CSM Remediation & Mitigation Strategies 2 — Questions and Answers
Question 1: Which bioremediation technique uses plants to extract heavy metals from contaminated stormwater sediments?
- Phytoremediation (Correct answer)
- Biofiltration
- Constructed wetland polishing
- Rhizofiltration
Correct answer: Phytoremediation
Phytoremediation uses hyperaccumulator plants to take up and concentrate heavy metals from contaminated soil and water.
Question 2: A stormwater pond is experiencing algal blooms due to excess phosphorus. Which in-situ chemical treatment is most commonly applied to precipitate phosphorus?
- Sodium hypochlorite
- Alum (aluminum sulfate) (Correct answer)
- Ferric chloride added at the outlet
- Calcium carbonate liming
Correct answer: Alum (aluminum sulfate)
Alum injected into stormwater ponds reacts with phosphorus to form insoluble aluminum phosphate that settles to the bottom.
Question 3: Which design feature of a bioretention cell is most critical for preventing clogging and maintaining long-term infiltration rates?
- Deep ponding zone above 18 inches
- Properly sized mulch layer and engineered soil media (Correct answer)
- Impermeable liner on all four sides
- Dense turf grass cover over the media surface
Correct answer: Properly sized mulch layer and engineered soil media
An engineered soil media (typically 60% sand, 20% compost, 20% topsoil) combined with a shallow mulch layer prevents fine sediment from clogging pores over time.
Question 4: When remediating a polluted stream channel, which approach best restores natural hydrologic function while providing sediment and nutrient mitigation?
- Installing concrete channel lining
- Stream daylighting with natural channel design (Correct answer)
- Placing riprap along the entire bank
- Deepening the channel to increase capacity
Correct answer: Stream daylighting with natural channel design
Stream daylighting removes culverts or hardened channels and restores natural meander patterns, reconnecting floodplains and improving pollutant removal.
Question 5: A detention basin is not meeting TSS removal targets. Which remedial modification is most likely to improve performance?
- Shortening the outlet riser pipe
- Adding a forebay and extending the permanent pool (Correct answer)
- Reducing the contributing drainage area
- Increasing the side slope steepness
Correct answer: Adding a forebay and extending the permanent pool
A forebay traps coarse sediment before it reaches the main pool, and a larger permanent pool increases hydraulic residence time, improving TSS settling.
Question 6: Which metric is used to quantify the effectiveness of a stormwater BMP in reducing peak runoff flow rates?
- Event mean concentration (EMC)
- Curve number (CN) reduction
- Peak flow attenuation ratio (Correct answer)
- Biochemical oxygen demand (BOD) loading
Correct answer: Peak flow attenuation ratio
Peak flow attenuation ratio compares post-BMP peak discharge to pre-BMP peak discharge, directly measuring a BMP's ability to reduce flooding risk.
Question 7: Under EPA's National Stormwater Best Management Practice database, which BMP type consistently shows the highest median total phosphorus removal efficiency?
- Grass swales
- Bioretention/rain gardens (Correct answer)
- Dry detention basins
- Porous pavement without underdrains
Correct answer: Bioretention/rain gardens
Bioretention systems with engineered media consistently demonstrate high TP removal (often 50–80%) through plant uptake, adsorption, and microbial processes.
CSM Remediation & Mitigation Strategies 2
Which bioremediation technique uses plants to extract heavy metals from contaminated stormwater sediments?