Chapter 85 – CRITICAL AREAS: GEOLOGICALLY HAZARDOUS AREAS
Sections:
85.05 User Guide
85.07 Purpose Statement
85.10 Applicability
85.12 Critical Area Maps
85.14 Erosion Hazard Areas
85.15 Required Information
85.20 Required Review
85.22 Peer Review
85.25 Performance Standards
85.30 Appeals
85.35 Bonds
85.40 Dedication
85.45 Liability
85.50 Notice of Geologic Hazard
85.05 User Guide
1. This chapter establishes special regulations that apply to development on property containing geologically hazardous areas. These regulations add to and, in some cases, supersede other regulations of this code. See Chapter 95 KZC for additional regulations that address trees and other vegetation within and outside of geologically hazardous areas.
2. If you are interested in developing property that contains a geologically hazardous area, or if you wish to participate in the City’s decision on a proposed development on any of these areas, you should read this chapter.
3. For properties within jurisdiction of the Shoreline Management Act, see Chapter 83 KZC.
(Ord. 4643 § 3, 2018; Ord. 4252 § 1, 2010; Ord. 4010 § 3, 2005)
85.07 Purpose Statement
These regulations were prepared to comply with the Growth Management Act and implement the goals and policies of the City’s Comprehensive Plan. The purpose of these regulations is to protect human life, property, and the environment. This purpose will be achieved by thoroughly evaluating development activity in geologically hazardous areas using best available science.
(Ord. 4643 § 3, 2018)
85.10 Applicability
1. General – This chapter applies to any property that contains any of the following hazard areas, including those shown on critical areas maps relating to this chapter entitled “Landslide Susceptibility” and “Liquefaction Potential”:
a. An erosion hazard area.
b. A landslide hazard area.
c. A seismic hazard area.
2. Conflict with Other Provisions of this Code – The provisions of this chapter supersede any conflicting provisions of this code. The other provisions of this code that do not conflict with the provisions of this chapter apply to property that contains a geologically hazardous area. If more than one (1) provision of this chapter applies to the subject property because of the presence on the subject property of more than one (1) type of geologically hazardous area, then the regulations that provide the greatest protection from the hazardous area shall apply to the area governed by multiple regulations.
3. SEPA Compliance – Nothing in this chapter or the decisions made pursuant to this chapter in any way affect the authority of the City to review, approve, condition, and deny projects under SEPA.
(Ord. 4643 § 3, 2018)
85.12 Critical Area Maps
The City’s critical area maps relating to this chapter are entitled “Landslide Susceptibility” and “Liquefaction Potential.” The City also maintains general mapping of other known critical areas. These maps and other available resources (such as topographic maps, soils maps, and aerial photos) are intended only as guides. They depict the approximate location and extent of known critical areas. Some critical areas depicted in these resources may no longer exist and critical areas not shown in these resources may currently be present. The provisions of this chapter and the findings of a geotechnical report and review of the report by the City take precedence over the City’s mapping in regard to identification and mitigation of potential geologic hazards. Site specific geologic hazard studies shall be conducted prior to approval of development, land surface modification, utility installation, or other activities to evaluate if a geologic hazard area actually exists, and to assess suitable options for hazard mitigation, if appropriate.
(Ord. 4643 § 3, 2018; Ord. 4551 § 4, 2017)
85.14 Erosion Hazard Areas
Regulations to control erosion are contained within KMC Title 15 and in other codes and ordinances of the City. Development activity within erosion hazard areas is regulated using these other provisions of this code and other City codes and ordinances and may be subject to increased scrutiny and conditioning because of the presence of an erosion hazard area.
(Ord. 4643 § 3, 2018)
85.15 Required Information
The City may require the applicant to submit some or all of the following information, consistent with the nature and extent of the proposed development activity, for any proposed development activity in a geologically hazardous area:
1. A topographic survey of the subject property, or the portion of the subject property specified by the Planning Official, with two (2) foot contour intervals. This mapping shall contain the following information:
a. Delineation of areas containing slopes 15 percent or greater, and identification of slopes 40 percent or greater.
b. Wetlands, streams and lakes on or adjacent to the subject property.
c. The location of storm drainage facilities on the subject property.
d. Existing vegetation, including size and type of significant trees.
2. A geotechnical investigation, prepared by a geotechnical engineer licensed in Washington State or engineering geologist licensed in Washington State, to determine if a landslide hazard area or seismic hazard area exists on the subject property.
