Chapter 9.62
Geologic Hazard Review
Sections:
9.62.020 Applicability - Geologic Hazards Land Use Matrix
9.62.040 Development Standards
9.62.050 Alquist-Priolo Earthquake Fault Zone
9.62.010 Purpose
This Chapter provides procedures for the filing, processing, and approval or disapproval of applications for Geologic Hazard Review, to protect the health, safety, and welfare of the residents of the City by minimizing the risk from carrying out development in areas subject to geologic and/or seismic hazards.
9.62.020 Applicability - Geologic Hazards Land Use Matrix
The Geologic Hazards Land Use Matrix in Table 6-1 shall apply throughout the City. Engineering geologic and/or soils engineering reports shall be required for new development in compliance with the schedule identified in the matrix.
A. ’R1’ report requirements. An engineering geologic report and a soils engineering report shall be prepared for the classes of development and hazard areas indicated by ’R1’ in the Geologic Hazards Land Use Matrix.
B. ’R2’ report requirements. An engineering geologic report shall be prepared for the classes of development and hazard areas indicated by an ’R2’ in the Geologic Hazards Land Use Matrix.
C. ’D’ discretionary report requirements. For the classes of development and hazard areas indicated by a ’D’ in the Geologic Hazards Land Use Matrix, the City Engineer and/or Building Official, after consultation with the Zoning Administrator, shall use the considerations listed below in Subsection C.1 (Criteria for requiring a report), to determine whether or not a report is required. Conditions which typically indicate that a report should be required are identified in Subsection C.2 (Soils Engineering Report) and C.3 (Engineering Geology Report), below.
|
Building Type/Land Use |
Earthquake Shaking Hazard |
Fault Rupture Hazard (1) |
Slope Stability Hazard (2) |
Liquefaction Potential (3) |
||||||
|---|---|---|---|---|---|---|---|---|---|---|
|
Low |
|
|
High |
Low |
|
High |
||||
|
SSZ |
PAF |
V |
IV |
III |
II & I |
III |
II |
I |
||
|
Critical Facilities |
||||||||||
|
Hazardous substance storage, reservoirs, natural gas storage tanks |
R1 |
R2 |
R2 |
D |
D |
R1 |
R1 |
R1 |
R1 |
P |
|
Hospitals, fire and police stations, emergency control centers, power plants, power and communications substations, schools, theaters |
||||||||||
|
Auditoriums, hotels, large motels, major office buildings, high density residential |
||||||||||
|
Non-Critical Facilities - Moderate Risk |
||||||||||
|
Residential structures on existing lots with footing loads greater than typical two-story wood frame dwellings, or residential structures with three stories or more |
D |
R2 |
D |
D |
D |
R2 |
R1 |
D |
R1 |
R1 |
|
Major subdivisions |
D |
R2 |
R2 |
D |
R2 |
R1 |
R1 |
D |
R1 |
R1 |
|
Heavy industrial |
R2 |
R2 |
R2 |
D |
R2 |
R2 |
R1 |
R1 |
R1 |
R1 |
|
Non-Critical Facilities - Low Risk |
||||||||||
|
Multi-family structures larger than 4-plexes |
D |
R2 |
D |
D |
D |
R2 |
R1 |
D |
R1 |
R1 |
|
Minor subdivisions |
D |
R2 |
D |
D |
D |
R2 |
R1 |
D |
R1 |
R1 |
|
Light industrial, warehousing, commercial |
D |
R2 |
D |
D |
D |
R2 |
R2 |
D |
R1 |
R1 |
|
Residential wood frame structures two stories or less on existing lots |
D |
D |
D |
D |
D |
R2 |
R2 |
D |
D |
D |
Notes:
P Development prohibited.
R1 Engineering geologic report and soils engineering report required. Engineering geologic report shall be prepared by a Certified Engineering Geologist, certified and licensed by the State of California. Soil engineering report shall be prepared by a California licensed Registered Civil Engineer with appropriate knowledge and experience, or by a California Certified Engineering Geologist with appropriate geotechnical knowledge and experience.
R2 Engineering geologic report required. The report shall be prepared by a California Registered Geologist with appropriate geotechnical knowledge and experience.
D Report requirement is left to the discretion of the City Building Official.
(1) SSZ refers to the Alquist-Priolo Special Study Zone; PAF means "Potentially Active Fault."
