WATER QUALITY BENEFITS OF BROWNFIELD REDEVELOPMENT, INFILL DEVELOPMENT, AND OTHER SMART GROWTH STRATEGIES

How and where development occurs can impact water quality. Development patterns can change sedimentation and pollutant loadings, alter stormwater runoff rates, and impact travel patterns and associated air deposition of automobile exhaust. Some impacts of development have been studied and documented extensively. For instance, a growing body of research shows that increasing impervious cover causes a decline in water quality and biological health of streams. Conversely, other studies have demonstrated that land use measures, such as leaving a vegetated buffer along streams, can help minimize water quality impacts. These studies have positive implications because they suggest possible ways to minimize water quality impacts from development by considering where development occurs and the physical characteristics of those developments.State and local governments are increasingly recognizing the link between water quality and the location and form of development. For instance, some states, such as New York, have pursued aggressive watershed land conservation strategies in order to avoid the need for expensive drinking water treatment plants and technologies. To be successful, such strategies require a comprehensive understanding and ability to quantify the water quality impacts of both largescale and small-scale development decisions.To provide states and local governments with information needed to assess development-related water quality impacts, the U.S. Environmental Protection Agency (EPA) is conducting a study of the water quality impacts of alternative development patterns and locations. Through its Water Quality Analysis, EPA hopes to produce tools and information that state and local governments will use to: (1) help them protect water quality while planning for growth; and (2) maximize the efficiency of current and projected water infrastructure, such as waste water, stormwater, and drinking water treatment systems.To better understand differences in potential water quality impacts at the site-versus the watershed-level, two scales will be examined: the project/individual development scale and the regional scale. To do this, EPA will examine: (1) alternative build-out scenarios within a particular watershed; (2) a site-or project-specific development located in various locations, including existing built-up areas and edge areas; and (3) the potential for mitigation strategies to reduce pollutants and runoff from developments that occur within already-developed areas. Water quality indicators to be measured include total suspended solids, nitrogen, phosphorus, and volume of stormwater runoff generated.Preliminary results indicate that low-density, dispersed development located in metropolitan edge areas transforms a large area that was previously undeveloped, resulting in far more runoff. Conversely, redeveloping a centrally located brownfield site with compact, mixed uses converts a relatively small area of one form of developed land into another form of developed land, resulting in far less impact to runoff quantity and quality.Table 1 compares the runoff characteristics between the greenfield site produces approximately 2.5 times as much (150 percent more) runoff, total suspended solids, and total nitrogen, and 13 percent more total phosphorus than the brownfield site. After development, the Greenfield site produces approximately 6 times as much (500 percent more) runoff, total suspended solids, total nitrogen, and total phosphorus than the brownfield site. In other words, while the greenfield site produces more runoff and pollutant loading than the brownfield site before development (∼150 percent more), the difference is far greater after development (∼500 percent more) indicating the relative water quality benefit of brownfields redevelopmentTable 2 compares pre- and post-development runoff characteristics for the greenfield site and the brownfield site. For the greenfield site, the development increases runoff by 230 percent, total suspended solids by 130 percent, total phosphorus by 980 percent (an 11-fold increase), and total nitrogen by 240 percent. In contrast, for the brownfield site the development increases runoff by 30 percent, total suspended solids by 5 percent, total phosphorus by 98 percent (a 2-fold increase), and total nitrogen by 50 percent. In other words, the runoff characteristics are far more impacted at the greenfield site than at the brownfield site.