PC 03/14/79 - Laserfiche WebLink

indicated possible boundaries of a large block slide. The overlay was prepared by Bissell & Karn and shows the boundaries running through lots 3, 4, 5, 6 and 7 and going out of the proposed project. He stated borings were done by Gribaldo et al. He then showed this in his overlay for the Commission to see. The Moore and Tabor report indicated that should there be any movement it would be on the boundary lines. He stated borings shown on the overlay are not necessarily to scale but placed in an area where homes are currently built. He stated that the site specific reports have already been done (by somebody) -- He doesn't see any reason to do more prior to filing a tentative map. Mr. Maines said he asked for soils reports from the staff and individual property owners for lots 4, 5, 6, 7, 8 and 9. He said he received reports for lots 6 and 8 from the City and for lot 7 from Mr. McGovern, the owner of that lot. He said the sites are buildable according to all reports. He stated that on lot 6, there were three borings done by Dunnam. & Associates. He stated this ties into the Moore and Tabor geological report. He then read from the report. He stated on lot 7 the borings done encountered shale - 50-1". This indi- cated firm bedrock. Mr. Maines stated William Widdington, president of Engio Geologists and Don Bissell, of Bissell and Karn are present to answer any questions. Pat Jennings, a Longview Drive resident, inquired as to who owns lot 6? Dr. Long responded that Bruce Sasak owned the property. Mr. Widdington then addressed the Planning Commission stating he is a certified geologist and is prepared to answer any questions concerning the ridge. Commissioner Leppert asked Mr. Widdington to describe a block slide. He responded by saying it is something which moves in one piece. He stated that Burkland maintains this slide to be 5 miles long and several thousand feet wide. Commissioner Geppert asked Mr. Widdington how thick this slide would be. Mr. Widdington responded it would be 100-200 feet. Commissioner Geppert then asked if there was a movement, would the soil break up? Mr. Widdington responded it would move as one piece unless you address a 500 ft. movement. He then cited the Alaska movement of one-half mile. Commissioner Geppert asked if it is the nature of a landslide to move at a rapid rate? Mr. Widdington then explained the slide in Alaska as moving one-half mile in distance and these slides moved in blocks. He stated that if there was a slide in 100-200 ft. in solid bedrock he would not expect it to break up. Mr. Widdington stated that from 1769 to the present time he couldn't find any record of movement on the Pleasanton Ridge. He stated the U.C. Berkeley maps of 1906 didn't show any changes in the contours. 1861 records show ground movement doesn't exist. At the time of the Calaveras quake, 1769, there was no movement. Mr. Widdington stated this situation is similar to the Vallecitos situation with regard to extensive trenching and various geologists not arriving at any conclusions. He stated he doesn't feel that the geologists have taken conflicting positions when it comes to building this property. He stated that Moore and Tabor are cautious but no one has said it is unbuildable. Commissioner Wilson read from the Moore and Tabor Report and said he doesn't understand what it means -- "no known methods to evaluate the ancient slides." Mr. Widdington stated there are known methods, but it would take 10 years. -8-