1. (a) The O/O of a PWS subject to this part shall conduct sampling and monitoring as specified in 40 CFR § 141.132 and § 141.133.

2. (b) Multiple wells for which a disinfectant is added at multiple separate points shall be considered as one treatment plant for determining the minimum number of TTHM and HAA5 samples specified in 40 CFR § 141.132, in accordance with the following criteria:

   1. (1) Routine monitoring at a frequency specified in 40 CFR § 141.132 shall have been performed for a minimum of one year;
   2. (2) Running annual average results shall be less than 0.040 mg/L for TTHM and less than 0.030 mg/L for HAA5;
   3. (3) For overburden wells, multiple wells shall be located within the same aquifer as determined using the stratified drift aquifer mapping of the U.S. Geological Survey;
   4. (4) For bedrock wells, multiple wells shall be located within an area of less than 4,000 feet in radius; and

   5. (5) The water quality of the multiple wells shall be within the following limits:

      1. a. pH within 0.5 units, using one of the analytical methods specified in 40 CFR § 141.23(k);
      2. b. Total hardness within 10 mg/L, as CaCO3;
      3. c. Alkalinity within 10 mg/L, as CaCO3; and
      4. d. Conductivity within 50 μmhos/cm2.
3. (c) If running annual average results for multiple wells initially considered as one treatment plant in (b), above, subsequently exceed 0.040 mg/L for TTHM or 0.030 mg/L for HAA5, each well shall then be considered as a separate treatment plant for monitoring purposes, subject to the routine and reduced monitoring frequency requirements specified in 40 CFR § 141.132.

Source. #9619, eff 1-1-10; ss by #12532, eff 6-1-18