---
kind: "range"
citation: "40 C.F.R. §§ 257.22–257.25"
title: "40"
from: "257.22"
to: "257.25"
count: 4
url: "https://uscodex.org/cfr/40/257.22..257.25"
---

# §257.22. Ground-water monitoring systems.

- (a) A ground-water monitoring system must be installed that consists of a sufficient number of wells, installed at appropriate locations and depths, to yield ground-water samples from the uppermost aquifer (as defined in [§ 257.5(b)](/cfr/40/257.5.md?p=b)) that:
  - (1) **Represent the quality of background ground water that has not been affected by leakage from a unit.** A determination of background quality may include sampling of wells that are not hydraulically upgradient of the waste management area where:
    - (i) Hydrogeologic conditions do not allow the owner or operator to determine what wells are hydraulically upgradient; or
    - (ii) Sampling at other wells will provide an indication of background ground-water quality that is as representative or more representative than that provided by the upgradient wells; and
  - (2) Represent the quality of ground water passing the relevant point of compliance specified by the Director of an approved State or at the waste management unit boundary in an unapproved State. The downgradient monitoring system must be installed at the relevant point of compliance specified by the Director of an approved State or at the waste management unit boundary in an unapproved State that ensures detection of ground-water contamination in the uppermost aquifer. The relevant point of compliance specified by the Director of an approved State shall be no more than 150 meters from the waste management unit boundary and shall be located on land owned by the owner of the facility. In determining the relevant point of compliance the State Director shall consider at least the following factors: the hydrogeologic characteristics of the unit and surrounding land, the volume and physical and chemical characteristics of the leachate, the quantity, quality and direction of flow of ground water, the proximity and withdrawal rate of the ground-water users, the availability of alternative drinking water supplies, the existing quality of the ground water, including other sources of contamination and their cumulative impacts on the ground water, and whether the ground water is currently used or reasonably expected to be used for drinking water, public health, safety, and welfare effects, and practicable capability of the owner or operator. When physical obstacles preclude installation of ground-water monitoring wells at the relevant point of compliance at existing units, the down-gradient monitoring system may be installed at the closest practicable distance hydraulically down-gradient from the relevant point of compliance specified by the Director of an approved State that ensures detection of groundwater contamination in the uppermost aquifer.
- (b) The Director of an approved State may approve a multi-unit ground-water monitoring system instead of separate ground-water monitoring systems for each unit when the facility has several units, provided the multi-unit ground-water monitoring system meets the requirement of [§ 257.22(a)](#a) and will be as protective of human health and the environment as individual monitoring systems for each unit, based on the following factors:
  - (1) Number, spacing, and orientation of the units;
  - (2) Hydrogeologic setting;
  - (3) Site history;
  - (4) Engineering design of the units; and
  - (5) **Type of waste accepted at the units.**
- (c) Monitoring wells must be cased in a manner that maintains the integrity of the monitoring well bore hole. This casing must be screened or perforated and packed with gravel or sand, where necessary, to enable collection of ground-water samples. The annular space (i.e., the space between the bore hole and well casing) above the sampling depth must be sealed to prevent contamination of samples and the ground water.
  - (1) The owner or operator must notify the State Director that the design, installation, development, and decommission of any monitoring wells, piezometers and other measurement, sampling, and analytical devices documentation has been placed in the operating record; and
  - (2) The monitoring wells, piezometers, and other measurement, sampling, and analytical devices must be operated and maintained so that they perform to design specifications throughout the life of the monitoring program.
- (d) The number, spacing, and depths of monitoring systems shall be:
  - (1) Determined based upon site-specific technical information that must include thorough characterization of:
    - (i) Aquifer thickness, ground-water flow rate, ground-water flow direction including seasonal and temporal fluctuations in ground-water flow; and
    - (ii) Saturated and unsaturated geologic units and fill materials overlying the uppermost aquifer, materials comprising the uppermost aquifer, and materials comprising the confining unit defining the lower boundary of the uppermost aquifer; including, but not limited to: thicknesses, stratigraphy, lithology, hydraulic conductivities, porosities and effective porosities.
  - (2) **Certified by a qualified ground-water scientist or approved by the Director of an approved State.** Within 14 days of this certification, the owner or operator must notify the State Director that the certification has been placed in the operating record.

