how a conventional ground absorption septic tank system...
TRANSCRIPT
Robert L. Uebler, Ph. D. Soil Scientist
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1. The purpose of this lecture is to explain how a conventional septic tank ground absorption system treats sewage.
Reported in August of 2002 “3.4 million people, mostly children, die annually from water related diseases” The most prominent reason for these deaths is that “2.4 billion people have inadequate sewage disposal facilities” Protection of public health is a primary goal of your job.
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2. If the sewage is not properly treated by the ground absorption system, the occupants of a house may be exposed to disease organisms that are found in sewage, causing them or neighbors to become sick. A properly designed septic tank system will prevent this from happening. The World Health Organization reported in August of 2002 that; “3.4 million people, mostly children, die annually from water related diseases”. Most of these deaths are attributed to the fact that 2.4 billion people have inadequate sewage disposal facilities. Please remember that the protection of public health is a primary goal of your job.
Requires water using fixtures to dispose of waste generated in every house This water carried waste must in turn be treated by either an on-site or central disposal system if Public Health is to be protected.
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3. The plumbing code requires houses in the United States to dispose of waste generated in the house through the use of water fixtures such as the toilet, sink, shower, and washing machine. This water carried waste must in turn be treated by either an on-site or central disposal system if Public Health is to be protected.
Combined wastewater stream from the house is first discharged to a septic tank thru a single pipe at the inlet of the tank.
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4. In a conventional septic tank system. The combined waste stream from these fixtures discharges to the septic tank through a single pipe at the inlet of the tank.
1.)Water - 98% 2.)Suspended Solids 3.)Oil and Grease 4.)Nitrogen 5.)Phosphorus 6.)Virus and Disease Organisms 7.)Fecal Coliform
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5. The combined waste stream from a normal house contains nearly 98% water. The remaining 2% percent of the waste stream may contain many forms of contamination. Household wastewater will normally contain suspended solids, oil and grease, nitrogen, phosphorus, and fecal coliform. The wastewater may also contain disease organisms if a person living in the house is infected with a disease, because our bodies will shed the organism into the waste we discharge.
Suspended solids(mg/l) - 250 Oil and Grease(mg/l) - 60 Total Nitrogen(mg/l) - 70 Total Phosphorus(mg/l) - 24 Fecal Coliform/ 100 ml - 10E6 Virus and Disease - present
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6. The concentration of contaminants in the wastewater is highly variable depending on who occupies the house and the type of fixtures found in the house. The following concentrations are commonly found: 250 mg/l suspended solids, 60 mg/l oil and grease, 70 mg/l total nitrogen, 24 mg/l total phosphorus, and 1 million fecal coliform organisms per 100 ml of water. Not every household will contain a disease-infected person, so the wastewater may not contain disease organisms, which cause polio, hepatitis or other diseases. The potential for the wastewater to contain disease-forming organisms is great though, and we must therefore assume, from a public health perspective, that the organisms are present in the wastewater.
Biochemical Oxygen Demand (BOD)
Def.-The amount of oxygen used during the decomposition of organic material contained in the wastewater.
Household Wastewater - 250 mg/l
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7. The strength of the wastewater is often determined by measuring Biochemical Oxygen Demand, which is abbreviated as BOD. Biochemical Oxygen Demand is defined as the amount of oxygen used during the decomposition of organic material contained in the wastewater. As BOD increases more oxygen is needed to decompose the waste. This is one of the main reasons why we tell users of a septic tank soil absorption system not to pour grease down their drain. Grease has a high BOD, and soil may not have enough oxygen supply to treat this high BOD. A typical household wastewater may have a BOD of 250 mg/l.
Primary Treatment -Settling -Anaerobic Digestion Required Detention Time - 2 days
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8. The wastewater generated in the house enters a septic tank prior to the ground absorption system in a conventional system. The tank is referred to as a primary treatment unit. Primary treatment occurs by two mechanisms in the tank: settling and anaerobic digestion. Septic tanks, which serve most households, are designed to provide a minimum of 2 days detention time for the wastewater. Settle-able solids fall to the bottom of the tank during this time. Organisms, which are able to live without oxygen (anaerobic organisms), may further digest some of the material, which settles in the tank.
