WAC 246-290-72220

This section takes effect on January 1, 2027.

(1) Each report must include the following definitions:

(a) Contaminant: Any physical, chemical, biological, or radiological substance or matter in water.

(b) EPA: United States Environmental Protection Agency.

(c) Maximum contaminant level or MCL: The highest level of a contaminant that is allowed in drinking water. MCLs are set as close to the MCLGs as feasible using the best available treatment technology.

(d) Maximum contaminant level goal or MCLG: The level of a contaminant in drinking water below which there is no known or expected risk to health. MCLGs allow for a margin of safety.

(2) A report for a community water system operating under a variance or an exemption issued under WAC 246-290-060 must include the following definition: Variances and exemptions: State or EPA permission not to meet an MCL or a treatment technique under certain conditions.

(3) A report that contains data on contaminants that the department regulates using any of the following terms must include the applicable definitions:

(a) Action level: The concentration of a contaminant which, if exceeded, triggers treatment or other requirements which a water system must follow.

(b) Hazard index or HI: The hazard index is an approach that determines the health concerns associated with mixtures of certain PFAS in finished drinking water. Low levels of multiple PFAS that individually would not likely result in adverse health effects may pose health concerns when combined in a mixture. The hazard index MCL represents the maximum level for mixtures of PFHxS, PFNA, HFPO-DA, and/or PFBS allowed in water delivered by a public water system. A hazard index greater than 1 requires a system to take action.

(c) Maximum residual disinfectant level or MRDL: The highest level of a disinfectant allowed in drinking water. There is convincing evidence that addition of a disinfectant is necessary for control of microbial contaminants.

(d) Maximum residual disinfectant level goal or MRDLG: The level of a drinking water disinfectant below which there is no known or expected risk to health. MRDLGs do not reflect the benefits of the use of disinfectants to control microbial contaminants.

(e) Treatment technique: A required process intended to reduce the level of a contaminant in drinking water.

(4) A report that contains level 1 or level 2 assessment information must include the applicable definitions:

(a) Level 1 assessment: A level 1 assessment is a study of the water system to identify potential problems and determine, if possible, why total coliform bacteria have been found in our water system.

(b) Level 2 assessment: A level 2 assessment is a very detailed study of the water system to identify potential problems and determine, if possible, why an E. coli MCL violation has occurred and, if applicable, why total coliform bacteria have been found in our water system on multiple occasions.

(5) Systems must use the following definitions for the terms listed below if the terms are used in the report unless the system obtains written approval from the department to use an alternate definition:

(a) Herbicide: Any chemical(s) used to control undesirable vegetation.

(b) Pesticide: Generally, any substance or mixture of substances intended for preventing, destroying, repelling, or mitigating any pest.

(6) A report that contains information regarding a detection of a contaminant with a SAL must include the following definition: State action level or SAL: The concentration of a contaminant or group of contaminants, without an MCL, in drinking water established to protect public health and which, if exceeded, triggers actions a water system purveyor must take. SALs are established for contaminants without an MCL, federal action level, or treatment technique.