1. A. The owner of a waterworks that uses a surface water source, a GUDI source, or both and provides filtration treatment shall monitor in accordance with this section.

2. B. Turbidity measurements shall be performed on representative samples of the filtered water every four hours (or more frequently) that the waterworks serves water to the public. The owner may substitute continuous turbidity monitoring for grab sample monitoring if the owner validates the continuous measurement for accuracy on a regular basis using a protocol approved by the department. For a waterworks using slow sand filtration or filtration treatment other than conventional treatment, direct filtration, or diatomaceous earth filtration, the department may reduce the sampling frequency to once per day if the department determines that less frequent monitoring is sufficient to indicate effective filtration performance. For a waterworks serving 500 or fewer persons, the department may 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.

   1. 1. The owner of a waterworks supplied by a surface water source, a GUDI source, or both using conventional filtration treatment or direct filtration shall conduct continuous monitoring of turbidity for each individual filter. The turbidimeter shall be calibrated using the procedure specified by the turbidimeter manufacturer. The owner shall record the results of individual filter turbidity monitoring a minimum of every 15 minutes.
   2. 2. If there is a failure in the continuous turbidity monitoring equipment, then the owner shall conduct grab sampling every four hours instead of continuous monitoring but for no more than five working days (for a waterworks serving 10,000 or more persons) or 14 days (for a waterworks serving fewer than 10,000 persons) following the failure of the equipment.
   3. 3. If a waterworks serving fewer than 10,000 persons consists of two or fewer filters, continuous monitoring of the CFE may be used instead of individual filter monitoring.

3. C. The residual disinfectant concentration of the water entering the distribution system shall be monitored continuously, and the lowest and highest values shall be recorded each day. If there is a failure in the continuous monitoring equipment, then grab sampling every four hours shall be conducted instead of continuous monitoring, but such grab sampling shall be conducted for no more than five working days following the failure of the equipment. The owner of a waterworks serving 3,300 or fewer persons may collect grab samples instead of continuous monitoring on an ongoing basis at the frequencies prescribed in Table 376.1.

   1. 1. The day's samples cannot be collected at the same time.
   2. 2. The sampling intervals are subject to department's evaluation and approval.

   3. 3. If at any time the residual disinfectant concentration falls below 0.2 mg/L in a waterworks using grab sampling instead of continuous monitoring, then the owner shall collect a grab sample every four hours until the residual disinfectant concentration is equal to or greater than 0.2 mg/L.

      TABLE 376.1 Grab Sample Monitoring Frequency
      WATERWORKS SIZE BY POPULATION	SAMPLES/DAY
      500 or less	1
      501 - 1,000	2
      1,000 - 2,500	3
      2,501 - 3,300	4

4. D. The residual disinfectant concentration shall be measured at least at the same points in the distribution system and at the same time as total coliform bacteria are sampled, as specified in 12VAC5-590-370 A and 12VAC5-590-380 D, except that the department may allow the owner of a waterworks that uses a groundwater source along with a surface water source, a GUDI source, or both to collect residual disinfectant samples at points other than the total coliform sampling points if the department determines that these points are more representative of treated (disinfected) water quality within the distribution system. Heterotrophic bacteria, measured as HPC as specified in 12VAC5-590-395 A 2 a (3), may be measured instead of residual disinfectant concentration.

5. E. The following information on the samples collected in the distribution system in conjunction with total coliform monitoring pursuant to 12VAC5-590-395 A 2 shall be reported monthly to the department by the owner:

   1. 1. Number of instances where the residual disinfectant concentration is measured;
   2. 2. Number of instances where the residual disinfectant concentration is not measured but heterotropic plate count (HPC) is measured;
   3. 3. Number of instances where the residual disinfectant concentration is measured but not detected and no HPC is measured;
   4. 4. Number of instances where no residual disinfectant concentration is detected and where the HPC is greater than 500/mL;
   5. 5. Number of instances where the residual disinfectant concentration is not measured and HPC is greater than 500/mL; and

   6. 6. For the current and previous month the waterworks serves water to the public, the value of "V," in percent, in the following formula:

      V = [(c + d + e) / (a + b)] X 100

      where

      a = the value in subdivision E 1 of this section;

      b = the value in subdivision E 2 of this section;

      c = the value in subdivision E 3 of this section;

      d = the value in subdivision E 4 of this section;

      e = the value in subdivision E 5 of this section.

Statutory Authority

§§ 32.1-12 and 32.1-170 of the Code of Virginia.

Historical Notes

Derived from Virginia Register Volume 37, Issue 20, eff. June 23, 2021.