Cost of Septic System Installation: 8 Expense Factors

The cost of septic system installation varies greatly from area to area; however, for the installation of a tank and absorption field, the EPA states a low of $1,500, a high of $8,000, and a rough average of $4,000. Of course, this average assumes favorable soil conditions and a suitable site on the property, as there a multiple factors that could cause this average cost for septic system installation to increase dramatically.

The Big Picture
Typically, the only time a completely new system is installed is during construction of a new home. If you’re interested in costs because your current septic system has failed, then there are even more factors to consider. The EPA states an average cost of $1,200 to $2,500 to revitalize a failed drain field, but a complete removal and replacement can range from $6,000 to as much as $25,000! So, in the case of a failed system, a big question is the existence of an alternate drain field site; if the property doesn’t have one, then removal and replacement or an expensive work-around are the only options. Clearly, we don’t want our system to fail because the cost of a new one is a huge burden.



Septic Installation Cost Factors
If any of these factors is poor, then a larger (higher cost) drainfield and/or an alternate (higher cost) system will be required :

  1. Local Government: In most areas, system installation is regulated, so you’ll have to pay their fees and meet their requirements.
  2. Absorption Level: According to the “Septic Tank – Soil Absorption Systems Fact Sheet” from the EPA, acceptable absorption levels range from 1 to 60 minutes per inch of water; however, the absorption rate affects the size of drainfield you need: 3 minutes per inch = 70 square meters of drainfield per bedroom, while 60 minutes per inch = 340 square meters per bedroom.
  3. Soil Type: As seen in the table below, percolation levels are higher in sandy soils and are much lower in clay-type soils.
  4. Topography: Local governments are most concerned about waste from a septic system getting into the water supply without spending enough time in the soil to be sterilized. If the land is too sloped, then a more elaborate, tiered drainfield might be required, leading to a higher septic system cost.
  5. Bedrock: If bedrock is too close to the surface, then effluent might saturate the ground and overflow to the surface, or it might flow along the bedrock and enter the water supply without being sterilized. If the bedrock is too close to the surface, a more expensive, mound or aerobic alternate system may be necessary.
  6. Groundwater: According to the EPA, effluent needs a layer of soil about 60cm thick to be completely sterilized. In low elevation properties or properties very close to water sources, the groundwater may be higher, or seasonably higher, leading to the need for an alternate-type, higher cost installation.
  7. Climate: If the soil is saturated with rainwater or frozen, then it won’t be able to absorb effluent effectively; in addition, in colder areas, tanks need to be buried deeper because bacteria inside the tank need heat to break down sludge. Finally, in warmer climates, water evaporation aids the absorption of the drainfield. All these factors will be taken into account before the county approves a perc site.
  8. Setbacks and other Codes: Local governments usually have requirements called “setbacks” that keep property owners from building too close to the edge of their property. These requirements also apply to septic system installations so that a drainfield doesn’t runoff into someone else’s property. In other words, you might have a perfect perc site, but it won’t work because it’s too close to the edge of the property. In addition, some counties might have more strict drainage and waste regulations making an alternate system the only possibility.

 Less vs. More Expensive Conditions

Installation Cost Factors




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