Owens Lake Dust Control Phases I-V & VII
Inyo County, California
Scope of Work:
- Geotechnical Evaluation
- Lakebed Sediment Logging/Sampling
- Field Hydraulic Conductivity Testing
- Geophysical Services
- Laboratory Testing
- Geologic & Engineering Analyses
- Design Recommendations
- Written Reports
Ninyo & Moore performed geotechnical evaluations relative to the dust mitigation measures currently being implemented by the Los Angeles Department of Water and Power (LADWP) at Owens Lake. Owens Lake, located at the eastern side of the Sierra Nevada, is a mostly dry lake covering approximately 108 square miles. During the early 1900's, the rivers and streams that fed the lake were diverted into the Los Angeles Aqueduct and the lake level began to drop rapidly. The current surface of the lake consists of a mixture of clay and sand, and a variety of minerals. Prior to implementation of the LADWP dust mitigation measures, periodic winds on the lake produced harmful alkali dust storms that carried dust from the surface of the lakebed to nearby residents, causing respiratory problems. The construction and implementation of the LADWP dust mitigation measures were performed in multiple phases over the course of several years.
Project Challenge: Ninyo & Moore's task was to explore the subsurface conditions to provide geotechnical information for use by the design/build contractor for the design and construction of the dust mitigation measures. Due to the wet, soft, clayey soil conditions of the dry lakebed, access to the exploration locations was a challenge requiring the use of a 4-wheel drive, all terrain drill rig and track-mounted excavators. Exploration sites were located in the field using GPS technology. Due to the presence of sensitive biological habitats, access to the exploration locations required coordination among various agencies, including LADWP, Great Basin Unified Air Pollution Control District, and the Department of Fish and Game. Specialized field equipment to measure the hydraulic conductivity of the groundwater and portable geophysical equipment to measure electrical resistivity of the soils had to be transported to remote areas of the lake by all terrain vehicles.
Innovative Solution: The dust mitigation measures that Ninyo & Moore provided services for included the design and construction of approximately 27 square miles of shallow flooding. The shallow flooding was comprised of an extensive system of water supply piping, berms for shallow flooding and deep pond areas, a vast array of bubblers used to apply water to the lakebed surface, a network of subsurface drain lines, several groundwater pumping stations, and over 100 miles of access roads. The mitigation measures also included approximately 3.5 square miles of managed vegetation for dust control. The vegetation consists of saltgrass, which is a native grass that is tolerant to high salt concentrations present in the lake sediments.
Services: Ninyo & Moore's services included geologic logging and sampling of 270 borings and 190 test pits, in-situ hydraulic conductivity tests, and field resistivity tests in remote locations of the dry lakebed. Extensive testing of the soil samples obtained from the borings and test pits was performed by our geotechnical laboratory, including Atterberg Limits, corrosivity, consolidation potential, direct shear, expansion index, gradation, Proctor density, organic matter content, R-value, specific gravity, unconfined and triaxial compression, and constant head permeability. Geotechnical data reports were prepared on-time and within budget for each phase of the project.