18.65.300 Additional critical area report requirements – Geologically hazardous areas

18.65.300 Additional critical area report requirements – Geologically hazardous areas.

(1) Before approving any alteration or development under this article, the City may require the applicant to submit the following information in addition to or as part of the critical areas report:

(a) A geotechnical report prepared by a geotechnical engineer or engineering geologist licensed in the State of Washington that describes how the proposed development will impact or be impacted by each of the following on the subject property and nearby properties:

(i) Slope stability, landslide hazard, and sloughing;

(ii) Erosion hazards;

(iii) Seismic hazards;

(iv) Ground water;

(v) Seeps, springs, streams and other surface waters;

(vi) Existing vegetation, including size and type of significant trees;

(vii) Identification of existing fill areas;

(viii) Soil description in accordance with Unified Soil Classification System; and

(ix) Depth to ground water and estimates of potential seasonal fluctuations;

(b) A topographic survey, in two-foot contours, that identifies the type and extent of geologically hazardous areas on site and off site that are likely to impact or be impacted by the proposal;

(d) The location of storm drainage facilities on the subject property;

(e) Recommended foundation and retaining wall design criteria and optimal location for buildings, roadways and other improvements. Including bearing layer(s), allowable capacities, minimum width, minimum depth, estimated settlements (total and differential, lateral loads, and other pertinent recommendations);

(f) Grading and earthwork, including compaction and fill material requirements, use of site solids as fill or backfill, imported fill or backfill requirements, height and inclination of both cut and fill slopes and erosion control and wet weather construction considerations and/or limitations;

(g) Surface and subsurface drainage requirements and drainage material requirements;

(h) Recommended methods for mitigating identified impacts and a description of how these mitigating measures may impact adjacent properties;

(i) Assessment of seismic ground motion amplification and liquefaction potential; and

(j) Any other information the City determines is reasonably necessary to evaluate the proposal.

(2) A decision by the Director to reduce the buffer shall be based on a critical area report that includes the following assessment criteria:

(a) Steep slope and landslide hazard development areas shall be subject to site-specific geotechnical studies;

(b) Steep slope and landslide hazard development areas shall be subject to engineering design considerations that ensure the stability of steep slope areas. Engineering design considerations shall include but are not limited to the following:

(i) Soil cuts require slope stability analysis to evaluate the change in relative stability. Based on the results of the stability analysis, retaining structures will be required to replace any lateral soil support lost. In no case shall the factor of safety be less than one and one-half;

(ii) Soil fills require slope stability analysis and engineering design measures, including keying the fill, compaction, drainage measures, reinforced earth, and structural retaining walls;

(iii) Foundations must be extended to firm, undisturbed native soil, and embedded deep enough to resist lateral loads caused by soil creep (surficial slope movement inherent to all steep slope areas) and other lateral loads which the foundation may be subject to (i.e., seismic and deep seated slope failures);

(iv) Provide subgrade (i.e., reinforced compacted subgrade) or retaining wall design that replaces the support of cuts; designed with a factor of safety of at least one and one-half. Compacted subgrade without reinforcement or retaining structures will not be considered for the support of cuts;

(v) Provide effective, positive drainage for all underground elements of structures or facilities; and

(vi) All utility connections within steep slope and landslide hazards shall have sufficient flexible connections to avoid utility failure;

(c) The City may employ an outside geotechnical engineer at the applicant’s expense for third-party review of any geotechnical analyses.

(3) The decision by the Director to reduce the buffer shall include the following conditions:

(a) The applicant shall establish a mechanism that is acceptable to the Director that notifies all future buyers of the lot that the steep slope buffer was reduced and that development has occurred within 50 feet of the steep slope or the steep slope has been eliminated (e.g., notice on title); and

(b) The applicant shall execute an agreement on a form approved by the City Attorney, which indemnifies and holds the City harmless for development within 50 feet of the steep slope.

Both conditions shall be met prior to the issuance of a building permit. The Director may attach additional conditions as necessary to achieve the purpose and intent of this section.

(4) If the City approves any development under this section, it may, among other appropriate conditions, impose the following conditions of approval:

(a) The recommendations of the geotechnical report are followed;

(b) A geotechnical engineer or engineering geologist shall be present on site during all development activities. As an alternative, the City may require minimum site visits by the geotechnical engineer or engineering geologist, as required by the City engineer, to establish proper methods, techniques and adherence to plan drawings;

(c) Trees, shrubs and groundcover are retained except where necessary for approved development activities on the subject property;

(d) Additional vegetation is planted in disturbed areas; and

(e) Submit a letter by the geotechnical engineer or engineering geologist stating that they have reviewed the project plan drawings and in their opinion the plans and specifications meet the intent of the geotechnical report. (Ord. 09-19 § 9 (Exh. D); Ord. 06-17 § 4 (Exh. B))