CPESC Stormwater Management 5 — Questions and Answers
Question 1: Which federal regulation requires municipalities in urbanized areas to obtain NPDES permits for their stormwater discharges?
- Section 404 of the Clean Water Act
- MS4 Phase I and Phase II rules under 40 CFR Part 122 (Correct answer)
- RCRA Subtitle C regulations
- Safe Drinking Water Act Surface Water Treatment Rule
Correct answer: MS4 Phase I and Phase II rules under 40 CFR Part 122
The MS4 (Municipal Separate Storm Sewer System) Phase I and II rules require NPDES permits for stormwater discharges from urbanized area storm sewer systems.
Question 2: What is the purpose of a vegetated filter strip in stormwater management?
- Store runoff volume during peak storm events
- Remove pollutants and slow runoff velocity through sheet flow over dense vegetation (Correct answer)
- Aerate stormwater to promote aerobic decomposition
- Concentrate flow for efficient conveyance to detention basins
Correct answer: Remove pollutants and slow runoff velocity through sheet flow over dense vegetation
Vegetated filter strips treat sheet flow runoff by slowing velocity and allowing infiltration and filtering of sediment and associated pollutants through dense grass.
Question 3: In the context of watershed hydrology, what does 'time of concentration' (Tc) represent?
- Time from storm start to peak runoff at the watershed outlet
- Time required for runoff to travel from the hydraulically most remote point to the watershed outlet (Correct answer)
- Duration of the design storm rainfall event
- Time needed for a detention basin to drain completely
Correct answer: Time required for runoff to travel from the hydraulically most remote point to the watershed outlet
Time of concentration is the travel time of runoff from the most remote point in the watershed to the outlet, used to determine the critical duration storm for peak flow design.
Question 4: Which condition would INCREASE the runoff curve number (CN) for a site?
- Converting cropland to native prairie with deep-rooted grasses
- Paving a gravel parking lot with asphalt (Correct answer)
- Implementing conservation tillage practices on agricultural land
- Installing a cistern to capture roof runoff
Correct answer: Paving a gravel parking lot with asphalt
Paving a gravel lot with asphalt increases imperviousness significantly, raising the CN value and increasing runoff volume and peak rates.
Question 5: A constructed wetland used for stormwater treatment primarily removes pollutants through which mechanisms?
- UV disinfection and chlorination
- Settling, biological uptake, microbial decomposition, and filtration through vegetation (Correct answer)
- Activated carbon adsorption and ion exchange
- Reverse osmosis and membrane filtration
Correct answer: Settling, biological uptake, microbial decomposition, and filtration through vegetation
Constructed stormwater wetlands remove pollutants through a combination of settling, plant uptake, microbial activity, and physical filtration through emergent vegetation.
Question 6: What is the significance of the 'bankfull discharge' concept in stormwater and stream management?
- The maximum flow a detention basin can hold before the emergency spillway activates
- The flow that just fills the stream channel to its banks and is most effective at shaping channel morphology (Correct answer)
- The discharge at which floodplain inundation causes property damage
- The minimum flow needed to maintain aquatic habitat
Correct answer: The flow that just fills the stream channel to its banks and is most effective at shaping channel morphology
Bankfull discharge, which statistically approximates the 1.5- to 2-year recurrence interval flow, is the dominant channel-forming flow that controls stream morphology.
Question 7: Which stormwater management approach focuses on managing runoff at the source rather than collecting and conveying it to a centralized facility?
- Regional detention basin strategy
- Distributed or decentralized source control (Correct answer)
- Combined sewer overflow management
- End-of-pipe treatment plant approach
Correct answer: Distributed or decentralized source control
Distributed or decentralized source control manages stormwater where it falls—through rain gardens, green roofs, and permeable pavement—rather than routing all runoff to large centralized systems.
CPESC Stormwater Management 5
Which federal regulation requires municipalities in urbanized areas to obtain NPDES permits for their stormwater discharges?