ABC Wastewater Collection Class II common mistakes
ABC Wastewater Collection Class II · Understand the traps and how to avoid them.
Confusing detention time with flow rate when sizing or troubleshooting a wet well - dividing when the formula calls for multiplying, or reporting the answer in the wrong units (hours vs. gallons per minute).
Candidates memorize 'detention time = volume / flow' but freeze when the problem gives flow in MGD and volume in cubic feet, then mislabel the result. Unit conversion is the actual failure point, not the concept.
What to do instead
Write the unit next to every number before calculating, convert to consistent units first (1 cubic foot = 7.48 gallons; 1 MGD = 694 gpm), and carry units through the division so the answer's label is forced by the math.
Entering or permitting entry into a confined space without verifying that atmospheric testing occurred in the correct order (oxygen first, then flammables, then toxics) and without a completed, signed entry permit.
Candidates conflate 'we tested the air' with a compliant entry program, or they recall the test instruments but not the required sequence and documentation. Test-day wording often rewards the procedural detail over the general safety sentiment.
What to do instead
Memorize the testing order (O2, LEL, H2S/CO), the acceptable ranges, and the permit elements as a checklist. Practice writing out a permit from memory so the sequence and signatures are automatic.
Selecting the wrong pipe slope or misapplying the 'fall per foot' relationship when computing invert elevations along a gravity sewer run.
Candidates treat slope as a percentage and a ratio interchangeably, or forget to convert between feet of fall and inches of fall per foot, producing an invert that is off by a factor of 12.
What to do instead
Always express slope as feet of fall per foot of pipe (or convert inches per foot to feet per foot by dividing by 12), then multiply by the run length. Check the answer against a rough order-of-magnitude estimate before committing.
Treating infiltration and inflow as the same problem and recommending the same remedy for both.
The terms sound interchangeable and both add clear-water flow, so candidates miss that infiltration is groundwater seeping in steadily through defects while inflow is direct stormwater dumping in during rain events. The diagnostic clue (dry-weather base flow vs. rain-response spike) is what the exam tests.
What to do instead
Anchor each term to its signature: infiltration = chronic, weather-independent; inflow = rapid, rain-correlated. When a question describes flow behavior, let the timing pattern pick the term before choosing the remedy.
Confusing the pump operating point with the pump curve's shutoff head, or picking a pump based on a single catalog number without locating the intersection of the system curve and pump curve.
Candidates learn 'head' and 'capacity' as separate facts and never internalize that the operating point is where the two curves cross, so they answer with a curve endpoint instead of the intersection.
What to do instead
Sketch both curves on scratch paper for any pump-selection item and mark the intersection. Remember shutoff head is at zero flow and runout is at zero head - neither is the operating point.
Reporting a spill or bypass to the regulatory agency only after cleanup is complete, or omitting the follow-up written report after the initial phone notification.
Candidates focus on the physical response and treat notification as paperwork that can wait, missing the clock-driven requirement for prompt oral notice followed by a written report within a set period.
What to do instead
Memorize the notification sequence as a timeline: immediate oral notice, then written follow-up by the deadline, then updates if conditions change. Build a one-page spill notification card and rehearse it.
Miscalculating grease interceptor sizing by using fixture count alone and ignoring the retention time and flow-rate basis the formula requires.
Candidates grab the simplest input (number of fixtures or seats) and skip the flow and detention-time terms, or they confuse grease interceptor sizing with septic tank sizing.
What to do instead
Learn the sizing formula as a flow-based calculation with a retention-time factor, and practice one worked example with real numbers so the input list is fixed in memory.
Describing CCTV inspection defect codes or condition ratings from general impression rather than applying the standardized structural vs. operational distinction.
Candidates remember that a crack or root intrusion is 'bad' but cannot classify whether it is a structural defect (pipe integrity) or an operational defect (flow obstruction), which drives the rehabilitation decision.
What to do instead
Build a two-column sort: structural (cracks, fractures, collapsed, deformed) vs. operational (roots, grease, debris, encrustation). Practice classifying a list of defects into the correct column until it is reflexive.
Answering asset-management or recordkeeping questions by choosing the most thorough-sounding option instead of the one that matches the required minimum record and retention practice.
These questions reward knowing what must be documented and kept versus what is merely good practice, and candidates over-select 'document everything forever' answers.
What to do instead
Separate mandatory records (permits, monitoring data, maintenance logs, spill reports with retention periods) from optional good practice, and choose the option that satisfies the actual requirement without overreach.
Handling a public odor or grease complaint by defending the utility's operations first rather than following the complaint-response sequence (log it, investigate the source, respond, document corrective action).
Candidates read public-relations items as 'be nice' questions and pick the empathetic-sounding answer, missing that the correct response is a documented investigative process, not a customer-service script.
What to do instead
Treat every complaint item as a procedure question: acknowledge and log, investigate and identify the source, take corrective action, follow up and document. Choose the option that includes the investigation and record, not just the apology.