Water and Wastewater Treatment, Discharge, and Stormwater Controls
What the exam tests
This domain tests the Clean Water Act framework, NPDES and pretreatment requirements, wastewater treatment performance, stormwater pollution prevention, and discharge monitoring. You should be able to read a permit limit, select the right averaging period, and recognize when a bypass, spill, or stormwater condition triggers reporting or corrective action.
Core rules
- The CWA prohibits unpermitted discharges of pollutants from a point source to waters of the U.S. NPDES permits contain effluent limits, monitoring, reporting, and special conditions.
- Limits may be technology-based or water-quality-based. Anti-backsliding generally prevents relaxation of existing limits.
- Industrial users discharging to a POTW are subject to pretreatment standards and local limits.
- Industrial stormwater permits require an SWPPP, BMPs, inspections, and monitoring. A no-exposure certification is available only when industrial materials and activities are not exposed to stormwater.
- Discharge Monitoring Reports are certified submissions. Bypasses, upsets, sanitary sewer overflows, and spills have separate notification duties.
Worked example
An NPDES permit sets a monthly average phosphorus limit of 1.0 mg/L and no daily maximum. Four weekly results are 0.8, 1.1, 0.9, and 1.2 mg/L. The monthly average is 1.0 mg/L, so the monthly average limit is met. If the permit also had a 1.0 mg/L daily maximum, the 1.1 and 1.2 mg/L results would be exceedances. The reasoning is to match each result to the correct limit type and averaging period before deciding compliance.
Traps
Averaging across the wrong period; comparing a single grab sample to a monthly average limit; treating a stormwater benchmark as a numeric permit limit; claiming no exposure while drums are stored outdoors; failing to report a bypass because the discharge was diluted; and assuming a lab’s detection limit below the permit limit automatically makes the result valid.