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The rules and regulations controlling septic systems are included in a regulation 64e-6 written and maintained by the Florida Department of Health (FDOH). Residents of Florida are being told that there are three alternatives to replacing conventional septic systems:

  1. Sewers including gravity fed and low pressure (Grinders)
  2. Passive Drainfields called In-ground Nitrogen-reducing Biofilter media layer systems
  3. Advanced Nitrogen Reducing electro-mechanical tanks.

It is a complete disservice to any homeowner to be told that a passive solution which is just a drainfield replacement is available. In-ground Nitrogen-reducing Biofilters (INRB) are nitrogen-reducing media layers placed beneath a conventional drainfield. The complex rules imposed on their installation render them impractical. The following information was taken from 64E-6.

1. The drainfield must be installed over a sand fill material that is at least 18 inches thick and conforms to the textures and colors defined by the regulations:

a. The sand must consist of fine aggregate having a texture of sand or fine sand but excluding those having color values less than or equal to 4 with chromas less than or equal to 3; or those with colors on the gley charts. The contractor will most likely have to create a soil by mixing organics and sand to comply with this regulation. Yes, you need special dirt!

2. The sand fill must extend at least one foot beyond the perimeter of the drainfield. The drainfield is to be centered above the sanded fill area. This enlarges the required area of a normal drainfield and may require the removal of trees. Trees cannot be just cut down and stumps ground out. The tree trunks and roots must be dug out with heavy equipment.

3. Below the sand fill material layer is the media layer that must be at least 12 inches thick and extend beneath the entire drainfield absorption surface and extend at least 24 inches beyond the perimeter of any portion of the drainfield absorption surface and/or any other effluent release point.

4. An example of nitrogen-reducing media are chips or shavings of untreated lumber, blended urban waste wood mulch, yellow pine sawdust, or 2-inch to 3-inch wood chips. The nitrogen-reducing media must comply with rules too. These rules control things like other contaminants in the material and its effectiveness at denitrification. There are no vendors right now who have agreed to supply wood chips in compliance with these rules. You could be made to dig up your drainfield if your contractor used the wrong material.

5. The media layer must also extend upward along the boundary of the sand fill material to a point four to six inches below the bottom of the drainfield. The drainfield must be centered above the media layer. This becomes a logistical problem for a contractor. They must make a bowl out of media and then fill it with sand. Most contractors would not be interested in this kind of project because of the level of difficulty.

6. The media layer is now the bottom of your drainfield and must sit 6 inches above the wet season water table in your yard.

7. As measured vertically, no portion of the media layer can be within 18 inches of the infiltrative surface of the drainfield. (where the effluent enters). These requirements mean that a contractor cannot just dig a hole and fill it with wood chips and sand.

8. The media layer is not just wood chips but a combination of nitrogen-reducing media and fine aggregate, which is to be composed of 40-60% nitrogen-reducing media by volume, with the remainder to be fine aggregate. This is a fancy way of saying that the air space between wood chips is to be filled with sand at a 40-60% ratio. For a contractor, they will need to have this mixed off site and trucked in. It is FDOH’s untested theory that they can keep oxygen away from the wood chips if they mix it with sand and loam that will retain moisture.

9. Again, the fine aggregate (sand) is to be mixed with the nitrogen-reducing media at specified textures: coarse sandy loam, sandy loam, loamy sand, fine sandy loam, very fine sand, loamy fine sand, and loamy very fine sand. This too must conform to the color requirements established through the Gley Scale. The media layer must be thoroughly mixed while dry, with the contents uniformly distributed when installed.

10. Drainfield repair does not necessitate media replacement provided the media has been in use for less than 10 years or if sampling within the previous 12 months shows denitrification is at or above the target level for mean total nitrogen (TN) removal efficiency which is a minimum 65%. Basically, this means that you should count on replacing your drainfield and media every 10 years. NOTE: It is unknown at this time what the “sampling requirements” will be for an INRB.

11. The final insult is that after installation and inspection, you will not be approved until you modify your property deed with the county courthouse as written notice to inform all subsequent property owners of the use of the nitrogen-reducing media onsite system that may require special repair or maintenance procedures. The notice is to include the department’s construction permit number for the system. You should talk to a realtor about the affect such a deed declaration will have on your property value or your ability to sell it in a timely fashion.


While FDOH requires any new design to go through an Innovative Permitting Process, the INRB did not benefit from such a review. This design has not even been installed and tested to see if it works. Typically, for wood chips or other media to denitrify, the media must be isolated from oxygen. Virtually all media systems used in designs found in other States submerge their media in water. Water being the insulating compound to keep air (oxygen) away from the process. Did you ever notice how an old pier decays up to the water line, but the pilings seem to last under water? That is the principle of science being applied here. Keep wood wet, keep oxygen away and it lasts and lasts. However, using a liner or tank to place the wood chips in for use as a drainfield is a patented process and FDOH cannot add that to their design. Neither has FDOH permitted any manufacturing company using liners to install their products in Florida. Confused? Don’t be. The INRB systems were never meant to be used by homeowners. They were created by FDOH to check the box on what homeowners have been asking for since this entire septic replacement process began, a PASSIVE SYSTEM. Best advice is that if you are ready to take a risk on an INRB, get a firm quote on installation, written guarantee that for at least 10 years the wood chips will not rot and your drainfield sink. Yes, we leave you with this last thought. Because the wood chips are not well-insulated from oxygen by water, they will decay and your drainfield could sink, leaving a nice 12 inch depression in your yard.