City of Richmond
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.
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
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
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.