# §257.23. Ground-water sampling and analysis requirements.

- (a) The ground-water monitoring program must include 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 [§ 257.22(a)](/cfr/40/257.22.md?p=a). The owner or operator must notify the State Director that the sampling and analysis program documentation has been placed in the operating record and the program must 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.**
- (b) The ground-water monitoring program must include sampling and analytical methods that are appropriate for ground-water sampling and that accurately measure hazardous constituents and other monitoring parameters in ground-water samples. Ground-water samples shall not be field-filtered prior to laboratory analysis.
- (c) The sampling procedures and frequency must be protective of human health and the environment.
- (d) Ground-water elevations must be measured in each well immediately prior to purging, each time ground water is sampled. The owner or operator must 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 must 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 must establish background ground-water quality in a hydraulically upgradient or background well(s) for each of the monitoring parameters or constituents required in the particular ground-water monitoring program that applies to the unit, as determined under [§ 257.24(a)](/cfr/40/257.24.md?p=a), or [§ 257.25(a)](/cfr/40/257.25.md?p=a). Background ground-water quality may be established at wells that are not located hydraulically upgradient from the unit if it meets the requirements of [§ 257.22(a)(1)](/cfr/40/257.22.md?p=a-1).
- (f) The number of samples collected to establish ground-water quality data must be consistent with the appropriate statistical procedures determined pursuant to [paragraph (g)](#g) of this section. The sampling procedures shall be those specified under [§ 257.24(b)](/cfr/40/257.24.md?p=b) for detection monitoring, § [257.25 (b)](/cfr/40/257.25.md?p=b) and [(d)](/cfr/40/257.25.md?p=d) for assessment monitoring, and [§ 257.26(b)](/cfr/40/257.26.md?p=b) for corrective action.
- (g) The owner or operator must specify in the operating record one of the following statistical methods to be used in evaluating ground-water monitoring data for each hazardous constituent. The statistical test chosen shall be conducted separately for each hazardous constituent in each well.
  - (1) 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 and the background mean levels for each constituent.
  - (2) 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 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 compliance well is compared to the upper tolerance or prediction limit.
  - (4) **A control chart approach that gives control limits for each constituent.**
  - (5) **Another statistical test method that meets the performance standards of paragraph (h) of this section.** The owner or operator must place a justification for this alternative in the operating record and notify the State Director of the use of this alternative test. The justification must demonstrate that the alternative method meets the performance standards of [paragraph (h)](#h) of this section.
- (h) Any statistical method chosen under [paragraph (g)](#g) of this section shall comply with the following performance standards, as appropriate:
  - (1) The statistical method used to evaluate ground-water monitoring data shall 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 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 comparison procedure is used to compare an individual compliance well constituent concentration with background constituent concentrations or a ground-water 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, the Type I experiment wise error rate for each testing period shall 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.
  - (3) If a control chart approach is used to evaluate ground-water monitoring data, the specific type of control chart and its associated parameter values shall be protective of human health and the environment. The 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) 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, 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 (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) 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.
    - (i) The owner or operator must determine whether or not there is a statistically significant increase over background values for each parameter or constituent required in the particular ground-water monitoring program that applies to the unit, as determined under §§ [257.24(a)](/cfr/40/257.24.md?p=a) or [257.25(a)](/cfr/40/257.25.md?p=a).
  - (1) In determining whether a statistically significant increase has occurred, the owner or operator must compare the ground-water quality of each parameter or constituent at each monitoring well designated pursuant to [§ 257.22(a)(2)](/cfr/40/257.22.md?p=a-2) to the background value of that constituent, according to the statistical procedures and performance standards specified under paragraphs [(g)](#g) and [(h)](#h) of this section.
  - (2) Within a reasonable period of time after completing sampling and analysis, the owner or operator must determine whether there has been a statistically significant increase over background at each monitoring well.

# §257.24. Detection monitoring program.

- (a) Detection monitoring is required at facilities identified in [§ 257.5(a)](/cfr/40/257.5.md?p=a) at all ground-water monitoring wells defined under §§ [257.22 (a)(1)](/cfr/40/257.22.md?p=a-1) and [(a)(2)](/cfr/40/257.22.md?p=a-2). At a minimum, a detection monitoring program must include the monitoring for the constituents listed in appendix I of [40 CFR part 258](/cfr/40/part258.md).
