Underground Stormwater Retention System – Marysville, Washington

Low Impact Development

Background Information and Challenges

The development of the property required a stormwater storage system with a storage capacity of 500,000 Gallons of water storage to meet permitting requirements. Tank installation required a 5′ excavation to encapsulate the system, but the existing grade was 2-4 feet below this. Tank installation could not be started until late October.


Working around the weather, Layfield crews installed Brentwood StormTank® 25 Series Single Stack Modular tanks with a ¾” clear rock fill within a Layfield Enviro Liner® 1030 LLDPE 30 Mil Liner, allowing for complete water storage requirements. The Earthworks contractor brought in a pit run style fill that allowed for compact fill around the tanks and then was able to cut out around the edges allowing for installation. Layfield supplied and installed Brentwood StormTanks® with Enviro Liner® 1030 liner covering the tanks. Layfield’s Enviro Liner® 1030 liner was used as a long-life liner system, with quality installation provided by Layfield Installation crews. Brentwood Debris Rows were installed to allow for the capture of particulates for periodic maintenance. Ports at the top of the system allow for clean-out.


The stormwater system completed in the building’s new facility has all the intended water storage needed to prevent stormwater runoff using an inground storage retention system featuring Brentwood H25 Tanks and Layfield Enviro Liner® system. The new system maximizes the available parking space. Flexibility in the layout allows for cutouts created for trees and plants in and around the stormwater system.  


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