Estimated Sanitary Flows and Peaking Factors 1

[GoldDredger]

I'm trying to estimate the volume of flow into an existing lift station to see if it has available capacity.

The lift station needs to support about 485 single family lots, one elementary school, and 20 acres of commercial (retail, office and restaurant).

For residential lots I've previously used 300 gal/lot/day (estimating 100 gpdc averaging 3 persons per lot). Calculated it down to gal/min, then used a peaking factor of 4.

Does anyone have a good reference source I might use to back up my assumptions? A colleague felt 300 gal/day is too high for residential, and felt 200-250 gal/day more appropriate. Peaking factor should probably be based on area of drainage shed I imagine, with larger areas having smaller peaking factors.

Any opinions?

Thanks

 

[gbam]

GoldDredger - Presuming you are in the USA, does your Wastewater agency have design criteria or is it within a State Regulation? The demands are located in our State Regulations for Wastewater.

 

[bimr]

The lcal sewer agency should be the best source.One usually has to make an engineering report to upgrade a lift station using that data.

Lacking thst information, you can use Ten States Standards.

http://10statesstandards.com/wastewaterstandards.html#11

a. The sizing of wastewater facilities receiving flows from new wastewater collection systems shall be based on an average daily flow of 100 gallons (380 L) per capita plus wastewater flow from industrial plants and major institutional and commercial facilities unless water use data or other justification upon which to better estimate flow is provided.

An appropriate infiltration and inflow factor should be added for existing sewers.

Peak flows are based on population using the graph from Fair & Geyer:

http://www.ilga.gov/commission/jcar/admincode/035/03500370ZZ9996dR.html

School flows can also be estimated from the population.

http://www.ilga.gov/commission/jcar/admincode/035/03500370ZZ9996bR.html

 

[BenJohnson]

As an added precaution, you should put a run-time clock on the pump. Nice to have one with a graph readout. This will give you a more accurate understanding of both the peak flows and when they occur. Normally, peak sewage flows happen during a commercial break for the SuperBowl (if you are in the US). This is called the Superbowl Flush!

But groundwater infiltration during a rain can really mess up your estimates. A pump time meter will alert you to any abnormalities. This is good information to have if you are presenting your report to a water board, or other agency.

To be safe, you should use the flows based on the standards with links as refereed to above - provided the run-time meter doesn't give you data that gives you cause to believe the true flows are actually higher.

Who says Civil Engineering isn't an art?