1. Wastewater Management
Civil Engineering and Architecture
© 2010 Project Lead The Way, Inc.

2. Wastewater Management
Civil Engineering and Architecture
Unit 2 – Lesson 2.3 – Residential Design
Table of Contents
Wastewater Management
Reuse
Recycle
Discharge and Treatment
Publically Owned Treatment Works
On-Site and Decentralized Wastewater Treatment Systems
How Do Septic Systems Work?
Soil Tests
Reasons for Failure
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Copyright 2010

3. Wastewater Management
Civil Engineering and Architecture
Unit 2 – Lesson 2.3 – Residential Design
Wastewater Management
Reuse
Recycle
Discharge and Treat
Most wastewater from a building is considered to be sanitary wastewater and can include human waste, cleaning solutions, oil and grease from cooking, food particles, and soil from cleaning clothes and floors. Commercial establishments may also discharge metals, acids and bases, and small particles of plastic, glass, stone, etc.
What happens to the wastewater that is discharged from a building through the drain-waste-vent (DWV) system? Wastewater is not safe to drink, and discharging this water directly into the environment (onto the ground or into a water body) can pose health and safety problems. After all, this water is part of the water cycle and will eventually make its way into a source for our water supply. The wastewater must be properly managed to protect human and environmental health and safety.
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4. Wastewater Management
Civil Engineering and Architecture
Unit 2 – Lesson 2.3 – Residential Design
Reuse
Some relatively clean wastewater can be reused without treatment.
Greywater is wastewater generated by washing, laundry, and bathing (not from toilets).
50–80% of domestic wastewater
Reused for irrigation or flushing toilets
Most of the wastewater generated within a residential or light commercial building is greywater and can be reused for nondrinking purposes such as landscaping or flushing toilets. The water can be stored until needed.
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5. Wastewater Management
Civil Engineering and Architecture
Unit 2 – Lesson 2.3 – Residential Design
Recycle
Wastewater can be treated (on-site or off-site) and reused for nondrinking purposes.
Closed-loop treatment systems are often used to capture, treat, and reuse wastewater on-site.
Wastewater reclamation involves treating the wastewater and using it for a different purpose.
Closed-loop systems are often used by car wash facilities to reuse the large quantity of wastewater generated.
An example of wastewater reclamation would be using water treated by a municipal wastewater treatment facility to irrigate public property (e.g., public golf course or park) rather than be discharged into a water body.
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6. Discharge and Treatment
Wastewater Management
Civil Engineering and Architecture
Unit 2 – Lesson 2.3 – Residential Design
Discharge and Treatment
Wastewater is transported to a treatment facility (on-site or off-site), treated, and discharged into a water body.
Publically Owned Treatment Works (POTW)
Decentralized Wastewater Treatment System
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7. Publically Owned Treatment Works (POTW)
Wastewater Management
Civil Engineering and Architecture
Unit 2 – Lesson 2.3 – Residential Design
Publically Owned Treatment Works (POTW)
Owned by a state or municipality
Stores, treats, recycles, and reclaims municipal wastewater
Includes sewers, pipes, and treatment plants
This picture shows a wastewater treatment facility near Atlanta, Georgia.
Photograph by Daniel J. Hippe, U.S. Geological Survey).Courtesy USGS
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8. Publically Owned Treatment Works (POTW)
Wastewater Management
Civil Engineering and Architecture
Unit 2 – Lesson 2.3 – Residential Design
Publically Owned Treatment Works (POTW)
Treatment includes
Primary treatment: Screening and settling
Secondary treatment: Biological treatment in which activated sludge “eats” pollutants
Disinfection: Kills bacteria, viruses, and protozoa
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9. POTW—Example Code Requirements
Wastewater Management
Civil Engineering and Architecture
Unit 2 – Lesson 2.3 – Residential Design
POTW—Example Code Requirements
Minimum Pipe Size
3 in. or 4 in. for residence
6 in. for multifamily or commercial facility
8 in. (at least) for industrial facility
Depth
2 ft below lowest floor with sanitary sewage drainage
Below frost depth
Minimum Sewer Lateral Slope
1/8” per ft (1% slope), BUT
Depends on drainage fixture units served (check code)
Separation
10 ft minimum horizontal distance between water and sewer lines
Sewer lines at least 18 in. below water supply lines
When specifying sewer lateral construction, the size, depth, slope, and separation of the wastewater pipe must meet local code requirements. Note that the IRC allows sewer pipes smaller than 3 in. but, 3-in. diameter pipe is the smallest pipe allowed to serve discharge from a water closet. Therefore, a sewer lateral from a residence can not be less than 3 in. in diameter.
