That would be a lot. 40 hours/week in the ER is not like 40 hours/week in an office, at least not where I work. I bust my tail at work seeing lots of patients, dealing with high-stress situations (intubating, cardiac arrests, central lines, etc. - high acuity at my primary site), and worst of all, dealing with disgruntled patients who are tired of their wait and who will be getting Press-Ganey surveys.
Even at 30 hours/week, you can still easily make $200k plus per year (that's taking into account 4 weeks of vacation/year).