28.32.070 Geologic hazard area detailed study requirements.
The minimum requirements for a geologic hazard area detailed study include the following in addition to the basic requirements identified in PMC 28.12.140:
(1) Basic Requirements. A geologic hazard area detailed study shall meet the following:
(a) The detailed study shall be prepared by a qualified professional engineer or geologist. Evidence of qualifications shall be provided with the detailed study.
(b) A map, of a scale no smaller than one inch equals 200 feet, of the site and the extent of the geologic hazard area as determined by the criteria in PMC 28.32.030.
(c) An assessment of the geologic characteristics and engineering properties of the soils, sediments, and/or rock of the subject property and potentially affected adjacent properties, and a review of the site history regarding landslides, erosion, and prior grading. The study shall include a soils analysis consistent with the accepted regional taxonomic classification system, and a description of the vulnerability of the site to seismic events. Documentation of data and methods shall be included.
(d) A geotechnical analysis, including a detailed description of the proposed project, its relationship to the geologic hazard(s), and its potential impact upon the hazard area, the subject property and affected adjacent properties shall be included.
(e) A mitigation plan, if appropriate, prepared by a professional engineer or geologist under the supervision of a professional engineer qualified to prepare a detailed study. The mitigation plan shall include a discussion on how the project has been designed to avoid and minimize the impacts discussed in the geotechnical analysis (see mitigation standards provided in PMC 28.12.170). The plan shall make a recommendation for the minimum building setbacks from any geologic hazard based on the geotechnical analysis. The plan shall also address the potential benefit of mitigation on the hazard area, the subject property, and affected adjacent properties.
(f) Where more than one geologic hazard exists within, adjacent to, impacts, or is impacted by the activity site, then only one detailed study is required to be completed to conduct a geologic hazard critical area review of the activity. The critical area review report shall meet all of the requirements of each critical area type, but may present a unified mitigation plan.
(g) Where a valid geotechnical report has been prepared within the last five years for a specific site, and where the proposed land use activity and surrounding site conditions are unchanged, said report may be incorporated into the detailed study. The applicant shall submit a geotechnical assessment detailing any changed environmental conditions associated with the site.
(2) Erosion and Landslide Hazard Areas. In addition to the requirements of subsection (1) of this section, an erosion hazard or landslide hazard area detailed study must also meet the following requirements:
(a) The map shall depict the height of slope, slope gradient, and cross-section of the site. The site plan shall also include the location of springs, seeps, or other surface expressions of groundwater. The site plan shall also depict any evidence of surface or storm water runoff.
(b) A description of load intensity, including surface and groundwater conditions, public and private sewage disposal systems, fills and excavations, and all structural development.
(c) An estimate of slope stability and the effect construction and placement of structures will have on the slope during the estimated life of the structure.
(d) An estimate of the bluff retreat rate that recognizes and reflects potential catastrophic events such as seismic activity or a 100-year storm event.
(e) An assessment describing the extent and type of vegetative cover.
(f) The geotechnical analysis shall specifically include:
(i) Slope stability studies and opinion(s) of slope stability;
(ii) Proposed angles of cut and fill slopes and site grading requirements;
(iii) Structural foundation requirements and estimated foundation settlements;
(iv) Soil compaction criteria;
(v) Proposed surface and subsurface drainage;
(vi) Lateral earth pressures;
(vii) Vulnerability of the site to erosion;
(viii) Suitability of on-site soil for use as fill; and
(ix) Building limitations.
(g) Mitigation proposals shall include the location and methods of drainage, surface water management, locations, and methods of erosion control, a vegetation management and/or restoration plan, and/or other means for maintaining long-term stability of slopes.
(3) Flood Hazard Areas. Flood hazard areas are addressed through Chapter 28.28 PMC, Flood Hazard Areas, and the floodplain regulations (PMC Title 24). If evidence exists that the proposed development area is subject to flood hazards that are not indicated on the City’s flood hazard boundary maps, and site characteristics do not warrant an erosion or landslide hazard detailed study, the City may require additional analysis and preparation of a mitigation plan to determine if the site is suitable for development.
(4) Seismic Hazard Areas. In addition to the basic requirements in subsection (1) of this section, a detailed study for a seismic hazard critical area shall also meet the following requirements:
(i) The site map shall show all known and mapped faults in the project vicinity.
(ii) The geotechnical analysis shall include a complete discussion of the potential impacts of seismic activity reasonably probable on the site (e.g., forces generated and fault displacement).
(5) Mine Hazard Areas. In addition to the basic requirements in subsection (1) of this section, a detailed study for a mine hazard critical area shall also meet the following requirements:
(i) The site plan shall delineate the existence of mine workings adjacent to or abutting the site, or nearby mine workings, which may impact the site; and
(ii) The geotechnical analysis shall include a discussion of the potential for subsidence on the site.
(6) Volcanic Hazard Areas. The City is located in an area of minimal risk from volcanic hazard areas. [Ord. 4525A § 1, 2021; Ord. 4525 § 1, 2021; Ord. 3911 § 2, 2009; Code 1970 § 28.32.060. Formerly 28.32.060.]