Appendix E - Geology and Soils Geotechnical Supporting Information COMBINED

LESTER-SHRINER PROPERTY 132-8-2 Page 12 no greater than 10 feet and not exceeding a slope of 15 percent. Preliminary recommendations are presented in the "Earthwork" and "Foundations" sections of this report. 5.1.2 Bedrock Excavation The conceptual site plan indicates that cuts up to approximately 30 feet are proposed near the western end of the development area. Therefore, bedrock will be encountered during mass grading and also during utility trench excavations in cut areas. Based on our review of geologic maps in the area, materials encountered in the previous and recent test pits and seismic refraction survey, conventional construction equipment should be capable of ripping and excavating the upper 15 to 20 feet of bedrock. Where fresh, competent bedrock is encountered below these depths, or in areas where resistant sandstone beds outcrop at the surface, then excavation with conventional grading equipment may be difficult. Our experience in the vicinity indicates that these resistant sandstone beds may require very heavy single-tooth ripping with a Caterpillar D10. Hydraulic jacking or light blasting may be necessary if hard rock areas are not rippable using conventional grading equipment. Preliminary recommendations for bedrock excavation and further discussion of rippability and reuse of materials are presented in the "Earthwork" section of this report. 5.1.3 Expansive Soils Expansive soils and bedrock can undergo significant volume change with changes in moisture content. They shrink and harden when dried and expand and soften when wetted. If structures are underlain by expansive soils it is important that foundation systems be capable of tolerating or resisting any potentially damaging soil movements. In addition, it is important to limit moisture changes in the surficial soils by using positive drainage away from buildings as well as limiting landscaping watering. The moderately to highly expansive clays (colluvial soil) that mantle the hillsides are generally 2 to 11 feet thick based on the previous and recent test pits, although variations could occur. Since significant cuts and fills are proposed, if feasible, we recommend that all expansive colluvial soil be buried in the deeper fills a minimum of 2 feet below finished grade, or be used to cover finished graded fill slopes to promote growth of the erosion control materials. Provided these recommendations are followed, in our opinion, the potential for moderately to highly expansive soils to impact foundations and pavements areas could be adequately mitigated. If expansive bedrock layers are encountered at or near the surface in foundation or pavement areas, these materials may need to be over-excavated to depths on the order of 2 to 3 feet and backfilled with non-expansive fill. We recommend that the final grading plans be reviewed, and that earthwork observation and testing be performed during construction to confirm that the native expansive materials are adequately buried and subdrains installed prior to placing engineered fill. 5.1.4 Potential for Liquefaction-Induced Settlements As discussed, southeastern and northeastern portions of the site that lie within or near the creek area and near the existing residential structures at the northeastern corner of the site are located within a State-designated liquefaction hazard zone. Structures or improvements to be located within or adjacent to these areas may need to be designed to tolerate or resist potential Ii! CORNERSTONE EARTH GROUP