1. (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:

   1. (a) Modifications of existing developments:

      1. (i) 120 gpd per bedroom; or
      2. (ii) 240 gpd per existing dwelling unit, residence or mobile home lot or space, whichever is greater.

   2. (b) New residential developments and new mobile home parks:

      1. (i) 120 gpd per bedroom; or
      2. (ii) 360 gpd per lot or space, whichever is greater.
2. (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. (3) For commercial and nonresidential developments or portions of developments that serve commercial and nonresidential facilities, the department may accept the following:

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

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

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

   2. (b) Comparable flow data from similar existing facilities, including:

      1. (i) From a minimum of three similar developments; and
      2. (ii) Using a peaking factor if average flows are recorded.

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