17.115.070 Critical area reports – Specific requirements for geologically sensitive areas.
In addition to the general requirements of SMC 17.114.160, critical area reports for geologically hazardous areas must meet the requirements of this section.
(1) Prepared by a Qualified Professional. A critical areas report for a geologically hazardous area shall be prepared by a geotechnical engineer or geologist, licensed in the state of Washington, with experience analyzing geologic, hydrologic, and groundwater flow systems; or by a geologist who earns his or her livelihood from the field of geology and/or geotechnical analysis, with experience analyzing geologic, hydrologic and groundwater flow systems, who has experience preparing reports for the relevant type of hazard.
(2) Erosion and Landslide Hazard Areas. In addition to the basic critical area report requirements, a critical area report for an erosion hazard or landslide hazard area shall include the following information at a minimum:
(a) Site Plan. The report shall include a copy of the site plan for the proposal showing:
(i) The height of slope, slope gradient, and cross section of the project area;
(ii) The location of springs, seeps, or other surface expressions of groundwater on or within 200 feet of the project area or that have the potential to be affected by the proposal; and
(iii) The location and description of surface water runoff.
(b) Hazards Analysis. The hazards analysis shall specifically include:
(i) A description of subsurface conditions based on data from site-specific explorations;
(ii) Descriptions of surface and groundwater conditions, public and private sewage disposal systems, fills and excavations, and all structural improvements;
(iii) An estimate of slope stability and the effect construction and placement of structures will have on the slope over the estimated life of the structure;
(iv) An estimate of the bluff retreat rate that recognizes and reflects potential catastrophic events such as seismic activity or a 100-year storm event;
(v) Consideration of the run-out hazard of landslide debris and/or the impacts of landslide run-out on down slope properties;
(vi) A study of slope stability including an analysis of proposed cuts, fills, and other site grading;
(vii) Recommendations for building siting limitations;
(viii) An analysis of proposed surface and subsurface drainage, and the vulnerability of the site to erosion.
(c) Geotechnical Engineering Report. The technical information for a project within a landslide hazard area shall include a geotechnical engineering report prepared by a licensed engineer that presents engineering recommendations for the following:
(i) Parameters for design of site improvements including appropriate foundations and retaining structures. These should include allowable load and resistance capacities for bearing and lateral loads, installation considerations, and estimates of settlement performance;
(ii) Recommendations for drainage and subdrainage improvements;
(iii) Earthwork recommendations including clearing and site preparation criteria, fill placement and compaction criteria, temporary and permanent slope inclinations and protection, and temporary excavation support, if necessary; and
(iv) Mitigation of adverse site conditions including slope stabilization measures and seismically unstable soils, if appropriate.
(d) Erosion and Sediment Control Plan. For any development proposal on a site containing an erosion hazard area, an erosion and sediment control plan shall be required. The erosion and sediment control plan shall be prepared in compliance with requirements set forth in the city’s stormwater management regulations (Chapter 17.140 SMC).
(e) Drainage Plan. The report shall include a drainage plan for the collection, transport, treatment, discharge and/or recycling of water prepared in accordance with the city’s surface water management plan. The drainage plan should consider on-site septic system disposal volumes where the additional volume will affect the erosion or landslide hazard area.
(f) Mitigation Plans. Hazard and environmental mitigation plans for erosion and landslide hazard areas shall include the location and methods of drainage, surface water management, locations and methods of erosion control, a vegetation management and/or replanting plan and/or other means for maintaining long-term soil stability.
(g) Monitoring Surface Waters. If the city determines that there is a significant risk of damage to downstream receiving waters due to potential erosion from the site, based on the size of the project, the proximity to the receiving waters, or the sensitivity of the receiving waters, the critical area report shall include a plan to monitor the surface water discharge from the site. The monitoring plan shall include a recommended schedule for submitting monitoring reports to the city.
(3) Seismic Hazard Areas. In addition to the basic report requirements, a critical area report for a seismic hazard area shall also meet the following requirements:
(a) The site map shall show all known and mapped faults within 200 feet of the project area or that have potential to be affected by the proposal.
(b) The hazards analysis shall include a complete discussion of the potential impacts of seismic activity on the site (for example, forces generated and fault displacement).
(c) A geotechnical engineering report shall evaluate the physical properties of the subsurface soils, especially the thickness of unconsolidated deposits and their liquefaction potential. If it is determined that the site is subject to liquefaction, mitigation measures appropriate to the scale of the development shall be recommended and implemented.
(4) Tsunami Hazard Areas. In addition to the basic report requirements, a critical area report for a tsunami hazard area shall also meet the following requirements:
(a) Site Plan. The site plan shall show all areas within 200 feet of the project area that have the potential to be inundated by wave action derived from a seismic event;
(b) Hazards Analysis. The hazards analysis shall include a complete discussion of the potential impacts of the tsunami hazard on the site; and
(c) Emergency Management Plan. The emergency management plan shall include plans for emergency building exit routes, site evacuation routes, emergency training, notification of local emergency management officials, and an emergency warning system.
(5) Volcanic and Other Geologically Hazardous Areas. In addition to the basic report requirements, the city may require additional information to be included in the critical area report when determined to be necessary to review the proposed activity and the subject hazard. Additional information that may be required includes, but is not limited to:
(a) Site Plan. The site plan shall show all hazard areas located within 200 feet of the project area or that have the potential to be affected by the proposal; and
(b) Hazards Analysis. The hazards analysis shall include a complete discussion of the potential impacts of the hazard on the project area and of the proposal on the hazard. (Ord. 1164 § 4, 2004).