Initial Study MND - Sonoma County Agricultural Preservation and ...

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Taylor MountainINITIAL STUDY/MITIGATED NEGATIVE DECLARATIONwould be in accordance with the California Building Code; by law, all project improvementsmust meet the requirements of the California Uniform Building Code (CUBC) for Seismic Zone 4.Liquefaction. Sonoma County Hazard Mitigation Plan mapping (Figure 8.1) of hazard areasindicates that the site is not within a zone of liquefaction susceptibility.Landslides. Several Quaternary landslide deposits are located in the northeast portion of theproperty along the fault zone. In the Sonoma County General Plan, most of Taylor Mountain ischaracterized by areas of relatively unstable rock on slopes greater than 15 percent, with aportion of the mountain also characterized as “Landslide Complex,” where previous slopefailure has occurred. Additionally, most of the site is identified as an area with high ormoderate potential for landslides (Sonoma County, 2008). The Master Plan does not proposeany structural development in these areas and development of new public trails through theseareas would be avoided, as required by Standard 99.b. Would the project result in substantial soil erosion or the loss of topsoil?LESS THAN SIGNIFICANT WITH MITIGATION INCORPORATED. Development and use of theTaylor Mountain Preserve has the potential to result in erosion, particularly due to thesteepness of some of the trails and ranch roads. In particular, the Goulding soil series are proneto erosion. Trail development will be required to implement measures to avoid erosion, asspecified in Standard 23. Master Plan Standard 66 references Master Plan Table 3 withrecommended vegetated setbacks which would minimize erosion. Closures of the trails wouldbe put into place during wet weather periods to minimize erosion, as required by Master PlanS267.Grading of the staging areas has the potential to result in erosion; however, staging areas areproposed on relatively level ground. The Master Plan contains many guidelines and standardsto minimize soil disturbance and erosion (see Section B.3.8, Hydrology). Both temporarymethods, such as laying down straw for trails (S3, S10, S14) and longer-term methods, such aslaying down gravel for trails (S108) and staging areas (shown on site plans in Section B.1,Project Description), would limit the potential for soil erosion. Implementation of the MasterPlan standards and the following mitigation measure would reduce this potential impact to aless-than-significant level:6-1 Best Management Practices such as preservation of existing vegetation and use of sedimentcatch basins and silt fencing shall be used to minimize erosion during construction,as required by the Construction General Permit (CGP). The staging areas and accessdriveways shall be improved between April 15 and October 15, prior to the winter rains,or Regional Water Quality Control Board (RWQCB) Best Management Practices for wetweatherconstruction will be utilized.With proper construction practices in accordance with the Master Plan and Mitigation Measure6-1, there should be no notable erosion or transport of sediment from the site.Final B-72 September 2012
Taylor MountainINITIAL STUDY/MITIGATED NEGATIVE DECLARATIONc. Would the project be located on geologic units or soil that is unstable, or that wouldbecome unstable as a result of the project, and potentially result in on- or off-sitelandslide, lateral spreading, subsidence, liquefaction, or collapse?LESS THAN SIGNIFICANT. The potential for landslide and liquefaction impacts is addressed above inItem (a). The staging areas will be located on relatively flat, stable ground that is not susceptible tospreading, subsidence or liquefaction. Some trails will be developed across sloped areas, but theMaster Plan includes several measures to ensure slope stability, such as: S98, which requiresthat new riparian and creek crossings be developed on stable sites (i.e., low slopes in channeland banks) and constructed to minimize, to the greatest extent possible, streambank and bederosion; and S101, which establishes an average trail slope of 10%. Therefore, the impact is lessthan significant.d. Would the project be located on expansive soil, as defined in Table 18-1-B of the UniformBuilding Code (1994), creating substantial risks to life or property?LESS THAN SIGNIFICANT. The proposed project site is characterized by expansive soils (SonomaCounty, 2008); these soils contain clay minerals that greatly increase in volume when theyabsorb water, and shrink when they are dry. As a result, they exhibit cracks in some locations.While cracks in the soil present some tripping hazard, use of the trails and ranch roads byhikers, bicyclists and equestrians would not create substantial risk to life or property. Inaddition, information at the staging area kiosks would alert users to the uneven surfaceconditions along portions of the trail and urge caution when hiking, bicycling or riding in areascharacterized by these conditions.e. Would the project have soils incapable of adequately supporting the use of septic tanks oralternative wastewater disposal systems where sewers are not available for the disposalof wastewater?LESS THAN SIGNIFICANT. Implementation of the Master Plan will rely on limited septic systemsto support permanent restrooms at the staging areas and visitor services at the Kawana SpringsResort staging area. The property is currently served by a septic system for the existingresidence in the life estate area. There are several soil types in the Kawana Springs Resort areathat have the potential to accommodate a standard septic system. Due to 100’ minimumsetbacks to water sources (wells and springs), streams and wetlands, there may be a need toinclude the use of a mound type system if onsite soils in close proximity to the developedcompound are not conducive to standard septic / leach field design.County permit requirements include provisions to ensure that soils are adequate for septicsystems. Both a pre-perc test and perc test will be required to confirm soil suitability prior toissuing septic system permits. Furthermore, the Master Plan includes S143, which requires soilstudies in advance of septic system design work. The Master Plan states that waterless toiletswill be installed, if septic systems are not practical.September 2012 B-73 Final
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