Clearing and grubbing of land during the construction process results in the loss of vegetative cover. The loss of this cover and the loss of stable topsoil during the site stripping process leave the underlying soils vulnerable to the erosion process. The exposed soils are subjective to wind forces that reduce air quality control. During rain events, the soils are transported downstream impacting aquatic habitats as well as infrastructure.
In 2006, The Greater Golden Horseshoe Area Conservation Authorities prepared a guideline entitled “Erosion & Sediment Control Guideline for Urban Construction”. Based on the guideline, all projects involving the removal of topsoil or site alteration requires an ESC (Erosion and Sediment Control) Plan in place prior to commencing construction. Failure to adhere to the plan could lead to the potential for prosecution under the various pieces of environmental legislation.
The following principles assist in creating an effective ESC Plan.
(Ref. Erosion and Sediment Control Guidelines for Urban Construction)
Adopt a multi-barrier approach to provide erosion and sediment control through erosion controls first.
Retain existing ground cover and stabilize exposed soils with vegetation where possible.
Limit the duration of soil exposure and phase construction where possible.
Limit the size of disturbed areas by minimizing nonessential clearing and grading.
Minimize slope length and gradient of disturbed areas.
Maintain overland sheet flow and avoid concentrated flows.
Store/stockpile soil away (e.g. greater than 15 meters) from watercourses, drainage features and top of steep slopes.
Ensure contractors and all involved in the ESC practices are trained in ESC Plan, implementation, inspections, maintenance, and repairs.
Adjust ESC Plan at construction site to adapt to site features.
Assess all ESC practices before and after all rainfall and significant snowmelt events.
The guideline stresses that prevention of erosion is the preferred mitigation measure for reducing the potential for sedimentation.
Erosion and sediment control measures can be categorized as Erosion prevention controls and Sediment controls.
Erosion controls include minimizing the reduction in vegetative ground cover or immediate stabilization of disturbed areas by top soiling, seeding, sodding, mulching, erosion control blankets, etc.
Sediment Controls are further broken down into Perimeter Controls, Settling Controls and Filtration Controls. Some major perimeter controls include silt fences, cut-off swales and mud-mats. Settling controls reduce run-off velocity allowing the soil particles to settle out. Settling controls include sediment traps, rock check dams, straw bales and sediment control ponds. Filtration controls are achieved by filtering silt laden water through the use of a filer media such as a geotextile or sand. Filtration controls include storm inlet filter cloths, sediment bags and filter rings.
It is the responsibility of all Project Managers to ensure they understand the approved ESC Plan for their site and ensure its implementation to avoid both on-site and off-site environmental impacts.
For additional information on this topic, contact MGM directly.