15 ATTACHMENT 9 - Laserfiche WebLink

Project No. 9929.G Response to Peer Review/1630 Vineyard Ave., Pleasanton, CA 12 March 2007 Estate Lot Cut Slope Evaluation As stated in Reference 1, the upper estate lot was not accessible for a drill rig to advance a 50 foot boring due to the steep terrain. Several attempts with several limited access drill rigs were unsuccessful in accessing the top of the hill. Upon discussion with Alan Kropp of AKA, advancing test pits were acceptable to initially evaluate this lot. On May 17, 2004, a TERRASEARCH, inc. Geologist excavated three test .pits (TP-3, TP-4, and TP-5) at the approximate locations shown in Figure 1. The test pits revealed the bedrock material observed along the upper ridge was an interbedded sandy .gravel, coarse sand, silty clay, clayey silt, and sandy silt, of the Livermore Gravel formation. The strike and dip of bedding was distinctly observed within test pit 3 and a strike and dip of N 15 W/ 14NE was measured. The cut slope is proposed to be inclined at 2.7:1 to 3:1 (horizontal:vertical) and oriented approximately east-west. Due to bedrock orientation and the low relative angle between the cut slope and the natural bedding angle, the chance of gross or surficial slope instability is very Iow. During heavy precipitation some erosion may occur, but given the proposed inclination of the slope, the likelihood is considered low. Based on the data obtained, it is our preliminary opinion that the proposed cut slope inclination is acceptable from a stability point of view. At this time specific comments with respect to erosion or sloughing is not possible until an additional boring is advanced or the exposed slope is observed during grading. If a boring or observations during grading show the slope to have some potential for erosion, a retention wall, slope erosion protection methods, or an increased structure set back from the toe of slope are acceptable mitigation methods. Based on our observations and measurements, it is the opinion of TERRASEARCH, inc. that the construction of a new residence on the proposed graded pad is feasible. We recommend the cut slope area be further evaluated either by drilling a 50-foot borehole when an access road is provided or to evaluate the slope during the grading process and determine if any mitigation of the slope is needed.