Question

1.   Calculate the sanitary flow for a 9,000 sf non-medical office building with

      Daily flow____________________________________________________________

     

2.   Minimum Required Size of Septic Tank ____________________________________

     

3.   Required leaching pools______________________________( specify number and depth )

     

Notes: Flow rate for non-medical office building is 0.06 gpd/sf

            Leaching rate is 1.5 gal/sq. ft./day

           . 8' diameter tank = 25.12 sf leaching area per vertical foot

Answer 1

1) Assuming 90% of water supplied change to sanitary flow

Water supplied = 0.06 gpd/sf

Area of building = 9000 sf

Thus total water supplied = 0.06*9000= 540 gpd

Thus total sanitary flow = 0.9* 540 = 486 gallons per day

2) As per thumb rule for 0-500 gpd of sanitary flow effective size of septic tank is 900 gallons but in most US jurisdictions the minimum septic tank size is 1000 gallons thus minimum required size of septic tank would be 1000 gallons

3) As a thumb rule Leaching tank size required = 0.45*1000 = 450 gallons

Surface area = 450/1.5 = 300 sf

Leaching area = 25.12 sf

Now maximum width =2'

Then length = 25.12/2 = 12.56' = 13'

Thus number of leaching pools = 300/(13*2)= 11.53 = 12 Nos