U.S. Environmental Protection Agency's Strategy for Ground Water Quality Monitoring at Hazardous Waste Land Disposal Facilities Located in Karst Terranes

摘要

Ground water monitoring of hazardous waste land disposal units by a network of wells is ineffective when located in karstic terranes. The U.S. Environmental Protection Agency (EPA) is currently proposing to modify its current ground water quality monitoring requirement of one upgradient well and three downgradient wells for disposal units located in karstic terranes. The convergent nature of subsurface flow to cave streams in karstic terranes requires that effective monitoring wells intercept the cave streams. Wells located around a hazardous waste disposal unit, but not in the specific cave stream draining the site, are only providing irrelevant data and a false sense of security because the water samples from such wells are not necessarily from the hazardous waste disposal unit. A case study is provided in the paper. EPA is drafting a guidance document that will allow monitoring by wells, only if the up and downgradient wells can be demonstrated to be hydraulically connected by means of dye-trace studies. If not, then the monitoring of springs shown to be hydraulically connected to the facility by dye-tracing studies would be required. Monitoring for sinkhole development will also be required to provide advance warning of sinkhole collapse. The investigation and determination of the probability of sinkhole collapse will be given special treatment.