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Chapter 4
Construction Practices for Environmental Stewardship
4.5. Erosion and Sedimentation Control

Erosion is a natural process that can be greatly accelerated by human activities, especially those that change or remove vegetation or that disturb the soil. All construction activities have the potential to cause soil erosion, a contributor to the excessive loss of topsoil nationwide. Environmental stewardship practices for erosion prevention reduce both the need for costly sediment controls and the risk of environmental damage.

Federal, state, and local water quality regulations prohibit the discharge of turbid water from construction activities into adjacent water bodies and require DOTs to use approved Best Management Practices (BMPs). Generally, highway construction projects and any activities involving earthwork require a Temporary Erosion and Sediment Control (TESC) Plan, Stormwater Management or Pollution Prevention Plan (SWMP) and may require a Stormwater Site Plan (SSP). A well-planned and well-maintained construction entrance with stabilized construction roads can prevent offsite sedimentation, keep sediments off of roads, minimize complaints from neighbors, and reduce future expenses and aggravation.

Temporary sediment control practices include those practices that intercept and slow or detain the flow of stormwater to allow sediment to settle and be trapped. These practices can consist of installing temporary linear sediment barriers (such as silt fences , fiber rolls, sandbag barriers, and straw bale barriers); providing fiber rolls, gravel bag berms, or check dams to break up slope length or flow; or constructing a temporary desilting basin, sediment trap, or sediment basin. Linear sediment barriers are typically placed below the toe of exposed and erodible slopes, downslope of exposed soil areas, around temporary soil stockpiles and at other appropriate locations along the site perimeter. Permanent control measures are installed in the course of construction and left in place to continue to provide water quality benefits after construction is complete. Permanent control measures generally require ongoing maintenance.

Erosion and sedimentation can occur at any time during the construction of the highway. The highest potential for erosion occurs during the grubbing, grading, and culvert/structure installation. General recommendations for preventing erosion include:

  • Consider how the site will be entered and treated.
  • Avoid steep slopes, and keep slope lengths short and gradients low to lower stormwater velocities and erosion hazards. Place terraces, benches, or ditches at regular intervals on longer slopes. Project drainage design should consider water generated both on and off of the site that can impact erosion potential.
  • Minimize amount of exposed soil. Clear the smallest practicable work zone to minimize erosion. All possible measures should be taken to minimize clearing and grading which exposes the site to erosion.
  • Minimize time of exposure (of soil).
  • Use slope roughening on the contour or tracking with a cleated dozer to minimize erosion during grading.
  • Keep water clean. Protect water quality through the use of best management practices including silt fences, sedimentation basins, and other control measures to reduce erosion, surface scouring, and discharge to water bodies.
  • Keep sediment on site, by applying perimeter control practices (BMPs) prior to construction, to protect the disturbed area from off-site runoff and to prevent sedimentation damage to areas below the construction site. This principle relates to using practices that effectively isolate the construction site from surrounding properties, and especially to controlling sediment once it is produced and preventing its transport from the site. Diversions, dikes, sediment traps, and vegetative and structural sediment control measures are classified as either temporary or permanent, depending on whether or not they will remain in use after construction is complete. Generally, sedimentation can be prevented by two methods: a) filtering runoff as it flows through an area and b) impounding the sediment-laden runoff for a period of time so that the soil particles settle out. The best way to control sediment, however, is to prevent erosion. Installation of initial controls should be discussed at the pre-construction conference. The contractor and the inspector should understand the inspection and maintenance requirements of the specified BMPs, as well as the location and proper installation procedures.
  • Preserve natural vegetative cover to the maximum extent practicable.
  • Ensure inspection and maintenance of BMPs by the contractor weekly and/or after significant rain events. Any failures should be analyzed to prevent recurrence. Substantial changes to the approved plan should be made or reviewed by the designer and approved by the appropriate regulatory agency.
  • Maintain low runoff velocities in channels by lining with vegetation, riprap, or using checkdams at regular intervals, in addition to minimizing steepness and slow length.
    • Trap sediment on-site. Many conventional BMPs available, in addition to always evolving new ones.
    • Use native grasses and plants in reseeding and planting
    • Use temporary vegetation to provide immediate ground cover until permanent landscaping is in place
  • Convey runoff from developed areas to a stable outlet using storm drains, diversion structures/techniques, stable waterways, or similar measures if stabilized areas, adequate conveyance, and/or protected inlets are available. Design conveyance systems to withstand the velocities of projected peak discharges, and make these facilities operational as soon as possible. Use diversion structures to divert surface runoff from exposed soils and grade stabilization structures to control surface water.
  • Have a contingency plan and the resources for emergencies.

 

4.5.1 Regulatory Requirements
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For stormwater, however, requirements are primarily process-based. The stormwater permittee is in compliance if it is implementing the control measures (best management practices or BMPs) contained in a stormwater management plan (for municipal-type runoff) or stormwater pollution prevention plan (for construction site runoff). An evaluation of the compliance status requires a subjective judgment regarding whether the appropriate mix of BMPs has been selected and whether they are being correctly implemented. The performance of the BMPs, whether they produce stormwater with 20 mg/l TSS or 200 mg/l, is not necessarily relevant. Because of variability in runoff pollutants and lack of information on impacts, neither EPA nor states have developed a set of universally applicable (i.e. regardless of location) technology-based effluent limits for stormwater.

In the Phase II regulation, EPA said that "[n]arrative effluent limitations requiring implementation of BMPs would generally be considered the most appropriate form of effluent limitations when designed to satisfy technology requirements, including reductions of pollutants to the maximum extent practicable, and water quality-based requirements of the CWA.

Examples of narrative effluent limitations include no floatables in stormwater discharges and no visible sheen on waterbodies.( FR 1580, II.H.3.) EPA allowed that "if after implementing the six minimum control measures there is still a water quality problem associated with discharges from the municipal separate storm sewer system, the municipality would need to expand or better tailor its BMPs within the scope of the six minimum control measures for each subsequent permit. EPA envisions that this process would take two to three permit terms," during which time, EPA envisioned revisiting the regulations for the municipal stormwater program. Additional stipulations are likely to be the result of TMDLs. EPA said that

If additional specific measures to protect water quality were imposed, they would likely be the result of an assessment based on TMDLs, or the equivalent of TMDLs, where the proper allocations would be made to all contributing sources. EPA believes that the municipality's additional requirements, if any, should be guided by its equitable share based on a variety of considerations, such as cost effectiveness, proportionate contribution of pollutants, and ability to reasonably assume wasteload reductions. Narrative effluent limitations requiring implementation of BMPs are generally the most appropriate form of effluent limitations when designed to satisfy technology requirements, including reductions of pollutants to the maximum extent practicable, and water quality-based requirements of the Clean Water Act. See Section II.L, Water Quality Issues, for further discussion of this approach to permitting, consistent with EPA's interim permitting guidance."(FR p. 1573, II.H.3.)

Traditionally, DOTs and municipalities have maintained that numeric water quality-based limits are not feasible for stormwater. Due to the unique nature of storm events and stormwater discharges, any numeric limit that is placed in a stormwater permit must take into consideration the episodic nature of storm events and be truly representative of stormwater discharges. In addition, DOTs have noted that they have little or no means to control polluted stormwater that "runs on" to the DOT site or conveyance. In general EPA has maintained that numeric effluent limits are impractical and/or inappropriate for stormwater regulation, but the issue continues to be discussed and reviewed by states and the courts.

Thus far, EPA has avoided specifying technology-based limits for stormwater BMPs. Currently, stormwater permits issued for DOT/MS4-type discharges generally require that stormwater management plans be designed to achieve compliance with water quality standards. The permits also require compliance with standards through an "iterative process" in which exceedances of standards are supposed to trigger implementation of improved best management practices (BMPs). In practice, cost-effective BMPs are lacking for many pollutants and stormwater runoff often exceeds standards at the point of discharge. A few regions and states and the District of Columbia have considered the feasibility of establishing numeric effluent limits or other quantifiable limits for use in stormwater permits.

Preventing the Imposition of Numeric Effluent Limits

Given that numeric effluent limits are not desirable for stormwater, but considering the ongoing pressure from public interest groups to impose limits in order to reach water quality standards, a number of practices can be employed to address the underlying needs and interests in BMP effectiveness: [N]

  • Rigorous design of individual BMPs and treatment trains. Effluent concentration distribution estimates for a number of BMPs are available in the International BMP Database (www.bmpdatabase.org) from more then 250 studies throughout the U.S. BMPs or treatment trains of BMPs that are rigorously designed and constructed with respect to the physical, chemical and/or biological processes that take place within them would provide greater confidence that treatment design targets are reached, if the BMPs are properly maintained. In selecting and designing BMPs:
    • Identify Whether Receiving Water Body is 303(d) listed and if TMDLs have been set
    • Identify Constituents of Concern
    • BMP selection based on removal efficiency
    • Require Technology-Based BMPs
    • Require BMP(s) by BAT for Constituents of Concern
    • Monitor BMP Maintenance for Compliance
  • Require a detailed maintenance plan and schedule that includes:
    1. Actions to be taken and when,
    2. Designation of the party legally accountable for the facility maintenance, and
    3. A whole-life cost estimate for the facility that include maintenance.
      Compliance with the design criteria and the maintenance plan and schedule may be considered to; constitute achievement of the design effluent criteria. In the event of failure by the responsible party to perform the required maintenance and/or to perform it to the required level of quality, the whole-life cost schedule could be used to determine the consideration that the defaulting responsible party would pay to the new responsible party that takes over the maintenance.
  • Employ practical and quantifiable enforcement mechanisms, such a checklist of items to be inspected.
  • Address and minimize impervious surface in a drainage area, as the latter "have been shown to be quite effective in reducing adverse hydromodifications in the receiving waters."
  • Set "upset" values or Action Levels above the normal observed variability, to allow "bad actor" catchments to receive additional attention. While not directly address the issue of establishing numeric effluent criteria and achieving desired effluent quality, this would help address one of the desired ends of ensuring that "bad actor" watersheds received needed attention.

