CESSWI Stormwater Management Practices 4 — Questions and Answers
Question 1: Which soil hydrologic group has the highest infiltration rates and is best suited for infiltration-based stormwater BMPs?
- Group A (Correct answer)
- Group B
- Group C
- Group D
Correct answer: Group A
HSG A soils (deep sands, well-drained gravels) have the lowest runoff potential and highest infiltration rates, making them ideal for infiltration trenches, basins, and permeable pavement.
Question 2: A stormwater inspector finds that the emergency spillway of a detention pond has been blocked by debris. What is the primary risk this creates?
- Increased mosquito breeding habitat
- Potential for dam overtopping and embankment failure during extreme storms (Correct answer)
- Reduced water quality treatment efficiency
- Accelerated eutrophication of the permanent pool
Correct answer: Potential for dam overtopping and embankment failure during extreme storms
The emergency spillway protects the embankment from overtopping; if blocked, flows exceeding the principal outlet capacity could overtop and rapidly erode the embankment, leading to failure.
Question 3: Green roofs reduce stormwater runoff volume primarily by:
- Increasing roof slope to speed drainage
- Retaining rainfall in growing media and releasing it through evapotranspiration (Correct answer)
- Directing runoff to underground cisterns
- Providing a permeable surface that allows direct infiltration to building structure
Correct answer: Retaining rainfall in growing media and releasing it through evapotranspiration
Green roof growing media absorb rainfall and plants release stored water through evapotranspiration, significantly reducing the volume and peak rate of runoff from rooftops.
Question 4: What design feature of a wet detention pond prevents short-circuiting of flow from inlet to outlet?
- Concrete-lined bottom
- Placement of inlet and outlet at opposite ends with a minimum 3:1 length-to-width ratio (Correct answer)
- Installing an oil/grit separator at the inlet
- Locating the outlet at the shallowest point
Correct answer: Placement of inlet and outlet at opposite ends with a minimum 3:1 length-to-width ratio
Separating the inlet and outlet at opposite ends and maintaining a 3:1 or greater length-to-width ratio maximizes flow path length, promoting settling and reducing short-circuit pathways.
Question 5: When performing a post-construction stormwater inspection, which document should the inspector reference to verify that BMPs were installed as approved?
- The contractor's bid schedule
- The approved stormwater management plan and construction drawings (Correct answer)
- The local zoning ordinance
- The NPDES Phase I permit
Correct answer: The approved stormwater management plan and construction drawings
The approved stormwater management plan and associated construction drawings define the required BMP types, sizes, locations, and specifications that the inspector verifies against field conditions.
Question 6: Which pollutant is most effectively removed from stormwater by a vegetated filter strip?
- Dissolved heavy metals
- Coarse sediment and associated particulate pollutants (Correct answer)
- Chlorides from road salt
- Dissolved nutrients in baseflow
Correct answer: Coarse sediment and associated particulate pollutants
Vegetated filter strips excel at removing coarse sediment through deposition and filtration as sheet flow passes through dense vegetation, along with particulate-bound pollutants.
Question 7: The concept of 'channel protection volume' in stormwater management addresses which specific problem?
- Reducing sediment delivery to wetlands
- Preventing streambank erosion caused by increased frequency of bankfull flows in urbanized watersheds (Correct answer)
- Protecting drinking water intakes from contamination
- Managing runoff from linear transportation projects
Correct answer: Preventing streambank erosion caused by increased frequency of bankfull flows in urbanized watersheds
Urbanization increases the frequency and duration of channel-forming flows; channel protection volume controls are designed to reduce the frequency of bankfull events that cause streambank erosion.
CESSWI Stormwater Management Practices 4
Which soil hydrologic group has the highest infiltration rates and is best suited for infiltration-based stormwater BMPs?