Post by L Roebuck on Nov 5, 2005 7:53:23 GMT -5
Woodbury's amazing disappearing pond
Kevin Giles, Star Tribune
Last update: November 4, 2005 at 10:28 PM
Where a large pond once sat, there's now a large sinkhole. City officials in Woodbury are working on the problem, which apparently was touched off by the huge downpour.
A few days after the rain came in buckets to Woodbury, 22 million gallons of water disappeared from a huge stormwater pond at a housing development.
Four weeks later, the mystery remains: What became of Dancing Waters Lake, which swirled away as if draining from a bathtub?
Bill Roth wonders. On Friday he stood at the edge of the massive lake bed across the street from his daughter's new house, pointing to a sinkhole at the bottom.
"There's going to have to be some resolution" to the problem, said Roth, of Lake Elmo. "They can't leave it open."
Steve Kernick, the city's environmental planner, is looking for a solution. He said that testing at more than 30 private wells a mile or so from the sinkhole showed no pollution, but he now wonders whether sinkholes might develop in other holding ponds in construction-busy Woodbury, one of the fastest-growing cities in Minnesota.
No homes are in danger of collapse, Kernick said, but Roth wonders about the crack that appeared in the foundation of his daughter's house at the same time the water disappeared.
Kernick said the sinkhole is 103 feet long, 63 feet wide and 15 feet deep, although the fractures at the bottom run to an undetermined depth. "It's got some sheer drops to it," he said.
A University of Minnesota geology professor, Calvin Alexander, said he has counted other sinkholes in the vicinity of the large one. Another geologist who inspected the sinkhole, Bob Tipping of the Minnesota Geological Survey, said it's a big one; he described the process this way: "Something similar to clogged plumbing becoming unclogged."
Kernick said a bulldozer operator working near the pond in the Beechwood section of the Dancing Waters development saw a whirlpool a few days after heavy rain fell in October. Eight hours later, the water was gone.
Tipping offers this likely explanation: The last glacier that moved through the metro area 10,000 years ago left a valley that runs from Lake Elmo, north of Woodbury in Washington County, to the Mississippi River. That valley, now buried, is full of fractures, joints and caves. The valley is just west of the holding pond that drained.
Below the pond is a bed of soft white sandstone, the same kind that's found in the caves along the river in St. Paul. Known as St. Peter sandstone, the bed runs underneath the metro area like a "sort of a layer cake," although it's been eroded away in some places. In the stormwater pond, the water's weight after the big rain flushed sediment that had clogged fissures in the sandstone. That's when the whirlpool occurred.
Within a few weeks, the city plans to map the bedrock to determine the size of the fissure. Then it will be sealed with concrete, clay or a plastic liner. In the meantime, the city built a dike to divert the water from the hole. And they want people to keep away for safety's sake.
The pond was built to collect water from several areas of the Dancing Waters development, Kernick said.
Paul Heuer, vice president of development for Laurent Development Co., declined to comment Friday except to say that "the city's handling this and we're working jointly on solutions."
Kernick said housing developers will have to assume the expense of bedrock testing.
"In the future we have to be careful where we locate these ponds," he said.
Kevin Giles • 612-673-7707
www.startribune.com/stories/462/5709646.html
Kevin Giles, Star Tribune
Last update: November 4, 2005 at 10:28 PM
Where a large pond once sat, there's now a large sinkhole. City officials in Woodbury are working on the problem, which apparently was touched off by the huge downpour.
A few days after the rain came in buckets to Woodbury, 22 million gallons of water disappeared from a huge stormwater pond at a housing development.
Four weeks later, the mystery remains: What became of Dancing Waters Lake, which swirled away as if draining from a bathtub?
Bill Roth wonders. On Friday he stood at the edge of the massive lake bed across the street from his daughter's new house, pointing to a sinkhole at the bottom.
"There's going to have to be some resolution" to the problem, said Roth, of Lake Elmo. "They can't leave it open."
Steve Kernick, the city's environmental planner, is looking for a solution. He said that testing at more than 30 private wells a mile or so from the sinkhole showed no pollution, but he now wonders whether sinkholes might develop in other holding ponds in construction-busy Woodbury, one of the fastest-growing cities in Minnesota.
No homes are in danger of collapse, Kernick said, but Roth wonders about the crack that appeared in the foundation of his daughter's house at the same time the water disappeared.
Kernick said the sinkhole is 103 feet long, 63 feet wide and 15 feet deep, although the fractures at the bottom run to an undetermined depth. "It's got some sheer drops to it," he said.
A University of Minnesota geology professor, Calvin Alexander, said he has counted other sinkholes in the vicinity of the large one. Another geologist who inspected the sinkhole, Bob Tipping of the Minnesota Geological Survey, said it's a big one; he described the process this way: "Something similar to clogged plumbing becoming unclogged."
Kernick said a bulldozer operator working near the pond in the Beechwood section of the Dancing Waters development saw a whirlpool a few days after heavy rain fell in October. Eight hours later, the water was gone.
Tipping offers this likely explanation: The last glacier that moved through the metro area 10,000 years ago left a valley that runs from Lake Elmo, north of Woodbury in Washington County, to the Mississippi River. That valley, now buried, is full of fractures, joints and caves. The valley is just west of the holding pond that drained.
Below the pond is a bed of soft white sandstone, the same kind that's found in the caves along the river in St. Paul. Known as St. Peter sandstone, the bed runs underneath the metro area like a "sort of a layer cake," although it's been eroded away in some places. In the stormwater pond, the water's weight after the big rain flushed sediment that had clogged fissures in the sandstone. That's when the whirlpool occurred.
Within a few weeks, the city plans to map the bedrock to determine the size of the fissure. Then it will be sealed with concrete, clay or a plastic liner. In the meantime, the city built a dike to divert the water from the hole. And they want people to keep away for safety's sake.
The pond was built to collect water from several areas of the Dancing Waters development, Kernick said.
Paul Heuer, vice president of development for Laurent Development Co., declined to comment Friday except to say that "the city's handling this and we're working jointly on solutions."
Kernick said housing developers will have to assume the expense of bedrock testing.
"In the future we have to be careful where we locate these ponds," he said.
Kevin Giles • 612-673-7707
www.startribune.com/stories/462/5709646.html