The freshwater clams will be happy.
By the end of this year the last commercial dredging company operating on the Allegheny River will scoop its last industrial-sized bucket of Ice Age-old aggregate from that flow, ending a century-old practice that in recent years has raised myriad environmental concerns.
Hanson Aggregates, a subsidiary of HeidelbergCement, the world's largest aggregates producer, confirmed last week that it plans to pull its only barge-mounted crane shovel from the Allegheny, where it's scraping the publicly owned river bottom in Pool 5, about 31 miles from Pittsburgh's Point.
The decision will end the "mining" of sand and gravel from the Allegheny River for commercial sale and use in road and building construction, although Hanson and another commercial dredger, Tri-State River Products Inc. of Beaver, will continue dredge barge operations in the Ohio River. Hanson will also continue to operate its land-based quarries for crushed rock.
"We're going to be winding down our Allegheny River operations and the equipment will either be redeployed or sold," said Jeff Sieg, a Hanson spokesman based in Houston, Texas. "Our permits are expiring in the Allegheny at the end of the year, and at this point we don't see any more economically viable areas to do that work in that river."
Part of Hanson's economic calculations involve the cost of complying with environmental rules that restrict commercial dredging to limited areas of the river to protect rare freshwater mussels, clams, darters and shallow, native fish habitat.
"There are certain areas of the river that we can't mine and other areas that if we do want to mine we must do so in an environmentally responsible way," Mr. Sieg said. "That's part of the economics. The environment is certainly a piece of that."
Hanson holds the lone permit on the Allegheny, issued by the state Department of Environmental Protection, which allows it to operate only in Pool 5, from river mile 30.7 to 31.7.
Myron Arnowitt, state director for Clean Water Action, an environmental group that has opposed dredging for two decades, welcomed the decision to end commercial dredging on the Allegheny River.
"We're glad to see there will not be further mining of aggregate from the river and hope the damage done to the river can be fixed and the river restored in the future," Mr. Arnowitt said.
Retreating glaciers dropped large deposits of rock, gravel and sand in Western Pennsylvania after the last Ice Age, and commercial dredgers began scooping up those moraine deposits more than a century ago, first the sand for glass making and, since the 1950s, the rock, gravel and sand for road and building construction. The harder glacial rock is valued by state road builders for its durability and skid resistance properties.
But by the 1990s, federal and state studies began to show increased environmental impacts from river dredging, including erosion of riverbanks and islands, increased siltation and sedimentation, damage to fragile freshwater mussel and clam beds, degradation and destruction of shallow water fish habitats and depletion of dissolved oxygen in dredge holes up to 60 feet deep. Commercial dredging is different than the shallower navigational dredging done to keep the river channels deep enough for industrial barge transportation.
The aggregates industry, which once pulled 4 million tons of sand and gravel from the rivers a year, has questioned the study findings, denied it caused those problems in the rivers and fought state and federal regulation.
But the amount of the publicly owned river bottoms available for dredging has continued to shrink. By 2006, the number of commercial dredgers had fallen to three and environmental concerns had restricted the scooping sand and gravel to a 100-mile stretch of rivers, that included Pools 4, 5, 7 and 8 on the Allegheny, from Harrison in Allegheny County to Washington Township in Armstrong County, and on the Ohio River in the Montgomery and New Cumberland pools, between Baden and Midland in Beaver County.
State dredging permits issued in 2006 required companies for the first time to conduct mussel and fish surveys, study water quality and fund habitat restoration programs. In 2009 the state Fish and Boat Commission decided not to follow the recommendations of its biologists and list two river mussel species, the salamander and rayed bean, as endangered and threatened, but the dredgers were required to accommodate them when they were found in permitted dredging areas.
"I think some of the environmental restrictions probably helped companies think about phasing out their operations," Mr. Arnowitt said. "The limitations helped protect some areas of the river, and now ending dredging is going to be the best thing for the river."
The retreat of commercial dredging is reflected in the sand and gravel production numbers reported by the DEP, which show sand and gravel pulled from the rivers totaled 2.8 million tons in 2006 and fell steadily in subsequent years. In 2011, the last year for which production totals were provided by the DEP, river aggregate tonnage totaled 1.2 million tons.mobilehome - region - environment
Don Hopey: email@example.com or 412-263-1983. First Published June 16, 2013 4:00 AM