The town of Pittsfield, Massachusetts has requested assistance regarding a failing stormwater drainage culvert.  The culvert pipe is located under Commercial Street in the east-central part of Pittsfield, just south of Massachusetts State Route 9, and runs under a section of the road to the edge of the Housatonic River.  The client has requested for a determination of the best option to rehabilitate or replace the failing 30-inch corrugated metal pipe that drains into the river.  Due to the broken and undersized nature of the pipe, sink-holes have formed in the nearby road surface, causing potential for damages to the vehicles and citizens using the street.  In addition, the existing corrugated metal pipe conflicted with an intercepting sewer line.  This conflict must be addressed and resolved in the design of the culvert rehabilitation or replacement.  Additionally, it is known that there is a stormwater detention pond upstream that holds water coming from the contributing catchment area prior to entering the section of culvert to be replaced.  This pond, located just north of the nearby railroad tracks and Route 9, played a significant role in determining an effective pipe diameter as it retains a considerable amount of water and thereby reduces the flow volume passing through the culvert. The team performed relevant calculations to determine the flow volume discharging into the Housatonic river through the culvert and concluded that the entire culvert was undersized. This led to their determination that the culvert should be replaced with a 42 inch diameter HDPE pipe based on a 5 year 24 hour storm model. Slopes of the 42 inch diameter HDPE pipe were set such that they would meet the minimum required slope of .05 ft/ft, while also maintaining sufficient clearance between the stormwater and the sewer system.