Chapter 14A.146GEOLOGICALLY HAZARDOUS AREAS

Sections:

14A.146.010
Purpose.
14A.146.020
Designation of Erosion and Landslide Hazard Areas.
14A.146.030
Protection Standards for Erosion and Landslide Hazard Areas.
14A.146.040
Designation of Seismic Hazard Areas.
14A.146.050
Protection Standards in Seismic Hazard Areas.
14A.146.010Purpose.

The intent behind the classification and designation of geologically hazardous areas is to classify and designate areas on which development should be prohibited, restricted, or otherwise controlled because of danger from geological hazards. For purposes of this Title, geologically hazardous areas include the following: erosion and landslide hazard areas and seismic hazard areas. (Ord. 362 § 3 (part), 2004.)

14A.146.020Designation of Erosion and Landslide Hazard Areas.

A. General. Erosion hazard areas are those areas that because of natural characteristics, including vegetative cover, soil texture, slope, gradient, and rainfall patterns, or human-induced changes to such characteristics, are vulnerable to erosion. Landslide hazard areas are areas potentially subject to risk of mass movement due to a combination of geologic, topographic, and hydrologic factors.

B. Classification.

1. Criteria.

a. Erosion hazard areas are identified by the presence of vegetative cover, soil texture, slope, and rainfall patterns, or human-induced changes to such characteristics, which create site conditions which are vulnerable to erosion. Erosion hazard areas are those areas that are classified as having moderate to severe, severe or very severe erosion potential by the Soil Conservation Service, United States Department of Agriculture (USDA). The geologic units considered as potential erosion hazards within areas of slopes greater than 15% may consist of the following: m (modified land, Qal (alluvium), Qw (wetland deposits), Qb (beach deposits), Qtf (tide flat deposits), Qls (landslide deposits), Qf (fan deposits), the Qvr and Qvs series (Vashon recessional outwash, and Steilacoom Gravel), and Qvi (Ice contact deposits). These units are identified because of density and composition.

b. Landslide hazard areas are those areas meeting any of the following criteria:

(1) Areas of historic failures, including areas of unstable old and recent landslides;

(2) Areas with all three of the following characteristics:

(a) Slopes steeper than 15%;and

(b) Hillsides intersecting geologic contacts with a relatively permeable sediment overlying a relatively impermeable sediment or bedrock; and

(c) Springs or groundwater seepage.

(3) Slopes that are parallel or sub-parallel to planes of weakness, such as bedding planes, joint systems, and fault planes, in subsurface materials;

(4) Slopes having gradients steeper than 80% subject to rockfall during seismic shaking;

(5) Areas potentially unstable as a result of rapid stream incision, streambank erosion, and undercutting by wave action;

(6) Areas located in a canyon or on an active alluvial fan, presently or potentially subject to inundation by debris flows or catastrophic flooding;

(7) Any area with a slope of 30 percent or steeper and with a vertical relief of ten or more feet. A slope is delineated by establishing the toe and top and measured by averaging the inclination over at least ten feet of vertical relief;

(8) Areas which have a “severe” limitation for building site development because of slope conditions, according to the Soil Conservation Service.

2. Mapping. Areas meeting the criteria established above may be delineated in the following documents:

a. Soil Survey of Pierce County Area, Washington, 1979, Soil Conservation Service, United States Department of Agriculture (USDA).

b. Coastal Zone Atlas for Washington, Washington Department of Ecology;

c. Areas designated as slumps, earthflows, mudflows, lahars, or landslides on maps published by the United States Geological Survey or Washington Department of Natural Resources Division of Geology and Earth Resources;

d. Geologic Map of the Steilacoom 7.5-Minute Quadrangle, Washington2003. (Ord. 362 § 3 (part), 2004.)

14A.146.030Protection Standards for Erosion and Landslide Hazard Areas.

A. Prohibited Development Areas. In areas meeting all three of the following characteristics, no structure or disturbance of vegetation is permitted:

1. An area with a slope of 100% or steeper (45 degrees); and

2. hillside intersecting geological contacts with a relatively permeable sediment overlying a relatively impermeable sediment or bedrock; and

3. springs or groundwater seepage.

