Groundwater has been intensively studied for years. Groundwater dye tracing, which serves to define groundwater basins, has been completed. Base-line water quality inventories have been done, as well as investigations into the mechanisms of non-point contaminant transport and water quality. The park also operates several continuous-recording digital water monitoring sites, which yield data relative to physical and gross chemical characteristics. Because large portions of the upper Green River watershed and the groundwater basins affecting Mammoth Cave National Park lie outside park boundaries, activities conducted in these areas greatly influence water quality within the park. The primary activities that influence the park's water quality include: disposal of domestic, municipal and industrial sewage, solid waste disposal, agricultural anf forestry management practices, oil and gas exploration and production, urban land-use and recreational activities.