The IRC allows sewer pipe slopes as shallow as 1/8” per ft if the estimated wastewater volume is low. But the size of the pipe and the number of drainage fixture units served dictates the minimum slope.
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10. Drainage Fixture Units (d.f.u.)
Wastewater Management
Civil Engineering and Architecture
Unit 2 – Lesson 2.3 – Residential Design
Drainage Fixture Units (d.f.u.)
Relative “load” of fixtures that are drained by a waste pipe
Type of Fixture
Drainage Fixture Unit Value (d.f.u.)
Bathtub 2
Clothes washer
Dishwasher
Floor drain
Kitchen sink
Lavatory 1
Lavatory tub
Shower stall
Water closet (1.6 gallons per flush) 3
Water closet (greater than 1.6 gallons per flush) 4
The code provides reductions in d.f.u. counts for groups of fixtures typically found together such as bathtubs, lavatories, and water closets in a bathroom. Use the Residential Plumbing Code Requirements to determine d.f.u. for the Affordable Home.
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11. Minimum Drainage Pipe Slope
Wastewater Management
Civil Engineering and Architecture
Unit 2 – Lesson 2.3 – Residential Design
Minimum Drainage Pipe Slope
No less than 1/8” per ft (1% slope)
Maximum Number of Fixture Units Allowed to Be Connected to Building Drain or Building Sewer
Diameter of Pipe (in.)
Slope per Ft
1/8 in.
¼ in.
½ in. 3 36 42 50 4
180
216
250
The minimum slope allowed for a building drain or building sewer is 1/8 in. However, the minimum slope may increase if the number of fixture units served by the building drain or building sewer exceeds specified limits.
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12. Wastewater Management
Civil Engineering and Architecture
Unit 2 – Lesson 2.3 – Residential Design
Building Sewer Slope
 elevation
Cleanout
Sewer Main
Inv. El.
FLOW
Inv. El.
Building Sewer (or Sewer Lateral)
distance from building to main
Building Drain
To meet the minimum pipe slope requirements, designers must be able to calculate the slope of a sewer pipe. Let’s look at the example here and calculate the slope of the sewer lateral. Note that the drawing is not to scale.
The building drain collects the discharge from all other drainage piping inside the house and extends beyond the exterior walls of the home.
The building sewer (also called the sewer lateral) [click] transports wastewater from the house to the sewer main [click]. A short vertical pipe, called a cleanout [click] provides access from the ground surface so that any blockages that cause slow drainage or backups can be more easily removed.
Because wastewater flow is typically dependent on gravity, the waste pipes must slope down [click] in the direction of flow in order for the wastewater to be transported to the sewer main.
You know from your math classes that slope is simply rise over run [click]. When applying this concept to a sewer lateral, the rise will be the distance the pipe drops—in other words the difference in the elevation of the pipe between where it leaves the house and where it connects to the sewer main. We will use the invert elevation of the pipe to calculate the change in elevation. The invert elevation is the elevation of the inside bottom surface of the pipe, where the water will flow. [click]
The run will be the distance from the building to the sewer main.
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13. Wastewater Management
Civil Engineering and Architecture
Unit 2 – Lesson 2.3 – Residential Design
Building Sewer Slope
 elevation
Note: Assume that the elevation of the building sewer invert is equal to the elevation of the center of the sewer main.
Cleanout
Sewer Main
Minimum slope varies
Crown El.
Building Sewer OD
Building Drain
Distance from building to main
Most local jurisdictions specify the connection details for a sewer lateral to a sewer main. For the purposes of this calculation, we will assume that the center of the sewer main is at approximately the same elevation as the invert of the sewer lateral.
The change in elevation (rise) will be the difference between the invert elevation at the building and the invert elevation at the main. [click]
Crown elevation refers to the elevation of the top of the pipe. Therefore the elevation of the center of the sewer main is approximately equal to the crown elevation minus the half of the outside diameter of the sewer main [click]. The elevation calculation may be slightly different than the actual invert elevation of the sewer lateral at the main because we are ignoring the thickness of the pipe and making an assumption that the lateral is installed such that the invert at the connection to the main is at the center of the main. However, in this application the approximation is close enough.
Note that OD stands for outside diameter.
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Copyright 2010

