The county Department of Public Works mismanaged the expansion of a west county bike path in 2007, forcing significant cost overruns and delays that otherwise could have been avoided, according to a lawsuit filed by the contractor that performed the work.

Among other things, Ox Construction of Silver Spring claims county officials failed to tell anyone about hundreds of tons of industrial plastic buried along the proposed path of the Washington, Baltimore & Annapolis Trail until after they had awarded a $801,000 construction contract.

That oversight, as well as changes to the contract, led the company to spend an...