Gloucester Chlorine Residual Evaluation

Water Street was retained to develop solutions for improving chlorine residuals in the Gloucester Area of the East Langley Water System (ELWS). Sampling data showed that chlorine residuals levels were often lower than the Township’s target.

Water Street created an extended period system hydraulic and chlorine decay model of the water system.  Observed system demands and chlorine residuals were used to calibrate the hydraulic and chlorine decay components of the model respectively. The model demand build included week-long demand patterns (separated by customer class) reflecting data from customer metering and source flow meters.

The system is supplied by two sources: GVRD water via the Brawn Pump Station and treated groundwater from the Aldergrove WWTP. Results confirmed that both water sources experience long detention times in the system causing low chlorine residuals. Water Street proposed options for re-chlorination and system control changes. These were intended to improve tank cycling, and reduce mixing of groundwater and surface water sources.

The original project scope was completed on budget. Following the original project, Water Street also completed additional analysis of the Aldergrove area of the ELWS, modelling the impact of a proposed new supply main intended to improve reservoir circulation. Water Street is now implementing recommendations from the original project at the Brawn Pump Station including the addition of a re-chlorination system and a jockey pump.