Nivaar worked solution (AI-drafted; not reviewed by a licensed engineer)
Paper format. National Examination, May 2015 — 98-Civ-B5 Water Supply and Wastewater Engineering. Three hours; closed book, with one aid sheet written on both sides and an approved calculator. Question 1 is compulsory and any three of Questions 2–5 are attempted; every question carries 25 marks, so the examinable total is 100. All five questions are solved below, because the set is intended as a study resource rather than an exam script.
Reference texts.
Check: the numbers in this paper are the solver’s own. The May 2015 sitting of 98-Civ-B5 is entirely descriptive — not one numerical datum is printed anywhere on the exam. Every quantity used below is an illustrative value chosen to put a defensible magnitude on a qualitative statement, and each one is declared in a Given. line before it is used. Dissolved-oxygen saturations are the standard fresh-water, one-atmosphere table values (9.08 mg/L at 20 °C, 7.54 mg/L at 30 °C); water properties are taken at 20 °C (\(\rho = 998.2\ \text{kg}\,\text{m}^{-3}\), \(\mu = 1.002\times10^{-3}\ \text{Pa}\cdot\text{s}\)). An examiner would award full marks for the descriptive argument alone; the arithmetic is offered because a number makes the mechanism concrete.
