Thompson Mechanical Contractors Inc., a Richland-based subsidiary of Zellweger Luwa Group, has won a contract worth about $4 million to provide a cooling tower for the Hanford Waste Treatment and Isolation Plant.

Bechtel National Inc., lead contractor on the $5.6 billion project to treat radioactive and hazardous tank wastes, signed a contract with Thompson on Wednesday.

Under the contract, the company will provide engineering, procurement and construction of the cooling tower, which will be centrally situated at the treatment site and will cool multiple buildings. The cooling system is needed because the melters used to vitrify the wastes generate excessive heat.

The cooling tower is to be complete by April 2004.