Maximum Volatile Organic Chemical Contaminant Levels and Monitoring Requirements

PURPOSE: This rule establishes maximum contaminant levels and monitoring requirements for volatile organic chemicals. (1) This rule applies to community and nontransient noncommunity public water systems. (2) The following are the maximum contaminant levels (MCLs) for volatile organic chemicals (VOCs). Maximum Contaminant Level, Milligrams Contaminant Per Liter (A) Eight (8) original VOCs 1. Benzene 0.005 2. Carbon tetrachloride 0.005 3. 1,2-dichloroethane 0.005 4. 1,1-dichloroethylene 0.007 5. para-dichlorobenzene 0.075 6. 1,1,1-trichloroethane 0.2 7. Trichloroethylene 0.005 8. Vinyl chloride 0.002 Maximum Contaminant Level, Milligrams Contaminant Per Liter (B) Thirteen (13) VOCs 1. cis-1,2-dichloroethylene 0.07 2. Dichloromethane 0.005 3. 1,2-dichloropropane 0.005 4. Ethylbenzene 0.7 5. Monochlorobenzene 0.1 6. o-dichlorobenzene 0.6 7. Styrene 0.1 8. Tetrachloroethylene 0.005 9. Toluene 1 10. 1,2,4-Trichlorobenzene 0.07 11. 1,1,2-Trichloroethane 0.005 12. trans-1,2dichloroethylene 0.1 13. Xylenes (total) 10 (3) For the purpose of determining compliance with MCLs, a supplier of water must collect samples of the product water for analyses as follows: (A) During the initial three (3)-year compliance, all community and nontransient noncommunity water systems must collect an initial round of four (4) consecutive quarterly samples for each of the contaminants listed in section (2) unless a waiver has been granted by the department. The department will designate the year in which each system samples within this compliance period; (B) All public water systems shall sample at points in the distribution system representative of each water source or at each entry point to the distribution system. Each sample must be taken at the same sampling point, unless conditions make another sampling point more representative of each source or treatment plant. The sampling point will be after the application of treatment, if any; (C) If the system draws water from more than one (1) source and the sources are combined before distribution, the system must sample at an entry point to the distribution system during periods of normal operating conditions; (D) The department may require more frequent monitoring than specified in subsection (3)(A) of this rule and may require confirmation samples for positive and negative results at its discretion; and (E) If one (1) sampling point is in violation of an MCL, the system is in violation of the MCL. 1. For systems monitoring more than once per year, compliance with the MCL is determined by a running annual average at each sampling point. 2. Systems monitoring annually or less frequently whose sample result exceeds the MCL must begin quarterly sampling. The system will not be considered in violation of the MCL until it has completed one (1) year of quarterly sampling. 3. If any sample result will cause the running annual average to exceed the MCL at any sampling point, the system is out of compliance with the MCL immediately. 4. If a system fails to collect the required number of samples, compliance will be based on the total number of samples collected. 5. If a sample result is less than the detection limit, zero will be used to calculate the annual average. (4) If contaminants are not detected during the first three (3)-year compliance period, systems may decrease their sampling frequency beginning in the next year. (A) Groundwater systems must sample annually. After three (3) years of annual sampling and no previous detection, groundwater systems may reduce their sampling frequency to one (1) sample per compliance period. (B) Surface water systems must sample annually after the initial sampling period if there are no contaminants detected in the initial sampling. (5) If contaminants are detected in any sample, then systems must sample quarterly beginning in the next quarter at each sampling point which resulted in a detection. (A) Groundwater systems must sample a minimum of two (2) quarters and surface water systems must sample a minimum of four (4) quarters to establish a baseline. (B) If the MCL is exceeded, as described in subsection (5)(E) or (F) of this rule, then systems must sample quarterly beginning in the next quarter. Systems must sample a minimum of four (4) quarters to establish a baseline. (C) If the baseline indicates a system’s analytical results are reliably and consistently below the MCL, the department may reduce the system’s sampling frequency to annually. (Annual sampling must be conducted during the quarter which previously yielded the highest analytical result.) (D) Systems which have three (3) consecutive annual samples with no detection of a contaminant may apply to the department for a waiver. (E) If a system conducts sampling more frequently than annually, the system will be in violation when the running annual average at any sampling point exceeds the MCL. (F) If a system conducts sampling annually or on a less frequent basis, the system will be in violation when one (1) sample (or the average of the initial and confirmation samples) at any sampling point exceeds the MCL. (6) A public water system may apply to the department for susceptibility waivers from required sampling. Systems are eligible for reduced monitoring in the initial three (3)- year compliance period. Waivers are effective for two (2) compliance periods. The waiver must be renewed in subsequent compliance periods, or the system must conduct sampling as required by section (3) of this rule. A public water system may apply to the department for susceptibility waivers for reduced monitoring contingent on the conduct of a thorough vulnerability assessment as required by 10 CSR 60-6.060(3). (A) As a condition of the susceptibility waiver, a groundwater system must take one (1) sample at each sampling point during the time the waiver is effective (that is, one (1) sample during two (2) compliance periods or six (6) years) and update its vulnerability assessment by the end of the first compliance period. The department must confirm that the system is not vulnerable. (B) Surface water systems must sample at a frequency determined by the department. A vulnerability assessment according to 10 CSR 60-6.060(3) must be required in subsequent compliance periods in order for the system to return to its nonvulnerable status. (C) For the purposes of this section, detection is defined as greater than 0.0005 mg/L. (7) As determined by the department, confirmation samples may be required for either positive or negative results. If a confirmation sample is used, the compliance determination is based on the average of the results of both the confirmation sample and the initial sample. (8) All new systems or systems that use a new source of water that begin operation after January 22, 2004 must demonstrate compliance with the MCL or treatment technique within a period of time specified by the department. The system must also comply with the initial sampling frequencies specified by the department to ensure a system can demonstrate compliance with the MCL or treatment technique. Routine and increased monitoring frequencies shall be conducted in accordance with the requirements in this rule. AUTHORITY: section 640.100, RSMo 2016.* Original rule filed June 2, 1988, effective Aug. 31, 1988. Rescinded and readopted: Filed March 31, 1992, effective Dec. 3, 1992. Amended: Filed May 4, 1993, effective Jan. 13, 1994. Amended: Filed Feb. 1, 1996, effective Oct. 30, 1996. Amended: Filed March 17, 2003, effective Nov. 30, 2003. Amended: Filed June 13, 2018, effective Feb. 28, 2019. *Original authority: 640.100, RSMo 1939, amended 1978, 1981, 1982, 1988, 1989, 1992, 1993, 1995, 1996, 1998, 1999, 2002, 2006, 2012, 2014.