The samples were taken on 3/15, then shipped to Anchorage to test 3/17, and they contacted him in April. 
I think they purposefully left out how much it was because it would help other saboteurs to figure out their dosage, right? That was my thought. But it was apparently in such high levels because someone AT the finish line dosed them, instead of before they finished, like they might have traces if it was administered before they finished the race.