AGS, as a joint venture partner, currently is providing project management and professional engineering services to support the design of a replacement for the portion of the Southeast Outfall (SEO) that crosses Islais Creek immediately parallel to the Third Street Bridge. The SEO is part of the combined sewer system, which collects and treats both wastewater and stormwater. The SEO Islais Creek crossing is currently comprised of two ductile iron pipes (36-inch and 42-inch). The pipes were constructed across Islais Creek and are buried in the bottom of the creek bed. The existing pipes are buried 20 feet under the lowest point of the creek sediments, and the water depth is 30 feet. The existing pipes were constructed in 1967 and have reached the end of their useful life. The new Islais Creek crossing design will consist of two new 54-inch outside diameter high density polyethylene (HDPE) buried pipes to replace the existing 36-inch and 42-inch pipes. The design, which will include one new structure on each side of the creek, is being proposed to tie the new pipes to the existing system. The new structure designs will contain actuated valves and pipes to divert flow to the new or existing systems.
AGS is providing project management and coordination, geotechnical engineering, environmental engineering, and design for the SEO project. AGS’ scope of work included an initial condition assessment and review of background information. The condition assessment involved evaluation of existing pipelines, vaults, the booster pump station, manholes, the boat dock, and other assets, and then assessment of the effects of the proposed construction of those existing structures. AGS also attended bi-weekly meetings with the Wastewater Treatment Operators to determine the effects of construction on the operations of the Treatment Plant.
As part of this work, AGS evaluated the effects of sea-level rise on the stability of Islais Creek shorelines and will develop the required mitigation measures to protect the existing shorelines from excessive lateral deformations and potential failure under a significant earthquake loading.