These authors recommend that water treatment plant designers and operators use an integrated approach to optimize the collective effects of the treatment train for removing NOM.Because it is not practical to analyze for each individual chemical compound present in natural organic matter (NOM), surrogate characterization methods were south that could identify interrelationships between NOM and its teratability. Source‐related and seasonal differences, effects of ozonation and coagulation on NOM, characterization of NOM in sequential unit processes including granular activated carbon, and aspects of bromide‐NOM interactions are explored. Whereas coagulants remove NOM intact, particularly higher‐molecular‐weight fractions, ozone converts humic to nonhumic material, resulting in NOM fractions that colud be difficult to remove by subsequent of separation techniques unles the bromide concentration is equalized in the individual fractions.

This article describes the overall development, including formulation and calibration, of linear and nonlinear multiple regression models for predicting total trihalomethane formation potential and kinetics during the chlorination of natural waters. The rationale behind each model formulation is discussed, and statistics relating to the calibration of each model are presented. The testing and attempted validation of these models are also addressed. Each model is subjected to a sensitivity analysis and a validation analysis using data derived from the literature.

Nitrosamine data reported from the first rounds of samples collected under the second Unregulated Contaminants Monitoring Rule (UCMR2) and the Ontario Drinking Water Surveillance Program were reviewed to assess the frequency and magnitude of occurrence and the effect of disinfectant type and other treatment factors on reported nitrosamine concentrations. Initial monitoring data reveal that N‐nitrosodimethylamine (NDMA) was detected in drinking water at concentrations higher than the UCMR2 minimum reporting level (MRL) of 2 ng/L in 1 of every 10 samples. Other nitrosamines (e.g., N‐nitrosodiethylamine, N‐nitroso‐di‐n‐butylamine, N‐nitrosopyrrolidine, and N‐nitroso‐methylethylamine) were rarely detected at levels above their MRLs. NDMA was primarily detected in systems using chloramines, with more than two thirds of all chloraminated water systems detecting NDMA in at least one sample. Follow‐up survey results from 45 water systems participating in UCMR2 and 6 water systems from Ontario, Canada, generally followed expected trends based on the literature. NDMA occurrence was more frequent and concentrations were higher in water systems having long contact times with chloramines. A comparison of maximum‐residence‐time distribution system samples with entry point samples indicates that NDMA concentrations may increase in a chloraminated distribution system if precursors have not fully reacted at the entry point.

A computer program was developed to simulate disinfection by‐product formation, removal of natural organic matter, inorganic water quality changes, and disinfectant decay in water treatment processes. This article presents equations that simulate the formation of total trihalomethanes (TTHMs), removal of total organic carbon (TOC) and ultraviolet absorbance by alum coagulation, and changes in alkalinity and pH. These equations represent only a small fraction of the entire computer model. Model simulations are compared with limited sets of observed values. The central tendency of the model is to underpredict finished‐water pH by 4 percent, finished‐water TOC by 7 percent, and simulated distribution system TTHMs by 20–30 percent. A discussion of model limitations and research needs concludes the article.

Water utilities need to begin now to evaluate their costs for complying with a lower MCL for arsenic. Compliance with a revised arsenic maximum contaminant level (MCL) for drinking water will require a substantial cost to water suppliers in the United States. A rigorous methodology was developed to estimate the national cost of complying with alternative regulatory limits for arsenic. This methodology considered the feasibility of available technologies based on existing treatment at utilities that are not in compliance and the level of water quality constituents that limit technology performance. A least‐cost method of selecting treatment alternatives was used to estimate compliance costs and the results were extrapolated nationally. Estimated national compliance costs ranged from $330 million per year for a 20‐μg/L MCL to more than $4.1 billion/year for a 2‐μg/L MCL. These estimates represent a 10‐ to 20‐fold increase in the US Environmental Protection Agency's (USEPA's) preliminary cost estimates. Although the effect on small systems would be substantial, this study found that the cost burden would be shared equally between small (<10,000 people served) and large (>10,000 people served) systems. USEPA also found that systems using groundwater would bear more of the total costs (62 to 82 percent) than systems using surface water.