(2) See the Slope Stability Hazard Map on file with the Department.
(3) See the Liquefaction Potential Map on file with the Department.
In lieu of making a determination, the City Engineer and/or Building Official, after consultation with the Zoning Administrator, may choose to accept a statement as described in Subsection D. (Report wavier).
1. Criteria for requiring a report. Considerations in determining whether a report is required shall include:
a. A site visit;
b. A review of geologic maps and reports covering the area;
c. An evaluation of the potential of the development to adversely affect adjacent property or improvements;
d. Consideration of the degree of public exposure to the risk;
e. A consideration of the size and scale of the proposed development;
f. For development within the Coastal Zone, a consideration of certified Local Coastal Plan policies; or
g. The proposed project is not exempt from reporting requirements in compliance with Subsection E. (Projects exempt from reporting requirements), below.
2. Soils engineering report. A soils engineering report is indicated when one or more of the following conditions exist or are proposed:
a. Depth (or height) of cut or fill is three feet or greater;
b. Fill is used to support structural footings;
c. Engineered cut or fill is required;
d. Soils are or may be subject to significant shrink-swell; or
e. The project area is underlain by material that may be subject to settlement or subsidence.
3. Engineering geology report. An engineering geology report is indicated when one or more of the following conditions exist or are proposed:
a. Finish cut or fill faces with vertical heights in excess of 10 feet;
b. On-site natural slopes steeper than five horizontal to one vertical;
c. Existing cut slopes having a vertical height in excess of 10 feet;
d. Existing stream banks in excess of 10 feet;
e. Significant existing or suspected seismic hazards;
f. Areas that are underlain by landslides or soil creep or by rock material susceptible to landslide or soil creep activity;
g. Areas that are underlain by materials that may be subject to settlement or subsidence; or
h. Areas subject to drifting or loose sand.
D. Report waiver. The R1 and R2 report requirements listed in the notes to Table 6-1 above may be waived or the contents modified by the City Engineer and/or Building Official when:
1. An adequate geologic and/or soil assessment at a useable scale already exist for similar project measures on the site proposed for development.
2. Reports are not indicated under the criteria listed in Subsection C., above.
3. A geologist or engineer, according to the type of report required in compliance with Section 9.62.020.C above, submits a statement that a report is not necessary with supporting reasons and any appropriate recommendations.
E. Projects exempt from reporting requirements.
1. Alterations, additions, or repairs to an existing structure; provided, the aggregate value of the work does not exceed 50 percent of the replacement cost of the existing structure and does not adversely affect the structural integrity of the existing structure.
2. Values shall be determined as "Replacement in Kind" as defined in the California Building Code. No change shall be allowed in use, character, or occupancy, which results in the conversion of a structure from one not intended for human occupancy to one which is so intended, unless the structure complies with the provisions of the Alquist-Priolo Earthquake Fault Zoning Act.
9.62.030 Report Contents
A. Engineering geologic report.
1. The above required engineering geologic reports, ’R1’ and ’R2’ shall provide a geological reconnaissance and evaluation of the project site and surrounding terrain. The degree of analysis should be appropriate to the degree of potential risk presented by the site and the magnitude of the proposed project.
2. Reports shall be prepared in compliance with the California Geological Survey (CGS) Note #44, "Recommended Guidelines for Preparing Engineering Geology Reports." CGS Notes #37, #43 and #49 shall be utilized as applicable when seismic or fault rupture hazards are identified as concerns.
3. In citing the Notes, it is not the intent of the City to seek lengthy dissertations on the area geology, but rather to provide uniform guidelines to serve as checklists with points to be discussed as applicable.
B. Soils engineering report.
1. The above required soils engineering report shall describe the nature and/or layout of the proposed development. The report shall include the locations and logs of test borings and percolation test results, if on-site sewage disposal is proposed.
2. The report shall delineate areas or issues of concern which require additional engineering or geologic evaluation. These reports shall, as a minimum, be prepared in compliance with the California Building Code Appendix Chapter 33, as applicable.
C. Consultation. Should it become apparent that an adequate development or subdivision design and/or building structural solution requires additional geologic input, it is incumbent upon the project engineer to consult a registered geologist. It is incumbent upon the project geologist to recommend that a soils engineering report shall be prepared when it becomes apparent that soils mechanics analyses are needed.
