Article II: Geologically Sensitive Areas

§ 18.90.160 Designation of geologically sensitive areas.

Geologically sensitive areas include areas susceptible to erosion, sliding, subsidence, earthquake, or other geologic events and conditions. Improper and incompatible development sited in these areas can pose a threat to the health and safety of citizens, placing not only itself at risk, but also potentially creating or increasing hazards to surrounding development and land uses. As defined in this title, areas susceptible to one or more of the following types of hazards shall be designated as a geologically sensitive area:

Mine hazard areas;

Steep slopes; and

Unstable slopes.

(Ord. 1059 § 2 (Exh. A (12.90.160)), 2010; Ord. 1060 §§ 5, 6, 2010; Ord. 1192 § 1 (Exh. A), 2022)

§ 18.90.170 Geologically sensitive areas.

Except as provided in RMC § 18.90.180(A) and 18.90.190(E) and (F), all single-family and duplex residential development within 100 feet of a designated geologically sensitive area and all commercial, industrial, or multifamily developments within 200 feet of a designated geologically sensitive area shall be considered adjacent to the area and shall be required to submit a critical area report.

The report shall be prepared by a qualified professional, as defined in Chapter 18.20 RMC, and shall meet requirements of this section and RMC § 18.90.180 and 18.90.190, as applicable. All critical area reports for geologically sensitive areas shall contain the following:

The name and contact information of the applicant, a description of the proposal, and identification of the permit requested; and

The dates, names, and qualifications of the persons preparing the report and documentation of any fieldwork performed on the site.

The report and its review by the city, which may include referral to independent qualified professionals, shall be at the applicant's expense. The planning official shall approve the report only if it demonstrates that the proposed development will not increase the risk of harm to public safety, neighboring properties or critical areas.

(Ord. 1059 § 2 (Exh. A (12.90.170)), 2010; Ord. 1060 §§ 5, 6, 2010; Ord. 1192 § 1 (Exh. A), 2022)

§ 18.90.180 Mine hazard areas.

A critical area report is not required for the following activities within or adjacent to mine hazard areas:

Construction of new nonresidential structures with less than 800 square feet of building footprint which are not used as places of employment or public assembly;

Single-family residential on infill lots in single-family residential zones; and

Installation of fences in accordance with city standards.

For all other development activities, a critical area report for a mine hazard area may be required, and shall include the following requirements:

A site plan, which shall delineate the following found within 200 feet of or directly underlying the project area, or that have potential to be affected by the proposal:

The proposed development, including the location of existing and proposed structures, fill, storage of materials, and drainage facilities, with dimensions indicating distances to critical areas and adjacent development;

The topography, in two-foot contours, of the project area and all geologically sensitive areas addressed in the report;

The location of any features of current or historic mines that may impact or be affected by the proposed activities;

The location of any known sinkholes, significant surface depressions, trough subsidence features, coal mine spoil piles, slag piles, or tipple piles, and other mine-related surface features; and

The location of any prior site improvements that have been carried out to mitigate abandoned coal mine features.

A hazards analysis, which shall include a discussion of the potential for subsidence on the site in response to an earthquake or other geologic event, and which shall classify all mine hazard areas within 200 feet of the project area, or that have potential to be affected by the proposal, as either low, moderate, or severe.

Alterations with a significant likelihood of affecting only mine hazard areas with a low potential for subsidence are permitted, subject to compliance with all other applicable requirements.

Alterations with a significant likelihood of affecting coal mine byproduct stockpiles or mine hazard areas with a moderate potential for subsidence are permitted, subject to a mitigation plan developed by a qualified professional to minimize risk of structural damage.

Alterations with a significant likelihood of affecting mine hazard areas with a severe potential for subsidence are not permitted except as authorized under subsection (A) of this section.

Access roads and utilities may be permitted within 200 feet of a mine hazard area with a moderate or severe potential for subsidence if the city determines that no other feasible alternative exists.

