Center for Environmental Excellence by AASHTO CENTER HOME  
skip navigation
CEE by AASHTO Home | Compendium Home | Online Compendium Help | Recent Updates | Inquiries | FAQs | State DOT Links
About Best Practices | Comment on Best Practices | Suggest A Best Practice | Volunteer to Vet Best Practices
Printer Friendly Version Print This Page    
« Back to Chapter 3 | Go to Chapter 5 »
Chapter 4
Construction Practices for Environmental Stewardship
4.2. Work Area

A "work area" is an area, defined by, the limits of which shall be established by the Contractor with the approval of the Project Engineer prior to commencement of work.


4.2.1 Preparing Access and Staging Areas
< back to top >

Several principles should guide design, placement, and construction of site access to ensure environmental stewardship:

Avoid any sensitive wildlife habitat or plant areas or threatened and endangered species and their designated critical habitat.

Avoid crossing streams if at all possible; where crossing is unavoidable, use bridges.

Minimize slope disturbance since effective erosion control is difficult on a sloped roadway that should be heavily used.

Construct roadways with low gradients; ensure that stormwater runoff drains to outlets; install an adequate roadbed; and, if possible, set up a truck-washing station at the entrance of the construction site to reduce offsite transport of mud and sediment by vehicles.

Every effort should be made to minimize and, where possible, avoid site disturbance. Emphasis should be placed on addressing protection of existing vegetation and sensitive habitat, erosion and sediment control, protecting air and water quality, protecting cultural resources, minimizing noise, and providing for solid waste disposal and worksite sanitation. Thus:

  • Limit the types of construction operations, including access and hauling, allowed in certain areas of the project that may be more susceptible to erosion. For example, do not allow unlimited vehicle crossing of streams: provide a temporary crossing at a single location and only when access is necessary.
  • Plan and designate areas that are not to be disturbed at all, or at which phase in the project the area is to be disturbed. This can include limiting the type of access or operation in a given area. For example, consider only hand clearing operations in areas susceptible erosion and fencing off areas that are not to be disturbed.

The benefits in limiting disturbed areas during construction are fourfold:

  • Maintaining existing vegetation preserves natural habitats that reduce the potential impact of the existing highway
  • Areas left undisturbed may not warrant any pollution prevention practices since their erosion potential may not increase
  • Existing vegetation can be utilized as an erosion control device acting as a vegetative buffer filtering and settling out sediment
  • Smaller disturbed areas are more manageable when trying to control runoff and erosion


4.2.2 Construction Phasing, Sequencing, or Acceleration
< back to top >

There are a variety of reasons for construction sequencing. On environmental, restoration, or bioengineering projects, sites often require earthwork as part of site restoration and/or before installing a soil bioengineering system. It is important to plan for and manage timing conflicts that can occur between scheduling heavy equipment, hand labor work, plant collection, and plant use.

One of the largest and most common environmental stewardship concerns that can be addressed by construction sequencing is minimization of unprotected soil and resultant erosion and sedimentation. Construction sequencing should be scheduled to minimize land disturbance at all times, but especially during the rainy or winter season. Scheduling should be considered when establishing permanent vegetation ( appropriate planting time for specified vegetation ) . The following environmental stewardship practices are recommended:

  • Minimize the extent and the duration of exposure of bare ground surface to be opened at any one time, to prevent erosion at the source. Limiting the area of erodible soil exposed at any given time also helps sustain a manageable area of construction activities.
  • Plan the phases or stages of construction to minimize exposure. On larger projects, sub-phases should be used to minimize the area of exposed soil. Before site disturbance occurs, perimeter controls, sediment traps, basins, and diversions should be in place to control runoff and capture sediments. Prioritize disturbed areas in the vicinity of water bodies, wetlands, steep grades, long slopes, etc. for effective stabilization within seven days of disturbance.
  • Complete and employ permanent structures, controls, and stabilized areas as soon as practical for use as erosion and sediment control measures for the remaining construction operations. For example, grade and revegetate ditch early on in the project so they can assist in reducing the effects of later construction operations.
  • Schedule land-disturbing activities during periods of low precipitation.
  • Complete grading as soon as possible after it is begun.
  • Maintain the maximum amount of existing vegetation to assist in the control of and to minimize the exposed erodible area. For example, do not clear or grub an area until work is necessary.
  • Establish permanent vegetative cover immediately after grading is complete. Graded areas that will not be worked on should be seeded and mulched immediately, rather than waiting until all project grading is done.
  • Monitor work to ensure progress according to the schedule and adjustments if necessary. When changes are warranted, amend the sequence scheduling in advance to maintain sediment control.

