1. (a) The groundwater monitoring program shall include consistent sampling and analysis procedures that are designed to ensure monitoring results that provide an accurate representation of groundwater quality at the background and downgradient wells, or other monitoring system, installed in compliance with §330.231(a)-(c) of this title (relating to Groundwater Monitoring Systems).

2. (b) The owner or operator shall submit a groundwater sampling and analysis plan (GWSAP) to the executive director for review and approval prior to commencement of sampling and shall maintain a current copy in the operating record. The GWSAP shall be a part of the site development plan (SDP); if necessary, the owner or operator shall obtain a modification of the SDP to incorporate the GWSAP. The GWSAP shall:

   1. (1) include procedures and techniques for sample collection, sample preservation and shipment, analytical procedures, chain-of-custody controls, quality assurance, and quality control;
   2. (2) provide for measurement of groundwater elevations at each sampling point prior to bailing or purging; measurement at an event shall be accomplished over a period of time short enough to avoid temporal variations in water levels; sampling at each event shall proceed from the point with the highest water-level elevation to those with successively lower elevations unless contamination is known to be present, in which case wells not likely to be contaminated shall be sampled prior to those that are known to be contaminated unless an alternative procedure is approved by the executive director; and
   3. (3) include sampling and analytical methods that are appropriate for groundwater sampling and that accurately measure hazardous constituents and other monitoring parameters in groundwater samples. The number of samples to be collected to establish groundwater quality data shall be consistent with the appropriate statistical procedures determined pursuant to subsection (g) of this section. The sampling procedures shall be those specified under §330.234(b) of this title (relating to Detection Monitoring Program) for detection monitoring, §330.235(b)-(d) of this title (relating to Assessment Monitoring Program) for assessment monitoring, and §330.236(b) of this title (relating to Assessment of Corrective Measures) for corrective action.
3. (c) Groundwater samples shall not be field-filtered prior to laboratory analysis for the constituents listed in §330.241 of this title (relating to Constituents for Detection Monitoring). Field-filtering may be used on other samples if authorized in writing by the executive director.
4. (d) The sampling procedures and frequency shall be protective of human health and the environment.
5. (e) The owner or operator shall establish background groundwater quality in hydraulically upgradient wells or in background wells for each of the monitoring parameters or constituents required in the groundwater monitoring program for a municipal solid waste landfill (MSWLF) unit, as determined under §330.234(a) of this title (relating to Detection Monitoring Program) or §330.235(a) of this title (relating to Assessment Monitoring Program) and pursuant to §330.231(a)(1) of this title (relating to Groundwater Monitoring Systems). Downgradient groundwater data shall not be adjusted by subtracting background groundwater data.

6. (f) The owner or operator shall specify in the GWSAP one or more of the following statistical methods to be used in evaluating groundwater monitoring data for each parameter or constituent analyzed as required under §330.234 of this title (relating to Detection Monitoring Program) and §330.235 of this title (relating to Assessment Monitoring Program). The statistical test(s) chosen shall be conducted separately for each tested constituent in each well or sampling point.

   1. (1) A parametric analysis of variance (ANOVA) followed by multiple-comparisons procedures to identify statistically significant evidence of contamination. The method shall include estimation and testing of the contrasts between each downgradient well's mean and the background mean levels for each constituent.
   2. (2) An analysis of variance (ANOVA) based on ranks followed by multiple-comparisons procedures to identify statistically significant evidence of contamination. The method shall include estimation and testing of the contrasts between each downgradient well's median and the background median levels for each constituent.
   3. (3) A tolerance or prediction interval procedure in which an interval for each constituent is established from the distribution of the background data and the level of each constituent in each downgradient well is compared to the upper tolerance or prediction limit.
   4. (4) A control-chart approach that gives control limits for each constituent.
   5. (5) Another statistical test method that meets the performance standards of subsection (g) of this section. The owner or operator shall submit to the executive director satisfactory justification for this alternative test.

7. (g) Any statistical method chosen under subsection (f) of this section shall comply with the following performance standards, as appropriate.

   1. (1) The statistical method used to evaluate groundwater monitoring data shall be appropriate for the distribution of tested constituents. If the distribution of a tested constituent is shown by the owner or operator to be inappropriate for a normal theory test, then the data should be transformed or a distribution-free theory test should be used. If the distributions for the constituents differ, more than one statistical method may be needed.
   2. (2) If an individual well (or sampling point) comparison procedure is used to compare an individual compliance well constituent concentration with background constituent concentrations or a groundwater protection standard, the test shall be done at a Type I error level no less than 0.01 for each testing period. If a multiple-comparisons procedure is used, each testing period shall be no less than 0.05, but the Type I error of no less than 0.01 for individual well comparisons shall be maintained. This performance standard does not apply to tolerance intervals, prediction interval, or control charts.
   3. (3) If a control-chart approach is used to evaluate groundwater monitoring data, the specific type of control chart and its associated parameter values shall be protective of human health and the environment. These parameters shall be determined after considering the number of samples in the background data base, the data distribution, and the range of the concentration values for each constituent of concern.
   4. (4) If a tolerance interval or a prediction interval is used to evaluate groundwater monitoring data, the levels of confidence, and for tolerance intervals the percentage of the population that the interval must contain, shall be protective of human health and the environment. These parameters shall be determined after considering the number of samples in the background data base, the data distribution, and the range of the concentration values for each constituent of concern.
   5. (5) The statistical method shall account for data below the limit of detection with one or more statistical procedures that are protective of human health and the environment. Any practical quantitation limit (PQL) that is used in the statistical method shall be the lowest concentration level that can be reliably achieved within specified limits of precision and accuracy during routine laboratory operating conditions that are available to the facility.
   6. (6) If necessary, the statistical method shall include procedures to control or correct for seasonal and spatial variability as well as temporal correlation in the data.
8. (h) The owner or operator shall determine within a reasonable period of time after completing sampling and analysis whether or not there is evidence of a statistically significant change from background values for each constituent required in the groundwater monitoring program for an MSWLF unit, as determined under §330.234(a) or §330.235(a) of this title (relating to Detection Monitoring Program or Assessment Monitoring Program). In determining if there is evidence of a statistically significant change from background, the owner or operator shall compare the groundwater quality of each tested constituent at each monitoring well or other sampling points designated pursuant to §330.231(a)(2) of this title (relating to Groundwater Monitoring Systems) to the background value of that constituent, according to the statistical procedures and performance standards specified under subsections (f) and (g) of this section.

Source Note:The provisions of this §330.233 adopted to be effective October 9, 1993, 18 TexReg 4023.