1315 MADRONA AVE 2016-01-01 MF Import

_:eoter_nn�ccl En9incer,��,� it�;,�rt � � i 3 fvladrona Avenue i verett, Washington �iarch 11, 2013 �iiJ File No. 2793-001A Page 4 Hydrologic Cond��tions Groundwater was encountered in both Boring 1 at 9'%z and m Bonny ?_ et 10 'n feet 7he ;eepag� was obs� rved ot the approximate contact between the mediwn �ense g!aaal drrft and the very dense acJ:ance outwash. Vde could not determine if the seepage was part of a larger ground water fable �elow the glacial drift or rf the water �s perched in a sand seam withm the glacial dnft The loose to dense glacial dnft interpreted to unde ;ie the site is considered pourly drainmg. Dunng the wetter times of the year, we expect perched water conditions will occur as pockets of water on top of the glacial drift layer. PercF�ed water does not represent a regional groundwater "table" �vithin the upper sod horizon, Volurr.es of perched aroundwzter vary depending upon the time of year and the upslope recnarge conrjit�ons. CONCLUSIONS AND RECOMMENDATIONS Generel It is our opinion ihat the site �s compatible with the planned development. The underly�ng medium dense to dense glacial dr�tt deposits are capable of supporting the planned structures and pavements We recommend that the foundations for the structures extend through any !�II, topsoil, loose, or disturbed soils, and bear on the underly�ng medwm dense or very dense, nauve glacial drift, or on structural idl extending to these soiis. Based on our site explorations, we anticipate these sciis v.�ll generally be encountered around 3 to 7 f�et belo�-v ground surface. Geologic Hazards Landslide Hazards: The core of the s�te is inferred to be composed of glac�ally overndden soils. We consider these soils to be of high strength and considered to be stable with regzrd tc deep seated slope failures. However we did observe indications of surficial seepage on the srte, and indications of shallow slope failures The trunk of the Uees located on the northwest ;lope appeared ro have slight bending in them indicating past siope movemeni. There is a potential that the suriicial soils on the steeper sections o( the slope cou�d slough over time. Any slough events are expected to be surficial, and are affected by surface water and man- made impacts. The risk of slough events can be minimized i( proper drainage is installed. ,�egetation on the slope is ma ntained, and yard waste and other debris are hept of( the slopes We would expect if a slough event were to occur, it could range in scale and depth We did noi observe any indication o( recent sloughing on site. Erosion Hazard: The erosion hazard cnteria used for det�rmination of a(fected dieas includes sod type, slope gradient, veyetation cover, and groundwater conditions The erosion sensitiv�ty is related ro vegetative cover and the specific surFace soil types (group classification), which arr. reiated to the underlying geolor�ir, soil units. We reviewed the Soil Survev of Snohomish CountY Area,_ Washinaton by the Soii Conservation Serwce (SCS) to determme the erosion hazard oi the on-ste soils. The site surface soils were classi(ied using the SCS classificaUon system as Alderwood-Everett gravelly sandy loams, 25 to 70 percent slopes (Un3 4l. The corresponding geologic unit for these soils is till and glacial outwash, which is in agreement ,n�ith the soils encountered in our srte explorations. The erosion hazard for the soil is hsted as being severe for the sloping conditions at the s�te Robinson Noble, Inc