CSM Remediation & Mitigation Strategies 3 — Questions and Answers
Question 1: Which type of permeable pavement system is most appropriate for areas with clay soils where infiltration into native soil is not feasible?
- Open-graded base permeable interlocking concrete pavers with full infiltration
- Permeable pavement over an impermeable liner with an underdrain (Correct answer)
- Standard asphalt with surface drainage slots
- Gravel-filled geocell with no underdrain
Correct answer: Permeable pavement over an impermeable liner with an underdrain
In clay soils, an impermeable liner prevents water from entering poorly draining native soil while an underdrain still allows water quality treatment within the stone reservoir.
Question 2: A municipality discovers that road salt applications are causing elevated chloride concentrations in receiving streams year-round. Which mitigation strategy most effectively reduces chloride loading?
- Installing additional storm drain inlets
- Implementing anti-icing and pre-wetting programs with precise salt application rates (Correct answer)
- Constructing wetlands downstream to dilute chloride
- Replacing all road surfaces with permeable pavement
Correct answer: Implementing anti-icing and pre-wetting programs with precise salt application rates
Anti-icing and pre-wetting techniques apply brine before storms, requiring far less salt than reactive de-icing while achieving the same road safety outcomes.
Question 3: Which condition triggers a 'Level 2' corrective action for a stormwater BMP under a typical state post-construction maintenance program?
- Inlet partially blocked by leaves during inspection
- Structural failure impairing BMP hydraulic function (Correct answer)
- Outlet pipe showing minor surface rust
- Vegetation 20% below target cover in non-critical areas
Correct answer: Structural failure impairing BMP hydraulic function
A Level 2 corrective action is required when structural integrity or hydraulic function is compromised, posing an imminent risk to BMP performance or downstream areas.
Question 4: Which sediment remediation technique involves placing clean material over contaminated sediment to isolate pollutants and prevent resuspension?
- Dredging
- In-situ capping (Correct answer)
- Monitored natural recovery
- Electrokinetic remediation
Correct answer: In-situ capping
In-situ capping isolates contaminated sediment by placing clean sand, gravel, or reactive materials on top, preventing pollutant release without sediment removal.
Question 5: When sizing a vegetated filter strip for stormwater pretreatment, which parameter is most critical for determining the required width?
- Soil pH of the filter strip
- Slope of the contributing impervious surface
- Hydraulic loading rate per unit width (Correct answer)
- Species composition of the vegetation
Correct answer: Hydraulic loading rate per unit width
Hydraulic loading rate (flow per unit width) determines whether sheet flow can be maintained across the filter strip, which is essential for effective pollutant removal.
Question 6: Which regulatory mechanism under the Clean Water Act requires stormwater dischargers to develop and implement a Stormwater Pollution Prevention Plan (SWPPP)?
- Section 404 nationwide permit
- NPDES Multi-Sector General Permit (MSGP) for industrial stormwater (Correct answer)
- Section 401 water quality certification
- Total Maximum Daily Load (TMDL) wasteload allocation
Correct answer: NPDES Multi-Sector General Permit (MSGP) for industrial stormwater
The NPDES MSGP requires industrial facilities in specified sectors to develop a SWPPP documenting BMPs, monitoring, and corrective action requirements.
Question 7: Which treatment mechanism is primarily responsible for nitrogen removal in a constructed stormwater wetland?
- Gravitational settling of nitrate particles
- Nitrification followed by denitrification in anaerobic zones (Correct answer)
- Adsorption of ammonium onto sand media
- Volatilization of nitrogen gas at the water surface
Correct answer: Nitrification followed by denitrification in anaerobic zones
Stormwater wetlands promote nitrification in aerobic surface zones and denitrification in anaerobic substrate zones, converting nitrate to nitrogen gas.
CSM Remediation & Mitigation Strategies 3
Which type of permeable pavement system is most appropriate for areas with clay soils where infiltration into native soil is not feasible?