16.18E.070 Critical area report – Additional technical information requirements for specific hazards.
In addition to the general critical area report requirements of Section 16.18A.220 critical area reports for geologically hazardous areas must meet the requirements of this section. Critical area reports for two or more types of critical areas must meet the report requirements for each relevant type of critical area.
A. Erosion and Landslide Hazard Areas. In addition to the basic critical area report requirements, the technical information for an erosion hazard or landslide hazard area shall include the following information at a minimum:
1. Site Plan. The critical area report shall include a copy of the site plan for the proposal showing:
a. The height of slope, slope gradient, and cross-section of the project area;
b. The location of springs, seeps, or other surface expressions of ground water on or within two hundred feet of the project area or that have potential to be affected by the proposal; and
c. The location and description of surface water runoff features;
2. Hazards Analysis. The hazards analysis component of the critical areas report shall specifically include:
a. A description of the extent and type of vegetative cover;
b. A description of subsurface conditions based on data from site-specific explorations;
c. Descriptions of surface and ground water conditions, public and private sewage disposal systems, fills and excavations, and all structural improvements;
d. An estimate of slope stability and the effect construction and placement of structures will have on the slope over the estimated life of the structure;
e. An estimate of the bluff retreat rate that recognizes and reflects potential catastrophic events such as seismic activity or a one-hundred-year storm event;
f. Consideration of the run-out hazard of landslide debris and/or the impacts of landslide run-out on down slope properties;
g. A study of slope stability including an analysis of proposed cuts, fills, and other site grading;
h. Recommendations for building siting limitations; and
i. An analysis of proposed surface and subsurface drainage, and the vulnerability of the site to erosion;
3. Geotechnical Engineering Report. The technical information for a project within a landslide hazard area shall include a geotechnical engineering report prepared by a licensed engineer that presents engineering recommendations for the following:
a. Parameters for design of site improvements including appropriate foundations and retaining structures. These should include allowable load and resistance capacities for bearing and lateral loads, installation considerations, and estimates of settlement performance;
b. Recommendations for drainage and subdrainage improvements;
c. Earthwork recommendations including clearing and site preparation criteria, fill placement and compaction criteria, temporary and permanent slope inclinations and protection, and temporary excavation support, if necessary; and
d. Mitigation of adverse site conditions including slope stabilization measures and seismically unstable soils, if appropriate;
4. Erosion and Sediment Control Plan. For any development proposal on a site containing an erosion hazard area, an erosion and sediment control plan shall be required. The erosion and sediment control plan shall be prepared in compliance with requirements set forth in Chapter 13.46;
5. Drainage Plan. The technical information shall include a drainage plan for the collection, transport, treatment, discharge, and/or recycle of water prepared in accordance with Chapter 13.46. The drainage plan should consider on-site septic system disposal volumes where the additional volume will affect the erosion or landslide hazard area;
6. Mitigation Plans. Hazard and environmental mitigation plans for erosion and landslide hazard areas shall include the location and methods of drainage, surface water management, locations and methods of erosion control, a vegetation management and/or replanting plan, and/or other means for maintaining long-term soil stability; and
7. Monitoring Surface Waters. If the mayor or designee determines that there is a significant risk of damage to downstream receiving waters due to potential erosion from the site, based on the size of the project, the proximity to the receiving waters, or the sensitivity of the receiving waters, the technical information shall include a plan to monitor the surface water discharge from the site. The monitoring plan shall include a recommended schedule for submitting monitoring reports to the city.
B. Seismic Hazard Areas. In addition to the basic report requirements, a critical area report for a seismic hazard area shall also meet the following requirements:
1. The site map shall show all known and mapped faults within two hundred feet of the project area or that have potential to be affected by the proposal.
2. The hazards analysis shall include a complete discussion of the potential impacts of seismic activity on the site (for example, forces generated and fault displacement).
3. A geotechnical engineering report shall evaluate the physical properties of the subsurface soils, especially the thickness of unconsolidated deposits and their liquefaction potential. If it is determined that the site is subject to liquefaction, mitigation measures appropriate to the scale of the development shall be recommended and implemented.
C. Mine Hazard Areas. In addition to the basic report requirements, a critical area report for a mine hazard critical area shall also meet the following requirements:
1. Site Plan. The site plan shall delineate the following found within two hundred feet of or directly underlying the project area, or that have potential to be affected by the proposal:
a. The existence of mines, including all significant mine features, such as mine entries, portals, adits, mine shafts, air shafts, and timber shafts;
b. The location of any nearby mines that may impact or be affected by the proposed activities;
c. The location of any known sinkholes, significant surface depressions, trough subsidence features, coal mine spoil piles, and other mine-related surface features; and
d. The location of any prior site improvements that have been carried out to mitigate abandoned coal mine features; and
2. Hazards Analysis. The hazards analysis shall include a discussion of the potential for subsidence on the site and classify all mine hazards areas within two hundred feet of the project area, or that have potential to be affected by the proposal, as either low, moderate, or severe. The hazards analysis shall include a mitigation plan containing recommendations for mitigation of the potential for future trough subsidence, as appropriate, for the specific proposed alteration and recommendations for additional study, reports, and development standards if warranted.
D. Volcanic Hazard Areas. In addition to the basic report requirements, a critical area report for a volcanic hazard area shall also meet the following requirements:
1. Site Plan. The site plan shall show all areas within two hundred feet of the project area that have potential to be affected by pyroclastic flows, lahars, or mud and debris flows derived from volcanic events;
2. Hazards Analysis. The hazards analysis shall include a complete discussion of the potential impacts of volcanic activity on the site (for example, inundation by mud flows resulting from volcanic activity); and
3. Emergency Management Plan. The emergency management plan shall include plans for emergency building exit routes, site evacuation routes, emergency training, notification of local emergency management officials, and an emergency warning system.
E. Other Geologically Hazardous Areas. In addition to the basic requirements, the mayor or designee may require additional technical information to be submitted when determined to be necessary to the review the proposed activity and the subject hazard. Additional technical information that may be required, includes, but is not limited to:
1. Site Plan. The site plan shall show all hazard areas located within two hundred feet of the project area or that have potential to be affected by the proposal; and
2. Hazards Analysis. The hazards analysis shall include a complete discussion of the potential impacts of the hazard on the project area and of the proposal on the hazard. (Ord. 1104-15 § 1 (Att. A)).