18-Env-A6 Solid Waste Engineering and Management · May 2013
Question 6 of 17: Key Considerations in Leachate Generation
Nivaar worked solution (AI-drafted; not reviewed by a licensed engineer)
Notes on this paper
National Examination, May 2013 — 04-Env-A6 / 18-Env-A6, Solid Waste Engineering and Management. 3 hours duration, closed book, one letter-sized aid sheet permitted. All 17 questions constitute a complete paper (100 marks total).
Reference texts: Tchobanoglous, Theisen & Vigil, Integrated Solid Waste Management: Engineering Principles and Management Issues; Vesilind, Worrell & Reinhart, Solid Waste Engineering; Davis & Cornwell, Introduction to Environmental Engineering (6th ed.); CCME, Guidance Document on Landfill Gas Management.
Check: several questions on this paper (Q1, Q13, Q14, Q17) supply an incomplete data set and explicitly invite the candidate to "make and state" assumptions. Every assumed value below is called out where it is introduced and is chosen from standard solid-waste-engineering practice; the governing METHOD, not the specific assumed number, is what the exam is testing.
Question 6: Key Considerations in Leachate Generation (2 marks)
(1) Moisture input to the landfill — precipitation infiltrating through the cover (net of runoff and evapotranspiration) is the primary water source driving leachate; and (2) the refuse's field capacity / moisture-holding capacity relative to its as-placed moisture content — leachate is not generated until the refuse's own storage capacity is exceeded, so density, compaction and initial moisture content all govern when (and how much) percolate becomes leachate. Question 14 works through both of these quantitatively: a water balance on the cover sets the percolation rate, and the gap between the refuse's field capacity and its initial moisture content sets how long that percolation is stored before any of it emerges as leachate.
