S.C. Code Regs. § 61-58.9.D

Current through Register Vol. 48, No. 07, July 26, 2024

Section 61-58.9.D - Variances from the Maximum Contaminant Level for Total Trihalomethanes

(1) The following are identified as the best technology, treatment techniques or other means generally available for achieving compliance with the maximum contaminant level for total trihalomethanes (TTHM):

(a) Use of chloramines as an alternate or supplemental disinfectant or oxidant.

(b) Use of chlorine dioxide as an alternate or supplemental disinfectant or oxidant.

(c) Improved existing clarification for THM precursor reduction.

(d) Moving the point of chlorination to reduce TTHM formation and, where necessary, substituting for the use of chlorine as a pre-oxidant chloramines, chlorine dioxide or potassium permanganate.

(e) Use of powdered activated carbon for THM precursor or TTHM reduction seasonally or intermittently at dosages not to exceed 10 mg/1 on an annual average basis.

(2) The Department will consider a request for a variance from the maximum contaminant level for total trihalomethanes only from a community system which has installed the best available technology or treatment method specified in paragraph (1) above unless the Department determines that such treatment method is not available and effective for TTHM control for the system. A treatment method will not be considered to be "available and effective" for an individual system if the treatment method would not be technically appropriate and technically feasible for that system or would only result in a marginal reduction in TTHM for the system. The Department's determination as to the availability and effectiveness of such treatment methods will be based upon studies by the system and other relevant information. If a system submits information intending to demonstrate that a treatment method is not available and effective for TTHM control for that system, the Department will make a finding whether this information supports a decision that such treatment method is not available and effective for that system before requiring installation and/or use of such treatment method.

(3) Pursuant to 61.58.9(B)(4)(c)(B)(4)(c) -(g), the Department will issue a schedule of compliance that may require the system being granted the variance to examine the following treatment methods to determine the probability that any of these methods will significantly reduce the level of TTHM for that system and, if such probability exists, to determine whether any of these methods are technically feasible and economically reasonable, and that the TTHM reductions obtained will be commensurate with the costs incurred with the installation and use of such treatment methods for that system:

(a) Introduction of off-line water storage for THM precursor reduction.

(b) Aeration for TTHM reduction, where geographically and environmentally appropriate.

(c) Introduction of clarification where not currently practiced.

(d) Consideration of alternative sources of raw water.

(e) Use of ozone as an alternate or supplemental disinfectant or oxidant.

(4) If the Department determines that a treatment method identified in paragraph (3) above is technically feasible, economically reasonable and will achieve TTHM reductions commensurate with the costs incurred with the installation and/or use of such treatment method for the system, the Department will require the system to install and/or use that treatment method in connection with its compliance schedule. The Department's determination will be based upon studies by the system and other relevant information. In no event will the Department require a system to install and/or use a treatment method not described in paragraph (1) or (3) above to obtain or maintain a variance from the TTHM maximum contaminant level or in connection with any variance compliance schedule.

S.C. Code Regs. 61-58.9.D