D. Supplementary information for reports required for development in the Coastal Zone.
1. Historic, current, and foreseeable shoreline erosion, including investigation of recorded land surveys in addition to the use of historic maps and photographs, where available, and possible changes in shoreline configuration and sand transport;
2. Ground and surface water conditions and variations, including hydrologic changes caused by the development (e.g., introduction of sewage effluent and irrigation water to groundwater systems; alterations in surface drainage);
3. Potential erodibility of the site and mitigating measures to be used to ensure minimized erosion problems, both during and after construction (e.g., drainage and landscaping design);
4. Detailed mitigation measures or alternative solutions for avoiding potential impacts;
5. Professional conclusions as to whether the project can be designed so that it would neither be subject to nor contribute to significant geologic instability throughout the life span of the project; and
6. Any additional information required by the City’s certified LCP.
E. Qualifications of preparers. The engineering geologic report shall be prepared by a State licensed certified engineering geologist. The soils engineering report shall be prepared by a State licensed registered civil engineer having geotechnical knowledge and experience or by a State licensed certified engineering geologist having geotechnical knowledge and experience. (Ord. 1432, eff. 12/20/2013)
9.62.040 Development Standards
A. Avoid significant geologic hazards. The applicant shall either provide additional information as recommended by the geologic and/or soils report, or modify the proposed development to avoid identified areas of significant geologic hazard. The proposed project shall be sited, designed, and constructed in compliance with the recommendations of the report(s) in order to minimize risk to life and property on the project site and for any other affected properties.
B. California Building Code. Each project shall be constructed in compliance with California Building Code (CBC) Earthquake Regulations, as a minimum. As referred to in the CBC, the seismic zone boundaries shall be defined as follows: Seismic Zone 4 applies south and west of the Grogan Fault. The Grogan Fault is located approximately 15 miles northeast of Arcata. (Ord. 1432, eff. 12/20/2013)
9.62.050 Alquist-Priolo Earthquake Fault Zone
A. Purpose. The purpose of the Alquist-Priolo Earthquake Fault Zone regulations is to determine potential surface fault rupture hazards and minimize damage during an earthquake event. This Section addresses geologic reporting requirements, development limitations, exemptions and project review procedures to satisfy the State mandated Alquist-Priolo Earthquake Fault Zoning Act.
B. Maps. The maps developed by the State which show traces of active faults and establish Earthquake Fault Zones and the Policies and Criteria of the Alquist-Priolo Earthquake Fault Zoning Act are hereby declared to be a part of this Section. Maps prepared for the Seismic Safety Element of the General Plan are also declared to be a part of this Section.
C. Compliance. The construction of subdivisions, land divisions, or structures near a known active fault and regulated by this Development Code shall only be allowed as identified in this Section.
D. Scope.
1. The provisions of this Section shall apply at the time of filing an application for any subdivision of land subject to the Subdivision Map Act which contemplates the eventual construction of structures for human occupancy.
2. These provisions shall also apply to applications for Planned Development Permits, Use Permits, site development permits, or Building Permits for any development and structures intended for human occupancy. This Section is not intended to supplant the geologic investigations required by Chapter 33, California Building Code.
E. Geologist. For the purpose of this Section, a geologist shall be a registered geologist, licensed by the State Board of Registration for Geologists and Geophysicists to practice geology in California.
F. Known active faults. For the purpose of this Section, known active faults are faults which have been active during the Holocene Age (approximately the last 11,000 years).
G. Construction limitations. No structure to be used for human occupancy shall be constructed over or within 50 feet of the trace of a known active fault which is shown on maps maintained by the City.
H. Trace of a known active fault. The locations or non-existence of the trace of a known active fault shall be determined by the geologist preparing the geologic report for the site(s), when the proposed subdivision or building site is within a study zone as designated by the Alquist-Priolo Earthquake Fault Zoning Act or the Seismic Safety Element of the General Plan.
I. Subsurface exploration.
1. In cases when a geologist has not otherwise made an accurate evaluation as determined by City review, the City shall require the geologist to perform subsurface exploration for the purpose of determining the absence or presence of a known active fault.
2. The subsurface exploration shall be required if a lack of distinguishable fault features in the vicinity prevents the geologist from determining by a site examination, review of aerial photographs, or by other means, that the fault trace does or does not underlie or exist within 50 feet of the proposed structure. Subsurface exploration shall be to a sufficient depth to verify faulting within the Holocene Age (approximately the last 11,000 years).
