NH Water/Wastewater Operator common mistakes
NH Water/Wastewater Operator · Understand the traps and how to avoid them.
Computing chlorine dose or CT from the wrong basis (using percent instead of mg/L, or forgetting to convert gallons to million gallons), so answers are off by orders of magnitude.
Candidates memorize a formula but never anchor the units; the exam mixes lb/day, mg/L, MGD, and percent strength in the same stem, and mental arithmetic is done before units are reconciled.
What to do instead
Before calculating, write the target unit and convert every given value to it first (percent strength to mg/L by multiplying by 10,000; gallons to MG by dividing by 1,000,000). Use the 'pounds formula' as a unit check: lb/day = mg/L x MGD x 8.34, and confirm the result is physically plausible for the plant size.
Selecting a disinfectant residual target or contact time that ignores the CT concept, treating chlorine residual alone as proof of adequate inactivation.
Operators in the field watch a residual number on a meter and assume residual equals disinfection; exam stems that vary pH, temperature, and contact time expose this gap.
What to do instead
Study CT as residual concentration multiplied by effective contact time, and learn that CT requirements rise with higher pH (for free chlorine), lower temperature, and higher target log inactivation. On questions, identify the limiting condition (worst-case pH, temp, or peak flow) rather than the average.
Confusing which contaminant is addressed by which treatment process (e.g., attributing nitrate removal to coagulation/sedimentation, or disinfection byproduct control to filtration).
Treatment trains are learned as a sequence of unit processes rather than as a mapping from contaminant to mechanism, so candidates pick the process that sounds most 'advanced'.
What to do instead
Build a two-column table: contaminant (turbidity, nitrate, arsenic, iron/manganese, radionuclides, DBPs, pathogens) against the process that removes it (coagulation/filtration, ion exchange, oxidation/filtration, RO, aeration, precursor removal, disinfection). Review it until each pairing is automatic.
Misjudging hydraulic loading and detention time in wastewater units, such as applying the surface overflow rate to the wrong tank area or using average flow when the stem specifies peak flow.
The formulas look similar across clarifiers, trickling filters, and lagoons, and candidates plug numbers into a remembered formula without confirming which flow and which area the question intends.
What to do instead
For each unit process, write the definition of the loading parameter in words (e.g., surface overflow rate = flow divided by clarifier surface area, not volume). Read the stem for 'peak', 'average', or 'design' flow and use exactly that value; check that the answer's units match the loading parameter's units.
Treating the activated sludge process as a fixed set of numbers, answering F/M, SRT, or MLSS questions with a memorized typical value instead of computing from the given data.
Candidates recall ranges (e.g., 'SRT is 5 to 15 days') and apply them as answers, missing that the question supplies mass and flow data that determine the correct computed value.
What to do instead
Practice computing F/M (food mass over microorganism mass), MCRT/SRT (solids in system over solids wasted plus effluent solids), and sludge volume index from raw data. When a stem gives numbers, compute; use typical ranges only to sanity-check the result.
Confusing collection system capacity problems with condition problems, such as recommending rehabilitation when the stem describes infiltration/inflow or a surcharge caused by undersized pipe.
Infiltration, inflow, and structural defects all present as 'too much water', and candidates answer with the remedy they have seen most often rather than diagnosing the source.
What to do instead
Classify the symptom first: dry-weather flow excess points to infiltration, wet-weather spikes to inflow, and capacity limits to sizing or storage. Match the remedy to the category (sealing/relining for infiltration, source disconnection for inflow, upsizing or storage for capacity) and state the diagnostic step (flow monitoring, smoke testing, CCTV) in your reasoning.
Reporting a result with the wrong significant figures or outside the method's reporting limit, or averaging duplicate samples without applying the required holding time and preservation checks.
Candidates treat lab math as simple arithmetic and overlook that reporting limits, significant figures, and holding times are part of regulatory compliance, not optional conventions.
What to do instead
For each parameter, memorize the preservation, maximum holding time, and typical reporting limit (e.g., chlorine and pH analyzed immediately, turbidity within method limits, bacteriological samples chilled and held within the specified window). Report at the method's significant figures and flag results below the reporting limit rather than reporting zero.
Misreading a bacteriological or turbidity result against the compliance rule, for example treating a single positive total coliform as an automatic violation or ignoring that repeat samples are required.
The rules are procedural: a positive triggers repeats and assessment, and a violation depends on the pattern of results, not one sample. Candidates answer from memory of 'any positive is bad'.
What to do instead
Learn the decision tree for each rule: total coliform positive leads to repeat sampling and, if confirmed, assessment or treatment technique violation depending on the system type; turbidity compliance depends on the specified percentage of measurements or a maximum limit. Practice walking a scenario through the tree rather than recalling a single threshold.
Mixing up which report goes to whom and when, such as confusing the Consumer Confidence Report with the monthly operating report or missing that some notifications are public and time-limited.
Reporting obligations are spread across rule-specific deadlines, and candidates study the content of reports but not the addressee and schedule.
What to do instead
Make a schedule table: report or notice, recipient (primarily state, public, or both), trigger, and deadline. Include the annual consumer confidence report, monthly operating reports, public notification tiers and their timeframes, and the monitoring/analytical reporting deadlines. Test yourself by covering the deadline column.
Answering safety questions with the general hazard control hierarchy in the abstract instead of the specific required practice, such as entry permit, atmospheric testing order, or lockout/tagout sequence.
Confined space and hazardous energy questions reward knowing the exact order of steps and the specific thresholds; candidates recall that 'testing is important' but not that oxygen is tested first, then flammables, then toxics, and that ventilation and continuous monitoring follow.
What to do instead
Memorize the confined space entry sequence (permit, isolate, ventilate, test oxygen then flammability then toxicity, continuous monitoring, attendant and retrieval system in place) and the lockout/tagout sequence (notify, shut down, isolate, lock and tag, verify zero energy, restore in reverse). Practice ordering the steps in scenario questions.