Drain fields, or leach fields, are an integral part of septic systems. They distribute wastewater from the septic tank to naturally filter and treat it through the surrounding soil. If you have a septic system, then you need to know the size of your drain field so you can ensure it functions properly and lasts long.
What is a Drain Field?
Better correctly known as a leach field, a drain field is the underground site or area where effluent from the septic tank is dispersed. The wastewater leaving the septic tank still contains impurities, which in their turn get treated in the soil by natural filtration. The drain field should act like the final stage of treatment in the septic system, with filtered wastewater returned safely to the environment.
An oversized or undersized drain field contributes to system overloads, thus the back up of waste water into your house or soil and water contamination. It is, therefore, very crucial to determine the correct size of the drain field for a healthy functioning septic system.
Determinants of Drain Field Size
Household Size and Water Use
The size of the drain field is mainly determined by the number of people that live in your house and how much water you use in a day. If a household uses more water, the drain field would have to be larger in order to handle the wastewater amount being produced.
Water Used Per Person: The water used per person can range from 60 to 100 gallons daily. Assuming that a house could house four people, water use daily can range from 240 gallons to 400 gallons. This would help estimate how many gallons of wastewater the drain field would need to get rid of daily.
Fixture Count: The size is also affected by the number of bathrooms, sinks, and other water-using appliances in your home. Homes with more bathrooms or water-using appliances such as dishwashers and washing machines will need larger drain fields to take care of the higher wastewater output.
Soil Type and Permeability
Another critical factor that will determine the size of a drain field is the type of soil. The soil should have a good ability to absorb and filter wastewater without the creation of any type of pooling, which could lead to contamination. The types of soil vary in their level of permeability; this means that some kinds of soil absorb water quicker than others.
Clay Soils: Clay is a dense material, offering very little permeability. That is to say, it does not readily absorb much water. The drain fields should be much more significant in soil with a high clay content to make up for the ” slow” absorption rates of the soil.
Sandy Soils: Sandy soils are much more permeable and allow for quicker absorption of water into them. Because of this fact, a smaller drain field may suffice where the soils are mostly sandy.
Loamy Soils: Loamy soils are soils that have a relatively equal mixture of sand, silt, and clay. They provide a good balance between permeability and filtration. Loamy soils are suitable for drain fields, as they require a normal or moderate-sized drain field.
Testing the soil is usually based on how long it takes water to percolate through the soil. This is actually measuring how well the soil will absorb the water entering it. Therefore, the size of the drain field is directly contingent upon this test.
Local Regulations and Codes
Most local health and environmental agencies will have regulations concerning septic systems and drain fields. These apply minimum size and design specifications to the drain field according to size of property, proximity to water sources, soil type, and so on. In any matter concerning a drain field, it is a great idea to consult the local guidelines as these are the basis upon which building codes are written.
Septic Tank Size
The size of your septic tank is directly tied to the size of your drain field. A larger septic tank can store more wastewater, and accordingly, the drain field must be designed to handle the increased effluent. Typically, septic tanks are sized based on the number of bedrooms in a house:
One- to Two-Bedroom Homes: 750-1,000-gallon septic tank
Three-Bedroom Homes: 1,000-1,250-gallon septic tank
Four-Bedroom Homes: 1,250-1,500-gallon septic tank
The size of the septic tank determines the amount of wastewater released to the drain field in one shot. If the size of the septic tank can adequately match the size of the drain field, overloads could be avoided.
Slope and Drainage
Topography of your lot can affect the size of the drain field. If the ground is sloping or uneven, for instance, the drain field may need to be larger to accommodate the pattern of water flow. In some cases, multiple trenches in the drain field are necessary to accommodate adequate dispersal of wastewater.
Apart from that, the surface topography should also be needed. In case the surface has poor natural drainage, then a bigger or higher kind of system should be used to avoid pooling of water or flooding of the field.
How to Calculate the Correct Drain Field Size
Calculating the right size of a drain field is done keeping in mind some of the variables highlighted above. Generally, this is done by a licensed septic system designer or engineer before installation, but the general formula used involves:
Determine Daily Wastewater Volume: Estimate the wastewater your household generates daily. Multiply the number of people in your household by the amount of water, on average, used by each person in a day. Typically, each person uses 60-100 gallons of water per day. If there are four people in a household and they use 75 gallons of water per person per day, then the daily wastewater volume is 300 gallons per day.
Determine the Soil Colloidal Absorption Rate This is usually accomplished with a percolation test, which yields the absorption rate of your soil-usually in minutes per inch. It’s essential, as this number will help you determine how large your drain field must be for your soil type.
Consider Septic Tank Size Make sure your drain field is compatible with the effluent output given the size of your septic tank. As it was earlier mentioned, the larger your septic tank, the larger your drain field should be.
Use Formulas for Drain Field Size Once you know how much wastewater will be produced daily and the percolation rate, you can apply a formula or use a table, often provided by local health departments, that shows the total area needed for your drain field.
How Important Proper Maintenance of Drain Field Is
Once you have the right size in your drain field, proper maintenance is necessary. Improperly maintained drain fields can lead to system failures that cause costly backups and repairs. Following are some tips for keeping your drain field functioning well:
Avoid Harming the System: Be conscious of water consumption and avoid passing extreme amounts of water through your septic system. Space out laundry, take shorter shower times and fix all drippy faucets to lighten the load on the system.
Regular Pumping: Sludge accumulates within the septic tank and needs to be pumped every three to five years so that buildup will not occur and cause overflow onto the drain field.
Keep the Drain Field Clear: Avoid planting trees or shrubs that have invasive roots near the drain field, as that can spur destruction to the pipes inside. Likewise, avoid parking vehicles or placing heavy objects on top of your drain field to prevent compacting the, soil-which will eventually damage the system.
Watch for Signs of Trouble: If your drain field is in trouble, you may notice slow draining, foul odors, or wet spots in your yard. If you observe these warning signs, have a professional plumber inspect and repair your system.
Conclusion
The size of the drain field depends upon the usage of water supply in the household. It should not be too small because it will decrease the life span of your septic system. Household size, soil type, code minimum requirements, and the capacity of your septic tank determine the size of your drain field. Regular maintenance and monitoring will go a long way in preventing costly repairs, adding to the longevity of your septic system. Rooter Man Plumbing are such companies that will walk you through the installation of a new septic system or resolving the problem with your drain field and will maintain your system as it should be.