Opinion

The Association in Saskatchewan regularly gets complaints from installers about rubber tire shreds used as aggregate in sand mounds. These complaints stem from contractors being contacted to repair or replace these systems, often within only a few years of the system’s life.

Installers report that in systems where the rubber shreds or tire chips do not meet the requirements for tire chip media, shreds can be much larger than prescribed.  Rubber shreds that are four to six inches or larger can compact over time and melt together forming an impermeable layer.  Alternately, some of the rubber shreds and wires may migrate to the surface causing a nuisance or even a danger to the homeowner when mowing and caring for their yard.  When using tire chip media, the system is intended to be covered with geotextile fabric to mitigate ‘floating’ tire chips, however this does not always occur.

Rubber Tire Shred or Tire Chip Media is allowed in the Saskatchewan Onsite Wastewater Disposal Guide under certain prescriptive requirements.

Firstly, quality counts!  The tire chip media must be virtually free of wire and fines.  Large pieces greater than 10 cm are prohibited. There are prescriptive requirements for the size and cleanliness of the media:

13.4  REQUIREMENTS

13.4.16 Materials

1) b) Tire Chip Media

1. i) Tire Chip Media shall be:

(1) free (95% or better by weight) of balls of wire and fine rubber particles less than 2 mm.

(2) clean and free (95% or better by weight) of any soil particles (fines) either adhering to the chips or floating loose within the chips.

(3) nominally 5 cm (2 in) in size and may range from 1.25 cm (½ in) to a maximum of 10 cm (4 in) in any one direction (95% or better by weight).

(4) Free of wire protruding more than 2.5 cm (1 in) from the sides of the chips (85% or better by weight).

1. ii) Tire-derived aggregate that meets type A TDA of the ASTM Standard D6270 “Standard Practice for Use of Scrap Tires in Civil Engineering Applications” may be used as a replacement for Tire Chip Media.

Next, vertical separation is a factor.  Under Article 13.4.5(4), tire chip media may only be used as aggregate in a soil treatment field that has a vertical separation of 1500 m or 5 ft.  Type II sand mounds are designed and installed when vertical separation is less than 1500 m (5’) removing the possibility for an in-ground system.  The requirement for 1500 m (5’) of vertical separation should preclude the use of tire chip media in Type II mounds.

13.4.5

Vertical Separation

4) A soil treatment field that uses tire chip media shall have a vertical separation between the tire chip infiltration surface and a restrictive layer of not less than 1500 mm (5ft).

Finally, the finishing details are important! The media is to be covered with a filter fabric prior to backfilling.  Any excess tire chip media is to be removed from the site and any tire chip media not covered by filter fabric must be covered in such a way that puncture from protruding wires doesn’t occur.

14.6.2 Trench Design

14.6.4 Gravelless Systems

5) For tire chip media, a) they shall be firmly compacted prior to covering with a filter fabric;

1. b) the tire chip aggregate shall be covered with a layer of non-woven filter fabric extending across the top of the tire chip aggregate before backfilling;
2. c) all tire chips not used in the soil absorption system shall be removed from the site by the installer or contractor of the system and the site shall be cleaned-up to ensure that no chipped tires or related material remain after completion of the system;
3. d) any tire chips placed on top of the filter fabric after system inspection shall be covered adequately to prevent persons or pets from being punctured by the wires; and,
4. e) contractors are responsible to ensure that an appropriate level of cover (which may include a straw layer above the filter fabric) to prevent an undue risk of freezing.

Summary

Tire chip media began to be used as aggregate in areas where drain rock was difficult to obtain.  It provided an opportunity to recycle and reuse discarded tires.

Unfortunately, there can be drawbacks to this media.  Shredding companies are often unaware of the material requirements for use in onsite wastewater systems and therefore the tire chips may be too large, have too many fines, and have longer than prescribed wires.  It is important for installers to be aware of the requirements for chip size and cleanliness before using tire chip media.

Best practice would include discussing the options for materials with the homeowner, explaining the pros and cons of the various available media options.

Although tire chip media is allowed under the SOWDG, it remains to be seen whether using it is a best practice.  There are other, readily available options for use in onsite wastewater systems.  Washed drain rock and chambers are available for use in both trench systems and Type II sand mounds. As well, for gravelless systems, pipe bundles with artificial aggregate are an option (Article 13.3.6).

If you have experience or information on the use of tire chip media in onsite wastewater systems, your industry association would like to hear from you.  Photos and testimonials, positive or negative would be appreciated to provide a well-rounded view of installers’ and other’s experience with tire chip media. Send your stories and photos to info@wcowma.com