Groundwater - Started November 10th 2011 Earth/Envir Sc...

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Unformatted text preview: Started November 10th, 2011 Earth/Envir Sc 1G03 Earth & the Environment Glacial deposits, groundwater & landfilling practices Outline 1. 2. 3. 4. * Introduction Glacial deposits in southern Ontario Groundwater system - aquifers, aquitards - sources of groundwater contamination Landfilling practices Read Chapter 15 GROUNDWATER Answer this question: What is a Thermal Aquifer Energy Storage System? Scarborough Bluffs 1. Introduction What is the connection between glacial deposits, water supply and waste disposal?? Need to understand deposits to - Locate, develop & protect aquifers (water supply) - Identify groundwater contaminant migration paths - Locate suitable future landfill sites 2. Glacial deposits in S. Ontario - Repeated episodes of glaciation over past 2 million years What kinds of deposits would you expect? lake muds TILLS - Also deltaic sands *typical glacial lake water - full of silt Glacial stratigraphy of S. Ontario Alternating layers of... - fine-grained sediment (tills, lake muds) - coarse-grained sediment (sands, gravels) 3. Groundwater System Groundwater water beneath the surface of the earth - fills cracks, cavities, pore spaces between grains Magnified sand - showing pore spaces Groundwater movement Groundwater moves through sediments and rocks - from areas of recharge - to areas of discharge (streams & lakes) Fig 15.4 Aquifers and aquitards Aquifer - a rock or sediment that holds and transmits enough water to be useful as a source of water Aquitard - a rock or sediment with slow rates of water movement (ex; clay, shale) ex; sand, sandstone Permeability Measure of how readily fluids pass through material How fast do you think fluids would move through sands? 10m/day sands *large pore spaces 1000m/day gravels 0.1-0.001m/day till 0.00001m/day clay Aquifers/aquitards in S.Ontario sands - Glacial deposits form a 'layer cake' of aquifers and aquitards muds sands - sands --> aquifers - tills/mud --> aquitard muds Sources of contamination What are the major sources of groundwater contamination? Agriculture - fertilizers, pesticides - 80% rural wells in S. Ontario contaminated by pesticides Agricultural sewage - Contamination by untreated agriculture sewage was responsible for Walkerton tragedy - shallow aquifer - jointed bedrock Lab report showing high E. coli counts Box 15.3 Domestic septic systems Most often work well BUT! Release chlorides, nitrates, potassium, organic carbon from cleaning fluids - fecal bacteria if not working eectively Fig. 15.8 Industrial activity Produces and stores wide range of chemicals Leaking underground storage tanks Gasoline tanks 1 litre of gas can contaminate 4 million litres of groundwater Surface storage of gas can be a problem Fig. 15.17 Road de-icing chemicals Road salt - in GTA --> 300,000 tons of salt are used each winter - 50% enters groundwater Leaking landfills - Municipal and industrial landfills leak contaminants 4. Landfilling practices Most residential garbage disposed of in SANITARY LANDFILLS - garbage compacted and covered each day with layer of earth - decomposing garbage produces: LEACHATE - liquid Gas METHANE Leachate plumes - Leachate escaping from landfills forms a leachate plume - Landfills can be the most significant source of groundwater pollution in urban areas Leachate plumes can contaminate water supplies Municipal water supply Leachate plume landfill Leaky landfills in Hamilton! - 41 closed landfills in Hamilton - 10 are monitored - Upper Ottawa St. landfill received liquid industrial waste - leachate escapes into bedrock below Modern landfills - Lined with impermeable clay - prevents leachate escaping Leachate is collected in pipes embedded in permeable gravels What happens to methane? released in sewage treatment plant Clay liner Methane collection system - Collected in pipes laid among garbage - can be used for power generation (Brock West, Pickering) Old landfill sites Where were these mostly located? - In old sand and gravel quarries (now leak, contaminate aquifers) worst Future landfills What would be the best type of site for a future landfill? - on thick, fine grained sediment - no fractures - slow rates of groundwater movement ...
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