"Impermeable substratum" means any subsurface material which is relatively impervious, such as hard pan, clay, slate-like materials and other materials having a percolation rate of greater than 60 minutes per inch.
N.H. Admin. Code § Env-Wq 1002.34
(See Revision Note at chapter heading for Env-Wq 1000) #9086, eff 2-9-08; renumbered by #9904-A (from Env- Wq 1002.33)