18E.100.030 Mine Hazard Area Review Procedures.
A. General Requirements.
1. The Pierce County Critical Areas Atlas-Mine Hazard Area Map provides an indication of where potential mine hazard areas are located within the County.
2. The Department will complete a review of the Critical Areas Atlas-Mine Hazard Area Map to determine whether the site for a proposed regulated activity is located within a potential mine hazard area.
3. When the Department's maps indicate that the site for a proposed regulated activity is located within a potential mine hazard area, the Department shall require a geological assessment, as outlined in subsection B below. (See Figure 18E.100-1 in Chapter 18E.120 PCC.)
4. Title and land division notification shall be required as set forth in PCC 18E.10.110 C.
B. Geological Assessments. A geological assessment is a site investigation process to evaluate the on-site geology affecting a subject property and define the extent and severity of potential mine hazard areas.
1. A geological assessment shall be submitted to the Department for review and approval together with a mine hazard application and associated fee.
2. A geological assessment shall include a field investigation and may also include review of public records and documentation, analysis of historical air photos, published data and references, subsurface investigations, etc.
3. The geological assessment shall include, at a minimum, the following information and analysis:
a. A discussion of the surface and subsurface geologic conditions of the site.
b. A discussion of the potential for subsidence on the site.
c. An evaluation of which portions of the site or within the vicinity of the site meet the criteria for a mine hazard area as set forth in PCC 18E.100.020.
4. A geotechnical professional shall complete a field investigation and geological assessment to evaluate whether or not the site is subject to mine hazards shall be completed under the responsible charge of an appropriately licensed geotechnical professional. (See Figure 18E.100-1 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 mine workings exist within 300 feet of the site. The geotechnical letter shall meet the requirements contained in 18E.100.040 – Appendix A.
b. The geological assessment shall be submitted in the form of a geotechnical evaluation when the geotechnical professional finds that mine workings exist, but are located more than 300 feet away from the proposed project area. The geotechnical evaluation shall meet the requirements contained in 18E.100.040 – Appendix B.
c. The geological assessment shall be submitted in the form of a geotechnical report when the geotechnical professional finds that mine workings exist within 300 feet of the proposed project area or when the services completed by the a geotechnical professional indicates that mitigation measures are necessary in order to construct or develop within a mine hazard area. The geotechnical report shall meet the requirements contained in 18E.100.040 – Appendix C.
5. Geological assessments shall be prepared, under the responsible charge of an appropriately licensed geotechnical professional and signed, sealed, and dated by the geotechnical.
6. Geological assessments that do not contain the minimum required information will be returned to the geotechnical professional for revision.
7. The Department shall review the geological assessment and either:
a. Accept the geological assessment and approve the application; or
b. Reject the geological assessment and require revisions or additional information.
8. 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 surrounding site conditions are unchanged. However, if any environmental surface or 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.