1. (a) Sampling locations.

   1. (1) Representative samples to determine standards attainment will be collected at locations approved by the commission. To ensure comparability with past sampling data, samples will be collected at established monitoring stations. Monitoring stations may be established or discontinued by the commission.
   2. (2) Field investigation samples may be collected at points not established or approved as standards attainment sampling locations at the discretion of the commission.

2. (b) 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 most recent version of the quality assurance program plan for the commission, or other reliable procedures acceptable to the commission.

   2. (2) Bacterial and temperature determinations will be conducted on samples or measurements taken within one foot of the surface. Depth collection procedures for chloride, sulfate, total dissolved solids, dissolved oxygen, and pH to determine standards attainment may vary depending on the waterbody being sampled. Where standards apply to the mixed surface layer, the depth of this layer is determined in accordance with procedures in the latest published edition of the Texas Surface Water Quality Inventory. Standards for chloride, sulfate, total dissolved solids, and pH are applicable to the mixed surface layer, but a single sample taken near the surface (at a depth of approximately one foot) normally provides an adequate representation of these parameters. For dissolved oxygen, the following procedures are generally applicable.

      1. (A) Non-tidal flowing streams. In flowing streams, a profile should be obtained to determine if the water column is uniformly mixed. Samples shall be collected one foot below the water surface in streams exhibiting a vertically mixed water column. A depth-integrated sample shall be used to determine attainment in unmixed streams. Where depth is less than 1.5 feet, the collection depth shall be one-third of the water depth measured from the water surface.
      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) Bays. A depth-integrated (vertical composite) sample shall be collected from the surface to the natural bottom. Dredged areas shall not be considered part of the natural bottom.
      4. (D) Tidal streams. A surface to bottom profile of DO, pH, conductivity, and temperature shall be obtained in all cases. Under conditions of density stratification, a composite sample collected from the mixed surface layer shall be used to determine standards attainment.
   3. (3) Numerical aquatic life criteria for toxic materials 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.

3. (c) Sample analysis.

   1. (1) Numerical values. Numerical values in the water quality standards shall be determined by analytical procedures recommended in the most recently published edition of the book entitled Standard Methods for the Examination of Water and Wastewater, the quality assurance program plan for the commission, Title 40 Chapter 136 of the Code of Federal Regulations, or other reliable methods acceptable to the commission.
   2. (2) Radioactivity. Measurements will be made on filtered samples to determine radioactivity associated with dissolved minerals.
   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).
   4. (4) Bacteria. Bacteriological levels shall be determined by either multiple-tube fermentation or membrane filter techniques.

4. (d) Sampling periodicity and evaluation.

   1. (1) Chloride, sulfate, total dissolved solids (TDS). Standards attainment determinations shall be based on the average of measurements taken on at least four different dates within 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. Conversion factors are presented in the latest publication of the Texas Surface Water Quality Inventory or may be based on additional site-specific data.
   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 for fecal coliform bacteria will be determined as described in §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 lifetime of 70 years. 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 will be evaluated for measurements or samples taken at a single point in time.

   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 taken at night (from sunset until two hours after sunrise).

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.