CPESC Stormwater Management 3 — Questions and Answers
Question 1: Which parameter is NOT part of the Rational Method formula for peak runoff calculation?
- Runoff coefficient (C)
- Rainfall intensity (i)
- Drainage area (A)
- Time of concentration (Tc) (Correct answer)
Correct answer: Time of concentration (Tc)
The Rational Method formula Q = CiA uses the runoff coefficient, rainfall intensity, and drainage area; time of concentration is used to determine rainfall intensity but is not directly in the formula.
Question 2: Green infrastructure practices that mimic natural hydrology are often grouped under what broad term?
- End-of-pipe controls
- Low Impact Development (LID) (Correct answer)
- Gray infrastructure
- Combined sewer overflow (CSO) controls
Correct answer: Low Impact Development (LID)
Low Impact Development (LID) encompasses practices that manage stormwater close to the source by mimicking natural hydrologic processes.
Question 3: A bioretention cell differs from a rain garden primarily in that it:
- Does not use vegetation
- Is designed for larger drainage areas and includes engineered soil media and underdrain (Correct answer)
- Only treats water quality, not quantity
- Is lined to prevent all infiltration
Correct answer: Is designed for larger drainage areas and includes engineered soil media and underdrain
Bioretention cells are engineered systems with specified soil media, gravel layers, and underdrains designed for larger areas, while rain gardens are simpler residential-scale features.
Question 4: What is 'first flush' in stormwater management?
- The initial surge of very clean water at the start of a storm
- The phenomenon where the highest pollutant concentrations occur in the early portion of a runoff event (Correct answer)
- The first inspection conducted after a rainfall event
- The initial discharge through an emergency spillway
Correct answer: The phenomenon where the highest pollutant concentrations occur in the early portion of a runoff event
The first flush effect describes the disproportionately high pollutant loads carried by the initial runoff that washes accumulated pollutants off impervious surfaces.
Question 5: Which of the following is an example of a volume-based stormwater management requirement?
- Limiting post-development peak discharge to pre-development rates for the 2-year storm
- Retaining the 1-inch water quality volume on-site (Correct answer)
- Maintaining 10-year pre-development time of concentration
- Matching pre-development curve numbers
Correct answer: Retaining the 1-inch water quality volume on-site
Retaining a water quality volume (typically 1 inch) on-site is a volume-based requirement focused on treating runoff from frequent, smaller storms.
Question 6: An infiltration trench is most suitable for soils with a minimum saturated hydraulic conductivity (Ksat) of approximately:
- 0.01 inch/hour
- 0.27 inch/hour (Correct answer)
- 0.52 inch/hour
- 1.0 inch/hour
Correct answer: 0.27 inch/hour
Infiltration practices typically require a minimum Ksat of about 0.27 inch/hour (0.5 cm/hr) to ensure adequate drainage within 72 hours.
Question 7: Which pollutant is of greatest concern in stormwater runoff from parking lots and roadways?
- Nitrogen from atmospheric deposition
- Polycyclic aromatic hydrocarbons (PAHs) and heavy metals (Correct answer)
- Phosphorus from detergent use
- Bacteria from wildlife
Correct answer: Polycyclic aromatic hydrocarbons (PAHs) and heavy metals
Parking lots and roadways generate PAHs from vehicle exhaust and tire wear, along with heavy metals like zinc, copper, and lead from vehicle components.
CPESC Stormwater Management 3
Which parameter is NOT part of the Rational Method formula for peak runoff calculation?