Nev. Admin. Code § 444.7485

Current through December 31, 2024
Section 444.7485 - Statistical methods for evaluating data; performance standards
1. An owner or operator shall specify in the records for the disposal site one of the following statistical methods to be used in evaluating data from monitoring groundwater for each hazardous constituent:
(a) A parametric analysis of variance followed by procedures for multiple comparisons to identify statistically significant evidence of contamination. This method must include an estimation and testing of the contrasts between the mean for each compliance well and the background mean levels for each constituent.
(b) An analysis of variance based on ranks followed by procedures for multiple comparisons to identify statistically significant evidence of contamination. This method must include an estimation and testing of the contrasts between the median for each compliance well and the background median levels for each constituent.
(c) A procedure using tolerance or predictional intervals whereby an interval for each constituent is established from the distribution of the background data and the level of each constituent in each compliance well is compared to the upper tolerance or prediction limit.
(d) A procedure using a control chart which gives limits of control for each constituent.
(e) Any other statistical method which meets the performance standards set forth in subsection 3. The owner or operator shall place a written justification for using the statistical method in the operating records for the disposal site and notify the solid waste management authority of the use of this alternative method. The justification must demonstrate that the alternative method meets the performance standards set forth in subsection 3.
2. The statistical method chosen pursuant to this section must be conducted separately for each hazardous constituent in each well.
3. Any statistical method chosen pursuant to this section must comply with the following performance standards, as appropriate:
(a) The statistical method used to evaluate data from monitoring groundwater must be appropriate for the distribution of chemical parameters or hazardous constituents. If the distribution of the chemical parameters or hazardous constituents is shown by the owner or operator to be inappropriate for a normal theory test, then the data must be transformed or a theory test that does not use data from the distribution of chemical parameters or hazardous constituents must be used. If the distributions for the constituents differ, more than one statistical method may be used, if needed.
(b) If a procedure which compares individual wells is used to compare the concentration of constituents for an individual compliance well with background concentrations of constituents or a standard for the protection of groundwater, the test must be done at a Type I error level that is no less than 0.01 for each testing period. If a procedure using multiple comparisons is used, the Type I error level for each testing period must be no less than 0.05, and the Type I error level of no less than 0.01 for comparisons of individual wells must be maintained. This performance standard does not apply to tolerance intervals, prediction intervals or control charts.
(c) If a control chart is used to evaluate data, the control chart and its associated values for its parameters must be protective of public health and safety and the environment. The parameters must be determined after considering the number of samples in the background database, the distribution of data and the range of the concentration values for each constituent.
(d) If a tolerance interval or a predictional interval is used to evaluate data from monitoring groundwater, the levels of confidence and, for tolerance intervals, the percentage of the population of samples which the interval must contain, must be protective of public health and safety and the environment. These parameters must 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.
(e) The statistical method must account for data below the limit of detection with one or more statistical procedures which are protective of public health and safety and the environment. Any practical quantitation limit which is used in the statistical method must be the lowest concentration level which can be reliably achieved within specified limits of precision and accuracy during routine conditions for the operation of a laboratory which are available to the disposal site.
(f) If necessary, the statistical method must include procedures to control or correct for seasonal and spatial variability and temporal correlation in the data.
4. As used in this section, "Type I error" means an error which occurs when a true null hypothesis is rejected erroneously and, as a result, a test for the monitoring of groundwater incorrectly indicates contamination or an increase in contamination at a regulated unit.

Nev. Admin. Code § 444.7485

Added to NAC by Environmental Comm'n, eff. 11-8-93

NRS 444.560