3. The City may require a more extensive investigation by the geologist as evidence to the absence of a known active fault trace before the issuance of a permit for Group A, B, E, F, H, I, M, R, and S occupancies in the City’s most recently adopted California Building Code.
4. A State licensed geologist, within or retained by the City, shall evaluate the required geologic reports and advise the body having jurisdiction and authority.
J. Geologic/seismic report requirements. All reports submitted for projects within an active fault zone shall contain all the information identified on pages 22 - 24 in Fault Rupture Hazard Zones in California, Special Publications #42 (March 1980) issued by the California Division of Mines and Geology, or the most recent equivalent. Changes to these requirements can be made by the City’s geologist with the consent of the Zoning Administrator.
K. Exceptions. The provisions of this Section for geologic/seismic reporting requirements do not apply to:
1. Structures not intended for human occupancy. A structure for human occupancy is a structure as defined by the California Building Code, which is expected to have a human occupancy rate of more than 2,000 person hours per year.
2. A single-family wood-frame or steel-frame dwelling not exceeding two stories when the dwelling is not part of a development of four or more dwellings. A mobile home whose body width exceeds eight feet shall be considered to be a single-family wood-frame dwelling not exceeding two stories.
A "single-family dwelling" may include a "second dwelling unit" as defined by this Development Code, as well as attached or detached accessory structures associated with a single-family residence, unless State law provides specific language regulating the units with respect to earthquake fault zone requirements. The structures shall meet the other limitations of this Subparagraph.
Construction of dwellings shall not be allowed over a previously identified "Known Active Fault" Trace.
3. Alterations, additions, or repairs to an existing structure provided that aggregate value of the work does not exceed 50 percent of the replacement cost of the existing structure and does not adversely affect the structural integrity of the existing structure.
Values, as used in this Subparagraph, shall be determined as "Replacement in Kind" as defined in the California Building Code. No change shall be allowed in use or character or occupancy, which results in the conversion of a structure from one not intended for human occupancy to one which is so intended, unless the structure complies with the provisions of the Alquist-Priolo Earthquake Fault Zoning Act.
4. Alterations, additions, or repairs to exempt structures.
5. Decorative walls, fences, non-occupancy accessory uses, swimming pools, and minor work of a similar nature. New improvements of this type shall not be included in the valuation totals for Subsection K.3, above.
L. Waivers.
1. Section 2523 of the Alquist-Priolo Earthquake Fault Zoning Act states "... If the city or county [having jurisdiction over the lands] finds that no undue [fault] hazard ... exists, the geologic report on the hazard may be waived, with approval of the State Geologist." The location of the proposed development or structure may be approved following the waiver.
2. The State geologist may approve waiver requests only after receiving the State Waiver Form (Appendix D; Fault Rupture Hazard Zones in California, Special Publication #42, page 25) completed by the City geologist and the property owner, and accompanied by supporting statements and data in writing that would justify approval of the waiver request.
M. Design requirements.
1. Structures within an active fault zone and areas indicated by the Seismic Safety Element of the General Plan shall be designed to resist the earthquake forces prescribed by the California Building Code.
2. Construction activities shall also incorporate the recommendations identified in the geological and/or geologic/seismic hazards report pertaining to ground ruptures, landslides, liquefaction, or settlement due to seismic compaction, et cetera.
N. Maps of active faults. The City shall maintain and make available to the public, maps showing the location of known active faults. When geologic investigations, mapping, aerial photographs, or other acceptable data showing the presence, absence or more precise location of a known active fault are made available to the City, the reports shall be submitted to the State geologist.
O. Appeals. Any person aggrieved by the decision of any City official, agency, board, or commission rendered in compliance with the Alquist-Priolo Earthquake Fault Zoning Act, this Development Code, or the Seismic Safety Element of the General Plan may appeal the decision in compliance with Chapter 9.76 (Appeals).
P. Fees.
1. The City shall require the project applicant to pay all costs for the City to contract for the review of the earthquake fault zone report by a licensed geologist, mailing fees, duplication costs, and public notification expenses.
2. The City shall provide a written estimate to the project applicant for the cost of the review (based on information from the City’s retained geologist plus related expenses). The applicant shall pay the full estimate at the time of project submittal, with a refund of surplus funds to be made after the appeal period is completed.