MI Water Operator common mistakes
MI Water Operator · Understand the traps and how to avoid them.
When computing disinfection CT, the candidate multiplies the highest dose applied (or the residual leaving the clearwell) by the full theoretical basin volume divided by flow, with no baffling-factor correction.
Most prep material teaches CT as C × T, and the candidate reaches for the biggest concentration number on the sheet because it looks conservative. The exam deliberately supplies a peak dose, a finished-water residual, and a basin geometry so that the wrong pairs look plausible.
What to do instead
Before calculating, write three labels on scratch paper: the residual at the sampling point that ends the CT segment, the T that comes from effective (baffled) volume ÷ flow, and the required CT from the table for the measured temperature and pH. Pick numbers only from those labels, and state the baffling factor in your work so a wrong factor is visible rather than silent.
The candidate computes a chemical feed rate using the dosage formula but plugs in gallons of water, or converts a tank volume to million gallons incorrectly, then carries the wrong order of magnitude into the answer.
The arithmetic pattern (dose × flow × 8.34) is memorized as a rhythm, not as units. Under time pressure the candidate skips the unit check and picks an answer that is off by a factor of 1,000 or by 10.
What to do instead
Always write the units next to every number and cancel them: (mg/L) × (MGD) × (8.34 lb/gal) = lb/day. Convert volume to MG or flow to MGD as a separate, labelled step before touching the formula, and sanity-check the result against a rough mental estimate of the feed rate.
Converting between pressure and head, the candidate divides psi by 2.31 when going to feet of head (or multiplies when going to psi), producing a head value that is wrong in the same direction every time.
The two operations look interchangeable and the constant is remembered without a reference point. Candidates who never anchor the constant to a physical example cannot catch the inversion.
What to do instead
Anchor it once: one psi lifts water 2.31 feet, so a 100-foot column reads about 43 psi. Feet = psi × 2.31; psi = feet ÷ 2.31. Before selecting an answer, test it against the anchor - a number near 43 psi for roughly 100 feet means the conversion is oriented correctly.
Selecting a backflow prevention assembly for a service, the candidate specifies a double check valve assembly for a hazard involving a toxic or otherwise health-endangering substance, or chooses an air gap only when one is not physically possible.
The device names blur together and the candidate sorts them by cost, size, or familiarity rather than by degree of hazard and by whether backpressure or backsiphonage is the concern.
What to do instead
Sort by hazard first: health hazard (toxic, sewage, chemical) requires reduced-pressure principle or an air gap; non-health hazard may allow a double check. Then check the failure mode - a device that discharges to atmosphere is the giveaway for RPZ and PVB, and an air gap is the choice whenever it can be physically installed.
Calculating specific capacity, the candidate divides the pumping rate by the difference between the static water level and the total well depth, or uses static level alone instead of the pumping level after drawdown has stabilized.
Static water level is the first measurement on the well log and the candidate grabs it as the reference point, forgetting that specific capacity is a measure of response to pumping.
What to do instead
Write the definition before the calculation: specific capacity = pumping rate ÷ drawdown, and drawdown = pumping water level − static water level. Identify both levels on the data given, subtract first, divide second, and report the units as gpm per foot of drawdown.
Answering a nitrate question, the candidate compares a lab result reported as nitrate (NO3) directly against the 10 mg/L limit, or converts a nitrate-as-nitrogen result upward to compare against 45 mg/L.
The two reporting bases share a name and the candidate does not check which form the lab number represents, so the comparison goes the wrong way and the well is called compliant when it is not, or the reverse.
What to do instead
Read the lab report's basis line before doing anything: the limit is 10 mg/L as nitrogen, which equals 45 mg/L as nitrate. Convert the sample into the same basis as the limit (multiply nitrate-as-N by about 4.4 to get nitrate, or divide nitrate by 4.4 to get nitrate-as-N), then compare.
Matching a violation to a public notice tier, the candidate assigns the 30-day Tier 2 timeline to an acute violation such as a confirmed E. coli result, or assigns an annual Tier 3 notice to a violation that requires same-day notice.
Candidates memorize the number 30 because it appears most often in practice, and they classify by how the violation feels administratively rather than by whether it is an acute health risk.
What to do instead
Classify by health risk before quoting a deadline: acute risk gets Tier 1 and notice within 24 hours; violations that do not pose immediate risk but require notice get Tier 2 within 30 days; lesser violations get Tier 3 within a year. Also confirm the delivery method required for that tier, because the tier question often turns on method, not just days.
On a total coliform positive routine sample, the candidate states that repeat samples can be collected any time before the end of the monitoring period, or collects fewer than three repeats and omits the upstream and downstream locations.
Monthly monitoring logic dominates the candidate's thinking, so the positive result is treated as something handled at month-end rather than as a 24-hour clock that starts when the lab notifies the system.
What to do instead
Trigger a fixed checklist on any routine positive: three repeat samples within 24 hours of notification - one at the original trigger tap, one within five service connections upstream, one within five connections downstream - plus repeats on each repeat that is positive, and all analyzed for fecal indicators. Recite the 24-hour clock and the three locations together as one unit.
Entering or authorizing entry to a wet well or vault, the candidate treats a quick oxygen reading as sufficient and skips testing for flammable gas and for hydrogen sulfide before anyone descends.
The space is familiar and the candidate has been in it many times, so the atmospheric test becomes a formality performed with one meter and one reading rather than a sequence.
What to do instead
Test in the required order and record each result: oxygen first, then flammables, then toxics (hydrogen sulfide and carbon monoxide), top to bottom of the space. Continue forced ventilation throughout, keep a retrieval line and attendant in place, and re-test before any re-entry after a break - even if the space was clear an hour earlier.
Responding to a chlorine gas release at the plant, the candidate's stated action is to walk toward the leak to close the valve, to stay low and downwind, or to spray water on the release.
The instinct to stop the source is strong, and the candidate pictures the valve rather than the gas cloud. Chlorine is heavier than air, so the intuitive 'stay low' rule is exactly backwards for escape.
What to do instead
State the sequence in order: evacuate upwind and uphill, account for personnel, activate the emergency plan and notify the required contacts, and re-enter the area only with appropriate respiratory protection and a second person. Never apply water to a chlorine release, and never approach the source without respiratory protection.