the horizontal wells can be effectively used to clear up heavily polluted industrial sites. The method pioneered by the oil industry is cheaper and quicker than conventional methods. Drilling vertical holes or excavation are the usual methods of clearing heavily polluted sites. But horizontal drilling causes less disturbance on the surface and could be quicker than vertical wells.

Drilex, a us based company, cleared nearly 526 ha of polluted land and groundwater at the Dow Chemical's Plaquemine plant in Louisiana, usa . The company took two years to complete the world's biggest soil remediation project. Instead of drilling 200 vertical wells, the company drilled just five hori-zontal tunnels at the site of the plant. The pumps sucked out chlorina-ted hydrocarbons and polluted salt water from the site. The horizontal system allowed the plant to continue its operation without any disturbance.

Apart from this project, the com-pany has removed pollutants like methane gas from a Colorado coal mine, solvents from beneath a computer manufacturing site in Silicon Valley and toxic wastes from the Rocky Mountain arsenal northeast of Denver, usa . Dow says that the technology may play an important role in decontamination of big indust-rial sites.

As the system can treat contamination on site, there is no need to transport the wastes. Though the initial installation of horizontal drills is expensive, the long-term maintenance cost is halved. A vertical well consists of nearly 80 different parts, the horizontal well has just eight parts making it easy to operate.