A septic system is an essential but costly part of building a home. The upside is you won’t have monthly sewer fees or the initial cost of tapping into the municipal sewer, which averages more than $2,000 and can, in many cases, cost more than a sewer connection.
This information in this guide is about septic system planning and installation. We include septic system cost for common septic and drain field systems. A leach field, the term used in many areas, is the same as a drain field.
Septic System Planning and Installation Overview
Here is an overview for this part of your land development and building process. Then, we’ll break down the steps with itemized costs and timeframes for each part of the process.
We’ll consider that you are starting from scratch with a vacant piece of land and want to build on it. The process varies slightly between communities, and your development or building department will have the local details. Here is a common scenario when there are no major issues to deal with such as nearby wetlands, lakes or streams:
- Test: Have a perc test done to determine if the ground soils are suitable for the installation of a drain field and what type it will be, standard or engineered.
Once the property is approved for a drain field, you will probably have to submit a site plan aka plot plan.The plan is a scale diagram of the property showing where you intend to put the house, any detached buildings, the driveway, deck or patio, in-ground pool and the septic system with drain field.
Related: See our guide to Site Plans: https://www.24hplans.com/what-is-a-site-plan-plus-12-elements-of-plot-plan/ — it includes details about:
- Obtain a Permit: If the land is approved, get a permit for the system from your building department.
- Design: Have an engineer design the drain field based on the soils as determined by the perc test. Some municipalities design systems in-house for a standard fee. Others have a list of approved engineering firms.
- Install: Install the septic tank and the drain field. The process includes at least one inspection during installation to ensure the system is being built according to the engineered plans.
- Inspect/Approve: Get the final inspection, which includes testing if it is an engineered system, often referred to as a mound system since it is built mostly above grade.
Those are the basics; next, we’ll delve into the details including who does the work, how long it takes, what you can expect as the property owner and how much every part of the process costs.
Testing Ground for Drain Field Suitability
The soils in and beneath a leach field must be absorbent enough to keep up with the effluent flowing from the septic tank. Sandy soils and gravel are best. Heavy clay and a high seasonal water table are problem.
Perc (percolation) tests might be done with a posthole digger or power auger, but a backhoe gives the inspector the best look at the underlying soil. Two or three cuts are made to a depth of 3-6 feet depending on what is known about local soils and how deep the inspector wants them tested.
Your local building department might do the test or give you a list of local excavation companies approved for performing these types of tests. The water table and composition of the soils are examined. The results are used to determine one of the following:
- The ground is suitable for a standard, inground drain field
- The ground conditions are poor, sometimes called “marginal,” and a raised, engineered system must be built
- The ground is not suitable for a drain field of any type
$300-$1,500 | Perc Test Cost
Timeframe: Up to 3 weeks to schedule the test, have it performed and get the results
Your perc test cost depends on the equipment used for the test, how many holes are dug and how deep they are. If your lot is in a development or part of a larger parcel split for individual building sites, the developer/seller likely had the land perc tested as part of determining how many individual lots could be created. If so, the survey you receive will show where perc tests were done and which sites were approved for a leach field.
Getting a Permit for a Septic System and Permit Cost
The permit is issued by your local building department. You can apply for it, or the contractor hired to build the system can obtain it and include the cost when billing you.
Remember that the cost of the permit includes a review of the septic system design drawing and at least two inspections of the system as it is being installed. In your community, the cost might also include the engineered design of the system. We cover the topics separately to avoid confusion.
Related: When a Building Permit is Required
$150-$400 | Septic System Permit without plans
Timeframe: A few days to two weeks
Planning a Septic System and Septic Design Costs
Once the type of system required is determined, engineering drawings will be produced that include:
- Size of the tank, based on the home’s size and number of bedrooms
- Location of the tank
- Location and dimensions of the drain field
- Materials required for each layer (such as stone and sand) of the field and the depth of each layer
- Configuration and size of the perforated pipe used to disperse the effluent into the materials beneath
- The location and specifications of any pump or pumps required and the supporting electrical system
$300-$1,500 | Septic System Design Fees
Timeframe: Two to three weeks is average, though it can take longer
It’s easy to think that engineers print ready-made septic system designs and charge handsomely for them, and there are times that might be close to the truth. However, in most cases, the engineer is working with a lot of factors including soil type, slope of the land, determining the best shape of the field given the lot’s size and shape, the location of a well, nearby water or wetlands and more. Designs are unique for most properties.
Septic System Installation and Cost
Once the plan is finalized, installation of the tank and leach field can be scheduled. On the appointed day, the installation company, using an excavation contractor, arrives with heavy equipment, a trailer full of hand tools and materials, and goes to work. The installation process is similar for a standard system and an engineered system.
- Dig the hole for the tank, have it delivered and set in the hole
- For a raised system, install the pump tank, pump, wiring and alarm (which will be subcontracted to an electrician)
- Remove the topsoil from the drain field location, and pile it for reinstallation
- For a standard system, remove additional soils where indicated on the drawings and to the prescribed depth
- Build the drain field bed, standard or raised, a layer at a time with the prescribed materials, methods and depths
- Build the pipe system by gluing together solid and perforated drain pipe according to the engineer’s design
- Run pipe out of the house to the tank and from the tank to the pump, if installed, and the drain field
- Wait for the building inspector’s approval to continue
- Cover the pipes with prescribed materials
- Wait for the inspector to test the system, if it is an engineered drain field with a pump
- Cover the drain field with the topsoil removed earlier, and plant grass seed or cover it with sod (only grass is allowed because it does not have roots that damage pipes and disrupt bed materials, and the grass roots and plant wick up effluent and promote the drying of the drain field)
- Wait for the final inspection and approval
$3,000-$5,000 | Average standard septic system cost
$11,500-$20,000 | Average engineered septic system cost
Timeframe: A few days to three weeks once the project starts
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