3. A geotechnical report, prepared by a geotechnical engineer licensed in Washington State or engineering geologist licensed in Washington State, showing and including the following information:
a. A description of how the proposed development will or will not affect slope stability, surface and subsurface drainage, erosion, and seismic hazards on the subject property and other potentially impacted properties.
b. Evidence, if any, of holocene or recent landsliding, sloughing, or soil creep.
c. The location of springs, seeps, or any other surface expression of groundwater, and the location of surface water or evidence of seasonal runoff or groundwater.
d. Identification of existing fill areas.
e. Soil description in accordance with the Unified Soil Classification Systems.
f. Depth to groundwater and estimates of potential seasonal fluctuations, if applicable to the project.
g. Subsurface exploration logs that assess geologic hazards at the site, meaning that soil descriptions on the logs shall be in accordance with the Unified Soil Classification System. In addition, the logs shall also identify each of the geologic units encountered (e.g., fill, Vashon lodgement till, Vashon advance outwash).
h. If the subject property is located within 100 feet of a high landslide hazard area, then a current LiDAR-based shaded relief map of the project area and a discussion of the licensed geotechnical professional interpretation of this mapping must be provided.
i. Results of a quantitative slope stability analysis for any project involving development within a horizontal distance “H” of a high landslide hazard area where “H” is equal to the height of the slope within the high landslide hazard area or 50 feet, whichever is greater. The evaluation of slope stability under seismic conditions shall be based on a horizontal ground acceleration equal to one-half of the peak horizontal ground acceleration with a two (2) percent in 50-year probability of exceedance as defined in the current version of the International Building Code.
j. A discussion of the presence or absence of site features potentially indicative of historic landslide activity or increased risk of future landslide activity. Such features include, but are not limited to, tree trunk deformation, emergent seepage, landslide scarps, tension cracks, reversed slope benches, hummocky topography, vegetation patterns, and area stormwater management practices.
k. Estimate of the magnitude of seismically induced settlement that could occur during a seismic event for any project involving development within a seismic hazard area. Estimation of the magnitude of seismically induced settlement shall be based on a peak horizontal ground acceleration based on a seismic event with a two (2) percent in 50-year probability of exceedance as defined in the current version of the International Building Code. This requirement may be waived if it can be demonstrated that construction methods will mitigate the risk of seismically induced settlement such that there will be no significant impacts to life, health, safety and property.
l. A summary or abstract of the geotechnical report for the property where the development activity is proposed. The abstract shall at a minimum include the type of hazard, extent of the hazard, hazard analysis and geologic conditions.
m. The geotechnical report shall state that the project can be undertaken safely as long as the measures/recommendations of the geotechnical report are incorporated into the project plans.
4. Geotechnical recommendations, prepared by a geotechnical engineer licensed in Washington State or engineering geologist licensed in Washington State, for special engineering or other mitigation techniques appropriate to the hazard area along with an analysis of how these techniques will affect the subject, adjacent and potentially impacted properties, including discussions and recommendations on the following:
a. 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 and other potentially impacted properties during each stage of development.
b. Location of buildings, roadways, and other improvements.
c. Grading and earthwork, including compaction and fill material requirements, use of site solids as fill or backfill, imported fill or backfill requirements, height and inclination of both cut and fill slopes and erosion control and wet weather construction considerations and/or limitations.
d. Foundation and retaining wall design criteria, including bearing layer(s), allowable capacities, minimum width, minimum depth, estimated settlements (total and differential), lateral loads, and other pertinent recommendations.
e. Surface and subsurface drainage requirements and drainage material requirements.
f. Assessment of seismic ground motion amplification and liquefaction potential.
g. Other measures recommended to reduce the risk of slope instability.
h. Any additional information believed to be relevant by the geotechnical engineer preparing the recommendations or requested by the Planning Official.
(Ord. 4643 § 3, 2018; Ord. 4551 § 4, 2017)
85.20 Required Review
1. General – Except as specified in subsection (2) of this section, the Planning Official will review and decide upon any proposed development activity within a geologically hazardous area.
2. Other Approval Required – If the proposed development on the subject property requires approval through Process I, IIA, or IIB, described in Chapters 145, 150, and 152 KZC, respectively, the proposed development activity within the geologically hazardous area will be reviewed and decided upon as part of that other process.
3. The decision on a proposed project shall be to approve, deny or approve with conditions.
4. The City may modify any decision, prior to completion of the project, made under this section when it has been determined that physical circumstances have markedly and demonstrably changed on the subject property or the surrounding areas as a result of natural processes or human activity. This authority does not include requiring removal of structures or additions to structures that have been legally constructed under this decision.
(Ord. 4643 § 3, 2018)
85.22 Peer Review
1. For projects that would disturb land located in high landslide hazard areas, and including those areas within a horizontal distance “H” equal to the height of the slope or 50 feet, whichever is greater, the City shall require applicant funding of a licensed in Washington State geotechnical engineer or licensed in Washington State engineering geologist, selected and retained by the City subject to a third party contract, to review the geotechnical report and recommendations.
