LARE LARE Stormwater Management 3 — Questions and Answers
Question 1: Which pollutant is most effectively removed from stormwater by vegetated swales compared to traditional curb-and-gutter conveyance?
- Dissolved nitrates
- Total suspended solids (TSS) (Correct answer)
- Coliform bacteria
- Soluble phosphorus
Correct answer: Total suspended solids (TSS)
Vegetated swales primarily remove total suspended solids through sedimentation and filtration as flow velocity is reduced by vegetation.
Question 2: Under NPDES Phase II regulations, which land disturbance threshold triggers the requirement for a stormwater pollution prevention plan (SWPPP)?
- Any disturbance greater than 0.25 acres
- Disturbance of 1 acre or more (Correct answer)
- Disturbance of 5 acres or more
- Disturbance of 10 acres or more
Correct answer: Disturbance of 1 acre or more
NPDES Phase II extended stormwater permit requirements to construction sites disturbing 1 acre or more, requiring a SWPPP and stormwater permit.
Question 3: A green roof is being considered for a commercial building. Which factor most significantly limits its stormwater retention capacity?
- Roof pitch greater than 2:12
- Substrate depth and composition (Correct answer)
- Plant species selection
- Solar exposure on the roof surface
Correct answer: Substrate depth and composition
Substrate depth is the primary determinant of a green roof's water retention capacity, as deeper media holds more water through its pore space.
Question 4: What is the key hydrologic concept behind 'time of concentration' (Tc) in stormwater design?
- The time required for pollutants to settle out of stormwater
- The time for runoff to travel from the hydraulically most distant point to the design outlet (Correct answer)
- The duration of the design storm event
- The lag time between peak rainfall and peak runoff
Correct answer: The time for runoff to travel from the hydraulically most distant point to the design outlet
Time of concentration is the travel time for runoff from the most hydraulically distant point in a watershed to reach the design outlet, which determines peak flow timing.
Question 5: Which stormwater practice is best suited for managing runoff from ultra-urban areas where land is extremely limited?
- Constructed wetlands
- Dry extended detention ponds
- Underground detention/infiltration systems (Correct answer)
- Grass channels
Correct answer: Underground detention/infiltration systems
Underground detention and infiltration systems maximize land use efficiency in ultra-urban environments where surface space is unavailable for conventional BMPs.
Question 6: During a site inspection, you observe that a sediment basin outlet structure is clogged and water is overtopping the embankment. What is the immediate priority?
- Document the failure and schedule repairs for the next maintenance cycle
- Breach the embankment to release water and prevent a catastrophic failure
- Clear the outlet structure to restore designed hydraulic function (Correct answer)
- Install additional silt fence downstream to capture sediment
Correct answer: Clear the outlet structure to restore designed hydraulic function
Clearing the outlet structure is the first priority to restore controlled drainage and prevent the uncontrolled embankment overtopping that could lead to catastrophic failure.
Question 7: What is the primary advantage of a wet pond over a dry extended detention pond for stormwater quality improvement?
- Lower construction cost
- Greater peak flow attenuation
- Permanent pool provides continuous biological and sedimentation treatment (Correct answer)
- Easier maintenance access
Correct answer: Permanent pool provides continuous biological and sedimentation treatment
A wet pond's permanent pool allows continuous biological uptake, sedimentation, and algal assimilation of nutrients between storm events, improving overall treatment.
LARE LARE Stormwater Management 3
Which pollutant is most effectively removed from stormwater by vegetated swales compared to traditional curb-and-gutter conveyance?