Four families living within 250 metres of the Basketstown landfill, outside Trim, Co Meath, have been evacuated from their homes by the county council after an electronic carbon dioxide monitor was activated.
Last night, a spokesman for the council said it had not been confirmed that the landfill was the source of the gas, but "we are not taking any chances".
It is understood that a gas "alarm", which detects the presence of carbon dioxide, was activated in a house 200 metres from the site.
The council will install temporary alarms in 14 additional houses within 500 metres of the landfill. A number of boreholes will be drilled and works will be carried out to allow for more efficient collection of gases on site.
These measures will take from six to 12 weeks to complete, and the council is offering the four families alternative accommodation for that time.
Mrs Mae Quinn, who lives 600 metres from the landfill, is unhappy about the quality of water in her well, where traces of the pesticide dieldrin have been detected.
A spokesman for the council said the pesticide was found upstream of the landfill and as a precaution it was providing water tankers to seven households.