More money often is spent cleaning up landfill volatile organic compound (VOC) problems when less costly measures could be used. Under Subtitle D, MSW facilities must monitor volatile organic compounds in the groundwater. Some-times, however, the VOCs are in the groundwater because of landfill gas - not leachate. In fact, landfill-gas VOC costs are only a fraction of the clean-up cost of leachate problems.
It is important to identify where the VOCs originate since it is more cost-effective to terminate the source of contamination than to treat affected groundwater. It is usually not practical to terminate the migratory process of leachate into groundwater. For leachate effects, pump-and-treat techniques, remedial measures that collect and treat groundwater, may be the only practical alternative. If landfill gas is the source of VOC contamination, it is possible to halt the source rather than to use the pump-and-treat remediation method.
Source control for contamination of groundwater from landfill-gas VOCs can be accomplished by fine-tuning existing gas-collection systems. Even in the worst-case scenario, when gas-collection system installation is required, the cost will be only a small fraction of the cost of a pump-and-treat system.
Geochemical data can be used to discover whether the VOCs are caused by landfill gas or leachate. Evaluation of the physical properties of groundwater constituents, inter-phase equilibrium, and stable and radiostopes can be used under the proper conditions. VOC contamination is commonly identified since VOCs are used to indicate contamination in groundwater monitoring.
Unfortunately, few landfill operators realize that VOCs in groundwater samples can be caused by landfill gas instead of leachate. For example, a Wisconsin program used low-detection-limit (high sensitivity) monitoring for VOCs to evaluate its public landfills. The program was designed without considering landfill gas as a possible cause of contamination and could have resulted in inappropriate remedial techniques.
The figure shows the frequency of detection of common VOCs and the maximum concentration in landfill gases in a study in Califor-nia. The maximum concentrations shown are not the groundwater concentrations that could result from landfill gas, but the concentrations in the gas itself. The maximum concentrations in that data are higher than would be expected from MSW since the study included hazardous-waste and codisposal facilities. The threat to groundwater is not directly related to the landfill-gas concentration in the figure, but is influenced by health-risk factors and physical/chemical properties of the specific compound.
As groundwater monitoring regulations become more stringent at MSW facilities around the world, the potential for misinterpreting VOC detections as an indication of leachate effects could increase. In addition, misinterpretation also could increase as laboratory analyses become more sensitive to VOCs. Through careful data evaluation by landfill operators and good communication with regulatory personnel, such problems could be minimized.