House Tank Suspended solids (mg/l) 250 100 Oil and grease (mg/l) 60 20 Total Nitrogen (mg/l) 70 40 Total Phosphorus (mg/l) 24 12 Fecal Coli (org / 100ml) 10E6 10E6 Virus and Disease pres pres
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9. How much treatment occurs in the tank after two days of detention? Wastewater entering the tank with a suspended solids concentration of 250 mg/l might contain 100 mg/l suspended solids upon exiting the tank. Why do some suspended solids remain in the effluent after 2 days of detention in the tank? Anaerobic digestion breaks much of the suspended solids down to a size, which is colloidal, meaning that they will stay in suspension for long periods of time, so called Brownian motion. These suspended colloids will remain in the septic tank effluent even after 2 days of detention time. b. Wastewater entering the tank with an oil and grease concentration of 60 mg/l might exit the tank with a concentration of 20 mg/l. What causes this reduction in concentration? We wash dishes with high temperature water, which in conjunction with detergents emulsifies the oil and grease. Emulsification means that large grease particles are broken down into smaller grease particles, which suspend in the water, and can be rinsed down the drain. Since the tank detains the water for 2 days, water will cool in the tank. As the water cools, the suspended grease and oil is able to congeal back into larger particles. The congealed oil and grease is lighter than water, and floats to the water surface in the septic tank. Since the outlet to the tank has a tee, the congealed material is retained in the tank, causing the observed reduction in concentration of the effluent c. Wastewater entering the tank with 70 mg/l total nitrogen might exit the tank with a concentration of 40 mg/l. One of the primary sources of total nitrogen entering the tank is urea. This is the body’s way of getting rid of excess nitrogen. Anaerobic digestion in the tank converts the urea to the ammonia form of nitrogen. Anyone who has left a disposable diaper in a kitchen garbage can for more than a day has observed the ammonia odor attributable to this process. Other organic forms of nitrogen may settle to the bottom of the tank. The combination of processes occurring in the tank results in a concentration of about 40 mg/l ammonia nitrogen in the effluent discharged from the tank. d. Wastewater entering the tank with 24 mg/l phosphorus might exit the tank with a concentration of 12 mg/l. The phosphorus detained in the tank is an integral part of the settle-able solids at the bottom of the tank. Phosphorus exiting the tank is due to the colloidal solids and components of detergents, such as sodium hexa-meta-phosphate, which are highly soluble, that are used to disperse dirt and grease on dishes. In areas where phosphate detergents are banned the concentration of phosphorus in the effluent will be greatly reduced. e. Wastewater entering the tank with a million fecal coliform per 100 ml is likely to leave the tank with a million fecal coliform per 100 m/l. To understand why fecal coliform concentration is relatively unaffected by detention of the waste in the tank, we need to understand more about the fecal coliform organism. Bacteria may be classified as aerobic, facultative, or anaerobic. Aerobic organisms require oxygen to live. Anaerobic organisms can survive when no oxygen is present. Facultative organisms are able to survive with or without oxygen. Coliform bacteria are anaerobic organisms, which thrive without oxygen. Wastewater in the septic tank is anaerobic owing to digestion of the BOD in the tank. Since water in the septic tank is anaerobic, the coliform bacteria are well adapted to survival in the septic tank, and will be present in the effluent. f. Will disease organisms be present in the effluent from the tank, if wastewater entering the tank contains disease organisms, either bacteria or virus? To answer this question, we must know more about the nature of disease organisms. Remember disease organisms can be shed in the waste we excrete. In order to pass through the digestive system the organisms must be able to survive in the absence of air in our intestines. Most disease organisms are therefore either anaerobes or facultative organisms. Disease organisms are therefore little affected by detention time in the anaerobic environment of the septic tank, and will be present in the effluent, if they are present in the wastewater entering the tank from a house. g. Please refer to the attachment 1, labeled Craven County Innovative and Alternative Demonstration Program. The Craven County Health Department, located in the eastern part of North Carolina, monitored several septic tank systems in the early 1990’s, as part of a demonstration program to find out how different on-site systems performed on difficult sites in the county. The attachment contains data from the effluent of a septic tank from one of the monitored systems during this project. h. If you look at the bottom of the column labeled fecal, you find that the average fecal coliform count in samples collected from the septic tank at this site was 648,667. The effluent ranges from 4 million on 10/20/92 to as low as 30,000 organisms per 100 ml on 3/30/92. The average is close to the one million-number quoted earlier, but why does the concentration vary by date? Think about the use of the system. What happens on laundry day? We often bleach our clothes. Bleach is a disinfectant, which is able to kill some of the organisms in the tank, and lower their concentration in the resulting effluent. Other days we may have company over. Toilet use, on such days, increases compared to other potential sources of wastewater in the house. The concentration of fecal coliform in the effluent will increase on those days. In short fecal coliform