Column from the Door County Environmental Council



Through the years, there has been much confusion about the design and the merits of created wetlands, a relatively new technology for possible use in Wisconsin. This confusion is due in part because there is a significant difference between homeowner wetland systems and wetland systems used by progressive municipalities.

This story will attempt to address only created (engineered) wetland systems for use by individual and grouped homeowners to replace outdated or failed systems presently in place. Wisconsin now allows use of these wetland systems for homeowners, on a site-specific basis, which means much preliminary work needs to be done to gain approval to utilize this technology.

To visualize how a homeowner created wetland system is constructed and to learn about its operation, we will need to begin with a conventional septic tank that has been approved for continued or new use. The effluent, that normally would exit the septic tank into a drainage field, is piped (under a controlled flow) to a newly constructed wetland cell that is engineered to allow large native plants to grow on the surface. These surface plants will have roots extending downward to absorb the nutrients and moisture from the effluent as it slowly migrates through the wetland cell. If the cell is designed large enough there will be very little water leaving at the far end of the cell(s).

The “cell” is constructed in any reasonable configuration; square, rectangle or long/narrow and is sized to accommodate the household being served. The “cell’ begins as an excavated level area with a 0.5 percent slope toward the exit end and with a berm around the perimeter. The depth usually will be about 24” depending on volume needed and the amount of soil that can be excavated. The berm can be utilized to establish the necessary depth.

The size of the created wetland will vary with the size of the home; however, the suggested size of the cell for an average home is 2,000 square feet, and almost any configuration is possible. This is then lined with an impervious liner (permanent and sealed) to prevent leakage. With the entrance and exit piping in place, the cell is then filled with pea-sized gravel to a depth of 18”.

This is then covered with a pervious covering to allow plant root penetration, with another layer of topsoil placed on top to support the plant growth. The entire cell (now at or above ground level) is planted with non-invasive high nutrient-consumption plants that are maintained for the life of the cell.

These plants establish root systems down into the pea gravel layer and utilize the nutrients and liquid from the effluent. There will be no discharge to the surface and you would be able to properly maintain the vegetative cover and remove the weed growth that may occur.

At the far end of the “cell” an effluent control device monitors any outflow that may occur and directs it to either be recycled to the “cell” or to an approved discharge area.

In Wisconsin a DNR Pollution Discharge Evaluation Study (PDES) is not required unless the system discharges more than 12,000 gallons daily. The average home would probably discharge less than 10 percent of that amount to the wetland.

If the wetland is properly sized there should be very little discharge occurring, as the wetland plants will absorb the moisture and nutrients. Any discharge will have to be utilized in a dispersal field or additional wetland structure or into a natural wetland area or returned to the cell itself.

A question often asked is will these systems function in wintertime when the plants are dormant, or will they freeze enough to stop the process? The plants are dormant above ground and the capacity of the cell should be such that it will accommodate needed discharge volume over winter with minimal exit liquid.

The plants have considerable above-ground volume. When combined with the continual bacterial action going on in the cell, there should be no freezing problems. The necessary piping is underground at the same depth as other conventional systems, such as mounds and traditional seepage fields.

The Door County Environmental Council (DCEC) has been involved in examining these systems for six years, with field trips to the existing wastewater facility at Riveredge Nature Center near West Bend (Newburg) and in discussion with the proponents at the Kettle Moraine Lutheran School, where there is a recycling closed system in place.

Crossroads at Big Creek has a segment of the demonstration project, which was engineered by Baudhuin Inc. of Sturgeon Bay, functioning as a small, created wetland.

A properly created wetland system would be a very cost-effective way for a neighborhood of failed system owners to solve their wastewater problems. By working together in a cooperative manner to find a suitable location for a large-enough created wetland, they could meet all of their wastewater needs into the future with minimal impact on the local environment.

These new engineered pseudo-wetland systems are especially adaptable to locations where the soil is shallow (preventing a conventional drainage field), where soil types do not permit adequate seepage, in limited lot sizes and locations, for poorly drained locations, or saturated areas from a previously overloaded or failed drainage field. They make a lot of sense!

For more information on created weltand systems contact DCEC at 920.743.6003 or [email protected].