WCW24

The City of Brandon's Water Treatment Facility (Facility) operates as a conventional lime softening plant with residuals treatment with a current capacity of 54 ML/d, with the intent to increase the water system capacity with the construction of a new membrane plant. The transition from a conventional solid contact unit (SCU) facility to a combined SCU and membrane water treatment facility may affect water quality stability and the potential for corrosion or scaling in the distribution system due to the lower pH and alkalinity of the filtered water. Consequently, filtered water will be mixed with treated facility water before distribution to mitigate these effects. Health Canada recently lowered the maximum allowable concentration (MAC) of lead from 10 to 5 µg/L at the consumer's tap. Despite the City's regular replacement of lead service connections within public rights-of-way, it seeks additional methods to reduce lead concentrations in its distribution system. As a result, the City is conducting a bench-top study (Rapid Response Rig) to assess current and future water quality impacts using harvested lead service connections. Current corrosion control treatment (CCT) at the water treatment facility includes pH adjustment with carbon dioxide. However, the City plans to implement orthophosphate-based CCT as part of the Facility upgrades. The findings from this Rapid Response Rig will guide the selection and dosage of the corrosion inhibitor. Jacobs conducted a desktop water quality assessment to understand the current corrosivity of the Facility's raw, treated, and distributed water, as well as the expected corrosivity of future treated water following the addition of the membrane plant, the blending of the existing Facility and membrane plant waters, and the addition of orthophosphate. Initial desktop modeling of the expected water chemistry and corresponding scaling and corrosion indices provided theoretical estimates for water chemistry and pipe scale behaviors. These modeling results were used to design the Rapid Response Rig, the operation of which will proceed in two phases. The reasoning behind and the details of these phases will be discussed, as well as the available results from the study. This presentation will be of interest to owners and operations staff who are implementing or optimizing corrosion control programs due to the reduction in lead and copper MAC values.