Soil from backyards in the north end of Tiverton is so contaminated that residents haven’t allowed their kids to play outside for seven years, but it is good enough to cap the state landfill in Johnston.

Since cleanup efforts began in Tiverton in early September, the landfill has been accepting soil from the Bay Street neighborhood, up to a total of 8,000 tons. The arrangement was critical in resolving a lawsuit brought by residents to force the cleanup of their property.

The soil is contaminated with arsenic, lead, cyanide and petroleum wastes left from the manufacture of gas from coal at the former Fall River Gas Co.

Since blue-tinged soil was discovered in August 2002, residents have been unable to use their yards even to plant vegetables or flowers.

While the contamination exceeds residential standards, it is similar to levels commonly found in soil at commercial or industrial sites, according to Terry Gray, assistant director for air, waste and compliance at the state Department of Environmental Management.

Leaching tests on the soil, which measure what happens when water flows through the dirt, show it does not meet the scientific criteria for hazardous waste, Gray said.

That’s not to say that the DEM would allow the contaminated soil to be introduced at a commercial or industrial site that is otherwise pristine, Gray said.

But “the landfill is engineered to deal with things much more hazardous than the materials in Tiverton,” said Gray.

And this is not the first time that the DEM has approved the use of low-level contaminant soils as “daily cover” at the landfill, he said.

What happens to the contaminants after a rainfall?

“Any water that comes down through the active area of the landfill is intercepted by collection pipes,” Gray said.

This water, called “leachate,” receives initial treatment and is sent via pipeline to the Cranston sewage treatment system, he said.

The acceptance of the Tiverton soil is part of a deal between the DEM and the Rhode Island Resource Recovery Corporation, the operator of the landfill, to resolve a $100,000-penalty for water pollution.

Resource agreed to waive tipping fees and use the soil as cover at the end of each day’s waste deposit to satisfy $55,000 of the $100,000 fine, according to a consent agreement signed last week.

The remaining $45,000 penalty will be resolved with improvements to groundwater collection and sedimentation control, according to the consent order.

Meanwhile, in a separate administrative proceeding, RIRRC also agreed to modifications in its water-discharge permit to encompass additional water-quality controls.

Taken together, the settlements wipe the slate clean on environmental violations at the landfill for the first time in years.

The recently resolved administrative proceedings revolved around an overtaxed settling pond that for years has been discharging murky water into Cedar Swamp Brook, the Upper Simmons Reservoir and nearby wetlands. The Simmons Reservoir is not a source of drinking water.

Compounding the problem was runoff from two nearby roads, Shun Pike and Green Hill Road, which added to the load on the pond.

“To make a long story short,” Gray said, “Resource Recovery agreed to put in another settling basin” and “the town agreed to collect the [road] runoff and direct it to the new settling basin.”

RIRRC also plans to remove the sediment that has accumulated in the wetlands and restore it by replanting, Gray said. In addition, RIRRC has agreed to redirect a trench that collects water under the landfill and treat it to reduce the levels of ammonia and iron, according to Joseph B. Haberek, principal sanitary engineer for the DEM.

gmacris@projo.com