Chapter 10: Stormwater Treatment Wetland Design

10.1 INTRODUCTION

The U.S. Environmental Protection Agency includes nonpoint source pollution as one of the remaining major stressors on our nations receiving water bodies. Stormwater runoff emanating from various land uses, for example, commercial, residential, industrial, and undeveloped, can transport a myriad of particulate and dissolved materials. These can take the form of oxygen-demanding substances, nutrients, and toxic materials that can negatively impact biota residing in or relying upon aquatic systems. In addition, stormwater runoff can cause physical degradation of aquatic systems, including erosion, sedimentation, and thermal stress.

In many cases, the pollutant concentration in stormwater runoff is dependent upon buildup during antecedent dry periods and subsequent exposure to runoff during precipitation events. Often, storm events produce differing amounts of runoff that, when coupled with multiple pollutant sources, result in varying degrees of contaminated runoff. The variability in rainfall amount, duration, and pollutant concentrations presents significant challenges to the engineer whose job is to treat these waters.

Although conventional treatment technologies exist that can remove the pollutants typically found in stormwater runoff, the variability in flow volume and pollutant strength would likely require conventional structures that would not be economically justified. Even though source control is the most preferred treatment technology, there are instances where treatment of runoff will be necessary. A potential treatment alternative is the use of engineered free water surface (FWS) constructed treatment wetlands.