9th St. and Harris Ave. Vault - Stormwater Discovery Tours

Where is this located? It lies under the street and parking area on 9th Street about fifty feet from the corner of 9th and Harris Avenue.

What’s special about this place? This vault is a large concrete structure that lies under the pavement and is designed to hold a lot of water – an amazing capacity of up to 90,000 gallons. What was an empty lot that might have infiltrated rain falling on the ground is now a four-story, mixed-use development. Lacking space above ground for stormwater capture and treatment, runoff is being collected in an enormous vault buried under the parking area on this street. An under-drain captures the filtered stormwater and pipes it under Harris Avenue where it finally enters Padden Creek.

About Vaults and Tanks

Vaults are typically large concrete boxes buried under a parking lot, street, play field, or tennis court. Vaults hold stormwater when there is not enough space above ground to infiltrate runoff or to build a holding area such as a detention pond. Vaults can be built strong enough to support heavy vehicles. Many times, vaults are filled with cartridge filters, typically cylindrical devices, filled with special material that traps particles and absorbs pollutants as the stormwater soaks through the filter. These pollutants include dirt, sand, sediment, hydrocarbons, fertilizers, and metals like zinc and copper that are toxic to fish.

Water Quality Benefit: Some vaults have a sand filter or cartridge filter system included in their design. Storm filters require frequent cleaning to remove accumulated sediment and are inspected to monitor their effectiveness and life span.

Water Quantity Benefit: Vaults delay the entry of runoff into streams and rivers during storm events which can prevent flooding and reduce erosion in rivers and streams. Holding water underground can also help reduce high creek temperatures during the summer months. High-temperature runoff (>70 degrees F) can be very harmful to migrating salmon, especially in the late summer.

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drainage area

Drains 1.9 acres.

Where does this stormwater runoff come from? Stormwater at this site comes from a single block of Fairhaven between 9th and 10 streets, and Harris and McKenzie Avenues. This very large underground vault is capable of holding 90,000 gallons of runoff.

Where does this stormwater runoff flow next? Runoff from this facility flows through pipes under Harris Avenue where most of the water is sent to the 8th Street and Harris Avenue Bioretention Basin. During high flows some water goes directly to Padden Creek.

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