What is lead? How do I remediate lead from soil?
Lead is naturally present in all soils. It generally occurs in the range of 15 to 40 parts lead per million parts of soil (ppm), or 15 to 40 milligrams lead per kilogram of soil (mg/kg). Pollution can increase soil lead levels to several thousand ppm. The major cause of soil lead contamination in populated areas is the weathering, chipping, scraping, sanding, and sand-blasting of structures bearing lead-based paint.
In the past, significant causes of soil contamination by lead included the use of tetraethyl lead as an anti-knock ingredient in gasoline and lead arsenate as an insecticide in fruit orchards. Automotive lead emissions have effectively ceased with the phasing out of leaded fuels. With the development of more effective pesticides and Integrated Pest Management (IPM), lead arsenate is no longer in use. Unfortunately, lead persists in soil for many hundreds of years, and past use of these products continues to present problems in some areas.
Due to the nature of the contamination process, lead in soil may be very unevenly distributed. The lead in paint removed from a structure will generally be concentrated near the source, but levels may vary greatly over small distances (e.g., one foot). Lead arsenate residues in old orchards closely reflect the locations of sprayed trees. Consider these facts carefully when sampling. If the purpose of testing is to establish the extent of play area contamination, combine several small, randomly spaced samples from the top 1- to 2-inches to create one sample for testing. If the concern is for lead uptake by garden vegetables, combine several vertical slices from the top 6- to 8-inches of soil to create a sample.
Soil lead becomes a health risk when directly ingested or inhaled as dust. Garden produce, which has accumulated lead in its tissue or has soil particles adhering to it, can also be a hazard if eaten. Lead poisoning is a particular concern for young children (under the age of six) because their rapidly developing bodies are very sensitive to the effects of lead, and their play habits tend to increase exposure. (Center for Agriculture and the Environment, UMassAmherst)
Remediation
Build raised beds.
Use soil amendments to stabilize contaminants in soil. Adding a thick layer of organic matter to your soil provides a physical barrier to contamination. Soil amendments have also been used to bind contaminants so that they are no longer mobile or bioavailable. Soil amendments improve the overall soil quality for growing plants and are a good addition to any soil.
?? do we really want to say this? Where do you deposit the contaminated soil? >> Remove all contaminated soil and replace it with clean soil. Make sure the replacement soil is clean by asking the supplier for proof that the soil that was tested to be contaminant-free.