Land that is located within 200 feet of a mine hazard area with a severe potential for subsidence may not be subdivided. Land that is located partially within such an area may be subdivided; provided, that each resulting lot has sufficient buildable area at least 200 feet away from the severe hazard.

All reclamation activities, including grading, filling, and stockpile removal, must have as-built drawings submitted to the city in a format specified by the planning official.

(Ord. 1059 § 2 (Exh. A (12.90.180)), 2010; Ord. 1060 §§ 5, 6, 2010)

§ 18.90.190 Steep and unstable slopes.

To determine if a critical area report is required for development on or adjacent to slopes between 15 and 39 percent, the planning official may require the applicant to provide a letter prepared by a certified geologist or engineer to determine whether springs, groundwater seepage or other causes of potential instability are present on or affecting the subject slope.

New structures and additions to existing structures within or adjacent to a geologically sensitive area shall be set back a minimum of 25 feet from the top or toe of a steep or unstable slope unless a larger setback is recommended in a critical area report. In no case shall the setback be less than 25 feet from a steep or unstable slope unless allowed through the reasonable use provisions and supported by a critical area report approved by the planning official. Decks that add no substantial loading weight to the sensitive area and accessory buildings 120 square feet or less may extend into the setback area to within 10 feet of the top or toe of a steep or unstable slope.

After completion of the project, the top and toe of the steep or unstable slope shall be identified with signs as a critical area or native growth protection area, in accordance with RMC § 18.90.140(B).

All clearing and grading shall follow at a minimum the current best management practices as contained in the Washington Department of Ecology's most current Stormwater Management Manual for Eastern Washington. If best management practices are not implemented, construction shall be stopped immediately until proper erosion control devices are implemented and established. Best management practices include, but are not limited to:

Water flows shall be directed away from steep or unstable slopes. At no time shall water be allowed to flow freely over steep or unstable slopes.

Exposed soils shall be protected from the forces of rain and flowing water within one day during the winter season and three days during the summer season.

Erosion control devices shall include as appropriate silt fences, straw mats, hay bales, filter fabrics, plastic sheeting, mulch, retention of vegetative buffers, or soil stabilization plant materials.

Development shall be phased to limit the area of exposed soils to no more than one acre at a time.

Vegetation removal or planting on steep slopes shall be conducted by hand or by nonimpacting procedures as approved by the planning official.

For the following single-family and multifamily residential development applications, the planning official may waive the requirements for a critical area report, if the development is unlikely to have any impact on a steep or unstable slope:

Additions to a single-family residence with a building footprint less than 200 square feet, located so that the existing structure is between the addition and a steep or unstable slope.

Detached auxiliary buildings such as garages and sheds that are 50 feet or more away from a steep or unstable slope.

Decks attached to single-family and multifamily structures where no additional load bearing weight is added to an adjacent steep or unstable slope.

For the following development activities, a letter as described in this subsection, prepared by a qualified professional, may fulfill requirements for a critical area report:

Additions to single-family homes less than 30 percent of the building footprint.

Additions to a building's height where the footprint of the existing structure is not changed.

Detached accessory buildings such as garages and sheds with no living spaces.

The letter shall include an assessment of the existing geologic and geotechnical site conditions, including surface water runoff, groundwater, soil types, erosion, and slope stability. The qualified professional shall prepare conclusions and recommendations on the suitability of the proposed development and any mitigation necessary to address existing site conditions that may need to be modified due to the proposed development.

All other development within or adjacent to a steep or unstable slope shall submit a critical area report that shall include a site assessment, geotechnical analysis, stormwater plan, grading and erosion control plan and landscape/revegetation plan, as described below:

Site Assessment. Along with standard site plan requirements, the following information shall be provided for the subject property, prepared by a licensed land surveyor:

Topography map at two-foot contour intervals for the entire site, including abutting public rights-of-way, private roads, or access easements;

Location of all significant trees;

Location of all manmade drainage structures or features including pipes, drains, catch basins, drainage structures, culverts, and under drain pipes;

Location of all frequently flooded areas, as defined in this title, and all wetlands, fish and wildlife habitat conservation areas, geologically sensitive areas, and other critical areas, as defined in this chapter, within 300 feet of the project area;

Location of all existing site improvements and the amount of existing impervious surface area;

Location of any existing cuts and fills; and

Location of all utilities, both above and below ground.

