Class I content is easiest to learn as one connected flow path rather than a stack of separate topics. A velocity answer depends on unit conversions; a cleaning decision depends on what an inspection shows; an entry decision depends on how you classify the space before anyone tests it. Work through this guide by tracing wastewater from a service lateral to treatment, classifying each decision point, and practicing the conversions and method choices that follow from the classification. Administrative details such as scheduling, eligibility, and exam format belong to Water Professionals International; neither issuer page could be fetched when this guide was prepared, so it teaches subject content only.
Map the Collection System as One Connected Flow Path
The Class I body of knowledge treats laterals, gravity mains, manholes, force mains, and lift stations as a single system. Learn each component by the job it does to keep wastewater moving toward treatment, not as a vocabulary list.
Draw the path first: a service lateral carries wastewater from one property to the main; the gravity main moves it downhill by slope alone; manholes sit where grades change, where mains intersect, and at access intervals; a lift station receives flow too deep or too flat to drain by gravity and a force main carries it under pressure to the next gravity section. Gravity mains depend on slope and depth; force mains depend on pump pressure. That single distinction explains why manholes exist and why lift stations do not.
Exercise: sketch a small system from three laterals through two manholes, down a gravity main, into a lift station, through a force main, and back to a gravity main. Label what changes at each point — grade, direction, pressure, or ownership. Expected observation: every change happens at a named component. When you can state why each component sits where it does, definitions stop being memorized facts and become conclusions you can re-derive on any scenario question.
- Lateral: one property's connection; the utility's responsibility line varies by jurisdiction, so check local rules rather than assuming.
- Gravity main: slope-driven flow; problems usually appear as slow flow, settling solids, or blockages.
- Force main: pump-driven, pressurized flow; problems usually appear at the pump station or as pressure-related failures.
Confined Space Entry: Classify the Space Before You Test the Air
Entry decisions follow a sequence: identify whether the space is a confined space, then whether it is permit-required, then test and ventilate before entry with an attendant. Classification comes first because it determines every step after it.
A confined space is large enough to enter and work in, has limited or restricted entry and exit, and is not designed for continuous occupancy. It becomes a permit-required confined space when it also has, or could have, a hazardous atmosphere, material that could engulf an entrant, walls that converge or slope inward, or any other recognized serious hazard. A manhole is the classic example: it meets all three baseline traits, and wastewater spaces carry atmospheric hazards as a matter of course. Learn the two categories as separate thresholds, because the permit requirements attach only to the second.
The practical skill is ordering your decisions. Classification is based on the space's characteristics and hazards, not on how the job feels that day; a manhole is not sometimes a confined space and sometimes not. After classification comes atmospheric testing in sequence, ventilation, the permit, the attendant, and the rescue plan. Practice this as a chain on paper: given a space description, state the classification, then list what the classification obligates. If you can classify a described space without prompting, the rest of the entry procedure has a hook to attach to.
Hydraulics: Convert Units First, Then Judge the Flow
The concept itself demands unit discipline before any reasoning about the answer. Convert flow and diameter into the units your formula expects, compute, then check the result against a plain-language expectation such as self-cleansing velocity.
Two habits carry most of the weight. First, memorize the conversion family rather than a single factor: million gallons per day to gallons per day to gallons per minute, and one MGD equaling roughly 694 gpm. Second, use formulas whose units you have verified; a common shortcut formula for velocity in a full pipe, velocity in feet per second equaling 0.408 times flow in gpm divided by diameter in inches squared, fails immediately if you substitute diameter in feet. For gravity mains, a self-cleansing velocity near 2 feet per second is the widely taught planning benchmark; force mains also carry guidance about upper velocity limits to limit wear, which you should treat as conditional design guidance rather than a universal rule.
Worked scenario: an 8-inch gravity main carries 0.5 MGD. Mistake version: you plug 0.5 into the gpm formula or substitute 0.67 feet for diameter, get a nonsense velocity, and pick an answer choice that looks plausible. Better decision: convert 0.5 MGD to about 347 gpm, compute 0.408 times 347 divided by 64, and get roughly 2.2 feet per second — just above the 2 feet per second self-cleansing benchmark, which is exactly what a well-operating main should show. Why it matters: the benchmark check catches arithmetic slips that answer options are built to exploit.
Exercise: conversion drill. Convert 400 gpm to MGD; convert 1.2 MGD to gpm; convert 90 gpm into gallons per day. Check answers: about 0.576 MGD; about 833 gpm; 129,600 gpd. Expected observation: you learn which conversions are automatic and which still need a written step, which tells you exactly what to drill next.
| Quantity | Typical conversion path | Self-check question |
|---|---|---|
| MGD to gpm | Multiply by about 694 | Does the gpm answer sit between 600 and 700 per MGD? |
| gpm to MGD | Divide by about 694 | Is the MGD answer under 1 for flows under 700 gpm? |
| Velocity, full pipe | 0.408 × gpm ÷ (diameter in inches)² | Is diameter in inches, and is velocity near 2 fps for a healthy gravity main? |
Maintenance: Match the Cleaning Method to the Confirmed Cause
Cleaning decisions should follow inspection evidence, not habit. Jetting, rodding, bucket machines, and root cutting each address different problems, and an inspection before and after the work is what makes the choice defensible.
Distinguish diagnosis from treatment. Hydraulic jetting uses pressurized water to move grease, grit, and debris; rodding pushes or pulls through lighter blockages; a bucket machine removes heavy debris in larger or severely blocked lines; root saws cut intruding roots, and chemical root treatment is aimed at slowing regrowth at joints. Closed-circuit television inspection is diagnostic and verification, not cleaning. Fats, oils, and grease accumulating near discharge points behave differently from root intrusion at a cracked joint, and the tools differ accordingly.
