Free Water Distribution Operator Exam Flashcards

PVC (C900/C905), ductile iron pipe (DIP), HDPE, and legacy asbestos-cement (AC) mains still found in older systems. Selection depends on soil corrosivity, pressure class, and installation method.

A roughness/smoothness coefficient. A higher C-factor (150 for new PVC) means smoother interior walls and less friction head loss; a lower C-factor (80-100) indicates a rough, tuberculated old iron pipe with more head loss for the same flow.

Flowing water changing direction at a fitting creates an unbalanced thrust force trying to push the joint apart. Concrete thrust blocks or mechanical joint restraints (retainer glands) resist that force and prevent joint separation or blowouts.

Corrosion-driven buildup of iron oxide nodules on the pipe interior. It reduces effective diameter and C-factor, increasing head loss and reducing carrying capacity, and can cause red-water/taste-and-odor complaints.

Periodically operating every distribution valve through its full range keeps it from seizing in one position, verifies it will close fully to isolate a main break, and updates valve condition and location records.

At least 2.5 feet per second. UDF isolates valves to force flow through a single-direction path and out one hydrant, achieving higher scouring velocity than conventional multi-directional flushing.

It measures the system's available fire flow and pressure. Static pressure (no flow) is read at a residual hydrant, then a flow hydrant is opened and the residual pressure (pressure drop under flow) and pitot-gauge flow rate are recorded.

Butterfly valves are common in larger mains because their compact disc design needs less space and torque to operate. Gate valves are common in smaller mains/services and provide a fully unobstructed bore when open.

1 psi equals 2.31 feet of head (water at about 60 degrees F). Conversely, pressure (psi) = height of water column (ft) times 0.433. A 100-foot elevated tank produces about 43.3 psi at its base.

7.48 gallons per cubic foot. This conversion moves between tank/pipe volume calculations (cubic feet) and gallons for dosing, storage, and flow-rate problems.

Area = 0.785 x D-squared, where D is the inside diameter in feet (0.785 is approximately pi/4). Multiplying area by velocity gives flow rate; doubling the diameter quadruples the area and capacity.

A sudden change in flow velocity - a valve slammed shut or a pump stopping abruptly - creates a pressure surge (transient) that travels through the pipe. It can rupture pipes, damage joints, and dislodge sediment; slow valve closure and surge-relief devices reduce the risk.

Supervisory Control and Data Acquisition. It remotely monitors and controls system parameters such as tank levels, pump status, pressure, and flow, and can automatically start/stop pumps or trigger alarms without an operator on-site.

Static water level is the level when the pump is off and water has fully recovered. Pumping water level is the lower level while the pump runs; the difference between them is the drawdown caused by withdrawal.

A centrifugal pump's flow varies with system pressure/head and can be throttled by a valve. A PD pump delivers a fixed volume per revolution regardless of pressure and must never be dead-headed - it needs a relief valve because pressure will keep rising against a closed discharge.

Cavitation - the formation and violent collapse of vapor bubbles at the impeller eye when available suction head drops below what the pump requires. Available NPSH must exceed required NPSH or the pump can suffer noise, vibration, and impeller damage.

Flow decreases as head increases - centrifugal pump curves slope downward from high flow/low head to low flow/high head. The pump's actual operating point is where its curve intersects the system curve.

WHP = (flow in gpm x total dynamic head in ft) divided by 3,960. Brake horsepower (BHP), the motor's input power, equals WHP divided by pump efficiency, and is always larger than WHP because no pump is 100% efficient.

Parallel pumps add their flows at a given head, but as combined flow rises, system friction head loss also rises, pushing the operating point up the (now steeper) system curve - so the flow gain is less than double, unlike series pumps, which add head rather than flow.

An elevated tank is raised on a tower to provide gravity pressure over a wide area. A standpipe is a tall, ground-mounted cylindrical tank where only the upper portion above the needed head is usable storage. A ground storage reservoir sits at grade and typically needs a booster pump station to deliver pressure.

A control valve on the fill line of an elevated tank or standpipe that automatically closes when the tank reaches a preset high level, preventing overflow, and opens to let the tank supply the system on demand.

AWWA C652. Depending on tank size and repair scope, operators use one of several chlorination methods (spraying/swabbing interior surfaces, a high-dose fill, or a lower continuous-feed dose) followed by a holding period and bacteriological clearance sampling before returning the tank to service.

Interior/exterior coating condition and corrosion, roof vents and overflow pipe screening (to keep insects/animals out), hatch security, structural cracks or leaks, cathodic protection function, and sediment accumulation on the tank floor.

The corporation stop ('corp stop') is the valve tapped directly into the main that connects the service line. The curb stop is a second shutoff valve near the property line/curb box that lets the utility isolate an individual service without shutting down the main.

AWWA C651. The new section is flushed, chlorinated to a high initial dose with adequate contact time, flushed again, and cleared with two consecutive satisfactory bacteriological samples before being placed in service.

Call 811 (or the local one-call center) to have all underground utilities located and marked, satisfying the utility locating and notification requirement before any digging begins.

Water that is produced but not billed - lost to real losses (main breaks, leaks) or apparent losses (meter inaccuracy, unauthorized use, billing errors). A water loss audit quantifies each loss category so operators can prioritize leak detection and meter replacement, supporting the system's water loss control program.

