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S-07-144 Letter to Applicant Regarding Peer Review Results.pdfr 2 c.1S()v CITY OF EDMONDS 121 5TH AVENUE NORTH • EDMONDS, WA 98020 • (425) 771.0220 • FAX (425) 771-0221 DEVELOPMENT SERVICES DEPARTMENT Planning • Building • Engineering October 24, 2007 Mr. Fred Brown 1013 — 1401h Street Ct. NW Gig Harbor, WA 98352 GARY HAAKENSON MAYOR Subject: GEOTECHNICAL REPORT PEER REVIEW FOR PROPOSED SHORT PLAT, FILE NO. S-2006-144 Dear Mr. Brown: This letter is to follow up on the required peer review of the geotechnical reports by Soil & Environmental Engineers for your proposed four -lot subdivision at 7005 and 7027 — 174th Street Southwest (File No. S-2006-144). Pursuant to ECDC 23.40.090.13, peer review by the City's consultant, Landau Associates, has been conducted at the expense of the applicant. The City will notify you of the cost of the peer review once a bill is received from Landau Associates, Please refer to the enclosed technical memorandum from Landau Associates for the results of their peer review. In order to confirm compliance with ECDC Chapters 23.40, 23.80, and 19. 10, your consultant must submit a report addressing the requirements stated in the attached technical memorandum from Landau Associates. Please note that we will be unable to continue processing your application until we receive a response regarding the peer review of your geotechnical reports. If you have any questions, do not hesitate to contact me at (425) 771-0220, extension 1224. Sincerely, Development Services Department - Planning Division Jennifer Machuga Planner Cc: File No. S-06-144 Mr. Greg Hinkel 7517-172 nd Street SW Edmonds, WA 98026 Mr. Steve Miles 7005 — 174th Street SW Edmonds, WA 98026 • Incorporated August 11, 1890 • Sister City - Hekinan, Japan TO: Rob Chave and Jen Machuga, Planning Division City of Edmonds; Development Services Department Cc: Jeannine. Graf, Building Division FROM: Dennis R. Stettler,l'.E. ���� t� ac r DATE: October 24, 2007 4 2Q�� RE: GEOTECHNICAL REVIEW PLANA'lAfG DEPT HINML / MILES SHORT PLAT SUBMITTAL 7005 AND 7027174T" STREET SW EDMONDS, WASHINGTON This technical memorandum provides the results of our geotechnical review of documents for a permit application related to a proposed short plat at the referenced properties. We understand that the property owners at 7005 and 7027 174"' Street SW have applied to subdivide their properties to create a 4 - lot short plat. Landau Associates has been requested to review the submittal materials and to provide comments related to compliance with Edmonds Community Development Code (ECDC) 23.80 and whether the development should be subject to the provisions of ECDC 19.10. Landau Associatesservices have been provided in accordance with our On -Call Geotechnical and Environmental Engineering Services agreement with the City of Edmonds. and Task Order No. 07-05. We have received the following information forwarded by the City of Edmonds for review: • Prelinrinaty Short Plat drawing prepared by Western Engineers, Inc, dated March 20, 2007 • Proposed Short Plats and Boundary Line Adjustments drawing prepared by F. F. Brown Design dated March 20, 2007 (Based on Survey and Topp by Lovell Sauerland and Associates, Inc.) • Geotechnical Engineering Services, Proposed Short Subdivision, 7005 and 7027174"r Street SW, Edmonds, Washington letter prepared by Soil & Environmental Engineers, Inc., dated March 14, 2007 • Report of Critical Area Study, Proposed Four -Lot Subdivision; 7005 and 7027 174`x' Street SII', Edmonds, Washington, File No. S-2006-144 prepared by Soil & Environmental Engineers, Inc., dated September 28, 2007 • Report of Geotechnical Investigation, Proposed Miles Short Plat, Edmonds, Washington, S & EE Job No. 622 prepared by Soil & Environmental Engineers, Inc., dated August 3, 2007 • Report of Geotechnical Investigation, Proposed Hinkel. Short Plat, Edmonds, Washington, S & EE .Job No; 623 prepared by Soil & Environmental Engineers, Inc., dated August 3, 2007. 130 2nd Avenue South • Edmonds, WA 98020 ■ (425) 778-0907 . fax (425) 778-6409 9 WW-W-Jandauina.cam GEOLOGICALLY HAZARDous AREAS The submitted materials were reviewed for compliance with the requirements for Geologically Hazardous Areas in accordance. with ECDC 23.80, Geologically hazardous areas were addressed in the Critical Areas Study report prepared by Soils & Environmental Engineers, Inc. {S & EE}. In addition, geotechnical investigation reports were prepared for each of the two proposed lots that included the results of test pit excavations, geotechnical engineering analyses, and preparation of geotechnical recommendations for design and construction of houses on each of the two proposed lots Critical areas reports for geologically hazardous areas must be prepared by a qualified professional as defined in ECDC 23.80.050.A. The Critical Area Study prepared by S & EE includes a resume of the report author that demonstrates appropriate education, licensing, and experience to prepare such reports. The following comments address each of the identified geologically hazardous conditions on the proposed lots. Erosion Hazard The Critical Areas Study report by S & EE identifies the site soils as composed of Alderwood- Everett gravelly sandy loam on slopes of 25 percent or more. These soils are classified as Erosion Hazard Areas in accordance with the designations in ECDC 23.80.020.A. The Soil Conservation Service. also considers such soils to have a high erosion hazard. Erosion mitigation recommendations are contained in the Critical Area Study Report and the geotechnical investigation reports prepared for the proposed. Lots 1 and 3. The reports also address the importance of surface water control. We agree with the geotechnical engineer's recommendations and recommend that their