Strategies for Addressing Runoff Volume and Peak Flows

Runoff volume and peak flows have been recognized as two of the most important stormwater factors needing control. Urbanization dramatically changes the hydrologic regime of urban waterways; the number of runoff events per year on developed land increases by a factor of 2 times the number of runoff events that occur in the undeveloped state, and the runoff volume increases by a factor of ten. The peak flows also increase dramatically, but the peak flow frequency curve can be adjusted back to its predevelopment character by the proper application of runoff controls. While these controls restore the peak flow frequency to its natural regime, the duration of flows at the low end (but still channel "working") of the flow frequency curve is greatly increased, which raises potential for channel scour in stream channels with erosive soils.

Since many of the stormwater pollutants are strongly associated with particulates, stormwater particulate control is also often a component of stormwater control programs. Therefore, an effective stormwater control strategy that could be encouraged is a combination of several practices, listed below in the order of increasing events: [N]

  • On-site stormwater reuse, evapotranspiration and infiltration for the smallest storms and up to specific targeted events, depending on site limitations (soil characteristics and groundwater contamination potential) usually by conservation design emphasizing infiltration, disconnecting paved areas, etc.
  • Treatment of excess runoff that cannot be infiltrated, again, up to a specific targeted runoff volume (usually by sedimentation or filtration).
  • For pollutants of concern, it should be demonstrated that the BMP(s) need to include the physical, biological, and/or chemical treatment processes that address the typical pollutants of concern and/or specific pollutants in the case of 303(d) listed water bodies or those with established TMDLs.
  • Control of energy discharges for the channel forming events (such as through storage-release, focusing on flow-duration analyses and peak flow frequency analyses). To be most effective, this should to be completed under a watershed management plan and not site-by-site.
  • Provide safe drainage for damaging events (conventional drainage, plus secondary drainage systems)
  • In watersheds that are already experiencing damaging flow impacts to streams, it could be in many circumstances much more cost-effective (and effective period) to develop through a watershed plan a natural stream stabilization approach that could address both the existing development and the remaining smaller infill or otherwise smaller new development. In these cases, requiring the remaining new development to implement flow-duration control would not solve the issue in a measurable way and resources would be better spent restoring the functions of the creek with instream enhancements.

Programmatic Approaches to Standards Attainment

MS4/DOT discharges are required to control pollutants to the maximum extent practicable (MEP). In addition, stormwater runoff is required to not cause an exceedance of water quality standards. BMPs can offer a programmatic approach to standards attainment.

Ohio DOT and Ohio EPA

For example, the Ohio DOT and Ohio EPA met to review and improve existing processes a number of times, culminating in OEPA satisfaction with stream protection measures implemented through ODOT's culvert design process and a decision that water quantity treatment requirements are satisfied when ODOT culvert design procedure is followed. OEPA agreed that vegetation treats water quality very effectively. Adjustments were made to determine ditch widths to satisfy OEPA concerns about water quality.

Oregon CETAS

Oregon's State Bridge Delivery Program includes more than 300 bridges to be repaired or replaced by 2011. As a result, ODOT decided to address regulatory requirements, as much as feasible, on a programmatic basis. That is, ODOT began working with its regulatory agency partners and consultants to address permitting needs for the bridge program as a whole. The goals were:

  • To reduce bridge design and environmental permitting times
  • To reduce cost and schedule impacts from re-design
  • To maintain ODOT's strong commitment to environmental stewardship


The key elements in this programmatic approach include programmatic permits and approvals, environmental performance standards, and a comprehensive program for mitigating environmental impacts. As a first step, ODOT took a programmatic approach to bridge assessment and permitting. Environmental assessments were done up front, for every bridge in the bridge program, using common data collection methods and a common reporting format. Permitting requirements were established for the entire bridge program. If the design and construction proposed for a particular bridge meets the programmatic requirements, the permits or approvals addressed by those requirements are assured. The approach coordinated the requirements of multiple agencies and put standards in place to ensure comprehensive environmental protection. While each bridge must still be reviewed individually, the programmatic permits are already in place and the requirements to obtain those permits have already been defined. As a result, permitting for individual bridges are cheaper and faster, and design efforts more efficient, than with the traditional approach.

The core of ODOT's programmatic approach is a set of environmental performance standards that define the requirements that project activities must meet. They are goal-oriented; i.e., they define the acceptable level of effect that a project activity may have on the environment, rather than specifying exactly how the activity must be performed. For example, the Habitat Avoidance performance standard limits stream bank protection activities to those not expected to have long-term adverse effects on aquatic habitats, and lists several protection techniques. Bridge design and construction personnel have the flexibility to choose the most cost-effective method to preserve habitat at a particular site.

Collectively, performance standards address all phases of the program: administration, bridge design, bridge construction, and post-construction mitigation. If a project meets all applicable performance standards, it will be in compliance with the programmatic requirements and will receive the required permits. Although some permits and approvals (e.g., noise variances, land use exceptions) must be addressed site by site, most can be addressed programmatically, resulting in significant time and cost savings and a smoother permitting process. Because performance standards describe desired outcomes, not specific construction techniques, they enable design teams to focus on creative solutions that accommodate the unique conditions at each bridge site.

Streamlined permitting efforts for the Oregon's Statewide Bridge Replacement Program have included a wide range of programmatic approaches to achieve environmental compliance.The use of Environmental Baseline Reports (EBRs) is being instituted for Statewide Transportation Improvement Program (STIP) projects. The EBR is an comprehensive environmental scoping mechanism intended to identify resources and constraints prior to the design process. Up through June 2006, progress toward instituting use of the EBR process has included: [N]

  • An ODOT policy paper was prepared to outline recommendations on how and where to best use baseline reports in ODOT project development.
  • Revisions have been made to ODOT Project Delivery Leadership Team (PDLT) Notice - 02 specifically requiring use of the EBR process, as appropriate, during early project development. The revised Notice also addresses staff roles and responsibilities for EBRs. The revision will become official once approved by the ODOT Project Development Leadership Team, which is expected to be imminent.
  • Criteria for determining EBR applicability have been drafted and are going through internal ODOT review.
  • Specific guidance (content, format, methods, etc.) for the EBR process is being developed for STIP project development. This guidance is based on experience from the OTIA III Bridge Program EBR process, and is being modified to the context of STIP project development.
  • Full implementation of the EBR process at the front end of STIP project development will require establishment of a new, earlier funding mechanism.

Construction Stormwater Pollution Prevention Plan - Considerations & Components

At a minimum any SW3P developed for a construction activity should include the following information:

  • A description of the nature of the construction activity and the intended sequence of major soil disturbing activities.
  • A site map indicating:
    • Drainage patterns
    • Areas not to be disturbed
    • Locations of major controls measures
    • Locations of areas that will be stabilized
    • Surface waters (including wetlands)
    • Locations where storm water is discharged to a surface water
    • Limits of construction and disturbed areas
    • Erosion control BMPs
    • Sediment control BMPs
    • Other controls, such as for waste disposal, hazardous and sanitary wastes and offsite vehicle tracking of sediments
  • A description of the procedures to ensure the timely maintenance and inspection of erosion and sediment control measures and other protective measures identified in the SW3P

The major considerations in the development of an effective and economical SW3P are:

  • Project sequencing and phasing
  • Grade management
  • Drainage features
  • Limiting disturbed areas
  • Stabilization practices
  • Storm water management
  • Basic principles of the erosion and sedimentation process

 

4.5.2 Manuals for Stormwater and Erosion & Sedimentation Control
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Almost 30 percent of state DOTs have developed manuals for construction (AR, CA, FL, GA, IH, IA, IN, LA, MI, MO, MT, NM, OH, WA). [N] Almost every state DOT has a guide to development of such plans and design of stormwater BMPs, though such BMPs are often combined and categorized in very different ways. The practices presented in this section are a compendium of highlights from these manuals, focusing on environmental stewardship practice and how to get to available resources on selection and implementation for best environmental effect. Following is list of highway runoff and construction BMP manuals available on-line:

California

California Stormwater Quality Association Stormwater BMP Handbooks
Los Angeles Stormwater Program (click "Publications")
California Department of Transportation (Caltrans) Stormwater Quality Handbooks
Stormwater Quality Handbook - Project Planning and Design Guide
Caltrans Construction Manual includes details for a wide array of construction drawings and standard water quality best management practices.

Georgia

Georgia Stormwater Management Manual

Idaho

Idaho Department of Transportation (IDT) Design Manual (July 2001)

Illinois

Illinois Department of Transportation. Erosion and Sediment Control NPDES for Standard Specifications for Road & Bridge Construction.

