This results in contaminated drinking water and other types of environmental damage. Combined sewer overflow events can also cause too much wastewater to reach sewage treatment plants. When this happens the plant is not able to treat the wastewater properly. Even worse, during extremely severe weather events combined sewers can even cause wastewater — including raw sewage — to back-up into inhabited buildings.
The cost to clean up this stinky mess is no insignificant amount. Sanitary sewers carry wastewater from homes and businesses to wastewater treatment plants. When you flush the toilet or wash dishes in the kitchen sink that water is carried away from your home or business through relatively small pipes to the sewer main in the street or to your septic system.
The pipes that take waste from your home or business to the sewer main are only large enough to remove toilet paper and human waste. From there it continues on until it reaches a wastewater treatment plant where the wastewater is treated so as to remove pollutants before it returns to the environment.
When non-biodegradable items are flushed, such as sanitary wipes, this interferes the public wastewater system potentially causing blockages and overflows and with processes at the plant.
Usually, sanitary sewers use gravity to carry the wastewater away. Sanitary sewers are accessed via manholes for routine maintenance and repair. The scum layer consists primarily of cooking fats and oils, soap scum and products of decomposition that are lighter than water. The greatest amount of bacterial action occurs in the sludge layer, which consists of solids heavier than water.
The liquid discharged from a septic tank is called effluent. Effluent from a properly maintained septic tank is slightly cloudy and contains fine suspended solids, bacteria and nutrients.
Septic tank effluent must not be discharged directly to the ground surface or into surface waters. The effluent must be delivered to a properly designed and constructed drainfield or lagoon for treatment.
All household wastewater must go to the septic tank. No matter the source, do not let water and other similar wastes bypass the septic tank. Grey water containing soap or grease sent directly to a drainfield will plug the soil pores quickly. Septic tanks are rated according to liquid-holding capacity, not total capacity. The liquid capacity of a septic tank is the volume of effluent it holds below the tank outlet.
For a house, the required working capacity is based on the number of bedrooms, not the number of people in the house at the time of construction. Each bedroom can hold two people, so the standard three-bedroom house could have six people generating household wastewater. The septic tank should be at least 10 feet away from the house. The tank should be aligned straight out from the point where the discharge sewer line leaves the house.
Installing the tank so it is level, with no slope in any direction, is important. For pumping and cleaning, the septic tank should be situated near a driveway or other access road. Most septic pump trucks carry between 50 and feet of hose, so the tank should be accessible from this distance. Select a location away from high vehicle traffic areas.
Never locate septic tanks under sidewalks or patios where the tank is inaccessible for pumping. A home sewage treatment system works best and is more easily maintained if both the septic tank and drainfield are near the ground surface.
A shallow septic tank and drainfield provides easy access to the component parts, plus the drainfield is more efficient at treating effluent. For new houses, the North Dakota Plumbing Code recommends using a basement sump Figure 3 designed to handle wastewater if the septic tank and drainfield can work by gravity and the home has basement toilets and fixtures. For these types of systems, the sewer pipe leaves the house through the basement wall.
The sump lifts the water to the sewer pipe. If the house sewer pipe is less than 4 feet below ground surface, it needs to be insulated in the trench for frost protection. Ready-to-install basement wastewater sump stations are available in most home supply or hardware stores. Having the lift pump in the basement has some major advantages. First, that allows the wastewater from the upper part of the house to flow by gravity to the septic system.
This has proven to be valuable during a flood or power outage. Third, a basement sump only turns on when basement fixtures are used. Many older houses have a septic tank installed lower than the basement floor level. New houses can have a deep septic tank, p roviding a high water table is not present Figure 4. If suitable slope is not present, a lift-pump station must be installed at the outlet side of the septic tank so the drainfield can be installed at a shallow depth.
In areas where the water table can rise above the top of the septic tank, homeowners must seal around the inlet and outlet pipe holes, any joints, the septic tank cover and manhole access so they are watertight.
