulfide has an odor threshold near 0.01-0.3 ppm, causes olfactory fatigue above about 10 ppm, and has an IDLH of 100 ppm; it is heavier than air.

Methane is flammable in air between a 5 percent lower explosive limit and a 15 percent upper explosive limit and accumulates in vaults and wet wells.

Chlorine gas is roughly 2.5 times heavier than air and has an IDLH of 10 ppm; leaking gas collects at low points and response requires SCBA with an escape pack.

Excavations 5 feet deep or more require a protective system, 20 feet or more require an engineered design, and a competent person inspects daily and after rain.

Spoil, tools, and materials stay at least 2 feet back from the trench edge, and ladders must be within 25 feet of lateral travel for every worker.

Lockout/tagout requires isolating every energy source, verifying zero energy, applying personal locks, and removal only by the person who applied the lock.

Engine-driven equipment in sewers and wet wells adds carbon monoxide and exhaust gases that can displace oxygen, so the atmosphere is tested before and during entry.

The Safe Drinking Water Act of 1974 sets national primary standards; states that obtain primacy enforce the rules and certify distribution and treatment operators.

Total coliform rule: no more than 5 percent of monthly samples may be total-coliform positive, and any routine sample positive for E. coli is an MCL violation.

Lead and copper action levels are 0.015 mg/L for lead and 1.3 mg/L for copper at the 90th percentile; exceedance triggers corrosion control and public education.

Disinfection byproduct limits are 80 micrograms per liter for total trihalomethanes and 60 micrograms per liter for HAA5, evaluated as locational running annual averages.

Primary MCL examples: nitrate 10 mg/L as nitrogen, nitrite 1 mg/L, arsenic 0.010 mg/L, and fluoride 4.0 mg/L.

The Clean Water Act of 1972 created NPDES permits with effluent limits; sanitary sewer overflows and combined sewer overflows must be reported to the state agency.

40 CFR Part 503 governs biosolids, including pathogen reduction, vector attraction reduction, and ceiling concentrations for metals.

Public notice deadlines are 24 hours for Tier 1, 30 days for Tier 2, and one year for Tier 3; the annual Consumer Confidence Report covers the prior calendar year.

Capacity reviews examine technical, managerial, and financial (TMF) capacity, and new systems must demonstrate capacity before state approval.

Retain monitoring data, chain-of-custody forms, and operating logs for the period set by the primacy agency, commonly at least 3-5 years and longer for some records.

Budgets separate O&M costs (chemicals, power, labor) from capital costs (replacement, expansion); rates must fund both plus a capital reserve.

Preventive maintenance intervals come from manufacturer recommendations, run hours, and condition monitoring, with a work order system documenting completion.

Emergency response plans list personnel roles, mutual aid agreements, notification lists, and alternate water or power sources; AWIA adds risk and resilience assessments for larger systems.

Operator certification requires continuing education units each renewal cycle and a certified operator in charge at the grade matching the facility classification.

A cross-connection control program needs an ordinance, site surveys, device installation, annual testing by certified testers, and recordkeeping.