South Fork Lost River
Flow Enhancement Geotechnical Investigation
Mendocino County, CA

 EBA prepared a Geotechnical Investigation Report for the South Fork Lost River Flow Enhancement Project, Tributary A, located in the upper reaches of the Mattole River watershed of northern Mendocino County, California.

This groundwater recharge project utilizes subsurface cutoff walls to retain wet season runoff for slow passive release during the dry season.

The purpose of EBA’s Geotechnical Investigation Report was to evaluate the soil and geologic conditions at the project site to provide geological conclusions, considerations, and recommendations for the design of the project.

The major geological considerations for the proposed project include:

• The stability and efficacy of proposed cutoff wall materials, including cement-bentonite and soil-bentonite backfill materials;
• Consideration of the hydrostatic forces imposed upon the cutoff wall due to the accumulation of groundwater;
• Recommendations for drainage improvement design measures to incorporate into the project to mitigate for potential issues due to the accumulation of excessive hydrostatic forces behind the proposed cutoff walls, and which may also be utilized to achieve project objectives if the project performance is deemed insufficient;
• Considerations of the effects of strong ground shaking from seismic events predicted during the life of the project on the proposed cutoff wall structures.