I found the same statistic: for MEM grads specializing in Energy and Environment, the average salary was around 65k. While the cost of living varies across the country, in general, for a single person per year, the cost is ~13k. Considering that the median income in the US was around $32k and the average income was around $48k, I would consider $65K a good salary to live on in the US for a single person, but again, this may depend on where you want to live/what your situation is.
As far as the cost of living in Durham, I have read mixed results, but compared to the US as a whole it falls right around the average. This site, while projecting the cost of living in Durham to be slightly above the national average, also offered average rent prices for various bedroom sizes and estimated the average cost for studio and one-bedroom apartments to be around $100 - $200 less per month than the national average. https://www.bestplaces.net/cost_of_living/city/north_carolina/durham
I can't speak from experience regarding the cost of living in Durham, but I'm hoping to ask more about this when visiting campus in the coming months. I can follow up after I learn more, and can post about it so the information is more readily available.