A detectable residual is required at all points; the operational benchmark is at least 0.2 mg/L free chlorine entering the distribution system, with a detectable residual maintained throughout the system to prevent microbial regrowth.

4.0 mg/L, measured as an annual running average. It is the highest disinfectant level allowed, balancing adequate disinfection against the health risk of excess chlorine and its byproducts.

Pounds per day = dose (mg/L) x flow (MGD) x 8.34. This 'pounds formula' converts a target concentration and flow rate directly into the chemical feed rate.

The point at which enough chlorine has been added to destroy all chlorine-demanding substances (ammonia, organics) so that any further chlorine added remains as free available chlorine rather than being consumed forming chloramines.

TTHM MCL = 80 micrograms/L (0.080 mg/L); HAA5 MCL = 60 micrograms/L (0.060 mg/L), both measured as locational running annual averages under the Stage 2 Disinfectants and Disinfection Byproducts Rule. Both rise with water age and chlorine contact time.

Lead action level = 15 ppb (0.015 mg/L); copper action level = 1.3 mg/L, both based on the 90th-percentile tap sample. The 2024 LCRI lowers the lead action level itself to 10 ppb (compliance beginning Nov 1, 2027) — removing the separate LCRR 'trigger level' construct — and requires utilities to inventory and replace nearly all lead service lines within about 10 years. The 15 ppb action level remains in effect until the LCRI compliance date.

The time water spends in mains and storage tanks between treatment and the customer's tap. Longer water age lets disinfectant residual decay and disinfection byproducts (TTHM/HAA5) accumulate, and can allow nitrification in chloraminated systems; storage tank turnover and looped mains help control it.

Under the RTCR (effective 2016), total coliform has NO MCL and NO MCLG — it is handled by a treatment-technique / Level 1-2 assessment trigger. The MCLG of zero applies to E. coli (which also carries an occurrence-based MCL). A total-coliform-positive routine sample triggers repeat sampling and an assessment; an E. coli-positive result is an acute, health-based (Tier 1) violation requiring immediate public notification.

At least 3 repeat samples within 24 hours: one at the original tap, one within 5 service connections upstream, and one within 5 service connections downstream, each also tested for E. coli.

Free (and total) chlorine residual testing, typically using the DPD colorimetric method, and pH testing, both performed routinely at representative distribution sampling points to confirm disinfectant residual and chemical stability.

Bacteriological sample bottles are pre-sterilized and typically contain a dechlorinating agent (sodium thiosulfate). Rinsing removes the dechlorinator and can introduce contamination, invalidating the sample.

Air gap (AG) provides the highest protection as a physical, non-mechanical break; then reduced pressure zone assembly (RP/RPZ); then double check valve assembly (DCVA); then pressure vacuum breaker (PVB) and atmospheric vacuum breaker (AVB), which protect only against backsiphonage, not backpressure.

Backpressure occurs when downstream pressure (from a pump, boiler, or elevated tank on the customer's side) exceeds supply pressure, pushing water backward. Backsiphonage occurs when supply-side pressure drops below atmospheric (e.g., a main break or high fire-flow withdrawal), creating a vacuum that pulls water backward.

A reduced pressure zone (RP/RPZ) assembly, or an air gap. Double check valve assemblies and vacuum breakers are approved only for low or non-health-hazard (aesthetic) cross-connections.

Annually, by a certified backflow assembly tester, per AWWA Manual M14 guidance and most state/local cross-connection control programs. Testing verifies the internal check valves and relief mechanism still function correctly.

It is large enough to enter, has limited entry/exit, is not designed for continuous occupancy, and contains (or could contain) a hazardous atmosphere, an engulfment hazard, or another serious safety hazard. Vaults, wet wells, and large-diameter mains often qualify.

To de-energize and physically lock out equipment (pumps, valves, electrical panels) before maintenance or repair, with a tag identifying who applied the lock, preventing unexpected startup or release of stored energy that could injure a worker.

For trenches 5 feet deep or more, unless the excavation is entirely in stable rock. A competent person must classify the soil type and select an appropriate protective system (shoring, shielding, or sloping) before workers enter.

Main breaks, valve operation, and hydrant work often occur in or near active traffic lanes. Proper cones, signs, and flagging, following an MUTCD-based traffic control plan, protect both the crew and the public.

Procedures for main breaks, loss of pressure, contamination events, and natural disasters or power outages, including notification chains, alternate water supply/interconnections, and steps to protect public health until normal operation is restored.

Within 24 hours of the system learning of the violation, using the most direct method reasonably available. Tier 2 (other MCL/treatment technique violations) allows 30 days, and Tier 3 (monitoring/reporting violations) allows up to 1 year, often via the annual Consumer Confidence Report.

Water quality sampling and lab results, maintenance and repair logs, flushing and valve-exercising records, main/service installation records (often in GIS), disinfection and bacteriological clearance records for new work, and cross-connection control program records.

A systematic approach to inventorying infrastructure condition, age, and criticality (pipes, valves, tanks, pumps) to plan maintenance, repair, and capital replacement proactively, reducing unplanned failures and supporting budget and rate decisions.