1. B
A sediment basin is designed to temporarily store runoff from disturbed areas, allowing sediment particles to settle through gravity separation before water is discharged. This reduces sediment pollution in receiving waters.

2. B
The K-factor in the USLE represents soil erodibility, which is the inherent susceptibility of soil particles to detachment and transport by rainfall and runoff. Different soil types have different K-factor values.

3. B
A 3:1 slope (three horizontal units to one vertical unit, or approximately 33% grade) is generally the maximum recommended slope for establishing vegetative cover without additional stabilization measures like erosion control blankets or terracing.

4. B
Terracing or benching steep slopes reduces the effective slope length and steepness, significantly reducing erosion potential. Combined with erosion control blankets, this provides immediate protection while vegetation establishes.

5. B
A minimum of 2 inches of mulch thickness is recommended to provide effective erosion control by protecting soil from raindrop impact, reducing runoff velocity, and maintaining soil moisture for seed germination.

6. A
The NPDES permit program under the Clean Water Act regulates point source discharges, including stormwater from construction sites disturbing one acre or more. Construction operators must obtain coverage under this permit.

7. C
Type C and Type D silt fence fabrics differ primarily in their opening size (measured in mm) and flow rate capacity. Type C has smaller openings for finer sediment filtration, while Type D has larger openings for higher flow rates.

8. B
Temporary erosion control measures must be installed before or immediately after land-disturbing activities begin to prevent soil erosion from the first rainfall event. Waiting until after earthwork is completed allows significant erosion to occur.

9. B
Standard silt fence installations are typically designed for drainage areas up to 0.5 acres. Larger drainage areas require additional sediment control measures or multiple silt fence installations.

10. B
Silt fence posts should be spaced at maximum intervals of 6 feet for standard installations to provide adequate support and prevent fabric sagging or failure under sediment and water pressure loads.

11. B
A construction entrance/exit, typically consisting of aggregate material, is designed to reduce the tracking of sediment and mud onto public roads by cleaning vehicle tires as they exit the construction site.

12. C
Turf reinforcement mats (TRMs) or hard armoring with riprap provide the highest level of protection for steep channel banks subject to high flow velocities, as they resist both erosive forces and provide immediate stabilization.

13. C
Research shows that approximately 70% ground cover is needed to significantly reduce soil erosion. This coverage interrupts raindrop impact and reduces runoff velocity across the soil surface.

14. B
Check dams are small temporary barriers placed across drainage channels to reduce flow velocity, increase ponding behind the structure, and promote sediment deposition while allowing water to pass through or over.

15. B
Rainfall intensity (amount per unit time) and drop size are the most significant factors affecting erosive power. High-intensity rainfall with large drops has greater kinetic energy to detach and transport soil particles.

16. C
On a 5% slope, check dams are typically spaced approximately every 100 feet to effectively reduce flow velocity and promote sediment deposition. Steeper slopes require closer spacing.

17. B
Polyacrylamide (PAM) is most effective when applied in irrigation water or low-flow situations where it can bind soil particles together, reducing sediment detachment. It is less effective during high-flow storm events.

18. C
Maximum allowable turbidity levels vary by NPDES permit conditions and the water quality standards of the receiving water body. There is no single universal standard; limits are site-specific and must be verified in the permit.

19. C
Sodding provides immediate soil stabilization and erosion control because it is mature vegetation with an established root system. However, it is also the most expensive method per square foot.

20. C
Erosion control blankets provide superior anchoring and resistance to displacement by wind and water compared to bare mulch. They maintain intimate contact with the soil surface and hold seed and mulch in place.

21. C
NPDES Construction General Permits typically require inspections at least once every seven calendar days and within 24 hours after any storm event producing 0.5 inches or more of rainfall.

22. B
Critical shear stress is the minimum force (typically measured in pounds per square foot) required to initiate movement of soil particles. Once exceeded, erosion begins and sediment transport occurs.

23. B
The Environmental Protection Agency (EPA) enforces federal erosion and sediment control requirements primarily through the NPDES permit program under the Clean Water Act, though states may have delegated authority.

24. C
A minimum of 12 inches (1 foot) of freeboard is recommended for temporary sediment basins to prevent overtopping during design storm events and to account for sediment accumulation.

25. B
The Revised Universal Soil Loss Equation (RUSLE) includes rainfall erosivity (R), soil erodibility (K), topographic (LS), cover management (C), and support practice (P) factors. Wind speed is not part of RUSLE as it addresses water erosion only.

26. B
Compost filter socks are tubular mesh structures filled with compost, used primarily for perimeter sediment control. They filter sediment from runoff while allowing water to pass through the compost material.

27. B
Most regulations and best practices require permanent vegetation to be established within 14 days (or as soon as possible) after reaching final grade to minimize erosion from exposed soil.

28. A
A sediment trap is a small excavated impoundment designed to capture sediment from drainage areas typically less than 5 acres. It uses gravity settling in a depression formed by excavation and/or earthen berms.

29. D
Compost and organic matter are most effective for improving water infiltration in compacted clay soils by improving soil structure, increasing porosity, and enhancing microbial activity.

30. B
Maximum flow velocities in vegetated channels should generally not exceed 3-5 feet per second to prevent vegetation damage and channel erosion. The specific limit depends on vegetation type and maturity.

31. B
Turbidity curtains (also called silt curtains) are floating barriers used in aquatic environments to contain sediment during in-water construction activities, preventing sediment from dispersing into surrounding water bodies.

32. C
Most erosion control guidelines recommend intermediate sediment controls when slope lengths exceed 200 feet to reduce the accumulation of runoff volume and velocity that increases erosive power.

33. C
According to NRCS standards, soils with an erodibility index (EI) greater than 8 are classified as highly erodible land (HEL). The EI is calculated using soil properties, slope, and climate factors.

34. B
Phasing construction activities minimizes the total area of exposed, disturbed soil at any given time, which directly reduces erosion potential and sediment generation from the construction site.

35. B
Removing accumulated sediment when it reaches approximately one-third of the silt fence height is critical to maintain filtering capacity and prevent fence failure due to sediment loading and hydrostatic pressure.

36. C
Typical erosion control seed mixtures are applied at rates of 80-120 pounds per acre, though rates vary based on species selection, climate, soil conditions, and desired coverage density.

37. C
Riprap-lined channels are structural practices involving physical construction of erosion control features. Non-structural practices include preserving vegetation, minimizing compaction, and work scheduling.

38. A
Erosion control focuses on preventing soil detachment at the source (keeping soil in place), while sediment control captures soil particles that have already been detached and are being transported by runoff.