Groundwater remediation means actions that are necessary to prevent, minimize, clean up, or mitigate damage to groundwater. This process is used in the removal of dissolved contaminants from the subsurface and containment of contaminated groundwater to prevent migration. This process consists of defining the remedial action objectives to be accomplished at the site. This involves gathering enough background information and field data to assess remedial requirements and possible cleanup levels. This process enables physical, chemical, or biological in situ treatment of contaminated groundwater by means of reactive materials. The most commonly used processes/reactions are: redox reactions, precipitation, adsorption, ion exchange and biodegradation. The reactive materials are placed in undergound trenches downstream of contamination plume, forcing it to flow through them. By doing so, the contaminants are treated without soil excavation or water pumping.