The Massachusetts attorney general announced final settlements with two companies involved in the Big Dig project on Thursday, concluding the state's litigation in a 2006 tunnel ceiling collapse that killed a Boston woman.

Attorney General Martha Coakley said Gannett Fleming had agreed to pay $1.5 million to help maintain the Big Dig tunnels in the future.

The Camp Hill, Pa.-based company, which designed the ceiling, will also pay $50,000 to the city of Boston and forgo $150,000 in payments from the Massachusetts Turnpike Authority.

Coakley also reached a settlement agreement with Sika Corp., of Lyndhurst, N.J. It made the epoxy glue used in the ceiling that collapsed. Sika sold the product to Powers Fasteners Inc., which has already settled.

Sika has agreed to pay $200,000 into the trust fund, which is being used for upkeep on the $15 billion tunnel complex.

Coakley said she was dismissing claims against Sigma Engineering International Inc., a Lincoln, R.I., structural engineering company, and Conam Inc., a materials inspection company, after finding the corporations were not liable for the ceiling collapse.

"The resolutions we have reached with the various companies involved in the project appropriately hold accountable those responsible for the problems in our tunnels, ensure that similar problems will be prevented in the future and provide the commonwealth with the necessary funds to maintain the tunnels and other transportation infrastructure in the years ahead," Coakley said in her statement.

Coakley, a potential candidate for U.S. Senate, also described the litigation as a priority of hers since taking office in 2007.

Milena Del Valle, 39, was killed and her husband injured when their car was crushed by tunnel ceiling panels that fell as the couple drove to Logan International Airport in July 2006.

The accident prompted a shutdown of a series of tunnels and ramps, a review of every bolt in the system and a series of civil and criminal litigation.

Investigators concluded the panels fell after the failure of epoxy used to hold metal attachment bolts into the concrete tunnel ceiling. The type of epoxy used was not intended for that purpose.