Sewer Flow Rates

[CPENG78]

Hi Everyone,
I received a sewer flow rate in DFUs and gpm from a plumbing engineer for a project site that has office and a maintenance shop. For now assuming 8 hr work day. However the ahj is interested in a gallons per day rate. What's the conversion factor? I'm assuming peaking factors are involved somewhere.

I've searched other threads here and I couldn't find anything on this topic. Any help is appreciated.

 

[GeoEnvGuy]

The rate provided likely assumes that every faucet, toilet, shower and anything else that can contribute is running. A senior engineer once told me for septic design called this the "party" factor. The plumbing engineer wants to ensure that if the building is having a party the sewer will work. Local building codes also specify how big the party is based on number of faucets and toilets.

Daily rates for sewers are based on average water bills assuming they all go to the sewer. The rates are usually broken down to gallons or litres per person, commercial is a bit harder to pin down how many people to design for and what share of the gallon per day to allocate. But assuming that they are not having a party all eight hours the flow rate is minimal.

The first stage of site investigation is desktop and it informs the engineer of the anticipated subsurface conditions. By precluding the site investigation the design engineer cannot accept any responsibility for providing a safe and economical design.

 

[Twinkie]

"The rate provided likely assumes that every faucet, toilet, shower and anything else that can contribute is running. A senior engineer once told me for septic design called this the "party" factor. The plumbing engineer wants to ensure that if the building is having a party the sewer will work. Local building codes also specify how big the party is based on number of faucets and toilets."

The 'ol Super Bowl halftime flush rate. It's in every engineering textbook.

 

[eea]

Your State permitting agency should have daily average and peaking flow guidelines. Our State uses PE (population equivalents) at 100gpd, IE a single family home equals 3.5PE. That's base flow and a x4 peaking factor is applied to that for downstream pipe capacity and plant treatment review. This is what you'll use to permit with the agency. The MEP's DFU should be used for the private site piping to convey the building flow to the point of connection at the public sewer.

 

[bimr]

There are plenty of posts regarding this subject. Here is an example:

Link

I believe that Pedarrin is working as a plumbing engineer. Search for some of his posts. You can also look into the plumbing forum.

"The rate provided likely assumes that every faucet, toilet, shower and anything else that can contribute is running

This is incorrect. The formulas use a statistical approach to estimate flows. The formulas do not assume everything is operating at the same time.

Before you do any work, you would be well advised to set the down with the AHJ to understand what he expects you to submit.