5720 EAST DR 2018-01-02 MF Import

Geotechnical Engineering Report Parcel 00471700002401- 57XX East Drive Everett, Washington December 12, 2009 RMI File No.53409 Page 3 Literature Review The Geologic Map mentioned above notes that this area was mapped as Vashon till but exposures identified the soil as advance outwash sands and gravels. Hydrologic Conditions There was no sign of groundwater exiting the slope or on the surface of the lot. Slope Stability The core of the lot comprises dense advance outwash sands and gravel. We did not observe signs of deep- seated slope failures nor would we expect any. It is our opinion that there is not a significant potential for deep-seated slope instability. Signs of backwasting (movement of near -surface soil) through exposed soil erosion processes or local surface slides are common to steep slopes, particularly where exposed to weathering, such as rain, wind, and freeze -thaw. There was no sign of backwasting. CONCLUSIONS AND RECOMMENDATIONS General It is our opinion that the site is compatible, from a geotechnical engineering standpoint, with the proposed development. The underlying deposits on the lot will support the proposed structure but certain precautions should be taken. The surficial slope soils can be subject to slow backwasting due to weathering, creep, shallow sloughing, local erosion, and significant storm events. This would result in slow recession of the slope faces but there was no evidence of this. Development Considerations A building setback from the top or toe of steep slopes is usually specified to allow for backwasting and slope failures. As the slopes are below the angle of repose for these soils (38 degrees, 78%) no setback is required. However we recommend that the home be setback 25 feet from the top of the steep slope RMI ASSOCIATES LLC D��