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CITY OF SANTA ANA Well No. 32 Nitrate Mitigation and Rehabilitation Study 3.3 Treatment Options Ion exchange (IX) is the most widely used treatment technology for reducing nitrate concentrations at well sites or other points of entry into potable water distribution systems. IX technologies are relatively simple to design, operate and monitor. IX is most suitable for waters with total dissolved solids (TDS) concentrations of less than 500 mg/L. Salts and organics in water will eventually foul IX resins, but many systems operate for 5 to 10 years without requiring resin replacement. The primary disadvantage of these systems is the production and costly disposal of concentrated brines, which can contain high concentrations of sodium chloride, nitrate, sulfate, and arsenate. Brines can be disposed of in sewers where adequate dilution is available, but long -term salinity control in some areas may limit this option. Two options are available for regenerating IX resins and include on -site and off -site regeneration. On -site regeneration requires an aboveground brine storage /brine maker tanks, water softener for brine make -up, brine/backwash discharge pump, air blower system for air block during media regeneration, and backwash conveyance system. Off -site regeneration involves contracting with a company that would slurry out a specific amount of ion exchange resin at a time and transport the resin to a facility to regenerate the resin. At the same time, an equal quantity of regenerated resin would be slurried back into the vessels ready for use. The City indicated that disposal of waste brine to the sewer is not a viable option. In addition, there is a lack of sufficient space at Morrison Park to accommodate the additional regeneration facilities. As a result, the off -site regeneration option was considered as part of the treatment system. Tetra Tech contacted several equipment suppliers to provide equipment sizing for the IX vessels. Based on an assumed nitrate influent concentration of 45 mg /L, a treated water level of 20 mg/L and a well flowrate of 2,500 gpm, approximately 70% (1,786 gpm) of the flow from Well No. 32 would need to be treated by IX. The remaining 714 gpm would be bypassed and blended with the treated water to meet the water quality goal. For off-site regeneration, 12 IX vessels (12 feet diameter each) would be required and would be operated as two trains of six vessels each. There would be approximately 3,600 cubic feet of nitrate resin installed, and 1,200 cubic feet of resin in float. The contract maintenance supplier would slurry out 1,200 cubic feet of resin at a time and transport the resin back to their facility to regenerate the resin. At the same time, 1,200 cubic feet of regenerated resin would be slurried back into the vessels ready for use. A preliminary footprint of the wellhead treatment facilities was prepared and is presented in Figure 2. As indicated, approximately 0.3 acres would be required for the treatment facilities that would include the IX vessels, electrical and control panels and other appurtenances. Based on this layout, there is insufficient room to locate any treatment facilities at Garthe Reservoir. If the treatment facilities are located at Morrison Park, that would require using a portion of the parking lot or the entire tennis court area. It should be noted that this analysis is based on the assumption that Well No. 32 will produce a constant raw water nitrate level of greater than 40 mg /L. However, based on historical records, it is anticipated that the nitrate level will decrease to the 20 - 25 mg/L range. P:T 0059T0086T ngineeft\ 05LWe11- 32- Nltm[e- Mifi1xiov[Dmft Rg0tb 21e #.do2 5I �O TETRA TECH