Information Collection Rule Data Evaluation and Analysis to Support Impacts on Disinfection By-Product Formation

Abstract

Information Collection Rule (ICR) water quality and treatment data were screened from an end-user’s perspective and data distributions were developed based on the screened data set. Questionable data were flagged and missing categorical variables were replaced where possible. Sparseness of flagged data indicated a high level of ICR data quality while recovery of missing descriptors substantially amplified the data set. Data patterns demonstrated anticipated relationships between disinfection practices and water quality: plants with high concentrations of organic precursors preferentially employed chloramines and avoided prechlorination; plants with high bromide levels also tended to employ chloramines although bromide did not impact prechlorination practice. Though plants employing chloramination used significantly higher chlorine doses than plants using only free chlorine, when normalized to total organic carbon (TOC) this difference largely disappeared. The median ICR chlorine to TOC ratio was 1.54mgCl2∕mgC. Applied chlorine to ammonia-nitrogen ratios at chloramine plants varied widely but the median value was near the theoretical 1:1molar ratio. Significantly higher bromide to TOC ratios at ground water plants, compared to surface water plants, resulted from the typically lower TOC and higher bromide levels in ground waters.