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CANOD.pdfADAMS RESC]URCE CONSULTANTS Slavik Miniaylo 7316 -164th Street SW Edmonds, WA 98026 APPROVED DA°ra BLDG. OFF10AL: PERMIT INUMBER Re: REVISED Geotechnical Assessment for New Retaining Wall at 7316-1641h Street SW Edmonds, Washington Transmitted electronically to: nwstonecraft@yahoo.com Our Reference: J 111- 01-16 Dear Slavik: Adams Resource Consultants (ARC) is pleased to provide this brief letter report addressing the need to apply for a permit to allow the newly constructed (March, 2016) concrete block retaining wall (Figures 1 through 3) at your above listed residence. As part of our assessment we have reviewed the following: 1) Letter dated January 7, 2005 from Cornerstone Geotechnical, Inc, to Clay Enterprises. 2) Plan Map titled: "Site Plan for House Construction," by Partners Architectural, dated June 10, 1999. 3) Applicable City of Edmonds codes: a) Chapter 23.40 Environmentally Critical Areas General Provisions, b) Chapter 23.80 Geologically Hazardous Areas and c) Retaining Wall Permit Submittal Requirements #1362. In summary, based on our site observations and the previously listed information, the site area in question that contains a newly constructed cement block wall is located in a Critical (steep (>40 percent) slope and landslide hazard) Area. It is our professional opinion that this wall does not create a hazard to neighboring properties, the older block wall above (south) nor to the slope beyond the lawn (north). The construction of the new wall improves the slope and planting area by removing an older (degraded) wall. We provide the details of our observations, opinions and recommendations below for your review and submittal to the City in support of a permit to build and maintain the block wall. BACKGROUND RECEIVED offiemm" Miniaylo - New Retaining Wall J-111-01-16 April 21, 2016 We understand from our conversations that two older block walls were overgrown and leaning prior to new re -construction. The lower block wall was replaced with the new wall (subject of this letter report). We understand the new wall was completed by excavating to a firm and stable base and provided with a 3/4 -inch crushed rock leveling surface about 8 inches thick. The blocks were placed with interlocking pegs at a slight facing batter. A footing drain was placed along the front foot of the wall. Filter fabric and 1 inch diameter drain rock was placed behind the wall to create a blanket drain approximately 12 inches wide that extends from the top of the wall to the foot. The upper (older) leaning wall was left in place as shown in Figures 1through 3. We noted that during a site visit in the past a geotechnical engineer noted (2005) the condition of the two walls and indicated that these walls complied with their recommendations. GENERAL OBSERVATIONS We used a hand auger and shovel to investigate the soil in front and behind the new wall. Our explorations extended to less than or equal to 4 feet deep and confirmed that the soil conditions associated with the new wall was as described. We also found determined that soil material behind the new wall consisted of between 1 and 1.5 feet of loose topsoil and sandy fill that overlies at least 2 to 3 feet of native sand. We did not observe any indications of significant movement, settlement, wet or soft areas along the wall foundation. The blocks appear level and the wall in good condition. OVERALL SLOPE STABILITY We observed soil conditions north and below the wall area where the slope exposes native sand, Figure 2. This slope extends down at an angle of between 45 and 50 degrees to a creek that flows to the west within and near the north property line. We did not observe any indications of groundwater seepage, slope movement or creep in this hillside north and below the block wall. It does not appear that past movement of the two block walls is related to a larger slope stability issue or landsliding. CONCLUSIONS AND RECOMMENDATIONS In our opinion the observed movement of the old wall is an indication of settlement from construction on loose fill soil materials. The lawn to the north and slope below do not exhibit any signs of landsliding and though this region has been mapped as containing old landslide features, the slopes described and noted on Figure 3 seem to be at equilibrium and have not moved for a very long time. In order to be assured that this area continues to perform well we recommend the following as a condition of permit: 1. All watering should be kept to a minimum. Planting should include draught resistance vegetation. No vegetation should be removed from the area between the new wall and the previously mentioned creek without advice from both a geotechnical and vegetation specialist. RECEIVED 2016 Miniaylo - New Retaining Wall April 21, 2016 )-111-01-16 2. With the exception of completing drain rock placement behind the new wall, no additional construction should take place in the area without the advice of a geotechnical specialist. 