As dangerous chemicals continued to approach Winters Run from the Tollgate Landfill in Bel Air, Harford County officials put out bids Wednesday for capping the defunct dump.
Work on the cap, projected to cost $6.5 million to $8 million, is expected to start within two months, said Jefferson L. Blomquist, deputy county attorney.
The cap is the latest step to contain the spread of methane gas and contaminated surface and ground water from the landfill, which was closed in 1987 after 33 years as the county's central dump.
County public works officials, who gave an update on remediation procedures at a recent Board of Health meeting, said that a key concern is the migration of contaminated ground water from the landfill downhill toward Winters Run, less than a mile south.
Large amounts of trichloroethene, a volatile organic compound classified by the U.S. Environmental Protection Agency as a suspected carcinogen, have been detected in monitoring wells on county land across Tollgate Road from the landfill, said Daniel Pazdersky, a civil engineer in the Public Works Department's division of environmental affairs.
The monitoring wells, which the Department of Public Works installed to examine ground water from the landfill, have revealed trichloroethene concentrations as high as 500 to 600 parts per billion at the landfill, Mr. Pazdersky told the County Council, which was sitting as the Board of Health.
He said levels of the chemical are substantially lower across Tollgate Road near the county's Equestrian Center and Parks and Recreation buildings, which lie between the landfill and Winters Run. But he said concentrations there still are high enough to warrant concern and that the flow is moving south.
The EPA allows a maximum five parts per billion of the compound as a safe level in drinking water, he said.
Trichloroethene was once widely used in paint, paint thinner and degreasing agents. It does not bond with water and evaporates when it is exposed to air, experts say. When it is mixed with water, the chemical settles to the bottom.
"Right now it hasn't reached a detectable level in Winters Run," said Mr. Blomquist, an environmental lawyer. "But any time something like this threatens to be discharged into a public waterway, there is concern for health and the environment."
He said that if the flow is left untreated, it is expected to reach the stream by 1998.
The county plans a two-phase project to stop the contaminants' southward migration.
The landfill cap -- a "sandwich" of geosynthetic liners, mesh material and layers of soil -- will cover 62 acres and will prevent rainwater from soaking into the ground at the site of the heaviest chemical concentration.
The water will run off the cap into sediment control ponds and into the surrounding streams.
In addition, perhaps by fall, workers will install a system of extraction wells to remove and treat already-contaminated ground water that has migrated toward the stream.
The start of the ground water treatment project depends on how soon the Maryland Department of the Environment approves a removal method, Mr. Blomquist said. County public works officials have submitted four alternatives to the state.
Mr. Blomquist said the approved method probably will be similar to others on the west side of the landfill, where a "pump and treat" system was put into operation in August 1992. That system works by extracting ground water through a series of wells and pumping it back to an air-stripping tower, where the chemicals evaporate and become harmless.
Mr. Blomquist said that the most protective pump-and-treat alternative, together with the cap, will keep the concentration of chemicals discharged into Winters Run and other streams at less than 1 part per billion. Both projects are expected to be completed in 1995.
The county has allotted $9 million in the capital budget for all remaining work at Tollgate. Most of the money will be spent on the cap, Mr. Blomquist said. The pumping facility will cost about $500,000 to build, he said, but its major expenses will be operational costs and maintenance.
The wells must be operated for at least 20 years, he said.
The county's last problem with migration of contaminated ground water was discovered in June 1992, when the pond in Heavenly Waters Park was found to contain six parts per billion of trichloroethene.
Public Works officials installed an aeration system that would continuously clean the water in the pond by dispersing it into the air.
About the same time, the county installed carbon treatment systems on each of the well-water supplies in the park so that any drinking water drawn by those wells went through two charcoal filters. That system filters drinking water supplied to the Equestrian Center and the adjacent Parks and Recreation buildings, Mr. Blomquist said.
Mr. Pazdersky told the County Council that the landfill capping will be very visible to area residents.