What is Area-Wide Soil Contamination?
“Area-wide soil contamination” refers to low- to moderate-level soil contamination that is dispersed over a large geographic area, covering several hundred acres to many square miles. For schools, childcare centers, and residential land uses, in general, Ecology considers total arsenic concentrations of up to 100 milligrams per kilogram (mg/kg)1 and total lead concentrations of up to 500-700 mg/kg to be within the low-to-moderate range. For properties where exposure of children is less likely or less frequent, such as commercial properties, parks, and camps, Ecology considers total arsenic concentrations of up to 200 mg/kg and total lead concentrations of up to 700-1,000 mg/kg to be within the low-to-moderate range. For comparison, the cleanup levels under MTCA for total arsenic and lead in soil are 20 mg/kg and 250 mg/kg, respectively. Arsenic occurs naturally in Washington State soils at approximately 5-9 mg/kg; lead occurs at 11-24 mg/kg. The Task Force considered area-wide arsenic