The Nova Scotia Transportation and Public Works has further defined the requirements for work area and construction phasing, to ensure that construction phasing does not become the weak link in erosion and sedimentation control: [N]

  • The size of the work area is determined by the grading, seeding and final slope protection the Constructor can complete within 30 calendar days. Such grading should include completion to the lines and grades shown on the plans, to prevent re-work.
  • Work will be considered started with grubbing and will be considered complete when the specified cover material is applied ( e.g., straw/hay/compost/bark mulch, erosion control blanket, Clear Stone, sod, hydroseeding).
  • Work Progression Schedule and Contingency Plan for failure of Erosion and Sedimentation Control measures shall be completed by the Contractor and approved by the Project Engineer prior to commencement of any grubbing.
  • Plan for unforeseen circumstances ; if conditions are encountered in an active work area which requires extra care or work which the Contractor is unable to continue at that time, the Contractor will be allowed to open up additional work area(s) with the approval of the Project Engineer only after the original work area is temporarily protected, i.e., straw/hay/compost/bark mulch. If unforeseen circumstances occur, the 30 calendar day period may be extended with the approval of the Project Engineer. This extension must be accompanied by a written report outlining the need for the extension and the measures to be taken to control erosion and sedimentation. Inconvenience to the Contractor, poor planning or not having adequate or appropriate equipment will not be considered unforeseen circumstances.
  • Identify measures for non-compliance . Once the grubbing operation within a specific work area has begun, work shall be continuous from grubbing through to the placement of seed (including fertilizer, lime) and final slope protection, where required. If after 30 calendar days the above described work is not completed, then: (a) No additional work area(s) will be allowed to commence until these work areas are completed; and (b) All work areas will be immediately protected with straw/hay or compost/bark mulch. If, in the Project Engineer's judgment, there is non-compliance with erosion and sediment control provisions or if the Contractor receives a warning or citation from DEL or DFO, then corrective action may require a shutdown of construction activities, until such time as the non-compliance is satisfactorily corrected.

EPA has also developed a Fact Sheet on Construction Sequencing, available on-line.

Grade Management

Proper planning and management of highway construction grading operations can significantly lower the erosion problems associated with these activities. No operation in highway construction increases the potential for erosion as much as excavation and embankment activities. The erosion potential of an area is increased as erodible areas are exposed and slopes are steepened and lengthened. The following is a list of items to consider when managing grading operations: [N]

  • Excavation and embankments should be completed to final grade and stabilized in a continuous operation; piles of loose material should be minimized at all times.
  • Offsite flow should be prevented from crossing into excavated areas by intercepting and/or diverting flows into and through undisturbed or controlled areas.
  • Perimeter controls should be installed at the toe of the slope in embankment sections to prevent sediment-laden runoff from leaving the site.
  • Small berms or dikes should be placed at the end of each days grading operations in cut and fill sections to divert or intercept runoff to controlled areas.
  • Prompt grading and stabilization of ditches will greatly reduce the potential sediment load.


4.2.3 Preserving Local Fish and Wildlife through Attention to Timing Restrictions
< back to top >

Timing restrictions might be imposed on the project due to the presence of nesting, migrating, or wintering threatened or endangered species. Restrictions are dependent upon the distance from the species' activity center, the type of activity proposed, and the time of year the activity is proposed. Pile driving, blasting, and other noise generating activities (addressed in Section 4.9, Noise Minimization) are of the greatest concern.

