Silt Fence Regulations
Silt fences are the black, temporary fences that surround a job
site around a lot that is being developed. This fence is designed to act
as a temporary barrier, to allow proper drainage and to keep the soil
from running off onto other properties and especially to protect
streams, rivers, ponds and lakes from runoff caused from construction.
All regulations are enforced by the particular state's Department of Forestry and the Municipal Zoning Department of that particular area based on minimum code requirements.
Silt fence comes in 24-inch and 36-inch rolls that are usually 100 feet or over. The fabric portion must be installed at least 6 inches under ground in a trench that is typically made by a trencher. The minimum fabric height once buried from ground level is 14 inches and the maximum height is 28 inches. All heights are based off of industry standards set forth by the Department of Forestry in cooperation and conjunction with the particular municipal zoning authorities.
The silt fence has to be made of a geotextile material, meaning
that it supports the soil, yet allows water to move through it at a rate
of 10 gallons/minute/square foot/50mm of constant head water. This is
possible by weaving nylon strips over each other to create a fabric that
filters well and is elastic enough to stretch when needed so it will
not break when loose soil carried by water puts pressure on the fence.
Non woven geotextile fabrics can be used but are not applied often in the field because of their relative weakness as compared to woven fabric.
The construction of silt fence is specified in ASTM D 4632, ASTM D 4335. ASTM D 4751, and ASTM 4491 standards.
The fence is required to be staked into the ground with 3 foot long wooden posts. The posts are required to be every 3 feet for non woven fabric and every 8 feet for woven fabric. The fabric is stapled in at least 3 places for support. At least 20 inches of the stack must be present from ground level as required by the standards of practice.
A silt fence always is placed on the contour of the property to catch possible soil run off, prevent erosion, and to keep unwanted soil off others' properties. This means that the silt fence is placed perpendicular to a slope and may not be installed parallel to a slope. The silt fence may be removed once erosion control measures have been established. This requires the planting of grass, plants and mulch beds, and may require extraordinary measures for severe sloped surfaces, such as retaining walls and swales. Any extraordinary measure will be marked by zoning authorities with specific instructions on where the silt fencing must be placed per federal and state guidelines.