Worked scenario: a main serving a commercial corridor has repeated backups. Mistake version: the crew jets the line on a routine cycle, backups continue, and the same segment is jetted again next month with no inspection in between. Better decision: CCTV the segment first, confirm the cause — suppose it shows root intrusion at one joint plus a grease film — then cut and treat the roots and jet the grease, and CCTV afterward to verify. Why it matters: treating the symptom without identifying the cause consumes passes on a problem the chosen method cannot fix.
Exercise: for three described segments — a grease-coated run near restaurants, a line with fine roots at joints, a heavily blocked large main — name the first method, the verification step, and what would tell you the method was wrong. Expected observation: your answer changes only when the evidence changes, which is the habit the decision table below reinforces.
| Method | Typical target | When it fits | Watch for |
|---|---|---|---|
| Hydraulic jetting | Grease, grit, loose debris | Routine cleaning and grease buildup | Will not cut established roots |
| Rodding | Light blockages in smaller lines | Short runs, tighter access | Limited reach and cutting power |
| Bucket machine | Heavy debris and severe blockages | Larger mains, hard blockages | More setup and traffic control |
| Root saw with chemical treatment | Root intrusion at joints | Confirmed roots on inspection | Regrowth is possible; verify later |
| CCTV inspection | Condition assessment | Diagnosing cause and verifying work | Diagnostic only; it does not clean |
Lift Stations and Pumps: Troubleshoot by Tracing the Wastewater's Path
Learn lift station components in flow order — wet well, level controls, pump, check valve, discharge — and most troubleshooting questions reduce to asking which link in that path failed.
A wet well equalizes incoming flow and gives the pumps something to cycle against; level controls — floats on simpler stations, transducers or similar on others — start and stop the pumps. A centrifugal pump's impeller adds velocity to the liquid that becomes pressure at the discharge; a check valve on the discharge prevents backflow into the wet well when the pump stops. Distinguish submersible stations, where the pump sits in the well, from dry-pit arrangements. Controls commonly include hand-off-auto positions, and auto is what lets level controls run the cycle.
Troubleshoot as a trace. Pump runs but nothing discharges: work the path — is the wet well level actually at the pump's range, is the impeller fouled with rags, is the check valve stuck, is the force main blocked? Pump cycles too rapidly: suspect a control setting or a check valve letting flow back. Electrical work adds a hard rule: lockout and tagout before anyone works on a pump or motor, which is different from simply switching equipment off. Exercise: write the trace for 'pump runs, wet well keeps rising' and list two candidate causes at two different links; the expected observation is that rising level plus a running pump points past the motor toward the discharge path or the pump itself.
Safety Beyond the Space: Traffic Control, Hydrogen Sulfide, and Lockout
Confined space entry is one safety domain among several. Work zone traffic control, hydrogen sulfide awareness, and lockout/tagout each have their own decision rules and each appears as its own line of reasoning.
Traffic control for street work follows a site plan: signs, cones, and barriers arranged to warn, channel, and protect, with high-visibility apparel for everyone on the roadway. Hydrogen sulfide deserves respect for its properties rather than memorized fear: it is heavier than air and pools in low points, it smells of rotten eggs at low concentrations, and at higher concentrations it deadens the sense of smell so that a space can smell safe precisely when it is not. The operational rule that follows is simple — the gas meter is the decision tool, never your nose.
Lockout and tagout is a procedure, not a switch. De-energize the equipment, apply a personal lock and tag, verify zero energy before working, and each worker holds their own lock so the equipment cannot be restarted while anyone is exposed. Distinguish this from routine operation: an operator at a control panel is operating; a hand inside a pump casing is servicing, and servicing requires the procedure. Exercise: for three described situations — a manhole in a live traffic lane, a rotten-egg odor at a shallow pit, a jammed pump to be cleared by hand — name the controlling safety rule first. Expected observation: the rule comes from the situation type, not from severity.
Records, Reporting, and a Two-Week Practice Sequence
Record-keeping questions test the difference between an operational log and a regulatory report. Build fluency by writing the entries yourself, then run a timed practice cycle against the self-check rubric below.
Separate two kinds of paperwork. Operational records — cleaning logs, inspection and CCTV findings, lift station checks, completed confined space permits — document what the crew did and support future maintenance decisions. Regulatory reporting — for example, notifying the applicable authority when an overflow reaches surface waters or leaves the system — is a compliance obligation under the utility's permit and local rules, with its own deadlines and recipients. In scenario form, the skill is recognizing which of the two the situation triggers; a routine jetting pass generates a log, while an overflow event generates both a log and, in the United States, a report under the system's permit requirements.
Suggested two-week sequence: days one to three, draw and label the component map and drill unit conversions until the MGD-gpm family is automatic; days four to six, work classification chains for confined spaces and LOTO decisions on paper; days seven to nine, run the cleaning-method exercise and pump-trace exercise against the table above; days ten to twelve, practice writing a cleaning log entry and an overflow notification checklist in your own words; days thirteen and fourteen, timed mixed practice using the free practice page linked below, then review every miss against its section. Treat the rubric as a learning milestone, not a passing prediction.
Self-check rubric, score each 1 to 4: classify a described space and list the resulting obligations without prompting; convert any flow unit pair in the drill family in one written step; select a cleaning method from inspection evidence and name the verification step; trace a pump fault to a named link in the path; write a complete log entry including time, location, method, and result. A consistent 3 or above across all five signals you are ready for full timed practice; any 2 tells you which section to revisit.
References and further reading
Use these references to explore the concepts and check the latest information from the relevant organizations.