New Hampshire Code of Administrative Rules
New Hampshire Department of Environmental Services
PART Env-Ws 1023 OPERATING REQUIREMENTS
Env-Ws 1023.01 Septic Tank Inspection and Pumping Requirements.
(a) Septic tanks shall be inspected for accumulation of sludge and surface scum at least once every year.
(b) When the combined thickness of the sludge and surface scum equal 1/3 or more of the tank depth, the tank shall be pumped by a licensed septic tank pumper.
Also reference NH RSA 485-A, 485-A:34,III