St. Mary's County, MD

ZIP 20621

In ZIP 20621, 3 of the 12 things we check have at least one part graded D or F.

• Drinking water: Persimmon Hills meets every EPA legal limit; 5 contaminants are above health goals, led by arsenic at 1,107× California’s Public Health Goal.
• Nearest Superfund site: Arrowhead Associates, Inc./scovill Corp., 8.9 miles away.
• Largest share of modeled toxic air from industry: Stella-Jones Corp (56%), mostly chromium.
• Fine particles (PM2.5) average 6.6 µg/m³; the WHO guideline is 5 and the EPA annual standard is 9.
• About 64,785 kg of agricultural pesticides are applied in the county each year.

Grades for ZIP 20621

• Superfund sites nearbyA
• Factories and industrial sitesA
• Oil and gas wellsA
• Parks and nature nearbyC
• Air qualityA
• Drinking water qualityC to D
• Pesticide useF
• Neighborhood health statusC to D
• Past wildfire impactsA
• Past flood impactsC
• Noise levelsA

Based on 3 census tracts · compiled September 10, 2026 · how each grade works and its sources

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