B. Regulation - Geotechnical Report Required. For all regulated activities proposed within landslide and erosion hazard areas, a geotechnical report prepared by a professional geotechnical engineer or geologist licensed by the State of Washington shall be submitted (See Subsection 2 below). Where the applicant can clearly demonstrate to the Department through submittal of a geological assessment (see Subsection 1 below) that the regulated activity or any related site alterations will not occur within the landslide or erosion hazard area or any associated buffers, the requirements for a geotechnical report may be waived. A geological assessment may be prepared by a professional engineer licensed by the State of Washington with expertise in geotechnical engineering or by a professional geologist/hydrologist or soils scientist who has earned a bachelor's degree in geology, hydrology, soils science, or closely related field from an accredited college or university, or equivalent educational training, and has at least five (5) years experience assessing erosion and landslide hazards.

1. Geological Assessments.

a. Should the applicant question the presence of landslide or erosion hazard areas on the site, the applicant may submit a geological assessment.

b. The geological assessment shall include at a minimum the following:

(1) A description of the topography, surface and subsurface hydrology, soils, geology, and vegetation of the site; and

(2) An evaluation of the analysis area's inherent landslide and erosion hazards; and

(3) A site plan of the area delineating all areas of the site subject to landslide and erosion hazards, based on mapping and criteria referenced in 14A.146.020 above.

The submittal must include a contour map of the proposed site, at a scale of 1"= 20 feet or as deemed appropriate by the Department. Slopes shall be clearly delineated for the ranges between 15 and 29 percent, and 30 percent or greater, including figures for aerial coverage of each slope category on the site. When site specific conditions indicate the necessity, the Department may require the topographic data to be field surveyed.

2. Geotechnical Reports. The geotechnical report shall be prepared by a professional geotechnical engineer or geologist licensed by the State of Washington, and shall address the existing geologic, topographic, and hydrologic conditions on a site, including an evaluation of the ability of the site to accommodate the proposed activity. The geotechnical report shall include at a minimum the following:

a. Site Geology Information required:

(1) Topographic data. Submittal must include a contour map of the proposed site, at a scale of 1"= 20 feet or as deemed appropriate by the Department. Slopes shall be clearly delineated for the ranges between 15 and 29 percent, and 30 percent or greater, including figures for aerial coverage of each slope category on the site. When site specific conditions indicate the necessity, the Department may require the topographic data to be field surveyed.

(2) Subsurface data. Submittal must include boring logs and exploration methods; soil and rock stratification, groundwater levels and seasonal changes of groundwater levels. Subsurface data shall include any evidence of the presence of any organic fill or other conditions that would have the potential to affect buildings or development on the site.

(3) Site history. Submittal must include a description of any prior grading, soil instability, or slope failure.

(4) Seismic hazard. Submittal of data concerning the vulnerability of the site to seismic events, including potential for liquefaction of soils.

b. Geotechnical Engineering Information required:

(1) slope stability studies and opinion(s) of slope stability for the pre-developed and post-developed condition. Site specific setbacks and buffers from landslide hazard areas should be based on the results of the stability analysis;

(2) proposed angles of cut and fill slopes and site grading requirements;

(3) structural foundation requirements and estimated foundation settlements;

(4) soil compaction criteria;

(5) proposed surface and subsurface drainage;

(6) lateral earth pressures;

(7) vulnerability of the site to erosion;

(8) suitability of on-site soil for use as fill;

(9) laboratory data and soil index properties for soil samples; and

(10) building limitations.

Where a valid geotechnical report has been prepared within the last five years for a specific site, and where the proposed land use activity and surrounding site conditions are unchanged, said report may be utilized and a new report may not be required. If any changed environmental conditions are associated with the site, or surrounding the site, the applicant shall submit an amendment to the geotechnical report.

The development proposal may be approved, approved with conditions, or denied based on the Department's evaluation of the ability of the proposed mitigation measures to reduce risks associated with the erosion and landslide hazard area.

3. Protection - Performance Standards. The Department shall evaluate all geotechnical reports for landslide and erosion hazard areas to insure that the following standards are met:

a. Location and extent of development:

(1) Development shall be located to minimize disturbance and removal of vegetation;

(2) Structures shall be clustered where possible to reduce disturbance and maintain natural topographic character; and

(3) Structures shall conform to the natural contours of the slope and foundations should be tiered where possible to conform to existing topography of the site.

b. Design of development:

(1) All development proposals shall be designed to minimize the building footprint and other disturbed areas within the identified geologically hazardous area;

(2) All development shall be designed to minimize impervious lot coverage;

(3) Roads, walkways and parking areas shall be designed to parallel the natural contours;

(4) Access ways shall be designed to avoid geological hazards to the extent feasible. If hazardous areas cannot be avoided, then hazards shall be mitigated as directed by a professional engineer licensed by the State of Washington.

The Department may approve, approve with conditions, or deny development proposals based on these performance standards.

