Wastewater Collection
Wastewater Collection
This domain tests sanitary sewers, lift stations, gravity flow, infiltration and inflow, sanitary sewer overflows (SSOs), cleaning, repair, and collection-system safety. North Dakota systems face frost, ice, snowmelt, and aging pipes; exam questions often ask how to respond to a pump alarm, a blockage, or high wet-well level.
Core rules
- Gravity sewers need adequate slope and velocity; about 2 ft/s is a common self-cleansing target.
- Lift stations need reliable alarms, emergency storage, and contingency power or bypass.
- Infiltration is groundwater entering through defects; inflow is direct stormwater connection.
- Fats, oils, and grease cause blockages; respond to backups before they reach basements or surface water.
- SSOs must be reported and corrected; contain, clean up, and document.
Worked example
A 400-ft sewer run drops 2.0 ft. Slope = 2.0 ft ÷ 400 ft = 0.005 ft/ft, or 0.5%. If the same drop were mistakenly entered as 2%, the calculated slope would be 0.02 ft/ft, four times too steep. The reasoning: slope is vertical drop divided by horizontal length, and percent slope is ft/ft × 100.
Traps
Confusing percent slope with ft/ft; assuming a pump alarm resets itself; ignoring grease buildup until a blockage occurs; using the wrong manhole for flow monitoring; entering a wet well without confined-space controls.