1. (1) General.

   1. (a) The purveyor shall be responsible for complying with the standards of water quality identified in this section. If a contaminant exceeds its MCL or its maximum residual disinfectant level (MRDL), the purveyor shall take follow-up action under WAC 246-290-320.
   2. (b) When enforcing the standards described under this section, the department shall enforce compliance with the primary standards as its first priority.

2. (2) Bacteriological.

   1. (a) An E. coli MCL under this subsection is considered a primary standard.

   2. (b) E. coli MCL. An E. coli MCL violation occurs each month in which a system is required to monitor for total coliforms when there is:

      1. (i) E. coli presence in a repeat sample following a total coliform presence routine sample;
      2. (ii) Total coliform presence in any repeat samples collected as a follow-up to a sample with E. coli presence;
      3. (iii) The system fails to take all required repeat samples following an E. coli presence routine sample; or
      4. (iv) The system fails to test for E. coli when any repeat samples test positive for total coliform.

3. (3) Inorganic chemical and physical.

   1. (a) The primary and secondary standards are listed in Tables 5 and 6 of this section:

      TABLE 5

      INORGANIC CHEMICAL CHARACTERISTICS

      	Contaminant	PrimaryMCLs (mg/L)
      	Antimony (Sb)		0.006
      	Arsenic (As)		0.010*
      	Asbestos		7 million fibers/liter (longer than 10 microns)
      	Barium (Ba)		2.0
      	Beryllium (Be)		0.004
      	Cadmium (Cd)		0.005
      	Chromium (Cr)		0.1
      	Copper (Cu)		**
      	Cyanide (CN)		0.2
      	Fluoride (F)		4.0***
      	Lead (Pb)		**
      	Mercury (Hg)		0.002
      	Nitrate (as N)		10.0
      	Nitrite (as N)		1.0
      	Selenium (Se)		0.05
      	Sodium (Na)		**
      	Thallium (Tl)		0.002
      	Contaminant	Secondary MCLs (mg/L)
      	Chloride (Cl)		250.0
      	Fluoride (F)		2.0***
      	Iron (Fe)		0.3
      	Manganese (Mn)		0.05
      	Silver (Ag)		0.1
      	Sulfate (SO4)		250.0
      	Zinc (Zn)		5.0

      Note*

      Does not apply to TNC systems.

      Note**

      Although the state board of health has not established MCLs for copper, lead, and sodium, there is sufficient public health significance connected with copper, lead, and sodium levels to require inclusion in inorganic chemical and physical source monitoring. For lead and copper, the EPA has established distribution system related levels at which a system is required to consider corrosion control. These levels, called "action levels," are 0.015 mg/L for lead and 1.3 mg/L for copper and are applied to the highest concentration in 10 percent of all samples collected from the distribution system. The EPA has also established a recommended level of 20 mg/L for sodium as a level of concern for those consumers that may be restricted for daily sodium intake in their diets.

      Note***

      If a water system provides community fluoridation, the level of fluoride and associated requirements are set under WAC 246-290-460.

      TABLE 6

      PHYSICAL CHARACTERISTICS

      Contaminant	Secondary MCLs
      Color	15 Color Units
      Specific Conductivity	700 umhos/cm
      Total Dissolved Solids (TDS)	500 mg/L

   2. (b) Compliance with the MCLs, except for nitrate and nitrite, in this subsection is determined by a running annual average at each sampling point. The system will not be considered in violation of the MCL until it has completed one year of quarterly sampling and at least one sampling point is in violation of the MCL. If one sampling point is in violation of the MCL, the system is in violation of the MCL.

      1. (i) If any sample will cause the running annual average to exceed the MCL at any sampling point, the system is out of compliance with the MCL immediately.
      2. (ii) If a system fails to collect the required number of samples, compliance will be based on the total number of samples collected.
      3. (iii) If a sample result is less than the detection limit, zero will be used to calculate the running annual average.
   3. (c) Compliance with the MCLs for nitrate and nitrite is determined based on one sample if the levels of these contaminants are below the MCLs as determined under Table 5 of this section. If the levels of nitrate or nitrite exceed the MCLs in the initial sample, a confirmation sample is required under 40 C.F.R. 141.23 (f)(2), and compliance shall be determined based on the average of the initial and confirmation samples.

