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REVIEWED PLN MEMO REV 1063618 Driessen Prop Fence and Landscaping Vegetation EdmondsNELSON GEOTECHNICAL ASSOCIATES. INC. MEMORANDUM DATE: November 9, 2020 17311-1351h Ave. N.E. Suite A-500 Woodinville, WA 98072 (425) 486-1669 www.nelsongeotech.com TO: Mr. Peter Driessen CC: Mr. Jed Miller— CASA Architecture FROM: Khaled M. Shawish, PE Lee S. Bellah, LG RE: Driessen Property Slope Vegetation and Fence (Revised) 9229 Olympic View Drive Edmonds, Washington NGA File No. 1063618 35215 �<v STE roNAL � INTRODUCTION This memorandum documents our opinions and recommendations for the proposed fence and landscaping plan within the steep slope area at your residence located at 9229 Olympic View Drive in Edmonds, Washington. We previously prepared a geotechnical report for the proposed residence development dated December 5, 2018. We understand that the City of Edmonds is requesting an evaluation of the proposed fence and landscaping improvements within the steep slope area to the south of the residence, and a letter verifying that the proposed plan is in accordance with City of Edmonds Codes 23.80.060 and 23.80.070. We understand that most of the existing shrubs and trees located within the steep slope to the south of the residence are to be removed. The new fence is to be constructed along the top of the steep slope along the sidewalk along Olympic View Drive. For our use in preparing this memo, we have been provided with a landscaping plan set prepared by Noriko Marshall Landscape Architecture dated August 4, 2020. We have been requested to provide our opinion and recommendations regarding the proposed fence and landscaping improvement plans in accordance with the City of Edmonds Code. Geotechnical Engineering Memorandum (Revised) NGA File No. 1063618 Driessen Property Slope Vegetation and Fence November 9, 2020 Edmonds, Washington Page 2 RECENT SITE OBSERVATIONS We visited the site on October 21, 2020 to observe the existing site conditions within the vicinity of the proposed fence and landscaping features. The steep north -facing slope descends to from the northern shoulder of Olympic View Drive to the relatively level yard area at inclinations in the range of 32 to 35 degrees (63 to 70 percent). The overall height of the steep slope is approximately 10 to 13 feet. The conditions within steep slope area appear to be similar to the conditions observed during our previous evaluation. We did not observe any indication or recent sloughing and/or landsliding issues within the steep slope area. The slope is generally vegetated with young to mature trees, landscaping plants and some underbrush. CONCLUSIONS Based on our review of the proposed plans, it is our opinion that the proposed fence and landscaping plans are feasible from a geotechnical standpoint. It is also our opinion that the proposed plans should not adversely impact the steep slope areas or neighboring properties and should be in compliance with the City of Edmonds Codes 23.80.060 and 23.80.070 if our recommendations are incorporated into the proposed plans and construction. Specifically, City of Edmonds Code 23.80.070.A.6 restricts clearing during the wet season (October 1 to April 30). However, it is also our opinion that the proposed vegetation removal and replanting plan can be performed during the wet season provided our recommendations in our previous report and this memo are followed during construction. We recommend that any trees to be removed from the steep slope area be cut near the existing ground surface and the remaining stumps be left in place. The resulting stumps can be grinded down to just below the existing ground surface provided that the remainder of the stump and root system remain intact and are left in place. All vegetation debris as a result of the vegetation removal within the steep slope area should be removed from steep slope and not allowed to remain on the slope. We recommend that the resulting surface of the steep slope and any exposed soils be covered immediately with heavy duty erosion control matting such as Tensar C350 Turf Reinforcement Mat, or equivalent. The erosion control matting should be staked to the surface of the slope at a minimum of 5 feet on center using 2- to 3-foot long metal stakes with a "T" welded to the end. After the matting is placed, we recommended that deep-rooted vegetation be planted within the slope area. NELSON GEOTECHNICAL ASSOCIATES, INC. Geotechnical Engineering Memorandum (Revised) Driessen Property Slope Vegetation and Fence Edmonds, Washington NGA File No. 1063618 November 9, 2020 Page 3 The steep slopes throughout the site are proposed to be vegetated with numerous shrubs, plants, and trees. It is our opinion that the lower -lying shrubs and plants should be feasible for vegetating the steep slope. However, if larger trees are planted on the steep slopes, they could have adverse impacts to the residence and slope stability as they mature. We recommend that larger trees be limited on the slopes, and if they are planted on the slopes, that they be maintained to reduce their size. These types of trees may need to be removed later if they pose a future risk to the residence or slope stability. Any exposed soils should be covered and maintained until vegetation is established. We recommend that the sloping areas within the site that receive vegetation be monitored throughout the wet season and repairs be implemented immediately should any signs of erosion or plant die off be observed. We recommend that the fence foundations be extended down and embedded two feet into competent native soils at depth. We recommend that no additional fill be placed on any portions of the steep slopes, and all soils from the fence foundation excavations should be hauled off site and not stockpiled or used anywhere else on the site. We trust this memorandum should satisfy your needs at this time. Please contact us if you have any questions or require additional services. ... NELSON GEOTECHNICAL ASSOCIATES, INC.