EXECUTTVE SUMMARYThis data qualification report uses technical assessment and corroborating data methods according to Attachment 2 of AP-SIII.2Q, Rev. 0, ICN 2, QzralrJication of Unqrraly5ed Data and the Doczlmentation of Rationale for Accepted Data, to qualify major ion and pH data. This report was prepared in accordance with Data Qualification Plan TDP-NBS-GS-00003 1, Revision 2. Additional reports will be prepared to address isotopic and precipitation-related data.Most of the data considered in this report were acquired and developed by the U.S. Geological Survey (USGS). The data qualification team considers the sampling and analytical protocols employed by the USGS over the time period of data ?cquisition to be state-of-the-art. The sample collection methodologies have evolved with no significant change that could affect the quality of the data considered in this report into the currently used Hydrologic Procedures that support the Yucca Mountain Project-approved USGS Quality Assurance Program Plan. Consequently, for USGS data, the data collection methods, documentation, and results are reasonable and appropriate in view of standard practice at the time the data were collected.A small number of data sets were collected by organizations other than the USGS and were reviewed along with the other major ion and pH data using corroborating data methods. Hydrochemical studies reviewed in this qualification report indicate that the extent and quality of corroborating data are sufficient to support qualification of both USGS and non-USGS major ion and pH data for generalized hydrochemical studies.