"Operating volume" means the volume of treated water that will be recirculated, that is contained within the pool envelope as measured from the horizontal centerline of the skimmer or top lip of the perimeter overflow system, as applicable, that includes water held in surge, balance or collection tanks, vented reservoirs, and transit pipes, and that accounts for areas created by benches, steps, foot wells, recessed stairs, underwater shelves, and other such areas.
N.H. Admin. Code § Env-Wq 1102.37
(See Revision Note at chapter heading for Env-Wq 1100) #8468, eff 11-1-05