GA Water/WW Operator flashcards

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

CT value

CT is disinfectant residual concentration in mg/L multiplied by contact time in minutes; the required CT rises with pH, falls with rising temperature, and depends on the target log inactivation.

Jar test

A bench-scale procedure that mixes raw water with varying coagulant doses and pH values to identify the dose producing the lowest settled and filtered turbidity before full-scale adjustments are made.

Filter backwash trigger

A rapid sand filter is backwashed when head loss reaches its terminal value, about 8 to 10 feet, or when effluent turbidity breaks through, typically every 24 to 72 hours.

Surface overflow rate

A sedimentation design parameter equal to flow rate divided by clarifier surface area, expressed in gpm per square foot; lower values give longer detention and better particle removal.

Chlorine demand

The difference between the chlorine dose applied and the chlorine residual remaining after a contact period; it reflects chlorine consumed by oxidizable material in the water.

Water hammer

A pressure surge caused by a rapid change in flow velocity, such as sudden valve closure or pump trip, that travels through the piping and can rupture mains and damage fittings.

Air gap

The only backflow prevention method providing absolute protection: a physical separation between the supply outlet and the flood-level rim of the receiving vessel or fixture.

Hazen-Williams formula

An empirical equation relating head loss to flow rate, pipe diameter, pipe length, and a roughness coefficient C; C is roughly 130 to 140 for new cement-lined or plastic pipe.

Distribution chlorine residual

Free chlorine measured at points throughout the distribution system; a detectable residual, commonly at least 0.2 mg/L, must be maintained to prevent microbial regrowth in the mains.

Main disinfection per C651

AWWA C651 requires new water mains to receive an initial 25 mg/L chlorine dose held 24 hours, leaving at least 10 mg/L residual before flushing and coliform sampling.

Food to microorganism ratio

Pounds of BOD applied per day divided by pounds of MLVSS in the aeration tank; conventional activated sludge operates in the range of 0.2 to 0.5.

Mean cell residence time

Total solids held in the aeration system divided by solids leaving the system per day; it is the sludge age that controls nitrification and the amount of waste sludge produced.

Sludge volume index

The volume in milliliters occupied by one gram of settled sludge after 30 minutes of settling; values of 80 to 150 indicate good settling and above 150 suggests bulking.

Nitrification alkalinity demand

Oxidizing one milligram of ammonia nitrogen to nitrate consumes about 7.1 milligrams of alkalinity as calcium carbonate, so nitrifying plants may need supplemental alkalinity to hold pH.

Primary clarifier overflow rate

A typical design surface overflow rate for a primary clarifier treating municipal wastewater is 600 to 800 gallons per day per square foot, with detention of 1.5 to 2.5 hours.

Manning's equation

An equation used to size gravity sewers in which velocity depends on pipe roughness, hydraulic radius, and slope, with n near 0.013 for new concrete or plastic sewer pipe.

Infiltration and inflow

Infiltration is groundwater entering sewers through defects, while inflow is stormwater entering through direct connections such as roof drains and manhole covers; both add clear water needing treatment.

Minimum sewer velocity

Gravity sewers are designed to carry at least 2 feet per second at design flow so solids stay suspended; velocities above 10 to 15 feet per second can erode the pipe.

Force main velocity

Wastewater force mains are typically sized for 2 to 4 feet per second to keep solids in suspension, and pumps cycle periodically to limit septic conditions and sulfide generation.

Confined space oxygen range

An acceptable entry atmosphere is 19.5 to 23.5 percent oxygen; below 19.5 percent is oxygen deficient, and above 23.5 percent creates a fire or explosion hazard.

Hydrogen sulfide IDLH

Hydrogen sulfide is immediately dangerous to life or health at 100 ppm; it deadens the sense of smell at higher concentrations, so odor is never a reliable warning of exposure.

Methane explosive range

Methane's lower explosive limit is 5 percent in air and its upper explosive limit is 15 percent; entry is stopped and the space ventilated when readings reach 10 percent LEL.

Excavation shoring threshold

OSHA requires a protective system for trenches 5 feet or deeper, a ladder within 25 feet of lateral travel for trenches 4 feet deep, and spoil piles set back at least 2 feet.

Lockout tagout

A six-step energy control procedure: notify affected workers, shut down equipment, isolate all energy sources, apply locks and tags, release stored energy, and verify zero energy before work begins.

Total coliform rule

A rule requiring routine coliform monitoring in distribution systems; any positive sample is checked for E. coli, which is an MCL violation, and repeat samples determine follow-up obligations.

Stage 2 DBPR limits

Disinfection byproduct limits evaluated as locational running annual averages: total trihalomethanes at 80 micrograms per liter and five haloacetic acids at 60 micrograms per liter.

Lead action level

The 90th percentile lead concentration in tap samples is 0.015 mg/L; exceeding it triggers corrosion control treatment, public education, and lead service line replacement obligations.

NPDES permit

A Clean Water Act permit issued to point source dischargers that sets effluent limits, monitoring requirements, and reporting, with results filed on monthly discharge monitoring reports.

BOD5 test

Five-day biochemical oxygen demand measured at 20 degrees Celsius in the dark; a seeded sample is incubated and dissolved oxygen depletion indicates biodegradable organic content, usually with nitrification inhibited.

Total suspended solids method

A measured sample volume is filtered through a glass fiber filter, dried at 103 to 105 degrees Celsius, and weighed; residue increase divided by sample volume gives TSS in mg/L.

DPD method

A colorimetric test in which the DPD indicator reacts with chlorine to form a colored compound measured by a photometer; it reports free or total chlorine depending on reagents used.

pH calibration

A pH meter is standardized with at least two buffers bracketing the sample, commonly pH 4, 7, and 10, and electrode slope should fall within 95 to 105 percent of theoretical.