Fundamentals of Environmental Engineering Chapter 6 While 67% of Earth’s surface is covered by water, only less than 2.7% of global water is freshwater. Most of the freshwater (2.05%) are locked in ice caps and glaciers. Only less than 0.7% is available for human use Reservoir Ocean Ice caps & glaciers Groundwater Lakes Soil Moisture Atmosphere Streams & rivers Biosphere Volume of water (106 km³) 1370 29 9.5 0.125 0.065 0.013 0.0017 0.0006 Percent of total 97.25 2.05 0.68 0.01 0.005 0.001 0.0001 0.00004 Climate change causes change in frequencies of droughts and floods. Depletion of aquifers caused by overconsumption as a result of population growth. Pollution and contamination by sewage, agricultural and industrial runoff. In a water molecule two hydrogen atoms form single polar covalent bonds with an oxygen atom. Gives water more structure than other liquids ◦ Because oxygen is more electronegative, the region around oxygen has a partial negative charge. ◦ The region near the two hydrogen atoms has a partial positive charge. A water molecule is a polar molecule with opposite ends of the molecule with opposite charges. Water has a variety of unusual properties because of attractions between these polar molecules. ◦ The slightly negative regions of one molecule are attracted to the slightly positive regions of nearby molecules, forming a hydrogen bond. ◦ Each water molecule can form hydrogen bonds with up to four neighbors. Hold water molecules together Each water molecule can form a maximum of 4 hydrogen bonds The hydrogen bonds joining water molecules are weak, about 1/20 th as strong as covalent bonds. They form, break, and reform with great frequency Extraordinary Properties that are a result of hydrogen bonds. ◦ Cohesive behavior ◦ Resists changes in temperature ◦ High heat of vaporization ◦ Expands when it freezes ◦ Versatile solvent Solution ◦ Solute ◦ Solvent Aqueous solution Hydrophilic (water-loving) ◦ Ionic compounds dissolve in water ◦ Polar molecules (generally) are water soluble Hydrophobic (water-fearing) ◦ Nonpolar compounds Any chemical, biological, or physical change in water quality that has a harmful effect on living organisms or makes water unsuitable for desired usage. WHO: 3.4 million premature deaths each year from waterborne diseases 1.9 million from diarrhea U.S. 1.5 million illnesses 1993 Milwaukee 370,000 sick Impaired Waters Section 303(d) of the Clean Water Act requires states to develop lists of impaired waters, those that do not meet water quality standards that states have set for them. Total Maximum Daily Load The law requires that states establish priority rankings for impaired waters and develop total maximum daily loads (TMDLs) for them. A TMDL specifies the maximum amount of a pollutant that a body of water can receive and still meet water quality standards. Pollutant build-up and wash off are affected by land use. Imperviousness increases runoff Land use changes impact build up Linking Land Use to Water Quality More Imperviousness = More Water What is impervious cover? roads, rooftops, parking lots, and other hard surfaces that do not allow stormwater to soak into the ground “predominant American vegetation” Impervious Cover • provides a surface for accumulation of pollutants • leads to increased polluted runoff and flooding • inhibits recharge of groundwater Pollutants Found in Runoff Sediment Soil particles transported from their source Biochemical Oxygen Demand (BOD) ● Oxygen depleting material Leaves Organic material Toxics ● Pesticides Herbicides Fungicides Insecticides ● Metals (naturally occurring in soil, automotive emissions/ tires) Lead Zinc Mercury ● Petroleum Hydrocarbons (automotive exhaust and fuel/oil) Debris Litter and illegal dumping Nutrients ● Various types of materials that become dissolved and suspended in water (commonly found in fertilizer and plant material): Nitrogen (N) Phosphorus (P) Bacteria/ Pathogens Originating from: ● Pets ● Waterfowl ● Failing septic systems Thermal Stress Heated runoff, removal of streamside vegetation Potential Sources of Pollutants Found in Residential Areas Nutrients: Fertilizers and septic systems Pathogens: Pet waste and septic systems Sediment: Construction, road sand, soil erosion Toxic: Pesticides, household products Debris: Litter and illegal dumping Thermal: heated runoff, removal of streamside vegetation Sediment Nutrients Pathogens Pesticides Why are these pollutants important? Sediment reduces light penetration in stream, clogs gills of fish and aquatic invertebrates. Nutrients act as fertilizer for algae & aquatic plants which can cause highly varying dissolved oxygen levels. At low DO levels, the aquatic life has the potential to be harmed. Toxics can impact life and contaminate drinking water supplies. Bacteria/Pathogens are an indicator of possible viruses present in the system. Which is generally more polluted? ~ Surface Water Which is harder to clean up? ~ Groundwater Ground water refers to water in the saturated zone -0.6% of the world’s total water supply 05/07/2020 23 landfills leaky underground storage tanks mines septic tanks hazardous waste - deep well injection any pollutant in runoff that percolates 05/07/2020 25 Groundwater can become contaminated No way to cleanse itself Little dilution and dispersion Out of sight pollution Prime source for irrigation and drinking REMOVAL of pollutant difficult • pesticides, herbicides, fertilizers: chemicals that are applied to agricultural crops that can find their way into ground water when rain or irrigation water leaches the poisons downward into the soil • rain can also leach pollutants from city dumps into ground-water supplies • Heavy metals such as mercury, lead, chromium, copper, and cadmium, together with household chemicals and poisons, can all be concentrated in ground-water supplies beneath dumps • liquid and solid wastes from septic tanks, sewage plants, and animal feedlots and slaughterhouses may contain bacteria, viruses, and parasites that can contaminate ground water. • acid mine drainage from coal and metal mines can contaminate both surface and ground water. • radioactive waste can cause the pollution of ground water due to the shallow burial of low-level solid and liquid radioactive wastes from the nuclear power industry. Nitrates Nitrates in water originates mainly from 4 sources: 1. Application of nitrogen fertilizers and animal manure 2. Atmospheric deposition 3. Human sewage deposited in septic systems 4. Cultivation of the soil 05/07/2020 29 • pumping wells can cause or aggravate groundwater pollution Water table steepens near a dump, increasing the velocity of ground-water flow and drawing pollutants into a well Water-table slope is reversed by pumping, changing direction of the ground-water flow, and polluting the well Groundwater Pollution: Causes Low flow rates Few bacteria Low oxygen Cold temperatures Hazardous waste injection well Pesticides Coal strip mine runoff De-icing road salt Pumping well Waste lagoon Gasoline station Water pumping well Landfill Buried gasoline and solvent tank Cesspool septic tank Sewer Leakage from faulty casing Accidental spills Discharge Confined aquifer Groundwater flow Prevention is the most effective and cheapest Monitor aquifers Find less hazardous substitutes Leak detection systems Strictly regulating hazardous waste disposal Store hazardous materials above ground Part of monitoring is trying to find the source of pollutants. Point Sources: ◦ Specific locations where a pollutant enters the environment. Unlike pollution from industrial and sewage treatment plants, comes from many diffuse sources. NPS pollution is caused by rainfall or snowmelt moving over and through the ground. As the runoff moves, it picks up and carries away natural and human-made pollutants, finally depositing them into lakes, rivers, wetlands, coastal waters, and even our underground sources of drinking water. Golf courses, construction sites Acid rain is a nonpoint pollutant.
