1. (a) General standards attainment sampling and assessment procedures. 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 latest version of the TNRCC Surface Water Quality Monitoring Procedures Manual, the most recently published edition of the book entitled Standard Methods for the Examination of Water and Wastewater, 40 CFR 136, or other reliable sources acceptable to the executive director. Unless otherwise stated in this chapter, additional details concerning how sampling data are evaluated to assess standards compliance are provided in the latest approved version of the TNRCC Guidance for Screening and Assessing Texas Surface and Finished Drinking Water Quality Data.
2. (b) Representative samples to determine standards attainment will be collected at locations approved by the agency. Samples collected at non-approved locations may be accepted at the discretion of the agency.

3. (c) Collection and preservation of water samples.

   1. (1) To ensure that representative samples are collected and to minimize alterations prior to analysis, collection and preservation of attainment determination samples will be 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 latest version of the TNRCC Surface Water Quality Monitoring Procedures Manual, 40 CFR 36, or other reliable procedures acceptable to the agency.
   2. (2) Bacterial and temperature determinations will be conducted on samples or measurements taken approximately one foot below the surface. Depth collection procedures for chloride, sulfate, total dissolved solids, dissolved oxygen, and pH to determine standards attainment may vary depending on the water body being sampled. Where standards apply to the mixed surface layer, the depth of this layer is determined in accordance with procedures in the latest approved version of the TNRCC Guidance for Screening and Assessing Texas Surface and Finished Drinking Water Quality Data. Standards for chloride, sulfate, total dissolved solids, and pH are applicable to the mixed surface layer, but a single sample taken near the surface normally provides an adequate representation of these parameters.

   3. (3) For dissolved oxygen, the following procedures are generally applicable:

      1. (A) Non-tidal flowing streams. The dissolved oxygen criteria is applicable to the mixed surface layer, but a single sample taken near the surface normally provides an adequate representation of this parameter.
      2. (B) Impoundments. Representative samples shall be collected from the entire water column in the absence of thermal stratification. Collection of representative samples shall be confined to the epilimnion when an impoundment is thermally stratified.
      3. (C) Tidal waters. Representative samples shall be collected from the entire water column in the absence of density stratification. Under conditions of density stratification, a composite sample collected from the mixed surface layer shall be used to determine standards attainment.
   4. (4) 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 concentration from the surface to the bottom. For the purposes of standards attainment for aquatic life protection and human health protection, samples which are collected at approximately one foot below the water surface will also be acceptable for comparison to numerical criteria.

4. (d) Sample analysis.

   1. (1) Numerical criteria. Procedures for laboratory analysis will be in accordance with the most recently published edition of the book entitled Standard Methods for the Examination of Water and Wastewater, the latest version of the Texas Surface Water Quality Monitoring Procedures Manual, 40 CFR 136, or other reliable procedures acceptable to the agency.
   2. (2) Radioactivity. Measurements will be made on filtered samples to determine radioactivity associated with dissolved minerals in accordance with current analytical methodology approved by the EPA.
   3. (3) Toxicity. Bioassay techniques will be selected as testing situations dictate but will generally be conducted using representative sensitive organisms in accordance with §307.6 of this title (relating to Toxic Materials).

5. (e) Sampling periodicity and evaluation.

   1. (1) Chloride, sulfate, total dissolved solids (TDS). Standards attainment determinations shall be based on the average of measurements taken over a period of at least one year. Results from all monitoring stations within the segment will be averaged to allow for reasonable parametric gradients. TDS determinations may be based on measurements of specific conductance.
   2. (2) Radioactivity. The impact of radioactive discharges on the surface waters in Texas will be evaluated utilizing information developed by the Sanitary Engineering Research Laboratory at the University of Texas and presented in the June 30, 1960, report entitled, Report on Radioactivity--Levels in Surface Waters--1958-1960.
   3. (3) Bacteria. Standards attainment will be based on a geometric mean of applicable samples and based on a single sample maximum, and data will be evaluated in accordance with the provisions of §307.7(b)(1) of this title (relating to Site-specific Uses and Criteria).
   4. (4) Toxic materials. 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 of 70 years. Refer to the latest approved version of the TNRCC Guidance for Screening and Assessing Texas Surface and Finished Drinking Water Quality Data for sampling periodicity and evaluation applicable to standards. Standards attainment for human health criteria will be based on the average of a minimum of four samples collected over at least a one year period.
   5. (5) Temperature and pH. Standards attainment based on single measurements will be evaluated according to the latest approved version of the TNRCC Guidance for Screening and Assessing Texas Surface and Finished Drinking Water Quality Data.

   6. (6) Dissolved oxygen.

      1. (A) Criteria for daily (24-hour) average concentrations will be compared to a time-weighted average of measurements taken over a 24-hour period.
      2. (B) Criteria for minimum concentrations will be compared to individual measurements. When data are collected over a 24-hour period, any single measurement may be compared to the applicable minimum criterion.
6. (f) Biological integrity. Biological integrity, which is an essential component of the aquatic life categories defined in §307.7(b)(3) of this title, is assessed by sampling the aquatic community. Attainment of aquatic life use may be assessed by indices of biotic integrity which are described in publicly available documents such as in the latest version of the TNRCC Receiving Water Assessment Procedures Manual.
7. (g) Additional parameters. Assessment of narrative criteria parameters shall be performed in accordance with the latest approved version of the TNRCC Guidance for Screening and Assessing Texas Surface and Finished Drinking Water Quality Data.

Source Note:The provisions of this §307.9 adopted to be effective July 10, 1991, 16 TexReg 3400; amended to be effective July 13, 1995, 20 TexReg 4701; amended to be effective August 17, 2000, 25 TexReg 7722.