18E.80.030 Landslide Hazard Area Review Procedures.
A. General Requirements.
1. The Pierce County Critical Area Atlas provides an indication of where active and potential landslide hazard areas are located within the County. The actual presence or location of an active landslide hazard area and/or additional potential landslide hazard areas that have not been mapped, but may be present on or adjacent to a site, shall be evaluated using the geological assessment procedures established in this Chapter.
2. The Department will complete a review of the Critical Areas Atlas – Landslide Hazard Area Map and other source documents for any proposed regulated activity to evaluate whether the site is or may be located within an active or potential landslide hazard area. Identification of an active or potential landslide hazard area may also occur as a result of field investigations conducted by Department staff.
3. When the Department's maps or sources indicate that the site for a proposed regulated activity is or may be located within an active or potential landslide hazard area, the Department shall require the submittal of a geological assessment as outlined in 18E.80.030 B. below. (See Figure 18E.80-5 in Chapter 18E.120 PCC.)
4. Unless otherwise stated in this Chapter, the critical area protective measure provisions contained in PCC 18E.10.080 shall apply.
B. Geological Assessment. A geological assessment is a site investigation process to evaluate the on-site geology affecting a subject property.
1. Geological assessments shall be submitted to the Department for review and approval together with a landslide hazard area application and associated fee.
2. A geological assessment shall include a field investigation and may include the use of historical air photo analysis, review of public records and documentation, and interviews with adjacent property owners, etc.
3. The geological assessment shall include the following information and analysis:
a. An evaluation of which areas on the site or within the vicinity of the site meet the criteria for an active landslide hazard area and stable area as set forth in PCC 18E.80.020 C.1. and 2.
b. Consider the run-out hazard of landslide debris to the proposed development that starts upslope (whether part of the subject property or on a neighboring property) and/or the impacts of landslide run-out on down slope properties.
c. The geological assessment shall include a detailed review of the field investigations, published data and references, data and conclusions from past geological assessments, or geotechnical investigations of the site, site-specific measurements, tests, investigations, or studies, as well as the methods of data analysis and calculations that support the results, conclusions, and recommendations.
4. Geological assessments shall be prepared under the responsible charge of an appropriately licensed geotechnical professional(s), and signed, sealed and dated by the geotechnical professional(s) (as defined in PCC 18.25.030 and established in this Chapter) and the format shall be pre-approved by the Department.
5. A field investigation and geological assessment shall be completed under the responsible charge of an appropriately licensed geotechnical professional(s) to evaluate whether or not an active landslide hazard area exists within 300 feet of the site. (See Figure 18E.80-5 in Chapter 18E.120 PCC.)
a. The geological assessment shall be submitted in the form of a geotechnical letter when the geotechnical professional finds that no active landslide hazard area exists within 300 feet of the site. The geotechnical letter shall meet the requirements contained in 18E.80.060 – Appendix A.
b. The geological assessment shall be submitted in the form of geotechnical evaluation when the geotechnical professional finds that an active landslide hazard area exists, but is located more than 300 feet away from the proposed project area. The geotechnical evaluation shall meet the requirements contained in 18E.80.060 – Appendix B.
c. The geological assessment shall be submitted in the form of a geotechnical report when the geotechnical professional finds that an active landslide hazard area exists within 300 feet of the proposed project area or when a geotechnical professional indicates that mitigation measures are necessary in order to construct or develop within a potential landslide hazard area. The geotechnical report shall meet the requirements contained in 18E.80.060 – Appendix C.
6. Geological assessments that do not contain the minimum required information or comply with the landslide hazard area standards set forth in 18E.80.040 will be returned to the geotechnical professional for revision.
7. The Department shall review the geological assessment and either:
a. Accept the geological assessment; or
b. Reject the geological assessment and require revisions or additional information.
8. When the geological assessment has been accepted, the Department shall issue a decision on the landslide hazard area application.
9. A geological assessment for a specific site may be valid for a period of up to five years when the proposed land use activity and site conditions affecting the site are unchanged. However, if any surface and subsurface conditions associated with the site change during that five-year period, the applicant may be required to submit an amendment to the geological assessment.