Ch. 3 Sec. B Part 4 Regulations That Apply in Sensitive Habitats and Hazardous Areas

SECTION B: REGULATIONS THAT APPLY IN ALL OR SEVERAL ZONES

PART 4: REGULATIONS THAT APPLY IN SENSITIVE HABITATS AND HAZARDOUS AREAS

313-121 Geologic Hazards Regulations

The purpose of these regulations is: (Former Section CZ#A314-16(A))

121.1.1To ensure that risks to life and property in high and potentially high geologic hazard areas shall be minimized, and further, (Former Section CZ#A314-16(A))

121.1.2To assure the geologic stability and structural integrity of development, and (Former Section CZ#A314-16(A))

121.1.3To ensure that development neither creates nor contributes significantly to erosion, geologic instability or destruction of development sites or surrounding areas, or in any way requires the construction of protective devices that would substantially alter natural landforms along bluffs and cliffs. (Former Section CZ#A314-16(A))

The Geologic Hazards Regulations shall apply throughout Humboldt County. (Former Section CZ#A314-16(B))

The provisions of the Geologic Hazards Regulations shall be in addition to requirements imposed by all other Zoning Regulations. Whenever the provisions of these regulations conflict with or are inconsistent in application with any other regulations, including any conflict with the County Grading Ordinance (see, Chapter 70 of the currently applicable Uniform Building Code), the most restrictive regulations shall apply. (Former Section CZ#A314-16(C))

New development shall be reviewed, approved and sited in accordance with the Geologic Hazards Land Use Matrix of this section. (Former Section CZ#A314-16(D))

Engineering geologic and/or soil engineering reports shall be required according to the following schedule: (Former Section CZ#A314-16(E))

121.5.1.1A preliminary engineering geologic report and a preliminary soil engineering report shall be prepared for the classes of development and hazard areas indicated by an “R1” in the Geologic Hazards Land Use Matrix. (Former Section CZ#A314-16(E)(1)(a))

121.5.1.2The preliminary engineering geologic report shall be prepared by a certified engineering geologist. The preliminary soil engineering report shall be prepared by a civil engineer experienced and knowledgeable in the practice of soil engineering or by a certified engineering geologist. (Former Section CZ#A314-16(E)(1)(b))

121.5.2.1A preliminary engineering geologic report and a preliminary soil engineering report shall be prepared for the classes of development and hazard areas indicated by an “R2” in the Geologic Hazards Land Use Matrix. (Former Section CZ#A314-16(E)(2)(a))

121.5.2.2The reports required under this subsection shall be prepared by either a registered geologist or a registered civil engineer experienced and knowledgeable in the practice of soil engineering. (Former Section CZ#A314-16(E)(2)(b))

121.5.2.3It is incumbent upon the project engineer to consult a registered geologist should it become apparent that an adequate subdivision design or structural solution requires additional geologic input. If, after preliminary investigation of the project site and the surrounding terrain, no geological consultation is felt by the engineer to be required, the engineer shall provide a written statement that such an evaluation is not required. It is incumbent upon the project geologist to recommend that a soils engineer be consulted when it becomes apparent that soils mechanics analyses are needed. (Former Section CZ#A314-16(E)(2)(c))

121.5.3 Discretionary Report Requirements. The Chief Building Official shall determine if a preliminary geologic report or a preliminary soil engineering report is required for the classes of development and hazard areas indicated by a “D” (discretionary) in the Geologic Hazards Land Use Matrix. The criteria for determining whether or not a report is required when it is designated in the Geologic Hazards Land Use Matrix as discretionary include the following; however, where evaluation of items listed below is inconclusive, a statement is required by a registered engineer that a geologic or soil report is not required for the safety of the project. (Former Section CZ#A314-16(E)(3))

121.5.3.1Criteria for either type of report shall include: (Former Section CZ#A314-16(E)(3)(a))

121.5.3.1.1results of a site inspection by the building inspector; (Former Section CZ#A314-16(E)(3)(a)(i))

121.5.3.1.2geologic maps and reports covering the area; (Former Section CZ#A314-16(E)(3)(a)(ii))

121.5.3.1.3the potential for the development to affect adjacent property or improvements; (Former Section CZ#A314-16(E)(3)(a)(iii))

121.5.3.1.4the degree to which public exposure to risk may be a factor; (Former Section CZ#A314-16(E)(3)(a)(iv))

121.5.3.1.5the size and scale of the proposed development; or (Former Section CZ#A314-16(E)(3)(a)(v))

