Free Wastewater Collection System Operator Exam Flashcards

A network of pipes, manholes, pump stations, and related infrastructure that conveys wastewater from homes, businesses, and industry to a treatment plant. Treatment occurs at the plant, not in the collection system.

A combined system carries sanitary wastewater and stormwater in one pipe; a separate system uses dedicated pipes for each. Combined systems are prone to overflows (CSOs) during heavy rain, so most modern systems are separate.

A pressurized pipeline that receives pumped wastewater from a lift station and conveys it to a gravity sewer or the plant. Used where gravity flow is not feasible due to terrain or other constraints.

A depressed section of gravity sewer that dips below normal grade to pass under an obstruction such as a river or highway, then rises back to grade. Upstream driving head pushes flow through the depressed section.

Grinder pumps at each property macerate solids and pump effluent into small-diameter pressurized mains. Economical for flat, rocky, low-density, or high-water-table areas where gravity sewers are impractical.

The most widely specified material for new 8-15 inch gravity sewers because of light weight, corrosion resistance, a smooth interior, and low cost. Smoothness gives a low Manning n-value.

A fired ceramic pipe virtually immune to chemical attack, including sulfuric acid from H2S corrosion. Long service life in aggressive environments, but heavier and more brittle than PVC.

Has higher pressure ratings and better resistance to external loads and water hammer than PVC, making it preferred for higher-pressure force mains or challenging installation conditions.

A minimum of about 2.0 ft/s at design flow keeps solids in suspension and transports them downstream, preventing deposition and blockages in gravity sewers.

V = (1.486/n) x R^(2/3) x S^(1/2). Calculates open-channel velocity in gravity sewers from hydraulic radius (R), slope (S), and roughness (n). The fundamental tool for sizing and evaluating gravity sewers.

A dimensionless coefficient for the frictional resistance of the pipe interior. Lower values (smooth PVC ~0.009-0.013) allow higher velocity; higher values (rough or deteriorated pipe) reduce velocity.

Slope provides the driving force for gravity flow. Per the Manning equation, velocity rises with the square root of slope, so steeper grades produce higher velocity and greater capacity for a given pipe.

A gravity sewer flowing 100% full because demand exceeds gravity capacity or a downstream blockage causes backwater. Design typically limits peak flow to 50-75% of full-pipe capacity for a surge margin.

1 cubic foot per second = 448.8 gallons per minute. A frequently used conversion: e.g., 2 cfs x 448.8 = 897.6 GPM. Memorize it for collection-system math.

Detention time = Volume / Flow, with matching units (gallons / GPM = minutes). Excessive wet-well detention causes septic conditions and H2S; design typically targets under 30 minutes at average flow.

Slope = drop / length. A 3-ft drop over 600 ft = 0.005 ft/ft = 0.50% = 5 ft per 1,000 ft. This exceeds the 0.40% minimum for an 8-inch sewer.

A section that settled below intended grade, creating a low point where wastewater and solids accumulate. Raises the risk of blockages, odor, and H2S generation; typically needs repair or replacement.

Adjacent pipe segments shifted out of alignment, creating a step or lip at the connection. It catches debris, causes blockages, allows infiltration, and worsens as soil continues to move.

High-pressure water (typically 2,000-3,000 psi) through a nozzle whose rear jets propel it upstream while it cuts grease, roots, and debris, flushing material to a manhole for vacuum removal.

Foaming herbicide (e.g., metam sodium or dichlobenil) applied through manholes contacts the root mass, killing roots and inhibiting regrowth for 1-3 years without harming the host tree. Cutting alone gives only short-term relief.

Proactive cleaning of high-risk segments (flat slopes, FOG areas, root-prone lines) on set intervals to prevent SSOs. Reactive cleaning alone leads to overflows and costly enforcement.

A trenchless rehab method: a resin-saturated liner is inserted into the host pipe and cured to form a structural liner (~50-year design life), sealing cracks and infiltration without excavation. Laterals are reopened robotically.

Best addressed at the source: mandate and inspect grease interceptors at food service establishments, schedule pumping, and educate kitchen staff. Sewer use ordinances enforce it; EPA promotes it within CMOM.

Infiltration is groundwater entering through cracked pipes, joints, or manhole walls (slow, water-table driven). Inflow is surface water entering through direct connections like downspouts or manhole covers (fast rain spikes).

Smoke testing finds inflow connections; dye testing confirms suspected connections; flow monitoring quantifies rain-dependent flow per basin; CCTV inspection reveals pipe defects that allow infiltration.

