Abstract
Disinfection with chlorine is a common practice to ensure secured drinking water, but results in potentially harmful disinfection by-products (DBPs), when excess chlorination is done. The US Environmental Protection Agency (US EPA) has established Stage 1 and Stage 2 disinfection by-product Rules (DBP rules) to control DBP exposure. A modified version of the Canadian Council of Ministries of the Environment water quality index (CCME WQI) is used to assess water quality. CCME WQI is a globally accepted index to assess water quality, but is too generic to be used for DBP rules. The study developed a scheme to make the index suitable for DBP rules. A scoring method based on an analytic hierarchy process (AHP) is applied to assign weights based on DBP rules. A previously modified CCME WQI (Islam et al., 2014) is adapted along with the weights to perform the assessment at the distribution network (DN). A case study was performed on 7 sampling stations in a Quebec City DN. The spatial water quality variations are presented using kriging – a geostatistical method, which identifies the regions with relatively poor water quality and highlights the potential locations for re-chlorination points. The proposed assessment formulation is flexible to handle situations with limited data, which makes it especially suited to smaller municipalities. Keywords: CCME water quality index, Stage 1 DBP Rule, Stage 2 DBP Rule, chlorination
Highlights
Chlorination at the treatment plant and distribution network (DN) is a common practice to ensure safe drinking water
Stage 1 and Stage 2 disinfection by-products (DBPs) Rules were implemented in 1998 and 2006, respectively. These regulations are focused on the control of DBP exposure by providing various parameter thresholds, such as maximum contaminant level (MCL) and maximum contaminant level goals (MCLG)
The methodology to assess the water quality based on DBP rules is stated in Fig. 1, which contains 7 steps: (1) water quality parameter selection, (2) converting parameters to sub-indices, (3) generating parameter relative weights, (4) aggregating sub-indices to get the modified CCME water quality index (WQI), (5) temporal and spatial analyses of a DN, (6) comparing with other WQI formulations, and (7) analysing sensitivity by increasing the number of parameters
Summary
Chlorination at the treatment plant and distribution network (DN) is a common practice to ensure safe drinking water. Stage 1 and Stage 2 DBP Rules ( referred to as DBP rules) were implemented in 1998 and 2006, respectively These regulations are focused on the control of DBP exposure by providing various parameter thresholds, such as maximum contaminant level (MCL) and maximum contaminant level goals (MCLG). ISSN 1816-7950 (On-line) = Water SA Vol 42 No 2 April 2016 with a disinfectant (e.g., chlorine, chloramine) other than UV light should follow the Stage 2 DBP Rule. This final rule recommends meeting MCLs as an average at a compliance monitoring location, rather than an average for the whole system.
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