CONSTRUCTABILITY OF LARGE CSO PIPELINES IN URBAN RICHMOND, VIRGINIA

The City of Richmond has 12,000 acres (about 30% of the City's total area) served by combined sewers. The new CSO conveyance systems collect the overflows. The new CSO flow regulators are designed to capture wet weather flow and divert the flow to the new CSO Conveyance System.CSO Project No. 1 comprises 5,500 linear feet of 90-inch low-head pressure concrete pipeline along the south bank of the James River. A nominal eleven-foot diameter tunnel was used in lieu of open cut to install the conveyance pipeline.CSO Project No. 2 comprises 5,500 linear feet of low-head pressure concrete pipeline contiguous with CSO Project No. 1. The pipeline was constructed using the open cut method incorporating blasting to remove rock. The pipeline diameters vary from 72-inch to 84-inch. Regulators were constructed at four locations.CSO Project No. 3 comprises 7,000 linear feet of 42-inch to 96-inch low-head concrete pipeline on the north side of the James River. The pipeline connects five new CSO regulators to the existing Shockoe Retention Basin. CSO Project No. 3 was combined with the Richmond Riverfront Development Project for the recreation of a historic canal through downtown Richmond.Overflows to the James River have decreased by about 40 percent. The actual WWTP performance relative to effluent suspended solids and CBOD5 is well below the permit allowance.