DDW Proposes Lower Perchlorate DLR

This morning (March 9, 2020) the State Water Resources Control Board (SWRCB) Division of Drinking Water (DDW) issued the enclosed Notice of Proposed Rulemaking (NPRM) to lower the perchlorate detection limit for purposes of reporting (DLR) from 4 µg/L to 2 µg/L.  DDW will hold a public hearing on April 28, 2020 and public comments are due by noon on May 1, 2020.   The enclosed NPRM (DDW NPRM_Perchlorate DLR) indicates that “Final regulations are expected to be adopted by the Board later this year, after consideration of all written and oral comments.”


The perchlorate Maximum Contaminant Level (MCL) is 6 µg/L and the DLR is 4 µg/L.  In 2015 the Office of Environmental Health Hazard Assessment (OEHHA) lowered the perchlorate Public Health Goal (PHG) from 6 µg/L to 1 µg/L.  In 2017, DDW presented a two-step process for possibly lowering the perchlorate MCL from 6 µg/L to a level closer to the PHG of 1 µg/L.  The first step involves lowering the DLR.  The intent of lowering the DLR would be to generate statewide occurrence data for perchlorate below the current DLR of 4 µg/L.  Using occurrence data collected with a lower DLR, in the second step, DDW may propose lowering the MCL from 6 µg/L to a level as close to the PHG as technologically and economically feasible.


[Note: on a separate topic, the enclosed NPRM includes a proposal to readopt the definitions of “Potential Contaminating Activity” and “Source Water Assessment” back into Title 22 regulations.]