4. (4) Disinfection byproducts.

   1. (a) The department shall consider standards under this subsection as primary standards. The MCLs in this subsection apply to monitoring required by WAC 246-290-300(6) and 40 C.F.R. 141.620 - 629.

   2. (b) The MCLs for disinfection byproducts are as follows:

      TABLE 7

      DISINFECTION BYPRODUCTS

      Disinfection Byproduct	MCL (mg/L)
      Total Trihalomethanes (TTHMs)		0.080
      Haloacetic acids (five) (HAA5)		0.060
      Bromate		0.010
      Chlorite		1.0

   3. (c) Whether a system has exceeded the disinfection byproduct MCLs shall be determined in accordance with 40 C.F.R. 141.133. Beginning on the dates specified for compliance in 40 C.F.R. 141.620(c), compliance with the TTHMs and HAA5 MCLs shall be based on the LRAAs as required by 40 C.F.R. 141.64 (b)(2) and 40 C.F.R. 141.620(d). Compliance with the bromate and chlorite MCL will continue to be determined in accordance with 40 C.F.R. 141.133.

5. (5) Disinfectant residuals.

   1. (a) The department shall consider standards under this subsection primary standards. The MRDLs in this subsection apply to monitoring required by WAC 246-290-300(6).

   2. (b) The MRDL for disinfectants is as follows:

      TABLE 8

      DISINFECTANT RESIDUAL MRDLs

      Disinfectant Residual	MRDL (mg/L)
      Chlorine		4.0 (as C12)
      Chloramines		4.0 (as C12)
      Chlorine Dioxide		0.8 (as C1O2)

   3. (c) Whether a system has exceeded MRDLs shall be determined in accordance with 40 C.F.R. 141.133.

6. (6) Radionuclides.

   1. (a) The department shall consider standards under this subsection primary standards.
   2. (b) The MCLs for radium-226 and radium-228, gross alpha particle activity, beta particle and photon radioactivity, and uranium shall be as listed in 40 C.F.R. 141.66.

7. (7) Organic chemicals.

   1. (a) The department shall consider standards under this subsection primary standards.

   2. (b) VOCs.

      1. (i) The MCLs for VOCs are as follows:

         Contaminant	Chemical Abstract Service(CAS) Number	MCL (ppb)
         Vinyl chloride	75-01-4	2
         Benzene	71-43-2	5
         Carbon tetrachloride	56-23-5	5
         1,2-Dichloroethane	107-06-2	5
         Trichloroethylene	79-01-6	5
         para-Dichlorobenzene	106-46-7	75
         1,1-Dichloroethylene	75-35-4	7
         1,1,1-Trichloroethane	71-55-6	200
         cis-1,2-Dichloroethylene	156-59-2	70
         1,2-Dichloropropane	78-87-5	5
         Ethylbenzene	100-41-4	700
         Monochlorobenzene	108-90-7	100
         o-Dichlorobenzene	95-50-1	600
         Styrene	100-42-5	100
         Trichloroethane	127-18-4	5
         Toluene	108-88-3	1,000
         trans-1,2-Dichloroethylene	156-60-5	100
         Xylenes (total)	1330-20-7	10,000
         Dichloromethane	75-09-2	5
         1,2,4-Trichlorobenzene	120-82-1	70
         1,1,2-Trichloroethane	79-00-5	5

      2. (ii) The department shall determine compliance with this subsection based on compliance with 40 C.F.R. 141.24(f).

   3. (c) SOCs, except PFAS.

      1. (i) MCLs for SOCs shall be as listed in 40 C.F.R. 141.61(c).
      2. (ii) The department shall determine compliance with this subsection based on compliance with 40 C.F.R. 141.24(h).

