May 31, 2007

Age of Infrastructure: The Wrong Focus

Having read articles about aging wastewater infrastructure in North America, I feel obligated to provide a rebuttal about |this phenomenon. In my work as a civil engineer, I have found a low correlation between pipe age and pipe condition. The majority of pipe failures and maintenance problems in wastewater collection systems are actually caused by defects—which have been present in the system from the day it was installed— or by damage caused by subsequent construction, poor judgment or objectionable activities adjacent to the piping.

Additionally, a wide variety of other problems lead to the deterioration of wastewater collection systems.

One example is the practice of tunneling under existing pipe to install subsequent utilities, and then failing to provide proper compaction, or flowable fill, between the two utilities. Another example involves the installation of utilities over the top of an existing pipe and crushing the existing pipe by using excessive compaction energy. A third may be poor construction techniques for lateral connections, such as the “hammer tap” method, which results in mortar and laterals protruding and obstructing main sewers.

As you can see, there is quite a variety of problems that may lead to the deterioration of wastewater collection systems. Here are a few more:

1. Breakage of existing wastewater collection piping followed by installation of a sleeve with flexible connectors at both ends as a “repair.”

2. Inspectors who fail to enforce the provisions of wastewater construc- tion contracts, such as the low- pressure air test and in-pipe inspection video.

3. Changes in pipe alignment, grade, diameter or material between man- holes. Install manholes at all loca- tions where these changes occur.

That which cannot be inspected cannot be maintained. 4. Sewer rehabilitation methods, which don’t perform as the vendor claims.

5. Use of excessive force and water pressures during cleaning, and when cutting roots.

6. Root intrusion caused by unsealed joints.

7. Hydrogen sulfide corrosion due solely to factors that should have been accounted for at the time of the original design.

8. Horizontal directional drilling through the existing piping.

9. Lack of enforcement of pretreat- ment ordinances, particularly for grease discharges.

10. Pipes laid on uneven slopes, or settlement caused by the failure to replace compressible soils under the pipe.

11. Allowing debris, rocks, gravel and grout to enter the pipes during the original or subsequent construction.

12. The installation of damaged or defective pipe or defective gaskets.

13. The installation of pipe with pulled joints or rolled/intruding gaskets.

14. Pipe laid with insufficient bedding material, or the wrong bedding material, leaving the pipe unprotected during compaction.

15. Installing the wrong type of pipe for the intended application, or a pipe too small to accommodate future flow rates.

16. Outside drops which serve to complicate the cleaning and inspection process.

This industry has wasted billions of dollars putting defective wastewater collection systems in the ground and then damaging them in the years following the construction. Sadly, this trend continues today.

Every crack has a cause. It is no coincidence that much of the damage to existing sewer pipes occurs under pavement patches that are associated with subsequent utility installation. Take a look at your own system.

While the contributions of professionals who work on aging infrastructure should be recognized, age is not the largest contributor to the problems in wastewater collection systems.

About the author

Steve Willie, PE, is project engineer with Morrissette & Associates. He can be reached by e-mail at [email protected].

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