Timing restrictions might also be placed on projects involving construction in or over water, such as culvert or bridge installation or pile driving. Sensitive times include winter periods, migratory periods, and breeding seasons.

During construction, clearly flag or place construction fencing around all habitat areas and features that are to be saved or avoided in the field, and include those locations in the plans of the project. This will minimize confusion and will help avoid impacting these areas and/or features.

Projects near stream or wetland habitat areas must have their erosion control measures carefully implemented and maintained during construction to avoid impacting aquatic species.

Occupied migratory bird nests may not be removed; however, nests can be covered prior to seasons when nests would be re-occupied.

See section 7.2, Avoiding and Minimizing Impacts to Fish and Wildlife and Enhancing Habitat for further discussion of timing restrictions.

4.2.4 Accelerated Construction
< back to top >

Though accelerated construction is often driven by increasing traffic demand, this practice is also highly useful to minimize environmental impacts on certain projects as it focuses on "getting in and getting out" as quickly as possible. Sponsored by the American Association of State Highway and Transportation Officials' (AASHTO) Technology Implementation Group (TIG) and the Federal Highway Administration (FHWA), the Accelerated Construction Technology Transfer process begins with a 2-day workshop in which a multidisciplinary team of 20 - 30 national transportation experts works with an equal number of their local counterparts to evaluate all aspects of a project and develop recommendations for reducing construction time and enhancing safety and quality. [N]

Transportation Research Board Task Force A5T60 on Accelerating Innovation was formed in 1999 to promote accelerated construction in the highway infrastructure. In 2002, the task force completed two ACTT pilot workshops in Indiana and Pennsylvania. AASHTO-TIG and FHWA are continuing the effort, and workshops in Texas, Louisiana, and California were conducted in 2003. Interest among State highway agencies has been very high, and six workshops already are occurring in 2004. Recent workshop recommendations have included using design-build contracting; coordinating with utility companies early in the project planning process; using long-life pavements with a 50-year design lifespan; improving general materials specifications; establishing a dedicated incident management system at the project site; and introducing various traffic flow strategies. In some cases project construction times have been cut in half. [N]


4.2.5 Pre-Contract and Pre-Construction Activities
< back to top >

Emphasize sensitive areas during precontract meetings. Note the kinds of activities that are not allowed in the sensitive areas and designated lands (such as clearing, grading, stockpiling materials, construction equipment, vehicle parking, etc.). This will help to minimize confusion and also help contractors and construction personnel avoid the sensitive areas. Items that should be specifically addressed at the prework meeting include: [N]

  • Access - Equipment access points that minimize disturbance, especially to less stable areas should be located.
  • Protection of Water Quality - Prevention of direct runoff of sediment containing water into streams, proactive prevention of erosion, qualitative design expectations relating to construction area drainage and treatment, preparation and protection of the site from potential storms during the work period.
  • Protection of Habitat - Preservation of riparian habitat, minimization of damage to existing vegetation, preservation and use of cleared large wood with stumps.
  • Dewatering Method Performance - Expectations of erosion control methods, sediment trapping and turbidity treatment of runoff, expectations of possible subsurface flow in the excavation and the method for handling it, including payment method. Capture and rescue of aquatic organisms may be an important part of dewatering that could be the responsibility of the contractor. Discuss expectation and coordination with other specialists (fish biologist).
  • Quality of Stream Bed Simulation Rock Placement - Emphasize that the intent is to reconnect the channel and create as natural a channel inside the pipe as possible. Photos of the site showing stream segments with similar channels to what is in the contact plans can be helpful. Discuss the proposed method of placing of bed material; this often requires hand labor and specialized equipment. The quality of labor and effort put into fitting and interlocking individual pieces of rocks together can have a substantial effect on their durability. Material dimensions, gradation, and permeability are vital to the simulated streambed's performance. Special specification and pay items are vital to describe and administer this area of work. These items may be a minor cost item in the overall contract, but they have a major impact on the effectiveness of the structure.

