DOVER, Del. -- Federal highway officials have confirmed suspicions that a large dirt pile dumped near an interstate bridge in Delaware is to blame for damage to several supporting columns and the emergency closure of the heavily traveled span.
In a letter formally approving emergency relief funds to repair the Interstate 495 bridge over the Christina River in Wilmington, the Federal Highway Administration also said the bridge's design and construction met applicable standards, and that it appears the bridge has been properly maintained and inspected.
"It does not appear ... there is anything that the state could have reasonably done to have anticipated or avoided this failure," the administration's local division administrator, Mary Ridgeway, wrote in a June 12 letter to Delaware Transportation Secretary Shailen Bhatt.
The letter was released by state transportation officials Wednesday as Bhatt appeared before a joint legislative committee to discuss the closure of the bridge and plans to repair it.
State officials have hired their own geotechnical expert to determine what caused the damage to the bridge, and Bhatt said he could not embrace the federal government's conclusions until he hears definitively from his own consultants.
But state officials have from the beginning suspected that the dirt mound, estimated to weigh about 50,000 tons, caused soft underground soils to move, damaging underground pilings that support the bridge columns. They said the dirt was not present when the bridge was last inspected in October 2012, and they still don't know where the contractor who dumped it got the soil.
Rep. James Johnson, who represents the district in which the bridge is located, said he found it unusual that no one knew about the dirt mound earlier because state environmental officials regularly visit the heavily industrialized area.
"I was surprised that they didn't mention anything about the dirt or they didn't have any communication" with the state transportation department, said Johnson, D-Wilmington.
Bhatt said his agency will look at improving lines of communication. He also indicated that future bridge inspections will incorporate rights of way and the use of surrounding land. Federal bridge inspection standards currently do not require that states ensure that rights of way are clear.
The bridge, which typically carries about 90,000 vehicles daily, has been closed since June 2. Traffic on the I-495 bypass around Wilmington is being diverted onto already congested I-95 through downtown Wilmington as crews undertake a $20 million repair project that officials hope will have the bridge at least partially reopened by Labor Day.
State officials have said they closed the bridge immediately after learning that several columns were tilting.
But a local businessman called 911 on April 15 to report that concrete barriers separating the bridge's northbound and southbound lanes, which are supposed to be level with each other, had separated in elevation by as much as a foot. Transportation officials also received a separate notice from an engineer working in the area on Thursday, May 29, that the bridge appeared to be tilting, but they did not send out an inspection team until the following Monday.
Bhatt reiterated Wednesday that a review of his agency's response to reports of problems with the bridge is underway, and that the findings will be disclosed to the public. He gave no timeline on when that might happen.
"I would say there is heightened awareness around the agency right now with regard to things stored beside bridges, bridges in general, inquiries from the public," Bhatt said.