   4. (d) PFAS.

      1. (i) The MCLs for PFAS, effective in accordance with 40 C.F.R. 141.6, are as follows:

         Contaminant	Chemical Abstract Service(CAS) Number	MCL (ppt or ng/L)	HBWC (ppt or ng/L) for hazard index calculation
         PFOA	45285-51-6	4.0	Not applicable
         PFOS	45298-90-6	4.0	Not applicable
         PFHxS	108427-53-8	10	10
         HFPO-DA	122499-17-6	10	10
         PFNA	72007-68-2	10	10
         PFBS	45187-15-3	No individual MCL	2,000
         Hazard Index PFAS (HFPO-DA, PFBS, PFHxS, and PFNA)	Not applicable	1 (unitless)1	Not applicable

         1

         The PFAS Mixture Hazard Index (HI) is the sum of component hazard quotients (HQs), which are calculated by dividing the measured component PFAS concentration in water by the relevant health-based water concentration when expressed in the same units (shown in ppt for simplification). The HBWC for PFHxS is 10 ng/l; the HBWC for HFPO-DA is 10 ng/l; the HBWC for PFNA is 10 ng/l; and the HBWC for PFBS is 2000 ng/l.

      2. (ii) The MCLs for PFAS will become effective according to the dates outlined in 40 C.F.R. 141.6.

8. (8) Other contaminants.

   The state board of health shall determine state MCLs for any additional contaminants as described in WAC 246-290-315 (5) through (8).

[Statutory Authority: RCW 43.20.050 and 70A.125.080. WSR 25-13-093, s 246-290-310, filed 6/17/25, effective 7/18/25. Statutory Authority: RCW 43.20.050, 70A.125.080, and 70A.130.010. WSR 21-23-097, § 246-290-310, filed 11/17/21, effective 1/1/22. Statutory Authority: RCW 43.20.050 and 70.119A.080. WSR 17-01-062, § 246-290-310, filed 12/14/16, effective 1/14/17. Statutory Authority: RCW 43.20.050. WSR 09-21-045, § 246-290-310, filed 10/13/09, effective 1/4/10. Statutory Authority: RCW 70.119A.180 and 43.20.050. WSR 08-03-061, § 246-290-310, filed 1/14/08, effective 2/14/08. Statutory Authority: RCW 43.20.050 and 70.119A.080. WSR 04-04-056, § 246-290-310, filed 1/30/04, effective 3/1/04. Statutory Authority: RCW 43.20.050 (2) and (3) and 70.119A.080. WSR 03-08-037, § 246-290-310, filed 3/27/03, effective 4/27/03. Statutory Authority: RCW 43.02.050 [ 43.20.050]. WSR 99-07-021, § 246-290-310, filed 3/9/99, effective 4/9/99. Statutory Authority: RCW 43.20.050. WSR 94-14-001, § 246-290-310, filed 6/22/94, effective 7/23/94; WSR 93-08-011 (Order 352B), § 246-290-310, filed 3/25/93, effective 4/25/93; WSR 92-04-070 (Order 241B), § 246-290-310, filed 2/4/92, effective 3/6/92. Statutory Authority: Chapter 43.20 RCW. WSR 91-07-031 (Order 150B), § 246-290-310, filed 3/15/91, effective 4/15/91. Statutory Authority: RCW 43.20.050. WSR 91-02-051 (Order 124B), recodified as § 246-290-310, filed 12/27/90, effective 1/31/91. Statutory Authority: P.L. 99-339. WSR 89-21-020 (Order 336), § 248-54-175, filed 10/10/89, effective 11/10/89. Statutory Authority: RCW 34.04.045. WSR 88-05-057 (Order 307), § 248-54-175, filed 2/17/88. Statutory Authority: RCW 43.20.050. WSR 83-19-002 (Order 266), § 248-54-175, filed 9/8/83.]