CME Stormwater Management & Drainage Engineering 2 — Questions and Answers
Question 1: A Stormwater Pollution Prevention Plan (SWPPP) is required under which regulatory framework for construction sites disturbing one or more acres?
- NPDES Construction General Permit (Correct answer)
- FEMA Floodplain Management Regulations
- CERCLA Remediation Standards
- Clean Air Act Title V Permits
Correct answer: NPDES Construction General Permit
The NPDES Construction General Permit requires construction sites disturbing one or more acres to develop and implement a SWPPP that identifies potential pollutant sources and describes Best Management Practices (BMPs) to reduce pollutants in stormwater discharges.
Question 2: A bioswale is best described as:
- A vegetated channel designed to slow stormwater runoff and filter pollutants through plants and soil (Correct answer)
- An underground pipe network for conveying stormwater
- A concrete-lined ditch that maximizes conveyance velocity
- A sediment trap placed at storm drain inlets
Correct answer: A vegetated channel designed to slow stormwater runoff and filter pollutants through plants and soil
A bioswale is a landscaped channel with dense vegetation that slows stormwater runoff, promotes infiltration, and removes pollutants through filtration, adsorption, and biological uptake.
Question 3: In the Rational Method, which factor primarily reflects the land use and surface characteristics of a drainage area?
- Runoff coefficient (C) (Correct answer)
- Rainfall intensity (i)
- Drainage area (A)
- Time of concentration (Tc)
Correct answer: Runoff coefficient (C)
The runoff coefficient (C) represents the fraction of rainfall that becomes surface runoff and varies by land use — for example, C ≈ 0.90 for impervious pavement versus C ≈ 0.25 for lawns with sandy soil.
Question 4: An MS4 (Municipal Separate Storm Sewer System) permit under Phase II NPDES regulations applies to municipalities with populations below:
- 100,000 (Correct answer)
- 500,000
- 50,000
- 250,000
Correct answer: 100,000
Phase II MS4 regulations extended NPDES permit requirements to regulated small MS4s serving populations under 100,000, requiring six minimum control measures to reduce stormwater pollutants.
Question 5: The 'first flush' phenomenon in urban stormwater refers to:
- The disproportionately high concentration of pollutants in the initial portion of a storm runoff event (Correct answer)
- The first rainfall event of the season after a dry period
- The rapid rise in stream stage at the beginning of a storm
- The initial flow entering a detention pond before it reaches capacity
Correct answer: The disproportionately high concentration of pollutants in the initial portion of a storm runoff event
The first flush effect describes how pollutants accumulated on impervious surfaces between storms are washed off in high concentrations during the early part of a runoff event, making initial runoff volumes particularly important to treat for water quality.
Question 6: A storm hydrograph depicts the relationship between:
- Discharge rate (flow) over time at a specific point in a watershed (Correct answer)
- Rainfall intensity versus drainage area
- Pollutant concentration versus runoff volume
- Pipe capacity versus pipe diameter
Correct answer: Discharge rate (flow) over time at a specific point in a watershed
A storm hydrograph is a plot of discharge rate versus time at a measurement point, showing how streamflow rises to a peak and recedes in response to a rainfall event.
Question 7: Low Impact Development (LID) is a stormwater management approach that primarily aims to:
- Replicate the pre-development hydrologic condition of a site using distributed, small-scale controls (Correct answer)
- Minimize construction costs by reducing the size of detention basins
- Eliminate the need for stormwater permits on sites under five acres
- Maximize impervious cover while increasing pipe sizes to handle runoff
Correct answer: Replicate the pre-development hydrologic condition of a site using distributed, small-scale controls
LID seeks to maintain or replicate pre-development hydrology by using distributed practices such as bioretention cells, rain gardens, permeable pavement, and green roofs to manage stormwater at the source.
CME Stormwater Management & Drainage Engineering 2
A Stormwater Pollution Prevention Plan (SWPPP) is required under which regulatory framework for construction sites disturbing one or more acres?