Heavy overnight rain led to a manhole overflow south of Thrasher’s Corner in Bothell Wednesday morning.

King County Wastewater Treatment Division employees quickly responded to the overflow alarm at 8 a.m., and immediately dispatched a crew to the area to investigate. The manhole is in a wetland west of the Bothell-Everett Highway between 208th Street Southeast (SR-524) and 214th Street Southeast.

An undetermined amount of highly diluted wastewater overflowed for about an hour from a manhole on the North Creek Interceptor, which is a major regional sewer line that carries wastewater collected from homes and businesses in unincorporated Snohomish County and the City of Bothell for treatment at the Brightwater Treatment Plant north of Woodinville.

The system is now operating normally.

King County reported the overflows to health and regulatory agencies and posted affected areas as closed. Employees with the County’s environmental laboratory will sample and monitor water quality in North Creek over the next few days.

The North Creek Interceptor has been in service since about 1970. King County purchased the line from the Alderwood Water & Wastewater District in 2001, and has a long-term capital plan to upgrade the line and add capacity in this portion of the service area to increase reliability and reduce the potential for storm-related overflows.

Construction is scheduled to begin in 2014.

Detailed information about the project, including maps, is available at http://www.kingcounty.gov/environment/wtd/Construction/North/NCI.aspx.

This release is also posted on the website for the Department of Natural Resources and Parks at http://www.kingcounty.gov/environment/dnrp.aspx