Innovative Strategy Helps Philadelphia Manage Combined Sewer Overflows
In addition to using the standard data collection and modeling, the City of Philadelphia employs methods to establish new watershed management plans that improve water quality and enhance the city’s waterways.
The Philadelphia Water Department (PWD)—one of the oldest municipal water departments in the United States—provides water treatment and supply, wastewater collection, and biosolids recycling services to the nation’s fifth-largest city, which has a population of more than 1.4 million people. Its massive sewer network contains 1,600 mi. of combined sewers, 1,200 mi. of separate sanitary and storm sewer lines, 150 mi. of intercepting sewers, 169 combined sewer-regulating chambers, 84,600 manholes, and 75,000 stormwater inlets.
PWD retained Camp Dresser & McKee Inc. (CDM) of Cambridge, MA, to assist in implementing the city’s National Pollutant Discharge Elimination System (NPDES) combined sewer overflow (CSO) permit compliance program. During the initial phase of the program, the team conducted a combined sewer system inventory and characterization, performed a sewershed hydrologic and sewer system hydraulic characterization, documented the implementation of the nine minimum controls, and developed a long-term CSO control plan. Ongoing activities include planning-level support for the design and construction of some of the compliance plan’s 17 capital improvement projects over the next five years and a comprehensive effort to identify priority areas in the watershed and actions to further improve water quality in Philadelphia’s receiving waters.
Data Collection and Modeling Are Foundation of Program
Initial CSO permit compliance program activities included collecting technical, environmental, institutional, and economic data; performing analyses to respond to regulatory requirements; and developing sound, technically feasible, and cost-effective water-quality improvement plans. The program included a physical inventory and hydraulic characterization of the combined sewer system, the development of hydrologic and hydraulic models of the collection system, and a Geographic Information System based on the city’s sewer infrastructure. Computer-based, mathematical model simulations of rainfall-runoff and pipe-flow processes were performed to characterize the sewer system’s response to wet weather and to identify opportunities for increased capture and treatment of wet-weather flows. Analyses were also initiated to assess the water quality of the city’s tributary watersheds and to understand the effects of all discharges on receiving waters.
Innovative In-System Storage Application
|Construction of a deep tunnel conduit to be used to drain the wastewater stored in the city's main relief sewer.
|One of more than 180 combined sewer overflow points located in the city of Philadelphia.
One of the capital improvements included in the long-term CSO control plan is a unique combined sewage storage option—an inflatable rubber dam within the city’s main relief sewer—to take advantage of existing in-system storage capacity and to reduce CSO discharges to the Schuylkill River. Manufactured by tire maker Bridgestone Corporation, the rubber dam will hold back up to 4 million gal. of combined sewage until downstream interceptors can convey flows for treatment at the southwest wastewater plant. By implementing this technology, the city will achieve a 70% reduction of overflows in this area. This alternative is the best way to optimize storage capacity while minimizing costs to PWD and, in turn, to the city’s customers.
Installed near the historic Fairmount Water Works, the 13.5-ft. dam—the largest of its kind—can be inflated in 15 minutes and deflated in five minutes, allowing a quick response to a wide range of storm conditions. Inflation and deflation of the dam are determined by automated control logics, prepared for both dry and wet weather conditions, with various redundant mechanical fail-safe features intended to protect the system in the event of malfunction.
Associated with the rubber dam installation is the boring of a 700-ft. tunnel, which will connect the storage facility with a downstream combined sewer interceptor. Automated sluice gates will allow the captured combined sewage to drain to the treatment plant without compromising the existing capacity of the interceptors to serve upstream sewage transport needs.
Watershed-Based Planning for Water Quality
Another important aspect of the city’s long-term CSO control program is a watershed-based planning and management approach to identify sources of potential water-quality impairments in local water bodies and make recommendations for improvements through the development of watershed management plans.
PWD has embraced a comprehensive watershed management program that minimizes water pollution from all sources in a manner based on good science and that achieves a sensible balance between ratepayer costs and environmental benefit. Watershed management integrates the department’s wet-weather programs—combined sewer overflow and stormwater management—with a new drinking-water–source protection program. This concept also takes full advantage of myriad pollution reduction, political, and environmental goals to foster city and regional initiatives that enhance the health of the region’s waterways and the public’s perception of its environment.
Over the past 30 years, management of water quality in the area’s streams and rivers has largely focused on the control of water pollution from regulated point sources: facilities that have pipes discharging into the river. This was driven by the Clean Water Act requirements, which caused the city and others to install the best pollution treatment system available.
The most significant remaining impact to the health of streams today is from stormwater runoff, or nonpoint-source pollution. During storm events, pollutants and sediment are washed into streams and creeks from farms, backyards, streets, and construction sites. Exacerbating this problem are hydrologic impacts caused by new developments, primarily outside of the city, that increase flooding and the associated environmental harms of erosion, siltation, and channel enlargement. The resultant erosion of streambanks decreases the habitat of aquatic life essential to healthy streams.
To protect property and life from flood damage, improve water quality, and still achieve environmentally sound land development, it is now widely accepted that responsible land-use and stormwater best management practices need to be coordinated on a watershedwide basis. The comprehensive watershed management approach recognizes the various causes of pollution and seeks a fair and equitable regional solution to addressing water-pollution issues. Watershed management fosters the coordinated implementation of programs to control all sources of pollution, reduce polluted runoff, and promote managed growth while protecting the region’s drinking-water supplies and recreational activities (e.g., fishing) and preserving sensitive natural resources (e.g., parks and streams).
