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3. Environmental Checklist San Leandro Treatment Wetland IS/MND 3-33 February 2024 improvements involve soil mixing and cement stabilization to meet the required grade, impermeable liner installation, and support the weight of retained water and construction equipment like excavators or bulldozers. The existing basin may not adequately support the proposed developments without proper engineering to contemporary standards. However, the Proposed Project will adhere to construction specifications for soil and cement mixing prepared by a licensed geotechnical engineer, including specifications for site preparation and compaction requirements for the basin's base. It's crucial to note that the Project does not involve constructing buildings or structures. With the supervision of a licensed geotechnical engineer, earthwork activities will be managed to mitigate potential impacts associated with unstable soils, ensuring they are less than significant. The Proposed Project aims to enhance the stability of the existing basin, facilitating construction and operations without increasing the likelihood of on- or off-site hazards like landslides, subsidence, liquefaction, or collapse. Impact Designation: Less than Significant Impact d) Risks from expansive soil: soils with significant clay and silt content, often referred to as expansive soils, can undergo volume changes with variations in water content, leading to potential damage to structures built upon them. However, the Proposed Project does not involve the construction of any buildings or structures that would be susceptible to such soil movements. Moreover, the Project includes soil stabilization measures such as filling and cement mixing, along with installing an impermeable liner over the basin surface. These actions aim to stabilize the water content levels in the soils within the basin, effectively mitigating the risks associated with expansive soils. Therefore, the Proposed Project's approach would eliminate any potential impacts related to risks to life or property arising from changes in expansive soils, as no structures are being built, and the soil stabilization measures would prevent soil movement. Impact Designation: Less than Significant Impact e) Soils capable of supporting septic tanks or alternative wastewater disposal systems: While the Proposed Project forms part of the WPCP wastewater treatment train, it does not involve using septic tanks or alternative wastewater disposal methods. Consequently, there are no impacts related to supporting septic systems. Furthermore, the Project does not introduce additional wastewater contributions, and the lack of septic systems in its design eliminates potential environmental or infrastructure impacts associated with their installation, maintenance, or operation. Hence, the wastewater treatment approach of the Proposed Project negates the necessity for septic systems or alternative wastewater disposal, leading to no associated impacts. Impact Designation: No Impact f) Less than Significant Impact. Based on cultural resource studies conducted for the site (refer to Appendix F), historical maps and aerial images indicate that the Proposed Project site was previously submerged under the San Francisco Bay. Sea levels in the bay have remained relatively stable over the last 4,200 years, a period known as the Late Holocene. Before this period (> 4,200 years ago), the