15 ATTACHMENT 9 - Laserfiche WebLink

Page 2 1696-16 orientations in Test Pit #2, is consistent with the gross overall structure of the Livermore Gravel, suggesting absence of rotation within a landslide mass. Therefore, our review of the supplemental test pits within the mapped portion of the landslide on the property (Nilsen et al., 1975) indicates the test pits provide positive evidence for the absence of active landsliding adjacent to the access road in the southeastern portion of the property. Estate lot cutslope Proposed grading for the hilltop estate lot consists of a significant cut up to 40 feet high. As stated on Page 17 of the initial Terrasearch report, "...the subsurface material that will form the SO foot cutslope planned for the estate lot is not known, but is anticipated to be Livermore Gravel bedrock material and the cutslope is expected to be preliminarily stable at an inclination of 2.75:1. This will be confirmed during grading or prior to grading when access for a drill rig is available." The supplemental report does not refine or describe the proposed height of the cutslope but does provide the orientation (east-west) and inclination (2.7:1 to 3:1, shallower than originally estimated). In addition, the supplemental report provides additional information in the vicinity of the proposed grading, including three test pits with bedding information obtained within Test Pit #3. The bedding orientation within the test pit is consistent with the shallow dip of the Livermore Gravel, as mapped by previous investigators. However, we still believe that more information is necessary on the height and possible stability of the proposed cut slope. We agree with the opinion expressed in the supplemental report by Terraseazch that recommends that either a boring be completed at the site to a depth greater than the proposed cut when an access road is constructed to determine whether mitigation of the slope is required or that the bedding orientation within the Livermore Gravel (assuming that bedrock at the estate site is Livermore Gravel) be more fully characterized and documented during grading. Appropriate erosion control and other possible mitigation controls may be required on the basis of the requested boring and/or observations during grading. Given the supplemental geotechnical information provided in the supplemental report, including the five additional test pits, and adoption of the recommendations by Terraseazch for either a 50-ft boring when an access road is provided and/or evaluation during grading for the proposed cutslope, we believe that our concerns as stated in our review letter are sufficiently addressed. However, we recommend that a representative of our firm make observations during grading of the estate lot to confum the geologic structure exposed is compatible with the recommendations made by Terraseazch Stock pond In the March 12, 2007 letter by Terrasearch, it is indicated the final grading plans for the lower lots have not been prepared. Terrasearch provides recommendations "should the pond be removed." Since there is no indication the pond embankment and associated improvements were engineered, we recommend all portions of the pond area be removed and re-established in accordance with the Terrasearch recommendations. In summary, it is our opinion the supplemental information provided by Terrasearch conforms to generally accepted geotechnicaUgeologic principles and practices. We should be provided an opportunity to review the final gradings for the lower lots, when they are prepazcd, and make observations during the grading of the estate lot. The opinions and conclusions presented in the letter are provided in accordance with generally accepted geotechnicaUgeologic principles and practices. No other warranties, expressed or implied, are made. Our services have been provided at the request of the City of Pleasanton. Our role has been to provide technical assistance to the City as it considers its permit decisions in this application and we understand our firm is provided the same protection as the City under state law. .'-~IL.r~N KR~PP