--- kind: "range" citation: "40 C.F.R. §§ 257.90–257.95" title: "40" from: "257.90" to: "257.95" count: 6 url: "https://uscodex.org/cfr/40/257.90..257.95" --- # §257.90. Applicability. - (a) **Applicability.** All CCR units are subject to the groundwater monitoring and corrective action requirements under [§§ 257.90 through 257.98](/cfr/40/257.90..257.98.md), except as provided in [paragraph (g)](#g) of this section. - (b) **Initial timeframes—** - (1) **Existing CCR landfills and existing CCR surface impoundments.** No later than October 17, 2017, the owner or operator of the CCR unit must be in compliance with the following groundwater monitoring requirements: - (i) Install the groundwater monitoring system as required by [§ 257.91](/cfr/40/257.91.md); - (ii) Develop the groundwater sampling and analysis program to include selection of the statistical procedures to be used for evaluating groundwater monitoring data as required by [§ 257.93](/cfr/40/257.93.md); - (iii) Initiate the detection monitoring program to include obtaining a minimum of eight independent samples for each background and downgradient well as required by [§ 257.94(b)](/cfr/40/257.94.md?p=b); and - (iv) Begin evaluating the groundwater monitoring data for statistically significant increases over background levels for the constituents listed in appendix III of this part as required by [§ 257.94](/cfr/40/257.94.md). - (2) **New CCR landfills, new CCR surface impoundments, and all lateral expansions of CCR units.** Prior to initial receipt of CCR by the CCR unit, the owner or operator must be in compliance with the groundwater monitoring requirements specified in paragraph [(b)(1)(i)](#b-1-i) and [(ii)](#b-1-ii) of this section. In addition, the owner or operator of the CCR unit must initiate the detection monitoring program to include obtaining a minimum of eight independent samples for each background well as required by [§ 257.94(b)](/cfr/40/257.94.md?p=b). - (3) **CCR management units.** No later than Monday, February 10, 2031, the owner or operator of the CCR management unit must be in compliance with the following groundwater monitoring requirements: - (i) Install the groundwater monitoring system as required by [§ 257.91](/cfr/40/257.91.md). - (ii) Develop the groundwater sampling and analysis program to include selection of the statistical procedures to be used for evaluating groundwater monitoring data as required by [§ 257.93](/cfr/40/257.93.md). - (iii) Initiate the detection monitoring program to include obtaining a minimum of eight independent samples for each background and downgradient well, as required by [§ 257.94(b)](/cfr/40/257.94.md?p=b). - (iv) Begin evaluating the groundwater monitoring data for statistically significant increases over background levels for the constituents listed in appendix III of this part, as required by [§ 257.94](/cfr/40/257.94.md). - (v) Begin evaluating the groundwater monitoring data for statistically significant levels over groundwater protection standards for the constituents listed in appendix IV of this part as required by [§ 257.95](/cfr/40/257.95.md). - (c) **Requirement to conduct groundwater monitoring and corrective action.** Once a groundwater monitoring system and groundwater monitoring program has been established at the CCR unit as required by this subpart, the owner or operator must conduct groundwater monitoring and, if necessary, corrective action throughout the active life and post-closure care period of the CCR unit. - (d) **Responding to a release from a CCR unit.** In the event of a release from a CCR unit, the owner or operator must immediately take all necessary measures to control the source(s) of releases so as to reduce or eliminate, to the maximum extent feasible, further releases of contaminants into the environment. The owner or operator of the CCR unit must comply with all applicable requirements in §§ [257.96](/cfr/40/257.96.md), [257.97](/cfr/40/257.97.md), and [257.98](/cfr/40/257.98.md). - (e) **Annual groundwater monitoring and corrective action report.** For existing CCR landfills and existing CCR surface impoundments, no later than January 31, 2018, and annually thereafter, the owner or operator must prepare an annual groundwater monitoring and corrective action report. For new CCR landfills, new CCR surface impoundments, and all lateral expansions of CCR units, the owner or operator must prepare the initial annual groundwater monitoring and corrective action report no later than January 31 of the year following the calendar year a groundwater monitoring system has been established for such CCR unit as required by this subpart, and annually thereafter. For CCR management units, the owner or operator must prepare the initial annual groundwater monitoring and corrective action report no later than January 31, 2032, and annually thereafter. For the preceding calendar year, the annual report must document the status of the