General Design, Construction and Operation Guidelines: Constructed Wetlands Wastewater Treatment Systems for Small Users Including Individual Residences, 2nd Edition

Constructed Wetlands

for Treating Wastewater

by Gerald Steiner, P. E. and James Watson, P. E.; 42 pages, free. Tennessee Valley Authority, May 1993. TVA, 1101 Market Street, Chattanooga, TN 37402. Fax orders: 615/751-7479.

Despite its cumbersome title, this publication will prove invaluable to anyone considering a constructed wetland wastewater treatment system. TVA, better known for power production, became interested in constructed wetland wastewater treatment in the mid-80s as part of an effort to reduce pollution of the Tennessee River watershed. This is the latest in a series of publications by TVA on the topic.

Constructed wetlands provide an alternative to in-ground leach fields for septic systems. They can be an attractive option on land that does not adequately perk or when bedrock or ledge is too close to the surface, and cost may be less than pumped mound systems. While primarily used in small municipal-scale wastewater treatment systems, constructed wetlands are now also being used occasionally for small commercial buildings, schools, agricultural operations, and houses.

The publication addresses only subsurface-flow constructed wetland systems (in which all water flows below ground through an aggregate layer that supports wetland plants).  Surface flow constructed wetland systems can be more cost-effective for large systems, but their design is more complex and the potential for odors, mosquito breeding, and other problems is greater. Subsurface flow constructed wetland systems also hold more potential for northern climates.

The authors readily admit that constructed wetlands design is an evolving science. In this guide they provide their current best information based on their research since 1986. The publication walks the reader through design, construction, operation, and maintenance of constructed wetland systems. Formulas are provided that can be used by a qualified septic system engineer to size and design a constructed wetland system. In the examples described, a two-cell system for a three-bedroom house designed to treat 450 gallons per day requires a total area of 369 to 574 ft² for both cells, depending on hydraulic slope, depth, and other considerations. Cells can be long and narrow, or short and wide.

The TVA small-scale constructed wetland guidelines will not be the last word in design of these systems. And even with a good design, getting the necessary permits to construct such a system can be difficult. But this book is a valuable resource nonetheless. This and other publications on constructed wetlands can be obtained by contacting the Water Management Resources Group at TVA (address above).