Sewer

Citywide Sewer System Project, City of Carnation

As City Engineer for the City of Carnation, Roth Hill designed a vacuum sewer system to serve the entirety of the last unsewered city in King County, Washington. The system consists of about 11 miles of vacuum sewer pipe, five main vacuum sewer trunk lines, a single vacuum station, and about 400 vacuum valve pits. Roth Hill coordinated closely with King County to implement the collection system in conjunction with the development of the County's new Carnation sewage treatment facility. The project required extensive permitting for both the City's collection and conveyance system and the County’s new treatment plant. We provided subconsultant coordination to collect the geotechnical, wildlife, wetlands and archaeological information necessary for construction, permitting, and project approvals at the Local, State, and Federal levels. Roth Hill prepared the NEPA Environmental Assessment and coordinated agency reviews and approvals with the Washington Department of Ecology and the United States Environmental Protection Agency (USEPA). We also coordinated the Endangered Species Act (ESA) Section 7 approval process with the USEPA, National Marine Fisheries Service, and the United States Fish and Wildlife Service.

Lift Station 10B, Soos Creek Water & Sewer District

Roth Hill provided surveying, permitting, easement acquisition and design services for this project. The purpose of the project was to replace an existing lift station where the incoming flows were approaching, and sometimes exceeding, the station’s pumping capacity with a new station that would have an ultimate pumping capacity of approximately 10,000 gpm. The project was designed with redundancy for all critical mechanical and electrical components. The redundancy included multiple pumps, motors, and control equipment as well as two dry wells, each with the ability to monitor pumping conditions in either dry well, from within either dry well, or within the control building. A telemetry system was included for the remote monitoring of the station from the District’s office. Liquid phase and air phase odor control facilities were incorporated to reduce or eliminate odors in the sewage that was entering and leaving the new station. The project also required the design of surge control facilities to address transients in the downstream force main. In addition, the project was located so that the City of Kent could use a portion of the site to relocate a stream from a concrete channel into a natural streambed.

Central Plateau Interceptor, Section 2, City of Renton

Roth Hill developed an Alternatives Analysis Report for the design of two steep slope sewers in the Central Plateau region of the City of Renton. The project consisted of analyzing the cost and constructability of installing sewer down the steep slopes and recommending a preferred alternative to the City. Several options were researched and analyzed including pipe material, overland versus underground construction, route selection taking into account existing and potential easements, permitting requirements, and conventional trench versus horizontal directional drilling (HDD). With the completion of the Alternatives Analysis Report, the City selected alternatives to be researched further and ultimately designed and constructed. Roth Hill is currently working on the pre-design phase of the project with design beginning in early 2006.

Sunset Interceptor Sewer, Phase 3, City of Renton

Roth Hill conducted preliminary design and sanitary sewer modeling for the upsizing of the existing sewer system on Sunset Boulevard (SR 900) and Duvall Avenue. We helped the City evaluate the most effective route for the discharge of two sewer lift stations. The preliminary design phase ended with a decision on which pipelines needed to be upsized prior to two transportation projects involving these two busy roadways. We are currently in the design phase for the project, which consists of upgrading approximately 1,250 feet of sanitary sewers within Sunset Boulevard from 8-inch diameter pipe to 15-inch diameter PVC pipe. We have also designed some local upgrades to the existing sewer system along Duvall Avenue, but those improvements won’t be constructed until the second transportation project is authorized. Due to the numerous utility conflicts and the extensive disruption that will already be happening along these busy streets, the decision was made between Roth Hill and the City of Renton to locate the new sewers a few feet north of the centerline of Sunset Boulevard.

Juanita Interceptor Sewer, City of Kirkland

Roth Hill designed this interceptor sewer project to remove a nearly 40-year-old pump station facility located in the middle of a large wetland near Lake Washington. Originally planned for replacement by the City, Roth Hill devised a feasible solution wherein 2,300 linear feet of 18-inch gravity interceptor sewer, at depths up to 20 feet, could drain the basin instead of utilizing a pump station. The cost comparison for a new pump station versus a gravity sewer revealed that the gravity sewer would be less expensive with lower long-term O&M costs. Another significant benefit of the sewer option was that the pump station site was restored to match the surrounding wetlands.

The sewer alignment is essentially along the edge of Lake Washington at elevations below the lake level; from the existing lift station site, the sewer extends through a steel casing which crosses under Forbes Creek (a salmon-bearing stream), across a wetland, and then north within 98th Avenue NE (a busy, four-lane arterial between downtown Kirkland and the Juanita community). Local, State, and Federal permits were required for the wetland and stream crossings. Roth Hill coordinated the services of a wetland biologist, and geotechnical and structural engineers. We also provided a full-time construction observation representative on site during the entire 11-month construction period.

East Bay Sewer Pre-design, City of Olympia

Roth Hill prepared a pre-design report to assess the condition of an existing sewer system consisting of approximately 4,600 linear feet of 8-inch asbestos cement gravity sewer pipe, and a pre-fabricated pump station, all located in the tidal zone of Budd Inlet. The purpose of the project was to evaluate the condition of the existing system, including the mains, manholes, and pump station, analyze and evaluate options for repairing or replacing the system if necessary, conduct a risk assessment on the existing facilities and any proposed improvements, and provide a recommended solution to the City. Field work to clean and video inspect the pipe as well as dig test pits to evaluate soils and pipe structural integrity was performed. The physical location of the facilities posed unique challenges, requiring the field work to be coordinated with tidal fluctuations and equipment to be delivered to the site via barge.

Meridiana, Soos Creek Water & Sewer District

Roth Hill performed the permitting, design and construction administration for the installation of 4,640 linear feet of 8-inch PVC sewer main and 2,480 linear feet of 6-inch PVC pipe for stub services. The purpose of this project was to provide service to existing homes on deteriorating septic systems. This was a joint project with King County Water District No. 111, who replaced old watermains in the area with 2,160 linear feet of 12-inch DI main, 3,710 linear feet of 8-inch DI main and 410 linear feet of 6-inch DI main. In constructing the two projects simultaneously, the Districts were able to share the restoration costs. Final construction cost came in about 6.9% under the Bid amount. Public Works Trust Fund money was obtained to finance the project.