Test results from a former rocket testing site, and nuclear lab near Simi Valley show there is a significant amount of radioactive contamination in an area which was once site of a reactor.
The EPA has released the first round of test results from a section of property at the Santa Susana Field Laboratory, where a partial reactor meltdown occurred in 1959.
About a sixth of the more than 430 samples taken from the former reactor site exceeded acceptable limits set by a coalition of state, and federal agencies.
The area in question has already gone through two cleanups, but standards were much lower at the time.
A second round of testing to further assess the problem at the site, to better plan cleanup efforts is now underway.