Water Distribution Operator Class IV flashcards

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

Hazen-Williams equation

An empirical formula relating head loss to pipe length, flow, diameter, and roughness coefficient C; higher C values indicate smoother pipe and lower friction loss.

Static pressure conversion

Each foot of elevation head produces 0.433 psi, and 2.31 feet of head equals 1 psi; used to convert between elevation and pressure in distribution systems.

Minimum residual fire flow pressure

Twenty psi is the minimum residual pressure maintained at the point of fire flow during a fire; falling below risks backflow and contamination intrusion into mains.

Water hammer

A pressure surge caused by rapid changes in flow velocity, such as fast valve closure; mitigated with slow-closing valves, surge arrestors, and air valves.

CT concept

CT equals disinfectant residual concentration in mg/L multiplied by contact time in minutes; the calculated value is compared to a required CT based on pH, temperature, and log inactivation.

Filtered water turbidity limits

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 surface water filtration compliance.

Breakpoint chlorination

The point at which added chlorine fully oxidizes free ammonia to nitrogen gas, after which additional chlorine produces a persistent free chlorine residual.

Chlorine demand

The difference between the chlorine dose applied and the residual remaining after a specified contact time; it reflects chlorine consumed by reducing agents and organics.

Langelier Saturation Index

A calculated index of water's calcium carbonate saturation; a negative value indicates corrosive tendency and a positive value indicates scaling tendency.

Unidirectional flushing

A flushing method that closes valves to create one-way flow at 2.5 to 3 feet per second, sequencing from clean to dirty sections to scour sediment from mains.

Non-revenue water

System input volume minus billed authorized consumption; real losses are leaks and breaks, while apparent losses are meter error and unauthorized use.

Boil water advisory trigger

Issued when system pressure drops below 20 psi or contamination is suspected; requires flushing and coliform and chlorine sampling before service is restored.

Tank turnover

The practice of maintaining adequate daily flow through storage tanks, sometimes with mixing or drawdown, to prevent stratification, nitrification, and chlorine loss.

Brake horsepower formula

BHP equals flow in gpm times head in feet times specific gravity, divided by 3960 times pump efficiency; used to size motors and estimate power cost.

Affinity laws

For a centrifugal pump, flow varies directly with speed, head with the square of speed, and power with the cube of speed; impeller trim follows similar relationships.

NPSH available

NPSHa equals atmospheric pressure head plus static suction head minus vapor pressure head minus suction friction losses; it must exceed the pump's NPSH required.

Specific speed

Ns equals speed times the square root of flow divided by head to the 0.75 power; low values indicate radial high-head impellers and high values indicate axial high-flow impellers.

Motor voltage unbalance

Voltage unbalance should stay below 1 percent and current unbalance below 10 percent; higher values cause overheating and shortened motor life.

Backflow causes

Backflow requires a cross-connection plus either backsiphonage from negative supply pressure or backpressure where downstream pressure exceeds supply pressure.

Air gap

A physical separation between a supply outlet and the flood level rim, typically twice the pipe diameter and at least 1 inch; it is the highest protection and needs no testing.

Reduced pressure zone assembly

An RPZ protects against both backpressure and backsiphonage and is required for high health hazards; it is tested annually with a differential pressure gauge.

Pressure vacuum breaker

A PVB protects against backsiphonage only, cannot be under continuous pressure, and is used for low to moderate hazards such as irrigation systems.

Containment versus isolation

Containment protects the public main at the meter, while isolation protects hazards inside a facility such as boilers, chemical feed, and irrigation connections.

Confined space atmospheric limits

Acceptable entry conditions are oxygen between 19.5 and 23.5 percent, combustible gas below 10 percent of LEL, hydrogen sulfide below 10 ppm, and carbon monoxide below 35 ppm.

Chlorine gas leak response

Evacuate upwind, wear SCBA, and never apply water to the leak; only trained responders with PPE attempt containment and repair.

Trench protective systems

Trenches 5 feet deep or deeper require protective systems; spoil piles stay at least 2 feet from the edge and ladders within 25 feet of workers.

Public notice tiers

Tier 1 notice is issued within 24 hours for acute violations such as E. coli or nitrate, Tier 2 within 30 days, and Tier 3 annually for less urgent issues.

Consumer Confidence Report

An annual report delivered by July 1 that summarizes source water, detected contaminants, and compliance status for customers of a public water system.

Sanitary survey

A primacy agency review of source, treatment, distribution, and records every 3 to 5 years; significant deficiencies require corrective action and may trigger violations.

Span of control

The number of direct reports a supervisor effectively manages, commonly 5 to 8; wider spans require greater delegation and standardized procedures.

Progressive discipline

A documented sequence of corrective steps from verbal warning to termination, applied consistently to protect against claims of unfair treatment.

Feed rate formula

Feed rate in pounds per day equals dose in mg/L times flow in MGD times 8.34; rearranged, it solves for dose or flow given the other two values.