18-Env-B2 Water Resources · May 2016
Nivaar worked solution (AI-drafted; not reviewed by a licensed engineer)
National Exams — May 2016 — 04-Env-B2 / Water Resources. 3 hours duration; closed book; Casio or Sharp approved calculator only. Six Problems are printed; any five constitute a complete paper (the first five answered are marked). Each Problem is worth 20 marks. All six are solved below for completeness.
Reference texts. Linsley, Kohler & Paulhus, Hydrology for Engineers (3rd ed.); Chow, Open-Channel Hydraulics; Freeze & Cherry, Groundwater; Davis & Cornwell, Introduction to Environmental Engineering (6th ed.); Ontario Ministry of the Environment, Stormwater Management Planning and Design Manual (2003); Fisheries Act, Ontario Water Resources Act, Clean Water Act, 2006 (Ontario).
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.
An algae bloom is the rapid, excessive proliferation of algae (often cyanobacteria, popularly called "blue-green algae") in a water body, most commonly triggered when the concentration of a limiting nutrient — almost always phosphorus in freshwater systems — rises well above background levels while temperature and light conditions favour growth. Visible symptoms include surface scums or discolouration, and the bloom's decay by bacteria consumes dissolved oxygen, driving hypoxic "dead zones" that kill fish; some cyanobacterial blooms also release toxins (e.g., microcystin) that threaten drinking-water supplies, recreational users, and wildlife. An algae bloom is the visible symptom of cultural (human-accelerated) eutrophication — the nutrient over-enrichment of a water body beyond its natural productivity.
| Source | Pathway |
|---|---|
| Municipal wastewater treatment plant effluent | Point-source discharge, especially from older or hydraulically overloaded secondary plants with limited phosphorus removal. |
| Combined sewer overflows (CSOs) | Untreated sewage-stormwater mixture bypasses treatment during wet weather and discharges directly to tributaries feeding the lake. |
| Lawn and turf fertilizer runoff | Phosphorus-based fertilizer washed off residential lawns, parks, and golf courses by rainfall/irrigation into storm sewers. |
| Pet waste and organic debris | Un-collected pet waste and decomposing leaf litter/grass clippings on streets are washed into catch basins, adding organic phosphorus. |
| Construction-site erosion and sediment | Eroded soil particles (phosphorus readily adsorbs to fine sediment) carried by runoff from disturbed, un-stabilized urban development sites. |
| Failing septic systems | Inadequately treated effluent from failing septic systems in unsewered urban-fringe areas leaches phosphorus to shallow groundwater and tributaries. |
| Legacy phosphate detergents | Historic phosphate-based household detergents (now largely restricted in Canada) remain a contributing legacy/residual source in some older systems. |
Controlling urban phosphorus loading to Lake Erie requires action at every stage between source and receiving water. At the treatment plant, upgrading to tertiary/enhanced phosphorus removal (chemical precipitation with alum or ferric chloride, or biological phosphorus removal) and expanding wet-weather capacity to reduce CSO frequency directly cuts point-source loading. At the source, provincial restrictions on phosphorus-based lawn fertilizer sale/use and phosphate-free detergent requirements reduce the mass of phosphorus entering the urban system in the first place, and public education/bylaws on pet-waste pick-up and proper fertilizer application reinforce this.
Within the drainage system, low-impact development (LID) and stormwater best-management practices — bioretention cells, vegetated bioswales, wet ponds, and permeable pavement — capture and treat runoff before it reaches a receiving watercourse, while routine street sweeping and catch-basin cleaning physically remove particulate-bound phosphorus before a storm can mobilize it. At the land-development stage, mandatory erosion and sediment control on construction sites and vegetated riparian buffer strips along urban streams filter sediment-bound phosphorus before it reaches the tributary network. Applied together, these source-control, conveyance-level, and end-of-pipe measures are what a watershed-scale nutrient-management plan for Lake Erie combines to reduce the urban phosphorus load driving its recurring algae blooms.
