WA Water/Wastewater Operator cheat sheet

Washington surface water sources are classified by the federal Surface Water Treatment Rule; groundwater under direct influence of surface water (GWUDI) must be treated as surface water.

Turbidity limits: conventional filtration must produce finished water ≤0.3 NTU in at least 95% of monthly samples, with no sample exceeding 1 NTU.

Total coliform Rule: no more than 5% of monthly samples may be positive for systems collecting 40 or more samples per month; any positive triggers repeat sampling.

Disinfection byproduct limits under Stage 2 DBPR: TTHM running annual average ≤80 µg/L and HAA5 ≤60 µg/L.

Lead action level is 0.015 mg/L and copper action level is 1.3 mg/L, measured at the 90th percentile of tap samples.

Nitrate MCL is 10 mg/L as nitrogen; arsenic MCL is 0.010 mg/L; fluoride MCL is 4.0 mg/L with a secondary limit of 2.0 mg/L.

Alkalinity, pH, and temperature govern corrosion control; negative Langelier Saturation Index indicates water tends to be corrosive.

Source water assessment and wellhead protection programs identify potential contamination threats within the contributing area.

Coagulation destabilizes particles by neutralizing negative surface charge; rapid mix velocity gradient typically 300-1000 per second for under 30 seconds.

Flocculation builds settleable flocs at a velocity gradient of roughly 10-75 per second with detention time of 15-45 minutes.

Sedimentation design overflow rate for conventional clarifiers is commonly 0.3-1.0 gpm/ft²; shallower settling depth improves removal per Stokes' law.

Rapid sand filtration rate is typically 2-6 gpm/ft²; filter run ends on headloss limit, turbidity breakthrough, or run time.

Backwash requires bed expansion of about 20-50% and air scour or surface wash to break up mudballs.

CT (disinfectant concentration × contact time) must meet the required value for the log inactivation credited; baffling factor reduces theoretical contact time.

Softening by lime precipitation removes calcium and magnesium; excess lime raises pH and requires recarbonation for stability.

Ion exchange, activated alumina, and reverse osmosis are used for nitrate, arsenic, and dissolved solids removal respectively.

Minimum residual disinfectant in distribution is typically 0.2 mg/L free chlorine; detectable residual must be maintained throughout the system.

System pressure must be maintained at a minimum of 20 psi under all conditions, including fire flow, to prevent backflow contamination.

Water age increases with low demand and oversized mains; long detention degrades residual and raises disinfection byproduct formation.

Head loss in pipes follows the Hazen-Williams equation; C factors of 100-140 represent roughness, with lower values for older unlined mains.

Cross-connection control requires an air gap or reduced-pressure-zone backflow assembly; testable assemblies are tested annually.

Storage tanks need turnover, vent screening, and overflow protection; altitude valves and mixing systems control level and quality.

Leak detection uses acoustic listening, correlators, or step testing; minimum night flow indicates the level of real losses.

Flushing velocity of at least 2.5 ft/s scours sediment; unidirectional flushing sequences from clean to dirty zones.

Sanitary sewer design velocity: minimum 2 ft/s for self-cleansing, maximum about 10 ft/s to limit scour and hydrogen sulfide release.

Manning's equation: Q = (1.486/n) A R^(2/3) S^(1/2); typical n for vitrified clay or concrete pipe is 0.013.

Infiltration enters through defective pipe and joints; inflow enters through direct connections such as roof drains and catch basins.

Peak wet-weather flow is estimated by the rational method Q = CiA or by unit hydrograph methods for combined systems.

Lift stations use wet wells with pumps alternating to equalize wear; check valves and air release prevent backflow and surge.

Hydrogen sulfide causes corrosion of concrete crown, odors, and toxicity; dosing ferric salts or nitrate controls sulfide.

Confined space entry into sewers requires atmospheric testing for oxygen, flammables, and H2S before and during entry.

Sewer rehabilitation methods include cured-in-place lining, slip lining, and grouting; smoke testing locates inflow sources.

Pump affinity laws: flow varies with speed, head with speed squared, power with speed cubed for a given impeller diameter.

Brake horsepower = (Q × H × specific gravity) / (3960 × pump efficiency) with Q in gpm and H in feet.

NPSH available must exceed NPSH required to avoid cavitation; cavitation causes noise, vibration, and impeller erosion.

Centrifugal pumps operate near best efficiency point; running far left or right of BEP shortens bearing and seal life.

Motor full-load current is read from the nameplate; overload heaters are sized at 115-125% of FLA per NEC.

Vibration analysis, thermography, and lubricant analysis are predictive maintenance tools; alignment and balance reduce wear.

Positive displacement pumps deliver nearly constant flow against varying head and require a relief valve on the discharge.

Mechanical seals and packing require controlled leakage or flush water; packing is adjusted to a slight drip.

Chlorine dose = demand + residual; free chlorine reacts with ammonia to form chloramines, which are weaker disinfectants.

Breakpoint chlorination requires a chlorine-to-ammonia weight ratio near 7.6 to 1 to convert ammonia to nitrogen gas.

Hypochlorite strength degrades over time and with heat; sodium hypochlorite solution is typically 12.5% and stored cool and dark.

Chlorine gas is 2.5 times heavier than air; one ton cylinder leak requires respiratory protection and emergency response.

CT requirement: log inactivation credit depends on disinfectant type, concentration, contact time, pH, and temperature.

Chemical feed pumps are calibrated by drawdown test; dose in mg/L = (feed rate in lb/day × 8.34) / flow in MGD.

UV disinfection dose is measured in mJ/cm²; transmittance of the water affects delivered dose.

Ozone is generated on site, requires contact chamber and off-gas destruction; bromate formation is a concern.

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

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

pH meter calibration uses two buffers bracketing the sample, commonly pH 7 and pH 10; slope should be 95-105%.

Jar testing determines coagulant dose by varying chemical dose and mixing conditions and measuring settled turbidity.

Total coliform presence/absence uses defined substrate methods; positive samples must be followed by repeat sampling.

TSS is measured by filtering a known volume and drying at 103-105 °C; volatile solids are ignited at 550 °C.

BOD5 measures oxygen consumed over five days at 20 °C; nitrification inhibition may be needed.

Quality control includes blanks, duplicates, spikes, and control charts; holding times and preservation must be met.

Washington operator certification is issued by the Department of Health; water treatment and distribution certifications are separate.

Consumer Confidence Report (annual water quality report) must be delivered to customers by July 1 each year.

Monitoring violations and MCL violations require public notification within 24 hours for acute risks and 30 days for others.

Confined space entry requires a permit, atmospheric testing, attendant, and retrieval system; IDLH atmospheres require supplied air.

Hazard communication requires Safety Data Sheets and labeling for all chemicals; chlorine and ammonia have specific emergency plans.

Records for bacteriological samples, chemical analyses, and operation must be retained at least five years per federal rule.

Lockout/tagout isolates energy sources before equipment maintenance; verify zero energy state before work.

Fall protection is required at 4 feet in general industry; ladder and guardrail rules apply to tank and basin access.