groundwater monitoring and corrective action program for the CCR unit, summarize key actions completed, describe any problems encountered, discuss actions to resolve the problems, and project key activities for the upcoming year. For purposes of this section, the owner or operator has prepared the annual report when the report is placed in the facility's operating record as required by [§ 257.105(h)(1)](/cfr/40/257.105.md?p=h-1). At a minimum, the annual groundwater monitoring and corrective action report must contain the following information, to the extent available: - (1) A map, aerial image, or diagram showing the CCR unit and all background (or upgradient) and downgradient monitoring wells, to include the well identification numbers, that are part of the groundwater monitoring program for the CCR unit; - (2) Identification of any monitoring wells that were installed or decommissioned during the preceding year, along with a narrative description of why those actions were taken; - (3) In addition to all the monitoring data obtained under [§§ 257.90 through 257.98](/cfr/40/257.90..257.98.md), a summary including the number of groundwater samples that were collected for analysis for each background and downgradient well, the dates the samples were collected, and whether the sample was required by the detection monitoring or assessment monitoring programs; - (4) A narrative discussion of any transition between monitoring programs (e.g., the date and circumstances for transitioning from detection monitoring to assessment monitoring in addition to identifying the constituent(s) detected at a statistically significant increase over background levels); and - (5) Other information required to be included in the annual report as specified in [§§ 257.90 through 257.98](/cfr/40/257.90..257.98.md). - (6) A section at the beginning of the annual report that provides an overview of the current status of groundwater monitoring and corrective action programs for the CCR unit. At a minimum, the summary must specify all of the following: - (i) At the start of the current annual reporting period, whether the CCR unit was operating under the detection monitoring program in [§ 257.94](/cfr/40/257.94.md) or the assessment monitoring program in [§ 257.95](/cfr/40/257.95.md); - (ii) At the end of the current annual reporting period, whether the CCR unit was operating under the detection monitoring program in [§ 257.94](/cfr/40/257.94.md) or the assessment monitoring program in [§ 257.95](/cfr/40/257.95.md); - (iii) If it was determined that there was a statistically significant increase over background for one or more constituents listed in appendix III to this part pursuant to [§ 257.94(e)](/cfr/40/257.94.md?p=e): - (A) Identify those constituents listed in appendix III to this part and the names of the monitoring wells associated with such an increase; and - (B) **Provide the date when the assessment monitoring program was initiated for the CCR unit.** - (iv) If it was determined that there was a statistically significant level above the groundwater protection standard for one or more constituents listed in appendix IV to this part pursuant to [§ 257.95(g)](/cfr/40/257.95.md?p=g) include all of the following: - (A) Identify those constituents listed in appendix IV to this part and the names of the monitoring wells associated with such an increase; - (B) Provide the date when the assessment of corrective measures was initiated for the CCR unit; - (C) Provide the date when the public meeting was held for the assessment of corrective measures for the CCR unit; and - (D) **Provide the date when the assessment of corrective measures was completed for the CCR unit.** - (v) Whether a remedy was selected pursuant to [§ 257.97](/cfr/40/257.97.md) during the current annual reporting period, and if so, the date of remedy selection; and - (vi) Whether remedial activities were initiated or are ongoing pursuant to [§ 257.98](/cfr/40/257.98.md) during the current annual reporting period. - (f) **Recordkeeping, notification, and internet requirements.** The owner or operator of the CCR unit must comply with the recordkeeping requirements specified in [§ 257.105(h)](/cfr/40/257.105.md?p=h), the notification requirements specified in [§ 257.106(h)](/cfr/40/257.106.md?p=h), and the internet requirements specified in [§ 257.107(h)](/cfr/40/257.107.md?p=h). - (g) **Suspension of groundwater monitoring requirements.