Inorganic Chemicals | Drinking Water Compliance Assistance

What to Do If There's an Exceedance

Nitrate or Nitrite Trigger Level 
If a system exceeds the trigger level (5.0 mg/L for nitrate or 0.5 mg/L for nitrite), t
hey must begin increased monitoring in the following quarter, until the system is able to obtain four consecutive quarters with results less than the maximum contaminant level (MCL) for groundwater systems and results less than the trigger level for surface water systems.

  • Groundwater systems, with ADEQ approval, are granted annual monitoring in which samples are taken in the quarter with the highest results. Future trigger level exceedances that are less the MCL DO NOT trigger increase monitoring.
  • Surface water systems, with ADEQ approval, are granted annual monitoring, in which samples are taken in the quarter with the highest results. Future trigger level exceedances DO trigger increase quarterly monitoring.

Nitrate or Nitrite Maximum Contaminant Level 
If a system exceeds the MCL for nitrate or nitrite, a confirmation sample must be taken within 24 hours of being notified. 
If a confirmation sample is not taken within 24 hours of the notification date, the original sample will be used for compliance to indicate the system has exceeded the MCLIf a confirmation sample is taken, the average of the original sample and the confirmation sample will be used for compliance. 

  • If the average from the two results is less than the MCL and the trigger level, no further action is required. 
  • If the average from the two results is less than the MCL, but greater than the trigger level, increased quarterly monitoring is required.
  • If the average of the two results more than the MCL, the MCL has been exceeded. 

An MCL exceedance triggers an MCL violation, increased quarterly monitoring starting the following quarter, and a Tier 1 Public Notice.

Inorganic Chemical MCL (Other than nitrate or nitrite)
If a system exceeds the MCL for any of the inorganic chemical contaminants (other than nitrate or nitrite), a confirmation sample must be taken within two weeks of being notified. If a confirmation sample is not taken within two weeks of the notification date, the original sample will be used for compliance to indicate the system has exceeded the MCL. If a confirmation sample is taken, the average of the original sample and the confirmation sample will be used for compliance. 

  • If the average from the two results are less than the MCL, no further action is required. 
  • If the average of the two results more than the MCL, the MCL has been exceeded. 

An MCL exceedance for arsenic triggers a MCL violation, increased quarterly monitoring starting the following quarter, and a Tier 2 Public Notice.