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Lesson 3 | Water Purification | Sewage Treatment

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Lesson 3: Watersheds Objective In this lesson we will answer the following questions:      What is a watershed? Why are watersheds important to water/wastewater treatment plant operators? How is contamination in water affected by the distance from the contamination source? How do we find the boundaries of a watershed on a topographical map? What problems in a watershed should a plant operator be aware of? Reading Assignment There is no set reading assignment for this lesson. However, you
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  Lesson 3:   Watersheds   Objective  In this lesson we will answer the following questions:     What is a watershed?    Why are watersheds important to water/wastewater treatment plantoperators?    How is contamination in water affected by the distance from thecontamination source?    How do we find the boundaries of a watershed on a topographical map?    What problems in a watershed should a plant operator be aware of? Reading Assignment  There is no set reading assignment for this lesson. However, you should use your textbook toclarify your understanding of watersheds. Lecture   The Importance of Watersheds   What is a Watershed?   By definition, a watershed is an area where all rainfall collects into a common location. Thecommon location could be a stream, a pond, a river, etc.Smaller watersheds flow into increasingly larger watersheds. For example, Mountain EmpireCommunity College contains three small watersheds. All three watersheds eventually flow intothe Powell River, so they are all part of the Powell River watershed, also known as the PowellRiver basin. The water in the Powell River ends up in the Gulf of Mexico, so Mountain EmpireCommunity College is also in the Gulf of Mexico's watershed.The headwaters of a river are made up of first order streams. The watershed of a first order stream cannot be broken down into smaller watersheds because water feeding first order streamsflows directly into the streams. The water may srcinate as runoff from rainfall or asgroundwater welling up from below the earth's surface.Each watershed has its own unique characteristics. Size, permeability of the soil, vegetationtype, soil type, slope, microorganisms, pH, DO (Dissolved Oxygen), and temperature all affectthe water in a watershed. As you will see, each watershed also presents its own problems for thewater treatment technician. Potable Water Treatment  There are many possible sources of contamination in a watershed. Septic tanks, airports,automobiles, industrial facilities, mining operations, and agricultural lands all contribute to thecontamination. In addition, various other sources and processes contaminate the water supply.We are not as concerned about the microbial contamination of the water supply in potable water treatment as we are about other types of contamination. Bacteria are killed or removed duringthe water treatment process as we flocculate, filter, and disinfect the water. But knowing theamount and type of contamination in the treatment plant's watershed can influence how muchchemical treatment (usually alum and lime) is necessary to produce floc from the water.Every watershed has different characteristics - different colloids, different pH, and so forth. Theonly thing that is common in water treatment with respect to a watershed is that every watershedis unique. So the reason we are interested in the front end of a watershed is to determine how best to treat the water. Waste Water Treatment Why are we interested in the sewage treatment end of a watershed? Communities must releasetreated sewage into streams and rivers. In addition to meeting standards set by theEnvironmental Protection Agency (EPA), waste water treatment facilities must also consider where the released water is going.There are often endangered species, such as mussels, and other organisms of concern in thestreams below waste water treatment facilities. We have to be sensitive to life downstream as werelease treated sewage water into our watershed. The wastewater treatment facility strives tomaintain the health of the downstream ecosystem.Our watershed also becomes the watershed of another water treatment facility somewheredownstream. That facility will be concerned about what we're putting into their watershed for treatment purposes just as we're concerned about the waste water treatment facilitiesupstream. So watershed is an important concept within both water treatment and sewagetreatment. BoundariesWatershed Boundaries and Contamination     How do we know the boundaries of the watershed? Edges of a watershed are usually found inthe highest areas around. There, water falling as rain on one side of the mountain or hill runsdown into one watershed while water falling on the other side of the mountain or hill runs downinto another watershed.As I mentioned previously, there are three watersheds on the property at Mountain EmpireCommunity College in Big Stone Gap, Virginia. All three watersheds eventually empty into thePowell River. If there is contamination in one watershed and none in the other two,contamination still reaches the Powell River.
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