Question 2 of 20: Generation Rate and Composition Survey

Question 2: Generation Rate and Composition Survey (6 marks)

Question text not reproduced: the examination questions are © Engineers and Geoscientists BC. Open the official past paper (linked at the top of this page) to read the question, then follow the worked solution below.

2.1 Approach. Begin by defining the generator categories to be surveyed separately (single-family residential, multi-family, commercial, institutional, industrial) since generation rate and composition differ materially by source. For each category, conduct a load-count/weigh-scale analysis at the disposal facility (weigh a statistically representative sample of collection routes over several consecutive weeks) to establish generation rate in kg/capita·day or kg/employee·day, and a physical composition (sort) analysis — hand-sorting a randomly selected sample (typically 90–200 kg per sample, per ASTM D5231-type protocol) into standard categories (paper, plastics, metals, glass, organics/food, yard waste, other) by wet weight, repeated across multiple sampling events to capture statistical variability. Cross-check the field-measured generation rate against records from existing hauling contracts and landfill scale-house tonnage where available.

2.2 Estimating the seasonal factor without time to measure it directly. With only 30 days available, direct year-round sampling is impossible, so the seasonal adjustment must be estimated by proxy rather than measured: (i) obtain historical monthly landfill/transfer-station tonnage records (if the community or a similar nearby jurisdiction has multi-year records) and compute the ratio of peak-month to average-month tonnage as a seasonal peaking factor; (ii) supplement this with published seasonal-variation factors from comparable climate/community-type literature (e.g. Tchobanoglous's typical seasonal variation curves, which show summer/yard-waste-season peaks of 15–30% above the annual average in temperate climates); and (iii) explicitly flag the 30-day estimate as provisional in the report, recommending a full 12-month monitoring program be initiated concurrently so the assumed factor can be replaced with directly measured data once available.

This proxy approach is defensible engineering practice precisely because the report explicitly discloses its own limitation rather than presenting a single-season snapshot as if it were annual truth. A junior engineer who instead extrapolated the 30-day sample directly to a full-year design basis would risk under-sizing collection routes and transfer capacity for the summer/yard-waste peak, or over-sizing them for the rest of the year — both are costly design errors that a documented, literature-anchored seasonal factor helps avoid, and both are far more expensive to correct after equipment and routes have already been procured than to prevent at the planning stage. The recommendation to launch concurrent 12-month monitoring also protects the client: it converts an assumption into a scheduled correction, so the design basis self-improves as real data becomes available rather than staying frozen at a 30-day approximation. Presenting the seasonal factor honestly as a bounded estimate, rather than a single precise figure, is itself part of professional practice under a tight reporting deadline.