  - (1) The Director of an approved State may delete any of the appendix I (Appendix I of [40 CFR part 258](/cfr/40/part258.md)) monitoring parameters for a unit if it can be shown that the removed constituents are not reasonably expected to be contained in or derived from the waste contained in the unit.
  - (2) The Director of an approved State may establish an alternative list of indicator parameters for a unit, in lieu of some or all of the constituents in appendix I to [40 CFR part 258](/cfr/40/part258.md), if the alternative parameters provide a reliable indication of releases from the unit to the ground water. In determining alternative parameters, the Director shall consider the following factors:
    - (i) The types, quantities, and concentrations of constituents in waste managed at the unit;
    - (ii) The mobility, stability, and persistence of waste constituents or their reaction products in the unsaturated zone beneath the unit;
    - (iii) The detectability of indicator parameters, waste constituents, and reaction products in the ground water; and
    - (iv) The concentration or values and coefficients of variation of monitoring parameters or constituents in the groundwater background.
- (b) The monitoring frequency for all constituents listed in appendix I to [40 CFR part 258](/cfr/40/part258.md), or in the alternative list approved in accordance with [paragraph (a)(2)](#a-2) of this section, shall be at least semiannual during the active life of the unit plus 30 years. A minimum of four independent samples from each well (background and downgradient) must be collected and analyzed for the appendix I (Appendix I of [40 CFR part 258](/cfr/40/part258.md)) constituents, or the alternative list approved in accordance with [paragraph (a)(2)](#a-2) of this section, during the first semiannual sampling event. At least one sample from each well (background and downgradient) must be collected and analyzed during subsequent semiannual sampling events. The Director of an approved State may specify an appropriate alternative frequency for repeated sampling and analysis for appendix I (Appendix I of [40 CFR part 258](/cfr/40/part258.md)) constituents, or the alternative list approved in accordance with [paragraph (a)(2)](#a-2) of this section, during the active life plus 30 years. The alternative frequency during the active life shall be no less than annual. The alternative frequency shall be based on consideration of the following factors:
  - (1) Lithology of the aquifer and unsaturated zone;
  - (2) Hydraulic conductivity of the aquifer and unsaturated zone;
  - (3) Ground-water flow rates;
  - (4) Minimum distance between upgradient edge of the unit and downgradient monitoring well screen (minimum distance of travel); and
  - (5) **Resource value of the aquifer.**
- (c) If the owner or operator determines, pursuant to [§ 257.23(g)](/cfr/40/257.23.md?p=g), that there is a statistically significant increase over background for one or more of the constituents listed in appendix I to [40 CFR part 258](/cfr/40/part258.md), or in the alternative list approved in accordance with [paragraph (a)(2)](#a-2) of this section, at any monitoring well at the boundary specified under [§ 257.22(a)(2)](/cfr/40/257.22.md?p=a-2), the owner or operator:
  - (1) Must, within 14 days of this finding, place a notice in the operating record indicating which constituents have shown statistically significant changes from background levels, and notify the State Director that this notice was placed in the operating record; and
  - (2) Must establish an assessment monitoring program meeting the requirements of [§ 257.25](/cfr/40/257.25.md) within 90 days except as provided for in [paragraph (c)(3)](#c-3) of this section.
  - (3) The owner/operator may demonstrate that a source other than the unit caused the contamination or that the statistically significant increase resulted from error in sampling, analysis, statistical evaluation, or natural variation in ground-water quality. A report documenting this demonstration must be certified by a qualified ground-water scientist or approved by the Director of an approved State and be placed in the operating record. If a successful demonstration is made and documented, the owner or operator may continue detection monitoring as specified in this section. If, after 90 days, a successful demonstration is not made, the owner or operator must initiate an assessment monitoring program as required in [§ 257.25](/cfr/40/257.25.md).

# §257.25. Assessment monitoring program.

- (a) Assessment monitoring is required whenever a statistically significant increase over background has been detected for one or more of the constituents listed in appendix I of [40 CFR part 258](/cfr/40/part258.md) or in the alternative list approved in accordance with [§ 257.24(a)(2)](/cfr/40/257.24.md?p=a-2).
