11831 AIRPORT RD WHOLE SITE FILE Geotech Report 2022-10-25

in GEI-13 to the depth explored. We interpret the dense silty sand encountered the hand auger to also consist of glacial till. Boring MW-1 and test pit PIT-1 were completed in the native growth protection area (NGPA)situated west of 3rd Avenue SE along the north side of 128th Street SE. Boring MW-1 was completed to a depth of 21/feet bgs,and test pit PIT-1 was completed to a depth of about 8 feet(after completion of the infiltration test). Boring MW-1 encountered loose to dense silty sand which might be fill or weathered glacial till to a depth of about 12 feet, underlain by very dense glacial till. Test pit PIT-1 encountered about 11h feet of fill consisting of loose silty sand with gravel underlain by medium dense silty sand with gravel. Weathered glacial till consisting of medium dense silty sand with gravel and cobbles was encountered at a depth of 5 feet.The till becomes unweathered and very dense at a depth of 7 feet. We did not encounter groundwater during drilling in GEI-13 or in hand auger HA-5. Groundwater was measured in MW-1 at a depth of 6.8 feet on March 11, 2017. 128th Street SE widening at 1-5 Borings GEI-20 and GEI-21 were drilled near the northbound 1-5 on-ramp. GEI-20 was drilled on the Interurban Trail in the northeast corner of the intersection; GEI-21 was drilled on the grass embankment on the west side of the on-ramp as shown on site plan Figure 2L. Borings GEI-22 and GEI-23 were drilled near the southbound 1-5 on-ramp. GEI-22 was drilled on the grass embankment on the east side of the on-ramp and GEI-23 was drilled at the toe of the existing rockery as shown on site plan Figure 2M. Borings GEI-20,GEI-21,GEI-22 and GEI-23 were drilled to depths of 111/2 to 161 feet. Fill was encountered on the east side of 1-5 to a depth of about 141 feet below the on-ramp.The fill consists of medium dense to dense silty sand with occasional gravel. Boring GEI-20 did not extend through the fill and very dense glacial till was encountered below the fill in boring GEI-21. Loose to dense silty sand fill was also encountered on the west side of 1-5 near the southbound on-ramp. The fill thickness is greater than the depth explored in boring GEI-22 (greater than 161/2 feet), and was approximately 12 feet in boring GEI-23 which was advanced from a lower elevation below the rockery.Very dense glacial till underlies the fill in boring GEI-23(beginning at approximately 12 feet below the toe of the rockery). Groundwater was encountered in GEI-23 at approximately 15 feet bgs at the time of drilling. Groundwater was not encountered in the other borings during drilling, however wet soil samples were obtained in GEI-20 and GEI-22, indicating perched water may be present from 5 to 7 feet bgs in GEI-21 and near the bottom of the boring in GEI-22. 128th Street SW at 4th Avenue West Boring GEI-14 was drilled in the grass in the southwest corner of the intersection of 128th Street SW and 4th Avenue West as shown on site plan Figure 2M.Approximately 11 feet of loose to medium dense fill with occasional asphalt debris was encountered overlying medium dense to very dense glacial till. GEOENGINEERS April 14,2017 : Page 8 File No.2095-032-00