the questions below

3 (a) (b) 4 (a) (b) (c) (d) 3081/205 Explain the steps followed in the use of the Thiessen polygon method for computing areal rainfall. (9 marks) A rainfall storm yielded the information in table 1. Compute the average depth of rainfall for the area. (11 marks) Table 1 Isohyet Intervals inmm |75-85 | 85-95 | 95-105 | 105-115 115-125 | 125-135 meee? is ee eee State four objective of water purification. (4 marks) With the aid of a diagram, show the zones in a rectangular sedimentation basin and state the activity in each zone. (7 marks) With regard to sewage sampling, describe the following: (i) grab sample; (ii) | composite sample. (4 marks) (1) Define BOD (Biochemical Oxygen Demand). (ii) | A waste water has 5-day BOD at 20C as 210 mg/l. Assuming the reaction constant ki is 0.2 day determine the ultimate first stage BOD of the waste water. (5 marks) 2