5.4 GEOLOGY EXISTING CONDITIONS. A. Regional and OPA Geology

Transcription

1 5.4 GEOLOGY EXISTING CONDITIONS A. Regional and OPA Geology Topography: The Orcutt Planning Area (OPA) is located along the southern foothills of the Santa Maria Valley. Most of the OPA is characterized by gently-sloped low hills underlain by ancient sand dune deposits. Slopes are generally less than 20% except on the banks of major creeks and in the Solomon Hills along the southern boundary of the OPA. Slopes in the Solomon Hills are commonly 40% or greater. Elevations range from 300 to 700 feet above sea level in most of the OPA and reach 1,000 feet in the Solomon Hills. Stratigraphy: The rocks and sediments exposed in the Orcutt Planning Area are Tertiary and Quaternary in age. These deposits reach a combined thickness of several thousand feet. The outcrop pattern of the various units trend east-west, parallel to the general trend of the Solomon Hills as illustrated on the geologic map of the OPA (Figure 5.4-1). The units exposed in the OPA are described below and Tertiary Rocks Sisquoc Formation: The Pliocene age Sisquoc Formation consists of marine light grey claystone and white to cream-white, punky diatomaceous claystone and diatomite. This unit is locally fossiliferous and in several areas, oil-saturated. In some areas, the oil-saturated portions of the Sisquoc have been burned in natural ground fires which change the diatomaceous rocks to a frothy red stone. The Sisquoc Formation ranges from 1,200 to 1,800 feet thick in the Solomon Hills and may reach 3,000 feet at depth below the Santa Maria Valley. The Sisquoc is exposed only along the southern edge of the OPA, on the flanks of the Solomon Hills. No outcrops of Sisquoc are located within the proposed "urban" area. Careaga Formation: The Careaga Formation is of Pliocene age. This marine geologic unit consists primarily of friable, grayish-yellow massive to thick-bedded sandstone. This sandstone is weakly-indurated (soft and erodible), pebbly, locally fossiliferous and, in places, tar-soaked. This formation is 300 to 600 feet thick in the Orcutt Planning Area. The Careaga is exposed near the southern boundary of the OPA on the flanks of the Solomon Hills. No outcrops of this unit are present within the proposed "urban" area. Paso Robles Formation: The Paso Robles formation is of Pliocene to Pleistocene age and is composed of non-marine, weakly-consolidated, greenish-gray to reddish-colored alluvial sand and conglomerate. Pebbles and cobbles in this unit are composed largely of fragments of siliceous shale of the Miocene Monterey Formation. This formation is up to 1,000 feet thick in the Orcutt area. The Paso Robles is exposed only in the hills on the southern edge of the OPA. No outcrops of this unit are present within the proposed "urban" area. Quaternary Rocks Orcutt Sand: The Orcutt Sand (or Orcutt Formation) is of Pleistocene age. This unit is composed of nonmarine wind-deposited (dune) sand. The sand is tan to rusty brown, poorly consolidated with a 5.4-1