- (b) Within 90 days of triggering an assessment monitoring program, and annually thereafter, the owner or operator must sample and analyze the ground water for all constituents identified in appendix II of [40 CFR part 258](/cfr/40/part258.md). A minimum of one sample from each downgradient well must be collected and analyzed during each sampling event. For any constituent detected in the downgradient wells as the result of the complete appendix II (Appendix II of [40 CFR part 258](/cfr/40/part258.md)) analysis, a minimum of four independent samples from each well (background and downgradient) must be collected and analyzed to establish background for the new constituents. The Director of an approved State may specify an appropriate subset of wells to be sampled and analyzed for appendix II (Appendix II of [40 CFR part 258](/cfr/40/part258.md)) constituents during assessment monitoring. The Director of an approved State may delete any of the appendix II (Appendix II of [40 CFR part 258](/cfr/40/part258.md)) monitoring parameters for a unit if it can be shown that the removed constituents are not reasonably expected to be in or derived from the waste contained in the unit.
- (c) The Director of an approved State may specify an appropriate alternate frequency for repeated sampling and analysis for the full set of appendix II (Appendix II of [40 CFR part 258](/cfr/40/part258.md)) constituents, or the alternative list approved in accordance with [paragraph (b)](#b) of this section, during the active life plus 30 years considering the following factors:
  - (1) Lithology of the aquifer and unsaturated zone;
  - (2) Hydraulic conductivity of the aquifer and unsaturated zone;
  - (3) Ground-water flow rates;
  - (4) Minimum distance between upgradient edge of the unit and downgradient monitoring well screen (minimum distance of travel);
  - (5) Resource value of the aquifer; and
  - (6) **Nature (fate and transport) of any constituents detected in response to this section.**
- (d) After obtaining the results from the initial or subsequent sampling events required in [paragraph (b)](#b) of this section, the owner or operator must:
  - (1) Within 14 days, place a notice in the operating record identifying the appendix II (appendix II of [40 CFR part 258](/cfr/40/part258.md)) constituents that have been detected and notify the State Director that this notice has been placed in the operating record;
  - (2) Within 90 days, and on at least a semiannual basis thereafter, resample all wells specified by [§ 257.22(a)](/cfr/40/257.22.md?p=a) to this section, conduct analyses for all constituents in appendix I (Appendix I of [40 CFR part 258](/cfr/40/part258.md)) to this part or in the alternative list approved in accordance with [§ 257.24(a)(2)](/cfr/40/257.24.md?p=a-2), and for those constituents in appendix II to [40 CFR part 258](/cfr/40/part258.md) that are detected in response to [paragraph (b)](#b) of this section, and record their concentrations in the facility operating record. At least one sample from each well (background and downgradient) must be collected and analyzed during these sampling events. The Director of an approved State may specify an alternative monitoring frequency during the active life plus 30 years for the constituents referred to in this paragraph. The alternative frequency for appendix I (appendix I of [40 CFR part 258](/cfr/40/part258.md)) constituents, or the alternative list approved in accordance with [§ 257.24(a)(2)](/cfr/40/257.24.md?p=a-2), during the active life shall be no less than annual. The alternative frequency shall be based on consideration of the factors specified in [paragraph (c)](#c) of this section;
  - (3) Establish background concentrations for any constituents detected pursuant to paragraphs [(b)](#b) or [(d)(2)](#d-2) of this section; and
  - (4) Establish ground-water protection standards for all constituents detected pursuant to paragraph [(b)](#b) or [(d)](#d) of this section. The ground-water protection standards shall be established in accordance with paragraphs [(h)](#h) or [(i)](#i) of this section.
- (e) If the concentrations of all appendix II (appendix II of [40 CFR part 258](/cfr/40/part258.md)) constituents are shown to be at or below background values, using the statistical procedures in [§ 257.23(g)](/cfr/40/257.23.md?p=g), for two consecutive sampling events, the owner or operator must notify the State Director of this finding and may return to detection monitoring.
- (f) If the concentrations of any appendix II (appendix II of [part 258](/cfr/40/part258.md)) constituents are above background values, but all concentrations are below the ground-water protection standard established under paragraphs [(h)](#h) or [(i)](#i) of this section, using the statistical procedures in [§ 257.23(g)](/cfr/40/257.23.md?p=g), the owner or operator must continue assessment monitoring in accordance with this section.
