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Construction Sequencing

Minimum Measure: Construction Site Stormwater Runoff Control

Subcategory: Construction Site Planning and Management

Photo description:  Sites are completed in stages in sequenced construction.

Description

Construction sequencing is a specified work schedule that coordinates the timing of land-disturbing activities and the installation of erosion and sediment control measures. The goal of a construction sequence schedule is to reduce on-site erosion and off-site sedimentation by performing land-disturbing activities and installing erosion and sediment control practices in accordance with a planned schedule (Smolen et al., 1988).

Construction site phasing involves disturbing only part of a site at a time to prevent erosion from dormant parts. Grading activities and construction are completed and soils are effectively stabilized on one part of the site before grading and construction commence at another part. A key consideration of grading activities should be the coordination of cuts and fills to minimize the movement and storage of soils on, off, and around the site. This differs from the more traditional practice of construction site sequencing, in which site-disturbing activities are performed initially for all or a large section of the site, leaving portions of the disturbed site vulnerable to erosion. To be effective, construction site phasing needs to be incorporated into the overall site plan early on. Elements to consider when phasing construction activities include the following:

  • Managing runoff separately in each phase
  • Determining whether water and sewer connections and extensions can be accommodated
  • Determining the fate of already completed downhill phases
  • Providing separate construction and residential accesses to prevent conflicts between residents living in completed stages of the site and construction equipment working on later stages (USEPA, 2004).

Applicability

Construction sequencing can be used to plan earthwork and erosion and sediment control activities at sites where land disturbances might affect water quality in a receiving waterbody.

Siting and Design Considerations

Construction sequencing schedules should, at a minimum, include the following: Design and Installation Criteria

  • The ESC practices that are to be installed
  • Principal development activities
    • Which measures should be installed before other activities are started
    • Compatibility with the general contract construction schedule

Table 1 summarizes other important scheduling considerations in addition to those listed above.

Table 1. Scheduling considerations for construction activities.

Construction activity

Schedule consideration

Construction access, entrance to site, construction routes, areas designated for equipment parking

This is the first land-disturbing activity. As soon as construction begins, stabilize any bare areas with gravel and temporary vegetation.

Sediment traps and barriers, basin traps, sediment fences, outlet protection

After the construction site is accessed, install principal basins. Add more traps and barriers as needed during grading.

Runoff control diversions, perimeter dikes, water bars, outlet protection

Install key practices after installing principal sediment traps and before land grading. Install additional runoff control measures during grading.

Runoff conveyance system, stabilize stream banks, storm drains, channels, inlet and outlet protection, slope drains

If necessary, stabilize stream banks as soon as possible, and install a principal runoff conveyance system with runoff control measures. Install the remainder of the systems after grading.

Land clearing and grading, site preparation (cutting, filling, and grading, sediment traps, barriers, diversions, drains, surface roughening)

Implement major clearing and grading after installing principal sediment and key runoff-control measures, and install additional control measures as grading continues. Clear borrow and disposal areas as needed, and mark trees and buffer areas for preservation.

Surface stabilization, temporary and permanent seeding, mulching, sodding, riprap

Apply temporary or permanent stabilizing measures immediately to any disturbed areas where work has been either completed or delayed.

Building construction, buildings, utilities, paving

During construction, install any erosion and sedimentation control measures that are needed.

Landscaping and final stabilization, topsoiling, trees and shrubs, permanent seeding, mulching, sodding, riprap

This is the last construction phase. Stabilize all open areas, including borrow and spoil areas, and remove and stabilize all temporary control measures.

Limitations

Weather and other unpredictable variables might affect construction sequence schedules. However, the ESC plan should plainly state the proposed schedule and a protocol for making changes due to unforeseen problems.

Maintenance Considerations

Follow the construction sequence throughout the project and the modify the written plan before any changes in construction activities are executed. Update the plan if a site inspection indicates the need for additional erosion and sediment control.

Effectiveness

Construction sequencing can be an effective tool for erosion and sediment control because it ensures that management practices are installed where necessary and when appropriate. Follow the plan and, if needed, update it to maximize the effectiveness of ESC BMPs under changing conditions. A comparison of sediment loss from a typical development and from a comparable phased project showed a 42 percent reduction in sediment export in the phased project (Claytor, 1997).

Cost Considerations

Construction sequencing is a low-cost measure because it requires a limited amount of a contractor's time to provide a written plan for coordinating construction activities and management practices. It might take additional time to update the sequencing plan if the current plan is not providing sufficient erosion and sediment control.

References

Claytor, R. 1997. Practical Tips for Constrcution Site Phasing. Article Number 54 in The Practice of Watershed Protection. Center for Watershed Protection, Ellicott City, MD. 2000.

Smolen, M.D., D.W. Miller, L.C. Wyall, J. Lichthardt, and A.L. Lanier. 1988. Erosion and Sediment Control Planning and Design Manual. North Carolina Sedimentation Control Commission; North Carolina Department of Environment, Health, and Natural Resources; and Division of Land Resources, Land Quality Section, Raleigh, NC.

USEPA (U.S. Environmental Protection Agency). 2004. Development Document for Final Action for Effluent Guidelines and Standards for the Construction and Development Category. EPA-821-B-04-001. Washington, DC.

 

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