2 Fig Geology and soils 5.4-2

3 pebble gravel locally present at the base of the formation. This sandy unit is, in general, easily eroded. The Orcutt Sand is up to 800 feet thick in the OPA. The Orcutt Sand is exposed in a 2,000-5,000 foot-wide band extending across the southern part of the OPA south of Highway 1, Rice Ranch Road and Chancellor Road. Many of the "Key Sites" discussed in the plan are underlain by this unit. Outcrops of Orcutt Sand are present within the proposed "urban" area. "Dune Sand": This unit is of Pleistocene age and is composed of poorly-consolidated to unconsolidated tan sand deposited in ancient sand dunes. These deposits underlie (i.e., form the ground surface) most of the Orcutt Planning area and represent the most recent episode of coastal dune deposition in this part of the Santa Maria Valley. The topography of the area reflects the ancient field of coastal sand dunes. These sands would vary in thickness due to topography and the transitional nature of the contact with the Orcutt Formation. These sands are estimated to be about 200 feet thick. Alluvium: Recent age alluvium is present along the major stream valleys crossing the Orcutt Planning Area. This material is composed of unconsolidated clay, silt, sand and gravel eroded from the surrounding older formations. The alluvium contains much more clay and silt than the adjacent units, the Orcutt Sand and the "Dune Sand." The alluvium is estimated to be less than 50 feet thick. Regional Structure/Seismic Hazards: The Orcutt Planning Area overlies the southern and deepest part of the structural "downfold" or syncline which forms the Santa Maria Valley. This valley is bounded by the northwest-trending San Rafael Mountains to the north and by the generally west-trending Solomon Hills to the south. A northward-thinning wedge of Tertiary to Recent age sediments fill the Santa Maria Valley syncline. The Solomon Hills are an "upfold" or anticline uplifted along a fault zone extending along the northern flank of this topographic highland. Only two faults are recognized within the Orcutt Planning Area. The Santa Maria Fault crosses the extreme northeast corner of the OPA (about 1,000 feet from the edge of the planning area). This fault was identified by the USGS (Worts, 1951) in their study of the Santa Maria Groundwater Basin. Pleistocene and Recent Age deposits (i.e., sediments near the ground surface) are not displaced along this fault. Thus, this fault is considered to be inactive. The Orcutt/Casmalia Fault is located in the southeast part of the OPA (Figure 5.4-1). This fault trends northeast-southwest and juxtaposes Quaternary Age rocks of the Orcutt Formation against older rocks of the Tertiary Sisquoc and Coreaga formations. Because Quaternary rocks are offset, this fault is classified as potentially active. This fault is located outside the proposed "Urban" area. It crosses only one of the Key Sites (#35) designated in the draft community plan. The Seismic Safety and Safety Element (SSSE) classifies the following faults in the general region of the Santa Maria Valley and the OPA as active (A) or potentially active (PA): the Bradley Canyon (PA), Nacimiento (A), Santa Ynez (A), Big Pine (A) and San Andreas (A) faults

4 The major potential hazards to the planning area from seismic activity involve ground shaking and related effects from earthquakes on local and major regional faults. These effects can include ground rupture, ground acceleration liquefaction, landslides and tsunamis. Ground Rupture: Ground rupture, as defined in this context, refers to the displacement of the ground surface along a fault trace during an earthquake. Only the Orcutt/Casmalia fault is classified as potentially active within the OPA and considered a ground rupture hazard. This hazard would be addressed by an existing County policy which prohibits development within 50 feet of the trace of a potentially active fault. Note that the ground rupture hazard associated with this fault is not a substantial concern in the OPA as this fault is located outside of the proposed Urban Area. Ground Acceleration: The term "ground acceleration" refers to the peak ground motion or shaking associated with a specific earthquake event. This ground motion is measured in terms of "g" forces, where 1.0 g equals the acceleration of an object under the influence of gravity. Ground shaking propagates away from the source of an earthquake (epicenter along a fault) with intensity diminishing with distance. Table lists estimated maximum earthquake magnitudes, peak accelerations in the OPA and Mercalli Scale intensities for the major active faults in the region. The Modified Mercalli Scale (Table 5.4-2) describes the physical damage to man-made structures and the effects on humans to various degrees of ground shaking. TABLE ESTIMATED POTENTIAL SEISMIC ACTIVITY ON MAJOR ACTIVE FAULTS Fault Approximate Minimum Distance From Site (Miles) Maximum Credible 1 Earthquake (In Richter Magnitude) 2 Approximate Peak Ground Acceleration 3 Estimated Mercalli Scale Intensity 4 Big Pine VIII Nacimiento IX San Andreas VIII Santa Ynez VIII 1 Defined as the maximum estimated earthquake capable of occurring. 2 Richter magnitude from Santa Barbara County SSSE 3 From Davenport, See Figure

