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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

Risk Assessment

Contra Costa County Sierra-Crete® Task Force Human Health Risk Assessment (summary and full text)

Risk Assessment Workshop Presentation

Short Version (143k PDF, 5pp.)
Longer Version (189k PDF, 9pp.)

Minutes of the Sierra-Crete Task Force meetings

Street Maps Showing Where Sierra-Crete Was Used

Information About Dioxins

California Air Resources Board 1997
Facts about Chlorinated Dioxins And Dibenzofura (30k PDF)

U.S. Department of Health and Human Services
Agency for Toxic Substances and Disease Registry (ATSDR)
Public Health Statement for Chlorinated Dibenzo-p-dioxins (CDDs) 1998

US Environmental Protection Agency
Questions and Answers about Dioxins 2000 (150k PDF)

World Health Organization
Dioxins And Their Effects On Human Health 1999

California Office of Environmental Health Hazard Assessment
Prioritization of Toxic Air Contaminants
Children's Environmental Health Protection Act Report 2001 (125k PDF)

United States General Accounting Office (GAO) Report
Environmental Health Risks: Information on EPA's Draft Reassessment of Dioxins 2002 (165k raw text)

Other Links

DuPont's page on Sierra-Crete®

For more information contact Hazardous Materials Ombudsman Michael Kent at 925-313-6587

Contra Costa County home page