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Sewer system modifications

A description of system modification projects and the roles and responsibilities of the Local Public Agency team and the local agency.


System modifications are alterations or upgrades to the sewer infrastructure, whether they are modifications to the local agency sewer system or to the King County sewer system as a result of other agency construction projects. Examples of system modifications include, but are not limited to, pipe relocations, raising King County maintenance hole lid frame and covers, installing a new pump station, or rerouting wastewater flows (such as permanent reroute, temporary diversion, or Sewer Heat Recovery projects). 

System modifications can be submitted by non-sewer agencies, such as transportation agencies, and can be a subproject as part of a larger construction project that requires relocation of King County’s sewer pipes.

System Modification Requirements

  • Please contact the Local Public Agency team as early as possible during preliminary design to verify whether a construction project may impact the King County sewer system. 
  • Agreement and/or Approval: Depending on the nature of the project, an interagency agreement or approval letter is often required between King County and the Local Agency. 
  • Construction Inspection: The project may also require LPA on-site inspection. Please see Construction Requirements for notification requirements prior to construction as well as requirements regarding submittals and change orders pertaining to modification and impacts to King County's sewer system.
  • As-Constructed Drawings: Modifications to the King County sewer or infrastructure will require the Local Agency to send as-constructed drawings after construction completion, if requested.

Our team’s role

The LPA Team is involved from the project’s preliminary design through construction. We provide King County construction requirements, inspection of construction, and review of submittals and change orders.

The LPA Team ensures that sewer modifications and any associated construction have minimal impact on the King County sewer system. We coordinate with the local agency, consultant, contractor, and internal King County stakeholders about the project’s scope, design plans, property rights, and easements.