Rich Ware, of Franklin Park, works the dredging machine for Dewatering Services in North Park.
By Len Barcousky Pittsburgh Post-Gazette
Visitors to North Park can expect to see some improvement in a popular fishing pond near Lake Shore Drive by this weekend.
Dennis Gold, the president of Dewatering Services, made that promise as work crews began to remove up to 15,000 cubic yards of silt from the small body of water.
The fishing-pond project is an effort by Dewatering Services to demonstrate that it can remove more than 60 times that much sediment from North Park Lake.
Allegheny County, which owns the park, is partnering up with the U.S. Army Corps of Engineers on a long-planned effort to restore the man-made lake to its original depth and size.
Dewatering Services says its patented technology can clear more than 70 years of soil and small gravel at lower cost and with less environmental damage than traditional dredging.
The company is doing the pilot project, which it values at more than $80,000, at no cost to the county. It hopes to win a maintenance contract for restoring the larger lake.
The county and the Army Corps of Engineers have budgeted almost $8 million for the lake project.
The company provided a demonstration of its process last Friday for about two dozen representatives of the county, environmental groups and people who live near the park.
The traditional method for underwater removal of materials involves "vacuuming" up a mix of water and solids, Mr. Gold said. That mixture can be as much as 90 percent water, he said.
On the other hand, the cutting head on his company's dredging machine buries itself under the surface and produces a denser slurry that contains a much higher proportion of sediment, he said.
After the material is pumped out of the lake, a food-grade polymer is added to the combination of silt and liquid, making it easier to remove water from the mix. The resulting paste-like material is then run between giant rollers that squeeze out much of the remaining moisture. The holding tanks and rollers used in the final stages of the process fill a 40-foot trailer.
The water is returned to the lake while the remaining damp solids, which have a texture similar to wet concrete, are pumped under pressure into large plastic bags. Those bags are being spread out along the shore. The bags will then be perforated to allow the material inside to dry completely. The area will later be leveled and reseeded.
The North Park Lake project would operate in a similar fashion, Mr. Gold said. Sediment from the lake, however, would be pumped about 11/2 miles to a former mine near Wildwood Road.
Pumping, rather than hauling away, the material will save the equivalent of thousands of dump-truck trips, he said.
Mr. Gold estimated that removing 4 feet to 6 feet of silt from the bottom of the 1.5-acre fishing pond will take two to three weeks.
The pilot project has the cautious support of the Allison Park Sportsmen's Club, the Friends of North Park and North Area Environmental Council.
"We are interested in seeing what Dewatering Services can do," said Gary Rigdon, a member of both Friends of North Park and the environmental council. "Everyone wants this project to succeed, but the proof will be in the pudding."
"I think this method is going to work," said Jim Rossmiller, president of the Allison Park Sportsmen's Club.
A dredging plan that does not require draining the lake for several years or transporting thousands of truckloads of sediment along narrow North Park roads would mean less environmental damage, he said.
North Park Lake, the largest body of water in Allegheny County, has lost about half of its original depth and shrunk from 75 acres to about 60 as the result of sedimentation from Pine Creek and the North Fork of Pine Creek.
The reduced depth has allowed water lilies and other aquatic plants to overwhelm large areas of the lake. The shallow water also has meant higher temperatures and reduced the numbers and types of fish in the lake.
Dredging began in 1980 but was abandoned when county officials realized silt was coming into the lake faster than workers could remove it.
"This is where I learned to fish in the 1940s," William Meyer, of Hampton, said. He had come to North Park to watch the Dewatering Services demonstration.
"When we lived in Shaler, I brought my kids here, and now I bring my grandchildren over to enjoy the park," he said. "I hope they can find a way to get this sediment out and to cut down on the new silt coming into the lake."