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On-Site Sewage System (OSS) Designers and Engineers
Lynn Schneider, Supervisor, On-site Sewage Program

New process for private well reviews and water service requirements

The purpose of this memo is to inform OSS designers and professional engineers about a process change for submitting applications for all new construction for on-site sewage systems. To avoid delays and process challenges when applying for an on-site sewage system site design, determination of the approved potable water source should be completed early in the proposed development process.

Since the mid-1980s King County has had a long-standing preference for limiting new permit exempt wells by requiring new development to be connected to Group A public water systems. In line with Chapter 90.94 RCW – Streamflow Restoration, King County has identified measures to ensure that the hierarchy of water service is being fully implemented. The requirements of Chapter 13.24 K.C.C. regarding water service indicate that the determination of an approved potable water source needs to be made early in the lot development process to ensure the appropriate water source is identified before the lot development takes place.

The Department of Local Services – Permitting (DLS-Permitting), formerly DPER, is the lead agency tasked with determining an appropriate water source for the proposed development. To assist property owners with developing an adequate source of water and implementing the hierarchy of potential service (Group A, Group B, private well, rainwater catchment) for the property, DLS-Permitting will identify if the property is located within or near a Group A water service area during the critical area determination (CAD) process. If the property is located in a water service planning area, a Certificate of Water Availability is required from the applicable water jurisdiction.

If the Certificate of Water Availability documents public water is available, connection to the Group A water system is required. If the client feels that connection to the public system is not "timely and reasonable" an appeals process is available via the Utilities Technical Review Committee (UTRC).

The same process is used if the proposed drinking water source is an existing Group B water system. Even if the parcel has an approved connection to a Group B system, if potable water from a Group A drinking water system is now available, connection to that Group A system is required as part of the building permit or subdivision review process.

If the property is not in a water service area and the parcel meets the minimum requirements for individual wells in King County Board of Health Code Title 13, a private individual well may be proposed. Alternatively, a rainwater catchment system may be proposed for a single-family residence if the health officer finds that requiring connection to an approved public water source or approved private well would cause undue hardship. An OSS site design application for new construction that proposes an individual well or rainwater catchment as the potable water source must include documentation demonstrating one of the following:

  1. DLS – Permitting determined the parcel is not located in a water service area.
  2. DLS – Permitting determined the parcel is located in a water service area and the water utility determined public water is not available to the property.
  3. DLS – Permitting determined the parcel is located in a water service area and the water utility determined public water is available to the property and the UTRC determined public water is not available in a timely or reasonable manner.
To find out if a particular property is located in a water service planning area, go to the King County Parcel Viewer with the parcel in question, click on District Reports, and then review the Water service planning area for the particular water utility. Maps of utility service areas will also be available at DLS. DLS provides a Water Service Requirements flow chart to document the process.