Maine

Erosion & Sedimentation BMP Manual

Maryland

Maryland Stormwater Design Manual, Volumes I & II

Massachusetts

Massachusetts Department of Environmental Protection Stormwater Handbooks

Michigan

DEQ Index of BMPs/Individual BMPs
Michigan DOT Drainage Manual

Minnesota

Protecting Water Quality in Urban Areas: A Manual
Urban Small Sites Best Management Practice Manual

Missouri

Protecting Water Quality: A Construction Site Water Quality Field Guide

Montana

Montana Department of Water Quality - Stormwater Program - BMPs and Erosion Control Plans

New Hampshire

Innovative Stormwater Treatment Technologies Best Management Practices Manual

New Jersey

New Jersey Stormwater Best Management Practices Manual

New York

New York State Stormwater Management Design Manual
NYSDOT Highway Design Manual

North Carolina

North Carolina Department of Environment and Natural Resources

Ohio

Ohio EPA Stormwater Program Index

Oregon

Department of Environmental Quality Guides
Oregon Department of Transportation. Field Manual for Erosion and Sediment Control (2000). The reference for the field guide is the ODOT Hydraulic Manual Volume 2 entitled Erosion and Sediment Control, which provides a source of more in-depth information.

Pennsylvania

Pennsylvania Handbook of Best Management Practices

South Carolina

NPDES Stormwater Program Guide
Sediment, Erosion and Stormwater Management Program Index to Guides

Tennessee

Tennessee Department of Environment and Conservation Water Pollution Index to Guides
City of Knoxville, Best Management Practices Manual

Texas

Texas Nonpoint Sourcebook
TxDOT " Stormwater Management Guidelines for Construction Activities Manual ." Texas Department of Transportation (2002)

Utah

Utah Department of Environmental Quality Stormwater Program Index to Guides
West Valley City Stormwater Utility Best Management Practices
Utah DOT Roadway Drainage Manual of Instruction

Virginia

Northern Virginia Regional Commission Best Management Practices
Virginia Department of Conservation & Recreation BMP Guides
Virginia DOT Drainage Manual

Washington

WSDOT 2006 Standard Specifications for Erosion Control (Section 8-01)
WSDOT Standard Plans Section I - Erosion Control
WSDOT Temporary Erosion Sedimentation Control (TESC) Plan Template
WSDOT When is a TESC plan needed?
WSDOT 2004 Highway Runoff Manual
WSDOT Hydraulics Manual

Wisconsin

Wisconsin Construction Site Erosion Control and Stormwater Management Procedures

Wyoming

Urban Best Management Practices for Nonpoint Source Pollution

The Stormwater Manager's Resource Center also maintains List of Acceptable Practices, Construction Specifications, and Checklists for Construction Inspection.

The Transportation Association of Canada, Erosion and Sedimentation Control Committee will be issuing a "National Guide to Erosion and Sediment Control on Roadway Projects" in April 2005. The guide contains a synthesis of Canadian and international practice and numerous Best Management Practices (BMPs) for project planning, site management, erosion control and sediment control. This national guide will discuss erosion and sediment control methods for road system planning, construction and maintenance in both urban and rural settings, and is intended to assist roadway authorities, consultants, contractors and regulators. Canadian transportation agencies will use it for the planning and design, implementation and review of Erosion and Sediment Control plans and in meeting environmental objectives in an appropriate, economic and effective fashion. It will also guide users in assessing ESC plans in terms of defining risk and level of effort, selecting appropriate methodologies for analysis and design, selecting appropriate ESC measures, evaluating Best Management Practices for application, and meeting legislative and regulatory requirements. The Guide is divided into two parts: Theory and Application. Sections included under Theory are: physical processes, legislation, and risk assessment. Sections included under Application are: plan development, site assessment, BMP selection and design, and implementation. The document will be presented in a format that is user-friendly and easily updated.

In addition to extensive design guidance available in both manual and on-line formats, a number of BMP evaluation systems are emerging. MDSHA has developed an evaluation system for all stormwater facilities and criteria for improvements. In the late 1990s WSDOT and FDOT also developed systems for categorizing outfalls and, in the case of WSDOT, assessing which projects provide the best return on investment in terms of environmental effectiveness and pollution reduction. WSDOT's system included a condition indexing methodology and support program that enables users to quickly evaluate and compare projects and generate benefit-cost ratios for projects. [N]

 

4.5.3 Procedural Management Practices for Water Quality
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Procedural BMPs affect how and when a project is built and can greatly affect the potential for erosion. Sequencing and scheduling are some of the most important aspects of erosion control planning. Construction sequencing should minimize the duration and extent of soil disturbance. Whenever possible, major soil disturbing activities should be done in phases to minimize exposed areas. Likewise, major grading operations should be limited to the dry season. An effective schedule prevents the site from becoming overexposed to erosion risks. The construction schedule should tie the installation of erosion control BMPs to the order of land disturbing activities. The types of activities that should be included in the schedule are:

  • Installation of perimeter control and detention BMPs prior to soil-disturbing activities.
  • Phasing and timing of clearing, grubbing, and grading.
  • Interim BMP strategies.
  • Installation of permanent BMPs and a description of how temporary BMPs have been coordinated with the development of permanent measures.
  • Erosion control inspection and maintenance schedule.

Some DOTs are reducing violations and the amount of sediment that moves off of construction sites into adjacent streams by employing additional erosion control staff and inspectors. MDSHA has made an agency-wide commitment to achieve 100 percent compliance with erosion and sedimentation control measures on all construction sites. The Missouri DOT (MoDOT) hired a retiree with erosion control expertise in a 1,000-hour position. This person inspects construction sites for placement and maintenance of adequate erosion control measures and makes recommendations for improvements. Photographs of the inspected projects are posted on the MoDOT intranet site to illustrate how erosion control measures should and should not be installed and how they work during a rain event. The number of Notices of Violations for erosion control have been reduced significantly since this program was put in place in 2003. [N]

 

4.5.4 Dewatering and Managing the Watercourse
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Watercourses are defined as the bed and shore of every river, stream, lake, creek, pond, spring, lagoon or other natural body of water, and the water therein, within the jurisdiction of the state (i.e. federal or state protection). Typically such measures must be applied whether the watercourse contains water or not. In-stream work is often allowed to occur only in specified periods, where there are species of concern. Protection measures for fish passage are included in Chapter 3, Design section 3.5.

Dewatering

Dewatering methods are temporary measures for filtering sediment-laden water, managing the discharge of pollutants or to keep water away from a worksite. Dewatering operations are used to manage removal of water from excavations, cofferdams, diversions, barges, and areas of ponding (accumulated precipitation). Sediment is the most common pollutant associated with dewatering operations. Whether the contractor manages dewatering operations by re-using the water on site, discharging it to an adjacent facility or land, or discharging it by NPDES permit to a storm drain or receiving water, the water will often require treatment to remove sediment. Dewatering usually involves pumping water from the location of accumulation to the treatment area on the construction site. Following treatment, the water is discharged or reused on site, in accordance with the authorizing permit.

Suggested stewardship practices for dewatering are summarized in the remainder of this section. [N]

If the water is free of pollutants other than sediment, consider the following management options prior to deciding to discharge to a storm drain or water of the U.S. :

  • Reuse the water on site for dust control, compaction during earthwork activities, or irrigation.
  • Retain the water on site in a grassy or porous area and allow water to infiltrate/evaporate.
  • Discharge to a neighboring property (by agreement) that may have irrigation needs or sufficient land for infiltration.
  • Discharge (by permit) to a sanitary sewer.

If the water contains pollutants other than sediment, contact the Stormwater Coordinator or environmental support staff for guidance. Water from areas of known or suspected soil contamination, or that has unusual visual features or odor, may contain pollutants other than sediment. If other pollutants are suspected, water quality testing may be required. Depending on the quality of the water, possible management options include:

  • Discharge to a sanitary sewer (by permit with or without treatment).
  • Transportation off site for disposal at a commercial recycling or disposal facility.

Sediment treatment requirements depend on the final disposition of the water. For dewatering discharges to a storm drain or water body authorized under a permit, in general, if water is not visibly clear, it should be treated using best management practices prior to discharge. A variety of treatment practices are available for use individually or in combination. Some common primary treatment methods include:

  • Desilting basins and sediment traps are traditional sediment removal methods. The site must accommodate a basin of adequate size to provide the time necessary for particles to settle out.
  • Weir tanks are steel tanks with interior weirs (or baffles) that allow sediment to settle prior to discharge from the tank. The tanks remove debris, some oils, and particles 0.05 mm in size and larger.

Dewatering tanks are open rectangular steel tanks. The water drains through a filter fabric to a discharge header to remove particles as small as 0.025 mm, depending on the filter material used.

When water is pumped into a gravity bag filter the sediment forms a soil blanket/filter that removes additional sediment as the water passes through the sides and bottom of the bag. A secondary filter of rock or straw bales is often constructed beneath the bag. Due to the need to form the soil blanket, it is difficult to guarantee particle size removal.

  • The following treatment methods remove finer-grained materials and may be useful as secondary treatment methods when needed to meet water quality goals.

A sand media filter is a portable unit that removes particles larger than 0.01 mm. Water flows through the unit and sediment is captured by the sand particles. This method is cost-effective due to a filter backwashing feature.

A pressurized bag filter is a unit composed of individual filter bags that are most effective when larger particles have been removed by prior treatment with a weir tank, sand filter, etc. It can remove particle sizes as small as 0.002 mm.

A cartridge filter provides the highest degree of sediment removal. It is capable of removing sediments larger than 0.002 mm, but is most effective when used for polishing after larger particles have been removed by other treatment methods.

