Use the slowest of the four perc rates for sizing the absorption field = 47 mpi. From the DOH sewage standards manual, a 47 mpi perc rate requires 300 square feet of absorption area per bedroom, so 300 x 3 = 900 square feet of absorption area. 900 square feet ÷ 2-foot width = 450 lineal feet of trench.
- When calculating for Absorption Area and Total Feet using Design Rates: Total Lineal Feet Total Depth Feet Design Rate: sf/1 00 gstc* Design Rate: sf/1 00 gstc* x x Gallon Tank Size Gallon Tank Size Absorption Area (SD Absorption Area (trench area) Absorption Area (SD Absorption Area (diameter x 3.14) Created Date 6/11/2015 9:14:46 AM
What is a good absorption rate for a septic system?
Soil with a percolation rate of less than 1 minute /inch or more than 60 minutes/inch is un-suitable for a conventional septic system design: the wastewater will be absorbed into surrounding soil too rapidly to permit adequate treatment.
What is septic absorption?
Septic tank absorption fields are areas in which effluent from a septic tank is distributed into the soil through subsurface tiles or perforated pipe. In these soils the absorption field may not adequately filter the effluent, particularly when the system is new. As a result, the ground water may become contaminated.
How do I calculate the size of my septic drain field?
Drainfield Size
- The size of the drainfield is based on the number of bedrooms and soil characteristics, and is given as square feet.
- For example, the minimum required for a three bedroom house with a mid range percolation rate of 25 minutes per inch is 750 square feet.
How do you calculate septic tanks in liters?
How to calculate the size of septic tank you need. C = 2000 litres + 180P. C = 2000 litres + 180 × 4 = 2720 litres, For 4 users, minimum size of septic tank could be 2.2m × 1.0m × 1.30m (7.2ft × 3.3ft × 4.25ft) in respect to their Length, breadth and depth.
What is an absorption area?
The absorption field is a subsurface leaching area within the soil that receives the liquid effluent from the distribution device and distributes it over a specified area where it is allowed to seep into the soil.
How far do field lines extend from septic tank?
Your septic system site plan is typically drawn right on top of your property survey showing the septic tank ‘setbacks’ with tank 5-10 feet from the house, the leach field at least 20 feet from the house, at least 100 feet away from wells and streams, 25 feet away from dry gulches, and 10 feet away from the property
How do you calculate soil absorption rate?
Divide the elapsed time by the number of inches the water level dropped from the 6-inch level in a hole during the last measurement interval. If, for example, 4 inches of water remained in a hole after 30 minutes, then divide 30 by 2 to get an absorption rate of 15 minutes per inch for that hole.
How do you absorb water in a septic tank?
From the septic tank, the waste-water passes through the outlet of the tank and enters the soil absorption field. The most common outlet is a tee fitting connected to the pipe going to the soil absorption field. However, an effluent filter can be placed in the outlet tee for additional filtering of the wastewater.
How big should an absorption trench be?
Trenches are usually 500 to 700 millimetres deep and up to around 600 millimetres wide. Beds are usually no deeper than 600 millimetres, but up to several metres wide and contain a number of distribution pipes or arches.
What is the slope for septic lines?
A typical septic tank has a 4-inch inlet located at the top. The pipe that connects to it must maintain a 1/4-inch-per-foot slope toward it from the house. This means that for every 10 feet of distance between the tank and the house, the inlet must be 2 1/2 inches below the point at which the pipe exits the house.
What should be the size of septic tank?
Length of septic tank (L) should be taken as 9feet 9 inches or 9.75 feet. Breadth of septic tank (B) should be taken as 6 feet 3 inches or 6.25 feet. The standard height (D) of septic tank should be taken as 5 feet 9 inches or 5.75 feet.
How many infiltrators do I need?
As a general rule, trenches ‘fingers’ should be no longer than fifty feet ( 12 or 13 Infiltrators long ) for best function and most even effluent distribution. Unless you are installing as a “bed” system (where the chambers are right next to each other), leave at least six feet of undisturbed soil between fingers.
Drainfield Size & Design
- The percolation rate of a soil is an essential soil feature that measures how long it takes water to descend one inch in a saturated hole drilled in the ground.
- In sandy soil, 1 inch can be achieved in 3 minutes
- In clay soil, 1 inch may be achieved in 48 minutes.
- If it takes less than 5 minutes for water to drop 1 inch in a saturated hole, the effluent will move too quickly for it to be properly treated, as is the case in sandy soil. If it takes more than 60 minutes for the water to drop one inch, the effluent will not be able to travel as quickly as it should, and effluent may rise to the top of the water table. This is something that may happen in clay soil.