5 Bradley Canyon VII-VIII Orcutt/Casmalia VIII Hosgri IX TABLE MODIFIED MERCALLI EARTHQUAKE INTENSITY SCALE M Intensity Effects v, cm/s g I. Not felt. Marginal and long-period effects of large earthquakes 3 II. III. Felt by persons at rest, on upper floors, or favorably placed. Felt indoors. Hanging objects swing. Vibration like passing of light trucks. Duration estimated. May not be recognized as an earthquake IV. Hanging objects swing. Vibration like passing of heavy trucks; or sensation of a jolt like a heavy ball striking walls. Standing cars rock. Windows, dishes, doors rattle. Glasses clink. Crockery clashes. In the upper range of IV wooden walls and frames creak. V. Felt outdoors; direction estimated. Sleepers wakened. Liquids disturbed, some spilled. Small unstable objects displaced or upset. Doors swing, close, open. Shutters, pictures move. Pendulum clocks stop, start, change rate. 5 VI. Felt by all. Many frightened and run outdoors. Persons walk unsteadily. Windows, dishes, glassware broken. Knickknacks, books, etc., off shelves. Pictures off walls. Furniture moved or overturned. Weak plaster and masonry D cracked. Small bells ring (church, school). Trees, bushes shaken (visibly, or heard to rustle). VII. Difficult to stand. Noticed by drivers of cars. Hanging objects quiver. Furniture broken. Damage to masonry D, including cracks. Weak chimneys broken at roof line. Fall of plaster, loose bricks, stones, tiles, cornices (also unbraced parapets and architectural ornaments). Some cracks in masonry C. Waves on ponds; water turbid with mud. Small slides and caving in along sand or gravel banks. Large bells ring. Concrete irrigation ditches damaged. 6 VIII. Steering of cars affected. Damage to masonry C; partial collapse. Some damage to masonry B; none to masonry A. Fall of stucco and some masonry walls. Twisting, fall of chimneys, factory stacks, monuments, towers, elevated tanks. Frame houses moved on foundations if not bolted down; loose panel walls thrown out. Decayed piling broken off. Branches broken from trees. Changes in flow or temperature of springs and wells. Cracks in wet ground and on steep slopes. 7 IX. General panic. Masonry D destroyed; masonry C heavily damaged, sometimes with complete collapse; masonry B seriously damaged. (General damage to foundations). Frame structures, if not bolted, shifted off foundations. Frame racked. Serious damage to reservoirs. Underground pipes broken. Conspicuous cracks in ground. In alluviated areas sand and mud ejected, earthquake fountains, sand craters. 8 X. Most masonry and frame structures destroyed with their foundations. Some well-built wooden structures and bridges destroyed. Serious damage to dams, dikes, embankments. Large landslides. Water thrown on banks of canals, rivers, lakes, etc. Sand and mud shifted horizontally on beaches and flat land. Rails bent slightly XI. Rails bent greatly. Underground pipelines completely out of service >1.2 XII. Damage nearly total. Large rock masses displaced. Lines of sight and level distorted. Objects thrown into the 5.4-5

6 air. Note: Masonry A, B, C, D. To avoid ambiguity of language, the quality of masonry, brick or otherwise, is specified by the following lettering (which has no connection with the conventional Class A, B, C construction). Masonry A: Good workmanship, mortar, and design; reinforced, especially laterally, and bound together by using steel, concrete, etc.; designed to resist lateral forces. Masonry B: Good workmanship and mortar; reinforced, but not designed to resist lateral forces. Masonry C: Ordinary workmanship and mortar; no extreme weaknesses such as non-tied in corners, but masonry is neither reinforced nor designed against horizontal forces. Masonry D: Weak materials, such as adobe; poor mortar; low standards of workmanship; weak horizontally. Average peak ground velocity, cm/s. Average peak acceleration (away from source). Magnitude correlation

