Chapter 16.30
GEOLOGIC HAZARDS
Sections:
16.30.010 Applicability.
16.30.020 Geologic report requirements.
16.30.030 Contents and preparation of geologic reports.
16.30.040 Mapping.
16.30.050 Brief report of on-site investigation.
16.30.060 Geologic feasibility report.
16.30.070 Detailed engineering and geologic report.
16.30.080 Evaluation of geologic reports.
16.30.010 Applicability.
The Kelso-Longview area is mapped into five slope stability zones or classification areas on a system of most to least probable stability by “Slope Stability of the Longview-Kelso Urban Area” with map (Allen J. Fiksdal, geologist, Division of Geology and Earth Resources, Washington Department of Natural Resources, 1973). Geologic report requirements shall reflect the Fiksdal classifications of the area to be developed and the soil survey findings, as follows:
A. Class 1 areas (areas believed to be stable): No geologic report is required, except that:
1. If a development site has natural slopes greater than sixty percent or if cut slopes greater than sixty percent are proposed, an on-site visual geologic investigation shall be required with findings presented in a brief report conforming to Section 16.30.050;
2. Notwithstanding Class 1 designation by Fiksdal, a geologic feasibility report conforming to Section 16.30.060 shall be required for sites where soils have “moderate” or “severe limitations for urban development” as identified in the soil survey and Table II-1 of the comprehensive plan.
B. Class 2 areas (areas probably stable under normal conditions, may become unstable if modified by development activities): A geologic feasibility report conforming to Section 16.30.060 shall be required:
1. For sites having slopes greater than thirty percent;
2. For sites where substantial cuts or fills are planned; and
3. For sites where soils have “moderate” or “severe limitations for urban development” as identified in the soil survey and Table II-1 of the comprehensive plan.
C. Class 3 areas (areas of poor natural stability): A detailed engineering and geologic report conforming to Section 16.30.070 shall be required.
D. Class 4 areas (areas of ancient landslide debris): A detailed engineering and geologic report conforming to Section 16.30.070 shall be required.
E. Class 5 areas (areas of historical or recently active landslides): A detailed engineering and geologic report conforming to Section 16.30.070 shall be required. (Ord. 3699 § 1 (Att. A), 2009)
16.30.020 Geologic report requirements.
The purpose of these requirements is:
A. To protect the public health, safety and welfare in the development of land, particularly sloped sites;
B. To provide understanding of the degree of geologic hazard, if any, of locations proposed for development;
C. To assure that development will reflect geologic conditions;
D. To implement the findings and recommendations of the Fiksdal report;
E. To implement the findings contained in the soil survey and the goals, objectives, and policies developed therefrom in the city municipal code. (Ord. 3699 § 1 (Att. A), 2009)
16.30.030 Contents and preparation of geologic reports.
Contents of geologic reports shall be as specified in Sections 16.30.050, 16.30.060 and 16.30.070. Preparation of brief reports of on-site investigation may be by a professional engineering geologist, soils scientist or civil engineer. Preparation of geologic feasibility reports and of detailed engineering and geologic reports shall be by a professional engineering geologist. (Ord. 3699 § 1 (Att. A), 2009)
16.30.040 Mapping.
A. The map accompanying the Fiksdal report shall be the controlling document in determining a proposed subdivision’s location by slope stability classification area; however, environmental overlay maps of the Cowlitz Wahkiakum Governmental Conference, showing the Fiksdal classifications to scale, may be used instead of the Fiksdal map. Determination of location by classification area shall be made by the city engineer and shall be conclusive.
