Capital Improvement Plan

Client—Three Rivers Regional Wastewater Authority (TRWWA), Cowlitz County, Washington

TRWWA provides conveyance and treatment of municipal sewage for the cities of Longview and Kelso, Beacon Hill Water & Sewer District and a small portion of Cowlitz County. The regional facility has a peak day capacity of 62.4 million gallons per day (mgd) and includes three pump stations (with associated forcemains) and 18,700 feet of 36 to 54 inch diameter gravity interceptor pipeline. The plant consists of two separate activated sludge secondary treatment plants and an RDP lime stabilization solids treatment process that can produce a Class A Exceptional Quality final biosolids product. Effluent is disinfected with sodium hypochlorite and dechlorinated with sodium bisulfite before being discharged to the Columbia River.

Gibbs & Olson prepared a capital improvement plan that evaluated the existing conveyance and treatment plant infrastructure. The plan included preparing an inventory and condition assessment for the conveyance components and the various systems within the plant, recommending improvements anticipated for a 20 year planning period, inspection of the gravity interceptor pipelines, preparing updated conveyance system maps, reviewing capacity projections and recommending anticipated improvements to meet anticipated capacity requirements over 5 and 20 year planning periods, preparing opinions of probable cost for recommended improvements anticipated over the 5 and 20 year planning periods and presenting all information to TRWWA in a final report.