Sampling, Cleaning and Disposal of Accumulated Debris in the Shockoe CSO Retention Basin

The Shockoe Combined Sewer Retention Basin was placed into service in the mid-1980s to capture the first flush combined sewer flow during wet weather events. The facility design provided an air and water system to maintain captured solids in suspension until the basin could be dewatered. Operation of this system proved ineffective in controlling the accumulation of debris. Over the years, approximately 38,000 cubic meters (50,000 cubic yards) of sand, gravel and other debris were deposited in the basin. In late 2008, the basin was taken out of service to facilitate the construction of an access ramp to the Shockoe Retention Bain floor and subsequently to remove the accumulated debris. This paper will discuss the methods employed to sample the waste in the basin and the results of the laboratory testing, to estimate of the quantity of accumulated waste to be disposed, and to develop alternatives and procedures for contracting the cleaning of the basin and the disposal of the waste.