URS has been working with the Louisville and Jefferson County Metropolitan Sewer District (MSD) for several years on projects involving green infrastructure (GI). The main focus of these efforts was to effectively evaluate the use of GI in accomplishing various programmatic goals which include, but are not limited to, municipal separate storm sewer systems (MS4s) applications, combined sewer overflow (CSO) applications and overall integrated planning efforts. The main component of these efforts include the evaluations of the use of specific GI in two CSO basins with the goal, which is in MSDs Consent Decree, of implementing GI as a cost-effective alternative to traditional gray storage solutions for reducing overflows.
URS developed a site selections process to identify areas of opportunity for GI that has the strongest potential of controlling the largest stormwater volume. Using the modeling platform Info Works, URS was able to estimate the effectiveness of these specific locations in controlling large amounts of stormwater. The effects of these locations were estimated and dimensions and storage volumes of the GI were determined. The selected suite of GI was then evaluated for cost and a cost curve of green vs. gray was established. URS has designed and provided construction administration services for GI for this specific project. This GI included the use of tree boxes, permeable pavers and roadside infiltration planters. This suite of GI was approximately a one-third less than traditional gray infrastructure based on a life-cycle cost analysis.
The most challenging aspect of this project is the requirement that the stormwater is to be completely eliminated from the CSO system. Infiltration was also critical to the success of this project. Since the sand layer was 20 feet deep an innovative shaft/trench was incorporated into the design to transport the stormwater to the pervious layer. Another important aspect of the project involved the U.S. EPA Office of Research and Development. The agency initiated a cooperative research and development agreement with URS to monitor and quantify the benefits of GI in the urban environment. The implemented practices are working well and URS has learned a significant amount about the application and operation and maintenance of GI in the urban environment. URS received the State of Kentucky’s “2013 Sustainability Award” for its work on this project.