Site work for a water / sewer project in Seattle, Washington. Completed plans call for site work for a water / sewer project.

Project Description 1. The purpose of the Project is to add conveyance capacity to accommodate population growth over time in a manner that meets the County’s commitments to provide conveyance services to the City of Blank Diamond (City). The City and WTD have worked closely for more than 10 years to coordinate infrastructure needs for a Master Planned Development (MPD) in the city, the largest ever in the County. WTD is obligated per the agreement for sewage disposal to accept all wastewater produced by the city. Development in the City of Black Diamond is now advancing rapidly. As a result, population growth, and hence sewer flows, are growing faster than anticipated. 2. The Black Diamond Trunk consists of approximately 6 miles of gravity sewer pipe that runs south to north between the cities of Black Diamond and Covington. The existing sewer pipe sizes range from 8” to 16” in diameter, with the smaller diameter pipes generally installed where there are steeper slopes, and the larger diameters located in portions with gentler slopes. To provide the future capacity needs of the community, the existing conveyance system needs to be replaced with larger diameter pipes that can handle up to 11.25 million gallons per day (MGD) of sewage flow. The Project aims to provide sufficient capacity to serve the community’s current and future wastewater capacity needs through 2070. Both open-cut and trenchless construction techniques are anticipated for the project. a. Maintenance Hole (MH) 97 through MH 113: The upstream portion is located on 228th Ave SE and Lake Sawyer Road SE and replaces the existing sewer with sewer pipes sized for the anticipated flow, representing a considerable increase in diameter with the intent to provide temporary storage capacity during storm events. The existing pipeline lengths and material to be replaced are as follows: 1) Approximately 1,000 LF of 15-inch reinforced concrete pipe (RCP) 2) Approximately 3,500 LF of 16-inch coated ductile iron pipe (DIP) 3) Replace MH 97 through MH 113 (48-inch-diameter structures) b. MH 01 through MH 97: begins immediately downstream of Section 1 above, located on 228th Avenue SE and runs north then west on SE Covington Sawyer Road, then turns northerly on 193rd Avenue SE, crosses the Burlington Northern Railroad and Cranmer Creek where it runs north on Timberlane Way SE to the intersection with 185th Way. This segment increases the sewer diameters to handle increased flow capacity needs based on population growth. The existing pipe lengths to be replaced are as follows: 1) Approximately 600 LF of 10-inch pipe 2) Approximately 7,300 LF of 12-inch pipe 3) Approximately 18,600 LF of 15-inch pipe 4) Replace MH 1 through MH 96 (48-inch-diameter structures) Total Construction Cost is anticipated to be $73 Million