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

SR 527 at 153rd Street SE and SR 527 at Trillium Boulevard Boring GEI-9 was drilled in the existing bus stop lane of northbound SR 527 north of the intersection with 153rd Street SE Road. Boring GEI-10 was drilled in the existing bus stop lane of southbound SR 527 south of the intersection with Trillium Boulevard.The locations of the borings are shown on site plans Figures 2H and 21. Borings GEI-9 and GEI-10 were completed at depths of 10/, and 111 feet bgs, respectively. Medium dense silty sand and sandy gravel fill was encountered below the pavement section to a depth of about 3 to 7 feet bgs. Medium dense to very dense silty sand with variable gravel (glacial till) was encountered below the fill to the depth explored. A perched layer of groundwater was observed from approximately 7 to 10 feet bgs in GEI-9 at the time of drilling. Groundwater was not observed in GEI-10 at the time of drilling. 132nd Street SE at 16th Avenue SE Boring GEI-11 was drilled in the right turn lane of westbound 132nd Street SE at 16th Avenue SE; boring GEI-12 was drilled in the grass in the southwest corner of the intersection as shown on site plan Figure 2J. Borings GEI-11 and GEI-12 were completed at depths of 16/ and 101/4 feet bgs, respectively. Medium dense to dense silty sand fill was encountered in both of the explorations extending to a depth of about 9 feet in boring GEI-11 and 4 feet in GEI-12. Underlying the fill in GEI-11,we encountered an approximately 3-foot thickness of wetland deposits consisting of soft peat and organic silt.Underlying the wetland deposits in GEI-11 and the fill in GEI-12 we encountered glacial till to the depth explored.The glacial till consists of very dense silty sand with variable gravel content. Groundwater was not observed at this location at the time of drilling. 132nd Street SE at Elgin Way/Dumas Road Hand auger HA-4 was completed at the toe of the existing rockery at the south corner of the intersection, as shown on site plan Figure 2K. Fill was encountered in the hand auger the full depth explored,to a depth of 41 feet below the toe of the rockery.The fill consisted of medium dense silty sand with occasional gravel and sand with silt and gravel. This is consistent with the test pit exploration completed in 1991 for the intersection improvements where 7 feet of fill overlying very dense glacial till was encountered.We did not encounter any indications of landfill debris in the fill. Approximately 16 feet of landfill debris was encountered on the northwest side of the intersection in boring B-1 completed in 1991. Groundwater seepage was not observed in the shallow hand auger. 128th Street SE at 3rd Avenue SE Boring GEI-13 was drilled in the right lane of eastbound 128th Street SE east of the intersection of 3rd Avenue SE; hand auger HA-5 was conducted in the grass behind the fence in the northwest corner of the intersection as shown on site plan Figure 2L. Boring GEI-13 and hand auger HA-5 were completed at 111/ and 21 feet bgs, respectively. Very dense glacial till consisting of silty sand with occasional gravel was encountered beneath the pavement section GEoENGINEERI April 14,2017 Page 7 File No.2095-032-00