The city finds that certain portions of the city are characterized by geologic hazards that may pose a risk to public and private property, human life and safety and the natural systems that make up the environment of the city if incompatible development is sited in areas of significant hazard. Such lands are affected by natural processes that make them susceptible to landslides, erosion, seismic activity, or rock fall. Incompatible development in areas characterized by geologic hazards may not only place itself at risk, but also may increase the hazard to surrounding development and use.
The intent of this article is to reduce the threat posed by geologic hazards. Some geologic hazards can be reduced or mitigated by engineering, design or modified construction so that risks to health and safety are acceptable. When technology cannot reduce risks to acceptable levels, building in geologically hazardous areas is best avoided.
(Ord. 1395 § 1 (Exh. A), 2011; Ord. 1597 § 1 (Att. A), 2019)
The city of Leavenworth designates geologically hazardous areas in the city and its UGA as follows:
A. 
Erosion. The city designates all erosion hazard areas, regardless of any formal identification, as geologically hazardous areas. At a minimum, the following shall be considered suspected erosion hazard areas for the purpose of determining the need for a preliminary evaluation:
1. 
Areas identified by the U.S. Department of Agriculture's Natural Resources Conservation Service as highly erodible or potential highly erodible land and areas identified by the Web Soil Survey as having soils with erosion hazard ratings of "moderate," "severe," or "very severe" due to slope/erodibility.
2. 
Areas impacted by shore land and/or stream bank erosion and those areas within a channel migration zone. (Please note that, per LMC § 16.08.130, critical areas within shoreline jurisdiction are regulated by the city's Shoreline Master Program when update is adopted.)
3. 
Areas in which maps, soil type, hydrology, or presence of historic failures, past modifications, or records indicate a high potential for erosion.
B. 
Landslide. The city designates all landslide hazard areas, regardless of any formal identification, as geologically hazardous areas. At a minimum, the following shall be considered suspected landslide hazard areas for the purpose of determining the need for a preliminary evaluation:
1. 
Those areas delineated by the U.S. Department of Agriculture's Natural Resources Conservation Service (NRCS) as having a significant limitation for building site development, including but not limited to areas identified by the Web Soil Survey as having soils "very limited" or "somewhat limited" for building site development due to slope (including those described as "too steep") or having a "severe" limitation for building site development.
2. 
Areas of historic failures, such as areas designated as quaternary slumps, earthflows, mudflows, lahars, or landslides on maps published as the United States Geological Survey or the Washington State Department of Natural Resources.
3. 
Any area exhibiting all three of the following characteristics:
a. 
Slopes steeper than 15 percent;
b. 
Hillsides intersecting geologic contacts with a relatively permeable sediment overlying relatively impermeable sediment or bedrock; and
c. 
Springs or groundwater seepage.
4. 
Areas that have shown movement during the Holocene epoch (from 10,000 years ago until today) or that are underlain or covered by mass wastage debris of that epoch.
5. 
Slopes that are parallel or subparallel to lines of weakness (such as bedding planes, joint systems, and fault planes) in subsurface materials.
6. 
Slopes having gradients steeper than 80 percent subject to rockfall during seismic shaking.
7. 
Areas potentially unstable as a result of rapid stream incision, stream bank erosion, and undercutting by wave action, including stream channel migration zones. (Please note that, per LMC § 16.08.130, critical areas within shoreline jurisdiction are regulated by the city's Shoreline Master Program.)
8. 
Areas that show evidence of, or are at risk from, snow avalanches.
9. 
Areas located in a canyon or on an active alluvial fan, presently or potentially subject to inundation by debris flows or catastrophic flooding.
10. 
Any area with a slope of 40 percent or steeper and with a vertical relief of 10 or more feet except areas composed of consolidated rock. A slope is delineated by establishing its toe and top and measured by averaging the inclination over at least 10 feet of vertical relief.
C. 
Seismic. The city designates all seismic hazard areas, regardless of any formal identification, as geologically hazardous areas. At a minimum, the following shall be considered suspected seismic hazard areas for the purpose of determining the need for a preliminary evaluation:
1. 
Those areas in Seismic Design Category D0 on the Seismic Design Category Map for Residential Construction in Washington, Sheet 2.
2. 
Areas underlain by cohesionless soils of low density.
3. 
Areas in which there is a record of earthquake damage in the past.
D. 