14. Wastewater Management
Civil Engineering and Architecture
Unit 2 – Lesson 2.3 – Residential Design
Building Sewer Slope
Note: Assume that the elevation of the sewer lateral invert is equal to the elevation of the center of the sewer main.
Cleanout
Sewer Main
Minimum slope varies
Inv. El.
Crown El. OD
Sewer Lateral
Building Drain
Finally, if we distribute the minus sign in front of the parenthesis and express the slope in percent (by multiplying by 100%), you get this formula. But remember, this is simply the rise over the run of the sewer lateral pipe. It is the same calculation that you have used in math class.
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15. On-Site and Decentralized Wastewater Treatment System
Wastewater Management
Civil Engineering and Architecture
Unit 2 – Lesson 2.3 – Residential Design
On-Site and Decentralized Wastewater Treatment System
On-site system that collects, treats, and disperses or reclaims wastewater from individual residences, businesses, or small clusters of buildings
Used when no municipal system is available
Approximately 25 percent of single residences in the U.S. and 33 percent of new developments use an on- site and decentralized system
Also called septic system, private sewage system, individual sewage treatment system, on-site sewage disposal system, or package plant
Municipal sanitary systems (POTW) are preferable to on-site systems, but if no municipal system is easily accessible from the site, an on-site system may be the only option.
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Copyright 2010

16. Percentage of State Residents Using Septic Systems
Wastewater Management
Civil Engineering and Architecture
Unit 2 – Lesson 2.3 – Residential Design
Percentage of State Residents Using Septic Systems
More than 40 percent of the population within the red states use septic systems. South Carolina, the location of the Palmetto Project, is a red state.
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Copyright 2010

17. National Water Quality Problems
Wastewater Management
Civil Engineering and Architecture
Unit 2 – Lesson 2.3 – Residential Design
National Water Quality Problems
10 to 30 percent of systems fail annually
At least 10 percent of systems are over 30 years old
Failing septic systems have caused a water quality problem throughout the United States—between 10 and 30 percent of septic systems fail annually. When septic systems fail, sanitary wastewater may leak into nearby surface or ground water sources. Such failures expose people, animals, and vegetation to unsafe contaminates. These pictures show wet areas in septic drainfields. Saturated soils allow raw wastewater to percolate to the surface.
Images courtesy South Carolina Department of Health and Environmental Control (SC DHEC)
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Copyright 2010

18. Wastewater Management
Civil Engineering and Architecture
Unit 2 – Lesson 2.3 – Residential Design
Septic Systems
Image courtesy South Carolina Department of Health and Environmental Control (SC DHEC)
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Copyright 2010

19. Conventional Septic System
Wastewater Management
Civil Engineering and Architecture
Unit 2 – Lesson 2.3 – Residential Design
Conventional Septic System
Septic tank
Distribution box
Drainfield (leach field)
Soil
Septic systems consist of a septic tank, a drainfield (or leach field), and soil.
Courtesy South Carolina Department of Health and Environmental Control (SC DHEC)
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Copyright 2010

