You have created a death trap. If you have a gas spill from a lawn mower or other source, the vapors will fill the stairwell first and the 4" step to the basement might not be sufficient so fume could just hang there. When someone opens the door from the basement, those vapors could flood in, find your water heater and blowup. The step from the garage floor up to the house allows the vapors to sit on the garage floor and seep out around the garage doors. But you have defeated that safety factor by putting a "well" in your garage floor. If I were you I would immediately consult an AIA Architect for a solution. The half door MAY have saved you if it is vapor tight but that seems doubtful.
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Floor-stained concrete
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