Hall County will present the findings of a study on groundwater pollution from an old landfill at 5 p.m. today in the Courthouse Annex.

Engineer Kevin McInturff said the county has prepared an Assessment of Corrective Measures for the Allen Creek Municipal Solid Waste Landfill, which has been closed since 1997.

"It’s an unlined facility. ... They weren’t required to be lined back then so there are some groundwater contamination issues," McInturff said. "As a result of that you have to do what’s called an Assessment of Corrective Measures."

The assessment defines the horizontal and vertical extent of the groundwater pollution and potential steps the county can take to correct the problem, McInturff said.

The county already has acted to contain any further pollution.

"One thing we’ve already done, when we closed the landfill in 1997, we put an impervious cover on the whole site, it is called a geosynthetic clay liner," McInturff said. "It doesn’t allow hardly any rain water or surface water to infiltrate into the waste. The theory behind that is that eventually that waste will dry out, and once it is completely dry it will quit seeping into the groundwater."

Methane vents also were installed to help relieve some of the pressure caused by the landfill gas.

McInturff said the contamination is limited to the site and poses no danger to nearby wells.

"There’s no off-site methane danger right now. We monitor it and those vents that we put in place have really alleviated that," McInturff said. "It’s never been detected in any drinking water wells in the area. It should be fairly confined to our site."

Methane gas is created by the breakdown of waste. Landfills create a methane gas mixture known as landfill gas that is not pure methane.

Removing that gas more quickly could help prevent it from infecting groundwater.

"Further measures might be to install an active gas system. The vents we have right now are really just pipes that are stuck in the ground and (the gas) just comes out on its own. An active gas system you would actually connect to those pipes and install some type of positive pump vacuum and actually pull the gas out and then flare it off," McInturff said.

Newer landfills meet the guidelines of Subtitle D of the Resource Conservation and Recovery Act and have extensive liners in place to stop the flow of garbage water, or leachate, into the groundwater.

Hall County’s current landfill at Candler Road meets Subtitle D requirements.

"It is this huge, huge plastic liner. It is made of 60-mil, high-density polyethylene and underneath that is a (geosynthetic clay liner) which is what we have on top of the old landfill and then under that has two feet of clay," McInturff said. "What we do at the new landfill is once that liner is placed down we’ll put two feet of sand and inside that sand will be a series of pipes to collect all of the water that goes through the garbage. ... We collect it all and we treat it at a wastewater treatment plant on site."

Landfill construction projects are funded through Special Purpose Local Option Sales Tax. There is $4 million budgeted in SPLOST VI for constructing a new eight-acre cell in the Candler Road Landfill.