Closed loop system

From Wikimarcellus

A closed loop system consists of using a small waste-water processing system on the well site. It removes pollutants from the frac water as well as additional water that may also be present in the formation itself--all of which flows back up a well. Solids extracted from the water by this processing method are removed by truck to a waste treatment station for disposal. Treated water that remains after on-site processing may then be reused on a later frac job.