60-acre water supply system design criteria

[staffgage]

Designing a domestic & fire water supply system for 60-ac mixed commercial/retail.

Very small municipal water dep't. will only supply static pressure test at an existing fire plug. We have survey of existing water system, length, pipe type, elevations, surface features (fire hydrants). No flow test, existing pump, reservoir or fitting information. Local fire marshal unresponsive.

No staff admits responsibility for supplying the fire flow requirement and duration, or existing domestic water system information & supply reqm'ts. I need information to analyse the existing, and proposed looped pipe, network to at least meet fire protection/max demand.

I get the impression that the municipality is short on professional engineering staff, and is between consulting engineering companies.

What basic questions should I ask city staff & fire marshal? Lacking answers and required design information, what simplifying assumptions can I make protecting life safety and domestic water quality to proceed with design?

If you have time for a short answer, what uniform codes are relevant?
Thanks!

 

[Maury]

You need fire flow test(s) to determine how much water the existing system can supply. This is necessary even if you want to model the exiting system. If the muncipal staff can't or won't do it, then you need to do the test yourself or hire it done.

 

[canman]

Unresponsive local water & fire department, yeah I hear ya. If they won't or can't help in getting the necessary fire flow test data then hire a 3rd party. I'm not sure what state your in but in California there are many companies that specialize in fire flow tests. Once you get the data make sure it includes static, residual, pitot gauge, hydrant opening size (either 2.5" or 4&quot, flow in gpm and flow in gpm at a residual of 20 psi. With all this information you'll be able to set up your model. Make sure when you run your model you increase the demand you need by 10%-12%. This is the industry standard for modeling water systems. It takes into account variables in times of the day and year. Example, an area with 60 psi at 10:00 AM in the winter might only have 55 psi at 5:00 PM during the summer.

In terms of sources for fire protection design guidelines you could use the National Fire Protection Agency Pamphlet #24 and/or #13, look up on internet. In California we have our own local fire code that I would use for getting the minimum requirements for fire hydrant numbers & distances between hydrants, gpm out of those hydrants at a residual of no less than 20 psi, and other design criteria. We also have our own local plumbing code that helps in sizing domestic water lines for buildings. There are so many different requirements you will have to try very hard to work with your local municipalities. You will have your work cut out for you sizing pipes, meters, backflow devices, etc. Keep velocities in domestic pipes under 10 fps and in fire systems (outside the buildings) under 12 fps.

Good Luck!

Canman

 

[gtrainor]

Yeah, I have had it both ways also. Sometimes the waterworks department will do it, sometimes not. If there are any questions to the reliability or who will do it, it's best to hire a firm that will do it. I would start with calling the fire department and ask them who can do the test. And maybe call a contractor specializing in water line installs; they may conduct these tests as part of their construction acceptance. For a little education, check out:

http://www.firehydrant.org/info/ftest1.html

This website has many interesting facts and humor for hydrants.