** - (1) The Participating State Director or EPA where EPA is the permitting authority may suspend the groundwater monitoring requirements under [§§ 257.90 through 257.95](/cfr/40/257.90..257.95.md) for a CCR unit for a period of up to ten years, if the owner or operator provides written documentation that, based on the characteristics of the site in which the CCR unit is located, there is no potential for migration of any of the constituents listed in appendices III and IV to this part from that CCR unit to the uppermost aquifer during the active life of the CCR unit and the post-closure care period. This demonstration must be certified by a qualified professional engineer and approved by the Participating State Director or EPA where EPA is the permitting authority, and must be based upon: - (i) Site-specific field collected measurements, sampling, and analysis of physical, chemical, and biological processes affecting contaminant fate and transport, including at a minimum, the information necessary to evaluate or interpret the effects of the following properties or processes on contaminant fate and transport: - (A) Aquifer Characteristics, including hydraulic conductivity, hydraulic gradient, effective porosity, aquifer thickness, degree of saturation, stratigraphy, degree of fracturing and secondary porosity of soils and bedrock, aquifer heterogeneity, groundwater discharge, and groundwater recharge areas; - (B) Waste Characteristics, including quantity, type, and origin; - (C) Climatic Conditions, including annual precipitation, leachate generation estimates, and effects on leachate quality; - (D) Leachate Characteristics, including leachate composition, solubility, density, the presence of immiscible constituents, Eh, and pH; and - (E) Engineered Controls, including liners, cover systems, and aquifer controls (e.g., lowering the water table). These must be evaluated under design and failure conditions to estimate their long-term residual performance. - (ii) Contaminant fate and transport predictions that maximize contaminant migration and consider impacts on human health and the environment. - (2) The owner or operator of the CCR unit may renew this suspension for additional ten year periods by submitting written documentation that the site characteristics continue to ensure there will be no potential for migration of any of the constituents listed in Appendices III and IV of this part. The documentation must include, at a minimum, the information specified in paragraphs [(g)(1)(i)](#g-1-i) and [(ii)](#g-1-ii) of this section and a certification by a qualified professional engineer and approved by the State Director or EPA where EPA is the permitting authority. The owner or operator must submit the documentation supporting their renewal request for the state's or EPA's review and approval of their extension one year before the groundwater monitoring suspension is due to expire. If the existing groundwater monitoring extension expires or is not approved, the owner or operator must begin groundwater monitoring according to [paragraph (a)](#a) of this section within 90 days. The owner or operator may continue to renew the suspension for ten-year periods, provided the owner or operator demonstrate that the standard in [paragraph (g)(1)](#g-1) of this section continues to be met for the unit. The owner or operator must place each completed demonstration in the facility's operating record. - (3) The owner or operator of the CCR unit must include in the annual groundwater monitoring and corrective action report required by [§ 257.90(e)](#e) or [§ 257.100(e)(5)(ii)](/cfr/40/257.100.md?p=e-5-ii) any approved no migration demonstration. # §257.91. Groundwater monitoring systems. - (a) **Performance standard.** The owner or operator of a CCR unit must install a groundwater monitoring system that consists of a sufficient number of wells, installed at appropriate locations and depths, to yield groundwater samples from the uppermost aquifer that: - (1) Accurately represent the quality of background groundwater that has not been affected by leakage from a CCR unit. A determination of background quality may include sampling of wells that are not hydraulically upgradient of the CCR management area where: - (i) Hydrogeologic conditions do not allow the owner or operator of the CCR unit to determine what wells are hydraulically upgradient; or - (ii) Sampling at other wells will provide an indication of background groundwater quality that is as representative or more representative than that provided by the upgradient wells; and - (2) **Accurately represent the quality of groundwater passing the waste boundary of the CCR unit.** The downgradient monitoring system must be installed at the waste boundary that ensures detection of groundwater contamination in the uppermost aquifer. All potential contaminant pathways must be monitored. - (b) The number, spacing, and depths of monitoring systems shall be determined based upon site-specific technical information that must include thorough characterization of: - (1) Aquifer thickness, groundwater flow rate, groundwater flow direction including seasonal and temporal fluctuations in groundwater flow; and - (2) 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. - (c) The groundwater monitoring system must include the minimum number of monitoring wells necessary to meet the performance standards specified in [paragraph (a)](#a) of this section, based