Non-toxic smoke is forced into a plugged sewer segment; smoke exiting at yards, downspouts, or building plumbing reveals illegal connections, broken cleanouts, defective vents, and inflow pathways.

A remotely operated camera crawler captures video of the pipe interior to document cracks, infiltration, root intrusion, offset joints, and blockages for asset management and SSO root-cause analysis.

The National Association of Sewer Service Companies Pipeline Assessment Certification Program provides standardized CCTV defect coding so condition data is consistent and comparable across operators for rehab prioritization.

Installing a weir or flume creates a known depth-to-flow relationship; measuring depth lets operators calculate flow rate from the device's calibration equation. A standard sewer flow-monitoring method.

The standard in modern lift stations: handles solids-laden flow, sits in the wet well (no separate dry well or priming), and is maintained by pulling the pump to the surface. Often uses non-clog or vortex impellers.

Grinds household solids into a fine slurry and pumps it through a small-diameter (about 1.25-3 inch) pressure main. Enables sewer service where gravity sewers are not feasible due to flat terrain or high water tables.

Allows flow in one direction only. On a lift-station discharge it prevents force-main wastewater from draining back into the wet well when the pump stops, protecting against reverse rotation and short cycling.

The pump starts and stops too frequently because wet-well effective volume is too small relative to pump capacity. It accelerates wear on the motor, starter, and seals.

The station's pumping ability with the largest pump out of service. With two identical 500 GPM pumps, firm capacity is 500 GPM. Stations are designed to meet peak flow at firm capacity for reliability.

The total resistance a pump must overcome: static head (elevation lift) plus friction losses in the force main plus minor losses through fittings and valves. TDH drives pump and motor selection.

NPSH-Available is the suction pressure above the liquid's vapor pressure; NPSH-Required is the manufacturer spec for cavitation-free operation. If NPSH-A drops below NPSH-R, the pump cavitates.

A transient pressure surge, often from a check valve slamming after a pump trip or rapid valve closure. Mitigated by slow-closing check valves, surge tanks, vacuum-relief valves, and VFD soft-stop ramps.

Manholes and wet wells qualify: limited entry/egress, not designed for continuous occupancy, with recognized atmospheric or engulfment hazards. Governed by OSHA 29 CFR 1910.146.

Acceptable entry: oxygen 19.5-23.5%, combustible gas (LEL) below 10%, H2S below 10 ppm, CO below 35 ppm. Test in order: oxygen first, then combustibles, then toxics, top to bottom.

Toxic and flammable. NIOSH IDLH is 100 ppm. Olfactory paralysis occurs around 100-150 ppm, so workers may stop smelling it as it becomes most dangerous — calibrated meters are mandatory, not the nose.

OSHA 1910.146 requires an authorized entrant (inside), an attendant (outside, never leaving post until relieved), and an entry supervisor (signs the permit and verifies conditions). Rescue services must be available.

Isolates all energy sources (electrical, mechanical, hydraulic, pneumatic) and physically locks them out before maintenance, with tags identifying who and why. Prevents accidental startup that could injure or kill a worker.

Beyond cutting electrical power, isolate hydraulic energy: pressurized force mains can drive a pump unexpectedly if a check valve fails to seat. Account for VFD capacitors, then verify the zero-energy state.

Forced fresh-air supply ventilation is generally preferred (ANSI Z117.1 / OSHA): it delivers clean air to the breathing zone with ducting near the bottom of the space. Continuous monitoring is still required throughout entry.

OSHA 1926.652 requires sloping, benching, shoring, or shielding at 5 ft or more (and at any depth with hazardous soil). A competent person inspects daily and after weather changes.

An unintentional discharge of untreated wastewater from the sanitary sewer before the plant. A Clean Water Act violation that must be reported. Common causes: blockages, pump failures, and capacity exceedances.

Capacity, Management, Operation, and Maintenance — an EPA self-audit framework documenting SOPs, asset inventory, preventive maintenance, training, and SSO response to minimize overflows and demonstrate NPDES compliance.

EPA or an authorized state agency issues NPDES permits. While the permit primarily regulates the POTW discharge, collection-system performance (SSOs, I/I, capacity, maintenance) is tied to permit compliance.

The local legal instrument that prohibits certain discharges, mandates pretreatment such as grease interceptors, requires inflow disconnection, and sets penalties. It implements EPA pretreatment requirements locally.

Protect public safety, stop/control the overflow (plug or bypass pump), prevent it reaching waters of the U.S., recover spilled wastewater, disinfect, and notify regulators within the state-required time with a written follow-up.