PC-2026-15 - Laserfiche WebLink

330 Land Company, LLC Arroyo Lago 9785.004.001 Design-Level Geotechnical Report Page | 7 April 16, 2024 Latest Revision October 31, 2025 Soil Classification System. The logs graphically depict the subsurface conditions encountered at the time of the exploration. 2.5.1 Existing Fill Existing fill was encountered up to at least 101½ feet bgs in our current exploration, and up to 162½ feet bgs in our prior explorations. Three of the four borings of our current explorations terminated in the fill layer prior to encountering native material. The fill material encountered in our borings generally consisted of stiff to hard sandy lean clay with varying amounts of fine gravel and sand, with interbedded silty and clayey sand layers with varying amounts of gravel. According to the SMP-31 application, the quarry slopes were graded to ¾:1 (horizontal:vertical) on the northern side of the pit and 1:1 on the western and southern sides of the pit prior to fill placement. The excavation depth ranged between 128 and 130 feet below existing grade. We are unaware of documentation detailing the fill specifications or operations that could verify that the fill was placed in conformance with the SMP-31 application. The clayey fill generally has a low to high plasticity, with plasticity indexes between 9 and 32. Debris was not observed in our current or previous explorations; however, debris may be encountered in locations not sampled given the site history and variability in fill placement. Moisture content tests from previous and current explorations within the site range between 7.9 to 18.6 percent, which is generally lower than the typical range of moisture contents encountered in the larger EPSP site and similar to a typical moisture content range for native soil or engineered fill. Similarly, dry unit weight tests from our current explorations range between 111.6 and 130.8 pounds per cubic foot (pcf), similar to a typical unit weight range for engineered fill. 2.5.2 Engineered Fill (Busch Pit) As described in Section 2.2, fill was placed and compacted under the observation of Haley & Aldrich up to approximately 70 feet bgs. According to documented fill placement and compaction records, the fill generally consists of brown sandy lean clay from site and import sources compacted to at least 90 percent relative compaction. No moisture content specification was recommended for soil placement. 2.5.3 Floodplain Deposits Floodplain deposits were interpreted as directly underlying the existing fill in both areas, and generally consist of dense to very dense clayey sand and gravel and stiff to very stiff lean clay. Boring 1-B3 encountered a dense to very dense clayey gravel layer from 88 feet bgs to termination depth at 101½ feet bgs. 2.6 GROUNDWATER CONDITIONS Static groundwater was estimated at approximately 45 feet bgs in 1-CPT2 according to pore pressure dissipation tests. Groundwater was not recorded in prior subsurface explorations. Plate 1.2 of the Seismic Hazard Zone Report for the Livermore Quadrangle (2008) maps the highest historical groundwater within the site vicinity to be approximately between 60 to 70 feet bgs.