Whenever development is proposed in a potentially geologically hazardous area or shoreline setback as defined in Chapters
19.300 and
19.400, or when the department determines that additional soils and slope analysis is appropriate on a particular site, the applicant is required to submit a geological assessment. This assessment may be in the form of a letter, a geological report, or geotechnical report, as determined in Chapter
19.400. These assessments evaluate the surface and subsurface soil conditions on the site.
A. Qualifications.
1. Geotechnical reports shall be prepared by a geotechnical engineer (defined at Section
19.150.365).
2. Geological reports or letters may be prepared by a licensed geologist (Section
19.150.360) or geotechnical engineer (Section
19.150.365).
B. General Provisions. Report recommendations for earthwork, clearing or siting structures in geologically hazardous areas shall be based on existing site conditions rather than measures that have not yet been successfully approved, designed, or constructed (e.g., slope recontouring, slope retaining walls, vegetation improvements, bulkheads, etc.). Shoreline bulkheads and retaining walls may only be utilized as an engineering solution where it can be demonstrated that:
1. An existing residential structure or other permitted existing public or private structures or public facilities such as roads or highways cannot be safely maintained without such measures;
2. Other nonstructural methods of beach stabilization have been considered and determined infeasible; and
3. The resulting stabilization structure is the minimum necessary to provide stability for the existing structure and appurtenances.
Minor repair activities on existing permitted structures (i.e., those that do not involve design modifications, changes in structure location, and/or demolition or abandonment of failed structure and replacement with new structure) are not subject to the following project submittal standards.
C. Geological Report Submittal Standards. A geological report is required for site development proposals that involve development activity or the installation of structures within a geologically hazardous area or shoreline setback, or as otherwise required pursuant to Chapters
19.300 and
19.400, but do not involve or require engineering design recommendations. The following minimum information is required:
1. Site information regarding the Kitsap County shoreline environment designation and critical areas designations that affect site features;
2. Description of surface and subsurface conditions, including ground materials, vegetation, surface drainage, groundwater, and a preliminary geologic hazard assessment which includes the locations of structures and the identification of the slope and/or coastal processes occurring at the site and factors that contribute to them;
3. Review of available site information, literature, and mapping;
4. Detailed description of slope and other topographic features;
5. A site plan depicting top or toe of slope and any required buffers and/or setbacks; and
6. Conceptual siting of structures and general recommendations, which include methods and practices that avoid and/or reduce slope and shore impacts. Minimum recommendations should include upland and slope drainage control, groundwater control, site vegetation management, and erosion control.
D. Geotechnical Report Submittal Standards. A geotechnical report is required when the department or a geological report determines that a site development proposal requires additional site information such as engineering design recommendations, slope stability analysis, subsurface exploration and testing, coastal process analyses, or construction recommendations. Depending on the level of activity proposed, the report will either be a more limited geotechnical slope evaluation report or a full geotechnical design investigation report as described below.
1. Geotechnical Slope Evaluation Report. A geotechnical slope evaluation report is required when slope stability analyses are confined to addressing only existing surface and/or drainage conditions, including the relationship of natural and constructed slope features to proposed changes in environmental conditions such as drainage, vegetation removal and slope geometry. The following minimum information is required:
a. All the information required under subsection
(C) of this section (geological report);
b. Subsurface data, exploration logs, and testing data, when required by the geotechnical engineer;
c. Estimated (or surveyed) site plan with ground surface profiles and typical cross-sections;
d. Relative location of ordinary high water (OHW) on the surface profile and cross-sections, which includes mean higher high water (MHHW) for the site location, where applicable;
e. Soil strength parameters;
f. Stability analysis of existing site;
g. Analysis of the relationship of vegetation and slope stability; and
h. Conceptual site development plans and cross-sections.
2. Geotechnical Design Investigation Report. A geotechnical design investigation report is required for site development activities that propose design and construction measures at the slope crest, face and/or toe. If a designed structure does not impact slope stability or coastal processes, the report will not be required to perform all items listed under this section, as long as each item is addressed and the report details why a particular item does not apply. The report shall include all items considered necessary by the engineer to fully address the engineering design requirements of the site. The following minimum information is required:
a. All the information required under subsection (D)(1) of this section (Geotechnical Slope Evaluation Report);
b. Geotechnical requirements and measures to reduce risks;
c. Geotechnical criteria used for any designs including all critical dimensions, lateral earth pressures, soil bearing pressures, location and limits of structures on or near the slope, maximum constructed slope angles, minimum soil reinforcement embedment, soil compaction requirements, and structure heights;
d. Temporary construction slope stability recommendations and analysis of proposed final site stability measures;
e. Required construction specifications and construction monitoring procedures;
f. Revegetation and surface and groundwater management requirements;
g. Evaluation of erosion potential, recommendations for erosion avoidance and any proposed mitigation measures;
h. Detailed tabulation of all basic geotechnical engineering test results pertinent to design and construction, and when required for clarification, detailed examples of tests conducted for the project; and
i. Information outlined in the geotechnical design investigation report site evaluation checklist (see subsection
(F) of this section).