Rock Fall. A rock-fall hazard area consists of three components, illustrated below: (1) a rock-fall source area, in general defined by bedrock geologic units that exhibit relatively consistent patterns of rock-fall susceptibility throughout the study area; (2) an acceleration zone, where rock-fall debris detached from the source gains momentum as it travels down-slope; and (3) a rock-fall runout zone, which includes gentler slopes where boulders have rolled or bounced beyond the base of the acceleration zone.
The city designates all rock-fall hazard areas, regardless of any formal identification, as geologically hazardous areas. At a minimum, the following shall be considered suspected rock-fall hazard areas for the purpose of determining the need for a preliminary evaluation:
1. 
Areas within a 22-degree shadow angle extending from the base of a rock source; and
2. 
Areas in which the city has a record of rock falls or in which there is visual evidence of past rock falls.
(Ord. 1395 § 1 (Exh. A), 2011; Ord. 1597 § 1 (Att. A), 2019)
The city of Leavenworth classifies geologically hazardous areas within the city and its urban growth area as follows:
A. 
Known or suspected risk: Documentation or projection of the hazard by a qualified professional exists, or the area is designated as a suspected critical area.
B. 
No known risk: Documentation or projection of the lack of hazard by a qualified professional exists.
C. 
Risk unknown: Data are not available to determine the presence or absence of a geologic hazard.
(Ord. 1395 § 1 (Exh. A), 2011; Ord. 1597 § 1 (Att. A), 2019)
A. 
Preliminary Evaluation. In determining whether a preliminary evaluation is required for development in a given area, the administrator shall consider the geologic hazard classification. Any approved geological assessment, geotechnical report, hydrogeologic evaluation, channel migration zone study, or other special or detailed study may be used to identify areas of known or suspected risk, unknown risk, or no known risk. The city may choose to use available data to map the approximate location and extent of geologically hazardous areas.
B. 
Site Assessment and Report Requirements. Geological assessments and geotechnical reports shall be prepared in compliance with the following provisions. A geotechnical report contains all of the provisions of a geological assessment and shall be considered to meet the requirements of a geological assessment.
1. 
A geological assessment shall include the following:
a. 
Evaluate the actual presence of geologically hazardous areas within or in the vicinity of the site and the need for a geotechnical report. Specifically mention the circumstances or conditions which require the report to be prepared (steep slopes, erodible soils, suspected landslide or avalanche hazard, adverse hydrologic or flood risk, etc.).
b. 
Evaluate safety issues related to proposed activities. Address issues that could involve personal injury, worksite safety, or property damage.
c. 
Address existing geologic, topographic, and hydrologic conditions on the site, including an evaluation of the ability of the site to accommodate the proposed activity. Describe the proposed development, including property size and location, nature and extent of the planned development (i.e., house, garage, shop, swimming pool, etc.), and its specific location on the property. Include evidence of prior grading, excavation, cut banks, fill areas, or mining activity, and their potential impact on the project. Note and evaluate any features that could adversely affect development such as drainage gullies, erosion channeling, alluvial fans, evidence for debris flow or avalanche, surface creep and slope failure, observed or suspected spring activity and flood risk potential.
d. 
A discussion of the surface and subsurface geological and engineering properties of the soils, sediments, and/or rocks on the subject property and adjacent properties and their effect on the stability of the slope. Where known from field inspection or reference maps and literature, include bedrock identification and age, structural attitude with respect to slope inclination, fracturing, faults and shear zones, hydrothermal alteration, weathering characteristics, presence of landslide diamictite and its age and consolidation, etc. Use cross-sections if necessary for better representation of subsurface character.
e. 
A description of the soils in accordance with the Unified Soil Classification System. Give general soil characteristics that could affect site development (i.e., frost action and shrink/swell potential, permeability, plasticity and wet/dry behavior, erodibility, etc.). Especially note the presence or suspected presence of clay-rich horizons and their position/location in the soil profile, and any indication that a building site could be subjected to differential soil compression or settling.
f. 
Evidence and history of avalanches, faults, significant geologic contacts, landslides, or downslope soil movement on the subject property and adjacent properties not detailed in subsection (B)(1)(c) of this section.
g. 
A summary of the site assessment and its conclusions, mentioning the presence or absence of geohazards and site suitability. Include any recommendations for mitigation of potential hazards that can be dealt with without requiring a complete geotechnical report (control measures such as footing or intercept drainage systems, retaining walls, erosion control, vegetative management and restoration, and the probable need for engineering consultation and design).
h. 
