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2013 inspection found holes in Fort Jackson dam that failed two years later

Federal inspectors found holes, broken equipment and “out-of-control’’ vegetation on a Fort Jackson dam two years before the earthen structure burst during a massive 2015 flood, according to a government report that provides new details about the dam’s condition.

The 2013 U.S. Army Corps of Engineers inspection report, obtained by The State newspaper, urged swift action to fix the Semmes Lake dam after federal officials said people could die if the dam failed.

Millions of dollars worth of property flooded and two people were killed downstream after the dam broke the morning of Oct. 4, 2015.

It remains unknown if Fort Jackson fixed the Semmes Lake dam after the 2013 report because Army officials won’t talk about the matter.

Fort Jackson officials plan to rebuild the dam, but they declined to say during a public hearing Wednesday why the dam broke in 2015. Base officials cited pending lawsuits as a reason for their silence.

Records show the Army made some improvements to the dam before 2009.

But Pete Strom, an attorney who is suing the government on behalf of downstream property owners, said details in the 2013 inspection report reinforce evidence the Army generally did a poor job overseeing the 76-year-old Semmes Lake dam.

“We are finding out what we hoped was not true,’’ Strom said. “All the evidence tends to lead to the conclusion that they did not maintain and repair the dam.’’

2013 inspection cited ‘serious’ issues

The Army Corps of Engineers’ inspection report gave the Semmes Lake dam a “serious’’ rating, one of the worst grades that can be assigned to a dam during an inspection. It is one of at least six dams on the Army training base that scored poorly in recent inspections, records show.

Emails obtained by The State last year showed Army inspectors had concerns about Semmes Lake and suspected deficiencies in the dam that contributed to it breaking. But the inspection report obtained by the newspaper provides the first details of the condition of the dam in 2013.

“Deficiencies were identified during the inspection that require immediate remedial action,’’ the Sept 10, 2013, inspection report says, noting improvements would upgrade “the condition of the dam and its capacity to operate safely for its current purpose.’’

The 2013 inspection report, which has 84 pages, gave bad grades to virtually every part of the dam that was examined. Among other things, the report found problems with the top of the dam, its side slopes and its spillway.

Asphalt on top of the dam had cracked and water appeared to be seeping out of the structure near an outlet, the report said. Inspectors also found medium to large voids — or holes — on the downstream slope of the Semmes Lake dam, evidence that animals had burrowed into the upstream slope of the dam, and signs of erosion on the upstream slope and at an outlet structure. In the latter case, the erosion was considered severe and may have contributed to seepage from the dam, the report said.

Holes and erosion on dams are a concern because they can weaken earthen structures and cause them to collapse, dam inspectors have said. In addition to animal burrows, trees and bushes also can cause weaknesses in dams because the roots create openings in the earthen structures.

The Corps of Engineers report noted numerous examples of trees and bushes growing out of the dam. In one spot on the downstream slope, the size and density of vegetation had increased since a 2009 inspection of the structure. The 2013 report said vegetation “can be considered out of control.’’

Problems not cited in 2009 inspection

Trees on a dam are a particular concern if they fall over, creating openings in the dam, said Mark Ogden, project manager at the Association of State Dam Safety Officials. Dam safety officials often recommend dams remain free of substantial vegetation other than grass.

“Typically, if a tree gets uprooted, that’s a serious concern,’’ Ogden said.

In addition to problems with erosion and weaknesses in the dam, inspectors also said a wheel used to control water levels in the lake was missing. The dam’s spillway, which sends excess water downstream to relieve pressure on the dam, also showed signs of weathering, the inspection report said.

Many of the problems noted by Corps of Engineers inspectors in 2013 were not identified in 2009 by inspectors from another division of the Corps, record show.

In 2009, for instance, inspectors said the dam’s outlet works appeared to be in good condition. But the 2013 report found a “clear seep coming from the right side of the outlet area.’’

The 2013 inspection was done by officials with the Corps’ Engineer Research and Development Center in Mississippi. The 2009 report was put together by the Corps’ Wilmington District office.

Dam 1 of 2 at fort that failed

The Semmes Lake dam was a 970-foot long structure built in 1940 to create a 29-acre reservoir on Fort Jackson. The lake has been used primarily for recreation and is one of many ponds on the military base.

The dam was one of two structures known to have failed on Fort Jackson during the morning of Oct. 4, 2015. When they breached during the storm, Semmes Lake and another pond, Lower Legion Lake, sent millions of gallons of water rushing down Wildcat Creek.

Property owners in the high-end King’s Grant neighborhood, next door to the base, have sued the government for damages. They claim flooding in their neighborhood resulted from the dam failures and caused up to $20 million in property losses.

After the dams failed, flooding also occurred in the Devine Street area downstream, where two people died when they drove cars into the rushing water.

But dam failures in other parts of Columbia, as well as torrential rain the morning of Oct 4, contributed to that flooding, experts have said. All told, more than 40 private dams failed in the Columbia area, including many in the Gills Creek watershed above Devine Street.

Parts of report blacked out

While the 2013 Corps of Engineers inspection report provides more details about the Semmes Lake dam’s condition, numerous pages of the document were blacked out by military officials.

Some sections of the report did not include any pages other than a cover page. The government is allowed to redact information from some types of reports, but it needs a reason.

The Corps refused to release the 2013 inspection report last year when it was sought by The State, saying information about Fort Jackson’s dams could be used by terrorists.

For Jackson officials have referred questions about the Semmes Lake dam failure to the U.S. Department of Justice, which is representing the Army in legal cases by downstream residents.

However, the Justice Department contact listed by Fort Jackson, legislative affairs advisor Karen Wilson, said she could not comment and referred questions to the department’s public information office. Attempts to reach a Justice Department spokesman were unsuccessful Friday.

Fort Jackson is proposing to reconstruct the Semmes Lake dam, with work starting in the fall of 2017. At a meeting to lay out the plans Wednesday, Fort Jackson and Corps officials said they want to build a stronger dam than the structure that failed in October 2015.

The Army has considered not rebuilding Semmes Lake but prefers a new dam to restore water to the lake for recreation.

A new lake also could store stormwater after heavy rains and help prevent an explosion of mosquitoes, which could occur if the lake bed returns to being a natural flood plain, according to the base.

Inspection cites weaknesses at Fort Jackson dam

Semmes Lake dam, which failed in the October 2015 flood, was inspected in 2013 by the Army Corps of Engineers. Here’s some of what inspectors found in 2013 showing potential weak spots in the structure:

▪  Animals had been burrowing in the dam.

▪  Water was seeping through the structure

▪  Erosion was occurring

▪  Voids, or holes, had formed

▪  Heavy vegetation was growing on parts of the structure

▪  Water control equipment was missing

SOURCE: Army Corps of Engineer report

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