Figure 4. Deep septic tank installation. Suitable for use where a high water table is not present. Always check with the tank manufacturer to make sure the tank has the load- bearing capacity to handle the soil overburden.
Wastewater from the house and bacterial action usually provide enough heat to keep the septic tank from freezing, even when located above the frost depth. When the top of a septic tank is installed within 2 feet of the ground surface, covering the top of the tank with 2 inches of rigid foam insulation board will help retain heat in the septic tank.
Whenever the system is built above frost depth, laying all sewer pipes at a uniform grade with no high or low spots is very important. Septic tanks are built using corrosion- and decay-resistant materials. If installed properly, they will be watertight for a long time 30 years or more.
Precast reinforced concrete tanks are the most common. However, tanks also may be constructed using poured-in-place concrete or built from concrete blocks with the cores filled with concrete reinforced with rebar.
Concrete block tanks must be sealed with at least two coats of concrete plaster. Fiberglass and durable plastic septic tanks also are available. The horizontal distance between the inlet and outlet of rectangular tanks should be about three times the width of the tank. Incoming solids will settle out in this distance and not flow out to the drainfield.
Circular tanks should have at least a 5-foot inside diameter. The liquid depth in a septic tank is the distance from the outlet pipe to the bottom of the tank. The septic tank inlet should be at least 3 inches above the outlet. The tank must have room above the liquid level for scum accumulation.
For most manufactured tanks, this will be about 12 inches. Inlet and outlet baffles are critical parts of a correctly installed septic tank Figure 2. The inlet baffle directs incoming sewage downward into the liquid zone of the septic tank. The outlet baffle allows sewage effluent to flow out of the liquid zone, retaining the scum in the tank.
Many new septic tanks have a removable filter incorporated into the outlet baffle. The filter prevents nondecomposable materials condoms, sanitary napkins and other items from reaching the drainfield. Baffles may be constructed as an integral part of the septic tank or fastened to the tank after construction. Four-inch diameter plastic tees often are used as baffles Figures 2, 3 and 4. Baffles must be durable and corrosion-proof. Durable concrete, fiberglass or plastic are excellent materials.
Never use steel baffles, as they will corrode quickly. If baffles are bolted in place, use only stainless steel bolts. The bottom of the inlet baffle should be at least 6 inches below the liquid surface when the tank is full.
The bottom of the outlet baffle should be at least 18 inches below the liquid surface. The top of the baffles must be open and extend no closer than 1 inch to the tank cover. This is necessary for proper venting of gases from the tank. Access to septic tanks is required for inspection and periodic cleaning. One manhole at least 15 inches in diameter must be on the top of the tank.
The manhole should have a concrete cover with an earth covering of at least 6 inches, but not more than 12 inches. If the top of the tank is more than 12 inches below ground level, extensions must be attached to the top of the tank to bring the cover within 12 inches of the ground surface. In high water table areas, the extensions and cover must be watertight. If the manhole access is at ground level, it should have a locking bracket or be chained shut with a padlock Figure 5.
One should be over the inlet baffle and one over the outlet baffle Figure 2. This allows for easy inspection to determine if sewage is flowing into or out of the tank properly or if plugging has occurred. The inspection ports must be capped at or just above ground level.
The caps prevent gas from escaping and children from dropping objects into the tank. Septic tanks must be cleaned regularly to remove the sludge that accumulates in the bottom of the tank.
Note that the manhole, not the inspection ports, must be used for cleaning the tank. For most houses, cleaning every three years is satisfactory. However, a house with a garbage grinder that the occupants use may require a one- to two-year cleaning interval. Garbage grinders increase the organic matter flowing into the septic tank. Some houses are in areas where a septic tank and drainfield will not work. Locations with a high water table, bedrock close to the surface and very small lots with insufficient drainfield area are the most common reasons.
Often the only option is to use a holding tank for household wastewater Figure 6. Holding tanks have to be pumped on a regular basis, and reducing daily water use in the house will contribute to lower annual pumping costs. Figure 6. Holding tank for household effluent.
