St. Mary's County, MD

ZIP 20656

In ZIP 20656, 1 of the 12 things we check have at least one part graded D or F.

• Drinking water: Villages At Leonardtown meets every EPA legal limit; 4 contaminants are above health goals, led by arsenic at 2,025× California’s Public Health Goal.
• Nearest Superfund site: Southern Maryland Wood Treating, 4.5 miles away.
• Largest share of modeled toxic air from industry: Stella-Jones Corp (62%), mostly arsenic compounds.
• Fine particles (PM2.5) average 6.3 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 20656

• Superfund sites nearbyA
• Factories and industrial sitesB
• Oil and gas wellsA
• Parks and nature nearbyB
• Air qualityA
• Drinking water qualityB to C
• Pesticide useD
• Neighborhood health statusB
• Past wildfire impactsA
• Past flood impactsC
• Noise levelsA
• Radiation signalsB

Based on 1 census tract · compiled October 25, 2026 · how each grade works and its sources

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