Quantifying the effects of residential infill redevelopment on urban stormwater quality

Abstract

The population of Denver, Colorado is expected to nearly double by 2050, raising concerns of local and regional decision makers regarding water supply and water quality. Urban redevelopment trends in the Denver metro area have been focusing on higher density development and infrastructure that support increased populations, typical of many cities undergoing similar changes. These redevelopment trends, referred to as infill redevelopment, typically include reducing the pervious lawn space and increasing impervious surface with building coverage. Urban redevelopment distinctly increases stormwater runoff quantity, but little work has been conducted on quantifying the effects on stormwater runoff quality. The focus of this project is to correlate water quality effects to urban redevelopment in order to aid data driven decision-making by local planners. In collaboration with the City of Denver, this study has been monitoring stormwater quality at three sites in a neighborhood of northwestern Denver that is undergoing rapid urban and commercial redevelopment. Each site is representative of a different stage of redevelopment, providing a redevelopment gradient. Stormwater sampling was conducted over 18 months: the first period started in May 2018 and continued through August 2019. A total of 15 wet-weather events were sampled and results indicate that phosphorous, total nitrogen, total dissolved solids, total recoverable copper and zinc concentrations are predominantly higher than previously reported values, which are currently used by local stormwater managers for water quality planning. While our goal to understand infill development impacts on water quality could not be realized, we did show that neighborhood scale sampling is likely to produce significantly different results than city-wide EMC averages. The City of Denver aims to use this locally collected data to inform new regulations associated with urban redevelopment, and potentially in the design of distributed green infrastructure or a regional stormwater treatment facility on City Parks and Recreation land near the study area. It is believed that locally focused stormwater monitoring can provide useful information for decision-making related to green infrastructure and water quality planning.