City of Baltimore Outfall and Outfall Relief Sewer Condition Assessment

The key objective for the condition assessment of the Outfall, Relief, and 99-inch Sewers is to provide existing condition information of the pipelines to maintain reliable wastewater flow from the City of Baltimore to the Back River Wastewater Treatment Plant (WWTP). Condition assessment data was collected to develop rehabilitation and/or replacement strategies for the three large diameter pipelines.The Outfall Sewer is a 12 × 11 - foot diameter, horseshoe shaped pipeline constructed prior to 1910 conveying wastewater flow from Baltimore City to the Back River WWTP. A 10-foot diameter circular Outfall Relief Sewer was constructed in the late 1960's adding additional capacity between the Herring Run Sewer shed to the Back River WWTP. Additionally, a large diameter circular sewer conveying wastewater flow from the Eastern Avenue Pump Station force main discharge to the Outfall Sewer was assessed. Preliminary field assessments indicated flow depths at approximately fifty percent of pipe capacity and sediment depths of up to three feet within the pipelines. Due to the flow and sediment depths within the pipelines, traditional crawler type inspection equipment could not be used so the pipeline was floated.This paper will describe the condition assessment results and the work undertaken to inspect the Outfall, Relief, and 99-inch Sewers, including descriptions of the modifications made to the inspection equipment during the approximately 46,000 linear foot assessment. The results of the modifications will be discussed in more detail as well as further modifications proposed to enhance data collection capabilities.