The Shady Lane Sewer Removal Project (Modified Project) addresses the Shady Lane portion of the Large Diameter Gravity Sewer Project II-3 (Original Project) (Phase 2) at Ross Creek under the Shady Lane Bridge. The District is undertaking voluntary action to remove the abandoned sewer pipe and concrete casing that traverses Ross Creek. The primary pipe rehabilitation method was CIPP, and the replacement/upsize method was pipe bursting. A steel casing was installed underneath Ross Creek just upstream of the Shady Lane Bridge using bore-and-jack method, with no direct disturbance to the creek bed or banks. This segment of the new sewer line replaced an exposed 21-in. reinforced concrete sewer line that was then abandoned in place within the Ross Creek channel, which remains in place today. The abandoned sewer pipe and concrete casing is a partial barrier to juvenile Coho salmon migration. The Ross Creek channel bed will be restored and will be replaced with a constructed riffle comprised of engineering stream bed material.
The total area disturbed is 0.06 acres. Approximately 30 cubic yards of abandoned 21-in. reinforced concrete pipe and will be removed from the channel bed. Excavation depth at the sewer line will be approximately 4 ft. Approximately 620 ft2 of existing channel bed materials will be excavated to prepare for the constructed riffle. Excavation depth at the channel bed will be approximately 3 ft. Native channel bed materials will be excavated and stockpiled for use in the constructed riffle. Any non-natural materials, such as asphalt, will be removed from the stockpile.
Following the demolition, engineered stream bed material (including boulders and cobbles) will be imported and staged under the bridge and below the former sewer crossing. The exposed subgrade will be compacted prior to the installation of the engineered stream bed materials. Imported rock will be installed along with the native bed materials stockpiled onsite. The Contractor, under the direction of the design team, will construct the riffle in layers using the stockpiled boulders, cobbles, and salvaged bed materials.
The area adjacent to the sewer line, and the construction access corridor, will be cleared and grubbed of invasive species. Existing streambank vegetation is currently dominated by English ivy and will be replaced by locally sourced box elder, California buckeye, western thimbleberry, and red flowering currant. A total of 775 ft2 of planted banks will receive 4 in. of mulch. All exposed soil surfaces outside of the active channel will be covered with a 100 percent biodegradable erosion control fabric and stapled in place, and two rows of wattles will be installed on the slope revegetated slopes.
Following the completion of the constructed riffle, the equipment will be removed from the channel bed. The access route will be restored with trees and shrubs and covered with erosion control fabric. The Modified Project is anticipated to be begin in summer of 2021 completed by mid-October 2021.