Middlesex, MA is tracked across three EPA datasets covering 50 Toxics Release Inventory (TRI) facilityies, 0 Safe Drinking Water Act systems, and 0 Superfund National Priorities List sites. Together these generate an environmental burden score of 56/100 (Moderate Risk), calibrated against national distributions for facility density, chemical release volume, Superfund concentration, and water-system health violations.

Industrial disclosures inside the county total 4.6M lbs of reported toxic releases under EPCRA Section 313, while 0 water systems carry an active health-based violation in the SDWIS record. EPA Air Quality System monitors logged a median AQI of 37 and a peak AQI of 93 in 2024, with 86% of observed days rated "Good" (0–50).

All figures below draw directly from federal EPA records, TRI self-reported emissions, SDWIS compliance history, NPL Hazard Ranking System scores, and AQS daily AQI summaries, and are not adjusted, weighted, or forecast. A past violation or elevated score does not itself indicate current unsafe conditions; it documents the regulatory and disclosure history publicly filed with the U.S. Environmental Protection Agency through the most recent reporting cycle.