on the site-specific information specified in [paragraph (b)](#b) of this section. The groundwater monitoring system must contain: - (1) A minimum of one upgradient and three downgradient monitoring wells; and - (2) Additional monitoring wells as necessary to accurately represent the quality of background groundwater that has not been affected by leakage from the CCR unit and the quality of groundwater passing the waste boundary of the CCR unit. - (d) The owner or operator of multiple CCR units may install a multiunit groundwater monitoring system instead of separate groundwater monitoring systems for each CCR unit. - (1) The multiunit groundwater monitoring system must be equally as capable of detecting monitored constituents at the waste boundary of the CCR unit as the individual groundwater monitoring system specified in [paragraphs (a) through (c)](#a..c) of this section for each CCR unit based on the following factors: - (i) Number, spacing, and orientation of each CCR unit; - (ii) Hydrogeologic setting; - (iii) Site history; and - (iv) **Engineering design of the CCR unit.** - (2) [Reserved] - (e) Monitoring wells must be cased in a manner that maintains the integrity of the monitoring well borehole. This casing must be screened or perforated and packed with gravel or sand, where necessary, to enable collection of groundwater samples. The annular space (i.e., the space between the borehole and well casing) above the sampling depth must be sealed to prevent contamination of samples and the groundwater. - (1) The owner or operator of the CCR unit must document and include in the operating record the design, installation, development, and decommissioning of any monitoring wells, piezometers and other measurement, sampling, and analytical devices. The qualified professional engineer must be given access to this documentation when completing the groundwater monitoring system certification required under [paragraph (f)](#f) of this section. - (2) The monitoring wells, piezometers, and other measurement, sampling, and analytical devices must be operated and maintained so that they perform to the design specifications throughout the life of the monitoring program. - (f) The owner or operator must obtain a certification from a qualified professional engineer or approval from the Participating State Director or approval from EPA where EPA is the permitting authority stating that the groundwater monitoring system has been designed and constructed to meet the requirements of this section. If the groundwater monitoring system includes the minimum number of monitoring wells specified in [paragraph (c)(1)](#c-1) of this section, the certification must document the basis supporting this determination. - (g) The owner or operator of the CCR unit must comply with the recordkeeping requirements specified in [§ 257.105(h)](/cfr/40/257.105.md?p=h), the notification requirements specified in [§ 257.106(h)](/cfr/40/257.106.md?p=h), and the internet requirements specified in [§ 257.107(h)](/cfr/40/257.107.md?p=h). # §257.92. Reserved # §257.93. Groundwater sampling and analysis requirements. - (a) The groundwater monitoring program must 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 downgradient wells required by [§ 257.91](/cfr/40/257.91.md). The owner or operator of the CCR unit must develop a sampling and analysis program that includes 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 groundwater monitoring program must include sampling and analytical methods that are appropriate for groundwater sampling and that accurately measure hazardous constituents and other monitoring parameters in groundwater samples. For purposes of [§§ 257.90 through 257.98](/cfr/40/257.90..257.98.md), the term constituent refers to both hazardous constituents and other monitoring parameters listed in either appendix III or IV of this part. - (c) Groundwater elevations must be measured in each well immediately prior to purging, each time groundwater is sampled. The owner or operator of the CCR unit must determine the rate and direction of groundwater flow each time groundwater is sampled. Groundwater elevations in wells which monitor the same CCR management area must be measured within a period of time short enough to avoid temporal variations in groundwater flow which could preclude accurate determination of groundwater flow rate and direction. - (d) The owner or operator of the CCR unit must establish background groundwater quality in a hydraulically upgradient or background well(s) for each of the constituents required in the particular groundwater monitoring program that applies to the CCR unit as determined under [§ 257.94(a)](/cfr/40/257.94.md?p=a) or [§ 257.95(a)](/cfr/40/257.95.md?p=a). Background groundwater quality may be established at wells that are not located hydraulically upgradient from the CCR unit if it meets the requirements of [§ 257.91(a)(1)](/cfr/40/257.91.md?p=a-1). - (e) The