(1) An owner or operator required to monitor ground water under this subchapter shall implement a ground water monitoring program that includes consistent sampling and analysis procedures that are designed to ensure monitoring results that provide an accurate representation of ground water quality at the background and downgradient wells installed in compliance with ARM 17.50.1304(1). The owner or operator shall submit to the department for approval a sampling and analysis plan that documents sampling and analysis procedures and techniques for:

(a) sample collection;

(b) sample preservation and shipment;

(c) analytical procedures;

(d) chain of custody control; and

(e) quality assurance and quality control.

(2) The owner or operator of a facility shall notify the department that the approved sampling and analysis plan has been placed in the operating record.

(3) The ground water monitoring program required in (1) must include sampling and analytical methods that are appropriate for ground water sampling and that accurately measure constituents and parameters that are required to be monitored in ground water samples. Any requirement in this subchapter for analysis of the concentration in ground water of a metal listed in Appendix I or II to 40 CFR Part 258 (July 1, 2008) is for analysis of the dissolved metal concentration, unless another alternative for analysis is approved in writing by the department on an individual facility basis.

(4) The sampling procedures and frequency must be protective of human health and the environment.

(5) Ground water elevations must be measured in each well immediately prior to purging, each time ground water is sampled. The owner or operator shall determine the rate and direction of ground water flow each time ground water is sampled. Ground water elevations in wells that monitor the same waste management area must be measured within a period of time short enough to avoid temporal variations in ground water flow that could preclude accurate determination of ground water flow rate and direction.

(6) The owner or operator shall establish background ground water quality in a hydraulically upgradient or background well(s) for each of the constituents and parameters required in the particular ground water monitoring program that applies to the Class II or Class IV landfill unit, as determined under ARM 17.50.1306(1) or 17.50.1307(1). Background ground water quality may be established at wells that are not located hydraulically upgradient from the Class II and Class IV landfill unit if they meet the requirements of ARM 17.50.1304(1)(a).

(7) The number of samples collected to establish ground water quality data must be consistent with the appropriate statistical procedures determined pursuant to (8). The sampling procedures must be those specified under ARM 17.50.1306(2) for detection monitoring, ARM 17.50.1307(2) and (4) for assessment monitoring, and ARM 17.50.1308(2) for corrective action.

(8) The owner or operator shall specify in the operating record one of the statistical methods in (8)(a) through (e) to be used in evaluating ground water monitoring data for each constituent or parameter. The statistical test chosen must be conducted separately for each constituent and parameter in each well:

(a) a parametric analysis of variance (ANOVA) followed by multiple comparisons procedures, to identify statistically significant evidence of contamination. The method must include estimation and testing of the contrasts between each compliance well's mean levels and the background mean levels for each constituent or parameter;

(b) an analysis of variance (ANOVA) based on ranks followed by multiple comparisons procedures, to identify statistically significant evidence of contamination. The method must include estimation and testing of the contrasts between each compliance well's median levels and the background median levels for each constituent or parameter;

(c) a tolerance or prediction interval procedure in which an interval for each constituent or parameter is established from the distribution of the background data, and the level of each constituent or parameter in each compliance well is compared to the upper tolerance or prediction limit;

(d) a control chart approach that provides control limits for each constituent or parameter; or

(e) another statistical test method that meets the performance standards of (9). The owner or operator shall place a justification for this alternative in the operating record and notify the department of the use of this alternative test. The justification must demonstrate that the alternative method meets the performance standards of (9).

(9) Any statistical method chosen under (8) must comply with the following performance standards, as appropriate:

(a) the statistical method used to evaluate ground water monitoring data must be appropriate for the distribution of constituents and parameters. If the distribution of the constituents or parameters 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 or parameters differ, more than one statistical method may be needed;

(b) if an individual well comparison procedure is used to compare a constituent or parameter concentration in an individual compliance well with background constituent or parameter concentrations or a ground water protection standard, the test must be performed at a Type I error level no less than 0.01 for each testing period. If a multiple comparisons procedure is used, the Type I experiment wise error rate for each testing period must be no less than 0.05; however, the Type I error of no less than 0.01 for individual well comparisons must be maintained. This performance standard does not apply to tolerance intervals, prediction intervals, or control charts;

(c) if a control chart approach is used to evaluate ground water monitoring data, the specific type of control chart and its associated parameter values must be protective of human health and the environment. The parameters must 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 and parameter of concern;

(d) if a tolerance interval or a predictional interval is used to evaluate ground water monitoring data, the levels of confidence and, for tolerance intervals, the percentage of the population that the interval must contain, must be protective of human health and the environment. These parameters must 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 or parameter of concern;

(e) the statistical method must 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 must be the lowest concentration level that reliably can be achieved within specified limits of precision and accuracy during routine laboratory operating conditions that are available to the facility; and

(f) if necessary, the statistical method must include procedures to control or correct for seasonal and spatial variability as well as temporal correlation in the data.

(10) The owner or operator shall determine whether there is a statistically significant increase over background values for each constituent or parameter required to be monitored in the particular ground water monitoring program that applies to the Class II or Class IV landfill unit, as determined under ARM 17.50.1306(1) or 17.50.1307(1).

(11) In determining whether a statistically significant increase described in (10) has occurred, the owner or operator shall:

(a) compare the ground water quality for each constituent or parameter at each monitoring well designated pursuant to ARM 17.50.1304(1)(b) to the background value of that constituent or parameter, according to the statistical procedures and performance standards specified under (8) and (9); and

(b) within a reasonable period of time after completing sampling and analysis, determine, for each monitoring well, whether there has been a statistically significant increase over background levels.