ITEM 23 ATTACHMENT 6 - Project Plans

December 21, 2022 Job No. 4031.101 Page 3 BERLOGAR STEVENS & ASSOCIATES BSA performed 2 Double Ring Infiltrometer Tests at the proposed drainage basin on July 22 and 25, 2022 and one Double Ring Infiltrometer Test was performed at the Park Site on July 26, 2022. The Infiltrometer Test results are presented in Appendix F. The Boring Logs and Test Pit Logs are presented in Appendices A and B, respectively. Boring Logs from BGC’s previous investigation are presented in Appendix C. 5. SITE CONDITIONS SURFACE CONDITIONS The rectangularly shaped project site is approximately 46.4 acres. The project site is bound by Foothill road on the west, I-680 on the east, and residential developments on the north and south. The site is currently developed with an existing residence located at the southwestern corner of the site adjacent to Foothill Road. The remainder of the site was previously used as a walnut orchard. The majority of the trees remain and have grown to maturity. An artificially made drainage ( unlined) is located along the southern property line. The existing residence is located at the highest portion of the site with an approximate elevation of 435 feet. The property slopes down to approximately elevation 378 feet. The remainder of the site is gently sloping from 378 feet to approximately 318 feet on the eastern portion of the site. SUBSURFACE CONDITIONS Materials encountered in our test pits and borings generally consisted of silty sands, silty clay. and sandy silts on the western portion and highly expansive clays on the eastern portion. The tree roots extended to depths between 3 to 4 feet. The soils in the upper 2 feet were generally loose/soft. This is likely a result of discing that has occurred in the orchard area. Below about 5 feet, soils become dense/stiff. Groundwater was not encountered in our test pits or borings. Previous borings by Harza Kaldveer encountered ground water at depths as shallow as 15 feet. Fill was encountered in our test pits on the southwestern knob. Fill was approximately 3 to 4 feet thick. The fill consisted of medium dense, dry silty sands. Fill was generally underlain by dry to moist, dense to very dense silty sands with gravel. The Site Plan shows the limits and depths of fill encountered. The Seismic Hazard Zone Report for the Dublin Quadrangle locates the site as having highest recorded groundwater levels between approximately 10 and 20 feet.