121.5.3.2A soil engineering report is indicated when one or more of the following conditions exist or are proposed: (Former Section CZ#A314-16(E)(3)(b))

121.5.3.2.1the depth (or height) of cut or fill is three feet (3') or greater; (Former Section CZ#A314-16(E)(3)(b)(i))

121.5.3.2.2the fill is to support structural footings; (Former Section CZ#A314-16(E)(3)(b)(ii))

121.5.3.2.3an engineered cut or fill is required; (Former Section CZ#A314-16(E)(3)(b)(iii))

121.5.3.2.4the soils are or may be subject to significant shrink-swell; or (Former Section CZ#A314-16(E)(3)(b)(iv))

121.5.3.2.5areas where material exists that may be subject to settlement or subsidence. (Former Section CZ#A314-16(E)(3)(b)(v))

121.5.3.3An engineering geologic report is indicated when one or more of the following conditions exist or are proposed: (Former Section CZ#A314-16(E)(3)(c)(i-ix))

121.5.3.3.1finish cut or fill slope faces with vertical heights in excess of ten feet (10');

121.5.3.3.2existing slope steeper than five (5) horizontal to one (1) vertical;

121.5.3.3.3an existing cut slope having a vertical height in excess of ten feet (10');

121.5.3.3.4existing sea cliffs, stream bank cliffs, etc. in excess of ten feet (10');

121.5.3.3.5existing or suspected earthquake or seismic hazards;

121.5.3.3.6existing or suspected groundwater hazards;

121.5.3.3.7areas that are underlain by landslides or soil creep or by rock material susceptible to landslide or creep activity;

121.5.3.3.8areas where materials exist that may be subject to settlement or subsidence; or

121.5.3.3.9areas subject to drifting or loose sand.

121.5.4 Report Waiver. The report requirements of subsections 121.5.1. and 121.5.2. may be waived or the contents modified by the Director when: (Former Section CZ#A314-16(E)(4))

121.5.4.1An adequate geologic and/or soil assessment at a suitable scale already exists for the site proposed for development; or (Former Section CZ#A314-16(E)(4)(a))

121.5.4.2Reports are not indicated as necessary under the criteria listed in subsection 121.5.3.1; and (Former Section CZ#A314-16(E)(4)(b))

121.5.4.3The proposed development is not within a Critical Water Supply Area as designated in the General Plan. (Former Section CZ#A314-16(E)(4)(c))

121.5.4.4Report requirements may not be waived within the Coastal Zone, except that for Coastal Zone portions of Shelter Cove only, the requirements may be waived if the proposed development is within a waiver area as specified in Appendix E of the Southcoast Area Plan, and the Chief Building Official concurs. (Former Section CZ#A314-16(E)(4)(d))

121.5.5The required soil report may serve to meet the soil report requirement under County Code Section 326-24 where, in the opinion of the Chief Building Inspector, it contains substantially the same information and addresses the concerns that may have been identified by the Department’s field inspection. (Former Section CZ#A314-16(E)(5))

121.5.6When a report is required pursuant to the Alquist-Priolo Fault Hazard Regulations of this ordinance, it should be combined with the reports required under this part where feasible. (Former Section CZ#A314-16(E)(6))

121.6.1 Engineering Geologic Report. The above required engineering geologic reports, designated “R1” and “R2,” shall provide a preliminary 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 proposed project. Reports shall be prepared in accordance with the California Division of Mines and Geology (CDMG) Note #44, “Recommended Guidelines for Preparing Engineering Geologic Reports.” CDMG Notes #37, 43 and 49 shall be utilized as applicable when seismic or fault rupture hazards are identified as concerns.

In citing the CDMG Notes, it is not the intent of the County to seek lengthy dissertations on the area geology, but rather to provide uniform outlines to serve as checklists with points to be discussed as applicable. (Former Section CZ#A314-16(F)(1))

121.6.2 Preliminary Soil Engineering Report. The above required preliminary soil engineering report shall describe the nature of the subsurface soils and any soil conditions which would affect the design and/or layout of the proposed development. The report shall include the locations and logs of any test borings and percolation test results if on-site sewage disposal is proposed. The report shall recommend areas or issues of concern which require additional engineering or geologic evaluation. These reports shall be prepared in accordance with the Uniform Building Code, Appendix, Chapter 70, Excavation and Grading, and/or Chapter 29, Excavations, Foundations and Retaining Walls, as applicable. (Former Section CZ#A314-16(F)(2))

