3800 RIVERFRONT BLVD Geotech Report 2023-05-04

March 26, 2019 HWA Project No. 2015-061-21 Task 600-7 placement ended in early fall of 2018. The imported material possesses high fines content and is highly moisture sensitive. 2016 Loose Fill: Approximately 8 feet of fill was placed across the northeastern portion of the landfill site in 2016. This material consisted of gravelly, silty sand with cobbles and minor amounts of concrete rubble. The fill was placed during poor weather conditions and was bulldozed into place without the application of compaction effort. Therefore, this material was not compacted to 90 percent of modified proctor at the time of placement. The upper reaches of this material were spread over the site and compacted during the 2018 site grading effort. However, we expect that some of the loose fill still remains in this area. The imported material possesses high fines content and is highly moisture sensitive. Surcharge Fill and Landfill Fill Cap: Fill placed upon closure of the landfill, during surcharging and prior to 2016 was encountered throughout the site. In select areas, the upper two feet of this material was cement-treated to form an all-weather working surface. The fill typically consisted of gravelly, silty sand, with clean sand and sandy silt encountered in a couple of borings. Blow counts (SPT values) obtained in this fill ranged from single digits to the 40's. In general, the fill was loose to medium dense, with cement-treated soil and scattered cobbles and concrete rubble resulting in high blow counts. Refuse: Refuse(municipal solid waste) was encountered in all but one of the explorations. The refuse was observed to consist of household waste with glass, assorted metal, plastic, 111 construction debris, porcelain, paper, etc. The refuse sampled in the majority of the area explored consisted of blackened silty sand to sandy silt with blackened to charcoaled wood and scattered non-burnable waste including glass, metal and porcelain. The refuse thickness varied from approximately 13 to 40 feet and extended to depths of approximately 27 to 45 feet below the existing ground surface. Blow counts within the refuse indicated loose to very dense conditions. However, the dense and very dense conditions in the refuse, areas with N-values greater than 30, were likely due to driving the sampler into large debris in the refuse and are not believed to indicative of the soil actual soil density. Alluvium: Each of the borings encountered alluvium beneath the refuse(except in BH-48 and BH-50). The alluvium consisted of soft to stiff, organic silt,peat and medium dense sand. The presence and thickness of these subunits varied throughout the site. In general, the alluvium increased in thickness toward the river. The blow counts within the alluvium, particularly within the peat and silts immediately beneath the refuse, were higher in the recent borings than in the before-preloading borings. This suggests consolidation as a result of preloading. Glaciolacustrine: One of the borings along the western margin of the site(borehole BH-48) encountered hard clay and silt beneath the refuse or alluvium. This deposit consisted of glacially over-consolidated glacial lake deposits. Geotechnical Report Revision 3 26 2019.doc 6 HWA GEOSCIENCES INC.