THMs presented at WQTC, Boston, 1996


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Strategic Diagnostics Inc. (SDI) markets a simple, colorimetric technology that can supplement trihalomethane (THM) testing using EPA methodology. Conventional analysis of total THMs requires the use of gas chromatography methods, which involve expensive equipment, extensive user training, and significant run time (30-45 minutes). This rapid, lowcost method enables water treatment facilities to respond quickly to changes in water quality. The utility of the method as a rapid, inexpensive and easy-to-use method for in-plant total trihalomethane (TTHM) determinations is apparent when the cost and time-to-result is considered. The data presented will demonstrate that the sensitivity, precision and performance of the SDI method compare favorably to the same properties of the GC methods.


Trihalomethanes (THMs) have been found to be the most widespread organic contaminants in drinking water, and occur at higher concentrations than other disinfection by-products. The four THMs (chloroform, bromodichloromethane, dibromochloromethane and bromoform) are formed when chlorine-based disinfectants are added to source water with fairly high organic content, such as surface water. THMs are included among the 25 volatile organic compounds regulated under the Safe Drinking Water Act (SDWA) of 1987. These compounds are persistent and mobile, and pose a cancer risk to humans.1,2

Regulations for the control of THMs in drinking water were promulgated by the EPA in 1979, setting the maximum contaminant level (MCL) of 100 mg/L (ppb) for systems serving populations of greater than 10,000 people. Since then, the increasing awareness of microbial risks in drinking water have caused disinfection and disinfection by-products to become more of an issue. Stage 1 of the proposed Disinfectants/Disinfection By-Products (D/DBP) Rule represents a lowered TTHM regulatory limit of 80 mg/L. Recently the AWWA Water Industry Data Base reported that a safety margin of 15% below the regulatory limit for total trihalomethanes (TTHMs) should be targeted; therefore, compliance with an 80 mg/L TTHM standard would require that a treatment process achieve < 64 mg/L to reliably stay below the regulatory limit. The stage 2 proposal, which will be reevaluated in a second negotiated rulemaking process, currently includes lowered MCLs of 40 mg/L for TTHMs.3

Because TTHMs are formed in proportion to the amount of organic matter in the source water, changes in TTHM concentrations may indicate changes in source quality. Timely measurement of TTHM concentrations can be a valuable tool in monitoring source water quality and making relevant adjustments to treatment processes.

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