Text Size
Sunday, February 18, 2018

Intermittent Sand Filters

The most common type of intermittent sand filter (ISF) system is termed the bottomless ISF. Such systems consist of a small drainfield underlain with 2 feet of sand. An air line in the sand feeds oxygen into the drainfield. This keeps the microbial environment oxygenated and the microorganisms "happy." Wastewater (the bugs call it food!) is fed to the drainfield in small doses throughout the day, by way of a lift station equipped with an intermittent dosing timer. The bugs consume the nutrients in the wastewater and convert it to cell mass the same way humans convert food into muscle and fat. The wastewater is treated as it passes through the sand and is then absorbed in the soil underneath the sand. In theory, the intermittent sand filter won't develop a biomat and clog-up like a conventional drainfield can. Enough of the engineering technobabble? What really matters is how this technology can help you. Here are several examples.

  • Drainfield sizes vary from 18' by 20' to 12' by 30'. These fields will serve up to five bedrooms and take up very limited space, reducing the aesthetic impact (less lawn and trees destroyed), and enhancing the value of the property.
  • On small lots which could only support a 2 or 3 bedroom conventional septic system, the installation of an ISF in the same area can allow for up to a 5 bedroom house. Again, enhancing value of the property.
  • The life of an ISF should be significantly more than that of a conventional mound type system, which have proven to have a high premature failure rate (many have failed in less than 5 years).
  • On undeveloped lots, which are very small, it is easier to find room for the primary and reserve drainfields, since only two small ISF sites would be required. In short, a lot that may have not been developable with a conventional septic may now be a developable piece of property.


Clearly, if you are trying to sell the property, these benefits correspond to increased marketability and a faster sale.

The cost for the bottomless ISF system (Year 2016), including test holes, engineering, permit fees, and contractor installation can range from $25,000 - $30,000. Not a small price tag, but if it makes a previously "worthless" piece of land into a homesite, or takes a house off of a holding tank, it is a bargain price. For more information on ISF systems, please contact us.

garness new logo


Garness Engineering Group, Ltd is a 100% Native American owned business enterprise.

 State of Alaska DBE Certification # 9900155

 Download Statement of Qualifications (PDF)

Product Line • Alaska Authorized Dealer
Quanics-logo logo-xerxes-2