  • In addition to sediment, these methods can also reduce some other potential water quality pollutants such as oil and grease and nutrients. However, none remove the colloidal particles natural to some soils that increase water turbidity. Pre-discharge testing for possible pollutants may be required, based on the source of the water, land use history of the construction site, and potential impacts to the quality of the receiving water.

For discharge to a sanitary sewer or to an adjacent facility/land, sediment treatment requirements are specified in the permit or agreement with the sanitary sewer agency or landowner.

For infiltration or reusing water on-site, water may require treatment to meet the specific reuse option.

On-line sources for dewatering practices and associated BMPs:

Measures to Minimize Impacts to Aquatic Habitat and Species during Dewatering of Project Site

When construction work must occur within a year-round flowing channel, the work site must be dewatered. Dewatering can result in the temporary loss of aquatic habitat, and the stranding, displacement, or crushing of fish and amphibian species. Increased turbidity may occur from disturbance of the channel bed. Following these general guidelines will minimize impacts.

Prior to dewatering, determine the best means to bypass flow through the work area to minimize disturbance to the channel and avoid direct mortality of fish and other aquatic vertebrates.

Minimize the length of the dewatered stream channel and duration of dewatering.

Maintain stream flow to channel below construction site.

Capture and relocate fish and amphibian species prior to dewatering to avoid direct mortality and minimize take. This is especially important if listed species are present within the project site.

Coordinate project site dewatering with a fisheries biologist qualified to perform fish and amphibian relocation activities.

Periodically measure air and water temperatures. Cease activities when water temperatures exceed temperatures allowed by resource agencies.

Exclude fish from re-entering work area by blocking the stream channel above and below the work area with fine-meshed net or screens. Mesh should be no greater than 1/8 inch. It is vital to completely secure bottom edge of net or screen to channel bed to prevent fish from re-entering work area. Exclusion screening should be placed in areas of low water velocity to minimize impingement of fish. Screens should be checked periodically and cleaned of debris to permit free flow of water.

Prior to capturing fish, determine the most appropriate release location(s). Consider the following when selecting release site(s): similar water temperature as capture location, ample habitat for captured fish, and low likelihood of fish re-entering work site or becoming impinged on exclusion net or screen.

Determine the most efficient means for capturing fish. Complex stream habitat generally requires the use of electrofishing equipment, whereas in outlet pools, fish may be concentrated by pumping-down pool and then seining or dipnetting fish. If fish are abundant, periodically cease capture, and release fish at predetermined locations.

Minimize handling of aquatic species; however, when handling is necessary, always wet hands or nets prior to touching fish.

Temporarily hold fish in cool, shaded, aerated water in a container with a lid. Provide aeration with a battery-powered external bubbler. Protect fish from jostling and noise and do not remove fish from this container until time of release. Place a thermometer in holding containers and, if necessary, periodically conduct partial water changes to maintain a stable water temperature. If water temperature reaches or exceeds those allowed by resource agencies fish should be released and rescue operations ceased. Avoid overcrowding in containers. Have at least two containers and segregate young-of-year (YOY) fish from larger age-classes to avoid predation. Place larger amphibians, in container with larger fish.

Visually identify species and estimate year-classes of fish at time of release. Count and record the number of fish captured. Avoid anesthetizing or measuring fish. If mortality during relocation exceeds 5 percent, stop efforts and immediately contact the appropriate agencies.

Submit reports of fish relocation activities to resource agencies in a timely fashion.

If feasible, plan on performing initial fish relocation efforts several days prior to the start of construction. This provides the fisheries biologist an opportunity to return to the work area and perform additional electrofishing passes immediately prior to construction. In many instances, additional fish will be captured that eluded the previous day's efforts.

Periodically pump seepage from the work area. Place pumps in flat areas, well away from the stream channel. Secure pumps by tying off to a tree or stake in place to prevent movement by vibration. Refuel in area well away from stream channel and place fuel absorbent mats under pump while refueling. Pump intakes should be covered with 1/8" mesh to prevent entrainment of fish or amphibians that failed to be removed. Check intake periodically for impingement of fish or amphibians.

Discharge wastewater from construction area to an upland location where it will not drain sediment-laden water back to stream channel.

Flow Diversion

The normal flow of a stream should be diverted and the work area isolated to allow a project to proceed. The watercourse should be managed to minimize adverse impacts to the jurisdictional waters. All projects should be planned to minimize the time that the watercourse will be diverted. Several methods of diverting a watercourse are provided in this section. There may be certain seasonal components to consider when attempting flow diversion of a stream, such as spawning times of individual fish species. [N]

Avoid having equipment in streams, wetland, or other environmentally sensitive area. When necessary in-stream, limit the type and number of equipment to those necessary to accomplish the work at that moment.

Design temporary diversion channels to accommodate expected watercourse flow from storm events (generally 1 in 5 year event, though the 1 in 2 year event may be used for noncritical situations). Leave the existing channels untouched until the temporary diversions are constructed.

Construct temporary diversion channels in the dry, starting from the downstream end.

Open diversion channels from the downstream end first.

Use clean, washed material to close existing channels and divert water to temporary diversion channels.

Use gradient controls to ensure that diversion channel slopes correspond to the existing channel gradients.

Protect unstable bends from erosion.

Armor discharge point with clean rock to prevent erosion.

In areas with fish passage concerns, avoid using pumped diversions, where a channel must be completely blocked to allow work ‘in the dry.'

Size and screen intakes to prevent debris blockage and fish mortality.

Environmental stewardship practices for flow diversion BMPs are contained within the following state fact sheets available on-line:

Cofferdams

Use cofferdams (earth fill, sheet pile or other proprietary designs) to separate instream work site from flowing water. Design cofferdams to accommodate the expected flows of the watercourse. Build rock platforms for equipment needed in-stream for longer periods.

Use clean, washed material for construction and face berms with clean granular material.

Limit cofferdams to one side of the watercourse at any one time and ensure that they block no more than one-third of the channel

Restore the original channel bottom grade after removing cofferdams

Treat all water pumped from behind the cofferdams to remove sediment before discharge.

Turbidity Curtains

In some instances, the depth of water downstream from a proposed work area may be too deep for an in-stream, silt fence-sediment trap to be effective, such as the outlet of a ponded area. At these times, turbidity curtains prove to work effectively in retaining suspended sediment. The barrier consists of a wire-mesh supported silt fence attached to a floating boom. The boom remains afloat, on top of the water, while the filtration mechanism, anchored to the streambed, retains suspended sediments in the work area.

Even though work is being conducted during months that typically promote low water conditions, seasonal increases in water flow can result from precipitation events. This BMP is used as a precautionary measure should a rise in water and/or flows occur. If water in the work areas were to increase, an in-stream sediment-trapping device would prevent increases in turbidity and sedimentation. This BMP can, and at times should be, used in conjunction with other BMPs depending upon proposed work. Sandbags and/or check dams can be used as a first line of defense with turbidity curtain downstream as a second defense. [N] Online implemented guidance and best practice resources for turbidity barriers may be found at:

Other Slope Stabilization and Drainage Techniques

NCHRP project 24-19 lists the following areas in slope stabilization to be discussed in the upcoming publication due in late 2004:

  • Diversion Dikes
  • Slope Drains
  • Live Pole Drains
  • Chimney Drains
  • Trench Drains
  • Drop Inlets
  • Fascines with Subsurface Drains
  • Flattening
  • Stone-Fill Trenches

Managing Excavated Material or Spoil

Excavated material or spoil should either be: [N]

  • Contained within the work area.
  • Stockpiled near the work area and contained by an appropriate Erosion and Sedimentation Control BMP.
  • Removed from the site and disposed of properly.
  • Spoil material shall not be placed in wetlands, protected riparian buffers, or other jurisdictional areas.
  • Used for reestablishing groundcover.

 

4.5.5 Interception
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Reducing Slope Length for Erosion Control

Slope length and inclination are two factors that directly affect the tendency of a slope to erode and introduce sediment into stormwater runoff. Although contractors cannot deviate from embankment and slope inclinations specified in construction plans, there are stormwater friendly methods available for shortening the effective length of a slope.

Best Management Practices (BMPs) for mitigating slope length make use of fiber rolls or gravel bag berms to build erosion control benches at specified intervals down the slope face. This strategy is effective at low surface velocity flows (< one cubic foot/second) for intercepting and filtering sediment from runoff. The decrease in velocity also reduces the concentration of sheet flows that create rills and gullies on slope faces. These measures should be used in combination with others to remove sediment and minimize sedimentation.

Fiber Rolls

A fiber roll consists of straw, flax, or other similar materials wood excelsior, rice or wheat straw, or coconut fibers that are is rolled and or bound into a tight tubular roll and placed on the toe and face of slopes at regular intervals to intercept runoff, reduce its flow velocity, release the runoff as sheet flow, and provide some removal of sediment from the runoff. Fiber rolls are biodegradable materials and prefabricated fiber rolls constructed of rice straw, wheat straw, flax or similar material can be purchased in diameters ranging from 200 mm to 300 mm. Fiber rolls can also be made in the field using erosion control blanket material rolled and bound with jute twine every 1.2 m along the length and at each end. Fiber roles are best suited for longer term protection of non-active disturbed soil areas and completed areas to help stabilize the slope while vegetation establishes. Fiber rolls may also be used for inlet protection and as check dams under certain situations.

For slope lengths of 30 m or more with inclinations between 1:20 and 1:2, install fiber rolls or an equivalent at intervals no greater than 15 m.