3. Surface survey monitoring points should be placed at several locations along the new wall and north edge of the lawn. These monitoring points should be tied back to nearby fixed (stable) reference points, such as the house foundation corners or established monuments in the street. Readings should be taken twice yearly or more often if movement is observed (before and after the rainy season) by a licensed surveyor or engineer. The readings should be tracked by a geotechnical specialist. 4. All retaining walls should be no more than a maximum height of 4 feet without specific engineering design recommendations and engineering construction observations/approval. (The existing block walls were designed by others for a maximum height of 48 inches.) 5. All new drainage lines from the wall area should be located. Drains should extend down to positive discharge at the creek on our client's property. In addition to the recommendations previously provided we also suggest that the owner consider extending two geotechnical boreholes in the lawn area in front (north) of the new wall. These boreholes would extend to elevations of the stream to the north and should be fitted with standpipe piezometers so that the engineer can monitor both groundwater levels and any slope movement. If these boreholes are completed as described we would recommend that data from the boreholes be collected and tracked in the same way during the same time frame as the surface survey readings. In our opinion if the walls noted in Figure 3 are built according to our recommendations, the construction will improve site conditions and stability. LIMITATIONS Subsurface conditions interpreted from observed soil materials and seepage conditions encountered formed the basis for developing the recommendations in this report. The nature and extent of conditions may change over time, often vary between observation locations and differences may not become evident until after the start of site work. If significant variations then appear evident, we should be consulted to re-evaluate the conclusions and recommendations in this report. It should be noted that groundwater seepage and any fluctuations in the level of the groundwater are dependent on seasonal variations in rainfall, temperature, and other climatic factors. Our work for this project was performed, and this report prepared, in accordance with our original contract with you, executed on April 13, 2016, including any approved changes. We have completed this work in accordance with generally accepted professional practices for the nature and conditions of the work done in the same, or in similar localities, at the time the work was performed. This report is intended for the exclusive use of you and your contractors and/or consultants for specific application to the referenced property. We make no other warranty, express or implied. Miniaylo - New Retaining Wall April 21, 2016 J-111-01-16 If we may provide any additional information or clarification about this report, please do not hesitate to contact Wayne by cell at 425.466.2891 or by message at 425.788.3244. Sincerely, ADAMS Resource Consultants Company WAYNE C. ADAMS, PE, PENG, EG President/CEO ADAMS Resource Consultants wa re�AdanResourccw.c01,rr ARTHUR J. FLEMING, PE Associate Engineer ADAMS Resource Consultants aflemin �AdamsResourc !.corn RECEIVED APR 2 6 2016 DEVELO PENT SERVICES Miniaylo - New Retaining Wall April 21, 2016 J-111-01-16 9 a 9LOZ Iljdy:a&e0 9i io-zuTr: VON 1321ad DEVELOPMENT SERVICES COUNTER Miniaylo - New Retaining Wall April 21, 2016 J-111-01-16 gToz IIjdV :v&80 gT•To•TTT•r: VON 1:01j01d 44 d 0 N CL V c 3 c Z AA U6 APR 2 6 2016 DEVELOPMENT SERVICES COUNTER Miniaylo - New Retaining Wall April 21, 2016 J New BlockWall (red dashed line) pez I 40 Scope at � percent grade M J-111-01-16 Lawn Area Older Leaning Block Wall (blue dash -dot I I ne)" 731& Older Block Walls T (dotted red.) H ..... . . . ............ Figure I Site Plan Sketch. Note: All locationsand dlmensionsshown are approximate. RECEIVED APR 2 6 2016 DEVELOPMENT SERVICES