Site Mitigation & Restoration Program

We protect and maintain California’s land and places
by setting strict standards for land restoration and cleanup

Caltrans Soil Management Agreement for Aerially Deposited Lead-Contaminated Soils

DTSC entered into an enforceable agreement with the California Department of Transportation (Caltrans) for the management of aerially deposited lead (ADL) contaminated soils that are excavated by Caltrans during highway improvement projects (Agreement). These activities were previously covered by a variance from certain hazardous waste laws from 1996 through June 30, 2016. DTSC made the decision in July 2015 to transition from a variance to this new agreement to ensure the continued protection of human health and the environment. The Agreement requires all ADL-contaminated soils with a lead concentration above unrestricted use (currently 80 mg/kg) to be properly managed by Caltrans. The Agreement applies to existing and new Caltrans projects as of July 1, 2016. The variance that previously covered the management of ADL-contaminated soils excavated during highway improvement projects by Caltrans terminated on June 30, 2016. The management activities to which this Agreement generally applies are the stockpiling, disposal, tracking, transportation and final placement of ADL-contaminated soils. DTSC will monitor compliance with the Agreement and track highway improvement projects that reuse ADL-contaminated soils.

Refiners in the United States started adding lead compounds to gasoline in the 1920s in order to boost octane levels and improve engine performance by reducing engine ‘knock’ and allowing higher engine compression. Tailpipe emissions from automobiles using leaded gasoline contained lead and resulted in ADL being deposited in and along roadways throughout the State. The phasedown of lead in gasoline began in 1974 when, under the authority of the Clean Air Act Amendments of 1970, the U.S. Environmental Protection Agency (EPA) introduced rules requiring the use of unleaded gasoline in new cars equipped with catalytic converters. The introduction of catalytic converters for control of hydrocarbon, nitrous oxide and carbon monoxide emissions required that motorists use unleaded gasoline because lead destroys the emissions control capacity of catalytic converters. By the early 1980s gasoline lead levels had declined about 80% as a result of both the regulations and fleet turnover. Beginning in 1992, lead was banned as a fuel additive in California.

ADL-contaminated soils still exist along roadsides and medians and can also be found underneath some existing road surfaces due to past construction activities. Transportation of such soil to hazardous waste landfills challenges the State’s limited hazardous waste landfill capacity and increases air pollution due to trucking. The alternative of transporting the soil out of state for disposal is State-resource-intensive, and contrary to Caltrans policy. Caltrans, by managing the soil in accordance with this Agreement, will be reducing hazards, preserving landfill capacity, and reducing the air quality impacts inherent in transporting the soil many miles to landfills, while still protecting human health and the environment.

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