recommendations .be appropriately incorporated into the project plans and specifications for construction on each of the lots. In addition, an erosion and sediment control plan should be prepared for the project in compliance with the requirements in ECDC 18.30. Landslide Hazard Areas Landslide Hazard Areas are identified in the Critical Areas Study on each of the two proposed lots. The designation of Landslide Hazard Areas are based on the criteria contained in ECDC 23.80.020.B.2, which designates any slope of 40 percent or steeper and with a vertical relief of 10 ft or more. Proposed Lot 1 has two steep areas classified as Landslide Hazard Areas and proposed Lot 3 has three steep areas classified as Landslide Hazard Areas based on this criteria. Each of the identified Landslide Hazard Areas is of limited horizontal extent, typically on the order of about 15 ft by 30 ft in 101211071YEdmdalelprojec[s107411401FlleRmSRlHinkel-NF[es_SuhmlllaTReview tm.doc LANDAv AssocsAfes 2 plan dimensions or less, and is typically on the order of 10 to 12 1t in vertical relief. The identified areas appear to be slightly steeper than 40 percent, based on the topographic information available. Soil conditions disclosed in test pits excavated by S & EE on the proposed lots disclosed relatively competent soils including recessional outwash, glacial till, and advance outwash. No areas of existing or historic landslide activity such as slumps, cracks, fissures, wet and unstable soils,. or springs were identified by S & EE in their reports. Slope stability analyses were completed for the existing slope conditions on each of the two lots and the results presented in the geotechnical investigation reports for each of the proposed lots. The computed factors of safety against slope instability appear to be satisfactory based on comparison to conventional geotechnical practice and the criteria of ECDC 23.80.070.A.3.a. Steep slopes are mapped in the vicinity and to the north of the proposed lots based on city-wide LiDAR mapping completed for the City of Edmonds. ECDC 23.80 requires that if the toe or top of a slope is located off of the subject property, then the location of the toe or top shall be delineated 200 horizontal feet from the property boundary or at its natural location, whichever is closer to the subject parcel. The Critical Areas report for a geologically hazardous area must address all geologically hazardous areas within 200 ft of the project area. From the topography and critical areas report submitted for the proposed short -plat; it is not possible to assess the extent of steep slopes adjacent to the proposed lots and whether these slopes, if present, could be affected by, or could impact, conditions on other properties. We recommend that the offsite conditions be addressed in accordance with .the ECDC 23.80 requirements. ECDC 23.80 requires that a minimum no disturbance buffer and minimum building setback be established from the edge of all landslide hazard areas. Suffers and setbacks were not specifically addressed in the .geotechnical reports, although a requirement is provided that foundations must be setback or deepened so that the base of the footing is located at least 1'0 ft horizontally from the. faceof the slope. We recommend that the recommended minimum no disturbance buffer and minimum building setback be specifically addressed by the geotechnical engineer for the proposed development. For alterations of an erosion or landslide hazard area or development within an erosion or landslide hazard area and/or buffer, the requirements of ECDC 23.80.060.A, sections 2 and 3 must also be addressed by the geotechnical engineer and the design team. It is not .clear from the submittal what efforts in terms of structure siting, no disturbance buffers, or other means are being taken to avoid or minimize impacts to critical areas as a part of the development. In accordance with ECDC 23.40.120, the applicant "shall demonstrate thatall reasonable efforts have been examined with the intent to avoid and minimize impacts to critical areas." This issue needs to be addressed by the applicant and the design team. 10124/07 ti%Edmdatp%projects1074S1401FlteRmlRWlnket-Miles 5ubmittaiReviewLtm.dae LANDAU AssOCIAMS 3 The geotechnical reports prepared- for each of the proposed lots appear :to be relaltively complete and address the standard geotechnical design criteria for typical grading, foundations; and retaining structures. However, the current submittal is for a proposed short plat. The documents submitted.indicate the location of proposed houses on the proposed lots and proposed grading. We assume that at this stage of the permit process, the location of the proposed house and the proposed grading is conceptual for purposes of illustrating the nature of the proposed development. However, the short plat application package does not represent a complete site development and building permit application package. As such, the actual configuration of the house, elevation, and site grading could change from the conceptual design presented. It appears that the existing geotechnical reports addressed the existing slope stability at the two proposed lots. According tothe geotechnical report, excavation depths of 13 to 20 ft are planned at the location of the proposed structures. The slope stability associated with the proposed excavations, retaining walls, and regrading on the property needs to be addressed in the geotechnical report. If the proposed short plat is approved and site development and building plans are prepared, we recommend that the geotechnical engineer provide additional consultation during the design of the. proposed building, grading, and site development plans for the proposed construction, and confirm or modify the geotechnical report recommendations