SSO Elimination in the Brandywine Hundred Watershed: Use of Dual Dry and Wet Weather Interceptors

New Castle County operates a separate sanitary sewer collection and transmission system in Delaware consisting of approximately 1,600 miles of gravity sewers, 200 miles of force mains, and 165 pump stations. Much of the modern interceptor system was built through the Construction Grants Program in the 1970s and 1980s. Some of this system, particularly in the Brandywine Hundred Watershed, has now failed due to hydrogen sulfide corrosion and other issues, while some has exceeded its design capacity. After extensive sewer rehabilitation, some interceptors would still have insufficient capacity for the design wet weather event and therefore need to be replaced. A Secretary's Order from Delaware's Dept. of Natural Resources and Environmental Control (DNREC) requires that these issues be resolved. This presentation describes the planning and design of a dual interceptor system to replace a failed and undersized interceptor. The smaller pipe carries the dry weather flows and the parallel larger pipe carries the design wet weather flows. The system is designed with ease of operation and maintenance as a high priority.