Cohen could not be reached for comment on his plans for the plaza. He has said in the past that he would build a plaza on his current land if the land swap was rejected.
Cahill said it is "our hope and expectation" that Cohen will build the shopping plaza on his land. Cahill said he expects to talk to Cohen next week.
"We are interested in him putting forward a proposal that will be good for him and good for the city both," Cahill said.
Cohen had proposed a plan to the state to reinforce the landfill by drilling crushed-stone piers. But in his letter, DePaola said shifting refuse in the landfill may create voids that could allow the crushed stone to migrate away from the piers and lose support for the road.
DePaola cited several other potential problems that would cause the road to settle, including decomposition, methane gas, and the presence of tires, boulders and tree stumps that could obstruct the installation of the supporting piers.
DePaola also said the state would face "significant risk and liability" in taking over a closed landfill, including inheriting responsibility for installing monitoring wells and conducting groundwater tests.
In addition, the state could incur increased costs and delays due to more complicated storm water management, environmental permitting, and land acquisitions along Sohier Road and Brimbal Avenue, he said.
Cahill said he is confident that building a new connector road in its current location will alleviate traffic problems in the area. The new road would include roundabouts at both ends, at Sohier Road and Brimbal Avenue, eliminating the current dangerous left-hand turns.
"The levels of performance are very comparable to if we had built the road on the CEA property," Cahill said.