Drainfield Size
- According to the number of bedrooms and soil qualities, the drainfield is measured in square feet, and its size is reported in square feet. It has been determined by the Nebraska Department of Environmental Quality (NDEQ) how many square feet of drainfield trench will be required. Title 124 of the North Dakota Department of Environmental Quality (NDEQ) contains the design, operation, and maintenance requirements for on-site wastewater treatment systems
- The table below is an excerpt from that title. A three-bedroom house with a mid-range percolation rate of 25 minutes per inch, for example, requires a minimum of 750 square feet of space to function properly.
Square Feet of Drain Field Trench Required for Single Family Dwelling
| Number of Bedrooms | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 |
|---|---|---|---|---|---|---|---|---|---|
| Perc Rate in Minutes Per Inch | 200 gpd | 300 gpd | 400 gpd | 500 gpd | 600 gpd | 700 gpd | 800 gpd | 900 gpd | 1000 gpd |
5Systems must be constructed with a 12 inch loamy sand liner that has a percolation rate of 15 to 20 minutes per inch and should be developed at a percolation rate of 11-20 minutes per inch, with a percolation rate of 15 to 20 minutes per inch.
| 5-10 | 165 | 330 | 495 | 660 | 825 | 990 | 1155 | 1320 | 1485 |
|---|---|---|---|---|---|---|---|---|---|
| 11-20 | 210 | 420 | 630 | 840 | 1050 | 1260 | 1470 | 1680 | 1890 |
| 21-30 | 250 | 500 | 750 | 1000 | 1250 | 1500 | 1750 | 2000 | 2250 |
| 31-40 | 275 | 550 | 825 | 1100 | 1375 | 1650 | 1925 | 2200 | 2475 |
| 41-50 | 330 | 660 | 990 | 1320 | 1650 | 1980 | 2310 | 2640 | 2970 |
| 51-60 | 350 | 700 | 1050 | 1400 | 1750 | 2100 | 2450 | 2800 | 3150 |
5Systems must be constructed with a 12 inch loamy sand liner that has a percolation rate of 15 to 20 minutes per inch and should be designed at a percolation rate of 11-20 minutes per inch, with a percolation rate of 15 to 20 minutes per inch for the 11-20 minute per inch level.
Septic Systems
Septic systems are responsible for the waste generated by building drain systems, and they do so by processing the waste through septic tanks and leaching areas. Waste water from septic tanks and leaching systems is disposed of into the earth, while solid waste and grease are held in septic tanks and grease.
Septic Tanks
Scum and fat/grease float to the top of the tank, where they are removed. Solids are deposited at the bottom of the tank. This table shows the maximum capacity of a septic tank for a typical single or multiple family dwelling, or, as an alternative based on the load, the Drainage Fixture Units (DFU):
| Septic Tank Volume | Maximum Capacity | |||
|---|---|---|---|---|
| gallons | m 3 | Single family units(number of bedrooms) | Multiple family units – one bedroom each(number of units) | DFU |
| 750 | 2.8 | 1 – 2 | 15 | |
| 1000 | 3.8 | 3 | 20 | |
| 1200 | 4.5 | 4 | 2 | 25 |
| 1500 | 5.7 | 5 – 6 | 3 | 33 |
| 2000 | 7.6 | 4 | 45 | |
| 2500 | 9.5 | 6 | 60 | |
| 2750 | 10.4 | 7 | 70 | |
| 3000 | 11.3 | 8 | 80 |
Grease Interceptors
Capacity of the grease interceptor is required:
Leaching Fields
Essentially, there are two elements that influence the size of the leach field.
- The loading rate, which is the quantity of wastewater that is discharged into the leach field on a daily basis
- And The percolation or absorption rate of the soil – the rate at which liquids will move through the soil
It is possible to estimate the adsorption capacity of the soil using tests, which are mandated in some countries. Examples of typical absorption capabilities for various soil types are shown in the table below.
| Type of soil | Typical Absorption Capacity for a 24-hour period | |
|---|---|---|
| gallons/ft 2 | liter/m 2 | |
| Clay with small amount of sand or gravel | 1 – 1.5 | 40 – 60 |
| Clay with small amount of sand or gravel | 1.5 – 2 | 60 – 80 |
| Sandy loam/clay | 2.5 | 100 |
| Fine sand | 4 | 160 |
| Coarse sand or gravel | 5 | 200 |
The needed area may be estimated by dividing the total volume of wastewater produced in a 24-hour period by the soil’s absorption capacity.
