AL Water Operator common mistakes
AL Water Operator · Understand the traps and how to avoid them.
Substitutes the numbers given in the stem straight into a memorized formula without converting to the units that formula assumes - e.g., plugs a flow of 350 gpm into a 'lb/day = 8.34 × mg/L × MGD' type formula, or uses pipe diameter in inches in a velocity equation that needs feet.
Formulas get memorized as letter strings (C × Q × 8.34) without the unit assumptions baked into them, and the exam deliberately supplies data in the units operators see in the field - gpm, inches, feet, psi, minutes - rather than the units the formula needs.
What to do instead
Before substituting, write each given value with its unit beside it and convert in a separate step: gpm ÷ 694.4 = MGD, gpm ÷ 448.8 = cfs, inches ÷ 12 = feet, psi × 2.31 = feet of head. Then do a one-line unit check on the answer: if the result is not in the units the question asked for (lb/day, ft/sec, gal, ft), a conversion is missing.
Uses MCL, MCLG, treatment technique, secondary standard and action level as if they were interchangeable - for example calling a lead action level of 0.015 mg/L an MCL, or treating a secondary standard for iron or manganese as an enforceable health limit.
The terms all describe 'a number you must meet' and are studied in the same regulatory chapter, so they blur together. MCLGs in particular look like MCLs because they are reported in the same mg/L format.
What to do instead
Build a four-row table and drill it: MCLG = health goal, not enforceable; MCL = enforceable maximum contaminant level; treatment technique = a required process (e.g., turbidity, LT1) used when a reliable numeric limit is not feasible; secondary standard = aesthetic, non-health. For lead and copper specifically, memorize that the number is an action level tied to a corrosion control treatment requirement, not an MCL.
Confuses free chlorine, total chlorine and combined chlorine, and computes CT or reports a residual using whichever number appears in the stem - for instance treating a total chlorine reading as the disinfectant residual that satisfies a free chlorine requirement.
Field test kits report total chlorine by default and 'chlorine residual' is used loosely in everyday speech, so the distinction is not reinforced on the job; under exam pressure the familiar number gets used.
What to do instead
Lock in the identity combined = total − free, and free = the active disinfectant. Read every stem for which species it states; if only total and combined are given, calculate free before doing anything else. When a question involves CT, confirm the residual used is free chlorine (or the specific disinfectant named) at the correct point in the process, and that pH and temperature are taken from the same location as the residual.
Treats coagulant dose as 'more is better' - answers that increasing alum or ferric dose will always improve turbidity removal, and ignores that the optimum dose is pH- and alkalinity-dependent and must be found by jar test.
Coagulation is taught as 'add chemical to make floc' and the dose-response curve (underdose → poor sweep, overdose → charge reversal and restabilization, plus alkalinity consumption and pH drop) is the part that gets skipped.
What to do instead
Memorize the jar test as the decision tool: it varies dose, sometimes pH, and selects the dose giving the lowest settled and filtered turbidity. Know the two failure directions - insufficient dose leaves colloids stable; excess dose reverses charge and re-stabilizes particles while depressing pH by consuming alkalinity. If a stem shows good floc at one dose and worse clarity at a higher dose, the answer is charge reversal/restabilization, not 'needs even more coagulant'.
Mixes up the three treatment stages on mixing intensity and time - assigns slow mixing to rapid mix, or says flocculation is where particles settle, or gives sedimentation a detention time measured in minutes.
The vocabulary overlaps (coagulation/flocculation are often used together in speech) and the units are learned as numbers without a feel for what each stage is physically doing.
What to do instead
Anchor each stage to its purpose and a rough time scale: rapid mix = intense, seconds to about a minute, disperses coagulant; flocculation = gentle, roughly 15–45 minutes, grows floc without breaking it; sedimentation = quiet, hours, particles settle out; filtration = removal of remaining particles. If a stem asks why floc is sheared or pin-floc appears, the answer is excessive mixing energy in flocculation, not too little coagulant.