The site plan shall also include a vicinity map, showing the location of the property in relationship to surrounding lots and other critical areas.

Geotechnical Analysis. The analysis shall include 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 shall be prepared in accordance with accepted classification systems in use in the region. The assessment shall include, but not be limited to:

Data regarding underlying geology, slope gradients, soil types, and subsurface information, including boring and/or test pit logs describing soil stratification and results of soil tests conducted;

Identification of any previous landslide activity in the vicinity of the project, and an assessment of the overall stability of slopes that could be affected by the development and the effect the development may have on these slopes over time;

Recommendations for grading procedures, fill placement, and compaction criteria, temporary and permanent slope inclinations and support, and design criteria for corrective measures and opinions and recommendations regarding the capabilities of the site;

Evaluation of the seismic stability of the site in drained and saturated conditions, including a statement that the design criteria of proposed structures consider a seismic event with a 10 percent probability of being exceeded in 50 years;

Potential for liquefaction and proposed mitigation measures;

A description of the hydrology (both surface and subsurface) of the site, including locations of any wetlands, streams, springs, seeps, and groundwater along with recommendations consistent with the city's critical area regulations for addressing any impacts;

A recommendation on building site location, foundation type and depths, minimum building setbacks, minimum deck and accessory building setbacks, and if necessary the minimum no-disturbance setback from any steep or unstable slope. The analysis shall also include recommendations on the design of temporary and permanent retaining structures if any are proposed;

An estimate of bluff retreat rate that recognizes and reflects potential catastrophic events such as seismic activity or a 100-year storm event; and

Recommendations and requirements for handling contaminated soils and materials if encountered on the site.

Stormwater plan, which shall demonstrate compliance with the substantive requirements of Chapters 13.15 and 18.110 RMC for any development creating more than 1,000 square feet of impervious surface. For development activities that create less than 1,000 square feet of impervious surfaces, stormwater runoff shall be designed for natural infiltration or dispersion. At no time shall concentrated stormwater runoff be allowed to flow directly over a steep or unstable slope, or impact a neighboring property, city street, alley, or public right-of-way.

Grading and erosion control plan, which shall include:

A schedule showing estimated starting and completion dates for each stage of the project, limiting the time that soil is exposed and unprotected to the shortest possible period.

Measures to be taken for slope stabilization and erosion control, using best management practices as contained in the Washington Department of Ecology's 2004 Stormwater Management Manual for Eastern Washington (Publication No. 04-10-076), or future updated publications or other methodology as approved by the planning official.

Landscape/revegetation plan, which shall include:

Measures to be taken to protect and replace natural vegetative cover;

A statement that vegetation trimming debris shall be removed from slopes in such a fashion as to not disturb existing vegetation; and

A schedule showing when each stage of the project will be revegetated, with estimated starting and completion dates.

(Ord. 1059 § 2 (Exh. A (12.90.190)), 2010; Ord. 1060 §§ 5, 6, 2010; Ord. 1192 § 1 (Exh. A), 2022)

§ 18.90.200 Repair of slope instabilities.

Repair of slope instabilities and slope failures on an emergency basis shall be allowed by the planning official as needed to correct an immediate danger to the public health, welfare and safety. The planning official shall use the guidance of this article when evaluating the necessary repairs and add mitigation measures as appropriate to ensure that the intent of this article has been met.

(Ord. 1059 § 2 (Exh. A (12.90.200)), 2010; Ord. 1060 §§ 5, 6, 2010)