content of the effluent will vary over time depending on activities in the house. If you look at the bottom of the column labeled NH3, the average concentration of ammonia is 41.0 mg/l, which is very close to the average of 40 quoted earlier. Looking at the range of concentration for ammonia in the data, we see it varies from a low of 32.3 on 03/24/92 to a high of 54.9 on 03/15/93. For the most part, the sample numbers have less variation around the mean than fecal coliform had. This is because each of use must excrete about the same amount of nitrogen in our urine per day in order to survive as human beings. As a result the concentration of ammonia coming out of the tank is relatively constant because the amount of urea coming into the tank is relatively constant, except perhaps on days when there is a party in the house and more beer is consumed than usual. j. If you look at the bottom of the column labeled total P, the average concentration given at the bottom is 8.6 mg/l, which is fairly close to the 12 mg/l quoted earlier. Phosphorus content varies some by sampling date but there is a narrow range around the average from 12.6 on 10/20/92 to 5.6 mg/l on 02/10/92. The narrow range indicates relatively constant input of phosphorus from the wastewater entering the tank. k. If you look at the bottom of the column labeled TSS, the total suspended solids average 127.6 mg/l, which is close to the figure of 100 quoted earlier. Suspended solids range from 35 mg/l on 10/15/91 to 394 mg/l on 02/10/93. The range is broad like fecal coliform, because it is greatly affected by the variation of activities in the house. If the family is on vacation, there is less total volume of water entering the septic tank, and more residence time in the tank, compared to periods of time when perhaps friends come to visit for a week. Periods of low flow equate to fewer suspended solids in the effluent because there is more detention time in the tank and more settling of solids than during periods of high flow and lower detention time in the tank. l. If you look at the bottom of the column labeled BOD, BOD averaged 252.8, which is fairly typical of a normal residence. The BOD varies widely from 179.8 on 11/23/92 to 375 on 06/16/92. The reasons for this variation are the same as those for the variation of TSS. This real world data is presented to demonstrate that the numbers quoted are not the abstraction of regulators. The numbers used for this discussion are based on factual information obtained in this state and others by the Environmental Protection Agency.
The sewage enters a distribution devise The sole function of this device is to spread the effluent equally to trenches in the soil of the yard. The trenches store the sewage until it infiltrates the soil. The soil must treat the remaining concentration of contaminants in the effluent.
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10. The wastewater, which leaves the septic tank, enters a distribution device in the conventional septic tank system, which then distributes the effluent to trenches in the soil of the yard around house. The trenches simply store the sewage until the soil is able to absorb the wastewater. The remaining contaminants in the wastewater must be treated by the soil, as the sewage seeps from the trench into the soil.
Suspended Solids 1.) Filtration 2.) Digestion by Organism > aerobic > products of digestion - carbon dioxide - water 3.) Aerobic soil, allows aerobic organisms to
digest the solids & prevent clogging of the trenches
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11. How does the soil absorption system treat the remaining 100 mg/l of suspended solids in the septic tank effluent? All soils have porosity that is not occupied by solid soil particles. The suspended solids have a physical size, which is larger than the majority of this soil pore space. The suspended solids are therefore filtered from the wastewater by the soil. If filtration were the only mechanism for treatment of suspended solids, the soil absorption system would rapidly clog with suspended solids. As clogging proceeds the soil would not be able to absorb the septic tank effluent faster than the rate of wastewater generation in the house. Under these circumstances the sewage will begin to come to the top of the ground over the trenches of the soil absorption system. Children playing in the yard might than be exposed to the untreated sewage and become sick. b. Clogging will not occur if soil organisms are able to digest the suspended solids filtered by the soil. You may remember from your Biology classes that when any living organism digests organic matter, the end products are carbon dioxide and water. The carbon dioxide is assimilated into the atmosphere and the water will percolate through the soil until it enters the groundwater or a stream. The suspended solids are therefore transformed into substances, which are harmless to the public’s health and the environment. c. What type of soil environment must exist for the digestion of the suspended solids to occur? Remember that the solids have undergone anaerobic digestion in the septic tank. The soil must therefore be aerobic for further digestion of the remaining solids to occur. That is, the soil pores must contain sufficient oxygen for aerobic organisms to live in the soil and digest the suspended solids. This is why wet soils are not good for a soil absorption system. When water occupies the soil pores, soil atmosphere is displaced, and there is not sufficient oxygen in the pores to maintain the necessary aerobic condition. The soil then becomes anaerobic and clogging will occur, because the remaining solids cannot be digested. Subsequent training in soil evaluation will help you to learn how to identify soils, which will remain aerobic and do not clog in a short periodof time.
