4/4/2017. Implementation of a PAX Mixing System for Nitrification Control. Loudoun Water Distribution System. Catherine Cogswell, Compliance Manager

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1 Implementation of a PAX Mixing System for Nitrification Control Catherine Cogswell, Compliance Manager Loudoun Water Distribution System Loudoun Water serves over 65, customers Over miles of water main Three Pressure Zones: 5, 58 and 6 HGL Daily water demand can vary between 8 to 6 MGD Two connections to Fairfax Water oco ecto sto a a ate Source split: / Fairfax Water, / Loudoun Water Seven WST s ranging from - MG each, 8 MG total Four WST s have PAX mixers

2 Goose Creek WTF Became Loudoun Water Jan, 4; Started up May 8, 4 Changes included: Free Chlorine all year to Combined Chlorine with Free Chlorine Switchover in Spring Increase in Target Residuals Collaboration with Fairfax Water Changeover from Chloramines to Free Chlorine System wide flushing March to June Target Chlorine Residuals History of Nitrification Monitoring - Concerns with chlorine residual in tanks and distribution system Identified nitrification as most likely cause Winter - Spring Research / Discussion with other utilities Develop Nitrification Monitoring Plan July Ju y Begin Nitrification Monitoring 4 Reevaluate Distribution System Sampling Points 5 Reevaluate Sampling Frequency

3 Nitrification Parameters and Sampling Schedule Tank Temperature Weekly or x Weekly and on SCADA Distribution Temperature Weekly or x Weekly Free Chlorine Weekly or x Weekly Monochloramine Weekly or x Weekly Total Chlorine Weekly or x Weekly and on SCADA Nitrite Weekly or x Weekly Free Ammonia Weekly or x Weekly Total Ammonia Weekly or x Weekly Nitrate Monthly HPC Monthly Dulles South Tanks Tank Loss (x) Chlorine Residual WTP Customer

4 PAX System PAX RCS PAX (x) Chlorine Residual Customer WTP PAX Ammonia Feed Skid 4

5 Smart Controller Home Screen Smart Controller Set Point Screen Daily Graph 5

6 Water Quality Station Water Quality Station Home Screen Water Quality Station Manual Sample Screen 6

7 7

8 Dulles South Year over Year.5 Total Chlorine, ppm 5 Nitrite (NO N), ppm 5 Free Ammonia (NO N), ppm Jun 8 Jun Jun 5 Jun Jun Jul 7 Jul 9 Jul 4 Jul 6 Jul Jul Jul 8 Jul Jul 4 Aug 6 Aug Aug Aug 8 Aug Aug 5 Aug 7 Aug Sep Sep 8 Sep Sep 5 Sep 7 Sep Sep 4 Sep 9 Sep 6 Oct 8 Oct Oct Oct Nov Dulles South Year over Year.5 Total Chlorine, ppm 5 Total Chlorine, ppm 6 Nitrite (NO N), ppm 5 Nitrite (NO N), ppm 6 Free Ammonia (NO N), ppm 5 Free Ammonia (NO N), ppm Lenah Run Year over Year.5 Total Chlorine, ppm 5 Nitrite (NO N), ppm 5 Free Ammonia (NO N), ppm Jun 8 Jun Jun 5 Jun 9 Jun Jul 6 Jul 9 Jul Jul 6 Jul Jul Jul 7 Jul Jul Aug 6 Aug Aug Aug 7 Aug Aug 4 Aug 7 Aug Aug Sep 8 Sep Sep 4 Sep 7 Sep Sep 4 Sep 8 Sep Oct 5 Oct 8 Oct Oct 9 Oct Oct 6 Oct 9 Oct Nov 8

9 Lenah Run Year over Year.5 Total Chlorine, ppm 5 Total Chlorine, ppm 6 Nitrite (NO N), ppm 5 Nitrite (NO N), ppm 6.5 Free Ammonia (NO N), ppm 5 Free Ammonia (NO N), ppm Glen Meadow Year over Year.5 Total Chlorine, ppm 5 Nitrite (NO N), ppm 5 Free Ammonia (NO N), ppm Jun Jun 9 Jun 6 Jul Jul 5 Jul 6 Jul Jul Jul 7 Jul Jul Aug 4 Aug 6 Aug Aug Aug 7 Aug Aug 4 Aug 7 Aug Aug Sep 8 Sep Sep 4 Sep Sep 4 Sep 8 Sep Oct 5 Oct 8 Oct Oct 9 Oct Oct 6 Oct 9 Oct Nov.5 Glen Meadow Year over Year Total Chlorine, ppm 5 Total Chlorine, ppm 6 Nitrite (NO N), ppm 5 Nitrite (NO N), ppm 6.5 Free Ammonia (NO N), ppm 5 Free Ammonia (NO N), ppm

10 PAX Pilot Statistics June 6 thru December 6, 6 June switchover from Free Chlorine to Combined Chlorine WST Chlorine Residual Target.8. ppm Free Ammonia Target.5.5 ppm Nitrite Target less than.5 ppm Lowest Chlorine Residual. ppm Highest Chlorine Residual.78 ppm Chemical Usage / Cost Ammonium Sulfate 6 gallons, $,8 Sodium Hypochlorite,.5% - 5 gallons, $4, Average Total Chemical Cost per Day = $97. Peak Chemical Cost per Day = $ PAX Pilot Observations/Lessons Learned Equipment The PAX Smart Controller and Water Quality Station equipment was reliable and accurate. The PAX alarm capabilities were excellent. We received and text messages for all alarms. The equipment shutdown if specific conditions were met. Highly recommend system be incorporated in utility s SCADA system. Additional Equipment Considerations For chemical addition to storage tanks consider the PAX Series 5 versus Series 4 mixers. As temperatures rise, diaphragm metering pumps will airlock because of chemical off-gassing. Prefer diaphragm over peristaltic pumps. PAX Pilot Observations/Lessons Learned Chemical Set-points The PAX RCS maintained residual chlorine levels consistent with target. On average we were able to maintain residuals within. ppm of the target. The ability to adjust ammonia feed rates based on ammonia levels in the storage tank. On average we were able to achieve.5 and.5 ppm ammonia and less than.5 ppm nitrite. Chemical Usage We observed an increased chemical demand when air temperatures hovered above 95 degrees for two or more days. Consider how your chemicals will be delivered: bulk, totes or drums.

11 PAX Pilot Observations/Lessons Learned The Role of High Water Quality Not as concerned if the tank did not meet our daily drafting goal because we could maintain a good residual. For new construction, our inspectors noted a quicker response in getting higher chlorine residuals during distribution system flushing. Throughout the pilot we saved significant labor, time and water because we were able to maintain good water quality parameters, i.e. chlorine residual, ammonia, and nitrite levels throughout the distribution system. Have consistent water quality testing protocol and equipment. We used the Hach SL and Chemkeys. Overall, the pilot was a great success. Future State / Path Forward Immediate Goal to receive Loudoun Water Board and VDH approval to install a PAX RCS in each of our two Brambleton,.5 MG WST s prior to the summer 7. Why? The Brambleton tanks have a high variability in chlorine residual, less than ppm to greater than ppm. High water age, impacted by 5 to 58 zone pumping volume and changes to our water supply coming from the Goose Creek WTP. More consistent water quality to areas served by the tanks and across zones Potential of lowering the chlorine residual leaving the Goose Creek WTP from 4 ppm in the summer months to something lower thereby reducing chemical cost while still addressing low chlorine and nitrification issues in our distribution system. Further reduce flushing demands More man-hours devoted to system maintenance