Siting New Odor and Corrosion Control Facilities for Brightwater Conveyance System

King County is constructing a new treatment plant and conveyance system for a rapidly growing part of its service area. The new conveyance system will divert flows away from two existing interceptors (Swamp Creek and North Creek) to a new 2.2-mile influent tunnel that will drain by gravity to a new influent pump station. The pump station will pump the flow 2.6 miles and lift it 235 vertical feet through two parallel force mains to the new treatment plant, as shown in Figure 1.King County policy states that no odors will be detectable at the fence line for any of its facilities. The detectable threshold is defined as 3 dilutions to threshold for all odors. King County also requires a hydrogen sulfide (H2S) removal efficiency of 99.9 percent. To achieve these goals for the new conveyance system, King County needed to identify potential off-gassing points in the new conveyance system, quantify the foul air that could be released to the environment, characterize the wastewater quality, select appropriate technology, and site the odor control facilities.After initial review of existing data for the Brightwater tributary conveyance system, it was determined that there was insufficient data to predict concentrations of odorous compounds upon which to base the sizing of odor control equipment. Therefore King County initiated a two-year sampling and monitoring study of the future Brightwater tributaries. Sampling and monitoring sites were selected based on either their proximity to the future Brightwater connections or their appropriateness for characterizing upstream flow conditions. This paper describes the wastewater and air quality parameters monitored and the analysis of monitoring results. It discusses how a sampling and monitoring program was used to select, size, and locate new odor and corrosion control technologies for the Brightwater conveyance system. Odor control technologies selected for the conveyance system included carbon adsorption, bioscrubbers, and chemical injection at various points within the conveyance system.