As used in this part, the following definitions shall apply:

1. (a) “Underground injection” means the subsurface emplacement of fluids through a well.

2. (b) “Well” means any of the following:

   1. (1) A bored, drilled, or driven shaft whose depth is greater than the largest surface dimension;
   2. (2) A dug hole whose depth is greater than the largest surface dimension;
   3. (3) An improved sinkhole; or
   4. (4) A subsurface fluid distribution system as defined in 40 CFR 144.3.

Source. (See Revision Note at part heading for Env-Wq 404) #9842, eff 12-23-10; ss by #12728, eff 3-1-19