as appropriate for the specific details of the proposed construction. In addition, we recommend that the geotechnical engineer review the design plans for the building and site development in order to confirm that the geotechnical recommendations have been properly interpreted and implemented in the project design. The City of Edmonds Development Services Department may desire to have a geotechnical peer review of the ,final development plans prior to issuance of a building permit to confirm that the geotechnical issues on the site have been :appropriately addressed in the final design. Seismic Hazards The Critical Area Study report and the .individual geotechnical reports prepared. for each of the proposed lots appropriately address seismic hazards. EARTH SUBSIDENCE AND LANDSLIDE HAzA D AREAS (ECDC 19.10) The proposed lots are outside of the designated. North Edmonds Earth Subsidence and Landslide Hazard Area as defined in ECDC 19.10. However, portions of each of the two proposed. lots have slopes that are 40 percent or more for a vertical height of 10 .ft or more. As such, they meet the definition of Landslide Hazard Area as defined in ECDC 23.80. In accordance with the definition of Earth Subsidence and Landslide Hazard Area contained in ECDC 19.10, such areas meeting the definition of Landslide 10124107 11Edmdalakprojeeisl07411401F[eRmIRW]nkel-Mile5_SubmlitalRexiew tm.dor LANDAU AssociATEa 4 Hazard Area in ECDC 23.80 shall also be considered to be an Earth Subsidence and Landslide Hazard Area. Consequently, applicants for permits in such areas shall submit a geotechnical report and complete plan set as required by ECDC 19.10 to the Building Official for review. SUMMARY Landslide Hazard Areas as defined by ECDC 23.80 are present on both of the proposed lots. The Landslide Hazard Areas are of limited extent on each of the lots, and evidence of current or previous slops instability on the proposed lots were not observed by the applicant's geotechnical consultant. The present information does not suggest significant problems with development of these lots with respect to Landslide Hazard Areas. However, development of any property with an identified Landslide Hazard Area presents some degree of risk and highlights the importance of careful consideration of design and construction practices in order to properly identify and reduce that risk. For purposes of considering the short plat application, we recommend the following issues be addressed: • The topography within 200 R of the proposed lots should be examined by the geotechnical engineer to assess the toe and top of adjacent slopes, whether these nearby slopes meet the definition of a landslide hazard area, and whether the proposed lots could be affected by adjacent offsite conditions or whether development of the proposed. lots could affect offsite conditions. • The provisions of ECDC 23.40.120 regarding avoiding or minimizing impacts to .identified critical areas should be addressed. The geotechnical engineer should specifically address buffers and setbacks from the landslide hazard areas identified on the site, and if alterations or development within an erosion or landslide hazard area are planned, then the development standards contained in ECDC 23.80.070 sections 2 and 3 should be addressed by the .geotechnical .engineer and the design team. If the City of Edmonds decides to approve the short plat application, the following .points provide a brief summary of Landau Associates' recommendations for additional considerations resulting from this review: • An erosion and sediment control plan should be prepared in accordance with ECDC .18.30 and the recommendations of S .& EE related to erosion control protection and handling of surface water should be incorporated into the plans. The geotechnical engineer should provide additional consultation during the development of site grading and building plans by the design team, and the geotechnical engineer should review the completed design plans and specifications to confirm that the geotechnical recommendations have been properly interpreted and implemented in the design. The additional consultation should include an assessment of the slope stability associated with the specifically proposed arrangement of building, retaining walls, ;and site grading, The City of 10124!07 I%Edmdatalpro[ec$107411491FOeRmlR4Hlnkol-Mles_subrroMiReview_tm,doe LANDAu ASSOCJATFS 5 i Edmonds may desire to have a geotechnical peer review conducted to confirm that the geotechnical recommendations have been appropriately incorporated into the design plans. • ECDC 19.10 appears to apply to this project and the permit submittal requirements of ECDC 19.10 should be addressed as a part of the project permit applications. This technical memorandum Inas been prepared for use by the City of Edmonds in evaluating the adequacy of permit submittal documents related to the proposed 4 -Lot Short Plat at 7005 and 7027 .174`0' Street SW. The focus of this review was the geotechnical aspects of the application,. The purpose of the review was to assess whether the geologically hazardous areas provisions of ECDC 23.80 have been appropriately addressed and whether ECDC 19.10 should apply to the proposed development, and to assess the adequacy of the application documents for compliance with City requirements and conformance with conventionally accepted geotechnical engineering practices. This geotecbnicaI peer review by Landau Associates. does not lessen the requirements for the applicant's geotechnical consultant and other design professionals to prepare an appropriate design for the site conditions. We appreciate this opportunity to be of service to the City. Please contact us if you have any questions or if we maybe of further service. DRS/kes 101241D7 LANDAU AssociATEs 6