During a statewide survey for NDMA occurrence conducted by the California Department of Health Services (CA DHS), N-Nitrosodimethylamine (NDMA) was discovered at the Anion Exchange Plant (AEP) in Pomona, CA. Uncertainty in the direction of the Action Level (AL) for NDMA, coupled with the importance of the AEP as a drinking water source for the City, led to measures to reduce the NDMA concentrations leaving the AEP, including construction of a pilot plant to investigate methods of inhibiting NDMA formation. The pilot plant tested several pretreatments to the existing resin, including aeration, oxidation with hydrogen peroxide, and adsorption to GAC, in addition to testing alternative resins. No alternative resin was found to prevent NDMA formation, and only GAC pretreatment was found to effectively reduce NDMA concentrations to below the detection limit. NDMA initially occurred at high concentrations in one new resin, but was rapidly rinsed from the vessel. Steady-state concentrations were achieved after 30 to 45 days of operation. More subtle observations that may not be distinguishable from analytical uncertainty include an increase in NDMA concentrations after aeration and oxidation, and an age effect, where fresh resins produced less NDMA than older resins of the same type. The exact mechanisms of formation and removal were unable to be determined due to the large discrepancy in sensitivity between the analytical methods for potential precursors, intermediates, and NDMA. Future efforts will focus on determining the capacity of GAC for precursor removal so that comparisons can be made between GAC pretreatment and proven post-treatment (UV) methods. The effects of post chlorination of the treated water will also be tested to determine if NDMA formation in distribution systems after ion exchange treatment is a concern. Includes 44 references, tables, figures.