For slope lengths of 15 m or more with inclinations of 1:2 or steeper, install fiber rolls or an equivalent at intervals no greater than 7.5 m.

Best practices with regard to fiber roll installation and use are available online: [N] [N]

Gravel Bags

An alternative to fiber rolls are berms constructed of gravel bags. Bags made from synthetic woven material or burlap are filled with ½ to 1-inch clean aggregate. The gravel bags are aligned end-to-end, tightly abutted, along a level contour to form a berm that creates the erosion control bench. A gravel bag berm consists of a single row of gravel bags that are installed end to end to form a barrier across a slope to intercept runoff, reduce its flow velocity, release the runoff as sheet flow and provide some sediment removal. Gravel bags can be used where flows are moderately concentrated, such as ditches, swales, and storm drain inlets. [N] Installation guidance and stewardship practices for use of gravel bags and gravel bag berms are available online:

Triangular Filter Dike

Triangular sediment filter dikes can be used to intercept and detain water-borne sediment from unprotected areas of limited extent, where there is no concentration of water in a channel or other drainage way above the barrier and the contributing drainage area is less than one acre. If the uphill slope above the dike exceeds 10%, the length of the slope above the dike should be less than 50 feet. If concentrated flow occurs after installation, corrective action should be taken such as placing rock berm in the areas of concentrated flow. This measure is effective on paved areas where installation of silt fence is not possible or where vehicle access must be maintained. The advantage of these controls is the ease with which they can be moved to allow vehicle traffic and then reinstalled to maintain sediment. [N]

Strawbale Barriers

Bale barriers may be the most common mitigation measures illustrated in Stormwater Pollution Prevention Plans (SWPPPs) and found on construction sites. [N] Hay or straw bale dikes, also known as straw bale barriers are used to intercept and detain small amounts of sediment-laden runoff from relatively small, unprotected areas. They bales are often used when it is not feasible to install other, more effective measures or when the construction phase is expected to last less than three months. They work well in conjunction with silt fence.

Although hay bales have been the traditional choice for erosion protection, especially in drainage channels, careful consideration should be taken during the selection process. Runoff waters may not readily seep through the bales. Bales are not an effective method for filtering sediment. Water can pond behind the bale structures and flow around, between, and under the structures causing channel degradation and sediment transportation. Furthermore, bales are often not inspected or maintained and are one of the more costly methods for controlling sediment in runoff waters. [N] When roadway median drains are on a grade and bale barriers placed around the inlets, the barriers divert runoff waters to downstream locations and diversion around inlets cause downstream flooding and downstream deposition of sediment and bale structures to experience massive failure. [N]

Only use hay bales as temporary check structures when the following conditions can be maintained:

  • Channel receives low volume flows.
  • Flow line slopes are less than 2%.
  • Installed in a trench, staked, and backfilled.
  • Enough bales are used on the channel side slopes to force runoff over the bales, rather than around the structure.
  • Bales are inspected and maintained frequently.

Consider other techniques. Properly sized rock check structures provide an excellent alternative as do some of the new methods (e.g. synthetic barriers) being introduced every year. Silt fence material must not be used unless it is properly supported. If vegetation is to be established, avoid bale check structures. Instead, properly install rolled erosion control products.

Instead of placing bales around an inlet, install a properly designed upstream sediment containment system. Since medians are long and narrow, they provide ideal conditions for efficient sediment traps. When properly installed and maintained, sediment traps will reduce sediment in runoff waters and allow inlets to function in a manner for which they are designed - as drainage systems.

If sufficient space does not exist for a containment system, then install a riprap check structure to serve as a sediment trap. Take care to ensure the rock used has sufficient diameter and mass to avoid failure from large flow events.

Avoid use of straw bales on areas where rock or other hard surfaces prevent the full and uniform anchoring of the barrier. [N]

Almost all state DOTs have installation guidance for strawbale barriers; the following DOTs have made such guidance and practice recommendations available online:

Geotextiles, Mats/Plastic Covers and Erosion Control Blankets

Erosion Control Blankets are biodegradable materials that can be used to protect disturbed slope and channel areas from wind and water erosion. The blanket materials are natural materials such as straw, wood excelsior, coconut, or are geotextile synthetic woven materials such as polypropylene. In addition to preventing erosion, erosion control blankets also increase water infiltration into the soil, protect seed mixes from being eroded during heavy rainfall or wind, and increase the retention of soil moisture to promote seed germination.

Testing at the San Diego State University Soil Erosion Research Laboratory (SDSU/SERL) as part of a Caltrans District 7 Erosion Control Pilot Study (ECPS) and the Soil Stabilization for Temporary Slopes study (SSTS) found that all of the blankets or RECPs tested reduced erosion and off-site sediment delivery by 90-100 percent. [N] These results are comparable to tests conducted at the Texas Transportation Institute (TTI) and other laboratories. Before specifying an erosion control blanket for a highway site, consider effectiveness, implementation costs, durability, longevity, whether the netting may pose any wildlife hazards, and long-term costs or maintenance considerations, e.g. will nets or staples be a factor if the area will be routinely mowed?

Function is dependent on proper installation and maintenance, including p roper soil surface preparation:

  • All rocks, clods, debris, and vegetation should be removed to ensure full contact between the blanket and the soil surface.
  • Check the special provisions or follow the manufacturer's recommendations for seed application requirements when used with blanket installation.
  • The blanket should be anchored to the soil using metal wire staples as specified in the special provisions or recommended by the manufacturer.
  • The staples should be driven through the blanket and into the soil, flush with the soil surface.

Inspection and maintenance of Erosion Control Blankets should include the following:

  • Inspect the site during installation.
  • Inspect the installation before, during and after significant rain events.
  • Repair or replace all damaged materials.
  • Recompact all soil washout areas.

Inlet Protection Information:

 

4.5.6 Infiltration - Sediment Basins and Traps
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Conventional sediment control BMPs are capable of removing a certain size soil particle, but in most cases it is not enough to bring the runoff in compliance with state water quality standards. Detention time and volume is critical in sediment control. Sand and gravel takes only seconds to trap, but silt and clay can take hours to weeks to settle.

Research has indicated that infiltration can be a viable alternative in the disposal of runoff at low metals concentrations, with appropriate siting criteria, which should include the following: [N]

  • Identify the presence of background metals in the soil.
  • Identify the organic content of the soil, which is likely to a better indicator of potential metal retention, and as such, should be included as a siting condition along with the cation exchange capacity (CAC) and silt and clay content.
  • Consider extending the minimum depth to groundwater from the existing value of three feet to ten feet (three meters) or more, particularly in those areas in which background metals are present. Here, geochemical controls are thought to produce effluents beneath the infiltration basins which may lead to detectable quantities (particularly copper and zinc) within underlying groundwater, wherein creating a situation that may violate the anti-degradation laws for groundwater resources.

Sediment Basins

A sediment basin is a basin or barrier constructed within a waterway or at another suitable location to intercept sediment-laden stormwater runoff and to trap and retain the sediment. The purpose of the sediment trap is to intercept sediment-laden stormwater runoff and reduce the amount of sediment leaving the disturbed area. A sediment basin applies where physical site conditions or land ownership restrictions preclude the installation of barrier-type erosion control measures to adequately control runoff, erosion and sedimentation. [N] Stormwater runoff from drainage areas with more than 5 acres disturbed area should pass through a sediment basin or other suitable sediment trapping facility. Sediment basins are more cost effective when most of the area draining to the basin is disturbed area, since their size must be based on total contributing area. Appropriately sized and stabilized conveyance channels will normally be required to funnel runoff to the basins. [N] It is also used for disturbed areas of more than 10 acres within the same drainage basin in order to comply with NPDES requirements. It may be used below construction operations which expose critical areas to soil erosion. Following are BMPs from various states that describe basins, construction and impacts: [N]

Sediment Trap

A sediment trap is a small temporary basin formed by excavation and/or an embankment to intercept sediment-laden stormwater runoff and to trap and retain the sediment-laden runoff. The purpose of the sediment trap is to intercept and retain runoff and allow the suspended sediment to settle out. A sediment trap is usually installed at points of discharge from disturbed areas. Constructing traps within ditches can be easy and effective and may require nothing more than a berm to create the volume and an outlet structure. Following are Sediment Trap BMPs from various states: [N]

Missouri DOT has developed a type of sediment trap, called a Type C Berm, that also allows for the movement of construction equipment through the area. The berm is placed long the stream bank and up slope of the stream at the slope limits to keep soil at bridge construction sites from entering the stream. Once the bridge is built, the rock in the ditch remains in place for permanent erosion control and the rock placed along the stream can then be spread and used as bridge protection.

