3815_PGSF WMVD Pkg 2_Vol 4-3_03.03.2026_BXWA_Certified

2 3/1/2021 The PSO 4 pipeline started at Lift Station No. 5 as a 10-inch diameter pipe, where it crossed under the railroad tracks to enter the former KC site. As the pipeline traveled west across the KC site, multiple revisions, pipe types, and pipe upsizing occurred over the years to accommodate the site’s historical industrial use, with multiple connections added from the KC facilities. By the time effluent reached the point of discharge, the pipe was 30 inches in diameter, an increase of nine times the flow capacity . Pipe types used included clay tiles, ductile, and concrete. Nine manhole structures were abandoned across the site, varying between brick and concrete. The methods used to abandon the pipeline and manholes were from documents provided to the Ecology Toxics Cleanup Program for this site (Aspect Consulting memorandum to Andy Kallus, Approach for Plugging Open Pipes at Shoreline, June 27, 2018) and were referenced in the February 2020 work plan. Each manhole and pipe access location along the pipeline alignment was filled with a control density fill mix (CDF) as specified in the submitted work plan. The CDF mix was applied for a length of at least five times the pipe diameter at each manhole and all connections. The CDF mix is lean cement, which upon setting has only a few hundred psi compressive strength. The work plan presented the metal analyses of the CDF aggregate materials from the gravel pit indicating the aggregate metal levels are well below MTCA Method A for soils. Figure 1 shows PSO 4 across the former KC site, the manhole locations, and the lay lengths that were fully filled with CDF. Concrete trucks were brought on site and delivered the CDF at a consistency and viscosity that allowed the CDF to be pumped to at least the five times the pipe diameter length for each manhole connection stated in the Aspect Consulting memo. The CDF supplier provided a mix that was able to fill the pipes (adjustments had to be made as viscosity specifications are not normal for concrete mixes). The pump hose was measured and marked with the required length to be used at each manhole location to ensure the volume requirement of five times the diameter length was met. At the end of the entire pour the volume required at all nine manhole locations was exceeded by one yard of CDF, surpassing the established quantity for the length requirement. The CDF was delivered in two pours due to the CDF viscosity and to ensure the head pressure of CDF in a manhole did not push the CDF beyond the length needed to keep the pipe’s full circumference filled. The first pour filled the pipes to the required length and then was allowed to set, preventing the CDF from being pushed further down the pipe due to the manhole head pressure. A visual inspection was completed after each pour to ensure the pipe’s circumference was filled after the pump hose was removed. Once the pipe connections were filled and