GA Water/WW Operator common mistakes
GA Water/WW Operator · Understand the traps and how to avoid them.
On a jar-test scenario the candidate answers "increase the coagulant dose" when the test results actually show the pH is outside the optimum range for the coagulant (e.g., alum working well below pH 6.5 or above 7.5).
Candidates memorize the shortcut "high turbidity = add more coagulant" and skip the step of reading the jar test as a two-variable problem (pH and dose). Test-writers exploit this by giving a jar test where dose is already adequate but pH drifted.
What to do instead
Drill the decision order explicitly: check raw turbidity/alkalinity, check settled pH and whether it sits in the coagulant's effective band, adjust pH first (lime or acid), then re-jar-test to fine-tune dose. Practice by reading jar-test tables and stating which single variable to change and why.
Chemical feed calculations: the candidate uses the pounds formula but plugs in the wrong flow units, forgets the 8.34 lb/gal conversion, or ignores percent purity/available chlorine when the chemical is not 100% strength.
Feed problems on this exam mix mg/L, MGD, gpm, lb/day, and product strength in one stem. Candidates who memorized "mg/L x MGD x 8.34" as a chant rather than as a unit-cancellation tool cannot spot when the flow is given in gpm or the product is 65% strength.
What to do instead
Rebuild the formula from units each time: mg/L = mg per L, MGD x 8.34 = lb of water per day per mg/L, so lb/day = mg/L x MGD x 8.34. Then divide by the decimal purity (e.g., 0.65) and by solution strength to get product feed. Do 20 problems with deliberately mismatched units until conversion is automatic.
Pressure/head conversions: the candidate multiplies psi by 2.31 when converting to feet of head instead of dividing (or vice versa), producing an answer that is off by a factor of about 5.3.
The number 2.31 is memorized without the direction attached. Under time pressure candidates grab the factor and apply whichever operation feels right.
What to do instead
Anchor the direction with a sanity check: one psi lifts water only about 2.3 feet, so a 100 psi main is roughly 230 feet of head, not 43. Write the relationship as ft = psi x 2.31 and psi = ft / 2.31 every time, and verify each answer against a known reference point (e.g., 1 ft of head = 0.433 psi).
Cross-connection control: the candidate selects a reduced-pressure-zone assembly (RPZ) for every hazard, or picks a double-check valve assembly (DCVA) or pressure vacuum breaker for a high-health-hazard situation such as a toxic chemical line or a lawn irrigation system with chemical injection.
Candidates learn the device names but not the hazard classification that drives selection, so they default to "the most protective one" or to the cheapest-sounding name.
What to do instead
Build a two-column table: health hazard (toxic, sewage, chemical) versus non-health hazard (aesthetic, low risk). Map RPZ and air gap to high hazard, DCVA to low hazard where backpressure/backsiphonage is possible, and PVB to low hazard backsiphonage only. Practice sorting 15 real fixtures into the correct device.
Activated sludge diagnosis: the candidate sees a rising SVI and answers that wasting should be decreased (sludge age increased), or conversely treats a low SVI with turbid effluent as the ideal condition.
The direction of the sludge-age/wasting relationship gets flipped under pressure, and candidates associate "low SVI" with "good" without considering pin floc and young sludge, which also settle poorly in the clarifier and carry over solids.
What to do instead
Learn the causal chain, not the label: more wasting = lower MCRT = younger sludge; less wasting = higher MCRT = older sludge. Then link symptoms: filamentous bulking with high SVI is commonly driven by low F/M (old sludge), low DO, or septicity, and the correction is usually more wasting plus fixing the root cause. Practice by writing the expected direction of MCRT, F/M, and SVI for each corrective action.
Nitrogen removal: the candidate states that nitrification occurs in an anoxic zone or that denitrification requires dissolved oxygen, and overlooks that nitrification consumes alkalinity and depresses pH.
The two processes are taught together and the zone labels are easy to swap. The alkalinity/pH link is a secondary detail that candidates skip because the primary reaction is the only thing they memorized.
What to do instead
Fix the pair with a one-line mnemonic tied to the chemistry: nitrifiers need oxygen (aerobic) and eat alkalinity; denitrifiers need the absence of oxygen (anoxic) and consume carbon. Then add the operational consequence: monitor alkalinity and pH in the aerobic zone because nitrification can drive pH down and stall the process.
Collection system hydraulics: the candidate computes slope as a ratio but reports or applies it incorrectly (e.g., treats 0.5% as 0.5 ft per foot, or converts inches of drop per foot to percent by the wrong factor), and cannot connect slope to the minimum scouring velocity.
Percent grade, feet of drop per 100 feet, and inches per foot are three ways of saying the same thing, and candidates practice only one form. The link between slope and self-cleansing velocity is treated as a separate fact rather than a consequence.
What to do instead
Convert between all three forms in both directions until they are interchangeable: 1% = 1 ft per 100 ft = 0.12 in per ft. Then attach the design target, roughly 2 ft/s at design flow to keep solids moving, and practice checks that ask "is this segment self-cleansing at the stated slope and pipe size?"
Confined space questions: the candidate picks an answer where the worker tests the atmosphere and enters, omitting the attendant, the entry permit, continuous ventilation, and the pre-planned rescue capability.
Atmospheric testing is the most memorable step and gets treated as the entire requirement. Candidates also conflate "test the air" with "the space is now safe," forgetting that conditions change and that a standby person is mandatory for permit-required spaces.
What to do instead
Memorize the full entry sequence as a checklist and rehearse it in order: identify and classify the space, obtain a permit, isolate and lock out, test from outside at multiple levels, ventilate, post the attendant, verify communications and rescue arrangements, then enter. Answer any option missing a checklist element as wrong.
Regulatory questions: the candidate mixes up public notice tiers and timelines, or treats a monitoring/reporting violation as if it were a maximum contaminant level exceedance with the same notification path.
The rule framework has parallel categories (acute versus non-acute health risk, MCL versus treatment technique versus monitoring), and candidates study the numbers without sorting the categories. Unfamiliar Georgia-specific wording then pushes them toward a guess.
What to do instead
Make a three-row table for the public notice tiers with the trigger type and the deadline for each, and a separate column for MCL, treatment technique, and monitoring/reporting violations showing which tier each falls into. Then practice classifying ten short violation descriptions into tier plus deadline before looking at answers.
BOD calculations: the candidate multiplies by the dilution factor when the factor should be applied as a multiplier of the depletion, applies the factor upside down (sample volume over final volume), or skips the seed correction on seeded diluted samples.
The dilution factor is a ratio and candidates do not write it out before substituting numbers, so the numerator and denominator get inverted. The seed correction is a detail that drops out when the problem statement buries it in a footnote-style line.
What to do instead
Always write DF = final volume / sample volume as a fraction with the sample volume on the bottom before any arithmetic, and state the working equation as (initial DO - final DO) x DF, minus the seed correction where seed is used. Check plausibility: a heavily diluted sample must be multiplied up, so the result should be larger than the raw DO depletion, never smaller.