ABC Wastewater Collection Class IV cheat sheet

Design velocity range for gravity sanitary sewers is typically 2 ft/s (minimum self-cleansing) to 10 ft/s (maximum to limit scour and H2S release).

Manning's equation for full circular pipe: Q = (1.486/n) A R^(2/3) S^(1/2), with n ≈ 0.013 for new ductile iron/PVC, 0.015+ for aged or slime-coated pipe.

Minimum sewer slope rule of thumb: slope (ft/ft) ≥ 1 divided by the pipe diameter in inches (e.g., 8-in pipe needs ≥ 0.00125 ft/ft) to sustain 2 ft/s when flowing full.

Grease blockages concentrate at low-velocity reaches, sags, and immediately downstream of service connections; root intrusion dominates at joints and cracks in the upper third of the pipe.

Hydrogen sulfide is generated where flow is pressurized, warm, and high-BOD; it corrodes concrete above the waterline by conversion to sulfuric acid and is an occupational exposure hazard.

Scheduled preventive maintenance intervals are set from condition and failure history, not fixed calendars; CCTV and flow data drive re-inspection frequency.

A sanitary sewer overflow (SSO) must be reported to the state regulatory agency within the timeframe set in the NPDES/collection system permit, and public notice is required for discharges reaching waters of the state.

Manholes are spaced to allow inspection and cleaning access, commonly 300–500 ft on straight runs and closer where there are changes in grade, alignment, or pipe size.

A drop manhole (outside drop) carries a high-elevation incoming sewer down the manhole wall to prevent turbulence, H2S release, and scour at the invert.

Inverted siphons carry flow under obstructions; because they operate under pressure and at higher velocity, they need provisions for flushing and for bypassing flow during maintenance.

Force mains are designed for a minimum scouring velocity of about 2 ft/s and a maximum of about 5–8 ft/s; air release and vacuum relief valves protect against surge and column separation.

Service connections must maintain the same minimum slope as the main and be installed with a wye or tee at the main, not a tapped hole in the crown.

Standard manhole components include the frame and cover, adjusting rings, cone or flat top, precast riser sections, benching, and the channelized invert.

Pump total dynamic head = static lift + friction losses in suction and discharge piping + velocity head; system curves shift upward as pipes foul or valves throttle.

Affinity laws: flow varies with speed (Q ∝ N), head with speed squared (H ∝ N²), and power with speed cubed (P ∝ N³).

Wet well operating volume is set so pump cycling does not exceed the motor manufacturer's starts-per-hour limit; excessive cycling overheats motors and stresses check valves.

A pump operating far left of its best efficiency point risks recirculation, cavitation, and vibration; far right risks motor overload and cavitation from low NPSH margin.

Net positive suction head available must exceed NPSH required by the pump; a submerged suction inlet and adequate wet well depth prevent vortexing and air entrainment.

Alternating lead/lag pump control equalizes wear; a failed pump should trigger an alarm and automatic transfer to the standby unit.

Lift station standby power, high-level alarms, and telemetry are the primary controls that prevent overflows during power loss or pump failure.

A permit-required confined space has one or more of: hazardous atmosphere, engulfment potential, internal configuration that can trap or asphyxiate, or any other recognized serious hazard.

Atmospheric testing order is oxygen first, then flammables, then toxics; entry is prohibited at O2 below 19.5% or above 23.5%, flammable gas at or above 10% LEL, or H2S at or above 10 ppm (or the permit's lower limit).

A sewer atmosphere is oxygen-deficient by displacement or biological consumption; H2S and methane are the common toxic and flammable gases encountered.

Forced-air ventilation must run continuously during entry and be tested again before re-entry after any break; ventilation alone does not eliminate the need for a permit.

An attendant stays outside the space, maintains communication, and summons rescue; the entrant wears a retrieval harness with a tripod/winch where vertical entry is used.

Rescue must be performed by trained personnel with supplied-air respiratory protection; more than half of confined space fatalities are would-be rescuers.

Lockout/tagout, traffic control per MUTCD, and trench protective systems (sloping, shoring, or shielding) apply to collection system work in streets and excavations.

Infiltration is groundwater entering through defects in pipe, joints, and manholes; inflow is direct stormwater or surface water entering through manholes, roof drains, and illegal connections.

Peak infiltration and inflow (I/I) is quantified by comparing dry-weather flow to wet-weather flow and by flow monitoring during storms; RDII is the rainfall-dependent component.