number of samples collected when conducting detection monitoring and assessment monitoring (for both downgradient and background wells) must be consistent with the statistical procedures chosen under [paragraph (f)](#f) of this section and the performance standards under [paragraph (g)](#g) of this section. The sampling procedures shall be those specified under [§ 257.94(b) through (d)](/cfr/40/257.94.md?p=b..d) for detection monitoring, [§ 257.95(b) through (d)](/cfr/40/257.95.md?p=b..d) for assessment monitoring, and [§ 257.96(b)](/cfr/40/257.96.md?p=b) for corrective action. - (f) The owner or operator of the CCR unit must select one of the statistical methods specified in [paragraphs (f)(1) through (5)](#f-1..f-5) of this section to be used in evaluating groundwater monitoring data for each specified constituent. The statistical test chosen shall be conducted separately for each constituent in each monitoring well. - (1) A parametric analysis of variance followed by multiple comparison 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 based on ranks followed by multiple comparison 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 (g) of this section.** - (6) The owner or operator of the CCR unit must obtain a certification from a qualified professional engineer or approval from the Participating State Director or approval from EPA where EPA is the permitting authority stating that the selected statistical method is appropriate for evaluating the groundwater monitoring data for the CCR management area. The certification must include a narrative description of the statistical method selected to evaluate the groundwater monitoring data. - (g) Any statistical method chosen under [paragraph (f)](#f) of this section shall comply with the following performance standards, as appropriate, based on the statistical test method used: - (1) The statistical method used to evaluate groundwater monitoring data shall be appropriate for the distribution of constituents. Normal distributions of data values shall use parametric methods. Non-normal distributions shall use non-parametric methods. If the distribution of the constituents is shown by the owner or operator of the CCR unit to be inappropriate for a normal theory test, then the data must be transformed or a distribution-free (non-parametric) theory test must 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 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 comparison 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 groundwater monitoring data, the specific type of control chart and its associated parameter values shall be such that this approach is at least as effective as any other approach in this section for evaluating groundwater data. The parameter values 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 groundwater monitoring data, the levels of confidence and, for tolerance intervals, the percentage of the population that the interval must contain, shall be such that this approach is at least as effective as any other approach in this section for evaluating groundwater data. 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 must account for data below the limit of detection with one or more statistical procedures that shall at least as effective as any other approach in this section for evaluating groundwater data. 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 must include procedures to control or correct for seasonal and spatial variability as well as temporal correlation in the data. - (h) The owner or operator of the CCR unit must determine whether or not there is a statistically significant increase over background values for each constituent required in the particular groundwater monitoring program that applies to the CCR unit, as determined under [§ 257.94(a)](/cfr/40/257.94.md?p=a) or [§ 257.95(a)](/cfr/40/257.95.md?p=a). - (1) In determining whether a statistically significant increase has occurred, the owner or operator must compare the groundwater quality of each constituent at each monitoring well designated pursuant to § [257.91(a)(2)](/cfr/40/257.91.md?p=a-2) or [(d)(1)](/cfr/40/257.91.md?p=d-1) to the background value of that constituent, according to the statistical procedures and performance standards specified under paragraphs [(f)](#f) and [(g)](#g) of this section. - (2) Within 90 days after completing sampling and analysis, the owner or operator must determine whether there has been a statistically significant increase over background for any constituent at each monitoring well. - (i) The owner or operator must measure “total recoverable metals” concentrations in measuring groundwater quality. Measurement of total recoverable metals captures both the particulate fraction and dissolved fraction of metals in natural waters. Groundwater samples shall not be field-filtered prior to analysis. - (j) The owner or operator of the CCR unit must comply with the recordkeeping