Too much water or not enough?
Sinking homes linked to excavations for new sewer lines
Updated: 09/29/07 8:04 AM

Gary Wright steered his riding mower toward the pond behind his home on Old Goodrich Road in Clarence. It was May, and the dandelions needed mowing.

Moments later, Wright was shocked to see that his 150-foot-wide trout pond, which a day before had been overflowing with the spring runoff, was almost empty.

“My 12-foot-deep pond was approximately 4 feet deep,” Wright said.

Looking beyond the pond, Wright noticed a construction crew with a large yellow excavator digging a trench for a new sewer line.

“They had pumps running, and there was water pumping all over,” he said. “I knew immediately what had happened.”

What happened was a sudden drop in the water table, causing Wright’s pond and others to lose water, including two ponds outside Clarence Town Hall.

Before long, Wright and his neighbors began reporting new cracks in their foundations. Then a large crack opened in the floor of the town’s new library. Sink holes appeared in lawns and driveways.

Three years have passed since then, but the ponds have not returned to their original depths. Clarence officials reject claims that these events were related to the sewer construction, and they released a copy of a hydrological report that they say backs up their position. But some experts say what happened to the Clarence ponds is not just related to the sewer incident; it could shed new light on why nearby Amherst’s homes are sinking and explain the dangers of development in areas with unsuitable soils.

‘Check dams’ help

A state Department of Environmental Conservation investigation found that sewer contractor Anthony Cimato violated five regulations when he was building the Clarence sewer line in 2004, including using improper fill material for the dams along the sewer line.

Cimato was fined $15,000 and agreed to fix the problem by properly installing “check dams,” which restrict the flow of groundwater.

Contractors usually bed sewer pipes in crushed rock or gravel and then backfill the trenches, often with some of the original soil or other more porous material, such as gravel.

Because the backfill is less resistant to moving water than the surrounding undisturbed soil, the sewer trenches become what experts call “French drains” for groundwater.

“You’re opening a hydraulic conduit . . . now you’re giving an avenue for that water to get away from that site. So you’re pulling that water away,” said Martin Derby, an Amherst resident and groundwater expert.

Contractors can prevent the loss of groundwater by blocking the trench at various spots with “check dams” made of an absorbent clay called Bentonite, a common ingredient in kitty litter.

Soil in the north suburbs is made up of clay particles with tiny amounts of groundwater that fill the spaces between the clay, said John Whitney, district conservationist with the Natural Resources Conservation Service in East Aurora.

When the soil dries, it compresses and cracks.

Given that understanding, it would seem reasonable if state and local officials required check dams for sewers in Amherst and Clarence and other areas with similar soils.

That’s not the case.

Groundwater’s role

Reports in The Buffalo News regarding the sinking homes of Amherst led to a $500,000 study of the town’s soil by the U.S. Army Corps of Engineers.

By 2003, an estimated 500 homes in Amherst had experienced serious foundation problems since 1996. The number is likely double or more, and the cost to fix the problem could be tens of millions of dollars.

Soil scientists began telling Amherst officials and developers as far back as the 1960s that the region’s silty, clay-laden soil posed “severe limitations” for home building.

But the corps study, which issued its report two years ago, did not address possible hydrological causes, including the effects that sewers and other developments play in changing the water table.

Darlene Torbenson, a leader of the North Amherst Residents Coalition, has done extensive research on subsidence problems and was a consultant on the corps study. Torbenson believes the drying of Amherst’s soil is one of the biggest causes, if not the biggest cause, of the housing damage.

Torbenson also said she asked study officials to include possible hydrological causes, but that didn’t happen.

“The time ran out, and the money ran out,” she said.

Some experts agree that groundwater plays an important role in Amherst’s soil and that development disturbs the balance of soil and water.

“Water is part of the soil matrix,” Derby said. “Once you remove that groundwater and the soil starts collapsing, you lose the structural integrity. And that’s why you start to get a lot of these structural cracks in these foundations.”

Daniel David, regional environmental quality engineer for the DEC, agreed that contractors building a sewer line in an area like Amherst would likely encounter groundwater.

The state does not regulate groundwater, and it requires check dams only when they are needed to protect wetlands, David said.

But, soil in northern suburban communities such as Amherst and Clarence is laced with water-bearing pockets and channels, and it is impossible to predict where water exists or flows without testing, said soil scientist John P. Wulforst, who helped write the soil survey of Erie County.

The sewer lines theory

Amherst Town Engineer Jeffrey S. Burroughs said contractors are required to install check dams on water supply lines serving Amherst homes but not on sewer lines.

“If you’ve got a rock trench up to the house and you’ve got groundwater, that’s going to follow that trench. So the idea is, you put this clay dam in to isolate it from any flow back to the house,” Burroughs explained.

But when it comes to sewer lines or other underground utilities, Burroughs called piping “an interesting theory.”

It’s not a theory to the Erie County Sewer Authority. The authority routinely requires check dams on its sewer lines in the Southtowns — even though the soil often is more suited for development than those in the north suburbs.

Erie County Deputy Planning Commissioner Thomas J. Whetham said the check dams are installed every 200 or 300 feet whenever a sewer line is built or rebuilt.

“We typically do it where groundwater might be present, or might be a concern,” he said. “It’s routine because water will seek the path of least resistance, and it will flow through the trench.”

Torbenson remembers that the yard of her Amherst home was wet for the first 10 years she lived there. One spring in the late 1990s, the yard dried up, and soon after, the house foundation began to crack.

Now, each spring, the Torbensons see “little depressions that appear in the lawn,” some of them as much as 10 feet in diameter. She and her husband try to regrade the yard, a process that requires them to pull up all the plants, fill in the depression with topsoil and then replant the area.

“You can’t control it. You can only do so much,” she said.

She is convinced that when Amherst development boomed, the sewers that came with it took away water, which dried out her soil and caused her foundation to crack.

When Gary Wright looks at his empty pond, he thinks she could be on to something.