Wastewater Treatment Division |
THE MAIN DRAINObjectivesThe student will do the following:
SubjectsScience, Language Arts, MathTime45-60 minutesMaterials
Background InformationPeople who live in small towns and rural areas are often not connected to a sewage treatment system; therefore, they must depend on an alternative method of disposing of wastewater. Septic tank systems provide a safe and effective means for waste disposal if they are properly sited, installed, and maintained. A septic tank is a large concrete or fiberglass tank that is buried underground. Drainpipes carry sewage and wastewater from buildings into the tank. By bacterial action, much of the sewage is reduced to liquid, which flows out of the tank through the drainpipe to the drainfield. The solids (sludge) settle to the bottom of the tank. This solid material must be periodically pumped out of the tank and disposed of at a waste treatment facility or an approved disposal site. The drainfield allows wastewater to seep into the soil. The soil filters bacteria and nutrients from the wastewater. The water is further purified by the microorganisms that live in the soil. Many states regulate the siting of septic systems and the distance between a septic tank and groundwater resource. They also may specify the types of soil where the system can be placed. Some states and local governments have regulations requiring inspection and maintenance schedules for septic systems. Lagoons, wetlands, and sand filters are other alternative methods that rural areas may use to treat wastewater. However, if these methods are improperly sited, poorly constructed, and/or poorly maintained, they become a serious threat to groundwater quality and public health. TermsDrainfield:the part of a septic system where the wastewater is released into the soil for absorption and filtration.Lagoon:an animal waste treatment method, which uses a deep pond to treat manure and other runoff from a livestock operation. Lagoons can be aerobic or anaerobic. Both use bacteria to break down materials.Sand Filter:a filter system used to treat wastewater where sand and gravel are mounted on top of the natural soil.Septic Tank or Septic System:a domestic wastewater treatment system into which wastes are piped directly from the home; bacteria decompose the waste, sludge settles to the bottom of the tank, and the treated effluent flows out into the ground through drainage pipes.Siting:the process of selecting the correct location for a septic tank.Sludge:solid matter that settles to the bottom of septic tanks or wastewater treatment plant sedimentation; must be disposed of by bacterial digestion or other methods or pumped out for land disposal or incineration.Wetland:an area that, at least periodically, has waterlogged soils or is covered with a relatively shallow layer of water.Advance PreparationA. Gather materials for septic tank model. Prepare the cartons and straws as follows:
C. Have copies of the model diagram (teacher sheet) for the students to refer to during the construction. D. Invite a water quality representative to come to speak to the class. Procedure1) Setting the stage A. Put the following questions on the board or use sentence strips and place them on a pocket chart. (These assume that you are located in an area not served by a wastewater treatment plant.) 1. What happens to the wastewater and sewage when it leaves your house? 2. Where does the sewage/waste water go when it leaves the school? B. Explain how a septic tank system works. Paraphrase the background information. C. Compare/contrast a septic tank system and a wastewater treatment plant. List advantages and disadvantages of both. 2) Activities A. The students will construct a model of a septic tank system with a drainfield. B. Show the class the diagram of the model of a septic tank system. 1. Instruct the students to prepare the large box for the septic tank system model. The box should be filled 1/2 full of soil. 2. Cut the tops from the milk cartons (if this has not previously been done). C. Assemble the septic tank system. 1. Instruct the students to connect the three boxes, from the largest to the smallest, with the straws (refer to diagram). Use ice pick or awl to make holes in boxes (if not already done). Fit the straws into the holes, connecting the boxes with the straws. Use small pieces of masking tape to seal leaks by making "collars" of tape around the connection between box and straw. 2. Instruct them to assemble the drainfield. Connect straws following the diagram of model. (To make the connections between straws, you will have to make large holes in the straw crosspiece; use the ice pick or awl.) Use a large needle to punch drain holes through the straws. Plug the ends of the drains (straws) with modeling or florist clay. Use masking tape to seal any leaks. 3. Test for leaks by putting the model in a sink and filling "house" with water. Water should only come out of the holes in the drain (straws). D. As the assembly progresses, discuss with the students what each part of the model represents. E. Test the septic tank system. 1. Put the model in the box with the porous soil. 2. Pour water in the "house" slowly. Observe what happens. Ask the students to explain what happens. (The water should go to the drainfield and trickle into the soil.) 3) Follow-Up A. Have the students ask their parents what type of wastewater disposal they have. Construct a bar or circle graph to represent the type of wastewater disposal the students have in their home: (1) wastewater treatment plant, (2) lagoon, (3) septic tank, (4) wetland, (5) sand filter. What percentage does each group represent? B. Did any parents tell what type of maintenance schedule has to be followed to keep the system working properly? C. Brainstorm with the group the answers to these questions: 1. What happens if the system does not function properly? (Malfunctioning septic systems will have a smell or have noticeable wetness on the ground above them. Such systems represent a threat to public health and to nearby groundwater supplies.) 2. What do you think will happen to the water supply in the area if the waste disposal system does not work properly or is not maintained adequately? 4) Extensions A. Invite a water quality representative to come and speak to the class about wastewater treatment in their area. 1. Ask what type of waste disposal systems are represented in the area. 2. What kind of local or state regulations or restrictions are mandated for maintenance, siting, and construction of wastewater facilities in the area? B. Write to a local or state water quality agency and ask them to send information about septic tanks. ResourcesBranley, Franklyn M., Water for the World,, Thomas Y. Crowell Junior Books, New York, 1982, p. 77.Environmental Resource Guide: Nonpoint Source Pollution Prevention (Grades 6-8) Air and Waste Management Association, Pittsburgh, Pennsylvania, 1992. Jorgensen, Eric P., ed, The Poisoned Well: New Strategies for Groundwater Protection, Island Press, Washington, DC, 1989. DISCLAIMERThis document was prepared for Legacy, Inc. (not for profit organization) by the Tennessee Valley Authority (TVA), through the Alabama Department of Environmental Management in cooperation with teachers in the southeastern United States and the U.S. Environmental Protection Agency (EPA). Neither the teachers, TVA, EPA, Legacy, Inc., nor any persons acting on their behalf: a. make any warranty or representation, expressed or implied, with respect to the use of any information
contained in this document, or that the use of any information, apparatus, method, or process disclosed in this
document may not infringe on privately owned rights; or
This document does not necessarily reflect the views and policies of the above partners. The use of specific brand names or products should not be construed as an endorsement by any of the partners. TVA, EPA, and Legacy, Inc. are equal opportunity and affirmative action employers. These partners also ensure that the benefits or programs receiving their financial assistance are available to all eligible persons regardless of race, color, national origin, handicap, or age. |