Perform construction surveys if needed for bioengineering projects. Additional surveys by the contract administrator may be helpful before excavation to help locate any additional specific features or objects not in the contract drawings or original survey. Surveys performed during construction to determine specific locations of the structure and details are extremely important and are in a larger sense verifying that the design meets the site geometry. Contractor survey accuracy should be checked. Contract administrator should be skilled in survey methods and able to verify contractor surveys. Survey errors can lead to costly construction mistakes and, therefore, should be caught as soon as possible. For instance, if the structure is placed at the wrong elevation, when the stream channel is constructed and reconnected to the adjacent channel, slopes into or out of the pipe may cause channel scour or passage problems that are difficult to mitigate. A structure placed in the wrong location may create road alignment problems later on.

Confine construction and staging areas to the smallest area necessary. Construction area boundaries, including staging areas, should be clearly marked to ensure and all construction activity and storage of construction materials should occur within these marked areas.

  • Use disturbed or developed areas for staging whenever possible.
  • Keep right-of-way for watercourse crossings as narrow as possible within the constraints of safety and construction requirements. Limit removal of vegetation to the width of the right-of-way.
  • Where possible, plan instream work to occur as a single event.
  • Restrict instream work to low flow periods where possible.
  • Limit machinery access to a single point on one bank.
  • Limit distance between machinery access point and work site.
  • Utilize new technologies such as prefabricated materials and Geosynthetic Reinforced Soil abutments and walls to minimize the access needed for large equipment.

Install construction fencing or flagging to protect sensitive areas from encroachment by construction activities, if appropriate. As in delineating work zones, fencing should be placed around all protected areas during initial site preparation, even before the access road is fully constructed, if possible, but certainly before wholesale earthmoving begins. Fencing material should be easy to see, and areas should be labeled as protection areas.

Delineate and mark wetland areas. Adjacent or nearby wetland areas not in the construction area should be fenced to reduce potential impacts from construction activities. Consider the following as indicators of possible wetland presence, and a potential "red flag" until the area is delineated by a trained wetland biologist:

Wetland Hydrology Indicators

    • Areas that have standing water at any time of the year.
    • Topographical low areas.
    • Areas near streams, lakes, or other shorelines.
    • Areas with water seeping out of a hillside.
    • Ditches that hold water long after rain events.
    • Ditches that flow to other water bodies such as streams, lakes, ponds, and the like.

Wetland Soil Indicators

    • Areas where vehicles get stuck or leave ruts.
    • Areas with dark, sticky soils.
    • "Unsuitable soils" for construction or foundation.
    • Highly organic soils.
    • Clay soils that are pale gray or mottled.
    • Sites within floodplains.
    • Soils that give off a rotten egg smell when disturbed.

Wetland Vegetation Indicators

    • Obvious wetland plants such as rushes or cattails.
    • Trees such as alders or willows dominating low-lying areas.
    • Shrub Thickets in low-lying areas.

Isolate the work area from other jurisdictional waters.

Prevent discharge of water from the work area prior to treatment. All runoff from the work area should drain through a Sedimentation Control BMP or a Dewatering Device BMP prior to entering jurisdictional waters.

Maintain a buffer area along streams and other waters of the state or waters of the U.S. Buffers are areas along jurisdictional waters such as streams, lakes, ponds and estuaries that often have legal protection. A typical riparian buffer is a 50-foot wide vegetative strip along each side of a jurisdictional stream measured from the top of bank or the mean high water line. The riparian buffer typically cannot be disturbed unless specific conditions are satisfied. Existing drainage ditches and roadside ditches are typically exempt from the buffer rules provided that they are managed to minimize sediment, nutrients and other pollution that enters jurisdictional waters. Existing drainage ditches may not be deepened beyond original pre-construction depths. New ditches through a riparian buffer are typically not allowed unless specific conditions are satisfied. [N]


< back to top >
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
Lists: Examples | Tables | Figures
Website Problems Report content errors and/or website problems
PDF Document Download Adobe Acrobat Reader