Grease and Oil 1.) Filtration 2.) Digestion > aerobic > products - water and CO2 3.) BOD - Higher for grease and oil than most other O. M.
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12. How does soil treat the remaining 20 mg/l of oil and grease in the septic tank effluent? a. Oil and grease is suspended in the wastewater because of detergents that emulsify these substances. Emulsification can be thought of as simply breaking down large grease particles into small particles. These small particles are still larger than the size of the majority of the soil pores, which absorb the wastewater. The oil and grease will therefore be filtered by the soil in the same manner as the suspended solids. b. The oil and grease is organic in nature, and must be digested by aerobic soil organisms in like manner to the suspended solids, if clogging is to be prevented. The by products of digestion are once again water and carbon dioxide, which are recycled to the atmosphere and groundwater. c. Grease and oil unfortunately have a much higher BOD than the suspended solids. This means that the soil pores must supply more oxygen to the aerobic organisms in order to digest the oil and grease compared to suspended solids. Since the soil has a fixed ability to supply oxygen per unit area of soil, this means that more soil area is needed to treat oil and grease than the same mass of suspended solids. Conversely for a given size of system, the absorption system will clog more quickly, if large amounts of oil and grease are flushed into the septic tank from the house. For this reason we educate owners of septic tank systems not to dispose of oil and grease in their kitchen sink. This waste should be separated and disposed of by a means other than the septic tank system, if at all possible. Still and all, the soil is able to digest some grease and oil that cannot be separated, if we are careful not to overwhelm the system with large amounts. The system is therefore able to effectively and safely recycle the grease and oil back to the environment without detrimentally affecting public health or the environment.
Nitrogen 1.) Most nitrogen converts to ammonia in the tank. 2.) Positively charged and attracted to negatively charged soil. 3.) Aerobic nitrifying bacteria - NO3 4.) 40 mg/l nitrate dilutes to <10 mg/l 5.) 40 mg/l nitrate must be diluted to <10 mg/l, if it is to be safe for reuse
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13. How does the soil absorption system treat the remaining 40 mg/l of ammonia nitrogen in the septic tank effluent? Almost all of the nitrogen in the raw wastewater was converted to the ammonium form by anaerobic digestion in the septic tank. b. You should remember from your Chemistry classes that the ammonium ion is a positively charged cation. Positively charged ions are attracted to negatively charged particles in the soil, such as clay, once the sewage effluent enters the soil. c. All well aerated soils naturally contain nitrifying bacteria, which rapidly convert the ammonia that is attracted to the soil particles to nitrite nitrogen. The nitrite-nitrogen is than rapidly converted to the nitrate form by other forms of aerobic bacteria. This rapid transformation is fortunate because nitrite is highly toxic. Since there was 40mg/l of ammonia in the septic tank effluent, the biological transformation process described should result in 40 mg/l of nitrate nitrogen in the treated wastewater leaching through the soil, if all the ammonia is converted to nitrate. If the percolating wastewater enters the groundwater with a nitrate concentration of 40 mg/l this can be problematic. d. The drinking water standard for groundwater is 10 mg/l nitrate-nitrogen. Concentrations of greater than 10 mg/l can cause blue baby syndrome, whereby the baby is not able to adsorb enough oxygen into the blood stream in order to survive. This same mechanism may occur in the elderly, and those with compromised immune systems. How can this problem be solved since groundwater is a primary source of drinking water in our state? e. You may have heard this phrase quoted in ecology class: “The solution to pollution is dilution”. The treated wastewater at 40 mg/l nitrate must be diluted by the naturally occurring groundwater to 10 mg/l nitrate, if problems are to be avoided. Fortunately, the way our rules require septic tank systems to be sited, we normally have enough dilution potential at a site to accomplish this task, and few problems have been observed, unless too many systems are placed in a small area. We have been advised, by US Geologic Survey staff, that the groundwater in our state is capable of diluting up to 1200 gallons of septic tank effluent per acre to safe levels below 10 mg/l.
Phosphorus 1.) Chemically bonds to soil.
