AVALON - Borough Engineer Thomas Thornton presented Mott MacDonald’s formal recommendations to Avalon Borough Council for the north end drainage improvements.
The study area was from 10th to 27th streets east of Avalon Avenue.
Previous recommendations based on earlier design concepts focused on a new water collection system infrastructure of larger drainage pipes and the augmenting of both the 11th Street and 22nd Street pump stations.
Those earlier concepts also involved improving the outfall system, with larger pipes, but still making use of the same locations, which discharge to both the inlet and the ocean.
The estimated construction cost for the earlier design was $9.5 million.
Continued work on design concepts focused on expanding the use of gravity systems rather than increasing the reliance on mechanical processes.
A goal: reducing the construction costs. Other priorities were increased resiliency and reducing the peak flow to the pump stations.
The recommendations presented to council showed how far the design team had come in achieving the objectives.
Foremost among the new design was an increased reliance on a gravity system with larger pipes under Avalon Avenue. In addition, suggestions call for constructing a box culvert, a structure that allows water to flow under an obstruction, in the dunes for the full length of the study area.
The proposed collections system, with its increased use of gravity, would allow for the elimination of the 22nd Street pump station and would also end the need for an outfall system through the dunes to the ocean. The box culvert and the Avalon Avenue gravity pipes would intersect near the only outfall point at the 8th Street jetty. All discharge would be to the inlet.
The 11th Street pump stations would not only be maintained but enlarged. Given that parts of the structure would be above ground, the pump station would have to be built to flood evaluation standards.
Thornton estimated that the actual structure, once the final design is completed, would be more minimalist than it sounds for those portions above grade level.
Thornton said that the design would lower the construction costs, but he was not yet in a position to offer new estimates.
The presentation summarized the benefits of the design as eliminating one pump station, lowering construction expense, reducing the ongoing pump station operational and maintenance costs, cleaner beaches due to the elimination of an ocean outfall pipe, and, as an incidental benefit, removing constraints on property owners at Second Street who may wish to bury their utility wiring.
The proposed schedule for the project calls for a pre-application meeting with the state Department of Environmental Protection as early as November, a completion of the detailed design by May 2020, obtaining needed permits by December of that year, with a bidding and award process completed by July 2021.
The project envisions a three-phase implementation process, with the pump station upgrade separate from the changes to the water collection systems. The proposed tentative schedule would have completion of each of the phases one year apart, beginning in May 2022 and extending to May 2024.
Thornton emphasized that imminent work to repair the 8th Street jetty would not be delayed by the drainage project.
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