Geotechnical Soil Infiltration Investigation <br />2610 Cal Young Road, Eugene, Oregon <br /> <br />5 | P a g e CORE GeoEngineering, Inc. Project No. 25-1127 <br /> Version 1.0, January 23, 2026 <br /> <br />7.5 feet bgs within test pit TP-4 indicated an in-situ moisture content of 36.2 percent. Sieve analysis <br />conducted in accordance with ASTM D6913 and D1140 indicated 78.4 percent passing the No. 200 sieve. <br /> <br />5.2 Depth to Groundwater <br />On December 5, 2025, soil moisture conditions were observed to range from moist to wet. Groundwater <br />seepage was not encountered within our explorations which extended to maximum depths of 8 feet bgs. <br />A review of water well reports filed with the Oregon Water Resources Department (OWRD) identified <br />static water levels reported at 23 feet bgs (Well LANE 57683, November 11, 1999) and 40 feet bgs (Well <br />LANE 69794, August 7, 2009) in the site vicinity. The Web Soil Survey indicates depth to water table ranges <br />from 0 feet bgs for the Courtney series to greater than 6.6 feet bgs for the Salem series mapped at the <br />site. Seasonal precipitation patterns significantly influence groundwater levels in the Willamette Valley, <br />with higher groundwater levels typically occurring during winter and spring months. <br /> <br />5.3 Infiltration Testing <br />Soil infiltration testing was performed within each test pit in accordance with the methods required by <br />Appendix G of the 2014 Eugene Stormwater Management Manual using the Open-pit Falling-Head <br />method. The approximate locations of the subsurface explorations is indicated on Figure 2. Infiltration <br />testing data tables are provided in the report appendix. A presoak period was conducted within each test <br />pit prior to testing. During testing the water level was measured to the nearest 0.01 foot (1/8 inch) from <br />a fixed point over specific time intervals, and the change in water level was recorded at regular intervals <br />until three successive measurements showing a consistent infiltration rate were achieved. Table 1 <br />summarizes the results of the infiltration testing. Infiltration rates have been reported without applying a <br />factor of safety. <br /> <br /> Table 1: Summary of Infiltration Test Results <br />Test <br />Location <br />Test <br />Designation <br />Depth <br />(feet bgs) <br />Soil <br />Type <br />Percent <br />Passing US <br />No. 200 <br />Sieve <br />Infiltration <br />Rate <br />(inches/hr) <br />Hydraulic <br />Head Range <br />(inches) <br />Test Type <br />TP-1 IT-1.1 3 CL 81.2 0 12 inches Open-Pit Falling-Head <br />TP-1 IT-1.2 8 CL 93.4 0 12 inches Open-Pit Falling-Head <br />TP-2 IT-2.1 5.5 CL - 0 12 inches Open-Pit Falling-Head <br />TP-3 IT-3.1 6.5 CL - 0 12 inches Open-Pit Falling-Head <br />TP-4 IT-4.1 7.5 CL 78.4 0 12 inches Open-Pit Falling-Head <br />TP-5 IT-5.1 7.0 CL - 0 12 inches Open-Pit Falling-Head <br /> <br />Infiltration testing at the site indicated no measurable infiltration capacity at the locations and depths <br />tested. Based on the test results, stormwater infiltration systems do not appear to be geotechnically <br />feasible within the clay soils encountered at the depths tested. Well logs from the site vicinity indicate <br />that coarser-grained gravel deposits may be present at depths below the clay layers, which could <br />potentially provide improved infiltration capacity. However, the presence, depth, and infiltration <br />characteristics of these deeper gravel deposits would need to be confirmed through deeper soil borings <br />and additional infiltration testing. CORE GeoEngineering can provide these services if determined to be <br />necessary for project design.