The Columbia River Crossing hopes one of these is the magic number: 115 or 116 feet.That’s about how high planners of the $3.5 billion project say they can build a new Interstate 5 bridge without creating significantly more impact to neighboring communities and the environment. Using that height — 20 feet higher than project leaders had long assumed — would add about $30 million to the project cost, according to the CRC.CRC leaders presented their analysis of a 115- or 116-foot-high bridge to a group of Washington state lawmakers Monday. They’ll use that number as the basis for the bridge permit application the CRC expects to file in January, said Oregon project director Kris Strickler.The U.S. Coast Guard holds permit authority over the bridge, and must approve that height for the CRC to move forward. But the CRC still has plenty of work to do if it hopes to secure that approval next year, according to a Coast Guard official.In a letter sent to CRC leaders last week, Coast Guard Rear Admiral J.A. Servidio asked for more detail on how the bridge would affect navigation on the Columbia River. That means a better explanation of how the CRC plans to work around river users, and better justification if they don’t, according to the letter, copies of which were not distributed at Monday’s meeting.A bridge with 115 or 116 feet of headroom would still affect vessels from between nine and 11 river users, according to the CRC. Going higher than that would affect fewer vessels. But too much higher would mean major logistical hurdles for the project itself and as much as $176 million in additional costs, according to the CRC.