Napa County, CA

ZIP 94558

In ZIP 94558, 6 of the 12 things we check have at least one part graded D or F.

• Drinking water: Spanish Flat Water District has 1 contaminant at or over an EPA legal limit; 8 contaminants are above health goals, led by arsenic at 364× California’s Public Health Goal.
• Closer to Superfund sites than 56% of U.S. neighborhoods, with no listed site within 10 miles of its center.
• Largest share of modeled toxic air from industry: Martinez Refining Co LLC (27%), mostly sulfuric acid.
• Fine particles (PM2.5) average 8.0 µg/m³; the WHO guideline is 5 and the EPA annual standard is 9.
• About 906,696 kg of agricultural pesticides are applied in the county each year.

Grades for ZIP 94558

• Superfund sites nearbyA to C
• Factories and industrial sitesA to C
• Oil and gas wellsA
• Parks and nature nearbyA to C
• Air qualityB to D
• Drinking water qualityC to D
• Pesticide useF
• Neighborhood health statusA to D
• Past wildfire impactsC to F
• Past flood impactsA
• Noise levelsA to D
• Radiation signalsA to B

Based on 29 census tracts · compiled October 25, 2026 · how each grade works and its sources

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