19.37.080 Geologically hazardous areas.
A. Designation. The following geologically hazardous areas shall not be altered except as otherwise provided by this chapter:
a. Those areas defined as high and very high/severe risk of landslide hazard in the Dames and Moore Methodology for the Inventory, Classification and Designation of Geologically Hazardous Areas, City of Everett, Washington: July 1, 1991, or as revised through best available science:
(1) Very high/severe: slopes greater than fifteen percent in the Qtb, Qw, and Qls geologic units; and slopes greater than fifteen percent with uncontrolled fill.
(2) High: slopes greater than forty percent in all other geologic units (not Qtb, Qw, and Qls or uncontrolled fill).
b. Those areas defined as medium risk of landslide hazard in the Dames and Moore Methodology for Inventory, Classification and Designation of Geologically Hazardous Areas, City of Everett, Washington: July 1, 1991, or as revised through best available science, when combined with springs or seeps, immature vegetation, and/or no vegetation:
(1) Slopes less than fifteen percent for Qtb, Qw, and Qls geologic units and uncontrolled fill.
(2) Slopes of twenty-five percent to forty percent in all other geologic units.
c. Any area with all three of the following characteristics:
(1) Slopes greater than fifteen percent; and
(2) Hillsides intersecting geologic contacts with a relatively permeable sediment overlying a relatively impermeable sediment or bedrock; and
(3) Springs, ground water seepage, or saturated soils.
d. Any area which has shown movement during the Holocene epoch (from ten thousand years ago to the present) or which is underlain or covered by mass wastage debris of that epoch.
e. Any area potentially unstable as a result of rapid stream incision, stream bank erosion or undercutting by wave action.
f. Areas of historic failures, including areas of unstable, old and recent landslides or landslide debris within a head scarp, and areas exhibiting geomorphological features indicative of past slope failure, such as hummocky ground, slumps, earthflows, mudflows, etc.
g. Any area with a slope of forty percent or steeper and with a vertical relief of fifteen or more feet, except those manmade slopes created under the design and inspection of a geotechnical professional, or slopes composed of consolidated rock.
h. Areas that are at risk of landslide due to high seismic hazard.
i. Areas that are at risk of landslides or mass movement due to severe erosion hazards.
2. Seismic/liquefaction hazard areas:
a. Those areas mapped as seismic/liquefaction hazards per the Dames and Moore Methodology for the Inventory, Classification and Designation of Geologically Hazardous Areas, City of Everett, Washington: July 1, 1991, or as revised through best available science.
b. Those areas mapped as high and moderate to high liquefaction susceptibility on the Liquefaction Susceptibility Map of Snohomish County, Washington, Washington State Department of Natural Resources, Palmer, Stephen, et al., September, 2004.
a. Those areas defined as high and very high/severe risk of erosion in the Dames and Moore Methodology for the Inventory, Classification and Designation of Geologically Hazardous Areas, City of Everett, Washington: July 1, 1991, or as revised through best available science:
(1) High erosion hazard areas include slopes of twenty-five to forty percent in Qva and Qal geologic units; and slopes of greater than forty percent in other (not Qva or Qal) geologic units.
(2) Very high/severe erosion hazard areas include slopes of greater than forty percent in Qva and Qal geologic units.
b. Those areas defined as medium risk of erosion in the Dames and Moore Methodology for the Inventory, Classification and Designation of Geologically Hazardous Areas, City of Everett, Washington: July 1, 1991, or as revised through best available science, when they contain debris and mud flows, gullying or rifling, immature vegetation, or no vegetation:
(1) Slopes of twenty-five to forty percent in other (not Qva or Qal) geologic units.
4. Other areas which the city has reason to believe are geologically hazardous.
B. Geologically Hazardous Slope Setbacks and Slope Protection.
1. Geotechnical Assessment Requirements. Development proposals on or within two hundred feet of any area designated as or which, based on site-specific field investigation, the city has reason to believe are geologically hazardous areas shall submit a geological assessment as required by subsection F of this section.
2. The setback buffer requirement shall be based upon information contained in a geological assessment, and shall be measured on a horizontal plane from a vertical line established at the edge of the geologically hazardous area limits (both from the top and toe of slope). In the event that a specific setback buffer is not included in the recommendation of the geological assessment, the setback buffer shall be based upon the standards contained in Chapter 19.18 of the International Building Code (IBC), or as the IBC is updated and amended.
a. If the geological assessment recommends setback buffers that are less than the standard buffers that would result from application of Chapter 19.18 of the IBC, the specific rationale and basis for the reduced buffers shall be clearly articulated in the geological assessment.
b. The city may require larger setback buffer widths under any of the following circumstances:
(1) The land is susceptible to severe erosion and erosion control measures will not effectively prevent adverse impacts.
