Step Tank Sizing 001RECEIVED
FEO O 1 2000
Bella Housa Community Center
Step Tank Sizing
The proposed community center for the Bella Housa Village does not Flt any of the categories
listed in either the City of Yelm Develop Guidelines or the Washington State Department of
Ecology Criteria for Sewage Works Design, making it difficult to determine a daily flow rater per
person in order top design the step tank far the facility.
The facility is a 3000 sf building with a women's bath room having two toilets and two sinks., while
the men's bathroom has one toilet, one urinal and one sink. In addition the facility will have a
utility room with a service sink along with a warming kitchen with a double sink and dishwasher.
The occupancy of the facility will be 75 people. The facility would be open approximately 12 hours
per day. It is anticipated that during periods of power outage the facility. It is highly unlikely that
the maximum occupancy would occur all day long. Because of the use of the facility it is
recommended to utilize the peak daily which is Flow per person stated for an offce building of 15
gal per day per person on a shift.
Detention Volume
V~..OQ (nonresidential strength)
Where
V =Liquid Volume
Q =Peak Flow per day for the structure being served
Q =Occupancy * Gallday per person based on usage type
Q= 75* 15
Q= 1125 gal
V~.O*1125ga1=2250 gal
The DOE manual states that Step tanks must have a minimum storage volume equivalent
to the daily one days flow into the tank. Therefore the storage volume required for this
facility is 1,250 gal
Working volume is the volume between the On and Off switch
Working volume is 246 gal
Total volume required
Liquid Volume + Working Volume + Storage Volume =Total Volume
2250 + 246 + 1250 = 3746 gal
Therefore a 4500 gal tank is required.