Another reason why it might be for you? Think about accidental spills during refilling. You might not think much about it, but the oil that seeps into the ground accumulates, giving it irreparable damage over time. As an environmental concern, this is huge, which is why some countries like the UK have made bunded oil tanks a requirement for commercial and domestic installations that exceed capacities of 2,500 liters.
Other points for environmental risk assessment include bodies of water that might be near the oil tank. In a major spill, oil might find its way towards the nearest body of water and pollute the water supply.