(Effective until April 1, 2025)
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. WSR 05-15-119, § 246-272A-0232, filed 7/18/05, effective 7/1/07.]
(Effective April 1, 2025)
Design requirements—Septic tank sizing.
Septic tanks must:
(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:
Table VII
Required Minimum Liquid Volumes of Septic Tanks
Number of Bedrooms | Required Minimum Liquid Tank Volume in Gallons |
≤4 | 1,000 |
Each additional bedroom | 250 |
(b) For OSS treating sewage from a residential source, other than one single-family residence, 250 gallons per bedroom with a minimum of 1,000 gallons;
(c) For OSS treating sewage from a nonresidential source, three times the design flow.
(3) Comply with chapter 246-272C WAC.
[Statutory Authority: RCW
43.20.050(3),
43.20.065, chapters
70A.105 and
70A.110 RCW. WSR 24-06-046, § 246-272A-0232, filed 3/1/24, effective 4/1/25. Statutory Authority: RCW
43.20.050. WSR 05-15-119, § 246-272A-0232, filed 7/18/05, effective 7/1/07.]