DRAFT <br />depths explored. The soils range from sand to silt and clay and are less variable in terms <br />of composition and relative consistency compared to the overlying volcanic soils. In <br />general, the sand soils are silty and contain a trace of clay. The silt and clay soils generally <br />have a variable sand content ranging from a trace of sand to sandy. The relative density of <br />the sand typically ranges from loose to medium dense. The relative consistency of the silt <br />and clay soils ranges from medium stiff to hard and is typically stiff to very stiff. The natural <br />moisture content of the sand ranges from about 42% to 44%, and the natural moisture <br />content of the silt and clay ranges from about 34% to 60%. The results of Atterberg-limits <br />determinations for samples of the decomposed siltstone/sandstone are summarized on <br />Figure 17A and indicate the soil has a moderate to high plasticity, with plasticity index <br />values of about 26% to 43%. The results of laboratory consolidation testing completed on <br />a sample of the decomposed siltstone/sandstone are summarized on Figure 18A and <br />indicate the soil is typically moderately to heavily overconsolidated and has a low <br />compressibility in the overconsolidated range of pressures. All the remaining borings were <br />terminated in the decomposed siltstone/sandstone at depths ranging from about 33.5 feet <br />to 81.5 feet. <br />4.3 Groundwater <br />The borings for this project were completed using mud-rotary drilling techniques, which <br />do not allow direct measurement of groundwater levels at the time of drilling. However, <br />our experience indicates relatively shallow groundwater levels are common in the project <br />area throughout most of the year. To allow measurement and continuous monitoring of <br />groundwater levels at the site, an electronic vibrating-wire piezometer equipped with a <br />datalogger was installed at a depth of about 16 feet below the ground surface in boring <br />B-3. Groundwater levels measured by the piezometer between June 3 and August 13, 2021, <br />ranged from about 6.5 feet to 7.5 feet below the ground surface, which is consistent with <br />our observations at nearby sites. We anticipate the groundwater level at the site will <br />fluctuate in response to seasonal precipitation and the level of the nearby sloughs, ponds, <br />and Willamette River and may approach the ground surface during periods of heavy or <br />prolonged precipitation. In this regard, we understand design flood elevations at the site <br />are typically above existing ground-surface elevations. <br />5 CONCLUSIONS AND RECOMMENDATIONS <br />5.1 General <br />The results of our investigation indicate the site is generally mantled with field surfacing <br />materials that extend to a maximum depth of about 5 feet. Fill soils consisting of silt and <br />sand were encountered in some locations and extend to a maximum depth of about 8 <br />feet. Scattered wood debris and organics were observed in some of the fill, and our <br />experience in the project area suggests fill materials containing larger amounts of wood <br />and other debris may be present at the site, which could be a significant consideration <br />GRI #6497-A - 2.M0 Indoor Football Practice Facility Page 6 <br />August 26, 2021 <br />