From Pilot Scale to City Scale: Implementing a large-scale green infrastructure program in Philadelphia Introduction
Dwayne Myers, P.E., D.WRE, Water Resources Engineer, CDM Smith, Philadelphia, Pennsylvania; Mark Maimone, P.E., D.WRE, Water Resources Engineer, CDM Smith, Woodbury, New York Tiffany Ledesma Public Affairs Specialist CDM Smith Philadelphia, Pennsylvania
The Philadelphia Water Department (PWD), the cityâ€™s water, wastewater, and stormwater utility, completed a Combined Sewer Overflow (CSO) Long Term Control Plan Update in 2009, a requirement of its National Pollutant Discharge Elimination System (NPDES) permits. In 2011, that update, with some modifications, was authorized for implementation through a Consent Order and Agreement (COA) with the Pennsylvania Department of Environmental Protection. The COA defines a Water Quality Based Effluent Limit including CSO volume reduction, pollutant load reduction, and implementation of green stormwater infrastructure, aimed at compliance with water quality requirements of the Clean Water Act and National CSO Policy by the end of the 25-year implementation period. The COA has now entered its sixth year of implementation. The program represents an innovative approach to manage urban water resources effectively through a combination of traditional infrastructure and green infrastructure distributed throughout the landscape, often incorporating trees and vegetation to provide community amenities. In order for green infrastructure to make a contribution to combined sewer overflow control, it is necessary to bring a significant portion of the drainage area tributary to the sewer system under control. Prior to completion of the COA, PWD had completed a variety of site-scale pilot and demonstration projects to help build public,
institutional and political support for taking the next step to a full-scale program. The Philadelphia program has met the challenges of scaling up from an early pilot-scale green infrastructure program to a city-scale program where many program elements are needed to allow green infrastructure to play a key role in the daily operation of the urban water system.
Key Program Elements Regulatory Compliance Tracking and Reporting. As a program scales up, one challenge is the ever-increasing amount of data that must be managed. Over time, PWD has developed increasingly sophisticated information management systems for tracking and reporting activities internally and to regulatory agencies. Elements that are important to track include implementation status of projects, geographic data such as potential and actual green infrastructure locations, design and as-built properties of constructed sites, cost and monitoring data. In addition to data storage, a program of data quality management, analysis and visualization capabilities is important to take full advantage of the data that is being collected. Implementation Planning. In the pilot phase, a small number of sites were selected that minimized technical and institutional challenges of implementation. As the program increases in scale, sites that pose more challenges need to be considered. Spatial planning plays an important role early in the process of bringing the program to scale. Planning staff help to identify opportunities to implement storm-
February 2018 issue of the APWA Reporter, the official magazine of the American Public Works Association