7800 EVERGREEN WAY HYUNDAI 2025-08-05

LMJ Enterprises, LP March 31, 2022 Page 3 Perched groundwater should be expected to vary as a function of season, precipitation, and other factors. Seepage zones should be expected to develop near the bottom of the fill material, perched above the dense glacial till deposits. PILOT INFILTRATION TESTING PIT-1 was conducted as a small-scale PIT test in accordance with the 2019 Ecology SWMMWW (Ecology 2019). Infiltration testing was not completed in PIT-2 due to groundwater seepage impacting the excavation above the test elevation. The following is a summary of test methods, field measured infiltration rates, and recommended design infiltration rates for the small-scale PIT. Test Method PIT-1 was initially excavated with a trackhoe to a depth of approximately 4 feet. The test excavation extended to the proposed subgrade elevation of the proposed infiltration facility, as requested by KPFF. The bottom of the PIT-1 excavation was approximately 4 feet wide by 4 feet long. Soil observed at the test elevation in PIT-1 generally consisted of fine to coarse sand with silt and gravel (glacial till). During testing, a graduated yard stick was driven into the floor of the excavation as a visual reference for monitoring water levels during testing. A piezoelectric pressure transducer was secured to the bottom of the yard stick to provide accurate water level records in 1-second intervals throughout the duration of the testing. Water used for the infiltration test was provided by a connection to a nearby City of Everett fire hyd ra Fit. Initial filling and maintaining of the water level in PIT-1 was performed by monitoring the declining water level in a series of stages. The excavation was filled to a predetermined depth (approximately 14 inches) for the 6-hour pre-soaking period. During the pre-soaking, the water level was allowed to drain approximately 2 inches before the pitwas refilled to the initial level again to maintain a constant minimum depth of 1 foot. This draining and refilling process was repeated a number of times (stages) in succession. At the end of the 6-hour pre-soaking period, the successive filling and draining was repeated at the same 12 and 14 inches of water depth for an additional hour, which is considered the testing period. Following this testing period, the waterwas turned off and the water level was recorded foran additional hour or until the excavation was drained. By periodically refilling the excavation to the starting level, then allowing the water level drop between two pre -determined levels, the apparent infiltration rate for each cycle was determined accurately using measurements from the pressure transducer. The rate of decline in the falling water levels recorded after each filling cycle was used to calculate the apparent infiltration rate for each stage of the test. The overall testing process for the PIT took about 7 hours with water levels measured continuously (every 1 second). The water -level measurements for PIT-1 is plotted on Figure 2. A plot of the measured infiltration rate calculated during each stage of the small-scale PIT is shown on Figure 3. After completingthe PIT, water remaining in the excavation was bailed out usingthe backhoe bucket. PIT-1 was excavated an additional 5 feet below the infiltration testing depth. The PIT excavation was overexcavated to observe and sample the soils below the level of the PIT. Hydraulically resistive layers consisting of glacial till were observed at and below the elevation that the PIT was performed. ■ GMENGINEER� File No. 24459 003 00