2.) Concentration increases 3.) Precipitates as combines
with- Al, Fe, Ca 4.) Insoluble 5.) Fixation
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14. How does the soil absorption system treat the remaining phosphorus in the septic tank effluent? The phosphorus is dominantly in a soluble form as phosphate, when effluent leaves the septic tank. The phosphate ion can chemically bond to the soil. b. The concentration of bonded phosphorus will increase over time as more septic tank effluent enters the soil. c. As the concentration of bonded phosphate increases, the phosphorus forms insoluble precipitates with aluminum, iron and calcium ions found in the soil. d. The precipitates are insoluble, so phosphorus is no longer found in the treated sewage effluent, as it leaches deeper into the soil. e. The process described above is called phosphorus fixation. We are blessed in our state in that almost all of our soils have a high phosphorus fixing capacity. Phosphorus concentrations of the effluent percolating through the soil reach undetectable levels after a short distance of travel through the soil. This is fortunate, not so much from a public health perspective, but more so from an environmental perspective. If high concentrations of phosphorus entered the groundwater, which recharges our rivers and streams through base flow, eutrophication could occur in those bodies of water, causing massive fish kills, due to the nutrient imbalances caused by the phosphorus.
Fecal Coliform Disease Organisms 1.) Anaerobes. 2.) Filtered by the soil and attracted to negatively charged sites. 3.) Cannot compete in aerobic environment 4.) Die off. 5.) Virus is small travels furthest. 6.) Fecal coliform are indicators of human contamination
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15. How does the soil absorption system treat fecal coliform and disease organism, which may be in the septic tank effluent? a. Organisms, which remain in the sewage effluent coming from the septic tank, have a physical size, and are often positively charged. The organisms are therefore attracted to negatively charged soil particles, and are filtered by the soil. b. The organisms, which spread disease, are anaerobes, which survive without oxygen. c. We have seen previously, in our discussion of the other wastewater contaminants, that it is important to have well-aerated soil in order to achieve treatment. This is also true for the treatment of fecal coliform and disease organism by the soil. The disease forming organisms are not able to successfully compete with other soil organisms in the aerobic soil environment. d. The disease forming organisms will die off, when they are detained in soil with an aerobic condition. Research has demonstrated, that fecal coliform are eliminated from the percolating effluent after the sewage effluent moves through as little as 1 foot of soil. e. Viruses are the smallest of the disease forming organisms, and are capable of traveling the furthest in soil. Fortunately, research by Dr. Mark Sobsey at the University of North Carolina at Chapel Hill has shown that even virus is effectively treated by soil absorption systems, as designed in our state. f. One final comment is in order regarding the organisms found in sewage. You may have learned in your ecology classes, that researchers often analyze for fecal coliform, to determine if water has been contaminated by human waste. This is true even though the fecal coliform organism is infrequently the cause of actual disease in humans. Fecal coliform is easy to assay for in the lab, and is a good indicator of the potential for other disease organisms to be present in water. For this reason it has long been used as an indicator of contamination from human waste that may have disease potential.
Simple Reasonable in cost Treatment effective Responsible for treating half of the sewage in
our state
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16. Well we have seen that the soil is able to very effectively treat all the contaminants, which leave the septic tank, without causing detrimental effects to the environment or public health. It is truly a miracle that a system, which is so simple, is able to treat sewage as well as a large municipal treatment plant. The system is also cost effective compared to large municipal systems. Because of their simplicity, reasonable cost, and treatment effectiveness, septic tank systems serve about one half of the households in North Carolina. We know that soil is an effective treatment media, but how much soil depth is required below the trench bottom in order to achieve this treatment. Work done by Dr. Ray Reneau and colleagues in Virginia provides some answers. Please refer to attachment number 2. Septic tank effluent was applied to large undisturbed soil columns, which were maintained in a field setting. The effluent had a BOD of 116 mg/l, Nitrate of 0.32 mg/l, Ammonium of 38.0 mg/l, Phosphate of 3.36 and Fecal Coliform of 35,800 organisms/100ml. The concentrations are similar to those previously discussed except for phosphate and Fecal Colifom. The phosphate concentration is low, because phosphate detergents are banned in the research area. The low Fecal coliform count is not explained by the researchers. You can see from the data in the attachment that, by the time the effluent leaches through 6 inches of clay loam soil, concentrations in the leachate have been reduced to 2.32 mg/l BOD, 1.68 mg/l ammonium, and phosphate was below the detection level of the instrument used to measure phosphate. Fecal coliform