STORMWATER QUALITY RELATED TO INFILL REDEVELOPMENT IN DENVER: RESULTS OF STORM SEWER MONITORING

The population of Denver Colorado is expected to nearly double by 2050, and thus policy makers and citizens are highly concerned about water supply for this western arid city. “Infill Redevelopment” will accommodate many of the additional people and infrastructure. With Infill, parcels that were formerly comprised of single-family homes with significant lawn space, are redeveloped with up to 100% impervious area (mostly building cover). Infil development clearly increases stormwater runoff, but the impacts on water quality (in the stormwater runoff) are unclear. We are working with the City and County of Denver to monitor urban stormwater in storms ewers in the Berkeley neighborhood of west Denver, an area that is experiencing heavy infil development. The sampling locations are in areas with different stages of infill development. Results show water quality impacts from bacteria, phosphorus, and metals, with the most highly developed area showing water quality differences for some pollutants but not others. This study also provides information on pollutant loads for different sizes and stages of storms. For example, pollutants generally experience peak concentrations at different times (first flush versus later in the storm). The City of Denver aims to use these results to inform new regulations associated with infill development (e.g., what percentage of the parcel must be comprised of infiltrative stormwater green infrastructure (GI) and what type of GI), and in the design of a potential regional stormwater treatment facility on Ciry Parks and Rec land in the Berkeley neighborhood. The decision-making implications of the research results will also be discussed.