The crash occurred around 8:55 a.m. just south of the junction with state Highway 24.
No injuries have been reported, but a Sig-alert was issued at 9:15 a.m., and CHP officials estimate the roadway will not be cleared until around noon.
Meanwhile, southbound traffic is backed up several miles, all the way to Monument Boulevard.
The chemicals in the delivery van are all fully contained and there is no current threat to public safety, according to the CHP.