AWWA QTC98228

The City of Concord developed and implemented an innovative full-scale remediation plan for improving its distribution system water quality. The objectives were: to discuss the phased approach to understanding and improving water quality distribution systems for lead and secondary disinfection problems, i.e. comprehensive baseline monitoring, data and chemical feed evaluation, full-scale implementation and on-going monitoring and process improvements; to discuss the baseline monitoring results, describe how the data was evaluated and analyzed (DIC, buffer intensity, etc.), and how the problems were identified; to discuss the chemical feed systems utilized for the lead control and secondary disinfection control; and, to present and discuss the results of the program and the recommended plan for future action. The recommended corrective program was to increase the dissolved inorganic carbonate (DIC) using carbon dioxide (CO2) and sodium hydroxide (or caustic soda, NaOH). This approach increased the DIC and buffering intensity, and stabilized pH throughout the distribution system. To achieve the desired pH and DIC levels, several chemical feed systems were evaluated. A NaOH and CO2 chemical feed system was recommended and implemented.