From mass.gov

"In Massachusetts, an environmental justice population is a neighborhood where one or more of the following criteria are true:

the annual median household income is 65 percent or less of the statewide annual median household income

minorities make up 40 percent or more of the population

25 percent or more of households identify as speaking English less than "very well"

minorities make up 25 percent or more of the population and the annual median household income of the municipality in which the neighborhood is located does not exceed 150 percent of the statewide annual median household income.

The Executive Office of Energy and Environmental Affairs (EEA) uses data from the 2019 American Community Survey to identify environmental justice population areas in Massachusetts. Policy makers and state agencies can then use this information to communicate more effectively with communities affected by their work"

More details on the thought behind it here

https://www.mass.gov/service-details/objectives-of-environmental-justice