PWD has implemented an approach to water-quality management that seeks to reduce water pollution from all sources in a manner that is based on measurable results - be it improvements to the dissolved oxygen and fecal coliform levels of the stream, streambank restoration and the addition of riparian buffers to the adjoining park land, or a mixture of both. These obvious improvements translate into a fair and equitable distribution of the costs related to pollution abatement and achieving water-quality goals. PWD has also engaged urban and suburban communities to explore interregional cooperation based on an understanding of the impact of land use and human activities on water quality. To date, its efforts have been extraordinarily successful.
Implementing a watershed management approach is a complex task. It requires land-use planning and coordination, the resources needed to model the pollution sources in a water body, mutually agreed upon goals for the water body, a cooperative regulatory climate, city and suburban dialogue and agreement, and a consensus on a solution and the sharing of costs.
PWD has assumed a leadership role in moving the region toward operating within a "watershed context." The programs are geared to reconnect the city with its waterways, to make the streams and parks valuable community assets that will induce citizens to join in protection efforts. This is achieved by recognizing community values and the importance of environmental aesthetics. It is recognizing that rainwater is an urban asset and that the old solution of moving water downstream as quickly as possible has resulted in the degradation of hundreds of miles of urban streams. New solutions, which involve more localized "green" development, can be aesthetically pleasing, environmentally friendly, and less costly.
Tackling this challenge has been greatly facilitated by PWD’s recent creation of the Office of Watersheds. This organization is composed of staff from the PWD’s planning and research, collector systems, laboratory services, and other key function groups, allowing the office to combine resources to realize the common goal of watershed protection. The Office of Watersheds and CDM are formulating watershed management plans for Philadelphia’s receiving waters. Initial efforts include characterization of the physics and biogeochemistry of the Darby and Cobbs Creeks watershed, identification of possible causes of water-quality impairments, and suggestions for appropriate remedial measures and management practices.
A Strategic Watershed Partnership
The PWD-sponsored Darby-Cobbs Watershed Partnership, which has been in place for more than a year, is a consortium of proactive environmental groups, community groups, government and municipal agencies, residents, and other watershed stakeholders. PWD has established an active and vital watershed partnership in the Darby-Cobbs watershed with the current focus on the nontidal portions of the streams.
The Darby-Cobbs Watershed Partnership was facilitated by PWD to create a framework for all stakeholders in the 75-mi.2 watershed basin to work together to find environmentally sound ways to improve the water quality of Darby and Cobbs Creeks. Permit holders, participating agencies, and community-based organizations are constructing this framework upon regulatory and voluntary activities. To this end, the partnership itself is a public-participation forum for participating members to work together to develop a watershed strategy that not only meets state and federal regulatory requirements but also embraces the environmental/publicly sensitive approach to improving streamwater quality and quality of life in communities.
As one of the first steps in defining its framework, the partnership developed a mission statement: To improve the environmental health and safe enjoyment of the Darby-Cobbs watershed by sharing resources through cooperation of the residents and other stakeholders in the watershed.
The partnership formed a public-participation committee to ensure that the partnership identifies and recruits representatives of the diverse array of stakeholders in this basin, including municipalities. Members of the public-participation committee include representatives of the following agencies/organizations: Philadelphia Water Department, Fairmount Park Commission, US Fish and Wildlife Service, Heinz National Wildlife Refuge Center, Pennsylvania Environmental Council, Cobbs Creek Community Environmental Education Center, Delaware Creek Valley Association, PA Department of Conservation and Natural Resources, PA Department of Environmental Protection, Trail Boss Program, Delaware County Planning Commission, EPA Region III, Delaware Riverkeeper Network, Academy of Natural Sciences, Delaware River Basin Commission, and representatives of the watershed’s 31 municipalities.
During 1999, the public-participation committee developed and published a Q&A brochure titled "Darby-Cobbs Watershed Partnership" to publicize its existence, raise awareness in the community about watershed issues, and provide information on the public and private organizations currently seeking to identify and address the sources of water-quality impairment. This brochure was distributed to the various partners to disseminate in their respective communities.
The public-participation committee also formed an education subcommittee to work with learning programs in the municipal school districts and to identify existing educational resources and/or to suggest the creation of resources that currently do not exist. This subcommittee, in conjunction with the larger committee, also sought to identify "action items"—that is, concrete projects that could be completed in the near future. Following a brainstorming session, 25 potential projects were identified. The committee then voted on the various projects to create a top 10 list to tackle. These 10 projects include, in the order of their ranking of importance:
1. Produce a watershed status report based on initial technical committee reports.
2. Conduct a resident survey of issues and awareness.
3. Hold an educational symposium.
4. Develop a watershed awareness video and public service announcements.
5. Develop other educational/promotional materials.
6. Provide targeted materials and workshops for the municipal audience—perhaps something about stormwater Phase II regulations, best management practices, stormwater ordinances, and so on.
7. Develop a watershed Web site.
8. Collect or create educational materials for municipal officials regarding watershed management and tools to improve watershed stewardship.
9. Create or provide access to teacher training opportunities.
10. Facilitate service learning projects.
Project teams will be created for each of these projects in 2000.
Within the next five years, PWD plans to have completed watershed management plans for four of the five major basins, reconnecting the citizens of Philadelphia with the city’s valuable waterways.
Author's Bio: James T. Smullen, Ph.D., P.E., is vice president of Camp Dresser & McKee in Cambridge, MA.
Author's Bio: Joanne Dahme is watershed programs manager for the Philadelphia Water Department