New Mexico Administrative Code
Title 20 - ENVIRONMENTAL PROTECTION
Chapter 9 - SOLID WASTE
Part 9 - SOLID WASTE FACILITY GROUND WATER MONITORING SYSTEM PLAN AND GROUND WATER MONITORING PLAN; CORRECTIVE ACTION
Section 20.9.9.10 - GROUND WATER MONITORING PLAN; SAMPLING AND ANALYSIS; ESTABLISHING BACKGROUND CONCENTRATION LEVELS AND ASSESSMENT MONITORING LEVELS

Universal Citation: 20 NM Admin Code 20.9.9.10

Current through Register Vol. 35, No. 18, September 24, 2024

A. Ground water monitoring plans shall describe in detail all aspects of the landfill's proposed ground water monitoring program. It shall include descriptions of sampling and analysis procedures to be used, proposed sampling frequencies, test methodologies, procedures that will be used to establish background concentrations of all constituents and parameters listed in 20.9.9.20 NMAC, assessment monitoring levels (AMLs), and practical quantitation limits (PQL) for each constituent listed in 20.9.9.20 NMAC, and any other information describing the program as required by this section.

B. The ground water monitoring plan shall include consistent sampling and analysis procedures that are designed to ensure monitoring results that provide an accurate representation of ground water quality at the upgradient and downgradient wells. The plan shall include procedures and techniques for:

(1) sample collection;

(2) sample preservation and shipment;

(3) analytical procedures;

(4) chain of custody control; and

(5) quality assurance and quality control.

C. The ground water monitoring plan shall describe sampling and analytical methods that are appropriate for ground water sampling and that accurately measure constituents and other monitoring parameters in ground water samples. A PQL for each constituent listed in 20.9.9.20 NMAC shall be proposed in the plan based on the proposed sampling and analytical method. A PQL will not be approved unless the level is the lowest concentration that can be reliably determined by an analytic methodology acceptable to the department. Ground water samples shall not be field-filtered prior to laboratory analysis unless otherwise allowed under 40 CFR Part 258 and the approved ground water monitoring plan. The owner or operator shall conduct ground water sampling in accordance with the "EPA solid waste disposal facility criteria technical manual" (1998, EPA 530-R-93-017, revised April 13, 1998) unless otherwise approved in the ground water monitoring plan.

D. Ground water elevations shall be measured within one-hundredth of a foot 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 which monitor the same waste management area shall be measured within a period of time short enough to avoid temporal variations in ground water flow which could preclude accurate determination of ground water flow rate and direction.

E. The owner or operator of a landfill seeking a background determination shall apply for specific approval of background ground water quality concentrations for each constituent and parameter referenced in Subsections A and C of 20.9.9.20 NMAC, and as required in the landfill's approved ground water monitoring plan within 14 months after any waste disposal at the landfill or lateral expansion. The application shall propose background concentrations based upon the following:

(1) the sampling results from at least four independent samples taken during the first semiannual sampling event and at least one additional sample during the subsequent semiannual sampling event for each individual monitoring well;

(2) the first sampling event shall occur prior to any waste disposal at a new landfill or lateral expansion; and

(3) if a constituent is not detected in the sampling used to establish background concentrations, the owner or operator shall propose the PQL approved in the ground water quality monitoring plan as the background concentration.

F. The background ground water quality concentrations and values must be approved by the department in writing. Once background ground water quality concentrations and values for the constituents and the parameters referenced in Subsections A and C of 20.9.9.20 NMAC are approved for a landfill, an individual well comparison procedure shall be used to compare constituent concentrations and parameter values with background constituent concentrations, ground water protection standards and parameter values for purposes of detection and assessment monitoring. Alternatively, if it is in accordance with the approved ground water quality monitoring plan, the background levels established from hydraulically upgradient wells may be used for comparison purposes.

G. For category 4 and 5 landfills, a background determination shall be made at each monitoring well as specified in Subsection E of this section unless the owner operator demonstrates that hydrogeological conditions are such that sampling at upgradient wells will provide an indication of background ground water quality that is as representative or more representative than that provided by making a determination at each monitoring well.

H. For category 2 and 3 landfills, a background determination shall be made at each individual monitoring well as specified in Subsection E of this section, except when the concentration of a hazardous constituent at an upgradient well is lower than the concentration at a downgradient well, in which case the concentration of that constituent at the upgradient well shall be used as the background concentration, unless the owner or operator demonstrates that use of the downgradient well to determine the background concentration of that constituent will provide an indication of background ground water quality that is as representative or more representative than that provided by the upgradient well.