B. Soil maps contained in the soil survey shall be controlling in determining limitations for urban development by soil type. Determination of location by soil type shall be made by the city engineer and shall be conclusive. (Ord. 3699 § 1 (Att. A), 2009)
16.30.050 Brief report of on-site investigation.
This section applies to those portions of Class I areas mapped by Fiksdal specified in Section 16.30.010A1. Contents of the brief report of on-site investigation shall be as follows:
A. Signature of professional geologist, soils scientist or civil engineer responsible for the investigation;
B. Index map showing the sites studied and the regional setting;
C. A statement of conclusions regarding the geologic suitability of the site(s) for the subdivision design and construction being proposed;
D. Recommendations for changes to subdivision design or other mitigating measures, if warranted;
E. Recommendations for further study, if warranted;
F. If the structural relationships are complex and difficult to describe, a geologic sketch map of the site and/or geologic structure section. (Ord. 3699 § 1 (Att. A), 2009)
16.30.060 Geologic feasibility report.
This section applies to those Class 1 and Class 2 areas mapped by Fiksdal as specified in Sections 16.30.010A2 and B. Contents of the geologic feasibility report shall be as follows:
A. Signature of the professional engineering geologist responsible for the report;
B. An index map showing the sites studied and regional setting of the study area;
C. A statement regarding methods of study and approximate time in the field. Methods of study may include but are not limited to field traverses and inspection, test pits or trenches, drill holes, aerial photo analyses, laboratory tests, and research of previously published or unpublished work;
D. Soils test information, including soil loading, soil shear and Atterberg limits;
E. A statement of conclusions regarding the interrelated effects of the proposed subdivision design and construction upon identified or potential geologic hazards;
F. Recommendations for changes in subdivision design or other mitigating measures, if warranted, including nondevelopment of hazard areas;
G. Recommendations for further study, if warranted;
H. If the structural relationships are complex and difficult to describe, a geologic sketch map of the site and/or geological structure section. (Ord. 3699 § 1 (Att. A), 2009)
16.30.070 Detailed engineering and geologic report.
This section applies to Class 3, 4 and 5 areas mapped by Fiksdal as specified in Sections 16.30.010C, D and E. Contents of the detailed engineering and geologic report shall be as follows:
A. Signature of the professional engineering geologist responsible for the report;
B. An index map showing the regional setting of the study area;
C. A statement regarding methods of study and approximate time spent in the field. Methods of study may include but are not limited to field traverses and inspection, test pits or trenches, drill holes, aerial photo analysis, laboratory tests and research of previously published or unpublished work;
D. Brief description of natural materials and subsurface and surficial features recognized or inferred within the subject area. The description should emphasize features of special significance, such as features indicating subsidence or settlement, creep, slump and slide masses in bedrock or surficial deposits, active faults and their recent effects and accelerated erosion;
E. An original geologic map of the site and as much of the surrounding area as practicable. The base map should be the same as that used for the preliminary plat, with contour intervals. Companion maps at a smaller scale may be prepared to emphasize special features or hazards. Test holes and other specific sources of subsurface information should be indicated on the map(s). The geologic map should reveal clearly areas to be avoided, if any, and areas of little apparent hazard;
F. One or more geologic structure sections to show actual or probable subsurface relations, clearly labeled as to which relations are conjectural;
G. Conclusions regarding the interrelated effects of the proposed subdivision design and construction upon identified or potential geologic hazards. The conclusions should state whether it is basically reasonable to develop the subject area and should address the lateral stability of earth materials, features in adjacent properties that could cause problems, and probable stability or problems of proposed cuts and fills;
H. Recommendations shall be given regarding the following factors, where appropriate:
1. Cuts. Repositioning of proposed cuts, reduction of cut slopes, development of compound cut slopes, buttressing, protection against erosion, handling of seepage, setbacks for structures above cuts.
2. Fills. Suitability of existing natural materials for fill, positioning of fill masses, provision for under drainage, buttressing, erosion protection.
3. Other. Areas to remain as open space, removal or buttressing of existing slide masses, position of structures with regard to faults or other features, need for further study. (Ord. 3699 § 1 (Att. A), 2009)
16.30.080 Evaluation of geologic reports.
The city engineer shall be responsible for evaluating submitted geologic reports for adequacy and conformance to Sections 16.30.050, 16.30.060 and 16.30.070. The engineer may consult with the Soil Conservation Service, Washington Department of Natural Resources or other qualified agencies or individuals with respect to the adequacy of the report. The engineer may require additional information to be submitted by the applicant. (Ord. 3699 § 1 (Att. A), 2009)