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5.ENVIRONMENTAL CHECKLIST MOUNTAIN HOUSE NEIGHBORHOODS KAND L IN171AL STUDY 6. GEOLOGY AND SOILS reduce project impacts related to soil erosion and loss of topsoil to less-than- significant levels. c) Would the project be located on a geologic unit or soil that is unstable, or that would become unstable as a result of the project, and potentially result in on-or off-site landslide, lateral spreading, subsidence, liquefaction or collapse? See responses under Items (a)(lii) and(a)(iv)above. The geotechnical engineering studies for these neighborhoods identified a number of ways to minimize such impacts. These measures would be integrated into the design of structures for Neighborhoods K and L to mitigate impacts to less-than-significant levels. d) Would the project be located on expansive soil, as defined in Table 18-1- B of the Uniform Building Code (UBC) (1994), creating substantial risks to life or property? The UBC classifies the expansive nature of soils based on an expansion index. It is generally accepted that soils with an expansion index greater than 50 are susceptible to soil expansion. Soil expansion was also addressed in Master Plan Policy 6.8.3.0.a(Soils, Geologic, and Seismic Hazards). Laboratory testing indicates that soils in Neighborhoods K and L have a medium to high expansion potential, creating the potential for substantial risks to life or property. Unless properly mitigated, soil expansion has the potential to damage foundations; cause large cracks in exterior walls,floors, and ceilings; and cause wavy`roller coaster'surfaces along driveways, sidewalks, and streets. Some techniques to mitigate these problems are moisture conditioning, lime treatment, or the replacement of expansive soils with engineered fill. Site preparation and structural design in Neighborhoods K and L would be completed in accordance with geotechnical engineering studies for these neighborhoods to mitigate the impacts. Therefore,the impacts would be less than significant. e) Would the project have soils incapable of adequately supporting the use of septic tanks or alternative waste water disposal systems where sewers are not available for the disposal of waste water? No septic tanks or alternative waste disposal systems are proposed for the project site. All wastewater would be collected in a piping system connected to the existing wastewater treatment plant located just east of Neighborhood L. The wastewater treatment plant is further discussed in Section 5.16, Utilities and Service Systems, of this Initial Study. The project would have no impact on septic systems or alternative wastewater disposal systems. Thus, no mitigation is necessary. {srrr„I 5-80