7 Note that major geologic studies of the seismic hazards and nature of faulting in Southern California are currently underway by organizations such as the Southern California Earthquake Center and the Institute for Coastal Studies. The hazard posed by active faults which do not break the earth's surface ("blind" thrust faults) is under particular study. The subsurface geometry of the identified surface faults is also under reevaluation. These studies are anticipated to increase the knowledge of seismic hazards in Santa Barbara County and in the OPA. Liquefaction: Liquefaction is the loss of shearing strength in saturated sandy soil due to ground shaking during an earthquake. The vibration causes an increase in pore pressure within the saturated soils sufficient to allow the material to flow as a liquid. Severe settlement of building foundations and slope failure can result. There is no historic evidence of liquefaction in Santa Barbara County (SSSE, 1979) and this phenomenon is not anticipated to occur in the OPA. This is because the water table in the OPA is generally more than two hundred feet below the ground surface (SBCWA Santa Maria Valley Water Resources Report, 1993). Landslides: A landslide is a mass of earth material which has moved (i.e., slid) downhill. Landslides typically occur in clay-rich or well-stratified sedimentary rocks exposed on steep (>30%) slopes. Areas where bedding dips at an angle shallower than the slope of the ground surface (i.e., the bedding is "daylighted") are particularly susceptible to landslides. Most of the OPA (and all of the designated urban area) is underlain by ancient dune sand deposits and has generally gentle slopes. The potential for substantial landslides to occur in this setting is very low. The most likely area for landslides to occur would be the area of Sisquoc Formation outcrops in the Solomon Hills at the southern edge of the OPA. Note that only one landslide has been mapped in the OPA. This landslide is present in the Solomon Hills where bedding is daylighted in the Careaga Formation. Note that landslides may occur in response to earthquakes or may occur solely due to changes in ground moisture content. Soil Problems: Geologic hazards associated with the physical nature of surface soils include expansiveness, severe erosion, collapsibility and the lack of septic capability. Expansive Soils: Expansive soils are composed of sediments rich in clays which swell (expand) upon wetting. These soils can cause severe damage over time to building foundations if not taken into account in the grading of the land and design of the structure. Expansive soils in the OPA occur in Quaternary Alluvium in the Graciosa Canyon area south of Old Town Orcutt and in the alluvial area along Orcutt Creek between Old Town Orcutt and Solomon Road. These soils are identified in the Soil Conservation Service Soil Survey for Northern Santa Barbara County (SCS 1972) as belonging to the Botella Series. Collapsible Soils: Collapsible soils are low density, fine-ground granular soils. When these soils become saturated with water, they may undergo a re-arrangement of grains resulting in substantial and rapid settlement under relatively low loads. Thus, these soils would be sensitive to increases in moisture content which could result from irrigation related to residential or other development. Most of the OPA (and nearly all of the proposed urban areas) is underlain by low density sandy soils of the Orcutt and "Dune Sand" formations. These soils are designated in the Soil Survey (SCS, 1972) as primarily in the Marina Sand and Oceano Sand series. These soils would be potentially subject to collapse 5.4-7

8 under certain load and moisture conditions. This potential geologic hazard can be effectively addressed through site specific measures involving site preparation (grading) and building design. Severe Erosion: The sandy soils which occur over most of the Orcutt Planning Area are generally unconsolidated and poorly cemented. These ancient dune sands are subject to severe erosion by wind and water, especially when disturbed by development. Sedimentation in nearby creeks could be substantial if large areas were developed concurrently. Design of developments to limit the creation of high cut or fill slopes and to prevent substantial new runoff across bare ground would minimize potential erosion problems. Septic Capability: Although most of the OPA is served by a public sewer system, some areas may develop with an onsite septic system. Percolation rates suitable for septic disposal are likely to be found in the areas underlain by the Orcutt and "Dune Sand" formations (i.e., the vast majority of the OPA). The only area within the proposed Urban boundary where septic disposal would be of concern would be the area discussed under "Expansive Soils" above. Portions of this area may experience difficulty in obtaining minimum percolation rates and in providing an adequate setback from the creek as required by regulations. B.OPA Sub-Area Setting The following sections list the geologic hazards, as described in the previous sections, which would be of concern in the four designated sub-areas of the Orcutt Planning Area. Central Urban Core: This area is almost entirely underlain by the "Dune Sand" deposits of Recent Age. A small area of sandy alluvium is present along Orcutt Creek. Severe erosion and collapsible soils would be potential geologic hazards in this area. South Orcutt: This area is underlain by "Dune Sand," the Orcutt Formation and sandy alluvium. Severe erosion and collapsible soils would be potential geologic hazards in this area. The potentially active Orcutt/Casmalia Fault is also a known geologic hazard. West Orcutt: This area is underlain by "Dune Sand," Orcutt Formation, sandy alluvial deposits and clayrich alluvial deposits. Other than the area of clay-rich alluvial deposits (described in the section on Expansive Soils), this area would have similar hazards to those discussed for the Central Urban Core. In addition to these constraints, the soil in the Graciosa Canyon/Orcutt Creek area is clay-rich and expansive. East of Hwy 101: This area is underlain by "Dune Sand" and the Orcutt Formation. Geologic concerns in this area would be similar as those described for the Central Urban Core

