- Arsenic: Arsenic ("As") is common, naturally occurring chemical that has long been used as a poison. Read more about arsenic.
- Background level: Soil typically has naturally occurring amounts of many toxic substances, like arsenic and lead. Just because soil contains naturally occurring chemicals, it does not mean the levels of these chemicals are “safe.” Never the less, the clean up standard is often based on the amounts of naturally occurring chemical in the soil.
- Child use area: Places such as parks, schools, and child care centers where children play.
- Clean up standard: Typically, soil should not have more than a certain amount of chemical contamination, depending on the use of the property. In Washington State, the amount of contamination that triggers action is determined by the Model Toxics Control Act (MTCA). On residential properties, for arsenic, the clean up standard is 20 parts per million in soils. For lead, it's 250 parts per million in soils.
- Lead: Lead ("Pb") is a common, naturally occurring chemical that has been used for thousands of years by people. Read more about lead.
- Plume: A chemical plume is the spread of the chemical in the environment, often through soil.
- Remediate or remediation: Remediate means to fix or improve a problem. In the case of soil contamination, remediation can mean to clean up or reduce the amount of contamination in the soil by digging out and bringing in new soil; dilute contaminates in the soil by mixing in new soil into the contaminated soil; or cover up the contaminated soil making it no longer accessible to people.
- Soil sample: A small amount of dirt that is collected and sent to a laboratory where it is tested for the presence of arsenic, lead, or other contaminants.
- Superfund site: Superfund is the name for a United States environmental law known as the Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA). The Superfund law was created to protect people and communities from heavily contaminated toxic waste sites. The Superfund policy provides federal authority to clean up hazardous substances that may endanger people or the environment. As of 2009, there are approximately 1,200 sites listed on the Superfund National Priority List nation-wide.
- Undisturbed soils: Soil that has not been significantly dug up, moved, or added to since the smelter began operations around 1900. Properties with undisturbed soils can have more contamination than properties where the soil has been disturbed because the arsenic and lead had more years to accumulate on the property.