single-time assays of trihalomethanes in drinking water. Furthermore, there is sufficient variation in even a large system so that a simple harmonic model cannot allow prediction of trihalomethane concentrations from one day to the next. If a maximum contaminant level for these compounds in drinking water is to be monitored, recognition of the 24-h variation is essential, but in addition the larger contribution of as yet undefined sources of day-to-day variability must be taken into account. The observed day-to-day variability may be of a systematic nature, i.e., possibly reflecting certain weekly cycles in water usage or in operations of the water treatment plant. Or, it may be simply a part of the broad scale irregular fluctuations known to be typical for the day-to-day behavior of river flow, ambient air and water temperatures, influencing the amount of humic material available for reaction with chlorine and the rate of trihalomethane formation. This question, although it cannot be answered with certainty given the available data, is, however, important, since it has a bearing on the potential predictability of trihalomethane concentrations in drinking water. An investigation is contemplated to address this matter.
Literature Cited(1) Fed. Re gist., 43 (No. 28) (Feb 9, 1978).(2) Keith, "Identification and Analysis of Organic Pollutants in Water", Ann Arbor Science Publishers, Ann Arbor, Mich., 1976, p 105. (3) "Standard Methods for Examination of Water and Wastewater", 12th ed.,