- (g) If one or more appendix II (appendix II of CFR [part 258](/cfr/40/part258.md)) constituents are detected at statistically significant levels above the ground-water protection standard established under paragraphs [(h)](#h) or [(i)](#i) of this section in any sampling event, the owner or operator must, within 14 days of this finding, place a notice in the operating record identifying the appendix II (appendix II of [40 CFR part 258](/cfr/40/part258.md)) constituents that have exceeded the ground-water protection standard and notify the State Director and all appropriate local government officials that the notice has been placed in the operating record. The owner or operator also:
  - (1)
    - (i) Must characterize the nature and extent of the release by installing additional monitoring wells as necessary;
    - (ii) Must install at least one additional monitoring well at the facility boundary in the direction of contaminant migration and sample this well in accordance with [paragraph (d)(2)](#d-2) of this section;
    - (iii) Must notify all persons who own the land or reside on the land that directly overlies any part of the plume of contamination if contaminants have migrated off-site if indicated by sampling of wells in accordance [paragraph (g)(1)](#g-1) of this section; and
    - (iv) Must initiate an assessment of corrective measures as required by [§ 257.26](/cfr/40/257.26.md) within 90 days; or
  - (2) May demonstrate that a source other than the non-municipal non-hazardous waste disposal unit caused the contamination, or that the statistically significant increase resulted from error in sampling, analysis, statistical evaluation, or natural variation in ground-water quality. A report documenting this demonstration must be certified by a qualified ground-water scientist or approved by the Director of an approved State and placed in the operating record. If a successful demonstration is made the owner or operator must continue monitoring in accordance with the assessment monitoring program pursuant to this § 257.25, and may return to detection monitoring if the appendix II (appendix II of [40 CFR part 258](/cfr/40/part258.md)) constituents are at or below background as specified in [paragraph (e)](#e) of this section. Until a successful demonstration is made, the owner or operator must comply with [§ 257.25(g)](#g) including initiating an assessment of corrective measures.
- (h) The owner or operator must establish a ground-water protection standard for each appendix II (appendix II of [40 CFR part 258](/cfr/40/part258.md)) constituent detected in the ground-water. The ground-water protection standard shall be:
  - (1) For constituents for which a maximum contaminant level (MCL) has been promulgated under section 1412 of the Safe Drinking Water Act (codified) under [40 CFR part 141](/cfr/40/part141.md), the MCL for that constituent;
  - (2) For constituents for which MCLs have not been promulgated, the background concentration for the constituent established from wells in accordance with [§ 257.22(a)(1)](/cfr/40/257.22.md?p=a-1); or
  - (3) For constituents for which the background level is higher than the MCL identified under [subparagraph (h)(1)](#h-1) of this section or health based levels identified under [paragraph (i)(1)](#i-1) of this section, the background concentration.
- (i) The Director of an approved State may establish an alternative ground-water protection standard for constituents for which MCLs have not been established. These ground-water protection standards shall be appropriate health based levels that satisfy the following criteria:
  - (1) The level is derived in a manner consistent with Agency guidelines for assessing the health risks of environmental pollutants (51 FR 33992, 34006, 34014, 34028, September 24, 1986);
  - (2) The level is based on scientifically valid studies conducted in accordance with the Toxic Substances Control Act Good Laboratory Practice Standards ([40 CFR part 792](/cfr/40/part792.md)) or equivalent;
  - (3) For carcinogens, the level represents a concentration associated with an excess lifetime cancer risk level (due to continuous lifetime exposure) within the 1 × 10−4 to 1 × 10−6 range; and
  - (4) For systemic toxicants, the level represents a concentration to which the human population (including sensitive subgroups) could be exposed to on a daily basis that is likely to be without appreciable risk of deleterious effects during a lifetime. For purposes of this subpart, systemic toxicants include toxic chemicals that cause effects other than cancer or mutation.
- (j) In establishing ground-water protection standards under [paragraph (i)](#i) of this section, the Director of an approved State may consider the following:
  - (1) Multiple contaminants in the ground water;
  - (2) Exposure threats to sensitive environmental receptors; and
  - (3) **Other site-specific exposure or potential exposure to ground water.**