In May, 2002 the DuPont Corporation notified the County that a material called Sierra-Crete they produced locally contained dioxins. Dioxins are a class of chemicals that can cause a wide range of long-term health effects, including cancer.
DuPont sold this material as a road base, and it was used on 36 miles of roads in east Contra Costa County. Some of the roads where the Sierra-Crete was used have developed cracks, leading to stain-like residues on the surface.
Studies conducted on behalf of DuPont and the County have concluded that the health risks from the dioxins in the Sierra-Crete were not significant.
The results of additional testing were completed in November and preliminary results of the updated health risk assessment were reviewed at the December 11 taskforce meeting. The results of the new testing were essentially the same as that initially conducted by DuPont.
Sierra-Crete resources online
Contra Costa County Sierra-Crete® Task Force Human Health Risk Assessment (summary and full text)
Risk Assessment Workshop Presentation
Minutes of the Sierra-Crete Task Force meetings
Street Maps Showing Where Sierra-Crete Was Used
Information About Dioxins
California Air Resources Board 1997
DuPont's page on Sierra-Crete®
For more information contact Hazardous Materials Ombudsman Michael Kent at 925-313-6587