EVALUATING GROUNDWATER QUALITY IMPACTS RESULTING FROM LANDFILLS

Specific groundwater parameters provide evidence of the source of water quality impacts. For landfills the nature of the contaminated groundwater depends on a variety of factors including the type of waste, site specific hydrogeology and aquifer mineralogy.

To assess the degree and magnitude of contamination at solid waste facilities, groundwater samples are collected from monitoring wells and nearby private water supplies. We routinely analyze the groundwater samples for the basic geochemical parameters and volatile organic compounds. Interpreting the resulting groundwater quality data can be a straightforward task when the site hydrogeology is well understood and the landfill is the sole contaminant source. More commonly this task is considerably more difficult because of one or more contaminant sources in addition to the landfill. This task is sometimes further complicated by the existence of naturally elevated dissolved metals (e.g., iron and arsenic).

This presentation outlines the approach we use to evaluate the potential impacts from landfill contamination. After a brief discussion of the geochemical characteristics of landfill leachate we explain the importance of both the common field parameters (e.g., specific conductance and dissolved oxygen) and the basic geochemical parameters. We describe the use of common graphical techniques to interpret chemical variations using time-series plots, Stiff and Piper Diagrams. More recently we have found both bromide and methane data can provide useful information about landfill related groundwater contamination. We detail our success using a published graphical method which uses bromide and chloride data to differentiate salt and landfill derived chloride. In closing, we emphasize the importance of characterizing the landfill waste as the waste may contain unique leachable compounds including low level volatile organic compounds.