The U.S. Environmental Protection Agency (EPA) has completed its second Six-Year Review (Six-Year Review 2) of national primary drinking water regulations (NPDWRs). The 1996 Safe Drinking Water Act (SDWA) Amendments require the U.S. Environmental Protection Agency (EPA or the Agency) to periodically review existing National Primary Drinking Water Regulations (NPDWRs). Section 1412(b)(9) of SDWA reads: 'the Administrator shall, not less than every 6 years, review and revise, as appropriate, each primary drinking water regulation promulgated under this title. Any revision of a national primary drinking water regulation shall be promulgated in accordance with this section, except that each revision shall maintain, or provide for greater, protection of the health of persons.' The primary goal of the Six-Year Review process is to identify NPDWRs for possible regulatory revision. Although the statute does not define when a revision is appropriate, as a general benchmark, EPA considered a possible revision to be appropriate if, at a minimum, it presents a meaningful opportunity to: (1) improve the level of public health protection, and/or (2) achieve cost savings while maintaining or improving the level of public health protection. For Six-Year Review 2, EPA implemented the protocol that it developed for the first Six-Year Review (USEPA, 2003), including minor revisions developed during the current review process (USEPA, 2009d). EPA obtained and evaluated new information that could affect a NPDWR, including information on health effects (USEPA, 2009f), analytical feasibility (USEPA, 2009b), and occurrence (USEPA, 2009a and 2009e). This technical support document provides the Agencys findings for its review of treatment feasibility information. EPA identified potential to revise NPDWRs for 23 contaminants. Consequently, EPA reviewed the best available technologies (BATs) and treatment techniques (TTs) specified in NPDWRs, and any emerging technologies, to determine whether treatment performance would pose a limitation to such revisions. This document describes these treatment feasibility reviews.