Before revision: In the US, sewers back up annually an estimated 400,000 times, and municipal sewer overflows on 40,000 occasions.Whitman, D. (2000) The sickening sewer crisis.
After revision: "In the US, sewers back up annually an estimated 400,000 times, and municipal sewer overflows on 40,000 occasions.Whitman, D. (2000) The sickening sewer crisis.