A water treatment plant has 6 settling tanks that operate in parallel (the flow gets split into six equal flow streams), and each tank has a volume of 600 m3. If the flow to the plant is 10 MGD, what is the retention time in each of the settling tanks? If, instead, the tanks operated in series (the entire flow goes first through one tank, then the second, and so on), what would be the retention time in each tank?