4. Protection - Buffer Requirement. A buffer, consisting of undisturbed natural vegetation, and measured (as shown in diagram 1) in a perpendicular direction from all landslide and erosion hazard areas, shall be required from the top of slope and toe of slope of all landslide or erosion hazard areas that measure 10 feet or more in vertical elevation change from top to toe of slope, as identified in the geotechnical report, maps, and field-checking. The minimum buffer distance requirements from the top of slope and toe of slope of landslide or erosion hazard areas shall be the same as for setbacks from slopes as identified in the International Building Code Section 1805.3, as may be amended by the State Building Code Council, or as indicated by a site-specific geotechnical report. In addition, a setback from the buffer area shall be provided as described in Subsection 6 below. In no case shall the building setback from the top, sides and toe of a landslide hazard area be less than 10 feet.

To increase the functional attributes of the buffer, the Department may require that the buffer be enhanced through planting of appropriate native species that will provide effective protection against erosion and landslides. The edge of the buffer area shall be clearly staked, flagged, and fenced prior to any site clearing or construction. The buffer boundary markers shall be clearly visible, durable, and permanently affixed to the ground. Site-clearing shall not commence until the engineer has submitted written notice to the Department that buffer requirements of this Chapter are met. Field-marking shall remain until all construction and clearing phases are completed, and final approval has been granted by the Department. The identified critical area and buffer shall be placed in a separate critical area tract or tracts, protective easement, public or private land trust dedication, or similarly preserved through an appropriate permanent protective mechanism as determined by the Department.

5. Modifications to Buffer Width. When the geotechnical report demonstrates that a lesser buffer distance, and design and engineering solutions, will meet the intent of this Chapter, such reduced buffer and design and engineering solutions may be permitted. Should the geotechnical report indicate that a greater buffer than that required by Subsection 4 is needed to meet the intent of this Chapter, the greater buffer shall be required.

6. Building Setback and Construction near Buffer. Eight foot minimum setback lines shall be required from the buffer area required in Subsection 4, for construction of any impervious surface(s) greater than 120 square feet of base coverage. Clearing, grading, and filling within eight feet of the buffer shall only be allowed when the applicant can demonstrate that vegetation within the buffer will not be damaged.

7. On-site sewage disposal systems. On-site sewage disposal systems, including drain fields within landslide or erosion hazard areas and related buffers as identified in Subsection 4. shall meet all requirements of the Tacoma-Pierce County Board of Health and the Washington State Department of Health for on-site sewage disposal (WAC Chapter 246-272).

8. Erosion Control Plan. Erosion control plans shall be required for all regulated activities in erosion hazard areas. The erosion control plans shall be consistent with the City Site Development Regulations, Section 3.04.

9. Notification.

a. Title Notification. The owner of any site within an erosion hazard or landslide hazard area, as identified in LMC 14A.146.020, on which a development proposal is submitted, shall record a notice with the Pierce County Auditor in the form set forth below:

b. Form of Notice:

EROSION OR LANDSLIDE HAZARD AREA NOTICE

Parcel Number: ______________________________________________________

Address: ____________________________________________________________

Legal Description: _____________________________________________________

Present Owner: ________________________________________________________

Notice: This site lies within an erosion or landslide area as defined by Chapter14A .___ of the Lakewood Municipal Code. The site was the subject of a development proposal for
application number ____________________________________________________
filed on (date)._________________________________________________________

Restrictions on use or alteration of the site may exist due to natural conditions of the site and resulting regulation. Review of such application has provided information on the location of the erosion or landslide hazard area and any restriction on use.

_____________________________________________________________________
Signature of Owner(s)

_____________________________________________________________________
(NOTARY ACKNOWLEDGMENT)

c. Plat Notification. For all proposed short subdivision and subdivision proposals within erosion hazard or landslide hazard areas, the applicant shall include a note on the face of the plat. The note shall be as set forth below:

Notice: This site lies within or includes an erosion hazard or landslide hazard area as defined in Chapter 14.146 of the City Code. Restrictions on use or alteration of the site may exist due to natural conditions of the site and resulting regulation.

(Ord. 362 § 3 (part), 2004.)

14A.146.040Designation of Seismic Hazard Areas.

A. General. Seismic Hazard Areas are areas subject to severe risk of earthquake damage from seismically induced settlement or lateral spreading as a result of soil liquefaction in an area underlain by cohesionless soils of low density and usually in association with a shallow ground water table.

