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May 2017

TSX-V:CLI


How the ClearConvey® sewer ends infiltration/inflow
and the costs of coping with them.


Why are new sewers suffering from unacceptable infiltration and inflow (I/I)?

It’s a widespread problem that causes many communities to run out of conveyance and treatment capacity faster than expected, endure many operational, environmental and social challenges—and it only gets worse over time.  Uncontrolled I/I can lead to many problems such as sewer backups and the need to treat higher volumes wastewater that is more costly to treat since it has become diluted.(1)

Conventional sewers are often installed incorrectly, so clean groundwater infiltration and stormwater inflow to sanitary sewers occur at the outset. These sewers can also experience broken joints, sags and deformations that initiate or exacerbate infiltration. Large volumes of above-ground water can also enter the sewer through leaky maintenance covers, or accidental and illegal stormwater connections. 

I/I can be extremely costly, adding significantly to operational budget for the collection system and at the treatment plant. One estimate suggests that I/I of only 1 litre/second can add as much as $50,000 in annual treatment costs for a municipal plant (2)—a significant expense to treat clean water! 

This rate of I/I (1 L/s) can be generated from only 3 km of regular sanitary sewer during wet weather—and a typical small town of 5,000 people can have over 30 km of sewers!  As I/I worsens over time, it can cause a treatment plant to reach its rated flow capacity earlier than planned, which then limits community growth and may result in unnecessary and avoidable plant expansion to handle the increased volume of clean I/I water into the wastewater system. 

How to solve the I/I problem? 

Unfortunately, regulators accept I/I in sewer systems and even make provisions for it in design standards. With limited inspection resources, regulators rely on voluntary compliance with construction standards and best practices that are difficult to check from testing submissions (ie. CCTV inspection) before final acceptance of the work. 

For example, the Ontario Design Guidelines for Sewage Works says, “When designing a sanitary sewer system, an allowance should be made for the leakage of groundwater into the sewers and building sewer connections (infiltration) and for other extraneous water entering the sewers from sources such as manhole covers (inflow).” 

Even new subdivisions employing the latest conventional sewer technologies are experiencing unacceptable base flow and unacceptable wet weather response, according to a research paper, Death by a Thousand Cuts; Why are New Subdivisions Contributing Significant I/I to our Sewer Systems? The paper was presented at the recent 2017 Water Environment Association of Ontario Technical Symposium, by the authors Barbara Robinson, Norton Engineering and Chris Smith, Peel Region.

Figure 1

 Figure 1 shows unacceptable wet weather response in a new sewer as I/I brings significant additional water volume into the sewer and to the wastewater plant, thereby reducing treatment capacity (3). 

It doesn’t have to be this way. 

The Clearford One® ClearConvey® sewer is made of flexible HDPE and incorporates fused joints, which eliminate I/I and associated problems such as increased base flows, wet weather peak flows, sanitary sewer overflows and overloading at the treatment facility. 

Each joint in the ClearConvey sewer is thermally fused to seal the HDPE pipe and make it the strongest point in the sewer line. Gasketed joints in conventional concrete or plastic pipes are much more likely to fail and leak because of field conditions and poor construction practices. But the sealed ClearConvey sewer, combined with the flexibility and durability of HDPE, makes the Clearford One® system much more resilient and resistant to ground movement.

As a result, the ClearConvey sewer has a rated lifespan of 90 years and won’t be susceptible to I/I. And just as the sealed pipe network keeps I/I out, it also keeps wastewater in the pipes so soils and groundwater are not contaminated by exfiltration. 

Once the ClearConvey sewer is installed, Clearford quality standards require a pressure test and visual check of each joint to ensure proper installation and perfect seals. This testing applies not only to the sewer main, but also the laterals at each residential connection. This level of rigor is above and beyond typical tests by municipalities. 

Fewer maintenance holes = reduced I/I 

In addition to fused joints, ClearConvey sewers offer other inherent advantages over conventional sewers. ClearConvey uses small sealed access points instead of large concrete maintenance holes for access to the buried sewer network. Whereas conventional maintenance holes can crack and separate over time leading to excessive inflow and infiltration, the sealed ClearConvey system access points keep water out. 



Furthermore, ClearConvey sewers are installed at significantly lower slopes than conventional sewers, which reduces the number of pumping stations needed to transport wastewater. Pumping stations, like conventional maintenance holes, can contribute significant I/I to the sewer system during wet weather conditions. 

Figure 3

Figure 3. Flow data from a pumping station that is part of a ClearConvey sewer system in Ontario.
Even after significant rainfall, no increase in average daily flow was observed at the pumping station, which confirms that ClearConvey sewer is not experiencing I/I. Note: Higher flows at “Tanks Pumped” notation are caused by normal maintenance activities.     

The low slope of the sewer can be achieved because each Clearford One system starts by separating wastewater solids at the source in the ClearDigest® smart digester. This underground component removes up to 75% of the solids and as much as 60% of organic material in the wastewater. As a result, the ClearConvey sewer can be sized significantly smaller than a conventional sewer and can maintain cleansing velocity with lower slope. 

An additional benefit of ClearConvey is the ability to continue operating efficiently even as communities implement water-saving initiatives and further reduce wastewater flows. By removing solids in ClearDigest, ClearConvey sewers transport only the liquid portion of wastewater and will have no trouble conveying lower volumes of water. 

In fact, Clearford One® systems in India operate with flow rates less than 70 litres/person/day (less than a third of typical flow in Ontario). However, conventional sewers that are designed to flush solids using a high volume of wastewater would face challenges (sewer blockages) under these water-conserving conditions. 

Reduced I/I means smaller, longer-lasting treatment plants

Eliminating I/I to the sewer system means that treatment plants don’t have to be oversized to accommodate the additional flow. As a result, a ClearRecover® treatment plant can be 25% smaller than one servicing a conventional sewer system. 

This is a stark contrast to treatment plants served by conventional sewers, which are typically sized to handle at least an additional 90 litres/person/day just to accommodate inflow and infiltration.
The ClearDigest tank further eases the load to the treatment plant by modulating peaks and reducing the need for messy solids handling at the plant.
In most cases, a ClearRecover plant can be built without any headworks at all. 

Read more about the range of compact and efficient wastewater treatment options for the Clearford One system. 

Pay for Performance (P4P®) enables any community to eliminate I/I
from its wastewater system


In many cases, municipalities can take advantage of Clearford’s Pay-for-Performance (P4P) financing program, which provides new, highly efficient wastewater infrastructure without taking on decades of debt or risky construction and performance promises.
The P4P model enables municipalities to pay only for results through a monthly fee for each connection to the Clearford One system, which covers all aspects of the system including construction, operation and maintenance. 

Learn more about the operational advantages of the Clearford One system and the sealed, ClearConvey sewer.

Contact us to discuss the ClearConvey sewer for your new development or to learn how a ClearConvey sewer can replace aging infrastructure in your community. 
 




Clearford is grateful to Norton Engineering Inc for the information and charts referenced in this article. 
Learn more about Norton Engineering at www.nortonengineeringinc.ca/.
 

References 
1.    Kesik, T., Institute for Catastrophic Loss Reduction; (2015), Best practices guide: Management of inflow and infiltration in new urban developments
2, 3    Robinson, B., Norton Engineering; Smith, C., Peel Region, (2015), Death by a Thousand Cuts; Why are New Subdivisions Contributing Significant I/I to our Sewer Systems? 


 

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