7505 SEAWAY BLVD Geotech Report 2022-10-25

November 11, 2016 HWA Project No. 2014-117-21 gravel overlaying the very loose to medium dense,poorly compacted soils as part of the roadway fill at BH-6. • Historic Wetland Soils: We encountered about 3.5 feet of historic wetland soil underlying the roadway fill at BH-6. The historic wetland soils consist of very loose, olive-gray, sandy silt, with fine to medium gravel, containing decomposing organic rootlets underlying the roadway fill at BH-6. • Weathered Glacial Till—Weathered glacial till was encountered near the ground surface in borings BH-1, BH-2 and BH-4. The weathered glacial till generally consists of medium dense to dense, silty, gravelly, sand. The weathered glacial till extends to a depth of 12 feet in boring BH-2 and 5 feet in borings BH-1 and BH-4. • Glacial Till—Glacial till soils were encountered in borings BH-1 through BH-6. The glacial till soils generally consisted of very dense, silty, gravelly, sand. The glacial till soil extended beyond the termination depth of each boring drilled at the site. 3.3 GROUND WATER CONDITIONS Ground water seepage was observed in several of the explorations. Ground water was encountered during drilling in boring BH-5 and BH-6 at depths of 18 and 30 feet, respectively. These borings were advanced on the north side of 75th Street SW, near the wetland area. Ground water seepage was also observed during excavation of hand-borings HH-1 and HH-2, immediately above and below the remnant HMA pavement structure. The pavement structure is relatively impermeable, allowing water to accumulate above its surface. The ground water encountered below the pavement structure at hand-borings HH-1 and HH-2 is likely perched on a shallow glacial till layer. Groundwater seepage was observed at a depth of 3 feet when advancing hand-boring HH-5. No ground water seepage was observed in any of our other Phase I or II explorations at the time of drilling. However, hand borings HH-3 and HH-4 were only advanced to 3.5 and 3.3 feet, respectively; and borings BH-1 through BH-4 were advanced in the dry summer months. Rust mottling observed at a depth of 10 feet at boring BH-2 indicates a seasonally varying ground water table exists at the site. Prospective contractors should be prepared to encounter and manage water intrusion emanating from perched zones above the glacial till, and potentially from water-bearing sand lenses within the glacial till material. We expect localized pump and sump systems will likely be the most effective dewatering method. Contractors should also be prepared to encounter groundwater at or near the approximate elevation of the adjacent wetland when excavating signal pole foundations along the north side of 75th street. 2014-117 Final Geotechnical Report 5 HWA GEOSCIENCES INC.