What to Look for
This report will consider day-one defects which were built into wastewater collection systems from the very first day of construction, as well as defects and failures which were caused by subsequent damage to the system. We are concerned about the most proximate cause (or causes) of defects and failures in public infrastructure. The causes which are most-responsible for the defects and failures should get the most blame. Blaming these defects and failures on aging infrastructure only encourages the same mistakes which created the defects in the first place.
Wastewater system defects and failures get blamed on old age because that is more politically-correct… it offends fewer people. Old age is nobody’s fault. Our infrastructure was just too old… right? Let’s see.
Case #1 – The Hammer Tap
At no time during the last 50 years was it an acceptable industry-standard to construct a new sewer lateral by smashing a ragged hole in the sewer main with a hammer.
Photo 1a.- This hammer-tap sewer lateral created three more subsequent-damage defects in the sewer main on the same day.
This construction technique is known as the “hammer-tap”. It usually creates three defects at the same time: (1) It creates an obstruction in the sewer main from the “protruding lateral” which can result in pipe blockage and difficult pipe cleaning. (2) It creates structural defects (cracks) in the sewer main which can lead to collapse in later years. (3) It is not usually water-tight so it creates another location for groundwater infiltration into the pipe, or exfiltration of raw sewage into the groundwater outside the pipe.
A large percentage of the total number of defects in sewer collection systems are concentrated at the service connection wyes. There is a specific reason for every one of those cracks. Some of the defects were caused by smashing the pipe with a hammer.
Hammer-taps exist either because somebody was not watching or nobody cared. Either way, you should not blame the resulting defects on aging infrastructure.
Case #2 – The Lift Station Was Flooded
The following fact is fundamental to the design of every pump station: You must either locate the pump station where it does not flood (during the specified design event), or you must provide the pump station with protection from flooding (from the specified design event). I don’t know of any exceptions.
A pump station in the Puget Sound area of Washington State had a flooding issue. City crews were aware that during rainstorms the circuit breakers would pop open and take both 75 HP pumps offline. The “dry” side would be flooded by surface runoff up to 6.8 feet above the floor, whereas the cooling air inlets at the motors were at 6.5 feet. The wet side would then overflow raw sewage to a wetlands area. The motors and related electrical controls were getting flooded and shorted. By the time crews got onsite, the sump pump was pumping out the floodwaters on the dry side, leaving behind only the watermarks on the interior walls. The wet side would continue to discharge sewage into the wetlands until the breakers were reset.
The electrical controls were replaced, and the motors were re-built because they were unreliable due to “old age”. In fact, the entire lift station was eventually reconstructed because it was “too old”….or was it?
Photo 2a. - Lift stations do not last as long when the consultant designs them to flood. The left side is the wet well. The right side is the “dry” (equipment) side. Both sides flooded.
Photo 2b. - Note the high-water marks on the interior wall of the “dry” (equipment) side of the pump station, at a height of almost seven (7) feet above the floor.
Case #3 – Poor Compaction Technique
Piping is always part of a larger system or environment which should not be ignored. The casual observer sees a broken pipe and blames the defect on aging infrastructure. However, a more educated inspection may reveal a problem with pipe support. For buried applications, the pipes must be supported by soil and bedding material from below and on both sides. The materials and methods for creating this support, and for subsequent trench backfill are contained in written industry standards.
The type of defect shown in Photo #3 is normally caused by either the wrong pipe bedding materials or poor compaction methods on the sides of the pipe, or by subsequent construction methods. This includes the possibility that it was not the initial backfill which damaged the pipe, but possibly subsequent utility construction. Either way, the crushed pipe has nothing to do with aging infrastructure.
Photo 3. – Every crack tells a story. Learn how to read that story.
Although I was not present on that day, it is very likely that the non-conforming work which created this pipe-crushing in Photo #3 was done on day-one, and it just took a number of years to reach this condition. If you blame this type of pipe-crushing on aging infrastructure, then you should educate yourself about pipe-soil interaction.<strong>Case #4 – Lack of a Solid Pipe Foundation</strong>In Photo #4, you can tell that either the far pipe was lifted up, or the closer pipe settled. Settlement is caused by a soft foundation which has nothing to do with aging infrastructure. Some of the more likely causes are as follows: (1) the foundation was over-excavated during construction, and not correctly re-compacted (to save money); or (2) the pipe was constructed in a high groundwater condition and the soil was not properly de-watered (to save money), which caused the trench bottom to heave, then settle after pipe-laying; or (3) The pipe was tunneled-under to install a subsequent utility, and the replacement trench backfill material was not properly compacted (to save money).So which part of this offset pipe defect is caused by aging infrastructure?
Photo 4. – This was caused by a soft pipe foundation, which is a violation of industry-standard pipe construction methods, and either a day-one defect or subsequent damage in every case.
So which part of this offset pipe defect is caused by aging infrastructure?
Case #5 – Roots Are Not Aging Infrastructure
Tree roots seek moisture and nutrients. They do not magically find the pipe and plug or crush it. Instead, there must be some type of initial opening which allows for leakage from the pipe and root entry. If the pipe is too old to have sealed joints, and there are deep-rooting trees over the pipe, then part of the required sewer maintenance procedure is to cut the roots out periodically and apply a root inhibitor. If this industry-standard maintenance does not get done in a timely manner, do you blame the resulting pipe damage and blockage on aging infrastructure?
Who selected the species of trees? Are the trees on property controlled by the sewer agency? Can the trees be cut down? Can trees with shallower roots be planted in their place? Can the landowner with the trees be sued for the property damage caused by their trees, as they might be if their trees fell down and damaged someone else’s property?
Photo 5a. - Root Intrusion is not aging infrastructure.
Case #6 – Shattered by Subsequent Damage
If you see a sewer line where the only distress in the pipe is at locations where there were subsequent construction activities, then do you blame the defects on aging infrastructure? In most public agencies, the answer is yes.
Photo 6a. – Was this shattered pipe caused by aging infrastructure or subsequent construction? It was not found until years later when the sinkhole finally formed.
How is a defect like this related to aging infrastructure? The answer is simple. It is not related to aging infrastructure.
The majority of wastewater collection systems are constructed with pipes made of clay, PVC, or polyethylene. It is very unlikely that defects in these materials are caused by aging infrastructure. All of these materials will last much longer than 75 years if they were manufactured and installed correctly to begin with, and then protected after installation. Clay pipe is particularly resistant to degradation due to aging. Clay pipe was used in Ephesus, Turkey over 2000 years ago. The same pipes could be re-used today (at their original low-pressure ratings) if the pipes were cleaned out and the joints were re-sealed.
Photo 6b. - Did ancient Ephesians blame their pipe damage on old age? 2000 years later, the pipe has earned the right to retire.
When day-one defects are built into wastewater collection systems from the very first day of construction, or the wastewater collection system is subjected to subsequent damage, it is not correct to blame the resulting failures on aging infrastructure.
For a PDF of this report, click here.