CESSWI Stormwater Runoff Management 5 — Questions and Answers
Question 1: A grassed swale is most appropriately used in place of a curb-and-gutter system when which site condition is present?
- Slopes greater than 6% with erodible soils
- Flat to gently sloping areas with adequate vegetative cover (Correct answer)
- High-traffic urban areas with limited right-of-way
- Sites with seasonally high water tables within 2 feet of the surface
Correct answer: Flat to gently sloping areas with adequate vegetative cover
Grassed swales work best on gentle slopes where vegetation can establish and flow velocities remain non-erosive, allowing infiltration and pollutant removal.
Question 2: Which metric is used to evaluate whether a stormwater BMP has maintained its designed pollutant removal performance over time?
- Hydraulic retention time only
- Effluent monitoring data compared to influent concentrations (Correct answer)
- Visual inspection of embankment condition
- Annual rainfall totals at the site
Correct answer: Effluent monitoring data compared to influent concentrations
Comparing influent and effluent pollutant concentrations (or loads) through monitoring data is the direct measure of a BMP's pollutant removal performance.
Question 3: What is the significance of the '2-year, 24-hour storm' in stormwater management design?
- It is used exclusively for emergency spillway sizing
- It represents the storm that controls channel-forming flows and is often used for channel protection design (Correct answer)
- It is the smallest storm regulated under the NPDES CGP
- It defines the maximum flood event for dam design
Correct answer: It represents the storm that controls channel-forming flows and is often used for channel protection design
The 2-year, 24-hour storm approximates the channel-forming or 'bankfull' flow and is commonly used as the design event for stormwater channel protection criteria.
Question 4: An inspector notices that a construction site's stabilized construction entrance is tracked out onto a public road. What is the correct immediate response?
- Issue a stop-work order for the entire site
- Require immediate road sweeping or washing of tracked sediment and improvement of the entrance BMP (Correct answer)
- Document the condition and schedule a follow-up inspection in 30 days
- Require the contractor to install a second construction entrance
Correct answer: Require immediate road sweeping or washing of tracked sediment and improvement of the entrance BMP
Tracked sediment on public roads must be removed immediately to prevent it from washing into storm drains, and the entrance BMP must be improved to prevent recurrence.
Question 5: Which post-construction stormwater requirement is commonly mandated by MS4 permits to address volume and water quality goals?
- Installation of perimeter silt fence around all impervious areas
- On-site retention or infiltration of runoff from a specified design storm (Correct answer)
- Annual dredging of all stormwater ponds
- Installation of vegetated roofs on all new buildings
Correct answer: On-site retention or infiltration of runoff from a specified design storm
MS4 post-construction programs typically require retention or treatment of the water quality volume on-site, often the 1-inch storm or 90th percentile event, to meet volume and pollutant load reduction goals.
Question 6: What does the term 'hydromodification' refer to in stormwater management?
- The chemical modification of stormwater pollutants through treatment
- Changes in watershed hydrology caused by land development that alter flow frequency, duration, and magnitude (Correct answer)
- The physical modification of stream channels through dredging
- Adding amendments to soil to increase infiltration rates
Correct answer: Changes in watershed hydrology caused by land development that alter flow frequency, duration, and magnitude
Hydromodification refers to alterations in the hydrologic regime of streams resulting from land development, including changes in peak flows, flow duration, and total runoff volume.
Question 7: Which inspection finding would indicate that a dry extended detention pond is NOT functioning as designed?
- Pond bottom has sparse grass cover between storm events
- Outlet structure riser has a dewatering orifice at the pond floor
- Permanent pool of water remains in the pond bottom weeks after the last storm (Correct answer)
- Side slopes are vegetated with erosion-resistant grass
Correct answer: Permanent pool of water remains in the pond bottom weeks after the last storm
A dry extended detention pond is designed to drain completely between storms; a permanent pool indicates a clogged outlet, high water table, or improper grading that prevents full drainage.
CESSWI Stormwater Runoff Management 5
A grassed swale is most appropriately used in place of a curb-and-gutter system when which site condition is present?