Must be pumped on a periodic basis usually every two weeks to a month. The holding tank must be watertight and hold at least gallons for each bedroom in the house. However, for any house, the minimum tank size should hold at least 1, gallons. For a common three-bedroom house occupied by four people, a 1,gallon tank will provide about six to 10 days worth of storage.
The holding tank must be situated so it is accessible to a pump truck under all weather conditions and where accidental spills during pumping will not create a nuisance. The tank must be level and placed on firm, settled soil capable of bearing the weight of a full tank.
The riser of a holding tank must come to the surface. The cover must have a lock or be chained shut to prevent children or other unauthorized individuals from entering it Figure 5. Since the tank is watertight, it could try to float out of the ground right after being pumped if the local water table is within 3 feet of the ground surface. In locations with high water table conditions, earth anchors may be necessary.
Keeping the tank above the water table and pumping sewage from the house if necessary usually are best. Installing a meter to measure water flow into the house, and thus the amount of water flowing into the holding tank, may be necessary. By periodically checking the water meter, you will be able to determine when the tank is full. A better method would be to use a high-water alarm. These can be either electronic with a remote reader in the house or a floating indicator that protrudes above ground surface.
P umping stations are required in situations where the effluent cannot flow by gravity and must be lifted to a destination. Many new houses are using lift stations in the basement, and outside the house the wastewater flows by gravity through the septic tank to the drainfield.
Many manufacturers make complete ready-to-install pump stations for basements. Many older on-site systems have pumping stations that pump all the water coming from a septic tank to the drainfield Figure 7. Pumping is required with a deep septic tank installation and shallow soil absorption unit or when the soil absorption unit is at a higher elevation than the septic tank.
A mound soil absorption system will require a pumping station. Figure 7. Septic tank effluent pumping chamber. Working capacity should equal about one-fourth the daily sewage volume. This allows time to correct any pumping problems. The tank containing the pump must be watertight.
If not, ground water may seep into the tank and the excess water easily will overload the drainfield. The tank should hold about one-fourth the daily wastewater volume between the on and off levels of the pump controls.
Some reserve capacity in the pumping tank must be available in case of pump failure. A reasonable reserve capacity is three-quarters of the daily estimated wastewater volume. For example, a three-bedroom house with a design volume of gallons per day gpd requires a tank with a working volume of about gallons volume between pump-on and pump-off and a reserve capacity of about gallons.
Pump controls often have a limited range between the on and off setting. Ranges of 12 inches to 30 inches are common. The following table gives some capacities of circular tanks in gallons per foot of depth.
The capacity of rectangular tanks in gallons per foot of depth can be calculated by multiplying length in feet by width in feet by 7. For example, a rectangular tank with an inside width of 4 feet and inside length of 5 feet has a capacity of 4 x 5 x 7.
With a inch on-off setting for the pump, this tank would handle a three-bedroom house easily. A circular tank would need a diameter of at least 48 inches, but if the on-off setting were 30 inches, a to inch diameter tank could be used. Pumping station tank materials include concrete similar to holding tanks , concrete culvert sections and complete, ready-to-install plastic units.
Metal tanks do not last very long because effluent is very corrosive. Installations with an open bottom, such as concrete culvert sections, must have a watertight, cast-in-place concrete floor.
All joints between culvert sections must be sealed so they are watertight. Flotation may be a problem with precast tanks under high water table conditions. Under this condition, soil anchors may be required to prevent upward movement.
A secure manhole cover must be located on the top of the pumping tank. The cover must be lockable to prevent children from removing the cover. Many manufacturers make lift pumps specifically for sewage effluent.
Lift pumps must be durable and corrosion-resistant with sealed motors and electrical connections. They must be able to withstand the acidic and corrosive environment present in sewage tanks. Sump pumps sold in home supply and hardware stores for basement drain water are not recommended for use in sewage lift stations.
