B08_Attach_3_Best_Management_Practices_for_the_Protection_of_Water_Quality.pdf

Attachment 3: Best Management Practices for the Protection of Water Quality

To maintain compliance with federal Clean Water Act Requirements, Contractor is responsible for adhering to Best Management Practices. The following list of Best

Management Practices (BMPs) will be employed at treatment sites depending on the nature of treatments and the applicability of a given BMP for the site.

Construction and reconstruction BMPs:

1. Minimize fill volumes at stream crossings by restricting width and height of fill to amounts needed for safe travel and adequate cover for culverts. For deep fills (generally greater than 15 feet deep), incorporate additional design criteria

(e.g., rock blankets, buttressing, bioengineering techniques) to reduce the susceptibility of fill failures.

2. Place sediment-trapping materials or structures such as straw bales, jute netting, or sediment basins at the base of newly constructed fill or side slopes where sediment could be transported to waters of the State. Keep materials away from culvert inlets or outlets.

3. Construct road fills to prevent fill failure using inorganic material, compaction, buttressing, sub-surface drainage, rock facing, or other effective means.

4. Locate waste disposal areas outside wetlands, Riparian Reserve, floodplains, and unstable areas to minimize risk of sediment delivery to waters of the State.

Apply surface erosion control prior to the wet season. Prevent overloading areas, which may become unstable.

5. Design stream crossings to minimize diversion potential in the event that the crossing is blocked by debris during storm events. This protection could include hardening crossings, armoring fills, dipping grades, oversizing culverts, hardening inlets and outlets, constructing critical dips, and lowering the fill height.

6. Design stream crossings to prevent diversion of water from streams into downgrade road ditches or down road surfaces.

7. On new construction, install culverts at the natural stream grade, unless a lessor gradient is required for fish passage.

8. Place instream grade control structures above or below the crossing structure, if necessary, to prevent stream head cutting, culvert undermining and downstream sedimentation. Employ bioengineering measures to protect the stability of the streambed and banks.

9. Prevent culvert plugging and failure in areas of active debris movement with measures such as beveled culvert inlets, flared inlets, wingwalls, over-sized culverts, trash racks, or slotted risers.

10. Utilize stream diversion and isolation techniques when installing stream crossings. Evaluate the physical characteristics of the site, volume of water flowing through the project area and the risk of erosion and sedimentation when selecting the proper techniques.

11. Disconnect road runoff to the stream channel by outsloping the road approach.

If outsloping is not possible, use runoff control, erosion control and sediment containment measures. These may include using additional cross drain culverts, ditch lining, and catchment basins. Prevent or reduce ditch flow conveyance to the stream through cross drain placement above the stream crossing.

Surface Drainage BMPs:

1. Effectively drain the road surface by using crowning, insloping or outsloping, grade reversals (rolling dips), and waterbars or a combination of these methods. Avoid concentrated discharge onto fill slopes unless the fill slopes are stable and erosion-proofed.

2. Consider using broad-based drainage dips or leadoff ditches in lieu of cross drains for low volume roads. Locate these drainage features where they will not drain into wetlands, floodplains, and waters of the State.

3. Avoid use of outside road berms unless designed to protect road fills from runoff. If road berms are used, breach to accommodate drainage where fill slopes are stable.

4. Design roads crossing low-lying areas so that water does not pond on the upslope side of the road. Provide cross drains at short intervals to ensure free drainage.

5. Divert road and landing runoff water away from headwalls, slide areas, high landslide hazard locations, or steep erodible fill slopes.

Cross Drain BMPs:

1. Locate cross drains to prevent or minimize runoff and sediment conveyance to waters of the State. Implement sediment reduction techniques such as settling basins, brush filters, sediment fences, and check dams to prevent or minimize sediment conveyance. Locate cross drains to route ditch flow onto vegetated and undisturbed slopes.

2. Choose cross drain culvert diameter and type according to predicted ditch flow, debris and bedload passage expected from the ditch. Minimum diameter is 18.”

3. Locate surface water drainage features (e.g., cross drain culverts, rolling dips, and water bars) where water flow will be released on convex slopes or other stable and non-erosive areas that will absorb road drainage and prevent sediment flows from reaching wetlands, floodplains, and waters of the State.

Where possible, locate surface water drainage structures above road segments with steeper downhill grade. Locate cross drains at least 50 feet from the nearest stream crossing and allow for a sufficient non-compacted soil and vegetative filter.

4. Armor surface drainage structures (e.g., broad based dips, and leadoff ditches) to maintain functionality in areas of erosive and low-strength soils.

5. Discharge cross drain culverts at ground level on non-erodible material. Install downspout structures or energy dissipaters at cross drain outlets or drivable dips where alternatives to discharging water onto loose material, erodible soils, fills, or steep slopes are not available.

6. Cut protruding ‘shotgun’ culverts at the fill surface or existing ground. Install downspout or energy dissipaters to prevent erosion.

7. Skew cross drain culverts 45–60 degrees from the ditch line and provide pipe gradient slightly greater than ditch gradient to reduce erosion at cross drain inlet.

8. Provide for unobstructed flow at culvert inlets and within ditch lines during and upon completion of road construction prior to the wet season.

9. Install critical dips down-grade of cross drain culverts to accommodate overtopping flows. Where road grades are too adverse for critical dip construction, provide for appropriate routing of overtopping flows across road tread or into adjacent, suitably-sized drainage structure.

General Erosion Control BMPs:

1. Where sediment could be transported to waters of the State, place sediment-trapping materials or structures such as straw bales, jute netting, or sediment basins at the base of newly constructed fill or side slopes. Keep materials away from culvert inlets or outlets.

2. Suspend ground-disturbing activity if projected forecasted rain will saturate soils to the extent that there is potential for movement of sediment from the road to wetlands, floodplains, and waters of the State. Cover or temporarily stabilize exposed soils during work suspension. Upon completion of ground-disturbing activities, immediately stabilize fill material over stream crossing structures. Measures could include but not limited to erosion control blankets and mats, soil binders, soil tackifiers, or placement of slash.