20. Wastewater Management
Civil Engineering and Architecture
Unit 2 – Lesson 2.3 – Residential Design
How Do Septic Systems Work?
Septic tank holds liquid for about two days
Sludge (heavy solids) settles out
Scum (grease, oil, floating debris) rises to surface
Anaerobic decomposition breaks down some solids
Tank should be pumped out regularly
The image on the left shows the internal workings of a septic system.
[click] The image on the right shows the installation of several septic tanks for a motel in Florida.
Courtesy South Carolina Department of Health and Environmental Control (SC DHEC)
Courtesy USGS
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21. Wastewater Management
Civil Engineering and Architecture
Unit 2 – Lesson 2.3 – Residential Design
How Do Septic Systems Work?
Septic Tank
Distribution Box
Drainfield
The wastewater is discharged from the septic tank [click] to the distribution box [click].
The distribution box disperses the liquid to the drainfield [click].
The drainfield is made up of perforated pipes on a bed of gravel which are buried underground.
The wastewater infiltrates the soil [click] surrounding the drainfield.
The intent is that the soil filters (treats) the wastewater before it enters the groundwater or a nearby body of water.
Courtesy South Carolina Department of Health and Environmental Control (SC DHEC)
Project Lead The Way, Inc.
Copyright 2010

22. Wastewater Management
Civil Engineering and Architecture
Unit 2 – Lesson 2.3 – Residential Design
Soil Tests
Required tests vary among jurisdictions
Check with local building department
Percolation (perc) test
Dig holes
Fill with water
Measure the rate of infiltration
Length of the drainfield pipes is based on infiltration rate
Some soils cannot adequately accept or treat wastewater. Most jurisdictions require that the soil on which the septic system will be built is evaluated to make sure it can provide adequate treatment. You should check with your local building department to determine how the soil must be evaluated. In some cases local officials must perform the testing.
One example of a soil evaluation method that may be required is the percolation test. A perc test is one method to estimate the rate of water infiltration into the soil. There are many different ways to perform a percolation test—the local building department may identify a specific testing method. A perc test basically consists of digging several holes in the proposed location of the drainfield, filling the holes with water, and timing the drop of the water level to determine the rate of infiltration in each hole.
The length of the drainfield is based on the infiltration rate.
Although some municipalities still require percolation tests in order to obtain a permit to construct a septic system, perc tests have been found to be unreliable in certain cases, especially during a season of heavy rain or drought. Many jurisdictions no longer allow the use of percolation tests to determine infiltration rates. It may be necessary to have the soil evaluated by a professional engineer, geologist, or environmental specialist in order to obtain a permit.
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Copyright 2010

23. Wastewater Management
Civil Engineering and Architecture
Unit 2 – Lesson 2.3 – Residential Design
Reasons for Failure
Poor soils
Drainfield within high water table
System undersized
Poor construction
Poor maintenance
The top picture shows a water-front property with a high water table. This property is not suitable for a septic system.
Proper maintenance is essential in order to keep the on-site decentralized system working properly. The second picture shows a pump truck removing sludge and scum from a commercial septic system tank.
Images Courtesy South Carolina Department of Health and Environmental Control (SC DHEC)
Project Lead The Way, Inc.
Copyright 2010

24. Wastewater Management
Civil Engineering and Architecture
Unit 2 – Lesson 2.3 – Residential Design
Table of Contents
Wastewater Management
Reuse
Recycle
Discharge and Treatment
Publically Owned Treatment Works
On-site and Decentralized Wastewater Treatment Systems
How Do Septic Systems Work?
Soil Tests
Reasons for Failure
Project Lead The Way, Inc.
Copyright 2010

25. Wastewater Management
Civil Engineering and Architecture
Unit 2 – Lesson 2.3 – Residential Design
Resources
South Carolina Department of Health and Environmental Control. (n.d.). Septic systems in coastal South Carolina for professional real estate professionals. Retrieved November 20, 2009, from ech/docs/septic_realtor.pdf
United State Geological Survey. (n.d.). South Florida information access - Hydrogeology of a dynamic system in the Florida Keys: A tracer experiment. Retrieved December 15, 2009, from flkeys/concerns.html
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Copyright 2010