Tinemaha Dam Geotechnical Field Investigation - Phase 2A and 2B
Summary
SCH Number
2023090232
Public Agency
Los Angeles Department of Water and Power
Document Title
Tinemaha Dam Geotechnical Field Investigation - Phase 2A and 2B
Document Type
NOE - Notice of Exemption
Received
Posted
9/12/2023
Document Description
LADWP proposes to conduct geotechnical explorations to investigate the existing conditions of the area surrounding and encompassing the Tinemaha Dam and reservoir. Built in the 1920s, there are several safety issues with the dam and appurtenant works which will eventually require replacement to resolve. The proposed field investigation will be used to inform how the dam will be replaced as a future project and would be comprised of drilling approximately 124 borings/test points split into two sequential phases, Phase 2A and Phase 2B.
Phase 2A of geotechnical explorations focuses in the upland areas of Tinemaha Dam, specifically with the drilling and/or testing of approximately half of the borings/test points to further characterize the geotechnical and geologic conditions at the site. The investigation will include the following: mud rotary borings to investigate the soil and bedrock properties for design of the proposed dam, outlet works structures, spillway, and river diversion structures; cone penetration testing along the potential dam alignment and outlet works to investigate foundation soil properties; hollow stem auger borings along the existing dam alignment to provide data on the embankment soils for re-use as fill for the new dam; and core borings to investigate the bedrock properties at the dam abutments, outlet works, auxiliary outlet, and coarse material borrow site.
Phase 2B would be conducted after the completion of Phase 2A, outside of nesting bird season, and includes work within the reservoir, adjacent shoreline, and possible wetlands. These geotechnical investigations are comprised of the drilling of the remaining borings and will include the following: vibracore borings within the reservoir to investigate soil properties for potential use as dam embankment fill, additional mud rotary borings to investigate the soil and bedrock properties, and core borings to further investigate the bedrock properties.
The mud rotary borings, hollow stem auger borings, and core borings are approximately 8 inches in diameter while the vibracore borings and cone penetration tests are 3-4 inches in diameter. The mud rotary and core borings will be backfilled to the ground surface or reservoir bottom elevation immediately upon completion of drilling and/or testing. The vibracore borings collapse when the core is removed so backfilling is unnecessary.
Contact Information
Name
Jazmin Martin
Agency Name
Los Angeles Department of Water and Power
Job Title
Environmental Specialist
Contact Types
Lead/Public Agency
Phone
Email
Location
Counties
Inyo
Regions
Southern California
State Highways
395
Waterways
Owens River
Other Location Info
Tinemaha Dam is located in Inyo County, situated on the Owens River approximately 8 miles south of Big Pine, California.
Notice of Exemption
Exempt Status
Categorical Exemption
Type, Section or Code
Section 15306, Information Collection
Reasons for Exemption
Section 15306, Information Collection - Class 6 consists of basic data collection, research, experimental management, and resource evaluation activities which do not result in a serious or major disturbance to an environmental resource. These may be strictly for information gathering purposes, or as part of a study leading to an action which a public agency has not yet approved, adopted, or funded.
County Clerk
Inyo
Attachments
Notice of Exemption
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