In short - it depends. In general, most experts agree that running burns around 100 calories per mile. However, this can vary greatly depending on your size, weight, and running efficiency. The "100 calories per mile" rule is for individuals of average weight. However, the more you weigh the more calories you burn because a bigger body requires more energy to move. (Typically, "average" for females is around 150 pounds and "average" weight for males is 200 pounds. If you weigh more or less than the average, you can roughly estimate that you'll burn more or less per mile.)
If you are a really efficient runner (meaning, your heart rate doesn't escalate dramatically as you run), then you'll burn less calories. Over time, as you get into better shape, you will become a more efficient runner and so you need to run faster and get your heart rate pumping harder in order to become inefficient and get your calorie burn up. It's also important to know that running faster doesn't immediately equate to more calories burned. Running a mile in six minutes burns the same amount as a 10-minute mile. However, the faster you run, the more miles you can get in in the same amount of time and ultimately, the more calories you'll burn in a specific time frame. And most importantly, the fast your run, the more EPOC (excess post-exercise oxygen consumption) you'll experience. This means that, although the immediate calorie burn is the same when comparing a 6-minute mile to a 10-minute mile, your heart rate will likely get higher running a 6-minute mile, and thus, it takes your body longer to recover. This means that your base calorie burn will remain heightened for a longer period of time FOLLOWING the end of your run. So you'll actually end up burning more calories later on.
You mentioned that you incorporate intervals into your run. I'm assuming you mean speed intervals, and if calorie burn is your goal, this is an excellent way to train! Speed intervals will rapidly increase your heart rate, and you'll burn more calories in the long term than if you were to just leisurely jog the entire 30 minutes at a steady pace.