9 5.4.2THRESHOLDS OF SIGNIFICANCE The following guidelines for determining the significance of geologic impacts was adopted by the Santa Barbara County Board of Supervisors in GEOLOGIC CONSTRAINTS GUIDELINES The purpose of these guidelines is to provide preliminary criteria for determining whether a particular activity could have a potentially significant impact on the environment as described in Section of the State CEQA Guidelines. Because geologic conditions are highly variable within Santa Barbara County, these guidelines are not fixed thresholds upon which a determination of significant impact would be made. They serve to point out when further study of site-specific conditions is required in order to assess geologic impacts. The level of project geologic impacts (i.e., potentially significant, potentially significant but subject to effective mitigation or not significant) is made by P&D staff (in consultation with licensed geologists and engineers as necessary) upon review of project plans, proposed mitigation measures and site-specific geologic information. Impacts are considered potentially significant if the proposed development activity, including all proposed mitigation measures, could result in substantially increased erosion, landslides, soil creep, mud slides and unstable slopes (Appendix G (q), CEQA Guidelines). In addition, impacts are considered significant when people or structures would be exposed to major geologic hazards upon implementation of the project (Appendix G (r), CEQA Guidelines). Impacts related to geology have the potential to be significant if the proposed project involves any of the following characteristics: 1.The project site or any part of the project is located on land having substantial geologic constraints, as determined by P&D or Public Works. Areas constrained by geology include parcels located near active or potentially active faults and property underlain by rock types associated with compressible/collapsible soils or susceptible to landslides or severe erosion. "Special Problems" areas designated by the Board of Supervisors have been established based on geologic constraints, flood hazards and other physical limitations to development. 2.The project results in potentially hazardous geologic conditions such as the construction of cut slopes exceeding a grade of 1.5 horizontal to 1 vertical. 3.The project proposes construction of a cut slope over 15 feet in height as measured from the lowest finished grade. 4.The project is located on slopes exceeding 20% grade. Mitigation measures may reduce impacts to a less than significant level. These measures would include minor project redesign and engineering steps recommended by licensed geologists and engineers subsequent to detailed investigation of the site

10 5.4.3IMPACT ANALYSIS Based on the preceding discussion, the proposed Orcutt Community Plan would have the potential for the following geologic impacts. A. Project Impacts As discussed in previous sections, development of the Orcutt area as proposed in the draft Orcutt Community Plan would be subject to hazards related to the predominance of generally unconsolidated and highly erodible sandy soils. The potential for blowing sand, severe erosion, and collapsible soils is present in all of the OPA, with the exception of the area of clay-rich soil along Graciosa Canyon and Orcutt Creek near Old Town Orcutt. In addition, the presence of expansive soils can lead to substantial foundation problems if not addressed in site preparation and structure design. The regional seismic hazard faced by the Orcutt area due to ground motion resulting from earthquakes is similar to that faced by the entire county. Central Urban Core: Blowing sand during development, sedimentation of Orcutt Creek and existing and proposed flood control retention basins, and the development of eroding (and unvegetated) artificial slopes are potential impacts associated with Key Site development in the central urban core. The issue of possible collapsible soils would have to be addressed in the engineering of any development. One particular concern would be the development of Key Site #18. Development of this site should be designed to avoid increased erosion of the banks of Orcutt Creek. These banks are comprised of highly erodible material and form the lot boundary of existing developed residential parcels. South Orcutt: Blowing sand during development, sedimentation of Orcutt Creek, Pine Canyon Creek, existing and proposed flood control retention basins, and the development of eroding (and unvegetated) artificial slopes are potential impacts associated with Key Site development in south Orcutt. As with the other areas underlain by the "Dune Sand" and Orcutt Formation deposits, the issue of collapsible soils would have to be addressed in project design. Of particular concern in the areas encompassed by Key Sites #3, 5, 6, 8, 10, 11 would be severe erosion caused by grading on the banks of Orcutt Creek, and on Key Site 12 on the banks of Pine Canyon Creek. In addition, extensive grading would be required for the proposed extension of Stillwell Road/Stubblefield Road on steep, highly erosive slopes greater than 20 percent which could result in increased sedimentation of Orcutt Creek and its local tributary drainages. Another area of concern is Key Site #35. The Orcutt/Casmalia Fault crosses the southeastern corner of this property. Placement of a dwelling within 50 feet of this fault would represent a potentially significant impact. The location of this fault would have to be clearly delineated and a setback established prior to approval of any development on this parcel. Note that south of the Urban limit line steep slopes are found along with outcrops of older formations on the flanks of the Solomon Hills. The land use designations for this area under the proposed plan would allow for continued grazing and oil production operations. Although future expanded oil exploration activities are possible, they are considered to be very unlikely given the age and declining production of the

