1. (a) The O/O of a community water system using groundwater, a non-transient non-community water system using groundwater, or a transient non-community water system using groundwater shall monitor for nitrate quarterly for at least one year following any one sample in which the concentration is greater than or equal to 50% of the nitrate MCL.
2. (b) After a minimum of one year of quarterly sampling, the O/O may submit a written request to the department for the monitoring frequency to be reduced.

3. (c) The written request shall include:

   1. (1) The name of the PWS;
   2. (2) The PWS identifier for the PWS;
   3. (3) A summary of all quarterly sampling results; and
   4. (4) An explanation of whether the PWS is operating any type of treatment to reduce the amount of nitrate.

4. (d) The department shall approve a reduction in monitoring from quarterly to annually if the department determines that:

   1. (1) Based on 4 consecutive quarterly samples, the nitrate levels are reliably and consistently below the nitrate MCL; and
   2. (2) The PWS is not operating any type of treatment to reduce the amount of nitrate.
5. (e) A surface water system shall return to quarterly monitoring if any one sample is greater than or equal to 50% of the nitrate MCL.
6. (f) After the initial round of quarterly sampling is completed, each community water system, non-transient non-community water system, and transient non-community system shall collect subsequent annual samples during the quarter in which the highest analytical result was obtained.

Source. #9700, eff 5-1-10; amd by #10771, eff 2-1-15; ss by #12668, eff 1-1-19