Grant Lake Outlet Valve Replacement Geotechnical Evaluation

The Los Angeles Department of Water and Power is initiating a geotechnical investigation to support the planning and design for the replacement of a malfunctioning outlet valve and the outlet tunnel gate at Grant Lake in California. The project focuses on understanding the geomorphology of the area through the use of sonic drilling methods, which are suitable for various soil types including sands, gravels, glacial tills, and bedrock. The scope of work includes a total of 14 sonic borings, with two conducted over the reservoir via barge or watercraft and twelve located along the dam access road and west of the existing shaft and shaft house. Additionally, two of these borings may be converted into groundwater monitoring wells, and all drill cuttings must be drummed and disposed of properly offsite. The project is categorized as a forecast under NAICS code 541360 and is exempt from California Environmental Quality Act review under Section 15306, Class 6, as it involves basic data collection and resource evaluation. The borehole drilling process is estimated to take place from September 2026 through the end of November 2026. Primary administrative oversight is provided by Environmental Specialist Marshall Cyr and Environmental Planning and Assessment Manager Jane Hauptman.