St. Tammany Parish Government’s Department of Utilities announces the conversion to Free Chlorine (Chlorine Burn) on the Cross Gates Water System is being concluded.
The Cross Gates Water System is being converted back to a Chloramine (Total Chlorine) disinfection system from the Free Chlorine disinfection system used for the Chlorine Burn. The Chlorine Burn was intended to raise the Free Chlorine residual to 1.0 ppm at all points in the distribution system for a duration of 60 days as recommended in the Owen & White report.
The Free Chlorine conversion was initiated on April 25, 2022 and after several days the system was able to convert to a Free Chlorine system and Free Chlorine residuals were achieved at all points in the distribution system; however, a mechanical failure of the dosing pumps resulted in the Free Chlorine residual dropping below 0.5ppm. A redundant dosing pump system was installed the next week while the Free Chlorine residual was re-established. Throughout the following weeks, the Free Chlorine residual remained above a 1.0 ppm in most of the distribution system and above a 0.5 ppm over the entire distribution. However, when a particular water well begins pumping due to a drop in system pressure, the chlorine residuals would intermittently drop below a 0.5ppm throughout the water system. The intermittent drop in Free Chlorine residual was investigated, and it was determined that the Free Chlorine residual could be achieved, but was unable to be maintained due to several limiting factors with the Cross Gates water distribution system.
The Free Chlorine conversion process disclosed several limiting factors for implementing Free Chlorine disinfection on the Cross Gates water system. The first limiting factor is that one of the water wells on the Cross Gates system requires more Sodium Hypochlorite (liquid bleach) chemical dosing than the legal EPA dosing limit to achieve and maintain a Free Chlorine residual. This means that all of the water this well pumps into the system does not have a stable Free Chlorine residual so it reacts with and consumes the Free Chlorine residual in the system causing a quick drop in the system wide Free Chlorine residual. The water chemistry from this well has naturally occurring Ammonia and organic compounds along with a high pH which requires the higher dosing of Chlorine to maintain a Free Chlorine residual. These water chemistry characteristics are favorable for Chloramine (Total Chlorine) disinfection with Sodium Hypochlorite (liquid bleach), which is able to provide a consistent Total Chlorine residual in compliance with both the EPA and Louisiana Department of Health (LDH) requirements. Second, this same well is needed to provide the required water capacity and flow for the Cross Gates water system so it must remain connected and functional. Third, the current control panels for the pumps on the water system operate using pressure readings on the distribution system so the well that experiences the pressure drop in the system from increased demand starts first. This creates a difficulty in establishing and maintaining a primary well, which compounds with the first two limiting factors and results in a Free Chlorine residual being able to be established but unable to consistently be maintained. The Precautionary Boil Water Advisory was left in place for the past three weeks due to the inconsistent Free Chlorine residual.
The Chlorine Burn process did result in a Free Chlorine residual of 0.5 ppm or higher for several days and all points in the system achieving the 1.0 ppm recommended Free Chlorine residual at some time during the Chlorine burn. Between May 10th and 11th, a total of 12 bacteria samples were collected from evenly distributed sites within the system all of which returned negative results. The Chlorine Burn also required significant flushing of all distribution lines within the Cross Gates water system. Valuable data was obtained to use to improve the understanding and operation of the water system going forward. New control panels that allow for improved well pump control and duplex chemical dosing pump skids will be purchased for the well sites. Additionally, the first project that will be performed as part of the East Slidell Regional Water Consolidation Phase 1 of the Water Sector Project will be a hydraulic model of the entire Cross Gates water system.
The Department of Utilities will continue to work diligently to provide safe, quality water to all of its customers. Upon completion of LDH Boil Water Advisory sampling, the Precautionary Boil Water Advisory will be rescinded. A full report of the Free Chlorine conversion will be completed by a consultant and will be posted on the Department of Utilities website when available.