Projects that will either extend more than one season or will still be active during the winter months need to take special considerations when planning for winter shutdown or an active winter construction season.
A winter construction plan should be developed to specifically address shutdown procedures or active construction plans. Projects that plan to continue construction during the winter seasons should sequence construction events such that areas having high potential for erosion and sedimentation be fully constructed and stabilized prior to the presence of frozen conditions whenever possible.
All winter shutdown activities should be performed before frozen conditions are present and must be completed within 14 days (7 days in some cases depending on construction stormwater permit requirements) following the end of construction for the season. Winter shutdown activities should be completed prior to snowfall whenever possible.
Construction during the winter months presents many additional challenges that require modifications to traditional construction practices in order to continue with work. Typically, a winter construction plan should be followed once the ground begins to freeze. Frozen ground can cause equipment slippage during operation, make excavations difficult or impossible with the available equipment, and material stockpiles can freeze, which hinders the ability to achieve adequate compaction or uniformly distribute materials. Fertilizer, liming materials, and soil additives should never be applied to frozen ground. These activities can resume after spring snow melt is complete.
Winter construction plans typically include the following provisions:
As winter construction progresses, there will be additional needs for stabilization, which cannot be addressed with traditional methods.
More specifically, MnDOT provides the following recommendations for best management practices during winter construction activity. Good housekeeping practices should be considered throughout the project to meet permit requirements. Additional information can be found in Minnesota Department of Transporation's (MnDOT) Winter Inspection Guidance and in the following table.
MnDOT winter guidelines
Link to this table
|Practice||Winter guidelines (MnDOT)|
|Winter site preparation||Practices include smoothing rough grading, frost tillage and harrowing.|
|Winter seeding/snow seeding||Apply seed over snow so that it melts into the snow surface during winter months. Seed will melt to the soil surface for germination after snow melt. All permanent and most temporary seed mixes can be snow seeded. Application on soft snow or during a sunny day is ideal.|
|Dormant seeding||Dormant sodding should be conducted between November 1st and soil freeze up. Winter sod cannot be placed within 10 feet from the shoulder of a road or in areas that require salt tolerant sod.|
|Mulching on bare frozen soils||Perform on bare frozen soils when temperatures are above 20 degrees Fahrenheit. If temperatures are below 20 degrees, delay mulching and perform snow mulching once ground is covered in snow.|
|Mulching on snow||Apply mulch over snow (any depth) at a rate of 1.5 to 1.75 tons per acre, or about an 80-90% cover. Sunlight will melt the straw into the snow to melt onto bare soil in the spring. Practice is not applicable to conveyance systems.|
|Winter erosion control blanket/turf reinforcement mats/snow blanket installation||Install practices over bare frozen ground or snow (no deeper than 2 inches) using appropriate anchors. If necessary, remove snow before placing erosion control blanket. Practices are useful for conveyance systems and other areas where mulching practices are not applicable. There are no limits to the application locations for snow blanketing except in known wildlife habitat areas. In these areas, use natural netted blankets.|
|Winter exits and street sweeping||If proper winter exits are not present, it may be necessary to sweep after each vehicle exits the site. Daily maintenance of exit should occur to determine if adjustments are needed. BMPs include creating an ice/snow road, installing mud mats, drivable base mats, slash mulches or timber pads, and use of proper depth crushed aggregate over geotextile separation fabric.|
|Ice/snow road||Remove snow cover to allow the soil and road to freeze solid to support every equipment hauling. Mud mats, drivable base mats, slash mulches or timber pads can be installed. BMP can be used to create a proper winter exit.|
|Winter inlet protection||Must be installed prior to any land disturbance on site. Winter inlets should be cleared daily of any ice or snow to ensure their full functionality. BMPs include removable inserts, filter logs, sediment moats and rings, oil and heavy metal trap logs. Most inlet protection BMPs should be removed once contributing erosion is properly stabilized.|
|Winter perimeter control||Should either be a temporary BMP or a BMP that is heavy enough to remain in place during melt conditions. Rebar and other sharp devices are not allowed. BMPs include filter logs, geotextile wrapped straw bales, clean and washed filter rock, and riprap or rock berms.|
Prepare a snow management plan for the site to account for adequate storage of cleared snow through the winter and control of meltwater. Snow storage locations should be placed down slope of all disturbed areas, but not located within stormwater treatment BMPs that are designed for infiltration or filtration or within natural wetlands. Snow mixed with significant amounts of soil should be stored in separate locations that are designed to handle larger volumes of sediment. Storing sediment-laden snow in stormwater treatment BMPs may increase the need for maintenance due to high levels of sedimentation following melt. See the management approaches section under cold climate impact on runoff management for additional recommendations.
Many earthwork operations can continue through the winter months on frozen soils with specific modifications. Occasionally, it may be necessary to relocate frozen or saturated soils to continue with construction.
Regardless of whether or not a construction site has been shut down for the winter, all installed BMPs must be monitored and corrective actions taken as necessary. Gravel, sandbags, Erosion control blankets, and mulch should be kept on site to address any immediate repair needs. Repairs to BMPs should be made immediately and any accumulated sediment should be remove upon each inspection.
The following guidance applies to inactive construction sites.
The following guidance applies to active construction sites.
During spring thaw, it may be necessary to suspend construction activities until soils are no longer saturated. Keeping vehicle travel areas free of snow at night and covered with snow during the day can help to maintain frost penetration in the ground. It is extremely important that all BMPs are being actively monitored and promptly maintained during the spring thaw period.
See cold climate impact on runoff management for recommendations for controlling snowmelt runoff.