Check Dams

A check dam is a small device constructed of rock, gravel bags, sandbags, fiber rolls, or other proprietary product placed across a natural or man-made channel or drainage ditch. [N] Check dams reduce scour and channel erosion by reducing flow velocity and encouraging sediment settlement. Following are various Check Dam BMPs:

Sandbag Barrier

Sandbag barriers or "berms are devices the purpose of which is to detain sediment carried in runoff from disturbed areas. This objective is accomplished by intercepting runoff and causing it to pool behind the sandbag berm. Sediment carried in the runoff is deposited on the upstream side of the sandbag berm due to the reduced flow velocity. Excess runoff volumes are allowed to flow over the top of the sandbag berm. [N] Sandbags can be used as a temporary interceptor to slow water velocity. Sandbags placed across access or interior construction roads provide for a means to divert or slow erosive water flows on a construction site. [N]

Sandbags work well as diversion structures, temporary cofferdams, sediment control devices and temporary flow dissipaters during any number of routine roadway maintenance activities. When appropriately designed and used as a cofferdam, these sandbags are stable enough for water to pond behind them. The ponded water behind the dam structure can then be pumped to a sediment retention basin or filter bag to allow work to be performed in-the-dry. When used in conjunction with other BMPs, sandbags can be useful in ensuring that sediment does not enter surface waters or wetlands, helping to retain sediment in a sediment retention basin, and/or diverting and/or dissipating runoff water during roadside ditch maintenance. [N]

Rock Berm

The purpose of a rock berm, or rock filter dam, is to serve as a check dam in areas of concentrated flow, to intercept sediment-laden runoff, detain the sediment and release the water in sheet flow (see Figures 5.6, 5.7 and 5.8). The rock berm should be used when the contributing drainage area is less than 5 acres. Rock berms are used in areas where the volume of runoff is too great for a silt fence to contain. They are less effective for sediment removal than silt fences, particularly for fine particles, but are able to withstand higher flows than a silt fence. As such, rock berms are often used in areas of channel flows (ditches, gullies, etc.). Rock berms are most effective at reducing bed load in channels and should not be substituted for other erosion and sediment control measures further up the watershed.

Maintenance of Sediment Basins and Traps

Sediment basins and traps and associated BMPs depend on maintenance for proper functioning: [N] [N] [N]

  • Inspection should look for:
  • Sediment accumulation in front of checkdams.
  • Erosion/scouring behind checkdam.
  • Proper checkdam configuration.
  • Erosion in contributing drainage area.
  • Periodically remove debris and litter.
  • Remove sediment when it reaches 50 percent of checkdam height.
  • Repair/replace checkdams if necessary.
  • Stabilize eroding soils on DOT right-of-way in the contributory drainage area by seeding and mulching or other appropriate means.

 

4.5.7 Vegetative Erosion Control
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Providing such detention time is not always possible. Thus, preventing erosion in the first place makes sediment control more effective. Vegetative erosion control is based on the assumption that soil can be kept in place with a vegetative cover. The reasons to keep soil in place include:

  • Protection of engineered grades
  • Reduction of maintenance on buildings, structures, and other man-made objects
  • Maintenance of surface water quality
  • Visual enhancement

Filter strips, also known as vegetated buffer strips, are vegetated sections of land similar to grassy swales, except they are essentially flat with low slopes, and are designed only to accept runoff as overland sheet flow. They may appear in any vegetated form from grassland to forest, and are designed to intercept upstream flow, lower flow velocity, and spread water out as sheet flow. The dense vegetative cover facilitates conventional pollutant removal through detention, filtration by vegetation, and infiltration.

Filter strips cannot treat high velocity flows, and do not provide enough storage or infiltration to effectively reduce peak discharges to predevelopment levels for design storms. This lack of quantity control favors use in rural or low-density development; however, they can provide water quality benefits even where the impervious cover is as high as 50 percent. WSDOT undertook a 17-month sampling campaign to investigate the potential for vegetated highway shoulders to retain suspended solids, metals, and total petroleum hydrocarbons. The data indicated that TPH and suspended solids were effectively removed. Metal concentration reduction was also effective when consideration was given to inadvertent pretreatment afforded by the highway runoff collection system. The study concluded the vegetated highway shoulder, located along hundreds of miles of highway can afford a cost effective means of contaminant retention. [N] Another WSDOT study found that the overall best Service Level for water quality benefits was excavating the first three quarters and retaining vegetation in the remainder. The ditch treated in this manner was capable of reducing TSS by approximately 40 percent, total phosphorus by about 50 percent, and total and dissolved Cu and Zn each by roughly 20 to 25 percent. [N] Analysis of survey data showed that biofiltration swales with broad side slopes, wide bases, and total storage volumes equivalent to 3 inches of runoff from the impervious drainage area consistently supported good vegetation cover and showed few signs of damage. For assisting grass growth, straw held in place with stapled jute mat had a clear advantage in effectiveness over the alternatives and a slight economy advantage over the coconut mat. [N]

The primary highway application for vegetative filter strips is along rural roadways where runoff that would otherwise discharge directly to a receiving water, passes through the filter strip before entering a conveyance system. Properly designed roadway medians and shoulders make effective buffer strips. These devices also can be used on other types of development where land is available and hydraulic conditions are appropriate.

Flat slopes and low to fair permeability of natural subsoil are required for effective performance of filter strips. Although an inexpensive control measure, they are most useful in contributing watershed areas where peak runoff velocities are low, as they are unable to treat the high flow velocities typically associated with high impervious cover. The most important criteria for selection and use of this BMP are soils, space, and slope. Further guidance and stewardship practices for installation and use of vegetated buffer strips are available online. Also, see section 4.13, Establishing Vegetation at Construction Sites.

 

4.5.8 Wind Erosion Control
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Wind erosion control consists of applying water and/or other dust palliatives as necessary to prevent or alleviate erosion by the forces of wind. Dust control should be applied in accordance with standard practices. Covering of small stockpiles or areas is an alternative to applying water or other dust palliatives. [N] Following are stewardship guidance resources from EPA and state DOTs:

 

4.5.9 Sediment Tracking Prevention
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Stabilizing Construction Entrances/Exits

Stabilized construction roads and entrances/exits are designed for the control of dust and erosion during construction and maintenance projects. In wet weather mud tracking occurs and in dry weather dust becomes the issue.

  • Stabilize construction exits and roadways with aggregate, asphalt concrete, or concrete.
  • Select the material used for stabilization based on the anticipated road longevity, performance, and site conditions.

Sediment tracking BMPs tend to be more effective in combination. BMPs such as limiting exits, stabilizing construction exits, and using existing paved areas should be considered in all sediment tracking control approaches. The following fact sheets from various state DOTs and EPA include construction and implementation guidance and stewardship practice:

Inspecting Adjacent Roads

Inspecting and cleaning adjacent public and private roads is an unavoidable obligation at each and every construction site:

  • Inspect roads near egress points commensurate with their use. If an exit is used daily, then the adjacent area should be inspected daily.
  • Clean roads near egress points before every predicted rain event and when visibly accumulated sediment has been deposited at other times.
  • Clean roads upon which dirt is hauled daily.
  • Clean roads using proper equipment. Use sweepers equipped with vacuums or a mechanical means of collection and removal. Do not just push the sediment around using only a mechanical broom.
  • Do not use a water truck or other hydraulic means to flush accumulated sediment on the roads into the storm drain system.
  • Limit egress points on the construction site to greatly reduce the time and effort expended on sediment tracking control. The fewer exits, the fewer areas that will require inspection and eventual cleaning.

Entrance/Outlet Tire Wash

A tire wash is an area located at stabilized construction roadway egress points to remove sediment from tires and undercarriages and to prevent sediment from being transported onto public roadways.

  • Construct on level ground when possible, on a pad of coarse aggregate.
  • Wash rack shall be designed for anticipated traffic loads.
  • Provide a drainage ditch that will convey the runoff from the wash area to a sediment trapping device.
  • Ditch shall be of sufficient grade, width, and depth to carry the wash runoff.
  • Remove accumulated sediment in wash rack and/or sediment trap to maintain system performance.
  • See Caltrans Fact Sheet Entrance/Outlet Tire Wash

Combining Recycling and Effective Erosion and Water Quality Control

Claassen also performed a review of the published literature on compost use and showed widespread use of composts to control erosion and improve soil conditions, with very few negative impacts. Protective mulch eliminates most sediment transport. Large rates of yard waste compost application have been shown to have low leaching rates, making them suitable for regenerating topsoil fertility and biological activity. Use of compost in erosion control applications increases soil organic content and increases microbial activity and populations, in contrast to chemical fertilizers, which do not. A thick compost layer can also improve access onto soft soils and can reduce tracking of mud onto local streets and into storm drains. Compost application also offers nutrient benefits. Long-term improvements resulting from compost application can be expected, but short term results may be variable depending on compost characteristics; considerable variability exists between producers and with different batches from a given producer. Evaluation of each product is needed before application to field sites, but better methods are needed for rapid evaluation of bioavailable nutrients in composts for use in field situations. Claassen's observations and state DOT and municipal recommendations are summarized here:

