Rehabilitation of Wastewater Collection and Water Distribution ...

congested or sensitive settings. Such work requirements may include payment for traffic lanes occupied
(i.e., A+B bidding method [Gilchrist and Allouche, 2005]), restrictions on work hours, noise barriers,
plating of excavations for traffic flow during peak periods, remote storage of excavated materials,
reimbursement for business loss and damage to adjacent utilities. The awareness of the issues and the
adjustment of working practices have had a significant impact in the wastewater sector where the typical
positioning of mainline services (large diameter, deep, and in the center of streets) makes their
replacement an operation involving major disturbance and cost. In the water sector, distribution pipes are
typically of smaller diameter, shallower and may be at the edge of or behind roadway curbs. But
technical difficulties arise in providing a pressure-tight rehabilitation system including the connections of
the relined mains to the service lines. This has traditionally required open-cut excavation at connections,
which negates some of the benefit of trenchless rehabilitation technologies and has kept the penetration of
water main rehabilitation approaches slower than that for sewers.
Selection of trenchless rehabilitation approaches involves a screening process followed by a more detailed
evaluation of the technologies. It is generally easy to exclude some technologies as evidently not suitable
for a particular application. The remaining technologies may be generally suitable but have different cost,
risk, setup area requirements, life cycle performance, compatible materials and environmental impacts. A
new element in these considerations is how “green” a product or process is. For example, many
trenchless methods have a much lower carbon footprint than open-cut repairs. Evaluation of technology
differences in a rational and impartial manner is a persistent but important challenge. Specifying a single
technology in request for proposals may have a negative impact on the competitiveness of bids received
for the use of that technology. Ideally, a level playing field is created when bidders can propose one of
several suitable technologies, so that a fair competition is created with similar performance characteristics
specified for each technology.
2.4 Special Applications
There is a wide range of rehabilitation needs within water distribution and sewer collection systems.
These needs include rehabilitation of various types of gravity and pressure piping systems and
rehabilitation of a wide variety of ancillary structures such as manholes, valve chambers, pumps and lift
stations. The most common situations are well provided for in terms of technologies, materials, and
design approaches – with some room for improvement in QA/QC approaches. However, certain special
application conditions are not well provided for, either in terms of suitable materials or design and
QA/QC approaches. Two particular areas are described below as examples of this issue.
2.4.1 Elevated Temperature Liner Service Conditions. The City of New York has extremely
congested utility conditions beneath its streets and the range of installed utilities includes steam lines,
often running in close proximity to sewer lines. Rehabilitation of the sewer lines is urgently needed; but
as a deeply-placed utility, open-cut access from the surface is prohibitive in terms of cost and impact on
traffic. Trenchless rehabilitation of the sewer lines is a very desirable option, but a complicating factor is
that the steam lines have condensate traps, leaks and venting systems that discharge condensate and/or
steam (~220 °F) into the sewers. The high temperature provides a very challenging environment that
cannot be met by the current thermoplastic or thermosetting lining materials available in the marketplace.
In addition, the temperature differential between the head section of the pipe (which is filled with steam at
220 °F) and the invert of the pipe (covered with water at 40 °F) results in differential strain and unique
loading mechanisms (i.e., limit states) not encountered in common applications. Currently, a search for
suitable materials and their testing to confirm applicability under the anticipated service conditions is
being funded jointly by the City of New York and Consolidated Edison Company of New York (Allouche
et al., 2009). It is worth mentioning that this problem is common to some older cities in the U.S. that
operate similar thermal energy systems including Boston, Philadelphia, Harrisburg, Milwaukee, and
Seattle. In addition to solving this particular class of problems, the research will open a range of new
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