CESSWI CESSWI Post-Construction BMP Maintenance and Long-Term Controls 1 — Questions and Answers
Question 1: Under the EPA's Construction General Permit (CGP), when is a permittee typically required to transition from construction-phase BMPs to post-construction stormwater controls?
- Immediately after final grading is complete
- When the site reaches final stabilization and permit coverage is terminated (Correct answer)
- After the first post-construction inspection
- 30 days after the last rainfall event exceeding 0.5 inches
Correct answer: When the site reaches final stabilization and permit coverage is terminated
Permit coverage — and the obligation to maintain construction BMPs — ends when final stabilization is achieved and the Notice of Termination (NOT) is filed, at which point long-term post-construction controls take over.
Question 2: A dry extended-detention basin is a post-construction BMP designed primarily to:
- Permanently pool water to provide wetland habitat
- Detain stormwater temporarily to reduce peak discharge rates and allow sediment settling (Correct answer)
- Infiltrate 100% of design storm runoff into groundwater
- Filter runoff through a sand/gravel media
Correct answer: Detain stormwater temporarily to reduce peak discharge rates and allow sediment settling
Dry extended-detention basins hold runoff for an extended period (typically 24–40 hours) after a storm to attenuate peak flows and remove suspended sediments before releasing water.
Question 3: Which post-construction BMP is specifically designed to reduce both runoff volume and pollutant loading through infiltration and evapotranspiration?
- Riprap channel lining
- Bioretention cell (rain garden) (Correct answer)
- Concrete flume
- Rip-rap energy dissipater
Correct answer: Bioretention cell (rain garden)
Bioretention cells use engineered soil media and vegetation to infiltrate, filter, and evapotranspirate stormwater, removing pollutants through physical, biological, and chemical processes.
Question 4: During a post-construction inspection of a wet retention pond, an inspector observes the permanent pool is 50% smaller than the design volume due to sediment accumulation. The required action is to:
- Document the condition and re-inspect in 12 months
- Notify the owner that sediment must be removed to restore design storage capacity (Correct answer)
- Add more water to compensate for lost volume
- Plant additional vegetation around the pond perimeter
Correct answer: Notify the owner that sediment must be removed to restore design storage capacity
Excessive sediment accumulation reduces the pond's water quality treatment volume and hydraulic performance; the owner must restore the pond to design capacity through sediment removal.
Question 5: Permeable pavement is classified as which type of Low Impact Development (LID) stormwater practice?
- Conveyance BMP
- Volume reduction / green infrastructure BMP (Correct answer)
- Sediment trapping BMP
- Slope stabilization BMP
Correct answer: Volume reduction / green infrastructure BMP
Permeable pavement allows runoff to infiltrate through the surface into a gravel reservoir below, reducing total runoff volume — the defining characteristic of a green infrastructure/LID approach.
Question 6: Which inspection finding would trigger an immediate corrective action for a post-construction outlet structure?
- Minor algae growth on the barrel walls
- Outlet pipe fully blocked with debris, causing the basin to overflow its embankment (Correct answer)
- Water surface 1 foot below the design permanent pool elevation
- Grass growing on the side slopes of the embankment
Correct answer: Outlet pipe fully blocked with debris, causing the basin to overflow its embankment
A blocked outlet that causes embankment overtopping is an emergency condition — uncontrolled overflow can erode and fail the embankment, causing catastrophic downstream flooding.
CESSWI CESSWI Post-Construction BMP Maintenance and Long-Term Controls 1
Under the EPA's Construction General Permit (CGP), when is a permittee typically required to transition from construction-phase BMPs to post-construction stormwater controls?