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This layer depicts the official TCEQ Poly Assessment Units (AU) for the State of Texas as listed in Title 30, Chapter 307 of the Texas Administrative Code (TAC), also known as the Texas Surface Water Quality Standards. Assessment Units are sub-areas of segments, defined as the smallest geographic area of use support reported in the assessment. These are reservoirs, estuaries, oyster waters, beaches, and ocean that have been individually defined by the TCEQ and assigned unique identification numbers. Intended to have relatively homogeneous chemical, physical, and hydrological characteristics, an AU provides a basic unit for assigning site-specific standards and for applying water quality management programs of the agency. AU's from both "classified" and "unclassified" segments have been included in this layer. Classified segments, also referred to as designated segments, refer to water bodies that are protected by site- specific criteria. The classified segments are listed and described in Appendix A and C of Chapter 307.10. The site-specific uses and criteria are described in Appendix A. Classified waters include most rivers and their major tributaries, major reservoirs, and estuaries. Unclassified waters are those smaller water bodies that do not have site-specific water quality standards assigned to them, but instead are protected by general standards that apply to all surface waters in the state. This layer also identifies which AUs and water bodies have been assessed in the 2014 Texas Integrated Report for Clean Water Act Sections 305 (b) and 303 (d). An impaired AU is included in Categories 4 and 5. Category 4 includes impairments that are not suitable for a TMDL or for which a TMDL has already been approved. Category 5 includes impairments which may be suitable for development of a TMDL and comprise the 303 (d) List. |