Guest Comment
By Gerry Beamer*
Low bids seen as a factor in sewer
Ihave instal ed sewer systems through
system faiiure
out British Columbia and Alberta for
the past 30 years and believe that there
I
are serious cost and environmental
problems being built into some sewers in stalled today. Many manhole structures will fail and leak well before the end of their
expected design life. There are three critical areas of weak ness built into some manhole structures:
1. The manhole benching and channelling. 2. The joint between manhole riser sections. 3. The manhole pipe connections. In my experience a common cause of early failures, occurring and re-occurring at these critical points, is the use of normal Portland cement mortar as a sealing and fin ishing compound. Normal portland cement mortar does not stand up in some adverse atmospheres or to
'Inter-Resource Consulting
Announcement
tt'j
Weeping riser joint. dynamic loading. The result Is fast deterio ration from chemical attack, hydrogen sul phide and hydraulic action, wearing away
design and available materials include nu merous types of adhesive and mastic seal ing compounds,epoxy applications and lin
of the "buttered-on" on mortar finish. This
ers.
can be accelerated by traffic forces trans mitted throughout the entire structure caus ing cracking and loss of the cold jointed mortar finish. A common argument oppos ing this observation has been that a man hole is a static structure; anyone who be
The best solution I have seen is a rigid plastic liner mechanically bonded to the
lieves this should be in a manhole when a
y Dr. K.L.(Keith) Murphy, P.Eng.
Dr. John Bell is pleased to announce that Dr. Keith Murphy is joining Enviromega Ltd.'s pro fessional staff as Senior Process Engineer. As Professor of Environmental Systems Engineer ing at McMaster University, from which he is currently on leave, Keith is renowned for his research on advanced water and wastewater
treatment. He was also a Principal with Beak Consultants Ltd. for twelve years. Keith will enhance Enviromega's commitment to excel lence in optimization of wastewater treatment design and operation. Keith's wealth of experience ranges from process design to assessment of environmen tal impacts. Past consulting assignments have included the World Bank, municipalities, con sultants, and legal firms. He has appeared as an expert witness at public meetings and en vironmental hearings. Enviromega, a process engineering firm in Hamilton, ON, can provide thorough analysis of an industrial or municipal treatment facility or in-depth analysis of specific unit processes using procedures such as Comprehensive Per formance Evaluations (CPEs) and process au
60 ton 7 axle truck goes by at 60 kmh. The use of normal portland cement mor tar has been recognized as an inadequate method for sealing manhole structures in many other countries and areas. This has been confirmed by the US Environmental Protection Agency who have been conduct ing studies on infrastructure systems for the past twenty years. Yet, this is still speci fied in the Master Municipal Specifications in much of Canada.
Many years ago, manufacturers of precast manhole barrels started producing manhole riser sections with jointing surfaces for gasket systems. But the specifying au thorities continue to require mortar at the joints, so little use has been made of this technology. Eroded and corroded channelling,joints and connections resulting from cracked and damaged cold joint mortaring increase tur bulence, compounding any hydrogen sul phide activity, and significantly contribute to the infiltration of groundwater into the sanitary system. The results are expensive treatment plant costs coupled with on-go ing repair and maintenance costs that must be absorbed by the taxpayers. This is a direct result of the low-bid pro curement process that drives the contractor to cut costs in both labour and materials and
dits.
M
ENVIRQ.MEGA
some Master Municipal Specifications that allow this ancient practice to continue. Modem technological advances in both
14
concrete base that assures smooth flow with
flexible pipe connections. This system al lows manhole bases to be built with a con
tinuous one piece wetted surface that is impervious to aggressive sewer chemicals abrasion and corrosive attack. The mechani
cal bond and rigidity also enhance the strength of the structure, an important con sideration in areas of earthquake potential. It is warranted for more than twice the de
sign life of the existing structures. The costs of treating excessive infiltra tion water in the sewer system and endless rehabilitation costs are being studied by many professionals. Millions of dollars are being spent on enlarging sewage treatment plants to handle the flows. Yet we are still installing manholes on some systems to a 19th century specification. The environmental damage of lowered water tables and raw sewage entering the ecosystem is incalculable. The cost to cor rect this will have to be faced at some point soon. Procurement practices must begin to review system-wide life cycle costing to obtain the 'best value', not the cheapest al ternative.
Engineers should insist on the proven, longer-lasting and more efficient technolo gies being incorporated into new systems. Normal portland cement mortar should be disallowed in the makeup of sewer systems. There has surely been enough time and money spent on studies. Now is the time for some basic common sense to be applied to implement a solution to this serious prob lem.
For more information,
Circle reply card No. 149
Environnienlal Science & Engineering, November 1994