E. Additional Requirements for Sites in Geologically Hazardous Areas. When a project site is located within a landslide-prone geologically hazardous area, as classified in Section
19.400.415, the following additional project submittal requirements shall apply:
1. Erosion Control Information. An evaluation of the erosion potential on the site during and after construction is required. The evaluation shall include recommendations for mitigation, including retention of vegetative buffers and a revegetation program. The geotechnical engineer shall provide a statement identifying buffer areas at the top or toe of a slope based on geotechnical site constraints and the impacts of proposed construction methods on the erosion potential of the slope.
2. Seismic Information. The geotechnical engineer shall submit a statement that the design criteria consider the one-in-one-hundred-year seismic event (an earthquake ground motion that has a forty percent probability of exceedance in fifty years). Calculations of soil bearing capacity, general soil stability, and wall lateral earth pressures shall be adjusted to reflect a one-in-one-hundred-year seismic event and the structural plans for the project shall be reviewed by the geotechnical engineer for consistency with these design criteria.
Analysis for the one-in-one-hundred-year seismic event shall be based on a near-crustal event having an assumed magnitude of 6.5 and occurring directly below the site. Based on regional studies performed by others, the department will allow the use of the following minimum general values of horizontal peak ground accelerations for this event:
a = 0.2g for fill, alluvial soils
a = 0.17g for till, firm glaciated soils
a = 0.15g for rock.
The appropriateness of the above accelerations shall be confirmed by the geotechnical engineer based on the actual site characteristics. Reduction in the above values may be considered when supported by the appropriate analytical evidence. Slope stability, lateral pressures, and liquefaction of the site shall be assessed by using subsurface soil, rock and groundwater conditions, as well as the seismic parameters discussed above.
3. Recommendations on Relative Site Stability. The geotechnical engineer shall make recommendations as to which portions of the site are the least prone to instability and the preferred location of the structure. The limits of any area proposed for grading activity shall be identified.
4. Construction Season Limitation. In general, no excavation will be permitted in landslide-prone geologically hazardous areas during the typically wet winter months. When excavation is proposed, including the maintenance of open temporary slopes, between October 1st and April 30th, technical analysis shall be provided to ensure that no environmental harm, threat to adjacent properties, or safety issues would result. In addition, recommendations for temporary erosion control and shoring/mitigating measures shall be provided. The technical analysis shall consist of plans showing mitigation techniques and a technical memorandum from the geotechnical engineer.
5. Revisions to Geotechnical Report. Further recommendations shall be provided by the geotechnical engineer should there be additions or exceptions to the original recommendations based on the plans, site conditions, or other supporting data. If the geotechnical engineer who revises the plans and specifications is not the same engineer who prepared the geotechnical report, the new engineer shall, in a letter to the department, express his or her agreement or disagreement with the recommendations in the geotechnical report and state whether the plans and specifications conform to his or her recommendations.
6. Plan and Specification Review. The geotechnical engineer shall submit a statement that, in his or her judgment, the plans and specifications (if prepared by others) conform to the recommendations in the geotechnical report and that all portions of the site which are disturbed or impacted by the proposed development have appropriate measures or specifications that permit construction to occur while addressing slope stability so that the work does not create additional risk. The statement shall also indicate whether or not a relative gain in slope stability will be achieved after construction is complete.
7. Construction Inspection. A final inspection report shall be provided by the geotechnical engineer stating that construction has or has not implemented the design recommendations of the geotechnical report, and evaluating any deviation from the design recommendations.
F. Geotechnical Design Investigation Report – Site Evaluation Checklist. The following are general report guidelines for geotechnical design investigation reports. The following guidelines are not intended to be all-inclusive. It is the responsibility of the geotechnical engineer to address all factors which in their opinion are relevant to the site. The checklist information shall be included as part of the geotechnical design investigation report. All items listed below must be addressed in the report. Information shall be provided for those items which are not relevant to a given site to demonstrate why the items are not applicable.
1. Project information:
c. Shoreline environment designation (where applicable); and
d. Critical areas ordinance (CAO) designations affecting site features.
2. Project description:
a. Description of proposed structures, site improvements, and adverse impact avoidance and reduction methods.
b. Location and total area of the construction zone.
(Ord. 351 (2005) § 36 (part), 2005; Ord. 545 (2017) § 5 (Appx. (part)), 2017; Ord. 633 (2024) § 5 (App.), 2024)