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Creating or replacing a water system

Public Health – Seattle & King County can help you create a new water system or replace an existing one. New and replacement private water source applications (394 KB) are handled by King County from start to finish. Public water systems are reviewed and approved by the Washington State Department of Health Office of Drinking Water. King County will do water source site inspections for the proposed well site of a public Group A or Group B water systems.

Public water sources

For public water systems, King County only conducts site inspections which involves surveying the proposed well site for potential contamination sources. Once completed, King County writes a report noting their findings which are then used by the Washington State Office of Drinking Water. The state Office of Drinking Water is responsible for reviewing public water system applications, including engineering designs, water quality and quantity, and supporting documents to ultimately approve or disapprove the water system.

  • King County conducts source site inspections for public water systems once they receive completed a Public (Group B) Well Source Site Application (355 KB).
    • Applications must be submitted by on-site sewage system designers or professional engineers specializing in water.
  • Group A and Group B public water system designs are reviewed and approved by the Washington State Department of Health’s Office of Drinking Water Northwest Regional Office.
    • The Health Officer may require additional information for new or replacement public water sources when reviewing permit applications. These can include Office of Drinking Water approval letters, water system designs, water quality tests, pump test results, water use agreements, covenants, and compliance history.

Individual private wells

Public Health – Seattle & King County handles individual private well applications from start to finish. Private wells serving a single-family residence and up to one ADU on the same property must apply to King County through a certified on-site sewage system design or water system engineer.

King County inspects the proposed well site looking for potential sources of contamination. After the water source location is approved, the water source can be built. After this, King County reviews water quality tests, pump tests, and supporting documentation, and ultimately makes the decision to approve the water source.

In general, to obtain final approval for the use of a private well, the following must be completed:

    • A Private Well Source Site Application (394 KB), submitted to King County. Applications can only be submitted by certified on-site sewage system designers or engineers
    • Receive a preliminary well site approval letter from Public Health – Seattle & King County
    • The well must be drilled in compliance with chapter 173-160 WAC by a licensed well driller
    • Signed, notarized, and recorded covenants
    • Submit a copy of the pump test to King County
      • Two (2)-hour pump test required (air tests and bailer tests are not accepted)
      • If the pump test results in a flow rate of 5 gpm or less, a 4-hour pump test and proof that the well produces at least 400 gallons per day is required
      • In areas with known low groundwater production, the Health Officer may require pump testing during months which are expected to have seasonally-low groundwater levels.
    • Two Satisfactory Bacteriological Analysis
      • Both samples may be collected the same day
    • Satisfactory Nitrate Analysis
      • Maximum contaminant level (MCL) 10 mg/l or 10 ppm
    • Results of the Arsenic Analysis
      • Maximum contaminant level (MCL) .01 mg/l or 10 ppb
      • Private wells with arsenic levels between 10 and 50 ppb can only be used with
        • An approved arsenic treatment waiver application (244 KB).
        • Arsenic treatment system designed by a professional engineer specializing in water treatment
        • Demonstrated post-treatment arsenic levels less that 10 ppb
        • A recorded notice on title of arsenic treatment

Note: Water quality samples should be collected and submitted to certified labs by a water professional.

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