2. For projects to which subsection (1) of this section is not applicable but that are located within moderate landslide hazard areas or a seismic hazard area, the City shall normally require applicant funding of a licensed in Washington State geotechnical engineer or licensed in Washington State engineering geologist selected and retained by the City subject to third party contract, to review the geotechnical report and recommendations. The Planning Official may waive the third party review requirement in some cases. Guidance criteria to be considered by the Planning Official when evaluating if third party review will be waived, include, but is not necessarily limited to, any of the following:
a. City staff have the technical expertise of code requirements and knowledge of best practice to review the submitted geotechnical materials;
b. The consequences of failure present a low level of risk (e.g., type of structure proposed, slope height, surrounding topography or structures);
c. There is not any presence of known, recent landslide activity (i.e., anytime after the last continental glaciation, during the Holocene period) that presents a potential heightened landslide hazard risk;
d. Stormwater infiltration or stormwater facilities that could potentially impact slope stability are not proposed; or
e. Slopes that are the result of legally permitted grading activity.
3. For projects subject to peer review, the recommendations of the peer review shall be addressed in a revised geotechnical report (or supplement to the originally prepared report).
(Ord. 4643 § 3, 2018)
85.25 Performance Standards
(See also Chapter 95 KZC)
As part of any approval of development in a landslide hazard area or seismic hazard area, the City may require the following to protect property and persons:
1. Implementation of the geotechnical recommendations to mitigate identified impacts and geologic hazards, including the retention of trees, shrubs, and groundcover, and if applicable, the immediate implementation of a revegetation plan.
2. Written acknowledgment from the licensed in Washington State geotechnical engineer or licensed in Washington State engineering geologist who prepared the report required by KZC 85.15 that they have reviewed the project plans and that they conform to their recommendations.
3. That a qualified geotechnical professional, working under the supervision of a geotechnical engineer licensed in Washington State or engineering geologist licensed in Washington State, be present on site during land surface modification and foundation installation activities, and submittal by a geotechnical engineer licensed in Washington State or engineering geologist licensed in Washington State of a final report prior to occupancy, certifying substantial compliance with the geotechnical recommendations and geotechnical-related permit requirements.
4. Specifically engineered foundation and retaining wall designs.
5. The review of all access and circulation plans by the Department of Public Works.
6. Limitation or restriction of any development activity that may:
a. Significantly impact slope stability on the subject property or other properties;
b. Significantly alter drainage patterns in a manner that would adversely impact the subject property or other properties;
c. Cause serious erosion hazards, sedimentation problems or landslide hazards on the subject property or other properties; or
d. Cause property damage or injury to persons on or off the subject property.
7. If a quantitative slope stability analysis is required with the geotechnical report, as specified in KZC 85.15(3)(i), the proposed development shall provide a factor of safety of at least 1.5 for static conditions and at least 1.1 for seismic conditions.
8. Dedication of one (1) or more natural greenbelt protective easements or tracts.
(Ord. 4643 § 3, 2018; Ord. 4010 § 3, 2005)
85.30 Appeals
All final land use decisions and determinations made under this chapter are appealable using the applicable appeal provisions of the underlying development permit.
(Ord. 4643 § 3, 2018)
85.35 Bonds
The City may require a bond under Chapter 175 KZC and/or a perpetual landscape maintenance agreement to ensure compliance with any aspect of this chapter or any decision or determination made under this chapter.
(Ord. 4643 § 3, 2018)
85.40 Dedication
The City may require that the applicant dedicate development rights, air space, or an open space easement to the City to avoid impacts associated with a landslide hazard area or seismic hazard area on the subject property.
(Ord. 4643 § 3, 2018)
85.45 Liability
Prior to issuance of any development permit, the applicant shall enter into an agreement with the City, which runs with the property, in a form acceptable to the City Attorney, indemnifying the City for any damage resulting from development activity on the subject property which is related to the physical condition of the property. The applicant shall record this agreement with the King County Recorder’s Office and provide evidence to the City that the agreement has been recorded.
(Ord. 4643 § 3, 2018; Ord. 4491 § 11, 2015)
85.50 Notice of Geologic Hazard
Prior to final inspection of any development permit, the applicant shall record (unless legally prohibited from doing so), on the title of the property, a notice stating that the property is potentially located in a geologically hazardous area. This notice will inform future owners that, at the time of the permit’s issuance, the property was potentially located in a geologically hazardous area.
(Ord. 4643 § 3, 2018)