WA Water/Wastewater Operator flashcards

33 cards. Read the term and the definition here. The deck at the top of this page is optional.

Turbidity 95% rule

Conventional and direct filtration systems must produce finished water at or below 0.3 NTU in at least 95% of monthly measurements, and no single sample may exceed 1 NTU.

GWUDI

Groundwater under the direct influence of surface water, meaning it is hydraulically connected to surface water and must be treated under surface water treatment rules.

Lead action level

The 90th percentile tap sample concentration of 0.015 mg/L for lead; exceeding it triggers corrosion control evaluation, public education, and additional monitoring.

Nitrate MCL

The maximum contaminant level for nitrate is 10 mg/L measured as nitrogen, set to prevent methemoglobinemia in infants.

Coagulation

A treatment step that neutralizes the negative surface charge on suspended particles so they can collide and stick together during flocculation.

Flocculation velocity gradient

The mixing intensity, typically 10 to 75 per second, applied with 15 to 45 minutes of detention to build settleable floc after rapid mix.

Filter backwash

Reversing flow through a filter to expand the bed about 20 to 50 percent and wash out captured solids, restoring headloss capacity.

CT concept

The product of disinfectant residual concentration and effective contact time, used to determine the log inactivation credit earned by a treatment process.

Minimum distribution pressure

Systems must maintain at least 20 psi throughout the distribution network under all flow conditions to prevent contamination from backflow.

Residual disinfectant

A detectable disinfectant concentration, typically at least 0.2 mg/L free chlorine, maintained throughout the distribution system to protect against microbial regrowth.

Hazen-Williams C factor

A pipe roughness coefficient used to compute head loss; values near 130 to 140 represent smooth new pipe and lower values represent rougher older mains.

Air gap

A physical separation between a potable water outlet and the flood level of a receiving vessel, providing the highest protection against backflow.

Minimum sewer velocity

Sanitary sewers are designed for at least 2 feet per second at design flow so solids stay suspended and the pipe self-cleans.

Infiltration versus inflow

Infiltration is groundwater entering through defective pipes and joints, while inflow is stormwater entering through direct connections such as roof drains.

Manning's equation

A formula relating flow to pipe slope, hydraulic radius, cross-sectional area, and a roughness coefficient n to size gravity sewers.

Hydrogen sulfide corrosion

Sulfide produced by anaerobic bacteria in sewers converts to sulfuric acid on wet concrete above the waterline, destroying the pipe crown.

Pump affinity laws

For a given impeller, flow changes with speed, head with the square of speed, and power with the cube of speed.

Brake horsepower formula

Pump power equals flow in gpm times head in feet times specific gravity, divided by 3960 times pump efficiency.

Cavitation

Vapor bubbles form and collapse in a pump when available NPSH is too low, causing noise, vibration, and damage to the impeller.

Best efficiency point

The flow at which a centrifugal pump operates with highest efficiency and lowest hydraulic loads; running far from it shortens equipment life.

Motor full-load amps

The current a motor draws at rated load and voltage, listed on the nameplate and used to size overload protection.

Breakpoint chlorination

The chlorine dose, near a 7.6 to 1 weight ratio to ammonia, beyond which free chlorine residual rises sharply after destroying chloramines.

Chlorine demand

The amount of chlorine consumed by reactions with organic and inorganic material before any free residual remains; dose equals demand plus desired residual.

Chemical dose formula

Dose in mg/L equals feed rate in pounds per day times 8.34 divided by plant flow in million gallons per day.

Chloramine formation

Free chlorine reacts with ammonia to form monochloramine and other species that are weaker disinfectants but persist longer in distribution systems.

DPD method

A colorimetric test using DPD indicator to measure free chlorine; subtracting free from total approximates the combined chlorine concentration.

Nephelometric turbidity

Turbidity measured by the light scattered at 90 degrees from a sample, reported in NTU and calibrated with formazin or approved standards.

Jar test

A bench-scale test that simulates rapid mix, flocculation, and settling at several chemical doses to select the coagulant dose for the plant.

BOD5

The oxygen consumed by microorganisms over five days at 20 degrees Celsius, used to measure biodegradable organic strength of wastewater.

Consumer Confidence Report

An annual water quality report that community water systems must deliver to customers by July 1, summarizing source, contaminants, and compliance.

Tier 1 public notice

Notification required within 24 hours for acute violations such as an MCL exceedance for nitrate or a situation posing immediate health risk.

Lockout tagout

A procedure that isolates and locks energy sources before maintenance so equipment cannot start unexpectedly, verified by testing for zero energy.

Confined space entry permit

A written authorization listing atmospheric test results, hazards, entrants, attendant, and rescue plan required before entering a permit-required confined space.