3800 RIVERFRONT BLVD Geotech Report 2023-05-04

1 March 26, 2019 HWA Project No. 2015-061-21 Task 600-7 2.0 FIELD AND LABORATORY INVESTIGATION 2.1 FIELD INVESTIGATIONS HWA's fieldwork consisted of a subsurface exploration program that included 15 borings designated BH-36 through BH-50. The approximate locations of these borings are shown on the Site and Exploration Plan, Figure 2. Exploration locations were surveyed and staked in the field prior to drilling. These subsurface explorations were performed to determine the character and extent of fill and refuse on the site, to characterize alluvial deposits below the refuse and determine depths to dense to very dense glacially consolidated deposits. Borehole drilling was conducted from November 5 to November 8, 2018 by Holocene Drilling, Inc. of Puyallup, Washington under subcontract to Shelter Holdings. Drilling equipment was selected based on site access conditions and included two track-mounted drill rigs. The boreholes were advanced to depths ranging from 50 to 81 feet below the existing ground surface. Hollow stem auger drilling techniques were used from the ground surface to the base of the refuse. Below the base of the refuse, each boring was continued using mud rotary drilling methods. Each of the explorations were advanced under full-time HWA supervision and were logged by an engineering or environmental geologist. Soil samples were classified in the field during the investigation. Other pertinent information including sample depths, stratigraphy, soil engineering characteristics and groundwater occurrence was recorded. Drilling spoils were collected in lined cardboard boxes during drilling for disposal at an approved on-site refuse disposal area. Representative soil samples were obtained from the explorations and taken to our laboratory for further examination and geotechnical testing. Field exploration methods are described in detail and logs of the explorations are presented in Appendix A. 2.2 REFRACTION MICROTRMOR(REMI)SURVEY HWA also performed Refraction Microtremor(ReMi) testing at the northeast corner of the site. The geophone array location is shown on the Site and Exploration Plan, Figure 2, labeled REMI-1. This seismic survey exploration was performed to record surface-wave velocity dispersion and to obtain a shear-velocity profile of the site. The array consisted of 12 geophones, spaced at 25 feet, spanning 275 feet total array length. Source energy was provided by the noise from the ambient environment and a work truck running up and down the line. The data was recorded using a Seistronix RAS-23 Exploration Seismograph. The SeisOpt ReMi V2.0 Vspect software module was utilized for velocity spectral (p-f) analysis and Rayleigh Phase-Velocity Dispersion Picking. The SeisOpt ReMi V2.0 Disper software module was utilized for shear- velocity profile modeling. Table 1 provides the estimated shear wave velocities of the geologic units underlying the site. Based on the data, the approximate average shear wave velocity for the soil profile in the upper 100 feet is about 740 feet per second. Geotechnical Report Revision 3 26 2019.doc 2 HWA GEOSCIENCES INC.