3535 RIVERFRONT BLVD Geotech Report 2023-02-22

HWA EXPLORATIONS A geotechnical subsurface exploration program was conducted by HWA in June and July 2010, consisting of 12 boreholes on land, and one in-river boring completed in September 2011. The exploration locations were determined in the field either by GPS coordinates, triangulating from site features shown on air photo site plans, or taping distances from surveyed site features, and are plotted on the attached Site and Exploration Plan, Figure 2. Their positions are to be considered approximate consistent with the level of accuracy of the location methods employed. The land borings, designated B-101 through B-106 were drilled during the period June 28 through July 1, 2010. The borings were drilled with a CME-850 track-mounted rig. The rig advanced 4.25-inch inside diameter(ID), continuous-flight, hollow-stem augers. The borings were advanced to depths of 16.5 to 86 feet. The in-river boring, B-107, was drilled on September 29, 2011, by Holocene Drilling Inc. with a truck-mounted Mobile B-59 drill rig on a barge,brought upriver with a tugboat. The drill rig employed hollow-stem auger with bentonite drilling mud pumped into the auger to counter sand heave encountered during the drilling operations. The boreholes were abandoned with bentonite chips upon completion of drilling. A standpipe piezometer was installed in borehole B-105, at the location of a proposed leachate pump station. The hole abandonment method consisted of pouring bentonite chips through the hollow stem auger, and removing one 5-foot section of auger at a time, keeping the level of bentonite chips up inside the auger to prevent collapse of the borehole walls prior to filling. Soil samples were collected at 2 '/2 to 5-foot intervals using Standard Penetration Test(SPT) sampling methods, which consisted of using a 2-inch outside diameter, split-spoon, sampler driven with a 140-pound hammer. The drill rigs were equipped with an automatic trip hammer for performing the SPT's. During the test, a sample was obtained by driving the sampler 18 inches into the soil with the hammer free-falling 30 inches per stroke. The number of blows required for each 6 inches of penetration was recorded. The standard penetration resistance of the soil is calculated as the number of blows required for the final 12 inches of penetration. If a total of 50 blows is recorded within a single 6-inch interval, the test is terminated, and the blow count is recorded as 50 blows for the number of inches of penetration. This resistance provides an indication of the relative density of granular soils and the relative consistency of cohesive soils. All explorations were advanced under the full-time observation of HWA geologists. Soil samples obtained from the explorations were classified in the field and representative portions were placed in plastic bags. These soil samples were then returned to our Bothell, Washington laboratory for further examination and testing. Pertinent information including soil sample depths, stratigraphy, soil engineering characteristics, and ground water occurrence was recorded and used to develop logs of each of the explorations. A Legend to the Terms and Symbols Used on the Exploration Logs is presented on Figure A-1. The summary logs of the explorations are presented on Figures A-2 through A-8.