Engineer's ReplyIn 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.
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