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V. MouNrAiN HOUSE PROPOSED ALTAMONT HEIGHTS TENTATIVE MAP 4. ENVIRONMENTAL CHECKUST 4.6 GEOLOGY AND SOILS of promoting liquefaction is a possibility during the life of the proposed project. However, given the relatively deep groundwater at the site and that a large majority of the soils encountered during the geotechnical investigation are generally high in cohesive clay content and are relatively dense,the potential for liquefaction is considered remote(Kleinfelder USA, 2006). Mitigation Measures No mitigation measures are required. r iv) Landslides? The MEIR indicated that the Mountain House Community,that includes the proposed project,is located outside areas of southwest San Joaquin County identified as susceptible to landsliding. Evidence of past slope failures and/or landslides have not been observed or mapped within or immediately adjacent to the project site. Despite the sloping terrain at the project site, the potential for landslides is remote due to the presence of cohesive soils at the site. Mitigation Measures � No mitigation measures are required. b) Result in substantial soil erosion or the loss of topsoil? i Construction of the proposed project would result in substantial loss of topsoil. Construction would have to comply with the National Pollutant Discharge Elimination System(NPDES) program requirements. The NPDES storm water program, administered by the State Water ` Resources Control Board's (SWRCB) Division of Water Quality, regulates construction sites that disturb five or more acres of land. Under the program, contractors are required to prepare and implement a Storm Water Pollution Prevention Plan that includes Best Management Practices(BMPs)to prevent soil erosion and off-site migration of sediment- laden runoff during construction. Additionally, MHMP Policy 6.83(b) and the County Development Title require that adequate efforts be implemented during construction to control or eliminate soil erosion and sedimentation associated with construction activities. Project development would increase the amount of impervious surfaces at the project site and increase the quantity of runoff. Storm runoff would flow into storm drains that would convey the flow to Water Quality Basin 1 located north of Byron Road on the east side of Mountain House Creek. This basin will substantially reduce flow velocities prior to discharge to Mountain House Creek. In addition, the Mountain House Master Drainage Plan Update requires that protection measures(e.g., riprap, soil-reinforcement products,etc.)be used to prevent erosion in locations where the velocity of the runoff can be expected to cause erosion (Pace,2002). With implementation of these requirements,construction of the proposed project would result in a less-than-significant impact. ` Mitigation Measures No additional mitigation measures are required. 4-31 L