I. The owner or operator shall identify ground water protection standards for which a numeric standard has been established and shall apply for specific approval of proposed assessment monitoring levels (AMLs) in compliance with 20.9.9.12 NMAC for constituents listed or referenced in Subsection A of 20.9.9.20 NMAC, and for the parameter of pH, within 90 days following approval of background ground water quality concentrations by the department. The ground water protection standard for a constituent and for pH shall be the more stringent of the maximum contaminant level (MCL) promulgated at 40 CFR 141, or the ground water protection standard established by the commission at 20.6.2.3103 NMAC.

J. The number of samples collected to establish ground water quality data shall be consistent with the appropriate statistical procedures determined pursuant to this section.

K. The owner or operator of a landfill using an individual well comparison procedure shall use one of the following statistical methods to compare an individual compliance well constituent concentration and parameter value with background constituent concentration and parameter value or the relevant ground water protection standard:

(1) a comparison using a t-interval or t-test with a type I error level of no less than 0.01 shall be made between the approved background concentration or value and any subsequent sample analysis results for each parameter or constituent from each individual well;

(a) background values and concentrations shall be established for each parameter or constituent for each individual well from at least four independent samples during the first semiannual sampling event and at least one additional sample during the subsequent semi-annual sampling event; and

(b) if the background concentration is below the practical quantitation limit (PQL), the PQL shall be used to establish background. A statistical method is not necessary for a comparison between the analytical results and the PQL; or

(2) another method that meets the performance standards of 40 CFR 258.53(h). The alternative must be approved in the ground water monitoring plan, and the owner or operator must demonstrate the method meets the performance standards of 40 CFR 258.53(h).

L. The owner or operator of a landfill using an upgradient well to establish background concentrations shall specify in the ground water monitoring plan one of the statistical methods described in 40 CFR 258.53(g). The statistical method to be used in evaluating ground water monitoring data must be demonstrated to meet the performance criteria of 40 CFR 254.53(h).

(1) If the background concentration at the upgradient well is below the practical quantitation limit (PQL), the PQL shall be used to establish background; a statistical method is not necessary for a comparison between the analytical results and the PQL.

(2) The number of samples collected to establish ground water quality data must be consistent with the appropriate statistical procedure that meets the performance standards of 40 CFR 258.53(h).

M. Ground water samples for the constituents and values referenced in Subsections A and C of 20.9.9.20 NMAC shall be collected from each monitoring well at least semi-annually during the active life of the facility.

(1) At a new landfill, or at a lateral expansion, the first sampling event shall be prior to the receipt of any waste.

(2) Once background concentrations and values have been established and approved, the owner or operator shall conduct detection monitoring for all constituents and parameters listed in or referenced in Subsections A and C of 20.9.9.20 NMAC and determine whether or not the AML has been exceeded for any constituent referenced in Subsection A of 20.9.9.20 NMAC and for the parameter of pH, or as required in the particular ground water monitoring plan that applies to the landfill.

(3) In determining whether the AML has been exceeded, the owner or operator shall compare the ground water quality for each constituent at each monitoring well to the background value for that constituent, according to the statistical procedures and performance standards specified in the ground water monitoring plan and this section.

N. Ground water documentation shall be submitted to the department within 90 days of completing sampling, in a form acceptable to the department, for each sample, and a copy of all monitoring results shall be kept in the operating record. The documentation shall include:

(1) the constituents and parameter tested;

(2) the test method (U.S. EPA or equivalent) for each constituent and parameter;

(3) the ground water protection standard for each constituent detected (if a numeric standard has been established);

(4) the method detection limit (MDL) for each constituent;

(5) the practical quantitation limit (PQL) for each constituent and parameter;

(6) the well number and location for each sample;

(7) the laboratory ID sample number;

(8) chain of custody documentation;

(9) the date sampled;

(10) the date received at the laboratory;

(11) the date analysis commenced;

(12) results, with constituent or parameter, chemical abstract system number, concentration with units, approved AML, ground water protection standard, PQL, qualifier code (e.g., J, B, U, etc.), well number, and sample date;

(13) sample preservation (field data);

(14) field blank results, and trip blank results;

(15) quality assurance/quality control summary report (laboratory blanks, spike recoveries, etc.);

(16) anomaly report (non-conformance with quality assurance/quality control plan, corrective actions, etc.);

(17) laboratory review (signature and date);

(18) an updated ground water elevation contour map for the facility or, if ground water elevation data is insufficient to contour, then the ground water elevation for each monitoring well, prior to purging, reported on a well location map;

(19) the approved background concentration levels as determined in accordance with Subsection E of this section; and

(20) a certification by a qualified ground water scientist that AMLs have or have not been exceeded.

O. Amendments to an approved ground water monitoring plan shall be by specific approval.

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