OEHHA Proposes Lower PHGs for Cis- and Trans-1,2-DCE

The Office of Environmental Health Hazard Assessment is proposing Public Health Goals for cis- and trans-1,2-dichloroethylene (1,2-DCE) in drinking water. This is the second version of the draft proposed PHGs. No changes were made from the earlier version in the proposed PHGs themselves. However, there were some changes made in the technical support document (TSD) supporting the proposal based on comments.

A PHG is the level of a drinking water contaminant at which adverse health effects are expected to occur during a lifetime of exposure. The California Safe Drinking Water Act requires OEHHA to establish PHGs based exclusively on public health considerations. The PHGs themselves have no regulatory effect other than occasionally used to establish clean-up standards for contaminated water. However, the Act requires the State Water Resources Control Board to establish a maximum contaminant level (MCL) for drinking water set as closely as feasible to the PHG after taking into account the technical and economic feasibility of achieving the PHG. Water suppliers are required to comply with MCLs in delivering water to their customers.

Cis-1,2-dichloroethylene and trans-1,2-dichloroethylene are two isomers of 1,2-dichloroethylene (1,2-DCE), which is a volatile, chlorinated and highly flammable organic compound used as a solvent for waxes and resins as well as a refrigerant, according to OEHHA. In 2006, OEHHA established a PHG of 100 parts-per-billion (ppb) for cis-1,2-DCE and 60 ppb for trans-1,2-DCE.Under the Act OEHHA is required to regularly revisit establish PHGs to determine whether they should be revised based on new evidence.

Last August OEHHA proposed to lower the PHG for cis-1,2-DCE to 13 ppb and to lower the trans-1,2-DCE to 50 ppb. A public comment deadline was set at September 18, 2017 and the proposal was submitted for peer review. In addition OEHHA held a workshop on the proposal on September 2018. Based on comments OEHHA has made some changes in the TSD. However, it has not changed the proposed PHGs themselves, which remain at 13 ppb and 50 ppb respectively.

U.S. EPA's MCL and Maximum Contaminant Level Goals (MCLGs) for cis-1,2-DCE are both 70 ppb. The current California MCL is 6 ppb. EPA’s MCL and MCLGs for trans-1,2-DCE are both 100 ppb, while the California MCL is set at 10 ppb. Thus OEHHA’s proposed PHGs are both more stringent than EPA’s standards. However, the proposed PHGs are both higher than the State Board’s current MCLs; a highly unusual occurrence.  

Interested parties will have through Monday, July 2 to submit comments on this revised TSD.

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