(a) General standards attainment sampling and assessment procedures. The procedures listed in this section are solely for the purposes of assessing water quality monitoring data to determine if water quality standards are attained in individual water bodies. Unless otherwise stated in this chapter, additional details concerning sampling procedures for the measurement, collection, preservation and laboratory analysis of water quality samples are provided in the Texas Commission on Environmental Quality (TCEQ) Surface Water Quality Monitoring Procedures, Volume 1: Physical and Chemical Monitoring Methods (RG-415) as amended, the most recently published edition of the book entitled Standard Methods for the Examination of Water and Wastewater, 40 Code of Federal Regulations (CFR) Part 136, or other reliable sources acceptable to the commission. Laboratory accreditation requirements are specified in Chapter 25 of this title (relating to Environmental Testing Laboratory Accreditation and Certification). Unless otherwise stated in this chapter, additional details concerning how sampling data are evaluated to assess standards compliance are provided in the TCEQ Guidance for Assessing and Reporting Surface Water Quality in Texas as amended.
(b) Samples to determine standards attainment are collected at locations approved by the commission. Samples collected at non-approved locations may be accepted at the discretion of the commission. Samples to determine standards attainment in ambient water must be representative in terms of location, seasonal variations, and hydrologic conditions. Locations must be typical of significant areas of a water body. Temporal sampling must be sufficient to appropriately address seasonal variations of concern. Sample results that are used to assess standards attainment must not include samples that are collected during extreme hydrologic conditions such as high-flows and flooding immediately after heavy rains. Further guidance on representative sampling, both spatially, temporally, and hydrologically, can be found in the TCEQ Surface Water Quality Monitoring Procedures, Volume 1: Physical and Chemical Monitoring Methods (RG-415), Surface Water Quality Monitoring Procedures, Volume 2: Methods for Collecting and Analyzing Biological Assemblage and Habitat (RG-416), and the TCEQ Guidance for Assessing and Reporting Surface Water Quality in Texas as amended.
(c) Collection and preservation of water samples.
  (1) For the purposes of assessing standards attainment, samples are collected and preserved in accordance with procedures set forth in the most recently published edition of the book entitled Standard Methods for the Examination of Water and Wastewater, the TCEQ Surface Water Quality Monitoring Procedures, Volume 1: Physical and Chemical Monitoring Methods (RG-415) as amended, 40 CFR Part 136, or other reliable procedures acceptable to the commission.
  (2) Bacterial and temperature determinations must be conducted on samples or measurements taken at or near the surface in accordance with the TCEQ Surface Water Quality Monitoring Procedures, Volume 1: Physical and Chemical Monitoring Methods (RG-415) as amended. Depth collection procedures for chloride, sulfate, total dissolved solids, dissolved oxygen, chlorophyll a, and pH to determine standards attainment may vary depending on the water body being sampled. Standards for chloride, sulfate, total dissolved solids, dissolved oxygen, chlorophyll a, pH are applicable to the mixed surface layer, but a single sample taken near the surface normally provides an adequate representation of these parameters. When the water column is entirely mixed according to determinations described in TCEQ Guidance for Assessing and Reporting Surface Water Quality in Texas as amended, standards may apply to any sample taken in the water column for parameters indicated in this section.
  (3) For toxic materials, numerical aquatic life criteria are applicable to water samples collected at any depth. Numerical human health criteria are applicable to the average (arithmetic) concentration from the surface to the bottom. For the purposes of standards attainment for aquatic life protection and human health protection, samples that are collected at approximately one foot below the water surface are acceptable for assessing standards attainment of numerical criteria.
(d) Sample analysis.
  (1) Numerical criteria. Procedures for laboratory analysis must be in accordance with the most recently published edition of the book entitled Standard Methods for the Examination of Water and Wastewater, the TCEQ Surface Water Quality Monitoring Procedures, Volume 1: Physical and Chemical Monitoring Methods (RG-415) as amended, 40 CFR Part 136, or other reliable procedures acceptable to the commission, and in accordance with Chapter 25 of this title.
  (2) Radioactivity. Measurements must be made on filtered samples to determine radioactivity associated with dissolved minerals in accordance with current analytical methodology approved by the EPA.
  (3) Toxicity. Bioassay techniques must be selected as testing situations dictate but are generally conducted using representative sensitive organisms in accordance with §307.6 of this title (relating to Toxic Materials).
(e) Sampling periodicity and evaluation.
  (1) Chloride, sulfate, total dissolved solids. Standards attainment determinations to demonstrate compliance with the annual average may be based on the long term mean in accordance with TCEQ Guidance for Assessing and Reporting Surface Water Quality in Texas as amended. Results from all monitoring stations within the segment are used to allow for reasonable parametric gradients. Total dissolved solids determinations may be based on measurements of specific conductance.
  (2) Radioactivity. The impact of radioactive sources on surface waters must be evaluated in accordance with Chapter 336 of this title (relating to Radioactive Substance Rules), and in accordance with Chapter 290 of this title (relating to Public Drinking Water).
  (3) Bacteria.
    (A) For coastal recreation waters, as defined in §307.3 of this title (relating to Definitions and Abbreviations), standards attainment must be based on a geometric mean or a single sample criterion. Data are evaluated in accordance with §307.7(b)(1) of this title (relating to Site-Specific Uses and Criteria).
    (B) For inland waters (tidal rivers, high saline inland waters, and freshwater), and other non-coastal recreation waters, standards attainment must be based on a long-term geometric mean of applicable samples in accordance with the TCEQ's Guidance for Assessing and Reporting Surface Water Quality in Texas as amended. Data are evaluated in accordance with §307.7(b)(1) of this title.
    (C) Samples may be evaluated with the single sample criterion for the purposes of swimmer safety notification programs and wastewater permit compliance.
    (D) Determination of attainment may account for statistical variability to reduce uncertainty in evaluations in accordance with the TCEQ's Guidance for Assessing and Reporting Surface Water Quality in Texas.
  (4) Toxic materials. Standards attainment must be evaluated in accordance with §307.6 of this title, and in accordance with §307.8 of this title (relating to Application of Standards). To protect aquatic life, specific numerical acute toxic criteria are applied as 24-hour averages, and specific numerical chronic toxic criteria are applied as seven-day averages. Human health criteria are applied as long-term average exposure criteria designed to protect populations over a life time. Standards attainment for acute and chronic toxic criteria for aquatic life and human health criteria must be in accordance with the TCEQ Guidance for Assessing and Reporting Surface Water Quality in Texas as amended. Standards attainment for human health criteria must be based on the mean of samples collected in accordance with the TCEQ Guidance for Assessing and Reporting Surface Water Quality in Texas as amended.
  (5) Temperature and pH. Standards attainment must be in accordance with the TCEQ Guidance for Assessing and Reporting Surface Water Quality in Texas as amended.
  (6) Dissolved oxygen.
    (A) Criteria for daily (24-hour) average concentrations must be compared to a time-weighted average of measurements taken over a 24-hour period in accordance with TCEQ Guidance for Assessing and Reporting Surface Water Quality in Texas as amended.
    (B) Criteria for minimum concentrations must be compared to individual measurements in accordance with TCEQ Guidance for Assessing and Reporting Surface Water Quality in Texas as amended. When data are collected over a 24-hour period, the lowest measurement observed during that 24-hour period is compared to the applicable minimum criterion.
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