Timeframe: 1993 to 1999

The Conoco site consists of two gasoline service stations located next to a residential neighborhood in Sacramento, California. Soil and groundwater contamination on the site was discovered in 1985, initiating remediation activities overseen by the Sacramento Metropolitan Air Quality Management District. The chemicals of concern included petroleum hydrocarbons (TPH), benzene, toluene, and others.

In 1992, the Agency for Toxic Substances and Disease Registry (ATSDR) was petitioned by residents who believed their health problems were being caused by the chemicals used in the soil and groundwater remediation activities. ATSDR engaged IAI to review and prepare two health consultations for the Conoco Service site, examining the concerns related to emissions from a thermal oxidizer and an air stripper used to treat soil and groundwater contamination. IAI research specialists examined site and environmental data, as well as samples collected from neighboring residential areas.

In the first health consultation, IAI reviewed the risk assessment created by Conoco as a part of the permitting process for the groundwater and soil treatment systems. Exposure point concentrations used in the risk assessment were derived from a screening level air model. This model type cannot account for the complex geography, fugitive emissions, proximity of residences, and multiple emission sources present in this situation. IAI concluded that the treatment systems should not have been permitted based on this model. IAI further concluded that while current sampling did not reveal elevated levels of dioxins in the soil, the treatment systems utilized by DuPont Environmental Remediation Services should not have been permitted based on environmental modeling of potential risks. The health consultants were prepared in collaboration with the California Department of Public Health.