Landfill gas effects on groundwater samples at a municipal solid waste facility

Area of Science:

• Environmental Science
• Hydrogeology
• Geochemistry

Background:

• Volatile organic compounds (VOCs) were detected in groundwater at a solid waste management facility.
• Monitoring wells were located between an old unlined landfill and a new clay-lined landfill.

Purpose of the Study:

• To determine the source of low concentrations of VOCs in groundwater samples.
• To investigate the role of landfill gas migration in VOC detection.
• To assess the influence of monitoring well characteristics on contamination source identification.

Main Methods:

• Subsurface landfill gas migration was assessed using gas pressure monitoring.
• Monitoring well headspace gases were analyzed for oxygen, methane, and VOCs.
• Groundwater VOC concentrations were compared to headspace VOC concentrations to evaluate phase transfer.

Main Results:

• Landfill gas migration into monitoring wells was confirmed by depressed oxygen and methane concentrations.
• Gas-to-water phase transfer of cis-1,2-dichloroethene was observed in two of four wells.
• Most VOCs detected in headspace gases were not found in groundwater, suggesting gas phase origin.

Conclusions:

• Landfill gas is a likely source of VOCs detected in the groundwater monitoring wells.
• Monitoring well construction and surrounding stratigraphy are critical factors in differentiating landfill gas contamination from other sources.
• The study highlights the importance of considering well characteristics when interpreting VOC data in contaminated sites.