King County Wastewater Treatment Division is designing a project to upgrade the county’s sewer pipelines on North Mercer Island and Southwest Bellevue. Installed during the 1970s, these pipelines are aging and reaching capacity.

The project team starts design by investigating what is underground, which helps define a final location for the pipeline.

This week, survey crews will start the effort by mapping the area and installing small markers as control points, according to a statement sent May 31.

Utility location crews will mark locations of underground gas, water, power, sewer and communications lines, and a boat-based survey crew will carry out a survey of the lake bottom traveling east from about 97th Avenue Southeast on Mercer Island to the Enatai shoreline.

This summer, crews will use drill rigs to look at soil and groundwater conditions, and will install equipment to measure groundwater in some locations.

Survey crews will be working on streets, along the I-90 Trail, in Enatai Beach Park and in residential areas along the pipeline route. During the boat survey, waterfront residents may see the boat near docks where King County’s existing pipeline is located.

Construction is expected to begin in 2019 and extend until 2022.

For more, visit www.kingcounty.gov/MercerEnataiSewer, or contact Monica Van der Vieren at 206-477-5502 or Monica.VanderVieren@kingcounty.gov.

To sign up for Mercer Island text alerts, text KING MERCERSEWER to 468-311. To sign up for Enatai text alerts, text KING ENATAISEWER to 468-311.