Leading with Green Infrastructure in Louisville
Background
The Louisville Metropolitan Sewer District (MSD) developed an Integrated Overflow Abatement Plan (IOAP) to meet the requirements of their 2005 consent decree and 2009 amended version. MSD worked with EPA and the Kentucky Environmental and Public Protection Cabinet to determine if green infrastructure could be incorporated into the IOAP. To begin, MSD conducted a cost-benefit analysis to evaluate the cost of green infrastructure versus gray infrastructure. MSD also modeled green infrastructure practices to determine how much stormwater could be removed from the combined sewer system (CSS). The results of these analyses informed MSD's approach in the IOAP, which includes a mix of gray and green infrastructure.
The IOAP begins with green infrastructure implementation to prevent and control sewer overflows. Green infrastructure projects were prioritized so their flow reduction benefits can be monitored and quantified. MSD used this monitoring data to inform the final design and sizing of gray infrastructure. Implementing green before gray infrastructure allows MSD to install fewer gray infrastructure projects, which are typically more costly than green infrastructure.
Quantitative Results
Approximately 17 percent of the initial IOAP budget was allocated to green infrastructure, with the majority of those funds going toward projects implemented in the first six years of the plan. Green infrastructure has reduced the initial cost of gray infrastructure projects by over $40 million.
Partnerships and Financing
MSD's consent decree allowed them to develop a green infrastructure incentive program to encourage private property owners to install green infrastructure in the combined sewer system service area. The program provides one-time financial incentives for downspout disconnections and urban reforestation, as well as credits to reduce drainage service charges for property owners who maintain green infrastructure on their properties. Over 100 projects have received incentives in the combined sewer service area.