DDW to Lower Perchlorate Detection Limit for Purposes of Reporting

On March 9, 2020 the State Water Resources Control Board (SWRCB) Division of Drinking Water (DDW) issued a Notice of Proposed Rulemaking and Initial Statement of Reasons (ISR) to lower the perchlorate detection limit for purposes of reporting (DLR) from 4 µg/L to 2 µg/L.

This afternoon (July 20, 2020) DDW released the enclosed documents that modify the March 9th proposal (revised_regtext_15day_perchlorate_070820 draft_israddendum_perchlorate_dlr_070820 notice_perchlorate_15day).  In the enclosed documents, DDW is proposing a two phase approach to the lower the perchlorate DLR.  The first phase will be to lower the DLR to 2 µg/L.  The second phase is to lower the DLR to 1 µg/L, effective January 1, 2024.   This revised proposal is open for a 15-day public comment period (comments are due by August 7, 2020).


The perchlorate Maximum Contaminant Level (MCL) is 6 µg/L and as stated above the current 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 1 µg/L PHG as technologically and economically feasible.

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