The last leachate control element is monitoring. Some landfills use lysimeters, geosynthetic membranes placed in the ground, to detect and collect material directly under the landfill. However, monitoring is most commonly accomplished by collecting groundwater from wells located around the landfill, both upgradient and downgradient of the landfill. Upgradient wells are important in determining whether downgradient contamination is caused by the landfill or some upgradient event. Groundwater is monitored regularly for a number of inorganic and organic constituents (CFR 40 Parts 257-258). Detection of a contaminant at a statistically significant higher concentration than background levels results in increased monitoring requirements. Detection of contaminants at concentrations above groundwater protection levels requires the operator to assess corrective measures. Based on this assessment, a corrective measure is selected that protects human health and the environment, attains the applicable groundwater protection standards, controls the source(s) of release to the maximum extent possible, and complies with the applicable standards for managing any waste produced by the corrective measures. Corrective measures may involve pump and treat, impermeable barriers, or bioremediation.
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