AGENDA 21 RADIO

BY CHRISS STREET

Given that Oroville Dam annual inspections found water “seepage” on the face of the dam and have warned about potential structural steel failures since 2014, a safety expert projects that the cost to rehabilitate that dam would be about $600 billion.

Breitbart News obtained the Oroville Dam’s annual ‘Inspection of Dam and Reservoir in Certified Status’ by State of California Division of Safety of Dam for the years 2014, 2015 and 2016 and forwarded the reports to Scott Cahill, widely published dam safety expert.

According to the September 18, 2014 inspection report, Oroville Dam had water seepage issues on the face of America’s tallest dam that that were described as a “long established wet area at the mid-slope of the left end of the dam.” Although the area was dry in 2014 due to drought, inspectors only approved “interim use” of the dam based on the implementation of a long term monitoring of the “phreatic surface within the dam.”

Inspectors also commented that the cracking around the cement seams at the gates on top of Oroville Dam’s main spillway were a serious concern because “tendon anchors are about 50-year old and could experience problems in the future based on the history of tendon breakage at dams of similar age and construction.”
Listen to the interview of Scott Cahill and Chriss Street regarding the Oroville Dam Inspection documents.

According to Scott Cahill the reports indicate dam seepage means that the phreatic line of the top of the ground water table has been leaking through or around the supposedly impervious clay core, chimney drain, internal barrier cut-off wall, and reaching high up on downstream face.

Although the Division of Safety of Dams did not detail in 2014 why the face of Oroville Dam had a long term history of suffering from seepage, the International Water Power and Dam Construction Magazine in a 2008 article titled, ‘Dangers at Embankment Dam Boundaries and Embedments,’ pointed to Oroville Dam as the text book example of issues associated with stress cracking within an earthen dam’s internal water barrier.

According to the article, during 1960s construction, a 900 foot long and 120 foot high concrete block wall was built on the dam’s rock foundation as a water barrier. But the “thrust” pressure as a sloping dirt wall was piled up to a height of 770 feet, caused rotation in the concrete cut-off wall. As a result, longitudinal cracking developed in the top 50 feet of the barrier block wall, which was only made of unreinforced concrete.

Scott Cahill calls attention to the “block and longitudinal cracking with openings of several inches” in the cut-off wall that was observed during construction. He is surprised that the barrier wall cracks and joints were only sealed by “injection of cement grout.” Normally, the type of serious issue would be addressed by the construction of a secondary wall. Instrumentation available at the time, deemed the repairs as “successful.”

The State of California Division of Safety of Dams 2015 inspection again only approved the Oroville Dam for “interim use,” subject to a number serious concerns being addressed. The report again stated concerns regarding seepage, but added that there are numerous cracks on the top of the Oroville Dam’s spillway and cracking in the pillars and construction joints of the dam’s water release gates that may be associated with the 1975 5.7 magnitude Oroville Earthquake. The report for the first time also suggests that the high-tensile structural steel anchor tendons “may be approaching the end of their useful life.”

Scott Cahill noted that 2015 report does indicate that a number of the 2014 inspection’s concerns had been addressed at all.

The Division of Safety of Dam’s 2016 inspection gave Oroville Dam another “interim use” approval, based on the same concerns as the 2015 report. But the Board of Safety of Dams specifically “expressed concern” about the risk of tendon anchors breaking due to age and stated that they “will make strong recommendations about the need to carefully monitor and test the tendons using the latest tools.”

Cahill states that some testing was completed in August 2016, but that the report acknowledge the engineering analysis may not be completed for up to a year.

Based on the reports, Scott Hill expects that corrective actions at a minimum would require a complete rebuild of the spillway, water gates and the resurfacing of the emergency spillway. But the real issue may be the risk of earthquake that could cause liquefaction of the soil on the embankment and result in the face of the dam collapsing.

Cahill believes the dam can be repaired, but it require at least $50 million to drill holes and inject grout into the dam, $300 million for the spillway, $50 million for the water gate replacement, and $200 million to cement and anchor the emergency spillway.

Breitbart News contacted the California Division of Safety of Dams to request interviews with the dam inspectors and copies of any follow-up reports regarding the 2014, 2015 and 2016 inspections of Oroville Dam. The DSOD stated that each questions or document request would require filing Freedom of Information Act request in writing.