A topographic map showing the proposed development site location and approximate parcel shape location, boundaries, and all buildable space on the property.
i. 
Cite all references and information used in the assessment preparation, such as United States Geologic Survey (USGS) and Department of Natural Resources Geologic Maps and Bulletins, soil studies, surveys and previous reports.
2. 
A geotechnical report shall include all of the information required for a geologic site assessment as well as the following:
a. 
A contour map of the proposed site, at a scale of one inch equals 20 feet or as deemed appropriate by the administrator. Slopes shall be clearly delineated for the ranges between 15 and 29 percent, and 30 percent or greater, including figures for a real coverage of each slope category on the site. When site-specific conditions indicate the necessity, the administrator may require the topographic data to be field surveyed.
b. 
The location of springs, seeps, or other surface expressions of groundwater. The location of surface water or evidence of seasonal surface water runoff or groundwater.
c. 
The extent and type of vegetative cover prior to development activity or site disturbance.
d. 
A description of site history, including any prior grading, soil instability, or slope failure. Identify all existing fill areas.
e. 
A determination regarding the appropriate hazard category or categories according to the classification of the geologically hazardous area consistent with LMC § 16.08.630.
i. 
An explanation of soil characteristics and geologic, topographic, and hydrologic conditions of the site that might be expected to create a significant risk due to any geologic hazard and show the location of such hazardous areas. Specifically, include:
(A) 
Slope stability studies and opinion of slope stability;
(B) 
Erosion vulnerability of site;
(C) 
Suitability of on-site soil for fill;
(D) 
A summary of all subsurface exploration data, including subsurface soil profile, exploration logs, laboratory or in situ test results, and groundwater information and an interpretation and analysis of the subsurface data; and
(E) 
Building limitations.
f. 
A site development plan, drawn to scale, which shows the boundary lines and dimensions of the subject property, the location, size and type of any existing or proposed structures, impervious surfaces, wells, drainfields, drainfield reserve areas, roads, easements, and utilities proposed or located on site.
g. 
A hazard analysis evaluating the proposed alteration's influence on the safety and stability of structures and any other risks of property damage, death, or injury resulting from development of the hazard area. Factors such as landscape irrigation, stormwater generation and the effect of street conveyance and utility placement should be included in the review of potential landslide and erosion hazard areas.
h. 
A description of appropriate mitigation measures, including specific design, development, and construction measures that will be taken to eliminate or minimize identified risks and to comply with the performance standards in LMC § 16.08.650 (Performance standards). Specify any recommended setbacks and/or buffers. Include specific engineering recommendations for design and any geotechnical special provisions. Specifically, include:
i. 
Proposed angles of cut and fill slopes and site grading requirements;
ii. 
Structural foundation requirements and estimated foundation settlements;
iii. 
Soil compaction criteria;
iv. 
Proposed surface and subsurface drainage; and
v. 
Lateral earth pressures.
i. 
A vegetation management and restoration plan or other means for maintaining long-term stability of slopes.
j. 
The proposed method of drainage and locations of all existing and proposed surface and subsurface drainage facilities and patterns, and the locations and methods for erosion control.
k. 
An erosion control plan that minimizes erosion (including both water and wind erosion) from all disturbed areas during construction and until permanent erosion control is achieved. Until the city adopts stormwater management regulations, the Regional Stormwater/Wetland Management Master Plan 2016, or as amended, shall be the preferred guidance for erosion control measures.
l. 
A monitoring program, to be marked on the face of the building permit.
m. 
Information demonstrating compliance with all applicable codes and ordinances for the proposed development permit.
C. 
Critical Area Study.
1. 
A required critical area study for geologically hazardous areas shall include a geotechnical report adequate to assess any risks of property damage, death, or injury resulting from development of the hazard area and establish mitigation measures.
2. 
If an applicant can demonstrate, through submittal of a geological assessment, that no landslide or erosion hazards exist on site, the requirement for a geotechnical report may be waived by the administrator.
3. 
Erosion and Landslide Hazard Areas. In addition to the basic report requirements, a critical area study for an erosion or landslide hazard area shall also meet the following requirements:
a. 
A site plan showing:
i. 
The height of slope, slope gradient, and cross-section of the project area;
ii. 
The location of springs, seeps, or other surface expressions of groundwater on or within 200 feet of the project area or that have potential to be affected by the proposal; and
iii. 
