More Sources for Constructed Wetlands

More Sources for Constructed Wetlands

This is with reference to the article on on-site wastewater treatment in the March/April 1994 issue of

Environmental Building News. In general, it was an excellent and comprehensive discussion of the various alternatives for on-site wastewater treatment.

My main concern is with the section of the article on constructed wetlands and specifically with the statement that the TVA [Tennessee Valley Authority] design manual is the only available set of specific guidelines. There are other sources of information, and your readers should also be aware of the limitations on the TVA design approach.

In 1993, at the request of the US EPA, I wrote a report which evaluated this constructed wetland technology, and Chapter 6 in that report covered on-site systems and included a comparative critique of the various methods for system design, including the TVA manual. In essence, the TVA approach may not be conservative in all situations since it does not include adjustment of the design for low temperature winter operation in cold climates, it does not include a design procedure for nitrogen removal, and it does not consider the actual soil characteristics in sizing the proposed disposal area or drainfield.

The TVA approach is probably sufficiently conservative if limited to single-family dwellings where nitrogen in the wastewater is not an environmental issue, and where the soils in the intended disposal area have a moderate to good permeability or percolation rate. In my opinion, the TVA approach should be used with caution in most other situations. Alternative design methods are available which do take into account all of the factors neglected by TVA.

The title of the EPA report is:

Subsurface Flow Constructed Wetlands for Wastewater Treatment—A Technology Assessment (EPA 832-R-93-008). Your readers can obtain a copy by contacting: Mr. Robert K. Bastian (WH 547), US EPA OWEC, 401 M Street SW, Washington, DC 20460 (fax: 202/260-1827).

Sherwood C. Reed, P.E.

Principal, Environmental

Engineering Consultants

Editor’s Note:Mr. Sherwood Reed, P.E., was inadvertently left out of the resource listing that accompanied our article on On-site Wastewater Treatment (EBN

Vol. 3, No. 2). He is one of the nation’s leading experts on constructed wetlands and can be reached at Environmental Engineering Consultants, RR1, Box 572, Butternut Road, Norwich, VT 05055; 802/649-1230; 802/649-5725 (fax). Our apologies for the omission.