Bureau of Reclamation geologists, as part of an ongoing dam earthquake-safety program, will begin studying the embankment and foundation of the Pineview Dam later this month.
BOR Regional Geologist Fred Thompson said exploratory drilling and geologic mapping will help the federal agency locate and measure any loose sand or silt layer that may "liquify" during a strong quake.Thompson said geologic tests conducted before the earthen dam was built indicate there is "some layer (of silt or sand) down there, but we don't know if it's there or not. There may be a layer of soft material."
The tests are being done under provisions of the 1978 Safety of Dams Act. The law was enacted by Congress following Idaho's Teton Dam disaster June 5, 1976.
Pineview Dam was built in 1935-36 as part of the Ogden River Project and enlarged between 1955 and 1957 as a part of the Weber Basin Project.
Although the dam has proved stable, BOR officials are concerned what effect a sizable earthquake might have on the structure.
"The potential does exist because the Wasatch fault is considered an active fault," Thompson said.
The evaluation will take about six months to complete, and will include geologic and geophysical tests - including the drilling of shafts 200 feet deep - to determine the makeup and strength of the dam.
"We will be taking samples all the way to the bedrock," Thompson said.
Results of the tests are expected to be released next spring.
Any needed repairs will be paid for by the BOR, because it owns the dam.