  • Use mulches in combination with revegetation seeding or planting. The combination effect of mulches plus revegetation seeding or planting gave the greatest reduction in erosion on decomposed granite (DG) materials in Idaho. [N] Although erosion processes during the first year after construction primarily involved mass wasting and slumping, subsequent years were entirely surface erosion processes such as rilling, raindrop impact and splash detachment and dry creep, all of which are effectively treated with mulch covers. [N]
  • When soils are compacted during disturbance, treatment by ripping improves hydraulic conductivity and reduces surface runoff and erosion. [N] This type of physical treatment may not restore the natural hydraulic conductivity of an undisturbed slope, however, because the pores formed may not be continuous or may not persist through multiple soil saturation cycles such as with winter rains.
  • Compost and mulch applications can preserve the open soil structure generated by ripping treatments. Wind tunnel tests indicated that soil surface roughness had little effect on reducing wind erosion or sandy soils (80 percent of particles within 150 to 300 mm), but that application of 5.6 ton/ha (5000 lb/ac) rates of garden and household waste compost (94 percent less than 5 cm length) increased the threshold wind speed for starting of wind transport from 6 m/s to 12-14 m/s. Composts were slurried onto the soil in a hydroseed-like mix using 1 part compost to 4 parts water with continuous agitation and then dried before testing. [N]
  • Compost compares favorably to shredded wood with tackifier and synthetic or organic blankets for erosion control. Texas Transportation Institute's Hydraulics and Erosion Control Field Laboratory Performed a study on compost application, testing three materials on 1:3 slopes with both clay and sand loam textured soils; these materials included co-compost (mixed yard trimming and municipal sewage sludge), shredded wood with polyacrylamide tackifier (6.75 kg/ha), and shredded wood with a hydrophilic colloid tackifier (56 kg/ha). The compost performed better and were cheaper than the synthetic or organic blankets tested by the facility. [N]
  • Of various compost methods tested by Portland Metro in nonpoint source pollution reduction "medium" mixed yard debris compost blanket yielded the lowest total suspended solids, surpassing sediment fence, compost barrier, "leaf litter" compost, hydromulch treatment, and coarse screened compost. [N] [N] The project used both "coarse" compost materials (containing chunks of wood and branches up to 152 mm [6 in] in length) and "medium" compost materials, the fraction remaining following screening of the coarse compost through a 16-mm (5/8-in) trammel. Results from subsequent Portland Metro demonstration documented that compost filter berms (83% reduction) can be twice as effective as sediment fences (39% reduction) in reducing total solids (TS) in runoff. [N] Results from subsequent Portland Metro demonstration projects suggest the following environmental stewardship practices using compost application:
  • Compost can be used to prevent vehicle and foot trafficking of soil. A thick compost layer can provide a surface covering for foot or vehicle traffic onto soils that are otherwise too muddy and wet to support traffic. A compost layer at the exit of a site will reduce mud tracking onto local streets and into storm drains. A 76-mm (3-in) layer of compost was found to be effective.
    • Compost screened to 38 mm (1½ in) or less is recommended for erosion control on steeper slopes. Slopes of up to 35 degrees were effectively treated. The compost layer should be extended over the top of the slope for 0.6 to 1 m (2 to 3 ft) at a 300-to 450-mm (12- to 18-in) depth to diffuse ponded water entering the top of the slope.
    • Compost that has been screened to 19 mm (3/4 in( or less is recommended for slopes that are to be landscaped. A moisture content of less than 25 percent makes application most efficient and enables the compost layer to readily adsorb larger amounts of rainfall soil more readily than immature compost.
  • Compost may be applied by hydroseeder. This technique replaces the low-nutrient cellulose or wood fiber amendment with a higher nutrient material. Compost screened to 3/8 inch has worked well in hydroseeders and did not plug the pump or nozzles. Erosion control was excellent with whole compost surface amendments. Hydroseeded compost should be applied with straw in order to provide structural strength. A typical application sequence would be:
    • Apply seed, 2000 kg compost/ha, 400-500 kg fiber/ha. (A 20-25 percent fiber mixture is needed to create a pumpable slurry.
    • Apply 4 Mg/ha wheat or barley straw (3.5 Mg/ha rice straw) evenly.
    • Apply 3000 kg/ha straw, 600 kg/ha fiber, slow release fertilizer (if needed), and 200 - 300 kg tackifier.
  • Higher application rates of compost may be more economically amended by dry application methods.

Two draft specifications on the use of compost for erosion and sedimentation control have been reviewed and approved by industry representatives and Technical Section 1a of the AASHTO Subcommittee on Materials. See AASHTO Standard Spec for Compost for Erosion/Sediment Control - Filter Berms, AASHTO Standard Spec for Compost for Erosion/Sediment Control - Compost Blankets, which specifies compost blanket parameters and application rates. Compost Use is also covered in section 10.13, Recycling in Roadside Maintenance Operations for a review of the water quality benefits of using compost.

 

4.5.10 Erosion Control Structure Removal
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  • When deemed by the Engineer to be no long required, Erosion Control Structures should be removed by use of an excavator, or other acceptable method approved by the Engineer, so that all erosion control materials and any retained sediment are excavated with minimal disturbance of the underlying ditches or slopes.
  • Removed materials and sediment should be disposed of at a location approved by the Engineer, at least 100 feet from a watercourse and such that it cannot wash into a watercourse.
  • Upon removal of the erosion control structure materials and retained sediment, the affected ditches and slopes should be shaped to match into adjacent final ditch and slope grades and immediately seeded as approved by the Engineer.

 

4.5.11 New Technologies
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California is one of the leading states in developing new technologies. Following is a link that consolidates and standardizes information on new technologies that are part of the Departments BMP identification, evaluation and approval process. It includes fact sheets for identified technologies. [N]

WSDOT's New Products Committee evaluates products submitted by vendors for use on WSDOT projects. Products meeting material and installation specifications are automatically added to the Qualified Products List. When no specification exists for immediate approval, the product is thoroughly evaluated by the appropriate material expert(s) on the New Products Committee.

 

4.5.12 Performance Monitoring Systems and Specifications for Contractors
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WSDOT Water Quality Sampling Protocol for Construction Projects

WSDOT's Instructional Letter 4049, Water Quality Sampling and Reporting for Construction Projects, established monitoring protocols to document whether WSDOT's most difficult projects meet water quality standards, during the most sensitive parts of construction and under the most challenging weather conditions. WSDOT plans to incorporate the content of this Instructional Letter into the WSDOT Construction Manual during its next revision. All construction sites are evaluated and categorized based on their inherent risk of erosion. Risk factors include size; timing and duration of work; soils; slopes; groundwater levels; and the need for in-water work. Runoff water from twenty percent of the projects that meet the risk criteria is tested during storm events and during critical periods of in-water work. Monitoring results are used to both evaluate specific project performance and validate results of the TESC Assessment Database. The results from the TESC Assessment Database and the water quality monitoring are published and widely distributed in WSDOT's Measures, Markers and Mileposts, a quarterly document that tracks various agency performance and accountability measures. WSDOT's statewide performance with the 13 erosion control minimum requirements is available on-line.

MDSHA System for 100 Percent Compliance in Construction Erosion & Sedimentation Control

MDSHA believes the agency maintains one of the better DOT enforcement systems in the country. To assess compliance, MDSHA implemented a six-layer system that includes independent quality assurance ratings for each project. Certified Quality Assurance inspectors inspect projects biweekly and rate the sediment controls on a letter grade scale. Projects can be shut down based on these inspections. Ratings for all projects are summarized quarterly and annually to comply with the MDSHA Business Plan. In the past the agency has pursued ratings of B or better on 95 percent of construction projects annually. As part of a primary agency commitment though, the Chief Administrator is seeking to improve performance to achievement of 100 percent compliance in construction.

NCDOT Delegated Erosion and Sedimentation Control Performance Tracking

NCDOT has its own sediment and erosion control program as delegated by the N.C. Sedimentation Control Committee and the North Carolina Department of Environment and Natural Resources. The Delegation Agreement has a self-monitoring component that requires NCDOT to inspect its projects for compliance with sediment pollution laws. Area Roadside Environmental Engineers (AREE) inspect all TIP and maintenance construction projects and whenever the AREE sees a significant erosion problem on a Department project that could result in issuance of a Notice of Violation (NOV) from DENR, the AREE will issue a Immediate Corrective Action (ICA) report to project personnel. This notifies project personnel that corrective procedures should be performed to resolve identified problems immediately. ICAs and NOVs are tracked and measured electronically and NCDOT has significantly raised environmental stewardship statewide through the program.

Automated Instream Monitoring at NCDOT

NCDOT is among those DOTs that have installed automated in-stream monitoring equipment to verify that the DOT is not contributing to a rise in turbidity, where water quality standards are such that no additional discharges worsening the TSS problem in local streams are allowable.

Caltrans Construction Inspection Program

The California Department of Transportation (DOT) construction inspection program employs multiple layers of oversight to ensure compliance from its staff and contractors. The California Department of Transportation (DOT) stormwater program has developed a multi-level construction inspection program that requires inspections to be conducted by the contractor, the Resident Engineer (RE), and consultant inspectors. These multiple levels of construction inspectors ensure compliance with erosion and sediment controls requirements and provides additional assurance that inspections are being conducted and BMP have been installed and are effective. Each inspection type is discussed below:

Contractor inspections

Caltrans requires contractors, through contract provisions, to conduct regular site inspections which are generally weekly during the rainy season and biweekly outside the rainy season. Contractors are also required to inspect the construction site before, after and during rain events. An inspection checklist (a copy of which is contained in the SWPPP/WPCP Preparation Manual) is required to be completed for each inspection and submitted to the RE within 24 hours.

Resident engineer inspections

The RE is required to conduct inspections at the same frequency as the contractor. Results of the inspections are forwarded to the contractor for correction. The RE may designate a SWPPP inspector to conduct the inspections for the RE, but this person should be trained on SWPPPs and have inspection experience.

Consultant compliance inspections

DOT contracts with a team of stormwater consultant compliance inspectors that review DOT construction projects statewide for compliance with NPDES permits. These inspections by the third-party contractors, also called the Storm Water Task Force, provide an independent evaluation of construction site compliance statewide in all Districts. DOT ranks projects with a priority ranking of 1-3 depending on amount of soil disturbance, location or project in a sensitive area, and the particular rainfall area for a project. The priority ranking help identify the frequency of inspections by the consultant inspectors. Resident Engineers are provided at least a 48-hour notification prior to any scheduled consultant inspection.

