Construction stormwater treatment - BMP removal after final stabilization
In general, when a temporary BMP is no longer needed on a construction site, most often after final stabilization has occurred, it must be removed by the contractor. However, some BMPs, such as temporary sediment basins, may be converted to permanent BMPs after construction is complete. Further, many BMPs used to prevent erosion, control sediment, and provide temporary or permanent stabilization of a construction site are often left in place.
While many construction stormwater BMPs must be removed from the site after final stabilization, it is generally acceptable for BMPs made of natural materials (such as fiber logs/rolls, natural fiber erosion control mats, etc.) to be left on the site to decompose. Erosion prevention practices constructed from degradable materials represent the most common class of stormwater construction BMPs that are left in place after construction is complete and the site is stabilized. Perimeter control BMPs constructed from degradable materials may also be left on site in some cases. However, temporary perimeter controls constructed from materials that do not readily decompose, such as silt fences, filter socks, straw bale barriers, sandbag barriers, metal stakes and reinforcement fencing, and other relatively low cost BMPs should be removed but are often forgotten on site after construction is complete.
Applicability
In general, whether a construction stormwater BMP is removed after the completion of construction and stabilization of the work site primarily depends on (1) the conditions of the contract and applicable permit(s), (2) the intended function and lifespan of the BMP, and (3) the nature of the materials used to construct the BMP.
MPCA’s 2018 Stormwater Construction Inspection Guide states that “all temporary synthetic and structural erosion prevention and sediment control BMPs (such as silt fence) must be removed on the portions of the site for which the Permittee is responsible”, and that BMPs “designed to decompose on site (such as some compost logs) may be left in place.”
Site applicability
Whether they are to be removed or left in place, all BMPs should still be cleaned of excess sediment and other accumulated debris at the completion of construction and final stabilization when they are no longer needed. However, depending on the expected rate of decomposition and intended use of the site, a contractor or site owner may wish to remove and dispose of some BMPs or BMP components in lieu of leaving them in place to decompose. The guidance in this BMP chapter pertains primarily to sites where the standard regulatory procedures for determining whether a temporary construction stormwater BMP should be removed, left in place, or converted to a permanent stormwater management feature.
The table below provides general recommendations for categories and types of temporary BMPs regarding whether they are typically removed or left in place on a construction site after final stabilization.
Typical recommendations for BMP removal for common construction stormwater BMPs