The location and description of surface water runoff features;
b. 
A hazards analysis that includes:
i. 
A description of the extent and type of vegetative cover;
ii. 
A description of subsurface conditions based on data from site-specific explorations;
iii. 
Descriptions of surface and groundwater conditions, public and private sewage disposal systems, fills and excavations, and all structural improvements;
iv. 
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;
v. 
An estimate of the bluff retreat rate that recognizes and reflects potential catastrophic events such as seismic activity or a 100-year storm event;
vi. 
Consideration of the run-out hazard of landslide debris and/or the impacts of landslide run-out on down slope properties;
vii. 
A study of slope stability including an analysis of proposed cuts, fills, and other site grading;
viii. 
Recommendations for building siting limitations; and
ix. 
An analysis of proposed surface and subsurface drainage, and the vulnerability of the site to erosion;
c. 
A geotechnical report prepared by a licensed engineer that presents engineering recommendations for the following:
i. 
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;
ii. 
Recommendations for drainage and subdrainage improvements;
iii. 
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
iv. 
Mitigation of adverse site conditions including slope stabilization measures and seismically unstable soils, if appropriate;
d. 
For any development proposal on a site containing an erosion hazard area, an erosion and sediment control plan prepared in accordance with the city's stormwater management regulations, when adopted;
e. 
A drainage plan providing for the collection, transport, treatment, discharge, and/or recycling of water, prepared in accordance with the city's stormwater management regulations, when adopted. The drainage plan should consider on-site septic system disposal volumes where the additional volume will affect the erosion or landslide hazard area;
f. 
Hazard and environmental mitigation plans that 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
g. 
If the administrator 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.
4. 
Seismic Hazard Areas. In addition to the general critical area study requirements specified in Article VII of this chapter, a critical area study for a seismic hazard area shall also meet the following requirements:
a. 
The site map shall show all known and mapped faults that are within 200 feet of the project area or that have potential to significantly affect or to be affected by the proposal.
b. 
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).
c. 
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.
5. 
Rock-Fall Hazard Areas. In addition to the basic report requirements, a critical area study for a rock-fall hazard area shall also meet the following requirements:
a. 
Any required critical area study for a rock-fall hazard area shall be prepared by a geotechnical consultant familiar with rock-fall hazards;
b. 
The study shall include a geologic vicinity map, at an appropriate scale (typically 1:24,000) and with references, showing the general surface geology (landslides, alluvial fans, etc.), bedrock geology where exposed, bedding attitudes, faults, other geologic structural features, and location of any rock-fall hazards;
c. 
The hazards analysis shall include an evaluation of available remote sensing data, which may include aerial photographs, oblique aerial photographs, and DEMs derived from detailed topography and/or LIDAR, for the potential presence of geologic hazards;
d. 
The study shall include final design plans and specifications for engineered mitigation signed and stamped by a qualified geotechnical engineer. If the geologic report is submitted with a land use application that is reviewed prior to the construction or building plans (e.g., preliminary plat or conditional use permit), the engineering level design and calculations of the improvement do not need to be submitted until after a land use approval is obtained and construction approval is requested. However, the proposed methods must still be identified;
e. 
The study shall include a statement regarding the suitability of the site for the proposed development from a rock-fall hazard perspective.
6. 
Where a geotechnical report has been prepared and approved by the city within the last five years for a specific site, and where the proposed activity and surrounding site conditions are unchanged (or, in the case of an individual lot within a subdivision, where the only changes in surrounding site conditions are development and mitigation as specified in the report), said report may be used and a new report may not be required. The applicant shall submit a geological assessment detailing any changed environmental conditions associated with the site.
(Ord. 1395 § 1 (Exh. A), 2011; Ord. 1597 § 1 (Att. A), 2019)
A. 
Any development or other alteration that would pose a foreseeable risk to the public, public or private resources and facilities, or the natural environment is prohibited.
B. 
The following standards apply to all development within geologically hazardous areas:
1. 
Development shall not increase instability or create a hazard to the site or adjacent properties, or result in a significant increase in sedimentation or erosion. Construction methods shall minimize risks to structures and shall not increase the risk to the site, or to adjacent properties and their structures, from the geologic hazard.
2. 
Site planning shall minimize disruption of existing topography and natural vegetation, and where feasible shall incorporate opportunities for phased clearing.
3. 
