Washington Administrative Code
Title 246 - Health, Department of
SEWER SYSTEMS
Chapter 246-272B - Large on-site sewage system regulations
Part 6 - DESIGN AND TECHNICAL STANDARDS
Subpart A - General Requirements
Section 246-272B-06150 - Design flows

Universal Citation: WA Admin Code 246-272B-06150

Current through Register Vol. 24-18, September 15, 2024

(1) The design engineer shall use the following minimum design flows, which include the appropriate peaking factors, for developments or portions of developments serving residential facilities such as single-family residences, multi-family dwellings, and mobile home parks with total LOSS design flows of 14,500 gpd or less:

(a) Modifications of existing developments:
(i) 120 gpd per bedroom; or

(ii) 240 gpd per existing dwelling unit, residence or mobile home lot or space, whichever is greater.

(b) New residential developments and new mobile home parks:
(i) 120 gpd per bedroom; or

(ii) 360 gpd per lot or space, whichever is greater.

(2) The design engineer shall use 270 gpd minimum design flow per dwelling unit, residence or mobile home lot or space for residential developments or portions of developments serving residential facilities, with total LOSS design flow greater than 14,500 gpd.

(3) For commercial and nonresidential developments or portions of developments that serve commercial and nonresidential facilities, the department may accept the following:

(a) Design flows listed in Table 4 in this section; or

(b) Design flows from other generally recognized sources, on a case-by-case basis.

Table 4: Typical Design Flows for Nonresidential Facilities

Type of Facility

Design Unit1

Design Flow (gpd)

Schools with showers and cafeteria2

per student

16

Schools without showers and with cafeteria2

per person

12.6

Schools without showers and without cafeteria

per person

10

Boarding schools2

per person

75

Temporary farm worker housing2

per person

50

Hotels, motels, and B&Bs

per room

130

Restaurants2

per seat

50

Truck stops and Interstate restaurants2

per seat

180

Offices, with showers

per person, per 8-hr shift

25

Offices, without showers

per person, per 8-hr shift

15

Nursing homes2

per bed

200

Elder care facilities, retirement homes2

per bed

100

Laundromats2

per machine

500

Churches, without kitchen

per seat

3

Churches, with kitchen2

per seat

5

Day care centers

per person

20

Picnic areas

per person

5

Campgrounds, RV parks with flush toilets only, no laundry or wet sewer hookup

per camp site

50

Campgrounds, RV parks with flush toilets, showers, laundry, no wet sewer hookup

per camp site

75

Campgrounds, RV parks with flush toilets, showers, and wet sewer hookup, with or without laundry2

per RV space

120

Trailer dump stations2

per dump

40

Resort cabin

per person

40

Bar, cocktail lounge2

per seat

20

1.

Does not include employees and staff, unless indicated.

2.

Indicates potential for waste strength to exceed that of residential strength sewage, requiring Treatment Level E or higher.

(4) For the department to evaluate alternate design flows, a written request and the following information must be submitted:

(a) The preceding year's actual metered flow data read at intervals acceptable to the department to capture seasonal and peak usage; or

(b) Comparable flow data from similar existing facilities, including:
(i) From a minimum of three similar developments; and

(ii) Using a peaking factor if average flows are recorded.

Statutory Authority: RCW 70.118B.020. 11-12-035, § 246-272B-06150, filed 5/25/11, effective 7/1/11.

Disclaimer: These regulations may not be the most recent version. Washington may have more current or accurate information. We make no warranties or guarantees about the accuracy, completeness, or adequacy of the information contained on this site or the information linked to on the state site. Please check official sources.
This site is protected by reCAPTCHA and the Google Privacy Policy and Terms of Service apply.