During an inspection, the consultant inspector documents the compliance status of the project in each of the BMP categories on the checklist and summarizes the inspection results on the first page. Since water pollution control requirements vary by season different checklists are used for the rainy season and the non-rainy season in most Rainfall Areas. The checklists include BMPs from six categories:

  • Soil stabilization
  • Sediment control
  • Wind erosion control
  • Tracking control
  • Non-storm water management
  • Waste management & materials pollution control

Only those BMP categories that are applicable to a given Rainfall Area and season are included on the checklist for a compliance inspection. Since the SWMP requirements vary throughout the state, designated Rainfall Areas may have separate inspection checklists.

Consultant inspectors use an alpha-numeric rating system to provide the most accurate assessment of the project's overall compliance with stormwater pollution prevention requirements, while maintaining a regulatory compliance approach. The inspector assigns a numeric designation of 0 to 4 for compliance at the site, with 0 indicating the site is substantially in compliance and 4 indicating the site has critical deficiencies. The inspector also assigns a letter designation indicating the effectiveness of the projects overall water pollution prevention effort.

Following a review, the on-site project team has the opportunity to appeal the compliance rating assigned by the compliance inspector before the rating is finalized. For sites with major deficiencies, District management and Headquarters personnel are immediately notified. In 2003, of the 255 projects inspected by the consultant inspectors, 86 percent had zero or minor deficiencies and 14 percent had major or critical deficiencies, a record on which Caltrans has been able to continue to improve.

Caltrans has also developed various stormwater guides include BMP manuals, SWPPP review guides, BMP field manual, and enforcement guide. In addition to the Caltrans Stormwater Web site the Division of Construction has developed a number of guidance documents to assist DOT staff and contractors in implementing the stormwater program. Some of these documents include:

  • A Construction Site BMP Manual
  • A SWPPP/WPCP Preparation Manual
  • SWPPP/WPCP Review Guidance Manual
  • Construction Site Storm Water Quality Sampling Guidance Manual
  • Construction Storm Water Coordinators Guidance Manual
  • BMP Field Manual and Troubleshooting Guide
  • SWPPP/WPCP Templates and Samples
  • Construction Site BMP Fact Sheet

Copies of these documents are available from the Division of Construction Stormwater Page.

Contractor Disincentive Specs for Inadequate/Improper Installation of BMPs

Thirteen state DOTs have implemented contractor disincentive specifications, allowing fines or withholdings in case of inadequate installation or maintenance of erosion and sedimentation control BMPs. [N] One such example is that of the Colorado Department of Transportation, which is available in Section 208 of the department's specifications: CDOT Erosion Control Contractor Disincentive Specification on page 28. Essentially, the specification states that "[t]emporary erosion and pollution control measures required due to the Contractor's negligence, carelessness, or failure to install permanent controls as a part of the work as scheduled or ordered by the Engineer or for the Contractor's convenience, shall be performed at the Contractor's expense. In the case of repeated failures on the part of the Contractor in controlling erosion, sedimentation, or water pollution, the Engineer reserves the right to employ outside assistance or to use Department forces to provide the necessary corrective measures. Such incurred direct costs, plus project engineering costs, will be charged to the Contractor, and appropriate deduction will be made from the Contractor's monthly progress estimate. Accepted work performed to install measures for the control of erosion and sedimentation, and water pollution, not originally included in the Contract will be paid for as extra work in accordance with subsection 104.03."

Utah DOT also has a $500.00 penalty each calendar day during which the project is in non-compliance with permits and regulations. The fine is above and beyond that assessed by regulatory agencies. Furthermore, no extension of contract time is allowed for any project delay resulting directly or indirectly from a violation. [N]

WSDOT Application of ISO 14001 to Erosion and Sedimentation Control

The Washington State Department of Transportation (WSDOT) Erosion Control Program has been working on applying the standards of an Environmental Management System (EMS) and ISO 14001 to proactively plan, implement, and monitor effective Temporary Erosion and Sediment Control (TESC) efforts. To do so, the Erosion Control Program performed an inventory and analysis of existing internal policies, procedures, and guidance documents. This allowed the Program to provide clarity and consistency with new regulations and erosion control technologies throughout the entire agency. To date, WSDOT has updated the Plans Preparation Manual, Standard Specifications for Erosion Control (Section 8-01) , Standard Plans Section I - Erosion Control , Highway Runoff Manual , Design Manual, Construction Manual, and Roadside Manual, to integrate Program improvements into existing WSDOT directional documents.

The second step involved establishing operational controls to address needs identified in the environmental aspect review process. Analysis revealed inadequate statewide standardization with WSDOT's erosion control plans that address a comprehensive set of thirteen minimum requirements. Internal discussions led to improved best management practice selection, quality of erosion control planning, and consistency with resource agency guidance. A variety of training resources, described in section 2.7, Environmental Training and Certification, have been developed.

The WDOT Erosion Control Program's third step involved creating compliance evaluation measures to monitor performance, analyze data, and report the Program's effectiveness. As part of this compliance effort, WSDOT identifies and makes compliance visits to all construction project sites in the state that possess a reasonable potential for erosion problems. Site assessments evaluate the quality of plans, implementation of the contract, and effectiveness of the best management practices. The assessment is viewed as an educational opportunity and the assessor works closely with project staff to solve any problems observed in the field. Program tools include the Daily Data Record Form and Excel Summary and Monitoring Report Forms.

All assessment results are stored in the TESC Assessment Database, providing Environmental Management System document control. The database generates reports for use at the project, regional, and state levels. Project reports provide answers to 150 questions. Recommendations are clearly identified and associated with precise standard specifications to be applied in addressing concerns. This report is the Program's primary technical assistance tool, providing the respective agency managers with a summary of all projects assessed and trends associated with the 13 minimum planning requirements. The state report provides the State Design Engineer and the State Construction Engineer with an overall picture of how the various regions are performing. In addition, the database generates two other reports specifically for use at the Erosion Control Program management level. First, the minimum requirements report determines how well the required planning components are being satisfied, in addition to other key issues that are instrumental in improving the Program. This is accomplished by applying database filters not used with the project, regional, or state reports. Second, the best management practice report reveals the frequency of use, correct application, maintenance, and overall effectiveness of 37 practices.

A recent agency Instructional Letter 4049, entitled Water Quality Sampling and Reporting for Construction Projects , established monitoring protocols to document whether WSDOT's most difficult projects meet water quality standards, during the most sensitive parts of construction and under the most challenging weather conditions. WSDOT plans to incorporate the content of this Instructional Letter into the WSDOT Construction Manual during its next revision. All construction sites are evaluated and categorized based on their inherent risk of erosion. Risk factors include size; timing and duration of work; soils; slopes; groundwater levels; and the need for in-water work. Runoff water from twenty percent of the projects that meet the risk criteria is tested during storm events and during critical periods of in-water work. Monitoring results are used to both evaluate specific project performance and validate results of the TESC Assessment Database. The results from the TESC Assessment Database and the water quality monitoring are published and widely distributed in WSDOT's Measures, Markers and Mileposts, a quarterly document that tracks various agency performance and accountability measures. WSDOT's statewide performance with the 13 erosion control minimum requirements is available on-line.

WSDOT found that the most effective method of achieving change in construction is in partnership with the agency Construction Office and with the construction industry and by documenting the necessary changes and required practices in those directional documents that govern the construction process and in individual construction contracts. Applying ISO 14001 Environmental Management System standards provides compliance documentation and a feedback mechanism. The TESC Assessment Program provides an audit component, identifying 1) how well WSDOT is protecting water quality; 2) what specific areas need improvement; 3) what strategies should be used to make improvements. The complete Erosion Control Program approach was developed with input and broad support of multiple stakeholders and reflects agency-wide ownership of the solution. The program has been accepted and institutionalized into the daily activities at all levels of those responsible for designing and building the state's transportations system. As a result, WSDOT expects agency-wide performance to continually improve. [N]

NHDOT Stormwater Quality Retrofits

NHDOT staff regularly attend meetings with the Chocorua Lake Association and other partners to monitor past accomplishments, plan and program new initiatives, and to share concerns and solutions with regard to future DOT projects. After installation of Best Management Practices at several highway culverts showed a reduction of phosphorus input by over 80 percent, the partners decided a long term commitment would best serve environmental stewardship goals. The stakeholders developed an agreement to protect and preserve the water quality of Chocorua Lake for the indefinite future with regard to stormwater management, requiring Best Management Practices in both construction and maintenance activities. The Memorandum of Understanding was the first of its kind between the NH Department of Transportation and a private organization. NHDOT anticipates using this MOU as a model for future partnerships with other similar environmental groups as opportunities become available.

 

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Table of Contents
 
Chapter 4
Construction Practices for Environmental Stewardship
4.1 General Construction Site Stewardship Practices
4.2 Work Area
4.3 Construction Involving Historic Properties and/or Other Cultural Resources
4.4 Construction in and around Drainage Areas and Streams, Wetlands, and Other Environmentally Sensitive Areas
4.5 Erosion and Sedimentation Control
4.6 Vehicle Fluid, Fuel, and Washwater Control
4.7 Air Quality Control Practices
4.8 Noise Minimization
4.9 Materials Storage, Collection and Spill Prevention on Construction Sites
4.10 Vegetation Management in Construction
4.11 Soil Management in Construction
4.12 Establishing Vegetation at Construction Sites
   
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