(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 point of compliance wells, or other monitoring system, installed in compliance with §330.403(a) - (c) of this title (relating to Groundwater Monitoring Systems).     
      (b) The owner or operator shall submit a groundwater sampling and analysis plan to the executive director for review and approval prior to commencement of sampling and shall maintain a current copy in the operating record. The groundwater sampling and analysis plan shall:      
        (1) include procedures and techniques for sample collection, sample preservation and shipment, analytical procedures, chain of custody controls, and quality assurance and quality control;       
        (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) include sampling and analytical methods that are appropriate for groundwater sampling and that accurately measure hazardous constituents and other monitoring parameters in groundwater samples.                  (A) For Type I landfills, the owner or operator shall collect an appropriate number of samples necessary to establish groundwater quality data consistent with the appropriate statistical procedures determined in accordance with subsection (f) of this section. The sampling procedures for Type I landfills shall be those specified under §330.407(a) of this title (relating to Detection Monitoring Program for Type I Landfills) for detection monitoring, §330.409(b) - (f) of this title (relating to Assessment Monitoring Program) for assessment monitoring, and §330.411(b) of this title (relating to Assessment of Corrective Measures) for corrective action.                   (B) For Type IV landfills, the owner or operator shall sample the groundwater monitoring parameters at the frequency specified in §330.417 of this title (relating to Groundwater Monitoring at Type IV Landfills).                   (C) For other solid waste management units that will have a groundwater monitoring program in accordance with §330.401(a), of this title (relating to Applicability) the executive director will specify groundwater monitoring parameters and frequencies appropriate to the facility conditions.         
      (c) Groundwater samples shall not be field-filtered prior to laboratory analysis.     
      (d) The owner or operator shall establish background groundwater quality that has not been affected by leakage from a solid waste management unit in hydraulically upgradient wells or in background wells for each of the monitoring parameters or constituents required in the groundwater monitoring program for a solid waste management unit, as determined under §330.419 of this title (relating to Constituents for Detection Monitoring). A determination of background quality may include sampling of wells that are not hydraulically upgradient of the waste management area if hydrogeologic conditions do not allow the owner or operator to determine which wells are hydraulically upgradient or if sampling at other wells will provide a better indication of background groundwater quality than is possible from upgradient wells. Point of compliance groundwater data shall not be adjusted by subtracting background groundwater data.     
      (e) The owner or operator shall specify in the groundwater sampling and analysis plan 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 §330.407 of this title and §330.409 of this title. The statistical test(s) chosen shall be conducted separately for each tested constituent in each well or sampling point:      
        (1) a parametric analysis of variance followed by multiple-comparisons procedures to identify statistically significant evidence of contamination. The method shall include estimation and testing of the contrasts between each point of compliance well's mean and the background mean levels for each constituent;       
        (2) an analysis of variance 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 point of compliance well's median and the background median levels for each constituent;       
        (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 point of compliance well is compared to the upper tolerance or prediction limit;       
        (4) a control-chart approach that gives control limits for each constituent; and       
        (5) another statistical test method that meets the performance standards of subsection (f) of this section. The owner or operator shall submit to the executive director satisfactory justification for this alternative test.       
      (f) Any statistical method chosen under subsection (e) of this section shall comply with the following performance standards, as appropriate.      
        (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) 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) 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 database, the data distribution, and the range of the concentration values for each constituent of concern.       
        (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) 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 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) 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.       
     Source Note:        The provisions of this §330.405 adopted to be effective March 27, 2006, 31 TexReg 2502