Example – Required Leach Field
The overall loading rate from a single-family residence is 1200 gallons per minute. It is possible to determine the needed leach field in a soil containing fine sand using the following formula:A = (1200 gallons)/4 gallons/ft 2)=300ft 2
Leach Lines
It is necessary to construct leach lines in the form of trenches filled with washed rock/gravel to flow level, with a perforated pipe installed at the top. Rock is utilized to cover the pipe, and a filter material that has been authorized is used to prevent soil from trickling down through the rock. The size of the leach line is determined by the amount of capacity required by the system. As a general rule of thumb
- During the winter, the maximum length of each line should not exceed 100 ft (30 m), and the spacing between lines should not be less than 10 ft (3 m). In addition, the minimum depth of the leach line should not be less than 12 in (0.3 m), or deeper if the soil freezes. The elevation rate should be approximately 1 percent.
How Your Septic System Works
Underground wastewater treatment facilities, known as septic systems, are often employed in rural regions where there are no centralized sewage lines. They clean wastewater from residential plumbing, such as that produced by bathrooms, kitchen drains, and laundry, by combining natural processes with well-established technology. A conventional septic system is comprised of two components: a septic tank and a drainfield, often known as a soil absorption field. It is the septic tank’s job to decompose organic matter and to remove floatable stuff (such as oils and grease) and solids from wastewater.
Alternate treatment systems rely on pumps or gravity to assist septic tank effluent in trickling through a variety of media such as sand, organic matter (e.g., peat and sawdust), constructed wetlands, or other media to remove or neutralize pollutants such as pathogens that cause disease, nitrogen, phosphorus, and other contaminants.
Prior to discharging wastewater into the environment, several alternative systems are designed to evaporate or disinfect the effluent.
Specifically, this is how a typical conventional septic system works:
- All of the water that leaves your home drains down a single main drainage pipe and into a septic tank. An underground, water-tight container, often composed of concrete, fiberglass, or polyethylene, serves as a septic system’s holding tank. Its function is to retain wastewater for a long enough period of time to allow particles to sink to the bottom and form sludge, while oil and grease float to the surface and produce scum. Sludge and scum are prevented from exiting the tank and moving into the drainfield region by compartments and a T-shaped outlet. After that, the liquid wastewater (effluent) exits the tank and flows into the drainfield. The drainfield is a shallow, covered hole dug in unsaturated soil that serves as a drainage system. Porous surfaces are used to release pretreated wastewater because they allow the wastewater to pass through the soil and into the groundwater. In the process of percolating through the soil, wastewater is accepted, treated, and dispersed by the soil, finally discharging into groundwater. Finally, if the drainfield becomes overburdened with too much liquid, it can flood, causing sewage to flow to the ground surface or resulting in toilet backups and sink backups. Finally, wastewater percolates into the soil, where it is naturally removed of harmful coliform bacteria, viruses, and nutrients. Coliform bacteria are a kind of bacteria that may be found in the intestines of humans and other warm-blooded animals, with humans being the most common host. As a result of human fecal contamination, it is a sign of this.
The Guadalupe-Blanco River Authority has built an animated, interactive model of how a residential septic system works, which you can view here.
Do you have a septic system?
It’s possible that you’re already aware that you have a septic system. If you are not sure, here are some tell-tale symptoms that you most likely are:
- You make use of well water. In your home, the water pipe that brings water into the house does not have a meter. In the case of a water bill or a property tax bill, you will see “$0.00 Sewer Amount Charged.” It is possible that your neighbors have a septic system
How to find your septic system
You can locate your septic system once you have confirmed that you have one by following these steps:
- Taking a look at the “as constructed” drawing of your house
- Making a visual inspection of your yard for lids and manhole covers
- Getting in touch with a septic system service provider for assistance in locating it
Failure symptoms: Mind the signs!
A bad odor is not necessarily the first indicator of a septic system that is failing to work properly. Any of the following signs should prompt you to seek expert assistance:
- Water backing up into the drains of homes and businesses
- It is especially noticeable in dry weather that the drainfield grass is bright green and spongy. The presence of standing water or muddy soil near your septic system or in your basement
- A strong stench emanating from the area surrounding the septic tank and drainfield
How a Septic System Works
| The septic system is a sewage treatment and disposal system.A basic system consists of a septic tank and drainage area. All flows from the house are directed by way of a main sewer line to the septic tank. 40% of household sewage is from the toilet, 30% is from bathing, 15% is from laundry and 10% is from the kitchen. |
What is a Septic Tank?
