Wastewater Collection Operator Class I cheat sheet

Design velocity: gravity sewers should carry at least 2 ft/s (0.6 m/s) at design flow to remain self-cleansing, and should not exceed about 10 ft/s (3 m/s) to avoid scour of the pipe wall.

Manning's equation: Q = (1.486/n) A R^(2/3) S^(1/2) in US customary units, where R = A/P. Typical roughness n: PVC 0.009-0.011, concrete and vitrified clay 0.013.

Common minimum slopes: 8-in = 0.40%, 10-in = 0.28%, 12-in = 0.22%. Place manholes at every change of grade, alignment, or pipe size, at junctions, and typically every 400-500 ft.

A drop manhole is used when the incoming invert is 24 in or more above the outgoing invert, so flow does not scour the manhole wall.

Infiltration versus inflow: infiltration is groundwater entering through defective pipe, joints, and walls and is present in dry weather; inflow is direct stormwater entering through downspouts, drains, and covers and appears only during rain.

Smoke testing locates illegal storm connections and broken laterals; dye testing confirms one specific cross-connection; CCTV inspection with standard defect codes rates structural condition.

Hydrogen sulfide control: keep velocity up and detention time down, add nitrate or ferric chloride, ventilate or treat manholes, and line the crowns of concrete pipe in low-velocity reaches.

SSO response sequence: stop and contain the flow, protect public health and receiving waters, clean and disinfect, notify the regulator and the public, then document volume, cause, and corrective action.

Design flow: typical residential contribution is about 70-100 gpcd, with a peaking factor applied to size the peak hourly capacity of mains and lift stations.

Brake horsepower: bhp = (gpm x total head in ft x specific gravity) / (3960 x pump efficiency). Water horsepower = (gpm x head in ft) / 3960.

Affinity laws: for a fixed impeller diameter, capacity varies with speed, head varies with speed squared, and power varies with speed cubed.

Cavitation signs: rattling noise, vibration, and falling head and flow. Fix by raising NPSH available - raise wet well level, enlarge or shorten suction piping, and remove fittings close to the suction.

Operate near the best efficiency point; far left of it causes recirculation and heat, far right causes cavitation and motor overload.

Three-phase motor current: amps = (hp x 746) / (1.732 x volts x efficiency x power factor). One horsepower = 0.746 kW.

The usable wet well volume between lead and lag pump settings sets the number of starts per hour; adequate storage keeps starts within the motor manufacturer's allowable limit.

A check valve on each discharge prevents backflow and reverse rotation; an air-and-vacuum relief valve on the force main prevents vacuum and column separation after a pump stops.

Motor enclosures: TEFC for general indoor service; explosion-proof Class I Division 1 in wet wells and other classified locations.

Condition monitoring: trend bearing temperature and vibration, check shaft alignment and coupling wear, lubricate on the manufacturer's interval, and megger windings at scheduled outages.

Test order with a four-gas meter: oxygen, combustible gas, hydrogen sulfide, carbon monoxide - before entry and continuously while the space is occupied.

Acceptable entry readings: O2 19.5-23.5%, combustible gas below 10% LEL, H2S below 10 ppm, CO below 35 ppm.

Methane LEL is 5% and UEL is 15%; it is lighter than air and collects at the top of structures. Hydrogen sulfide is heavier than air (specific gravity 1.19) and collects in low spots.

H2S limits: OSHA ceiling 20 ppm, NIOSH 10-minute ceiling 10 ppm, IDLH 100 ppm; the sense of smell is deadened at high concentrations, so odor is not a warning.

Never enter a permit space without a permit, a trained attendant stationed outside, a harness with retrieval line, forced ventilation, and a rescue plan.

Trenching: a protective system is required at 5 ft depth; slope Type B soil at 1:1 and Type C at 1.5:1; provide a ladder within 25 ft of lateral travel.

Keep spoil, equipment, and materials at least 2 ft back from the trench edge, and have a competent person inspect the excavation at the start of each shift and after rain.

Lockout/tagout: isolate every energy source, apply your own lock and tag, release stored energy, then try the controls to confirm the equipment is de-energized.

For an incapacitated entrant, call 911 and use the retrieval system first; do not enter without SCBA and backup, because most confined-space fatalities are untrained would-be rescuers.

The Clean Water Act (1972) requires an NPDES permit for any discharge to waters of the United States; POTW permits typically limit BOD, TSS, pH (6-9), ammonia, and chlorine residual.

40 CFR 403 pretreatment: the POTW issues industrial user permits, sets local limits, samples and inspects significant industrial users, and enforces against violators.

SSO and CSO notification: report to the state agency within the time its rules require (commonly 24 hours), stating location, volume, receiving water, and corrective action taken.

CMOM covers Capacity, Management, Operations and Maintenance: capacity assurance, asset management, training, and an overflow emergency response plan.

Monitoring records must be retained at least 3 years under 40 CFR 122.41(j), or longer if the permit requires; discharge monitoring reports are signed by a responsible official.

Bypass and upset: notify orally within 24 hours and in writing within 5 days, including cause, duration, and corrective action taken.

Operator certification is state-issued and matched to the system's classification, with a designated operator in direct responsible charge and continuing education contact hours for renewal.

Key OSHA rules for collection work: 1910.146 permit-required confined spaces, 1910.147 lockout/tagout, 1910.1200 hazard communication, and 1910.120 HAZWOPER for emergency response.

The local sewer use ordinance is the enforcement tool for prohibited discharges, connection permits, fees, and industrial pretreatment requirements.