Compliance with the MCL is based on a running annual average (RAA) of quarterly samples of sources beginning in the first quarter of 2025. For wells placed into service after March 31, 2025, initial monitoring begins during the first quarter of well operations. The exact date a source exceeds the MCL will depend on the concentration of Cr(VI) in that source, and an exceedance is determined when the RAA exceeds 10.4 µg/L. When a source exceeds  the MCL, your utility must provide Tier II notification within 30 days and a compliance plan must be submitted to the Division of Drinking Water (DDW) within 90 days.