Citation:

Brown, R. A., M. BORST, H. Kazemi, J. Gray, AND L. Kurtz. Case Study: Installation and Monitoring of Green Infrastructure Stormwater Controls in Louisville, Kentucky . In Proceedings, ASCE-EWRI World Environmental and Water Resources Congress, Albuquerque, NM, May 20 - 24, 2012. American Society of Civil Engineers (ASCE), Reston, VA, #148, (2012).

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To inform the public.

Description:

In 2005, the Louisville and Jefferson County Metropolitan Sewer District (MSD) entered into a Consent Decree with the U.S. Environmental Protection Agency (EPA), Kentucky Department for Environmental Protection, and the U.S. Department of Justice. In 2009, MSD submitted the Integrated Overflow Abatement Plan (IOAP) to address combined sewer overflows (CSOs) and sanitary sewer overflows. As part of the IOAP, MSD performed a cost/benefit analysis for each overflow location to determine the highest value overflow reduction project. MSD modeled solution alternatives for CSO abatement and completed a cost/benefit analysis for each alternative. The solutions with the lowest cost for avoided overflow unit volume were implemented in the Long Term Control Plan. Many of the solutions involve large storage basins that capture and store overflows at the end of the pipe until it can be returned to the system for treatment. To reduce the size and cost of ‘gray’ solutions and increase the benefits of projects, MSD included plans to incorporate ‘green’ solutions. MSD committed to monitor the performance and effectiveness of the green infrastructure stormwater controls to assure ongoing reductions of stormwater volume entering the system. MSD will base later decisions to incorporate green infrastructure into the plans based, in part, on monitoring results of initial installations. An early set of installations is located in CSO basin #130, an 11 ha (28-acre) sewershed. EPA and the Center for Infrastructure Research at the University of Louisville are collaborating with MSD and URS Corporation to monitor the individual performance of selected green infrastructure stormwater controls and to evaluate the effectiveness of groups of controls. URS used InfoWorks, a combined sewer hydraulic model, to determine a cost-effective approach for CSO basin #130 – ‘gray,’ ‘green,’ or a combination of the two. The resulting solution to meet the regulatory targets outlined in the IOAP was an entirely ‘green’ approach – 17 permeable pavement strips (permeable articulating concrete blocks) and 29 tree boxes. The permeable pavement strips are 2.4 m (8-ft) wide, range in length from 12.2 to 36.6 m (40 to 120 ft), and will be installed in the parking lanes of roads leading to five targeted intersections. This basin has a deep water table and the underlying soils have higher permeability at depths greater than 3.7 m (12 ft), so all of the tree boxes and 11 of the permeable pavement strips will be constructed with a series of 0.46-m (18-in) diameter shafts. The remaining six permeable pavement strips will be/have been constructed with a 0.6-m (2-ft) wide trench that runs along the entire length of the control. The targeted depth of the trenches and shafts is approximately 4.6-m (15-ft) below the paver surface. Soil structural strength and infiltration rate were the site-specific factors used for determining whether to use a trench or a series of shafts. A subset of these controls (six permeable pavement strips and six tree boxes) will be instrumented with time domain reflectometers, water level sensors, thermistors, and passive capillary lysimeters (drain gauges) at various depths in the profile to evaluate the infiltration processes and the overall hydrologic performance of the individual controls. In December 2011, two permeable pavement strips with trenches were constructed, and both were instrumented with the previously described monitoring equipment. The remaining controls are scheduled to be installed in the spring of 2012. As an additional measure of hydrologic performance, surface infiltration rates for the permeable pavement strips will be measured at least quarterly and immediately before and after maintenance. The presentation of this case study will provide an overview on the design, construction, and monitoring used to evaluate these controls, and preliminary data from ongoing monitoring will be presented as available. Before installing the stormwater controls, MSD continuously measured flow rates at multiple locations within the basin, including the overflow location. They will continue to measure flow rates at these locations during and after construction. These flow results and the results of monitoring individual controls will be combined with basin-wide modeling to determine the overall effectiveness of installing green infrastructure stormwater controls to reduce CSO volume and frequency and to reduce stormwater discharge. This will assist MSD with their decision making process for incorporating green infrastructure in future projects.

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