Salary
Average Salary: $87,000
Expected Lifetime Earnings: $3,632,076
You're a hot, hot commodity. And hot, hot commodities make bank. Or at least enough to easily pay back those student loans from undergrad.
While there aren't specific numbers for geothermal engineers, there's data for people working in the electric power and transmission industry. Environmental scientists in the industry make an average $87,000 per year (source). Meanwhile, mechanical engineers, who have the same bachelor's degree you're likely to hold, make an average $87,000 as well (source).
For mechanical engineers in general, the benefits are pretty good too. Ninety percent of engineers have medical coverage, more than 75% have vision, and over 50% have dental (source). Starting pay will likely be in the $60,000 ballpark, and if you build up enough experience you might end up making close to $100,000 per year.
Even if you have to settle for a paltry $90,000, it'll still be enough to make your sister with the art history degree (working as an indentured servant to the non-profit industry) green with envy.