§ 24.35.130. Geologic hazards—Minimum standards for special reports—Geologic assessment.

A geologic assessment, as outlined below, shall be required when the resource stewardship department's mapping, source documents, and/or field investigations indicate a proposed activity is located within or adjacent to an erosion, landslide, marine bluff, seismic, or mine hazard area.

A.

A geological assessment shall be submitted to the review authority for review and approval together with the appropriate permit application and associated fees.

B.

A geological assessment shall include a field investigation and may include review of available geologic hazard maps, historical air photo analysis, public records, and any other pertinent documentation, as required by the county.

C.

A geological assessment shall be prepared, signed, sealed, and dated by an appropriately licensed geotechnical professional, as defined in Chapter 24.03 TCC and as applicable to the specific geologic hazard identified on or near the project site.

D.

A geological assessment shall be submitted in the form of a geotechnical letter, geotechnical evaluation, or geotechnical report, as determined in this chapter.

E.

After reviewing the geological assessment submitted by the applicant, the approval authority may request additional information or studies specific to the conditions of the development proposal site.

F.

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 surrounding site conditions are unchanged. If any environmental surface or subsurface conditions associated with the site change during that five-year period, the applicant may be required to submit an amendment to the geological assessment.

G.

When a development has the potential to impact slope stability on, below, or above adjacent property, particularly where public health and safety are at risk, the geotechnical studies presented must comply with the guidelines defined as standard of practice under the Washington State Geology Licensing program, as presented in the Washington State Department of Licensing "Guidelines for Preparing Engineering Geology Report in Washington," as amended. Such reports must include an assessment of each of the following parameters:

1.

Slope gradient and existing slope stability conditions.

2.

Stratigraphy (affecting infiltration rates, transmissivity, and groundwater flow paths).

3.

Precipitation patterns (regional, seasonal and storm-related).

4.

Land cover (vegetation type and density as it affects water available for infiltration — evapotranspiration and interception loss).

5.

Previous and proposed land use (affecting percent infiltration versus run-off).

6.

Specifically, a geologic assessment shall include analysis that addresses the following questions:

a.

How will the project affect the stability of the slope?

b.

What are the expected effects on groundwater levels during different seasons from development?

c.

What specific mitigation actions will be used to minimize or avoid effects of the development?

d.

What is the geologic/hydrologic basis for any proposed structural stabilization?

e.

Do alternatives exist that would better protect the functions and values of the critical area?

H.

All geological assessments submitted under this chapter shall include the following information:

1.

The dates when the geological assessment was conducted and when the assessment letter was prepared.

2.

The parcel number(s) of the subject property.

3.

Site address of the subject property.

4.

The name, mailing address, and telephone number of the geotechnical professional who prepared the letter.

5.

The name, mailing address, and telephone number of the property owner.

6.

A description of the proposed project and the area to be developed.

7.

A map showing the property lines for the site, existing two-foot contours of the existing topography, and the location of any existing structures, utilities, wells, stormwater or septic systems, or other development.

8.

A site plan delineating the boundaries of the proposed development site and the location of all areas of the site subject to the potential geologic hazard, and if applicable, limits of associated buffers.

9.

If a site plan is required pursuant to this title, the site plan shall be prepared at a scale of one inch equals fifty feet (or other scale deemed appropriate by the department). The department may require that the site plan information listed below be based on a field survey by a licensed surveyor. The site plan shall include:

a.

The limits/location of the geologic hazard area(s), including adjacent lots if necessary.

b.

The location of any existing structures, utilities, on-site septic systems, wells, and stormwater management facilities.

c.

The location of any proposed structures, utilities, on-site septic systems, wells, and stormwater management facilities.

d.

The full geographical limits of the proposed project area (area to be developed).

e.

Dimension of the closest distance between the identified geologic hazard area boundary (and associated buffers, if applicable) and the proposed project area.

f.

Existing contours on the site at two-foot intervals.

g.

Property lines for the site.

h.

North arrow and scale.

10.

Detailed discussion of the technical information, best available science and site-specific data on which the determination of hazard was based, including background assumptions. References to any sources of best available science used shall be included.

11.

A paragraph that states the following:

a.

A statement that the assessment was prepared under the responsible charge of (individual's name) and that the individual meets the qualifications defined for a geotechnical professional in Chapter 24.03 TCC to prepare a geological assessment for the specific type of geologic hazard.

b.

A statement that a(n) (erosion, landslide, marine bluff, mine, or seismic) hazard geological assessment, including a field investigation, and research of available historic records, has been completed by the geotechnical professional on the subject site.

c.

A statement that the scope of services completed for this project is adequate to meet the requirements of this title.

d.

For geotechnical letters: A statement that it does not appear that a hazard area exists within the following areas adjacent to a development proposal.

i.

Within two hundred feet for erosion hazards areas;

ii.

Within three hundred feet for landslide, marine bluff, or mine hazard areas;

iii.

Within the development proposal site for seismic hazard areas.

e.

For geotechnical evaluations: A statement that it does not appear that a(n) (erosion, landslide, marine bluff, mine, or seismic) hazard area exists within 200 feet for erosion hazards areas; three hundred feet for landslide, marine bluff, or mine hazard areas; within the proposed project area for seismic hazard areas of the proposed project area.

12.

All geological assessments proposing infiltration or dispersion of stormwater that are submitted under this chapter in relation to landslide and marine bluff hazards shall include the following additional information regarding the applicant's proposed solutions for handling stormwater:

a.

An estimate of the amount and percentage increase of added stormwater that will be infiltrated as a result of the proposed development, both during peak storm events and month-by-month over an average one-year period.

b.

Detailed discussion of the science, site-specific data on which the estimate of infiltrated stormwater was based, including background assumptions regarding groundwater incorporated into analysis.

c.

A professional estimate of where the added water is expected to flow under the ground, and where and in what volumes it will daylight on the slope or bluff during peak storm events.

d.

Detailed discussion of the science and site-specific data on which the hypothesized stormwater flows were based, including background assumptions incorporated into the analysis.

e.

An analysis of whether the added stormwater daylighting the slope during peak storm events will increase the frequency, duration and severity of landslide events on the slope.

f.

Detailed discussion of the science and site-specific data on which the estimate of the landslide risk was made, including background assumptions incorporated into the analysis.

g.

A discussion of the alternative approaches to handling stormwater which were considered in the development process and discussion of why the proposed approach was chosen.

h.

A discussion of the long-term impacts of stormwater and other sources of added water due to development (e.g. on-site sewage treatment systems and underground springs altered by development).

(Ord. No. 14773, § 3(Att. B), 7-24-2012)