Nivaar worked solution (AI-drafted; not reviewed by a licensed engineer)
National Exams — December 2015 — 04-Env-A4 / Water and Wastewater Engineering. 3 hours duration; closed book with one double-sided aid sheet; approved calculator permitted. Question 1 is compulsory; the paper instructs candidates to attempt any three of the remaining four (100 marks total); all five are solved below for completeness. (The source page prints an internal header inconsistency — "NATIONAL EXAMINATION, MAY 2015" beside a page footer reading "December 2015" — the period is taken as December 2015 per the footer; this does not affect any question content.)
Reference texts. Metcalf & Eddy, Wastewater Engineering: Treatment and Resource Recovery; Davis & Cornwell, Introduction to Environmental Engineering; MWH's Water Treatment: Principles and Design; Guidelines for Canadian Drinking Water Quality (Health Canada).
