WAC 246-272A-0232
Design requirements -- Septic tank
sizing. Septic tanks shall:
(1) Have at least two compartments with the first
compartment liquid volume equal to one-half to two-thirds of
the total liquid volume. This standard may be met by one tank
with two compartments or by two single compartment tanks in
series.
(2) Have the following minimum liquid volumes:
(a) For a single family residence use Table VII, Required
Minimum Liquid Volumes of Septic Tanks:
TABLE VII
Required Minimum Liquid Volumes of Septic Tanks
| Number of Bedrooms |
Required Minimum Liquid
Tank Volume in Gallons |
| ≤3 |
900 |
| 4 |
1000 |
| Each additional bedroom |
250 |
(b) For OSS treating sewage from a residential source,
other than one single-family residence, two hundred fifty
gallons per bedroom with a minimum of one thousand gallons;
(c) For OSS treating sewage from a nonresidential source,
three times the design flow.
[Statutory Authority: RCW 43.20.050. 05-15-119, §
246-272A-0232, filed 7/18/05, effective 7/1/07.]