11 Casmalia and Orcutt Hill oil fields and the extensive exploratory efforts to date. Thus, potential future geologic effects from oil activities in the Solomon Hills would not be substantial. West Orcutt: Blowing sand during development, sedimentation of Orcutt Creek and existing and proposed flood control retention basins, and the development of eroding (and unvegetated) artificial slopes are potential impacts associated with Key Site development in west Orcutt. The issue of possible collapsible soils would have to be addressed in the engineering of any development. The possible lack of adequate percolation for septic disposal may also be a potential constraint to development in the area of clay-rich soils. Foundation problems and septic limitations would be of concern in this area and would involve Key Sites #14, 15, 19 and D. Site specific percolation tests would be required to determine the severity of potential septic problems. Note that west of the Urban limit line are steep slopes and outcrops of older formations on the flanks of the Casmalia Hills. The land use designations for this area under the proposed plan would allow for continued grazing and oil production operations. Although future expanded oil exploration activities are possible, they are considered to be very unlikely given the age and declining production of the Casmalia and Orcutt Hill oil fields and the extensive exploratory efforts to date. Thus, potential future geologic effects from oil activities in the Casmalia Hills would not be substantial. East of Hwy 101: The primary geologic concern east of Hwy 101 is related to grading and site preparation activities on soils underlain by "Dune Sand" and Orcutt Formation deposits. The issue of collapsible soils and blowing sand would have to be addressed in project design. IMPACT SUMMARY Impact GEO-1: Increased erosion. Development and increased run-off in the highly erosive soils of the Solomon foothills would create potentially significant impacts to Orcutt Creek, Pine Canyon Creek, and unnamed local drainages through substantial increases in erosion, possible collapse of new cut and fill slopes and subsequent sedimentation associated with large scale grading and clearing on steep slopes with collapsible soils. Impact GEO-2: Blowing sand: Grading and site preparation activities associated with future development on soils underline by "Dune Sand" and Orcutt Formation deposits would create potentially significant impacts due to blowing sand which would contribute to the County's PM 10 air quality problem, as well as creating a nuisance for surrounding land uses. Impact GEO-3: Seismic hazards: Development of the proposed Community Plan would be subject to potential significant seismic hazards through earth shaking and subsequent damage to structures and potentially residents. Impact GEO-4: Septic constraints: The presence of clay-rich soils in areas not served by sewer service could result in potentially significant impacts to septic disposal systems

12 B. Policy Impacts The draft geology/soils policies identified in the draft Orcutt Community Plan would not result in direct or indirect geology impacts. C. Cumulative Impacts Since much of the Santa Maria Valley is underline by "Dune Sand" and Orcutt Formation deposits, future development associated with buildout of the City of Santa Maria Sphere of Influence annexation areas, as well as proposed buildout associated with the Santa Maria Airport Research Park will have similar impacts due to blowing sand and the presence of collapsible soils. The level of significance for these impacts would be determined on a case-by-case basis MITIGATION MEASURES A. Existing Policies that would Mitigate Impacts Slope Constraints Slopes 30 Percent and Greater: No development should be permitted on these lands because of the possibilities of landslides and other geologic hazards in certain areas and endangering lands at lower elevations, the virtual inevitability of marring the scenic beauty of hillsides, and the other adverse effects of building roads and providing public services to sparsely settled areas. (Open Space Element) Slopes 20 to 30 Percent: Although not as hazardous as steeper slopes, these hillsides should be subjected to a minimum of development. Lands this steep often exhibit geologic problems or comprise portions of important watersheds. (Open Space Element) Hillside and Watershed protection policies 1 through 9 (Land Use Element) Seismic Hazards Conformance to Uniform Building Code - The latest edition of the UBC indicates that all of Santa Barbara County is within seismicity zone IV, where the expected maximum ground acceleration may be greater than 70 percent of gravity. Accordingly, the County of Santa Barbara requires that all structures be built to Zone IV standards of UBC