Disturbed areas shall be replanted within one year of project completion, in accordance with an approved revegetation plan.
4. 
Impervious surface coverage shall be minimized.
5. 
Excavation and grading shall be limited to the minimum necessary to accomplish engineering design. The clearing and grading schedule shall consider limitations based upon seasonal weather conditions.
6. 
Any limitations to site disturbance, such as clearing restrictions, imposed as a condition of development approval should be marked in the field and approved by the city prior to undertaking the project.
7. 
All authorized clearing for roads, utilities, etc., should be limited to the minimum necessary to accomplish engineering design. Alterations should meet the following requirements:
a. 
Clearing, grading or filling of sloped sites containing erosion or landslide hazard areas should be limited by weather conditions and an approved erosion control plan;
b. 
All clearing shall be marked in the field for inspection and approval prior to alteration of the site;
c. 
The face of cut and fill on slopes shall be prepared and maintained to control against erosion.
C. 
The following additional standards apply to erosion hazard areas:
1. 
In order to prevent or mitigate potential hazards to life, property or the natural environment, development in or adjacent to erosion hazard areas shall be discouraged. No public or private development will be permitted in erosion hazard areas where mitigation approved by the city and adequate to protect members of the public and public and private resources and facilities from injury, loss of life, property damage or financial losses due to erosion, landslide, seismic events or steep slope failure is not feasible.
2. 
Alterations.
a. 
Alterations of an erosion hazard area may occur only for activities for which a hazards analysis is submitted and certifies that:
i. 
The development will not increase surface water discharge or sedimentation to adjacent properties beyond predevelopment conditions;
ii. 
The development will not decrease slope stability on adjacent properties; and
iii. 
The alterations will not adversely impact other critical areas.
b. 
Excavation and grading shall be minimized in all erosion and steep slope areas and shall comply in full with the relevant provisions of building codes adopted by the city.
3. 
Development within an erosion or landslide hazard area or buffer shall be designed to meet the following basic requirements unless it can be demonstrated that an alternative design provides greater long-term slope stability while meeting all other provisions of this chapter. The requirement for long-term slope stability shall exclude designs that require regular maintenance to maintain their level of function. The basic requirements are:
a. 
The proposed development shall not decrease the factor of safety for landslide occurrences below the limits of 1.5 for static conditions and 1.2 for dynamic conditions. Analysis of dynamic conditions shall be based on a minimum horizontal acceleration as established by the current version of the Uniform Building Code;
b. 
Structures and improvements shall be clustered to avoid geologically hazardous areas and other critical areas;
c. 
Structures and improvements shall minimize alterations to the natural contour of the slope, and foundations shall be tiered where possible to conform to existing topography;
d. 
Structures and improvements shall be located to preserve the most critical portion of the site and its natural landforms and vegetation;
e. 
The proposed development shall not result in greater risk or a need for increased buffers on neighboring properties;
f. 
Retaining walls that allow the maintenance of existing natural slope area are preferred to graded artificial slopes; and
g. 
Development shall be designed to minimize impervious lot coverage.
4. 
Unless otherwise provided or as part of an approved alteration, removal of vegetation from an erosion or landslide hazard area or related buffer shall be prohibited.
5. 
Clearing shall be allowed only during the dry season, which shall depend on actual weather conditions but is generally considered to run from May through September.
6. 
Utility lines and pipes shall be permitted in erosion and landslide hazard areas only when the applicant demonstrates that no practical alternative is available. The line or pipe shall be located above ground and properly anchored and/or designed so that it will continue to function in the event of an underlying slide. Stormwater conveyance shall be allowed only through a high-density polyethylene pipe with fuse-welded joints, or similar product that is technically equal or superior.
7. 
Point discharges from surface water facilities and roof drains onto or upstream from an erosion or landslide hazard area shall be prohibited except as follows:
a. 
Discharge is conveyed via continuous storm pipe down slope to a point where there are no erosion hazard areas downstream from the discharge;
b. 
Water is discharged at flow durations matching predevelopment conditions, with adequate energy dissipation, into existing channels that previously conveyed stormwater runoff in the predeveloped state; or
c. 
Discharge is dispersed up-slope of the steep slope onto a low-gradient undisturbed buffer demonstrated to be adequate to infiltrate all surface and stormwater runoff, and where it can be demonstrated that such discharge will not increase the saturation of the slope.
8. 
On-site sewage disposal systems, including drain fields, shall be prohibited within erosion hazard areas and related buffers.
