Complex sentence: USTs, used to store petroleum, are regulated in the United States to prevent release of petroleum and contamination of groundwater, they are used throughout North America at automobile filling stations and many have leaked, allowing petroleum to contaminate the soil and groundwater.
Split into simpler sentences: USTs, used to store petroleum, are regulated in the United States to prevent release of petroleum and contamination of groundwater. USTs are used throughout North America at automobile filling stations and many have leaked, allowing petroleum to contaminate the soil and groundwater.