Answers pump questions as if a centrifugal pump delivers a fixed flow regardless of the system - assumes doubling pump speed doubles flow and leaves head alone, or assumes adding a second pump in series doubles flow.
The affinity laws and the pump/system curve intersection are abstract, and in the field the operator usually sees only one operating point, so the relationship between head, flow and speed is never tested against real numbers.
What to do instead
Memorize affinity laws as two families: flow varies directly with speed, head with the square, power with the cube; and remember they apply to the pump curve, with the actual operating point set where the pump curve crosses the system curve. Pumps in series add head at the same flow; pumps in parallel add flow at the same head. If a stem says flow rose far less than expected after a speed increase, the answer is the higher system head, not a broken pump.
Applies one treatment assumption to every source - assumes all groundwater needs no disinfection or full conventional treatment, or assumes a spring or infiltration gallery is 'groundwater' for regulatory purposes, or conflates hardness with alkalinity when reading a water analysis.
Source water quality and the rules that follow from it are studied in a separate chapter from treatment and regulations, so the link from 'what is in the water' to 'what must be built and what must be monitored' is never practiced.
What to do instead
Practice mapping source to consequence: surface water or groundwater under the direct influence of surface water (GWUDI) triggers filtration and virus inactivation requirements; true groundwater may only need disinfection, but still requires the applicable treatment technique and monitoring. For analyses, keep hardness (calcium + magnesium) and alkalinity (carbonate/bicarbonate buffering capacity, what coagulants consume) as two separate definitions, and know iron and manganese are aesthetic/secondary concerns that still foul filters and stain water.
Treats any positive routine coliform sample as an MCL violation, or forgets that a positive routine sample triggers repeat samples at the same site, upstream and downstream, plus a check of the original for fecal indicators.
The compliance logic is procedural rather than numeric - a single result is only the start of a sequence - and candidates memorize the MCL (presence of fecal coliform/E. coli, or a percentage of positives) without the sampling steps that lead to it.
What to do instead
Write the sequence out once: routine positive → repeat samples at the site, upstream, downstream (and any additional required sites) within the required timeframe → if repeats confirm, the result escalates (fecal/E. coli triggers public notice and additional steps). Note that a single positive routine sample alone is a monitoring/repeat requirement, not automatically an MCL violation, and that failure to take the repeats is itself a violation.
Ignores disinfectant residual decay and storage turnover in distribution answers - assumes a residual set at the plant will hold at the far end of the system, or that a large tank with low demand is good because it holds plenty of water.
Plant-side disinfection and distribution-side water quality are taught separately, so the idea that residual is consumed by pipe walls, biofilm, sediment and long detention time (and that warm water and long dead ends accelerate loss) never gets connected to the treatment chapter.
What to do instead
Treat residual as something that is spent, not stored: expect it to fall with distance, detention time and temperature, and expect the fixes to be flushing dead ends and looping mains, not just raising the dose at the plant. For storage, know that low turnover leads to stale water, lost residual and possible nitrification or DBP increases, and that tank mixing and cycling matter as much as tank volume. If a stem shows a good clearwell residual and a zero at a distant dead end, the answer is distribution-side depletion, not inadequate disinfection.
Answers safety items from general caution rather than the specific procedure - says the correct move in a suspect confined space is to ventilate and enter, or describes approaching a chlorine leak without reference to the required respiratory protection, escape route and uphill/upwind approach.
Safety questions read as obvious, so they are answered quickly by intuition; the permit-required entry sequence (test → ventilate → test again → attendant → retrieval) and the specific properties of chlorine gas are not rehearsed.
What to do instead
Memorize two sequences cold. Confined space: atmospheric test first (oxygen, then flammables, then toxics), ventilate, retest, entrant with attendant and retrieval system, permit, communications - never enter to rescue without full protection. Chlorine: heavier than air, so evacuate upwind and uphill, use the required respiratory protection matched to concentration, and never attempt a repair in the release path. If an answer choice skips the initial test or the attendant, it is wrong.