9. 
Development may occur in steep slope areas only after the following standards have been met:
a. 
Development must be located to minimize disturbance and removal of vegetation and also to protect the most sensitive areas (including areas of erosive soils, areas at risk of erosion by wind or water, and areas of dense vegetation) and retain open space. The use of continuous greenbelt areas shall be encouraged; and
b. 
Structures must be clustered where possible to reduce disturbance and maintain natural topographic character. Common access driveways shall be considered as a means of reducing construction disturbances; and
c. 
Where possible, structures must conform to the natural contour of the slope and foundations must be tiered to conform to existing topography of the site.
10. 
Unless a grading plan prepared by a licensed civil engineer is provided and approved by the administrator, disturbance of a development site shall generally not exceed the following for the slope categories indicated:
Table 16.08.650.1 Maximum Amount of Slope That May Be Disturbed
Slope Category
Factor
Slopes 30 – 40% (60% of the site or more)
.60
Slopes 40% + (also see landslide hazard area)
.30
The overall amount of disturbance allowed on development sites which have any combination of the above slope categories shall be determined by the following formula:
[Square footage of the area within the slope category x slope factor] = Total amount of allowable disturbance for that slope classification.
The total amount of allowable disturbance for the site is the sum of all the allowable disturbance totals for each slope category.
D. 
The following additional standards apply to landslide hazard areas:
1. 
Areas identified as landslide hazard areas or within 250 feet of landslide hazard areas shall be altered only when the administrator concludes, based on environmental information provided by a qualified professional, that:
a. 
There will be no increase in surface water discharge or sedimentation to adjacent properties; and
b. 
There will be no decrease in slope stability on adjacent properties; and
c. 
Either:
i. 
There is no evidence of recent landslides in the vicinity of the proposed development, and a quantitative analysis of slope stability indicates no significant risk to the proposed development, adjacent properties, or the health or safety of humans or the environment; or
ii. 
The hazard can be mitigated, modified or the project can be designed so that the risk (including risks to the project and risks beyond the project site) is no greater than the risk posed by development on a site without a landslide hazard; or
iii. 
The proposal is so minor as not to pose a threat.
2. 
The following standards apply to all development in landslide hazard areas:
a. 
Disturbance of trees and vegetation shall be minimized in and within 250 feet of landslide hazard areas in order to prevent erosion, stabilize slopes, and preserve the natural character of the area;
b. 
Structures and improvements shall be located to preserve the most sensitive portion of the site and its natural landforms and vegetation.
3. 
A buffer shall be established from all edges of landslide hazard areas. The size of the buffer shall be determined by the administrator to eliminate or minimize the risk of property damage, death, or injury resulting from landslides caused in whole or part by the development, based upon review of and concurrence with a critical area study prepared by a qualified professional.
4. 
Alterations.
a. 
Alterations of a landslide hazard area or its buffer may occur only for activities for which a hazards analysis is submitted and certifies that:
i. 
The development will not increase surface water discharge or sedimentation to adjacent properties beyond predevelopment conditions;
ii. 
The development will not decrease slope stability on adjacent properties; and
iii. 
The alterations will not adversely impact other critical areas.
5. 
Subdivision.
a. 
Land that is located wholly within a landslide hazard area or its buffer may not be subdivided.
b. 
Land that is located partially within a landslide hazard area or its buffer may be divided; provided, that each resulting lot has sufficient buildable area outside of, and will not affect, the landslide hazard or its buffer.
c. 
Access roads and utilities may be permitted within a landslide hazard area and associated buffers if the city determines that no other feasible alternative exists.
6. 
On-site sewage disposal systems, including drain fields, shall be prohibited within landslide hazard areas and related buffers.
E. 
Seismic Hazard Areas. All development activities in seismic hazard areas shall conform to the applicable building code.
F. 
Rock-Fall Hazard Areas. Development of structures intended for human occupancy or critical facilities in a rock-fall hazard area shall be discouraged unless the hazard is mitigated to an acceptable and reasonable risk level, based on information provided by a qualified professional who is a geotechnical consultant familiar with rock-fall hazards. Development of any such structure in a rock-fall hazard area in which the hazard is not mitigated to an acceptable and reasonable risk level shall require a recorded waiver of liability.
(Ord. 1395 § 1 (Exh. A), 2011; Ord. 1597 § 1 (Att. A), 2019)