Challenging Aspects of Deep Tunnel Construction in Petersburg Granite
Abstract:The City of Richmond, Virginia is located at the head of tide on the James River and has a wastewater collection system comprised of separate and combined sewers. The area of the City served by combined sewers comprises about 12,000 acres, or about 32 percent of the City. During dry weather, sanitary wastes collected in the combined sewer system (CSS) are conveyed to the wastewater treatment plant (WWTP). During periods of rainfall, the capacity of a combined sewer is often exceeded and the excess flow is discharged directly to the James River or tributary waters. Combined Sewer Overflow (CSO) 4 (Hampton Street) and CSO 5 (McCloy Street) are two (out of 32 listed) combined sewer outfalls located on the northside of the James River.
Over thirty alternatives, using a variety of control technologies, were developed to address CSOs in the City. For CSOs No. 4 and 5, the City evaluated twenty-four of these alternatives and narrowed the options to conveyance pipelines to the WWTP or a retention storage structure. In order to minimize the disruption to the riverfront environment, a deep tunnel retention structure was selected.
The tunnel depth and alignment were chosen such that the entire 5,900 linear foot tunnel would be in Petersburg Granite. When completed, the concrete lined retention tunnel will have less than 40 gpm of infiltration and a storage capacity of nearly 7 million gallons of CSO wastewater. This project will resolve a major CSO environmental concern and improve the water quality of the James River.
Document Type: Research Article
Publication date: January 1, 2002
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