An earthen dam in Lexington County has sprung a leak and may threaten a dozen or more houses below it in a low-lying Irmo area flood plain.
The dam is what is called a “high hazard” dam, meaning that it could cause loss of human life or serious property damage if it fails, according to federal records and the S.C. Department of Health and Environmental Control. DHEC monitors about 2,400 dams around the state.
County emergency officials said Wednesday evening, however, the dam is now not likely to burst in such a way that would threaten the people who live below it.
Workers this morning were deepening the trench to increase drainage. The dam is still seeping water, but the seepage has declined as water levels in the pond have been drawn down, DHEC spokesman Thom Berry said Thursday.
“The water is now below the spillway, which is a good sign,’’ he said.
It was not known Thursday morning how much work would need to be done to repair the dam.
The 20-foot high, 300-foot long dam, built in 1950, holds back a 5-acre pond in the Coldstream area of Irmo, northwest of Columbia.
Occupants – some of them initially surprised and alarmed – of more than a dozen houses on Shadowood and Wildleaf courts have been alerted about the situation and advised to be ready to evacuate. They are below the dam.
“Lexington County Sheriff’s department went door-to-door to notify the residents and put them on standby so if we saw additional compromising of the dam, we could make the assumption that the structural integrity was threatened,” Collins said
To lower water pressure on the dam, county emergency workers Wednesday dug a spillway around the dam that lets more water out.
Lexington County emergency manager Thomas Collins characterized the leak as “fairly large.”
The houses lie along the bed of the stream whose flow the dam was meant to block. Today’s laws would prevent developers from building houses in low-lowing stream beds that could be subject to extreme flooding, Collins said.
Meanwhile, county fire officials were to check on the dam “every hour” from Wednesday night on into today to verify that the leak has not grown.
“If it continues to deteriorate, we will do a notification to the residents,” Collins said.
Even if the leak did grow, Collins said, the dam is made of clay and would normally not be expected to give way quickly. The leak is also at the top of the dam and is not in a place where it would cause a fast structure failure, he said.
“Of course, anything is possible, but we don’t expect it.”
The leak may have been caused by beavers gnawing at the dam, Collins said. “I have not been able to confirm that.”
In any case, he said, heavy rains have caused water behind the dam to build up in recent days. The spillway will help, Collins said.
“That will drop the water level tonight somewhere between 6-9 inches tonight,” Collins said. “We will come out in the morning and evaluate it.”
If needed, workers will release more water Thursday, Collins said.
“We will continue this process until we stop the water leaking out of the backside of the dam,” he said.
Workers on Wednesday also “did some compaction of the dam.”
Collins said the county became involved about 11:30 a.m. Wednesday when it got a call from DHEC.
“DHEC had been on the scene since last Thursday and been monitoring it,” Collins said.
DHEC had been notified by the Lake Nursery Hill Association, the group of homeowners in the community around the pond that the dam was leaking. The group also is the owner of the pond.
The dam is a long stone’s throw away from Nursery Road Elementary School, but the school is on an incline and not threatened, officials said.
Residents learned about the situation Wednesday afternoon.
A sheriff’s deputy knocked on Linda Morgan’s door on Wildleaf Court at about 4 p.m. to tell her about the leak. While officials had not ordered an evacuation, the deputy told Morgan to be prepared for the worst.
“She packed half the house and the car,” her husband, Stephen Morgan said. “She called me at work in a panic saying, ‘Quick! You’ve got to come home!’ But I went over there and talked to them and they seemed to have it under control.”
The Morgans have lived on Wildleaf Court since 1982. Stephen Morgan said they’ve never had an issue with the dam, though they had street flooding problems about five years ago. He said his house was probably the lowest point from the dam.
Officials had warned every person on Morgan’s street of a possible flood, and by 7 p.m. most of his neighbors were at his house eating pizza and drinking wine.
“We’re all discussing the impending doom,” he said.
Morgan said residents first noticed a hole in the dam about a week ago. They assumed it was from a beaver and contracted with a trapper to trap it. They even scheduled an association meeting for Sunday night to discuss how much it would cost to repair the hole.
DHEC spokesman Adam Myrick said his agency has been monitoring the dam since at least Monday. With plentiful rainfall expected in the next two days, Myrick urged pond owners to check dams to make sure they are working properly.
“This is the type of dam that is mainly out there, these earthen dams on private property,’’ he said. “It’s the responsibility of the dam owner to maintain the dam. We would urge anyone who owns a dam or has one on their property to keep an eye on it.”
At least 153 of the state’s more than 2,300 regulated dams are high hazard structures, the national Association of Dam Safety Officials reports. About 500 other dams are considered significant hazards, it says.
It was not immediately known Wednesday the last time the Lexington County dam was inspected by DHEC.
But it would be unusual for DHEC to have looked at the dam more often than every other year. The department doesn’t inspect most high hazard dams annually, agency officials say, because they don’t have the money. At best, the agency examines most high hazard dams every two years.
View Breach at the Lake Nursery Hill dam in a larger map