Before the Excavator Moves, Have an Erosion Control Plan

Onsite system installers face greater scrutiny where sediment can have an environmental impact on sensitive wetlands

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In the last decade or two there has been an increased interest and focus on erosion and sediment control on construction sites by permitting authorities. This has meant additional requirements for installers. These measures are important to prevent soil from washing into our lakes and streams. Keeping soil from washing into the surface water also reduces nutrient delivery. Halting the threat of phosphorus and other contaminants helps reduce lake algal blooms. 

As a part of the permitting process, installers are often required to prepare a stormwater pollution prevention plan. Sensitive areas to be protected should be identified. Sensitive areas are often lakes, streams, wetlands or ditches. Other sensitive areas need protection from runoff and sediment accumulation, such as areas with endangered or protected vegetation. In our area an example of a protected plant would be lady slippers. In a place like Arizona there are certain cactus species that need to be protected. 

Work with local planning and zoning officials to identify all potential areas that need protection. Having the plan in place and approved ahead of time will eliminate a lot of headaches later, like having to stop in the middle of an installation to address erosion and runoff concerns. The best way to prevent soil from moving off site is by keeping the disturbed area as small as possible and shortening the duration of time these areas are open to erosion. Including the sequence of installation as a part of the erosion plan can stop a problem before it becomes one.

Given the area usually involved with installation of an onsite sewage treatment system is not that large, this involves installing a silt fence to stop erosion and leaving it there until vegetation is established after the project is complete. We thought it would be good to review how to properly install a silt fence.

Look at the terrain

Just like many other parts of installing a good septic system, plan for properly locating the silt fence. First choose the appropriate place to set up a silt fence by considering site terrain and slope, water flow and projected soil disturbance during installation. Set the silt fence perpendicular to the slope of the land, curving the fence inward toward slope. It should be placed at the bottom of the slope to intercept runoff before it reaches the area to be protected. It should be spaced away from the toe-of-slope, leaving enough room to accumulate sediment. 

In the location dig a 6- to 8-inch-deep trench (either V shaped or flat-bottomed) directly up-slope or upstream of the silt fence. On the downstream edge, drive in wood stakes, rebar or steel stakes at least 1 foot into the sediment. The stakes or rebar should be long enough to accommodate the trench depth and height of the silt fence fabric. Run a continuous length of fabric along the inside of the stakes and into the trench. The fabric should extend 2 to 3 feet above the soil surface. Secure the fabric to the stakes with nails, staples or zip ties allowing at least 1 foot at to line the trench. The trench should be backfilled with soil or rock. This keeps the fabric in place when water and sediment run from upslope.

A common problem we have seen with silt fence is that the trench was not part of the installation process. The fabric is attached to the stakes, but the fabric only extends to the soil surface. This makes the fence less effective at capturing sediment and a large amount escapes past the fence.

At each end of the fence, the fabric should be wrapped uphill so the water and sediment cannot just collect behind the fence and then run around the ends, defeating the purpose of the fencing. Use a continuous piece of fabric whenever possible, avoiding having a seam which could become a point of failure. If a joint is necessary, overlap the fabric at least the width of one stake spacing and secure in place using another stake. 

A watchful eye

Merely installing the fence is not enough. It needs to be maintained during the installation and until the disturbed area has vegetation established and the site is stabilized. The fence should be periodically checked for damage to the fabric or for failure to withhold sediment. Fix or install additional backup silt fence if needed.

Sediment should be removed before it reaches one-third the height of the silt fence. It is especially important to inspect the fence to make sure it is doing its job. Very often we have seen cases where the fence has had sediment behind it but since the fence was not maintained it has allowed sediment to move beyond the fence. When the fence is no longer needed, it should be removed so it is not an eyesore for the homeowner. 


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