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. Typically, up to 50 percent of the frac water can be recovered and reused.

This method generally lowers total drilling cost, as well as the amount of water used and its cost. It contributes to higher drill rates which also provides a cost savings.