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i� <br /> � <br /> DAVID L. NELSON AND ASSOCIATES, INC. <br /> Consulting Engineering Geology <br /> � October 6, 1992 <br /> Project No. 9892 <br /> � Page 5 <br /> � <br /> Erosion Iiazard <br /> � The erosion hazard criteria used for determination of affected <br /> areas include soil type, slope gradient, vegetation cover and <br /> � ground water �onditions. The erosion sensitivity is related to <br /> vegetative cover and tha specific surface soil types (group <br /> clessification) , which are related to the underlying geologic <br /> soil/rock units. The following table outlines erosion hazard for <br /> � the on-site soils that have been stripped of vegetation. The <br /> surface soils found wa.thin the site have been classified in <br /> accordance with the Soil Conservation Service (SCS) <br /> � classification system and have been grouped with respect to the <br /> corresponding geologic unit. <br /> � Geoloaic Unit Surface Soil Sensitivitv At Sloae 0 15$ 16 39� >40$ <br /> QvDr Alderwood Low Med High <br /> (Glacial Drift) <br /> � QvA Everett Low 1led High <br /> (Advance Outwash) <br /> � Springs/Ground Water Seepage Areas <br /> � During our evaluation of the site, we observed the surface areas <br /> for springs and seeps, and observed our backhoe exploration <br /> (test) pits for ground water seepage conditions . <br /> ' We did not encounter any evidence of springs or seeps within the <br /> upper portion of the site. Wet soils and seepage areas were <br /> � observed near the toe of the slope, below th_ outcropping gr.ound <br /> water line, but were not considered of signi[icance to the <br /> proposed development upslope. <br /> � CONCLUDING OpINIONS <br /> In general, we conclude that the evaluated site area should be <br /> ' suitable for residential development, provided the guideline <br /> recommendations and precautions as presented herein are followed. <br /> From an engineering geologic standpoint, the native soils areas <br /> ' above the top-of-slope appear stable, and should be capable of <br /> supporting the planned development, where "conventional" <br /> foundations are placed within the native glacial soils. The <br /> undisturbed glacial deposits should provide a reasonable subgrade <br /> � for support of the anticipated development improvements, and <br /> toqether with the recommended building setback, should establish <br /> a stable residence structure area. <br /> ' <br /> I <br />�6,. �'��fi'i�` s ° : z..-- � �r�y-= <br />