121.6.3Within the Coastal Zone, Supplementary Information for Reports for Development Located in the Coastal Zone. Within the Coastal Zone, the reports should give particular treatment and analyze the following, as applicable: (Former Section CZ#A314-16(F)(3))

121.6.3.1Historic, current and foreseeable cliff erosion, including investigation of recorded land surveys in addition to the use of historic maps and photographs where available, and possible changes in shore configuration and sand transport; (Former Section CZ#A314-16(F)(3)(a))

121.6.3.2Ground and surface water conditions and variations, including hydrologic changes caused by the development (i.e., introduction of sewage effluent and irrigation water to the ground water system, alterations in surface drainage, etc.); (Former Section CZ#A314-16(F)(3)(b))

121.6.3.3Potential erodability of site and mitigation measures to be used to ensure minimized erosion problems during and after construction (i.e., landscaping and drainage design); (Former Section CZ#A314-16(F)(3)(c))

121.6.3.4Effects of marine erosion of seacliffs; (Former Section CZ#A314-16(F)(3)(d))

121.6.3.5Detailed mitigation measures or alternative solutions for avoiding potential impacts; (Former Section CZ#A314-16(F)(3)(e))

121.6.3.6Professional conclusions as to whether the project can be designed so that it will neither be subject to nor contribute to significant geologic instability throughout the life span of the project; and (Former Section CZ#A314-16(F)(3)(f))

121.6.3.7Currently acceptable engineering stability analysis method should be used. The method(s) of field analysis should be described, and the degree of uncertainty of analytical results due to assumptions and unknowns should be described. (Former Section CZ#A314-16(F)(3)(g))

Table: Geologic Hazards Land Use Matrix
BUILDING TYPE/LAND USE		EARTHQUAKE SHAKING			SLOPE STABILITY** 0 1 2 3		LIQUEFACTION MOD. HIGH
Hazardous	Nuclear power plants, major dams, hazardous chemical storage	R1
Essential	Hospitals, fire and police stations, civil defense headquarters, life line utility systems, ambulance stations
High Risk	Schools, theaters, auditoriums, hotels, large motels, major office buildings, high density residential, redundant utility systems, major highway bridges
Low Risk	Final map subdivisions, heavy industrial	D	R2	R2	R1	R1	D	R2
	Multi-family structures greater than 4-plexes	D	D	D	R2	R1	D	R2
	Parcel map subdivisions	D	D	D	R2	R2	D	D
	Light industrial, warehousing, commercial	D	D	D	D/A	R2	D	D
	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	D	D	R2	R2	D	D
	Residential wood frame structures two stories or less on existing lots	D	D	D	D/A	D/R2*	D	D

“R” Means preliminary report is required.

“D” Means preliminary report is discretionary.

“A” Within a Coastal Zone Area of Demonstration, an R2 report is report is required, and is not discretionary.

*Within the Coastal Zone an R2 report is required and is not discretionary; except as provided in subsection 313-121.5.4: Report Waiver.

**As designated on the Geological Map of the Humboldt County General Plan.

121.7.1The applicant shall either provide additional information as recommended by the preliminary geologic and/or soils report, or modify the proposed development to avoid identified areas of potential instability. The proposed development shall be sited, designed and constructed in accordance 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. (Former Section CZ#A314-16(G)(1))

121.7.2Projects shall be constructed in accordance with the currently applicable Uniform Building Code, Section 2312, Earthquake Regulations, or any successor provision, as applicable. As referred to in the Uniform Building Code (UBC), Section 2312, the seismic zone boundaries shall be defined as follows: UBC Seismic Zone 4 applies south and west of the Grogan Fault; and Zone 3 applies north and east of the Grogan Fault. (Former Section CZ#A314-16(G)(2))

121.7.3Within the Coastal Zone, the following shall also apply: (Former Section CZ#A314-16(G)(3))

121.7.3.1Developments shall be sited and designed to assure stability and structural integrity for their expected economic life spans while minimizing alteration of natural landforms; (Former Section CZ#A314-16(G)(3)(a))

121.7.3.2Bluff and cliff developments (including related storm runoff, irrigation, wastewater disposal and other activities and facilities accompanying such development) shall not create or contribute significantly to problems of erosion or geologic instability on the site or on surrounding geologically hazardous areas; (Former Section CZ#A314-16(G)(3)(b))

121.7.3.3Alteration of cliffs and bluff tops, faces, or bases by excavation or other means shall be minimized. Cliff retaining walls shall be allowed only to stabilize slopes. (Former Section CZ#A314-16(G)(3)(c))