PC-2026-15 - Laserfiche WebLink

330 Land Company, LLC Arroyo Lago 9785.004.001 Design-Level Geotechnical Report Page | 4 April 16, 2024 Latest Revision October 31, 2025 until it was used to backfill Busch Pit in 2013. The approximate extent of the stockpile is shown in Figures 2A, 2B, and 2C. From November 2018 to November 2019, rough grading of the overall site occurred under the testing and observation of Haley & Aldrich, encompassing both the Busch Pit and northern pit areas according to the final testing and observation report provided by Haley & Aldrich dated December 12, 2019. Up to approximately 2½ feet of fill was placed and 2 feet of cut was excavated to achieve current grades. The extent of the rough grading activities is shown in Figures 2A, 2B, and 2C. In 2023, an emergency drainage swale was constructed on the project site. The swale begins in the northwestern corner of the site and ties into an existing drainage swale at the southeastern project boundary. The swale has a base width of approximately 4 feet and at a 4:1 slope. 2.2 EXISTING AND NEARBY GEOTECHNICAL DATA In 2006 and 2009, Treadwell & Rollo performed a geotechnical investigation throughout the greater EPSP site. The explorations within the site boundary included one hollow-stem auger boring drilled to a depth of 100 feet bgs and four cone penetration tests (CPTs) advanced to depths ranging from approximately 45 feet to 99 feet bgs. The logs and associated laboratory test results from the Treadwell & Rollo investigation are presented in Appendix E. The approximate locations of the previous explorations are shown in Figures 2A, 2B, and 2C. In 2013, Haley & Aldrich tested and observed the placement and compaction of backfill for Busch Pit reportedly in accordance with SMP-31. A subsequent preliminary geotechnical report was prepared by Haley & Aldrich in 2017, providing preliminary discussion on subsurface conditions and seismic hazards. No additional subsurface investigation was included as a part of their scope. Between November 2018 and November 2019, Haley & Aldrich tested and observed the rough grading activities for the overall site in general conformance with rough grading plans prepared by Kier and Wright. Up to 2½ feet of fill was placed and 2 feet of cut was performed. A drainage swale was also constructed to facilitate drainage from the northern portion of the site to an off-site culvert to the east of the site. ENGEO performed field explorations at the site as part of our preliminary geotechnical study in 2023. We retained a CPT rig in November 2022 to advance five CPTs to a maximum depth of 162½ feet bgs. The CPT contractor performed pore pressure dissipation (PPD) tests to measure piezometric water pressure in each CPT at various depths and collected seismic shear -wave velocity (VS) measurements in one of the CPT using the downhole seismic method specified in ASTM D7400. As part of our 2023 preliminary geotechnical study, we also retained the services of a contractor to excavate test pits from 10 to 10½ feet bgs. We observed the test pit excavation and logged the subsurface conditions at each location. The location of the CPTs and test pits are shown in Figure 2, with logs from both explorations presented in Appendix D.