The management of Trihalomethanes in water supply systems preferred access arrangement

The formation of potentially harmful trihalomethanes (THM) when using chlorine as a disinfectant in potable water supplies has led to tighter regulatory controls and hence a need for better models for THM management. The prediction of THM concentration is difficult due to the complex and changing hydrodynamic and chemical regimes found in water treatment works (WTWs) and distribution systems. The purpose of the study is to increase understanding of THM formation and chlorine decay through six water treatment works (WTWs) and distribution systems operated by Severn Trent Water Ltd and ultimately develop an efficient, robust, cost effective model for chlorine decay and THM formation. With knowledge of the bulk chlorine decay characteristics and the THM productivity of the water, this model offers a simple and straightforward tool which can be readily applied to WTWs and distribution systems alike to provide an initial assessment of the risks of total THM formation at different sites, and to identify sites and systems at risk of compliance failure. Relying only on the measurement of analytically undemanding parameters (in particular, chlorine and its decay with time), under appropriate circumstances this model offers advantages of simplicity and cost-effectiveness over other, more complex models. The model can thus be applied to assess the chemical risk under different scenarios allowing for informed decision making