Cascades Inc. is closing three plants as part of changes to its containerboard operations that will affect 310 employees. The paper and packaging company says its corrugated medium mill in Trenton, Ont., that is currently idled will not restart operations, while converting plants in Belleville, Ont., and Newtown, Conn., will close by May 31. It says it decided to close the facilities due to a combination of market conditions, higher operating costs, aging technology and the need for significant capital investment. Cascades will work with the impacted employees to mitigate, where possible, the effect of the closures.