Smoke testing locates inflow sources and illegal connections; dye testing confirms a specific service connection is cross-connected.

CCTV inspection identifies infiltration points, and rehabilitation methods include CIPP lining, cured-in-place pipe, joint sealing, manhole lining, and lateral lining.

Removing I/I reduces treatment costs, hydraulic surcharge, and SSOs; it is prioritized by cost per gallon of inflow removed, not by defect count.

A sanitary sewer should be designed to carry peak wet-weather flow without surcharging to the ground surface; capacity analysis uses peaking factors applied to average dry-weather flow.

Average dry-weather flow is estimated from water use records or population × per-capita contribution; peak factors are applied to size pipes and pumps.

Manning's equation governs gravity flow; the hydraulic capacity of a pipe varies with diameter to the 8/3 power, so doubling diameter multiplies capacity by about 6.5.

Partially full pipes reach maximum velocity at about 0.8 depth ratio and maximum flow at about 0.94 depth ratio; full-flow Manning's equation overstates capacity near full.

Flow monitoring uses area-velocity meters; depth is measured by pressure or ultrasonic sensor and velocity by Doppler, and Q = A × V.

Capacity management requires comparing existing peak flows to design capacity, identifying hydraulic bottlenecks, and planning capital improvements before surcharge occurs.

Surcharging occurs when downstream capacity is exceeded; surcharge analysis uses the hydraulic grade line and must not result in basement backups or SSOs.

CCTV inspection uses NASSCO PACP defect codes: structural defects (cracks, fractures, collapse) versus operational/maintenance defects (roots, grease, debris, infiltration).

Defect grades 1–5 indicate severity; grade 4 and 5 defects drive rehabilitation decisions, while grade 1–2 may be monitored.

Smoke and dye testing, air testing, and infiltration/exfiltration testing verify new construction and locate defects.

Rehabilitation methods: CIPP lining, slip lining, pipe bursting, spot repairs, grouting, and manhole lining; selection depends on defect type, pipe condition, and hydraulic impact.

Post-rehabilitation verification includes CCTV of the lined pipe, dimensional checks, and leak testing to confirm the liner meets specification.

Inspection frequency should be risk-based, weighing pipe age, material, soil, flow, and history of failures or SSOs.

The Clean Water Act and NPDES permit program regulate discharges; SSOs and bypasses must be reported and corrected per permit and state requirements.

The collection system permit or state rule may require a capacity, management, operations, and maintenance (CMOM) program with SSO reporting and public notification.

Spill reporting thresholds and timelines vary by state; SSOs reaching waters of the state require immediate notification and follow-up written reports.

The Safe Drinking Water Act's cross-connection requirements and state plumbing codes prohibit unauthorized connections between storm and sanitary systems.

OSHA 29 CFR 1910.146 governs permit-required confined space entry, and 29 CFR 1926 Subpart P governs trenching and excavation.

Recordkeeping obligations include SSO logs, inspection and maintenance records, monitoring data, and training records, retained for the period the permit specifies.

Asset management records include asset inventory, condition assessment, work order history, and remaining useful life estimates to prioritize capital and O&M spending.

A computerized maintenance management system (CMMS) tracks work orders, labor, parts, and failure history; it supports preventive versus corrective maintenance decisions.

Key performance indicators include SSO rate per 100 miles of pipe, backup rate per 1,000 connections, and mean time to repair.

Records must be accurate, dated, and retrievable for the permit retention period; electronic records must be backed up and access-controlled.

Failure mode analysis (likelihood × consequence) drives rehabilitation priority and is the basis for risk-based asset management.

Reporting to the regulatory agency must be on the required form and schedule, with supporting data retained and available for inspection.

Operator certification requirements are set by the state; Class IV operators must meet education/experience and continuing education requirements to maintain certification.

Training records must document confined space entry, respiratory protection, lockout/tagout, and traffic control for each employee, with refresher intervals.

Emergency response plans address SSOs, pump station failures, power outages, and hazardous material releases, with call-out lists and notification procedures.

Incident command principles apply to collection system emergencies; a designated incident commander coordinates field crews, notifications, and public information.

Supervisors must ensure pre-job briefings, hazard assessments, and permit review occur before confined space or excavation work begins.

Post-incident review identifies root cause and corrective actions, which feed back into maintenance schedules and training.