SITE INFORMATION AND CORRESPONDENCE

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5.11:SOILS could be subject to different (higher or lower) rates of water and wind erosion than the native soils, depending on their actual properties and degree of compaction. 5.11.1.4 Other Significant Soil Characteristics While the surface and subsurface soils beneath the LEC project and associated facilities are not indicated to have high shrink-swell potential, the potential for soils with this property could represent a significant soil characteristic concerning the proposed LEC project site (NRCS,1992). Because there was no shrink-swell information on the subsoil layer in the 149 soil mapping unit (Devries sandy loam, drained, 0 to 2 percent slopes) and because moderate shrink-swell potential was indicated in the adjacent soil mapping unit (169-Guard clay loam, drained, 0 to 2 percent slopes),it is possible that soils with some shrink-swell potential could be found in the subsurface beneath the LEC site and along the gas pipeline alignment. The presence of expansive clays in the soil may affect its suitability as a bearing surface for foundations and pipelines because expansive clays shrink when dry and swell when wet, and thus have the potential to cause foundations or other structures built on them to crack,heave, or collapse. A preliminary geotechnical soil investigation (Carlton Engineering,2008) confirmed that this soil condition could exist at the site and that additional geotechnical engineering evaluations were required to support design and construction for the LEC. The 149 soil mapping unit (Devries sandy loam,drained, 0 to 2 percent slopes) soil unit may be subject to rare flooding events,particularly during years of abnormally high precipitation. These soils are characterized by an indurated hardpan at a depth of 20 to 40 inches. This characteristic may cause the soils above the hardpan to remain saturated after periods of prolonged precipitation. The hardpan will also limit the effective plant rooting depth,which will affect efforts to revegetate cleared soil areas. This hardpan will also affect the difficulty of excavation for the pipeline installation. The presence of existing subsurface drainage facilities within agricultural fields will also affect the way in which the gas pipeline excavation is planned and executed. Because deep ripping may be an agricultural practice in use in these fields for crop productivity,it will be necessary to install the gas pipeline deep enough so that the land may be returned to agricultural use after construction. 5.11.2 Environmental Analysis The following sections describe the potential environmental effects on soils during the construction and operation phases of the project. 5.11.2.1 Significance Criteria The potential for impacts to soils resources and their uses (such as agriculture) were evaluated with respect to the criteria described in the Appendix G checklist of the California Environmental Quality Act (CEQA). An impact is considered potentially significant if it would: • Involve changes in the existing environment which,because of their location or nature, could result in conversion of farmland to non-agricultural use • Impact jurisdictional wetlands 5.11-6 SAC/371322/082330009(LEC_5.11_SOILS.DOC)