7000 HARDESON RD Geotech Report 2022-10-25

Geotechnical Engineering Report Community Transit Merrill Creek Operating Base 7100 Hardeson Road Everett, Washington February 28, 2018 RN File No. 3224-002A Page 4 observed indications of groundwater seepage. These pressure transducers provide continuous groundwater readings. Two sensors were installed in the wells. One sensor was to continuously measure groundwater elevations with the second sensor being installed to measure barometric pressure for correcting the water level data. Data was obtained from the devices on December 8, 2017 graphed and compared to rainfall data obtained from the Washington State University weather website. The groundwater elevation graph with rainfall data for that monitoring period is shown on Figure 22. The pressure transducer in Boring 6 malfunctioned and was replaced in December. The monitoring wells, located throughout the south parking lot have assumed top of casing elevations taken from the topographic survey. Our data shows groundwater fluctuations throughout the approximate two month monitoring period with maximum and minimum elevations as follows: Maximum Minimum Minimum Static level Boring Top of Casing Groundwater Groundwater Groundwater measured Elevation (feet) on January Elevation (feet) Elevation (feet) Depth (feet) 25, 2018 6 432.5 - - 9.58 7 434.5 424.05 422.98 10.45 9.64 9 438 432.90 431.78 6.22 3.98 10 435.5 dry dry dry dry The monitoring period from November 20, 2017 to January 25, 2018 has shown the groundwater elevations steadily increase. It also shows variable groundwater conditions. We expect this is due to the variable soil types in the fill underlying the site. CONCLUSIONS AND RECOMMENDATIONS General It is our opinion that the site is compatible with the planned improvements. The underlying fill varies in density and composition. We recommend that the pavement be founded on compacted structural fill as described in the Site Preparation and Grading subsection of this report. Geologic Hazards Erosion Hazard: The erosion hazard criteria used for determination of affected areas includes soil type, slope gradient, vegetation cover, and groundwater conditions. The erosion sensitivity is related to vegetative cover and the specific surface soil types (group classification), which are related to the underlying geologic soil units. We reviewed the Web Soil Survey by the Natural Robinson Noble, Inc.