Major Outfall Replacement in a Highly Urbanized Setting

Sewer systems across the country are facing a similar challenge — aging infrastructure with limited funds to implement programs to repair or replace facilities on a regular, ongoing basis. What happens when the “heart” of the sewer system, an interceptor or outfall, needs to be replaced due to its condition or capacity? Generally these major pipelines are constructed in areas that may have once been undeveloped, but over the years have gradually been incorporated into the urban landscape. While its installation 50 or 100 years ago may have been an engineering marvel, replacing this same pipe today has many different challenges.The City of Greensboro, NC has ridden the weather–induced roller coaster of drought and flood just like most communities across North Carolina in the past several years. The prolonged drought of 1998–2002 caused attention to be focused on the City's water system, until heavy rains in 2003 and 2007 resulted in several sewer overflows and helped to refocus priorities on the condition of the sewer system. An area of particular concern has been the North Buffalo Creek Outfall, a 3–mile section of 36 to 48 inch gravity sewer located in the heart of the City and draining a significant portion of the system. Overflows within Latham Park, an urban oasis with bike trails, exercise stations, tennis courts, ball fields, and other recreation facilities, has generated particular concern from the public.This paper will address the myriad of challenges associated with replacing a sewer of this type in a highly urbanized setting. The entire process, from preliminary design to final construction, took approximately five years, and was completed in 2008. The sewer was not only replaced, but was upsized to 60 inch diameter to account for significant growth experienced in portions of the drainage basin. In addition to reviewing the project's design issues and public involvement efforts, we will also return to the site to show how the improvements have now been incorporated into the landscape since the completion of construction.The route of the sewer posed potential impacts to a number of diverse and environmentally sensitive areas, including a high profile City park, a historically significant textile mill structure in a redevelopment area, a bird sanctuary area operated by the Audubon Society, a large hospital, an industry under bankruptcy protection having control over a significant portion of the route, and abandoned Norfolk Southern Railroad spur lines. The route also crossed five high volume NCDOT roadways which required a significant amount of coordination to ensure uninterrupted traffic flow.Soil conditions impacted the design and construction of the sewer in a number of locations. Most notably, the new sewer passed through rock within 10 feet of a historical textile mill, requiring special blasting patterns and monitoring equipment, both inside and outside the facility. The sewer also was bored under a creek and large flood berm adjacent to the WWTP, requiring a modified approach to protect against creek water entering the excavation area.Public input and involvement was crucial to overall project success. An area of particular concern was Latham Park, which included a stream restoration component to take advantage of the sewer construction adjacent to an impaired stream. By combining input from various City departments and the public, a coordinated plan was developed to incorporate the new sewer and stormwater BMP's into the park landscape, resulting in a valuable asset for all concerned.The North Buffalo Creek Sewer Replacement project showcases the various difficulties and opportunities facing a community when having to replace a larger portion of its underground infrastructure within the confines of an urban setting. Careful planning, public involvement, and a vision for the future all contributed to making this a successful project, and the lessons learned here could certainly benefit other communities facing similar challenges.