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18 certerra.com 4660 Main Street, Suite 100, Springfield, Oregon 97478 T: 541.393.6340 Our infiltration testing was conducted on March 20, 2026, March 24, 2026 and March 26, 2026. In both infiltration test locations, IT-1 and IT-2, we encountered topsoil, overlying stiff native Fat Clay (CH), overlying hard Eugene Formation Siltstone. No groundwater was observed in either IT-1 or IT-2 during installation of the standpipes. The infiltration tests were conducted in accordance with the current City of Eugene Stormwater Management Manual - Encased Falling Head Test, available at https://www.eugene-or.gov/477/Stormwater-Management-Manual. A six- inch diameter casing (stand pipe) was embedded into the soil at the bottom of the holes. We placed approximately 3 inches of clean gravel in the bottom of each stand pipe to protect the soil at the bottom from scouring. We then filled the stand pipes with a 12-inch head of water for the initial pre-soaking trial. The 12-inch head of water did not completely infiltrate in 10 minutes (pre -soak trial was performed twice), therefore we performed our first trials upon completion of the required 4-hour pre-soak. According to the procedure, trials are to be conducted for at least 1 hour, until the m easured infiltration rate between two successive trials does not increase, and the percent change is minimal. The standpipes will be retrieved and the infiltration test locations loosely backfilled with the excavated soil, upon completion. Note that the average infiltration rates presented in Table 2 below are the unfactored infiltration rates (i.e. no Factor of Safety applied). Table 2: Infiltration Test Results. Infiltration test Trial Depth (inches) Infiltration Rate (inches per hour) Washed Gradation (% passing #200 sieve) Soil Stratum Tested IT-1 16 Less than 1/8 72 Hard Eugene Formation Siltstone IT-2 16 1-1/2 50 Hard Eugene Formation Siltstone