Engineer's Reply

In the article, the Rockland County Sewer District states that the overflow at the manhole on S. Monsey Road will be solved by installing an additional pipe in the siphon, and that the problem will be solved before the winter.


There is no proof that installing this pipe at this location will stop the overflows.
 
The backup and overflow may in fact be caused by an undersized section of pipe upstream or downstream of the siphon, not the siphon itself.  If this is the case, increasing the capacity of the siphon will DO NOTHING.  It is merely a perfectly timed, politically convenient "solution."
 
The sewer district does not know exactly where the system is undersized. To figure this out, they have to look at the existing flow, the pipe diameters, and at what slope the pipe was laid. This is exactly what they are planning to do. They have hired consultants to install the flow meters, look at the pipe diameters and slope (modeling) and calculate the maximum capacity of each pipe link (run between manholes). The run with he lowest calculated maximum capacity is the weak link, causing the backup.
 
Again, the weak link MAY NOT BE THE Siphon. Installing the additional pipe may do nothing to stop the overflows on S. Monsey Road. Why would they spend $ 571,600 to hire an engineering firm to install flow meters and do a study to "find out the locations, causes and solutions to the problem" if they already know that adding the pipe at the siphon will solve the problem before the winter?
 
The cited causes of the overflows by the RCSD are blockages, tree roots, rainfall, etc.  There is no mention of over development. Over development is the only politically sensitive issue, and most likely the only real reason.
 
Blockages, tree roots, rainfall etc are common problems that affect every sanitary sewer system. Not all systems, however,  are overflowing at the rates and frequency of our system. How is our system different? Because the system is already overloaded or close to overloaded from too much flow from too many people, in numbers that were not anticipated by the design engineers when the system was initially designed. The design engineers are given projected population density figures, based on allowable zoning density at the time of the design. Had they known that the zoning densities would be ignored, and that 50 people would be allowed to someday live on a lot where only 4 people in a single family house had been allowed to live, they would have made the sanitary sewers a LOT LARGER.
 
The additional flow from rainfall and interruption from temporary blockages NOW cause overflows, which would not occur if the population density was still where the design engineers anticipated. There is no mention of this in the article.
 
The system is overloaded, and the solution will be expensive, if not impossible to implement. This is the reality that no one wants to address due to the political ramifications. (Ask yourself, would you make the right decision, knowing it would end your career and livelihood ? Or would you string it out long enough until you could move away and retire in Florida, passing on the problem to someone else)
 
No increase in allowable population density in single family neighborhoods should be allowed until we get the facts and are CERTAIN that the problem is solved.
 
The study will determine this. The results of the study will become available on July 2. Why not wait until then before any decisions are made?
 

Ronald A. Glisci, P.E.