We just designed a sewer force main connecting three lift stations.  The first station has an 8" PVC FM that discharges to a gravity manhole and into the second lift station.  The length is 3180 feet.  The second station has a 14" PVC FM that extends 9087 feet to the third lift station.

The force mains and lift stations are currently under construction.  Out of the blue in the midst of construction, the sewer agency asked us to provide evidence that "surge forces" will not be a problem in the force mains.  This is the first time we have had an agency request this data.

Has anyone else had to deal with "surge forces" and what kind of data must we produce to satisfy the agency.  I understand that surge forces are due to sudden changes in pressure due to starting and/or stopping pumps or power failures.  Once determined, are there such things as "surge relief valves" to address the forces? 

I would disagree that checking a force main design for surge is an extra.  A 9,000 feet long force main is quite long and one could expect that water hammer may be an issue.  This is something that should have been considered in the original design.  I wouldn't expect the owner to make the determination that surge would not be a problem (that's why they hire an Engineer).  And if they did, I would want to verify that for myself and specifically exclude it from the scope of work on the basis that it is assumed unnecessary.

and you should be able to quickly approach the design engineer and communicate the concerns by the agency.  THe engineer, will then be more than happy to provide you with the answer because the analysis, albeit maybe cursory in nature, is one component of complete design.  From this analysis, the engineer should have been able to determine whether soft starts/stops are/were required, the pipe diameter, the pipe wall thickness, check valve requirements (and locations along the forcemain and thrusting requirements.  If your engineer had not done this, perhaps a professional reminder is in order because you may have more questions now than just the agency query.

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