3800 RIVERFRONT BLVD Geotech Report 2023-05-04

I I APPENDIX A IFIELD INVESTIGATION The subsurface exploration program consisted of 15 boreholes, drilled to depths ranging from 50 to 81 feet below the existing ground surface. Drilling equipment was selected based on site Iaccess conditions and included two track-mounted drill rigs. Exploration locations were surveyed and staked in the field prior to drilling. The approximate 1 exploration locations are shown on the Site and Exploration Plan, Figure 2. Each of the explorations was completed under the full-time observation of an HWA engineering or environmental geologist. HWA personnel recorded pertinent information including soil sample depths, stratigraphy, soil engineering characteristics and groundwater occurrence as the I explorations were drilled. Soils were classified in general accordance with the classification system described in Figure A-1, which also provides a key to the exploration log symbols. Soil layers containing refuse are left blank in the left-hand column for soil symbols because of the I wide variety of conditions in the refuse. The summary logs of boreholes are presented on Figures A-2 through A-16. The stratigraphic contacts shown on the individual logs represent the approximate boundaries between soil types. The actual transitions may be more gradual. I Under subcontract to HWA, Holocene Drilling, Inc. of Puyallup, Washington, drilled the borings in November, 2018. HWA sampled soils to depths of up to 81 feet in the borings. Holocene Iemployed a track-mounted CME 830 drill rig, and a Diedrich D-50 Turbo tracked drill rig. All 15 subsurface explorations conducted for the 2018 Phase 1 area were joint hollow stem auger and I mud rotary borings. Two rigs were deployed onsite, both equipped with eight-inch outer diameter hollow stem augers and 4.5-inch diameter tri-cone bits for mud rotary. Each boring used the hollow stem augur technique down past the bottom of the refuse, then switched over to I mud rotary for the rest of the boring. The switchover depth generally varied from approximately 35 to 60 feet below the existing ground surface across the site. Where possible, intact soil samples were obtained using Shelby tubes and 1-inch and 6-inch rings inside of 3-inch O.D. Modified California samplers. Shelby tubes were advanced into soft soils by drill rig hydraulics. The modified California samplers were driven with a 140-lb hammer with a 30-inch drop. Standard Penetration Test(SPT) samples were obtained by driving a two-inch split spoon Isampler at the end of drilling rods (threaded heavy steel pipe). The SPT sample rods were driven with a 140-lb hammer with a 30-inch drop, at depths of 2.5 and 5 feet below the ground surface I and then at 5-foot intervals after that. Additional samples between the 5-foot intervals were obtained were advanced and additional higher-resolution observation was necessary. Soil samples were collected in sample bags and catalogued.