The CHP had to shut down Northbound I-15 near Castaic Monday afternoon, after a big rig spilled hydrogen peroxide.Traffic was backed up for miles while crews tried to clean up the spill, which occurred about 5 miles north of Lake Hughes Road. Authorities had temporarily opened some lanes of the freeway to try and relieve the traffic pressure, but shut them down again after a short time. Live television pictures showed a wall of cars backed up for miles.