Black Diamond wastewater infrastructure upgrade

Phase One alternatives

Four storage alternatives are being considered in the general location near the existing King County pump station.

Alternative A - Below-grade storage tank at pump station site      

A 750,000 gallon tank (approximately dimension 230-feet long, 70 feet wide and 10 feet deep) with four flushing chambers built in the gravel driveway between Railroad Avenue and the existing King County pump station near Jones Lake. The tank would be oriented along the gravel driveway, extending east from the pump station site. Wastewater flows beyond the pump station's capacity would flow by gravity into the storage facility and drain by gravity into the pump station after heavy flows subside.

Retaining walls up to 40 feet tall would be built to the north, south, and east of the tank. A small pump station would be required to drain out residual storage volume. Odor control equipment would also be installed.
View Map and Diagram- A - Below-grade storage tank at pump station site (PDF 1.5MB)

Alternative B - Removed from consideration      

Alternative B required significant community impacts and did not provide sufficient technical or operational benefits to pursue. It was removed from further consideration in March 2008.

Alternative C - Storage tunnel      

A 12-foot diameter in-line storage tunnel would be installed west of the existing King County pump station towards the abandoned lagoon site. A flushing station/odor control facility would be required at the upstream end of the tunnel. A pump would lift flow from the tunnel to a smaller sewer pipe for transport back to the pump station after heavy flows subside.
View Map and Diagram- C - Storage tunnel (PDF 1.5MB)

Alternative D - Pipeline storage open cut option        

A 12-foot diameter in-line storage pipes installed immediately upstream of the pump station connecting to the existing pipeline approximately 900 feet to the north of the existing King County pump station near Jones Lake. Odor control equipment would also be installed. Access to a flushing station/odor control facility would be required at the upstream end of the tunnel. A small pump station would also be installed to pump out the lower reach of the tunnel after heavy flows subside.
View Map and Diagram- D - Pipeline storage open cut option (PDF 1.6MB)

Alternative E - Storage at the abandoned treatment lagoon site      

A 750,000 gallon tank approximately 170 feet long, 90 feet wide and 10 feet deep built at a former wastewater lagoon 1,300 feet southwest of the existing pump Station A 12-inch sewer pipe would connect the storage tank and the pump station. The existing King County pump station near Jones Lake would be upgraded and outfitted with odor control and emergency generator equipment in order to pump excess flows to the storage facility.
View Map and Diagram- E - Storage at the abandoned treatment lagoon site (PDF 1.5MB)