MN Water Operator flashcards

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

Rapid mix purpose

Rapid mix disperses coagulant into raw water within seconds, destabilizing particle charges so particles can collide and form floc during later gentle flocculation.

Flocculation velocity gradient

Gentle mixing for 15 to 45 minutes at a velocity gradient of about 10 to 75 per second builds floc that settles without being sheared apart.

Surface overflow rate

Flow divided by sedimentation basin surface area, expressed in gpm/ft²; particles whose settling velocity equals or exceeds this rate are removed.

Filter backwash expansion

Backwashing at roughly 15 to 20 gpm/ft² expands the filter bed about 20 to 30 percent, releasing trapped solids; inadequate expansion leaves mudballs and media clumps.

Jar test purpose

A bench test that mixes raw water with varying coagulant doses and pH values to identify the lowest dose meeting the turbidity target.

Lime-soda softening

Lime and soda ash precipitate calcium carbonate and magnesium hydroxide to reduce hardness; excess lime raises pH and usually requires recarbonation for stability.

Iron and manganese removal

Soluble iron and manganese are oxidized by aeration, chlorine, or permanganate and then filtered out; manganese greensand is a common catalytic medium.

Minimum distribution pressure

Public water systems should maintain at least 20 psi at all points in the distribution system under normal and fire-flow conditions to prevent backflow.

Distribution chlorine residual

A detectable free chlorine residual, commonly 0.2 mg/L or higher, is maintained throughout the distribution system to limit bacterial regrowth.

Hazen-Williams head loss

Friction loss in a pipe increases with flow raised to about 1.85 and decreases with pipe diameter raised to about 4.87.

Air gap backflow protection

An air gap is a nonmechanical backflow preventer in which the supply pipe ends at least one pipe diameter above the flood rim of the receiving fixture.

Main break boil order

A boil water notice is issued when a main break drops pressure below 20 psi and contamination may enter; it remains until sampling clears the system.

Unidirectional flushing

Flushing in one direction at 2.5 ft/s or more scours sediment and biofilm from mains; valves are sequenced so flow travels a single path.

Convert psi to feet

Multiply pressure in psi by 2.31 to obtain feet of water head; for other liquids, divide the result by the liquid's specific gravity.

Water horsepower formula

Water horsepower equals gallons per minute times total head in feet times specific gravity, divided by 3960.

Affinity laws

For a centrifugal pump, flow varies directly with speed, head varies with speed squared, and power varies with speed cubed.

Pumps in series

Series pumps move the same flow and add their heads; parallel pumps operate at the same head and add their flows.

Cavitation cause

Cavitation occurs when available net positive suction head falls below required NPSH, causing vapor bubbles to collapse and damage the impeller.

Three-phase power

Electrical power in kilowatts equals voltage times amperage times power factor times 1.732, divided by 1000.

HOCl versus OCl

Hypochlorous acid is a much stronger disinfectant than hypochlorite ion; the two are roughly equal near pH 7.5, and lower pH favors HOCl.

Combined chlorine

Combined chlorine equals total chlorine minus free chlorine; it is mostly chloramines, which are weaker disinfectants and cause taste and odor.

Chlorine demand

Chlorine demand is the applied dose minus the residual remaining after the specified contact time; demand must be satisfied before a residual persists.

CT concept

CT is disinfectant residual in mg/L multiplied by contact time in minutes; required CT rises as temperature falls or pH rises.

Breakpoint chlorination

About 7.6 mg of chlorine per mg of ammonia nitrogen oxidizes ammonia to nitrogen gas; free chlorine persists beyond that breakpoint.

Bacteriological sample handling

Collect 100 mL in a sterile thiosulfate-treated bottle, keep near 4°C, and deliver to the laboratory within 30 hours of collection.

Turbidity limits

Conventional filtration must produce 0.3 NTU or less in at least 95 percent of monthly samples and must never exceed 1 NTU.

Confined space atmosphere

Entry requires oxygen between 19.5 and 23.5 percent, flammable gas below 10 percent of the lower explosive limit, and hydrogen sulfide below 10 ppm.

Lockout tagout verification

After locking and tagging the energy source, attempt to start the equipment and confirm a zero-energy state before work begins.

Chlorine gas detection

A dilute ammonia solution held near a suspected leak forms a white cloud with chlorine gas; responders wear SCBA and approach from upwind.

Nitrate MCL

The maximum contaminant level for nitrate as nitrogen is 10 mg/L; infants under six months are at risk of methemoglobinemia.

Consumer confidence report

Community water systems must deliver an annual drinking water report to customers by July 1 covering source water, detected contaminants, and health effects.

Tier 1 public notice

A Tier 1 notice must be issued within 24 hours for violations or situations with immediate health risk, such as an E. coli MCL.