3800 RIVERFRONT BLVD Geotech Report 2023-05-04

May 13, 2019 HWA Project No. 2015-061-21 development areas. A site plan, showing the maximum anticipated extent of lateral spreading is shown in Figure 6. As can be seen in Figure 6, some level of lateral spreading is expected to extend into the eastern edge of the proposed Phase III and IV development areas. Our analysis shows that the lateral spreading displacements at the east end of the proposed parking lot may be on the order of 3 to 7 inches for the IBC maximum considered earthquake (2,475-year return period). These displacements are expected to result in some pavement distress within the parking lot, along the eastern edge of these development areas. The impact to Phase III and IV buildings will be dependent on the geometry of the subject phases and will be evaluated at a future date. Additional Comments HWA would like to note that most of the boring logs conducted between the leachate collection trench and the river were not completed with the assessment of liquefaction in mind and appear to have been conducted using hollow stem auger drilling techniques. Significant heave was noted in many of the borings within the alluvial sand units below the groundwater table. As a result, HWA believes that many of the low blow counts noted within the alluvial sands are unrepresentative of the actual conditions. We expect that these understated values have resulted in the identification of a greater level of liquefaction than actually exist in the field. As a result, further explorations and analysis may be required to more accurately determine unit susceptibility to liquefaction and better assess the site potential for lateral spreading for Phases III and IV. 0•0 Everett Riverfront Development Addendum 5 HWA GeoSciences Inc.