Correlations Between Trihalomethanes And Total Organic Halides Formed During Water Treatment

Data obtained from 12 full‐scale treatment plants in six states were evaluated to determine the extent to which correlations exist between trihalomethane (THM) and total organic halide (TOX) formation. Surface waters that had undergone conventional treatment at near‐neutral pH were found to contain a TOX‐to‐TTHM ratio of approximately 3.4:1. On a chlorine‐equivalent basis, the TTHMs comprised approximately 26 percent of the TOX concentration. This TOX‐to‐TTHM ratio corresponded closely to the ratio of TOX formation potential to THM formation potential found in raw waters after a chlorine contact time of seven days at pH 7. In waters subjected to precipitative softening at alkaline pH values, the TTHMs, on a chlorine‐equivalent basis, comprised 39 percent of the TOX concentration.