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City of Richmond Sewer Overflow
John Blankenship, P. E.

The City of Richmond recently completed a Combined Sewer Overflow Control Program project (CSO) consisting of three phases, and encompassing both banks of the James River through the center of the city. The first three phases of the project are designed to reduce the amount of untreated sewage discharge into the James River during peak flows, and to extend the discharge points further down river below the fall line.

The City's combined system of sanitary and storm sewers has not had enough capacity to handle storage and treatments of all sewage and storm water during peak flows, typically experienced during heavy rainfalls. The EPA mandated Richmond correct the problem and the city has responded by authorizing the CSO work. The first three phases are now complete and additional phases are being engineered.

Greeley and Hanson performed the engineering design and project engineering work for the first three phases. CSO-1 and CSO-2 projects on the south side of the river were constructed by general contractor English Construction Co. Kewit Construction Co. performed the work for CSO-3, on the north side, which also included renovation and reconstruction of the historic Haxall and Kanawha Canals and a turning basin. Hanson Concrete Products, Hanover and Southside plants, furnished all conveyance pipe and manhole structures for all phases.

CSO-1 included a series of 12 36-inch outlet diffusers below the fall line on the south side. From the outlet, 5,600 feet of the 90-inch pipe proceeded along the river's south side westward. At the point, CSO-2 began with 320 feet of 84-inch pipe, 3,400 feet of 78-inch pipe paralleling the railroad and 1,460 feet of 72-inch pipe extending westward to a new 42nd Street Regulator.

The first 650 feet of 90-inch pipe was installed in the river by conventional open-cut trench method, with a cofferdam and pumps to displace the river water. The next 4,950 feet of 90-inch pipe was installed by boring a 10-foot diameter tunnel between two large access pits through the bedrock below river bottom and installing concrete pipe with a unique pipe-carrying vehicle. CSO-2 piping that runs along the railroad track was installed by standard open-cut trench method. The removal of rock in the vicinity of the railroad and existing CSO piping made for a challenging installation.

CSO-3 included a 1,300-foot section of 96-inch concrete pipe, 275 feet of 60-inch pipe, and 84-inch pipe that extended westward for 2,550 feet under the newly reconditioned Haxall Canal. Just west of the Gambles Hill Regulator is a new Headgate Structure, which regulated water flow into the canal. A 2,580 foot run of 42-inch pipe extends westward alongside the CSX Railway tracks to a new regulator. CSO-3 also included 1,110 feet of 48-inch pipe.
The 96-,84-, 48- and most of the 42-inch pipe for CSO-3 was installed by tradition open-cut trench. The run of 60-inch pipe was jacked into an 84-inch diameter tunnel liner beneath a recently constructed floodwall. A portion of the 42-inch pipe was jacked to avoid road closures and existing utilities. As with CSO-1 and CSO-2, a lot of rock was excavated to make way for the pipe.

All of the reinforced concrete pipe for CSO-1,2 and 2 sizes 42-inch to 96-inch was west cast in precision formwork in standard lay lengths ranging from 16 to 20 feet. Pipe consisted primarily of concrete joints with either one or two O-ring gaskets. A 400-foot section of the 48-inch pipe had to withstand 50psi hydrostatic pressure due to its location immediately adjacent to a 12-inch water main. The section of 48-inch was produced with steel joint rings. The two O-ring gaskets also had an air test port between the two gaskets to allow for pressure testing after installation of each section.

Other pipe with a single o-ring gasket was tested during installation with an internal ring joint tester per ASTM C1103. Testing of the joints during installation provided immediate information about the joint seal and any problems were solved before additional pipe was laid. The top quality pipe and joint testing procedure proved a great success during the final field hydrostatic testing of the pipe lines, which witnessed outstanding water tightness. With more than 50 special fittings, elbows, tees, wyes and reducers and several thousand feet of beveled pipe, the versatility of precast concrete pipe proved a big benefit to the project's success.

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