19.70.435 Critical area report additional requirements

19.70.435 Critical area report additional requirements.

A. Additional Report Contents for Geologically Hazardous Areas. In addition to the minimum report contents required per AMC 19.70.115, Critical area report, reports must also include the applicable information outlined in this section.

B. Third Party Review Required. Critical areas reports on geologically hazardous areas are subject to third party review at the owner’s sole expense as provided in AMC 19.70.115(B) and in any of the following circumstances:

1. A buffer reduction or alteration of a landslide hazard area is proposed.

C. Minimum Report Contents for Geologically Hazardous Areas. The written critical area report(s) must contain the following information, at minimum:

1. The report must generally follow the Washington State Department of Licensing Guidelines for Preparing Engineering Geology Reports in Washington (2006) and at a minimum report contents required per AMC 19.70.115, Critical area report;

2. A detailed overview of the field investigations, exploration locations, site photos, published data and references; data and conclusions from past assessments of the site; investigations or studies that support the identification of geologically hazardous areas;

3. A description of the methodologies used to conduct the geologically hazardous areas evaluations, classification, hazards assessments, and/or analyses of the proposal impacts, including references.

4. Assessment of Geological Characteristics. The assessment must include the following:

a. Classification of the type of geologic hazard(s) present in accordance with AMC 19.70.415, Designation;

b. An assessment of the geologic characteristics of the soils, sediments, and/or rock of the project area and potentially affected adjacent properties, and a review of the site history regarding landslides, erosion, and prior grading. Soils analysis must be accomplished in accordance with accepted classification systems in use in the region;

c. A description of load intensity, surface and groundwater conditions, public and private sewage disposal systems, fills, excavations, and all structural development;

d. A description of the extent and type of vegetative cover; and

e. An analysis of proposed surface and subsurface drainage, and the vulnerability of the site to erosion.

5. Analysis of Proposal. The report must include a detailed description of the project, its relationship to the geologic hazard(s), and its potential impact upon the hazard area, the project, the subject property, and affected adjacent properties.

6. Minimum Buffer and Building Setback. The report must make a recommendation for the minimum no-disturbance buffer and minimum building setback from any geologic hazard based upon the geotechnical analysis.

a. Erosion and Landslide Hazard Areas. The technical information required in a critical area report for a project within an erosion or landslide hazard area must also include the following:

i. An estimate of the present stability of the subject property, the stability of the subject property during construction, the stability of the subject property after all development activities are completed, and a discussion of the relative risks and slide potential relating to adjacent properties during each stage of development, including the effect of construction and placement of structures, clearing, grading, and removal of vegetation will have on the slope over the estimated life of the structures. Quantitative analysis of static and seismic slope stability, modeling, and/or seismic displacement analysis may be required by the decision-maker;

ii. A trend analysis of prior rates of erosion, if available;

iii. Consideration of the run-out hazard of landslide debris and/or the impacts of landslide run-out on downslope properties;

iv. Recommendations for stormwater improvements, locations and methods of erosion control, vegetation management, and/or other means for maintaining long-term soil stability;

v. 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;

vi. 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

vii. Recommendations for mitigation measures to be implemented in order to minimize the risk to the site and adjacent properties, including slope stabilization measures, if appropriate.

b. Seismic Hazard Areas. The technical information required in a critical area report for a project within a seismic hazard area must also include the following:

i. A complete discussion of the potential impacts of seismic activity on the site (for example, liquefaction, lateral spreading, fault rupture);

ii. An evaluation of the subsurface soil and groundwater profile, physical properties of the subsurface profiles, and the liquefaction potential of the site;

iii. Recommendations for mitigation measures to be implemented in order to minimize the risk to the project, and adjacent properties if appropriate.

c. Tsunami Hazard Areas. The technical information required in a critical area report for a project within a tsunami hazard area must also include:

i. A discussion of the potential impacts of the tsunami hazard on the site;

ii. Recommendations as to structure construction techniques including but not limited to the use of coastal high hazard performance standards; and

iii. For all development other than single lot, single-family residences, an emergency management plan including plans for emergency building exit routes, site evacuation routes, emergency training, notification of local emergency management officials, and an emergency warning system.

d. Marine Bluffs. A geotechnical engineering report will be required when development is proposed within 50 feet (in all directions) of or to the crest of a marine bluff, or a distance equal to the height of the slope up to a distance of 100 feet from the crest (measured from the top), whichever is greater.

i. The report must be based on best available science, existing and proposed uses, risks of slope failure, and coastal erosion rates over the last 75 years, if applicable.

ii. All proposed development on a marine bluff or in the required buffer must be prohibited, except as may be allowed per AMC Chapter 19.72, Shorelines, and applicable shoreline master program development regulations for marine bluffs, or minor development to provide public access (e.g., public trails, stairs or view points); provided, that impacts are mitigated and the development can be shown to be safe.

D. All Geologically Hazardous Areas. The Director may require additional information deemed necessary to adequately review the proposal.

1. Site and Construction Plans. The critical area submittal for geologically hazardous areas must include a copy of the site plans for the proposal, drawn at an engineering scale, showing:

a. The type and extent of geological hazard areas, any other critical areas, and recommended and required buffers on, adjacent to, off site within 200 feet of, or that are likely to impact or be affected by the proposal;

b. Proposed development, including the location of existing and proposed structures, fill, clearing limits, significant trees to be removed, vegetation to be removed, proposed material stockpile locations, and stormwater management facilities;

c. The topography, in two-foot contours, of the project area and all hazard areas addressed in the report;

d. Height of slope, slope gradient, and cross-section of the project area indicating the stratigraphy of the site;

e. The location of springs, seeps, or other surface expressions of groundwater on or off site within 200 feet of the project area or that have the potential to affect or be affected by the proposal;

f. The location and description of surface water on or off site within 200 feet of the project area or that has the potential to be affected by the proposal. (Ord. 3064 § 2 (Att. A), 2021)