Groundwater Monitoring

Groundwater monitoring is required for owners or operators of surface impoundments, landfills, land treatment facilities, or waste piles used to manage hazardous wastes. These requirements assess the impact of a facility on the groundwater beneath it. Monitoring must be conducted for the life of the facility, except at land disposal facilities, which must monitor for up to 30 years after closing.

The groundwater monitoring program requires installing a system of four monitoring wells: one up-gradient from the waste management unit and three down-gradient. The down-gradient wells must be placed to intercept any waste from the unit, should a release occur. The up-gradient wells must provide data on groundwater that is not influenced by waste coming from the waste management unit (called background data). If the wells are properly located, data comparisons from up-gradient and down-gradient wells should indicate if contamination is occurring.

After the wells are installed, the owner or operator monitors them for one year to establish background concentrations for selected chemicals. These data form the basis for all future comparisons. There are three sets of parameters for background concentrations: drinking water, groundwater quality, and groundwater contamination.

If a significant increase or decrease in pH is detected for any of the indicator parameters, the owner or operator must implement a groundwater assessment program to determine the nature of the problem. If the assessment shows contamination by hazardous wastes, the owner or operator must continue assessing the extent of ground-water contamination until the problem is ameliorated, or until the facility is closed.

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