have been reduced to 910 organisms/100ml. By the time the effluent leaches thru 12 inches of clay loam soil nearly all of the BOD, ammonium, and phosphorus are removed from the leachate. The BOD is filtered and digested and the phosphorus is fixed by the soil in an insoluble form. Where did the ammonium go? We see from the data in the table that there are 21.3 mg/l of nitrate-nitrogen in the leachate from 18 inches of soil. The ammonium has been converted to the nitrate form by the bacteria in the soil. The high rate of ammonium conversion to the nitrate form indicates that the soil used in the study was well aerated. Why is the concentration of nitrate not equal to the concentration of ammonium, 38.0 mg/l, that was applied to the soil? Some dilution may have occurred and some de-nitrification may have occurred. De-nitrification is the conversion of nitrate to nitrogen gas, which would be released to the atmosphere. Looking at the Fecal Coliform column in the table we see that the leachate contains only 70 organisms after moving thru 12 inches of soil and none are detected in the leachate that has moved thru 18 inches of soil. This supports the fact that the soil must have been well aerated, so the anaerobic fecal organisms where not able to survive in the soil. Our rules require septic tank systems to be designed with 12 inches of suitable well-aerated soil below the bottom of the trenches. The data from this study provide the rational for this requirement. The concept of 12 inches of soil depth below a trench and well aerated soil are central to our work. Please remember these concepts. They may show up on a test one day.
1.) The volume of sewage produced in the house 2.) The long-term acceptance rate, LTAR, that the soil maintains for absorption of the sewage.
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17. In addition to soil depth, we must also determine how much area is needed to install the trenches of a system. The amount of area required depends on two factors: 1.) The volume of sewage produced in the house and 2.) The long-term acceptance rate, LTAR, that the soil maintains for absorption of the sewage from the trench into the soil.
Many studies have shown the average household occupant generates 60 gallons of wastewater in a day.
- we assume 2 people per bedroom - 2 x 60 = 120 gal/bedroom/day - 3 bedrooms x 120 = 360 gal/day
* Smallest design flow for any house = 240 gal/day*
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18. The actual volume of wastewater generated in a home depends on the number of occupants. Many studies have shown that the average household occupant generates 60 gallons of wastewater in a day. You can look at your own water bills to see how close your water usage comes to this figure. I was amazed at how close my water use came to this figure, because I always assumed I used less water than most. Now, for design purposes, we assume that no more than 2 people will occupy each bedroom. The design flow per bedroom would therefore be 120 gallons/day. For a 3-bedroom home this means that the design flow would be 360 gallons/day. For each additional bedroom, another 120 gallons per day is added to the design flow. There is one exception to this Rule. The smallest design flow for a house allowed by our Rules is 240 gallons per day, even if the house only has one bedroom.
Design flow in gallons per day Divided by LTAR in gallons per square foot per day
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19. The design flow in gallons per day is divided by the LTAR in gallons per square foot per day to determine the required trench bottom area when designing the septic tank system for a site. Two of your most important job duties will be to properly assign design flow and determine the correct LTAR for a site so that the house has an adequately sized septic tank system to serve the house.
Match the assimilative capacity of the soil to treat wastewater to the amount of water coming from the house so that the septic system does not fail
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20. In subsequent lectures you will learn how to correctly perform a site and soil evaluation. In a nutshell, the purpose of your evaluation is to match the assimilative capacity of the soil to treat wastewater to the amount of wastewater coming from the house so the septic tank system does not fail.
Surfacing of untreated waste -direct exposure to disease
Contamination of Groundwater Contamination of Surface Water
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21. System failure would result in: a. The surfacing of untreated wastewater and the exposure of people to disease potentially contained in the waste; or b. The contamination of groundwater; or c. The contamination of surface water. d. Public and Environmental Health are jeopardized if any of these 3 forms of failure occur. Your job is therefore an important one whose responsibilities need to be taken seriously. Conclusion: We sincerely hope that the information provided by this presentation helps you understand the scientific background of the career you have chosen, and gives you a clear understanding of the purpose of your job. Information from biology, chemistry, geology, math and physics classes is used extensively in this field of endeavor. The purpose of this training is to help you apply what you have already learned, in college and high school, to your chosen occupation. Hopefully you can now see that all the studying you did had a useful purpose. Good luck to you in the pursuit of your career.