They totally polluted the water tables in the area with by-products of rocket fuel and other industrial chemicals used to clean engines.
They were fined in the 90s and supposedly worked with local water authorities to setup a filtration system... but decades later, they're still finding the pollutants are actually SPREADING to adjacent water tables in communities miles from the original location.
Even worse... many women from the community I grew up in have developed strange autoimmune disorders in their 40s and 50s. Like, a truly abnormal number of them. Many of these women are upper middle class, health conscious, non-smokers, including many athletes. Among those disorders, one of the common ones is issues with their thyroid.
Turns out that one of the major byproducts of rocket combustion - if consumed - is known to fuck up your thyroid.
Am I saying that I know for sure that the pollution of the water tables caused all these women to develop these strange disorders? I can't say for sure. I respect the scientific process and I certainly don't want to jump to any unfair or drastic conclusions, but it seems likely.
As recently as 2011 the area was again hit with a $60 million fine for cleanup. A slap on the wrists for the level of ecological damage they've caused. The water basin in this area is permanently damaged, and seems (even after decades or rain fail) to still be seeping into surrounding areas.
EDIT: For those wanting more specifics...
Aerojet / Rocketdyne is the company. Rancho Cordova is the city.