Compare the advantages and disadvantages of a combined sewer system versus a separate sewer system. What kind of system does San Francisco have?

Choose your favorite three of the following four questions:
4. (10) Compare the advantages and disadvantages of a combined sewer system versus a separate sewer system. What kind of system does San Francisco have?
5. (10) Explain why turbidity measurements are a poor method to use for assessing the presence of small particles (< 0.01 mm) in your water.