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

3rd Interim Action Construction Report Kimberly-Clark Upland Site 0121049.080.084 July 30, 2024 2-6 landauinc.com Subgrade utilities were installed in trenches ranging from 1 to 2 ft below the former grade shallow enough to be within clean fill material placed at the Site during implementation of the 2nd Interim Action completed by K-C in 2020, up to approximately 8 ft below ground surface (bgs). Select structures required excavation of up to 18 ft bgs (i.e., the stormwater lift station upstream of the stormwater treatment system and Outfall M). Excavated material generated during trenching was managed in accordance with the Work Plan and is described in further detail in Section 2.6. Utility trench cutoff walls were also installed to reduce the risk of contaminating adjacent properties, or contamination from nearby properties impacting the Site at the Site boundary on Federal Avenue and at the two reconstructed outfalls—Outfall A and Outfall M. Cutoff wall details are provided in as-built sheets C5.2 (Federal Avenue utilities) and C4.10 and C4.14 (outfalls). 2.5 Outfall Reconstruction Consistent with project plans, existing Outfalls A and M were reconstructed for discharge from the new stormwater system. Outfall reconstruction activities were conducted in the dry during low tide windows in the mornings of July 25 through July 27. Soil excavated from around the former outfall pipes consisted of brown to black, silty sand with some cobbles and debris (bricks); clean imported quarry spalls and rip rap was used as fill during reconstruction. As the former Outfall A outlet daylighted north of the new Outfall A, abandonment of the former outfall pipe was completed after reconstruction of the new outfall. The former Outfall A pipe was shown on historical plans, but initially could not be located along the shoreline and had to be located in the upland portion of the Site. A pipe, suspected to be the former Outfall A pipe, was located upstream near an existing storm drain structure near the existing warehouse in a pothole excavation approximately 8 ft bgs. On August 2, 2022, a camera was placed in the pipe. The camera initially followed the pipe approximately 69 ft to the west before encountering water. The camera was in the pipe at the time of a falling tide and proceeded down the pipe as the tide decreased up to a total of 128 ft west of the point of entry. Based on a tide elevation at the time of the camera’s furthest travel distance, the elevation of the pipe at the furthest point the camera progressed was -0.8 ft, or approximately 16 ft bgs. Based on the fact that the water in the pipe was fluctuating with the tide, and the location of the pipe generally matched historical plans, this pipe was determined to be the former Outfall A pipe and was abandoned by filling with CDF from the access point in the pothole excavation. The outfall was later identified along the shoreline on August 11, 2022, and the pipe was also plugged at this point with grout placed behind sandbags. As-built sheets C4.9 and C4.10 present details for the reconstructed outfalls. Select photographs of the outfall reconstruction are included in Appendix D. 2.6 Soil and Groundwater Management Management of contaminated soil and groundwater during construction of subgrade utilities was conducted in accordance with the soil and groundwater management plan (SGMP), which was an attachment to the Work Plan. The project also included excavation outside the Site boundary to the