B. Classification.

1. Criteria. Seismic hazard areas are generally those areas susceptible to ground failure during seismic events. Failure can consist of soil liquefaction, slope failure, settlement, ground rupture, or lateral displacement. Settlement and soil liquefaction conditions occur in areas underlain by cohesionless soils, usually fine sand, of low density, typically in association with a shallow groundwater table.

2. Mapping. Seismic hazard areas may be identified using the Geologic Map of the Steilacoom 7.5-Minute Quadrangle, Washington 2003; and the “Preliminary Liquefaction Susceptibility Map of Pierce County, Washington, September 2003” published by the Washington Department of Natural Resources. (Ord. 362 § 3 (part), 2004.)

14A.146.050Protection Standards in Seismic Hazard Areas.

A. Regulation – Geotechnical Report Required. For all regulated activities, except the construction of wood frame structures under 5,000 square feet, mobile homes, fences, and/or subdivision of property, proposed within seismic hazard areas, a geotechnical report prepared by a professional engineer licensed by the State of Washington with expertise in geotechnical engineering shall be submitted (see Subsection 2. below). Retaining walls may also be excluded from the requirement of a geotechnical report when the height of soil fills on the upper side are not in excess of 4 feet above the toe of the wall, backfills do not exceed a top surface slope of 4:1 (H:V), and there is no permanent structure existing or proposed within a distance of 3 times the height of the wall. Where an applicant can demonstrate through submittal of a geological assessment (see Subsection 1.), that there are no seismic hazards on site, the requirement for the geotechnical report may be waived. A geological assessment may be prepared by a professional geotechnical engineer or by a professional geologist licensed by the State of Washington.

1. Geological Assessments.

a. Should the applicant question the presence of seismic hazard areas on the site, the applicant may submit a geological assessment.

b. The geological assessment shall include at a minimum the following:

(1) A description of the topography, surface and subsurface hydrology, soils, geology, and vegetation of the site; and

(2) An evaluation of the analysis area's inherent seismic hazards; and

(3) A site plan of the area delineating all areas of the site subject to seismic hazards, based on mapping and criteria referenced in LMC 14A.146.040 above.

If the geological assessment demonstrates, to the satisfaction of the Department, that the proposed site is not located in any seismic hazard areas, based upon the criteria set forth in Subsection B. above, then the requirements of this Section shall not apply.

2. Geotechnical Report. The geotechnical report shall be prepared by a professional engineer licensed by the State of Washington with experience in geotechnical engineering and shall address the existing geologic, topographic, and hydrologic conditions on a site, including an evaluation of the ability of the site to accommodate the proposed activity. The geotechnical report shall include at a minimum the following:

a. A discussion of the surface and subsurface geologic conditions of the site;

b. A site plan of the area delineating all areas of the property subject to seismic hazards, based on mapping and criteria referenced in LMC 14.146.040 above;

c. A discussion of mitigation measures which can be taken to reduce seismic risks associated from liquefaction, ground shaking, settlement or slope failure with the underlying surficial geology; and

d. An evaluation of the effectiveness of the proposed mitigation measures. Where a valid geotechnical report has been prepared within the last five years for a specific site, and where the proposed land use activity and surrounding site conditions are unchanged, said report may be utilized and a new report may not be required. If any changed environmental conditions are associated with the site, or surrounding the site, the applicant shall submit an amendment to the geotechnical report.

The development proposal may be approved, approved with conditions, or denied based on the Department's evaluation of the ability of the proposed mitigation measures to reduce seismic risks associated with the underlying surficial geology.

3. Notification.

a. Title Notification. The owner of any site within a seismic hazard area as identified in LMC 14A.146.040, on which a development proposal is submitted, shall record a notice with the Pierce County Auditor in the form set forth below:

Form of Notice:

SEISMIC HAZARD AREA NOTICE

Parcel Number:

Address:

Legal Description:

Present Owner:

Notice: This site lies within a seismic hazard area as defined by Chapter 14.146 of the Lakewood Municipal Code. The site was the subject of a development proposal for

application number

filed on (date).

Restrictions on use or alteration of the site may exist due to natural conditions of the site and resulting regulation. Review of such application has provided information on the location of a seismic hazard area and any restrictions on use.

Signature of owner(s)

NOTARY ACKNOWLEDGMENT

b. Plat Notification. For all proposed short subdivision and subdivision proposals within seismic hazard areas, the applicant shall include a note on the face of the plat. The note shall be as set forth below:

Notice: This site lies within a seismic hazard area as defined in Chapter 14.146, of the City Code. Restrictions on use or alteration of the site may exist due to natural conditions of the site and resulting regulation.