13 B. Proposed Mitigation Measures Mitigation GEO-1: The County shall apply the Orcutt Open Space Overlay (Figure 2-14) on slopes of 20 percent or greater to minimize geologic hazards associated with development on steep slopes. (addresses Impact GEO-1) Mitigation GEO-2: Ground disturbances and development on slopes of 20 percent or greater shall be avoided, unless such avoidance would prohibit development, wherein the portion of the site which exhibits the lowest slope shall be utilized. All new development shall be sited in close proximity to the nearest existing access road to minimize the need for new roads/driveways, where such roads/driveways would require substantial grading. (addresses Impact GEO-1) Mitigation GEO-3: New structures shall not be allowed in areas of unstable or highly erosive soils on slopes greater than 20% unless an evaluation by a qualified soils engineer or engineering geologist establishes that the proposed project will not result in unstable slopes or severe erosion. (addresses Impact GEO-1) Mitigation GEO-4: Silt fencing, straw bales, sand bags, sediment basins, etc., shall be used in conjunction with other methods to prevent erosion on slopes and siltation of stream channels. In foothill areas, cut and fill slopes shall be planted with slope-stabilizing vegetation -- native only within open space corridors -- including oak trees and appropriate shrubs and irrigated until established. (addresses Impacts GEO-1) Mitigation GEO-5: Development in areas of high erosion potential shall be sited and designed to minimize increased erosion and may be required to have a site-specific evaluation of erosion-control measures. Project approval shall be conditioned to ensure that erosion will be reduced to acceptable levels. (addresses Impact GEO-1) Mitigation GEO-6: Landscape plans shall be required for all new development in areas of sandy soils to ensure revegetation of graded areas. All landscape plans shall be reviewed by the County BAR; landscape securities (bonds) shall be required unless expressly waived by P&D. (addresses Impact GEO-1 and 2) Mitigation GEO-7: Erosion control measures, such as plantings or hard surfaces, shall be incorporated into the drainage plan for all projects as required by the Flood Control District and P&D. (addresses Impact GEO-1) Mitigation GEO-8: All surface water runoff shall be culverted and diverted to avoid exposed slopes and directed to the nearest natural drainage channel across an energy-dissipating outfall. (addresses Impact GEO-1) Mitigation GEO-9: All finished cut and fill slopes and other areas of exposed soils shall be revegetated with ground cover immediately after construction. A landscape maintenance plan shall be prepared for County review and approval. (addresses Impact GEO-2)

14 Soils Constraints Mitigation GEO-10: Based upon information in this EIR, a site-specific geologic and soils investigation shall be conducted to determine if expansive or collapsible soils are present on the project site. Where necessary, expansive and/or liquefiable soils shall be identified, removed and replaced with suitable engineered backfill; expansive soils shall be reused for landscaping only. In addition, appropriate site preparation and foundation design recommendations based on this investigation shall be incorporated into the project design. This investigation shall be conducted by a Certified Engineering Geologist. (addresses Impact GEO-1 and 4) Seismic Hazards Mitigation GEO-11: Construction of buildings of all types on, or within 50 feet of, an active or potentially active fault shall be avoided. Where a question exists as to the location of an active or potentially active fault, a fault study conducted under the guidance of a Registered Geologist or Certified Engineering Geologist shall be conducted. Such a study will not be required if meaningful information would not likely be obtained or no planning/siting decision would be affected, as determined by the P&D Geologist. (addresses Impact GEO-3) Septic Constraints (For projects not on public sewer) Mitigation GEO-12: Prior to approval of a discretionary project, adequate septic disposal capacity shall be physically demonstrated by onsite testing as determined by Environmental Health Services. (Standard regulatory practice) (addresses Impact GEO-4) Mitigation GEO-13: Prior to issuance of a building permit for a ministerial project, adequate septic disposal capacity shall be demonstrated by onsite testing as determined by Environmental Health Services. (Standard regulatory practice) (addresses Impact GEO-4) RESIDUAL IMPACTS Although the extent of new development allowed under the proposed Orcutt Community Plan is substantial, most geologic hazards identified for this area are capable of being mitigated to less than significant after mitigation (Class II). with implementation of the measures listed above. However, because of the highly erodible and collapsible nature of many of the soil types in the foothills, potential impacts associated with erosion, slope collapse and subsequent downstream sedimentation are considered unavoidable and significant(class I)