Tire Chips

Indiana State Department of Health has included the following in their new residential septic Rule 410 IAC 6-8.2, which went into effect January 1, 2011:

(c) Tire chips may be used in place of stone for soil absorption fields on a one-for-one basis, volumetrically. Tire chips used for soil absorption fields must have a nominal size of two (2) inches with chip dimensions being no less than one-half (1/2) inch and no greater than four (4) inches. The local health department shall:
(1) maintain an inventory of on-site systems installed using tire chips; and
(2) provide that information to the department upon request.
When construction permits are issued for on-site systems that incorporate tire chips, they should note in writing that tire chips will be utilized and should include requirements for nominal tire chip size and removal of fines. Tire chips will have protruding wires and shall be removed from the ground surface during site clean-up.

My county has been allowing the use of tire chips as a replacement for stone aggregate for a few years now. But it hasn't gotten popular with installers until the past year and a half. I'd say about 4-5 installers regularly use tire chips in my county. It is indeed too early to tell, but so far we have not had any sites go into failure that contain tire chips. Of course the oldest site I'm aware of with tire chips in my county is at most 4 years old.

I have done alot of research as of late on the internet concerning the pros and cons of using tire chips, and the following is a list I drafted up summarizing these pros/cons:

Pros
•   Increased drain field capacity by up to 30% compared to gravel.
•   Tire chips = ~62% void space. Gravel = ~44% void space.
•   Tire chips much lighter than gravel. 800 lbs/cubic yard vs. 2800 lbs/cubic yard
•   Cut installation time due to light weight.
•   Diminished costs. Cheaper material and spend less on freight.
•   Eliminates need to excavate natural rock.
•   Provides alternative to tire disposal in landfills.
Cons
•   Wires sticking out of chips are very sharp – requires gloves and boots.
•   All those handling the chips should be up to date on tetanus shots.
•   Some concerns of tire chips compacting as weight of backfill placed over top.
•   Concerns of contaminants leaching into groundwater, i.e. a study in Clark County, Ohio (2000) showed higher levels of iron, manganese, zinc in tire chip trenches when compared to gravel trenches.
•   All tire chips must be removed from the ground surface during site cleanup due to the threat of injury from metal shards.
•   Size of chips can vary greatly between tire recycling facilities, as well as over time from the same facility due to shredder blades getting dull.
•   Clean, fine-free chips, if left exposed to the weather, will develop rusty fines.

I'm curious to hear what other folk's opinions are conerning tire chips in spetic systems.