Pedestal sump pumps with an open motor should not be used except in an emergency. All lift pumps are designed to be submersible. Pump bodies are commonly made from cast bronze, cast iron and plastic. All bolts, nuts and screws are stainless steel. The pump must be set on a concrete block or pedestal in the tank bottom so grit and other solids are not drawn into the pump and sent to the drainfield.
Pump capacity is rated by how much flow rate can be produced versus the amount of head vertical lift plus friction losses it is lifting. With a lift of 25 feet, the same pump will have a flow rate of only 15 gpm. Flow rate usually is not a limiting factor in pump selection when pumping to trenches or an absorption bed.
However, the maximum lift capability of the pump may be a limiting factor. To prevent this issue, it is important to monitor the placement of trees and pipes. Broken, Crushed, or Disconnected Pipes : Over time, pipes can burst, corrode, break down, and disconnect as the ground shifts.
This can cause sewage to begin surfacing through the ground and will require the immediate attention of certified sewage repair plumbers. Improperly Discarded Waste : Sewer backup can be caused by flushing napkins, diapers, tampons, and other materials down the toilet.
It is important never to flush any garbage that can be disposed of in another way. It is also important not to flush or pour any grease down your drain as grease and fat can build up and line your pipes, preventing proper water flow. Should you experience any issues with your sewer line, be sure to contact Harris Plumbing as soon as possible.
Where does sewage water come from? When they do, these bacteria consume oxygen in the water. The resulting lack of oxygen kills fish.
The suspended solids in wastewater make the water look murky and can affect the ability of many fish to breathe and see. The increased algae, reduced oxygen and murkiness destroy the ability of a stream or lake to support wildlife, and all of the fish, frogs and other life forms quickly die.
No one wants to live in an place that stinks, is full of deadly bacteria and cannot support aquatic life. That's why communities build wastewater treatment plants and enforce laws against the release of raw sewage into the environment. Private Treatment: The Septic Tank In rural areas where houses are spaced so far apart that a sewer system would be too expensive to install, people install their own, private sewage treatment plants.
These are called septic tanks. The tank looks something like this in cross-section: In this picture, you can see three layers. Wastewater comes into the septic tank from the sewer pipes in the house, as shown here: A septic tank naturally produces gases caused by bacteria breaking down the organic material in the wastewater , and these gases don't smell good.
The following diagram shows an overhead view of a house, septic tank, distribution box and drain field: A typical drain field pipe is 4 inches 10 centimeters in diameter and is buried in a trench that is 4 to 6 feet about 1.
The gravel fills the bottom 2 to 3 feet of the trench and dirt covers the gravel, like this: The water is slowly absorbed and filtered by the ground in the drain field. Urban Wastewater Systems In urban and suburban areas where people are packed closer together and where there is a lot more wastewater to treat, the community will construct a sewer system that collects wastewater and takes it to a wastewater treatment facility.
Here's what each stage does: The first stage, known as primary treatment , does the same thing a septic tank does. It allows the solids to settle out of the water and the scum to rise. The system then collects the solids for disposal either in a landfill or an incinerator. The second stage, known as secondary treatment , removes organic materials and nutrients. This is done with the help of bacteria -- the water flows to large, aerated tanks where bacteria consume everything they can.
Typically, the third stage will use chemicals to remove phosphorous and nitrogen from the water, but may also include filter beds and other types of treatment. Chlorine added to the water kills any remaining bacteria, and the water is discharged. Measuring the Effectiveness of a Treatment Plant The effectiveness of wastewater treatment plants is measured on several different scales.
Here are some of the most common: pH - This is the measure of the water's acidity once it leaves the plant. Ideally, the water's pH would match the pH of the river or lake that receives the plant's output. BOD bio-chemical oxygen demand - BOD is a measure of how much oxygen in the water will be required to finish digesting the organic material left in the effluent.
Ideally, the BOD would be zero. Dissolved oxygen - This is the amount of oxygen in the water as it leaves the plant. If the water contains no oxygen, it will kill any aquatic life that comes into contact with it. Dissolved oxygen should be as high as possible and needs to cover the BOD.
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