(2) The area has a severe risk of slope failure or downslope stormwater drainage impacts.
(3) The increased buffer is necessary to protect public health, safety and welfare based upon findings and recommendations of the geological assessment.
3. Unless otherwise permitted as part of an approved alteration, the setback buffers required by this subsection shall be maintained in native vegetation to provide additional soil stability and erosion control. If the buffer area has been cleared, it shall be replanted with native vegetation in conjunction with any proposed development activity.
4. The city may impose seasonal restrictions on clearing and grading within two hundred feet of any geologically hazardous areas.
C. Permitted Alterations. Unless associated with another critical area, the planning director, using the review process described in EMC Title 15, Local Project Review Procedures, may allow alteration of an area identified as a geologically hazardous area or the setback buffers specified in the IBC if an approved geotechnical report demonstrates that:
1. The proposed development will not create a hazard to the subject property, surrounding properties or rights-of-way, or erosion or sedimentation to off-site properties or bodies of water;
2. The proposal addresses the existing geological constraints of the site, including an assessment of soils and hydrology;
3. The proposed method of construction will reduce erosion potential, landslide and seismic hazard potential, and will improve or not adversely affect the stability of slopes;
4. The proposal uses construction techniques which minimize disruption of existing topography and natural vegetation;
5. The proposal is consistent with the purposes and provisions of this chapter and mitigates any permitted impacts to critical areas in the vicinity of the proposal;
6. The proposal mitigates all impacts identified in the geotechnical letter or geotechnical report;
7. All utilities and access roads or driveways to and within the site are located so as to require the minimum amount of modification to slopes, vegetation or geologically hazardous areas; and
8. The improvements are certified as safe as designed and under anticipated conditions by a geologist.
D. Additional Requirements. As part of any approval of development on or adjacent to geologically hazardous areas or within the setback buffers required by subsection B of this section:
1. The city shall require:
a. Geologically hazardous areas not approved for alteration and their buffers shall be placed in a critical area protective covenant or tract as required by EMC 19.37.220;
b. Any geologically hazardous area or required setback buffer that is allowed to be altered subject to the provisions of this chapter shall be subject to a covenant of notification and indemnification/hold harmless agreement in a form acceptable to the city attorney. Such document shall identify any limitations placed on the approved alterations.
2. The city may require:
a. The presence of a geologist on the site to supervise during clearing, grading, filling and construction activities which may affect geologically hazardous areas, and provide the city with certification that the construction is in compliance with his/her recommendations and has met with his/her approval, and other relevant information concerning the geologically hazardous conditions of the site;
b. Vegetation and other soil-stabilizing structures or materials be retained or provided;
c. Long-term maintenance of slopes and on-site drainage systems.
E. Prohibited Alterations. Modification of geologically hazardous areas shall be prohibited under the following circumstances:
1. Where geologically hazardous slopes are located in a stream, wetland, and/or a fish and wildlife habitat conservation area or their required buffers, alteration of the slopes is not permitted, except as allowed under EMC 19.37.050. The required buffer for such slopes shall be determined through the site-specific geological assessment, but in no case shall be less than twenty-five feet from the top of slopes of twenty-five percent and greater.
2. Any proposed alteration that would result in the creation of or which would increase or exacerbate existing geological hazards, or which would result in substantial unmitigated geological hazards either on site or off site, shall be prohibited.
F. Geological Assessment. A geological assessment is a site investigation process to evaluate the on-site geology affecting a subject property and contiguous properties and the extent to which geological factors may be impacted by the proposed development activity.
1. Geological assessments shall be submitted to the department for review and approval as part of the integrated permit review process described in EMC Title 15, Local Project Review Procedures. 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.
2. When the geological assessment has been accepted, the department shall issue a decision on the land use permit application as provided for in EMC Title 15, Local Project Review Procedures.
3. 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 or if there is new information about a geological hazard, the applicant may be required to submit an amendment to the geological assessment. (Ord. 3676-19 § 10, 2019; Ord. 2909-06 § 8, 2006.)