The septic tank is a watertight chamber constructed of concrete or poly material. An average size is approximately 1000 gallons to 1500 gallons in capacity. Most septic tanks have one or two compartments. Two compartment tanks, or two single compartment tanks in series, provide better settling of the solids.Each septic tank has an inspection port over each baffle as well as a manhole access port. The manhole lid needs to be accessed for the tank to be pumped. These can be found at or below the ground surface. Typically you will find 4” diameter plastic lids at the ground surface that are the inspection ports over either of the baffles on the tank and not where the tank is to be pumped through.The baffles of the tank are one of the most important components in the septic tank. The inlet baffle forces the wastewater from the sewer line down into the tank instead of across the surface of the tank and into the outlet pipe leading to the absorption area. The outlet baffle prevents the scum layer from moving into the soil absorption area. In a properly functioning septic tank the solids and sludge settle to the bottom and accumulate, scum (lightweight materials including paper, fats and greases) rises to the surface and the effluent (liquid) in the tank existing between those layers overflows to the absorption area.| The absorption area uses the ability of the stone and soil to filter and treat the remaining effluent. Examples of absorption areas are seepage beds, trenches, sand mounds or older cesspools / seepage pits. A cesspool is a block walled dirt bottom pit. Cesspools are no longer an installation choice but there are many properties that still have functioning cesspools. Odors and gasses from the septic system, that are always present, are vented through pipes on the house roof.For further information: -On Lot Sewage System Owner Manual -A Homeowner’s Guide to Septic Systems – by EPA |
Misconceptions of Septic Systems
| You never have to have the septic tank pumped.As the septic system is used, the solids (sludge) accumulate on the bottom of the septic tank(s). When the sludge level increases, sewage has less time to settle properly before leaving the tank through the outlet pipe and a greater percent of suspended solids escape into the absorption area. If sludge accumulates too long, no settling of the solids will occur, and the solids will be able to directly enter the absorption area. These solids will clog the distribution lines and soil and cause serious and expensive problems for the homeowner. To prevent this, the tank must be pumped out on a regular basis.If you use additives you don’t have to have the tank pumped.The claims made by companies that sell additives are that you never have to pump your tank. What the products do is break up the scum and sludge so that there is a greater percent ofsuspended solidsin the tank that then flow down the over flow pipe with the effluent to your absorption area, causing your system to fail.The absorption area is designed to treat water or effluent, not solids.The septic tank is designed to contain and treat the solids and they should remain in the tank. It is much less costly to pump your tank on a routine basis than ultimately having to replace your absorption area.It takes years between having the tank pumped for the septic tank to fill to its capacity.The average usage for a family of four will fill a septic tank to its working capacity of 1000 – 1500 gallons in approximately one week. When the contents (liquids and solids) in the tank reaches the level of the overflow pipe, the effluent flows down the overflow pipe to the absorption area every time water is used in the house.The tank works at this full level until it is emptied when it is pumped again.When the alarm for the pump sounds it means you need to pump your tank.If you have a system designed with a pump to pump the effluent to the absorption area you also have an alarm for the septic system.The alarm sounds when the water level rises in the pump tank and alerts you that there is a malfunction with your pump, float switches, or other component in the pump tank.It does not mean that it is time for a routine pumping of your tank. |
SEPTIC DESIGN
Septic systems require special consideration in the selection of the site, the design, and the construction. Residential Sewage Disposal Systems explains how each unique traditional septic tank absorption field system must be planned and installed in accordance with State Board of Health rule, 410 IAC 6-8. (available through your County Board of Health). A FACTS computer program is available at your local County Extension office that can give suggestions for different types of on-site septic systems that may be used with a variety of site and soil conditions.
It will tell you whether or not a conventional system is appropriate for your scenario and will offer you with the following design information: estimates of the septic gravel volume that will be required, total trench bottom area that will be required, and depth to the trench bottom.
This will include the following:
THE PROCESS
- Identify soils and evaluate their appropriateness for use as a soil absorption field on-site. Locations for the septic tank, feedline trench, and centerline of all soil trenches should be determined. Determine the distance between trenches
- Completely enclose the complete area necessary for the soil absorption field, as well as a distance of at least 50 feet downslope
- If the trenches are on the side of a slope or at the foot of a slope, specify where a diversion ditch and/or subsurface curtain drain should be created and backfill with gravel.
DETERMINE YOUR SYSTEM
A septic permit from the local government is obtained through the preparation and handling of the necessary papers by Paul Swoyer Septic’s. Throughout central Texas, we employ an engineer (P.E.) to meet all of your residential and commercial septic system design requirements. Other factors that can affect the septic system include medications taken by residents of the home, bleaches, as well as non-edible plastics and paper that have not been consumed.
Is there enough soil present in the drain field area? At least four feet of good soil (no rock or clay) is necessary.Is there enough room for a drain field?Is the ground level or is it sloped greater than 15%?Is there sufficient drop from the house to the tank location and down to the drain field?
If a traditional septic system cannot be erected, an aerobic septic system can be designed, which does not require the use of test holes to ensure that it is working properly.
PERMITS
- A plot plan or a survey of the land
- Warranty deed that has been recorded
- Home’s living square footage and the number of bedrooms in the house/floor plan Address for 911 (which can be received from the County Office)
- Aerobic systems simply require an affidavit to public form with all signatures notarized, as well as a service contract. The installer will provide you with the necessary forms.