R309-215-10. Residual Disinfectant

  Treatment plant management shall continuously monitor disinfectant residuals and report the following to the Division within ten days after the end of each month that the system serves water to the public, except as otherwise noted:

  (1) For each day, the lowest measurement of residual disinfectant concentration in mg/L in water entering the distribution system, except that if there is a failure in the continuous monitoring equipment, grab sampling every 4 hours may be conducted in lieu of continuous monitoring, but for no more than 5 working days following the failure of the equipment. Systems serving 3,300 or fewer persons may take grab samples in lieu of providing continuous monitoring on an ongoing basis at the frequencies listed in Table 215.2 below:

TABLE 215-2

RESIDUAL GRAB SAMPLE FREQUENCY

     System size by population Samples/day

     Less than 500 1

     501 to 1,000 2

     1,001 to 2,500 3

     2,501 to 3,300 4

     Note: The day's samples cannot be taken at the same time.

The sampling intervals are subject to Director's review and

approval.

  (2) The date and duration of each period when the residual disinfectant concentration in water entering the distribution system fell below 0.2 mg/L and when the Division was notified of the occurrence. The system shall notify the Division as soon as possible, but no later than by the end of the next business day. The system also shall notify the Division by the end of the next business day whether or not the residual was restored to at least 0.2 mg/L within four hours.

  (3) The following information on the samples taken in the distribution system in conjunction with total coliform monitoring pursuant to R309-211 and R309-210-8(3)(a)(i):

  (a) number of instances where the residual disinfectant concentration is measured;

  (b) number of instances where the residual disinfectant concentration is not measured but heterotrophic bacteria plate count (HPC) is measured;

  (c) number of instances where the residual disinfectant concentration is measured but not detected and no HPC is measured;

  (d) number of instances where no residual disinfectant concentration is detected and where HPC is greater than 500/ml;

  (e) number of instances where the residual disinfectant concentration is not measured and HPC is greater than 500/ml;

  (f) for the current and previous month the system serves water to the public, the value of "V" in the formula, V = ((c+d+e)/(a+b)) x 100, where a = the value in sub-section (a) above, b = the value in sub-section (b) above, c = the value in sub-section (c) above, d = the value in sub-section (d) above, and e = the value in sub-section (e) above.

  (4) The residual disinfectant concentration must be measured at least at the same points in the distribution system and at the same time as the total coliforms are sampled as specified in R309-211. The State may allow a public water system which uses both a surface water source or a ground water source under direct influence of surface water, and a ground water source, to take disinfectant residual samples at points other than the total coliform sampling points if the Director determines that such points are more representative of treated (disinfected) water quality within the distributions system. Heterotrophic bacteria, measured as heterotrophic plate count (HPC) as specified in paragraph R309-200-4(3), may be measured in lieu of residual disinfectant concentration.