CPESC Sediment Control Best Practices 4 — Questions and Answers
Question 1: What is the recommended minimum length of a construction entrance/exit stabilization pad?
- 25 feet
- 50 feet (Correct answer)
- 75 feet
- 100 feet
Correct answer: 50 feet
A stabilized construction entrance is typically at least 50 feet long to allow adequate tire cleaning before vehicles reach public roads.
Question 2: Polyacrylamide (PAM) is used in erosion and sediment control primarily to:
- Kill invasive vegetation in sediment basins
- Flocculate fine particles and reduce turbidity in stormwater runoff (Correct answer)
- Increase soil infiltration rates on compacted sites
- Prevent freeze-thaw damage to silt fences in cold climates
Correct answer: Flocculate fine particles and reduce turbidity in stormwater runoff
PAM is an anionic flocculant that causes fine clay and silt particles to aggregate, settling out of runoff and significantly reducing turbidity.
Question 3: When installing a silt fence on a slope, the bottom of the fabric should be buried in a trench and backfilled to prevent:
- UV degradation of the geotextile material
- Undercutting by runoff flowing beneath the fence (Correct answer)
- Wind displacement of the fence during dry periods
- Weed growth along the base of the fence
Correct answer: Undercutting by runoff flowing beneath the fence
Burying the toe of the silt fence fabric prevents runoff from flowing under the fence (undercutting), which is one of the most common failure modes.
Question 4: A construction SWPPP (Stormwater Pollution Prevention Plan) must be prepared for sites that disturb:
- More than 0.5 acres of land
- 1 acre or more of land (Correct answer)
- 5 acres or more of land
- 10 acres or more of land
Correct answer: 1 acre or more of land
Under the federal NPDES Construction General Permit, a SWPPP is required for all construction activities disturbing 1 or more acres (or less than 1 acre if part of a larger common plan).
Question 5: What is the main disadvantage of using straw bale barriers compared to silt fences for sediment control?
- Straw bales are more expensive per linear foot
- Straw bales decompose quickly and can introduce weed seeds (Correct answer)
- Straw bales cannot be used on slopes greater than 3%
- Straw bales require professional installation by a licensed contractor
Correct answer: Straw bales decompose quickly and can introduce weed seeds
Straw bales decompose within a single construction season and often contain weed seeds that can establish invasive species on the disturbed site.
Question 6: The concept of 'phased grading' as a sediment control strategy involves:
- Grading the entire site at once to reduce total construction time
- Limiting the amount of bare soil exposed at any one time by sequencing earthwork (Correct answer)
- Using heavy equipment only during dry weather to avoid mud
- Installing all permanent drainage structures before any grading begins
Correct answer: Limiting the amount of bare soil exposed at any one time by sequencing earthwork
Phased grading minimizes the area of disturbed soil exposed simultaneously, reducing the potential for erosion and sediment transport during construction.
Question 7: Which of the following BEST describes the difference between erosion control and sediment control?
- Erosion control uses vegetation; sediment control uses structural practices
- Erosion control prevents soil detachment at the source; sediment control captures soil after it has been mobilized (Correct answer)
- Erosion control applies only to slopes; sediment control applies only to flat areas
- Erosion control is required by law; sediment control is voluntary
Correct answer: Erosion control prevents soil detachment at the source; sediment control captures soil after it has been mobilized
Erosion control focuses on preventing soil particles from detaching and being transported (source control), while sediment control captures particles that have already been mobilized by runoff.
CPESC Sediment Control Best Practices 4
What is the recommended minimum length of a construction entrance/exit stabilization pad?