Aerially Deposited Lead and Lead in Soil

Lead occurs naturally in soils, at concentrations ranging from 10 to 50 mg/kg (milligrams of lead per kilogram of soil, equivalent to parts of lead per million parts of soil, or ppm). Because of the widespread use of leaded paint before the mid-1970s and leaded gasoline before the mid-1980s, and contamination from various industrial sources, urban soils often have lead concentrations much greater than normal background levels. These concentrations can range from 150 mg/kg to as high as 10,000 mg/kg at the base of a home painted with lead-based paint. Lead doesn’t biodegrade or disappear over time, but it remains in soil for thousands of years.

Serious human health risks, particularly for children under 6 years of age, are associated with lead poisoning. It’s estimated that between 5.9 and 11.7 million children nationwide are potentially exposed to lead in soil or dust. Low-level, chronic exposure to lead in contaminated residential soil can cause developmental and behavioral problems in children. They may suffer from reduced IQ and attention span, hyperactivity, impaired growth, learning disabilities, hearing loss, and insomnia. At high levels of exposure, lead attacks the brain and your central nervous system causing coma, convulsions and even death.  People may be exposed to lead either by inhalation of lead particles or by ingestion of lead contaminated dust, water, or food.

Until the mid-1980’s, gasoline and other fuels petroleum refiners added lead to reduce engine “knock”. As motor vehicles traveled the highways, tiny particles of lead were emitted in the exhaust and settled on the soils next to the freeways and roads.  Over the years, lead built up in the soils alongside the highways and roads.  This contaminated soil is referred to as Aerially Deposited Lead (ADL) soils.  

The other major source of lead in soils is leaded paint. It’s estimated that lead paint was used on 75% of houses built before 1978, when it was banned. Chalking, leaching, flaking, weathering, scraping, and sandblasting of leaded paint result in lead deposits in the soil near the base of these houses, creating a "halo" of lead contamination. Although less widespread, airborne lead from industrial sources such as metal shops, burn dumps, or battery recyclers may have contaminated some nearby soil.

The State of California- Department of Toxic Substances Control (DTSC) regulates and enforces hazardous waste laws in California. The State of California-Office of Environmental Health Hazard Assessment (OEHHA) evaluated potential exposures to estimate lead concentrations in soil that would lead to an incremental increase in blood lead. Using the risk-based screening levels developed by OEHHA, the DTSC has developed models where excavated soils with a lead concentration less than or equal to 80 mg/kg total lead-Total Threshold Limit Concentration (TTLC-analyzed by USEPA Method 7420) would be acceptable for reuse without restrictions. Based upon similar models developed by the EPA, soils containing lead with levels below 320 mg/kg but above 80 mg/kg are considered appropriate for use at commercial properties but not residential properties.

When hazardous waste is disposed in a landfill, a small amount of the toxic constituents in the waste may “leach out” into the soil and groundwater. Two major test methods for determining “leachability”, identifying, and characterizing hazardous wastes are the STLC-Soluble Threshold Limit Concentration as determined by the California-Waste Extraction Test (WET) and the TCLP-Toxicity Characteristic Leaching Procedure based on federal guidelines.  

The first step in the waste classification process is to determine if the waste is a Resource Conservation and Recovery Act (RCRA) hazardous waste under Federal standards.  The RCRA hazardous waste limit for lead is a waste that leaches equal to or greater than 5.0 mg/l lead when analyzed by the TCLP analytical method.  RCRA hazardous wastes must be disposed of in a Class 1 hazardous waste landfill.  Wastes that contain concentrations of lead less than 5 mg/l may still be regulated under the California DTSC who utilizes a combination of both TTLC and STLC analyses to characterize wastes.  Soils with lead are considered a non-RCRA California hazardous waste with TTLC concentrations greater than or equal to 1,000 mg/kg or a STLC concentration greater than or equal to 5 milligrams per liter (mg/L).  California hazardous wastes also must be disposed of in a Class 1 hazardous waste landfill. 

Guzi-West has staff of lead inspectors with experience evaluating sites for the presence of lead in soils; preparing site specific work plans; sampling and laboratory analysis; site health and safety plans; overseeing and monitoring the removal and appropriate disposal of lead contaminated soils. Please contact our office for assistance addressing lead contaminated soils and your projects.