§ 24.35.170. Geologic hazards—Additional requirements for geologic assessments in marine bluff hazard areas.

In addition to the requirements in 24.35.130 TCC, the following shall be required for geologic assessments in marine bluff hazard areas, as specified:

A.

The geological assessment for a marine bluff hazard area shall be prepared by a geotechnical professional who is licensed as a professional engineer or engineering geologist with a minimum of four years of relevant professional employment, as determined by the director.

B.

The geological assessment shall be submitted in the form of a geotechnical letter when the geotechnical professional finds that no marine bluff hazard area exists within three hundred feet of the development proposal site (i.e. legal lot). A geotechnical letter shall, at a minimum, include the following:

1.

The letter shall be labeled, identifying the submittal as a "marine bluff hazard geotechnical letter" and shall include all mandatory elements listed in 24.35.130 TCC.

2.

The geotechnical letter shall be prepared under the responsible charge of a geotechnical professional(s) and be signed, sealed and dated by the geotechnical professional(s).

C.

The geological assessment shall be submitted in the form of a geotechnical evaluation when the geotechnical professional finds that a marine bluff hazard area exists, but is located more than three hundred feet away from the proposed development, and in their opinion, will not impact the subject site. A geotechnical evaluation shall, at a minimum, include the following:

1.

The cover letter for the document shall clearly identify the submittal as a "marine bluff hazard geotechnical evaluation" and shall include all mandatory elements listed in 24.35.130 TCC.

2.

A site plan, as defined in TCC 24.35.130(H)(9).

3.

A general description of the on-site geology and shoreline processes affecting the subject property as well as a detailed discussion of how the site could be developed without the use of a bulkhead along the shoreline.

4.

Assessments and conclusions of the stability or instability of the site including past slope failures if any, their timing, size, frequency, and mechanism; assessment of the likelihood of future failures, and identification of those aspects of the potential development that may contribute to future failures.

D.

The geological assessment shall be submitted in the form of a geotechnical report when the geotechnical professional finds that 1) a marine bluff hazard area exists within three hundred feet of the proposed project area; or 2) a marine bluff hazard area is located more than three hundred feet away from the proposed project area, but in their opinion, will impact the subject site. A geotechnical report shall, at a minimum, include the following:

1.

The cover letter for the document shall clearly identify the submittal as a "marine bluff hazard geotechnical report" and shall include all mandatory elements listed in 24.35.130 TCC.

2.

A site plan, as defined in TCC 24.35.130(H)(9).

3.

A description of the surface and subsurface geology, hydrology, and soils on the site, as well as a detailed discussion of how the site could be developed without the use of a bulkhead along the shoreline.

4.

Assessment of the role of existing vegetation on maintaining slope stability on site.

5.

Subsurface characterization data must be provided. The data shall be based on both existing and new information that may include soil borings (SPT or other appropriate driven sample collection methods), test pits, geophysical surveys, or other appropriate subsurface exploration methods, as approved by the director, development of site-specific soil and/or rock stratigraphy, and measurement of groundwater levels including variability resulting from seasonal changes, alterations to the site, and other factors as determined by the director.

6.

Soil strength and index properties (i.e., unit weight, cohesion, etc.) shall be provided for each soil unit interpreted from the subsurface characterization of the site. Refer to requirements under TCC 24.35.160.

7.

Shoreline processes including an evaluation of erosion and bluff retreat over the past decade, and an estimate of probable rate of erosion over the useful life of the development (normally fifty years).

8.

A detailed description of any prior grading activity, soil instability, or slope failure.

9.

Assessments and conclusions regarding slope stability for both the existing and developed conditions shall be presented and documented. These assessments and conclusions shall include:

a.

Evaluation of the potential types of landslide or bluff failure mechanisms (e.g., debris flow, rotational slump, translational slip, etc.) that may affect the site.

b.

Quantitative stability evaluation of slope conditions of the various failure mechanisms using state-of-the-practice modeling techniques. Limiting equilibrium methods of analysis shall state the stability conditions as a factor of safety. The most unstable failure geometry(ies) shall be presented in the form of a cross-section(s), with the least stable failure geometry for each failure mechanism clearly indicated. The stability evaluation shall also consider dynamic (earthquake) loading, and shall use a minimum horizontal acceleration as established by Title 14 TCC, Buildings and Construction.

c.

An analysis of the slope regression rate shall be presented in those cases where stability is impacted or influenced by erosional processes (e.g., wave cutting, stream meandering, etc.) acting on the toe of the slope.

10.

Assessments and conclusions of the stability or instability of the site including past slope failures if any, their timing, size, frequency, and mechanism; assessment of the likelihood of future failures, and identification of those aspects of the potential development that may contribute to future failures.

11.

Evaluation of site development alternatives that use nonstructural erosion control measures such as vegetation alone or in combination with rock at the toe of the marine bluff, beach berm, an earthen berm, logs anchored at the toe of the slope or beach nourishment.

12.

Mitigation recommendations using engineered measures to protect the proposed structure(s) and any adjacent structures, infrastructure, adjacent wetlands, or critical fish and wildlife habitat from damage or destruction as a result of proposed construction activities shall be designed by a professional engineer. The geotechnical report shall contain.

a.

Design plans and associated design calculations for engineered structures or drainage systems (e.g., structural foundation requirements, retaining wall design, etc.).

b.

Recommendations and requirements pertaining to the handling of surface and subsurface runoff in the developed condition.

c.

Identification of necessary geotechnical inspections to assure conformance with the report mitigation and recommendations.

d.

Proposed angles of cut and fill slopes, site grading requirements, final site topography (shown as two-foot contours), and the location of any proposed structures, on-site septic systems, wells, and stormwater management features or facilities associated with the development detailed within the body of the report and shown on a site map at the same scale as required by the review authority.

e.

Soil compaction criteria and compaction inspection requirements.

f.

An analysis that indicates how the proposal meets the standards outlined in TCC 24.15.030-240.

g.

Structural foundation requirements and estimated foundation settlement shall be provided if structures are proposed.

h.

Lateral earth pressures.

i.

Suitability of on-site soil for use as fill.

j.

Mitigation measures for building construction on each lot for short plats, large lots, or formal plats such that additional geotechnical professional involvement is minimized during building construction.

(Ord. No. 14773, § 3(Att. B), 7-24-2012)