New Hampshire Code of Administrative Rules
Env - Department of Environmental Services
Subtitle Env-Ws - Division of Water
Chapter Env-Ws 300 - NEW HAMPSHIRE DRINKING WATER RULES
Part Env-Ws 380 - FILTRATION, DISINFECTION, TREATMENT PLANT AND WASTE RECYCLING
Section Env-Ws 380.19 - Monitoring Requirements for Systems Using Filtration Treatment

(1) The measurement as required by Env-Ws 380.12 shall be performed on representative samples of the system's filtered water at leastevery 4 hours, that the system serves water to the public;

(2) A public water system may substitute continuous turbidity monitoring for grab sample monitoring if it validates the continuous measurement for accuracy on a regular basis using a protocol recommended by the equipment manufacturer;

(3) For a systems using slow sand filtration or filtration treatment other than conventional treatment, direct filtration, or diatomaceous earth filtration, the department shall reduce the sampling frequency to once per day if it determines that less frequent monitoring is sufficient to indicate effective filtration performance;

(4) For a system serving 500 or fewer people, the department shall reduce the turbidity sampling frequency to once per day, regardless of the type of filtration treatment used, if the department determines that less frequent monitoring is sufficient to indicate effective filtration performance;

(5) The determination of sufficiency of less frequent monitoring in sections (3) and (4) shall be based on the following criteria:

(1)The residual shall be monitored continuously, and the lowest value shall be recorded each day, except that if there is a failure in the continuous monitoring equipment, grab sampling every 4 hours shall be conducted in lieu of continuous monitoring, but for no more than 5 working days following the failure of the equipment;

(2) Systems serving 3,300 or fewer people may take grab samples in lieu of providing continuous monitoring on an ongoing basis at the frequencies each day prescribed in Table 380-11 below:

Table 380-11

Disinfectant Residual Sampling For Filtered Systems

(3)The day's samples taken according to (2) aboveshall not be taken at the same time; and

(4) If at any time the residual disinfectant concentration falls below 0.2 mg/l in a system using grab sampling in lieu of continuous monitoring, the system owner shall take a grab sample every 4 hours until the residual disinfectant concentration is equal to or greater than 0.2 mg/l.

(1)The residual disinfectant concentration shall be measured at least at the same points in the distribution system and at the same time as total coliforms are sampled, as specified in Env-Ws 325.02, except that a public water system which uses both a SW/GWUDISW, and a ground water source, may take disinfectant residual samples at points other than the total coliform sampling points if the department determines that such points are more representative of disinfected water quality within the distribution system;

(2) The department shall make the determination of whether alternate sampling points are more representative of disinfected water quality within the distribution system based on the following criteria:

(3)Heterotrophic bacteria, measured as heterotrophic plate count may be measured in lieu of residual disinfectant concentration.