Spokane Municipal Code

Title 17E Environmental Standards

Chapter 17E.040 Spokane Geologically Hazardous Areas

Section 17E.040.090 Geohazard Evaluation and Mitigation Plan

1. Geohazard Evaluation, Preliminary Report.

The intent of the geohazard evaluation and preliminary report is to produce a site design that protects life, property, critical area functions and values through sensitivity to the limitations and hazards inherent in the site’s geologic setting. If the director determines that a development proposal contemplates activity or development regulated by this chapter, the applicant shall submit a geohazard evaluation or feasibility report that has been prepared by a qualified geotechnical engineer. The geohazard evaluation shall document the extent and nature of geohazard on the subject property through the use of graphics and text and shall provide mitigating measures and an assessment of geohazards associated with the proposal. A more detailed geohazard mitigation plan may be required at the time of building permit application or actual construction approvals.

1. 1. Work necessary for land use submittal, such as surveys, soil logs, percolation tests and other related activity shall be minimized to the greatest extent feasible. Examples include core samplings as opposed to mass soil removal. Disturbed areas shall be restored immediately.

1. 2. Vegetation, including trees, shrubs and forbs in the project area and all critical areas addressed in the report shall be documented and evaluated for relation to slope integrity, stability, erosion control. Vegetation management plans shall adhere to best management practices and should identify opportunities to retain or augment existing native vegetation for slope stability, erosion and sedimentation control.

2. The International Building Code chapter 16, Structural Design, chapter 18, Soils and Foundations, and Appendix J, Grading, as now or hereafter amended, shall be used when activities and uses are proposed within or partly within geologically hazardous areas.

3. Geohazard Mitigation Plans.

When the director determines that the significant adverse impact of a use or activity located in a geologically hazardous area cannot be mitigated through standards identified in SMC 17E.040.100, the project proponent shall prepare a geohazard mitigation plan to identify construction standards for the proposal. Geohazard mitigation plans shall conform to City of Spokane guidelines for stormwater management or any subsequent regulation adopted by the City of Spokane providing erosion and landslide protection. A geohazard mitigation plan, prepared by a qualified geotechnical engineer, shall be prepared for all development and activities subject to this chapter within a geologically hazardous area. An analysis of how the plan will affect the subject and adjacent properties, with discussions, recommendations and mitigation sequencing alternatives shall be included. The following must be included in the analysis:

1. 1. The present stability of the proposed development, stability of the proposed site during construction, stability after all development activity is completed and a discussion of the relative risks and slide potential relating to adjacent properties during each stage of development.

1. 2. Proposed location of buildings, roadways, and other improvements. Locations shall reflect careful consideration of geohazards and efforts to avoid or minimize impacts.

1. 3. Identify and quarantine trees and other vegetative cover to be retained to provide slope anchoring and stability. Indicate proposed removal of trees and other vegetative cover and potential replacement vegetation to provide anchoring and stability.

1. 4. 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 considerations and/or limitations.

1. 5. 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.

1. 6. Surface and subsurface drainage requirements and drainage material requirements.

1. 7. Other measures recommended to reduce the risk of slope instability.

1. 8. Any additional information believed to be relevant by the geotechnical engineer preparing the recommendations or requested by the director.

Date Passed: Monday, December 3, 2007

Effective Date: Sunday, January 6, 2008

ORD C34149 Section 8