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Low Impact Development (LID) is gaining popularity in some development communities, but it can be challenging to incorporate LID into redevelopment projects within fully built-out cities. Designers must work within the confines of the existing roadways, water lines, sewer lines and other physical infrastructure systems. However the greatest challenge often lies within the city's bureaucratic infrastructure, which can be skeptical of new development techniques and unwilling to deviate from the perceived norm. Additionally, older cities that are not facing great development pressures often have outdated codes and standards that make it difficult to implement some of the basic tenets of Low Impact Development. This paper will present a case study and valuable lessons learned while incorporating LID into a 20-acre public housing redevelopment project within a combined sewer section of Philadelphia.

In 2001, the Philadelphia Housing Authority (PHA) was awarded a 35 million HOPE VI grant from the U.S. Department of Housing and Urban Development to demolish and rebuild the Mill Creek housing development and invest in the surrounding areas. In the grant application, PHA committed to working with the Philadelphia Water Department (PWD) to create an innovative storm water management design that called for 100% on-site management of storm water runoff from the development. This demonstrated a significant departure from the typical redevelopment approach in the older sections of Philadelphia, in which housing infrastructure and street inlets are connected to the existing combined sewer system.

The initial design for the development included LID techniques, such as vegetated swales, disconnected roof leaders, and biofiltration of stormwater. However, as design concepts were more clearly developed, PHA became concerned about site maintenance and liability issues that it perceived would result from accepting the LID concepts. The Philadelphia City Planning Commission and some units within the Water Department also expressed skepticism about many of the proposed LID elements. Furthermore, much of what was proposed was in direct conflict with City codes.

As a result, most of the innovative “softscape” design features were replaced with more traditional infrastructure. For instance, instead of using vegetated swales to convey runoff to a detention/infiltration area, the parties involved opted to construct two dedicated stormwater lines. Also, all detention and infiltration of site runoff occurs underground and is not visible to community residents. Therefore, at the surface, very little separates this development from other past developments.

However, by introducing the concepts of LID throughout City agencies, PWD can still claim great success. In fact, several personnel are now ardent supporters of LID and now advocate on PWD's behalf. Despite the challenges along the way, the ultimate goal was realized: the final design separates a sizable proportion of the site runoff from the existing combined sewer system and manages it in an underground detention/infiltration structure. Given that this development is located in a combined sewer area seriously plagued by overflows, the agreed upon approach provides a good demonstration of redevelopment that fulfills the tenets of the City's Combined Sewer Overflow Long Term Control Plan. Furthermore, the “hybrid” combined sewer/separate storm sewer system provides an innovative and economical balance between total sewer separation and reuse of existing combined sewers. Finally, the design process and the development that resulted lay the groundwork for more innovation in the future.
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Document Type: Research Article

Publication date: 01 January 2004

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