requirements specified in [§ 257.105(h)](/cfr/40/257.105.md?p=h), the notification requirements specified in [§ 257.106(h)](/cfr/40/257.106.md?p=h), and the Internet requirements specified in [§ 257.107(h)](/cfr/40/257.107.md?p=h). # §257.94. Detection monitoring program. - (a) The owner or operator of a CCR unit must conduct detection monitoring at all groundwater monitoring wells consistent with this section. At a minimum, a detection monitoring program must include groundwater monitoring for all constituents listed in appendix III to this part. - (b) Except as provided in [paragraph (d)](#d) of this section, the monitoring frequency for the constituents listed in appendix III to this part shall be at least semiannual during the active life of the CCR unit and the post-closure period. For existing CCR landfills and existing CCR surface impoundments, a minimum of eight independent samples from each background and downgradient well must be collected and analyzed for the constituents listed in appendix III and IV to this part no later than October 17, 2017. For new CCR landfills, new CCR surface impoundments, and all lateral expansions of CCR units, a minimum of eight independent samples for each background well must be collected and analyzed for the constituents listed in appendices III and IV to this part during the first six months of sampling. - (c) The number of samples collected and analyzed for each background well and downgradient well during subsequent semiannual sampling events must be consistent with [§ 257.93(e)](/cfr/40/257.93.md?p=e), and must account for any unique characteristics of the site, but must be at least one sample from each background and downgradient well. - (d) The owner or operator of a CCR unit may demonstrate the need for an alternative monitoring frequency for repeated sampling and analysis for constituents listed in appendix III to this part during the active life and the post-closure care period based on the availability of groundwater. If there is not adequate groundwater flow to sample wells semiannually, the alternative frequency shall be no less than annual. The need to vary monitoring frequency must be evaluated on a site-specific basis. The demonstration must be supported by, at a minimum, the information specified in paragraphs [(d)(1)](#d-1) and [(2)](#d-2) of this section. - (1) **Information documenting that the need for less frequent sampling.** The alternative frequency must be based on consideration of the following factors: - (i) Lithology of the aquifer and unsaturated zone; - (ii) Hydraulic conductivity of the aquifer and unsaturated zone; and - (iii) **Groundwater flow rates.** - (2) Information documenting that the alternative frequency will be no less effective in ensuring that any leakage from the CCR unit will be discovered within a timeframe that will not materially delay establishment of an assessment monitoring program. - (3) The owner or operator must obtain a certification from a qualified professional engineer or approval from the Participating State Director or approval from EPA where EPA is the permitting authority stating that the demonstration for an alternative groundwater sampling and analysis frequency meets the requirements of this section. The owner or operator must include the demonstration providing the basis for the alternative monitoring frequency and the certification by a qualified professional engineer or the approval from the Participating State Director or approval from EPA where EPA is the permitting authority in the annual groundwater monitoring and corrective action report required by [§ 257.90(e)](/cfr/40/257.90.md?p=e). - (e) If the owner or operator of the CCR unit determines, pursuant to [§ 257.93(h)](/cfr/40/257.93.md?p=h) that there is a statistically significant increase over background levels for one or more of the constituents listed in appendix III to this part at any monitoring well at the waste boundary specified under [§ 257.91(a)(2)](/cfr/40/257.91.md?p=a-2), the owner or operator must: - (1) Except as provided for in [paragraph (e)(2)](#e-2) of this section, within 90 days of detecting a statistically significant increase over background levels for any constituent, establish an assessment monitoring program meeting the requirements of [§ 257.95](/cfr/40/257.95.md). - (2) The owner or operator may demonstrate that a source other than the CCR unit caused the statistically significant increase over background levels for a constituent or that the statistically significant increase resulted from error in sampling, analysis, statistical evaluation, or natural variation in groundwater quality. The owner or operator must complete the written demonstration within 90 days of detecting a statistically significant increase over background levels to include obtaining a certification from a qualified professional engineer or approval from the Participating State Director or approval from EPA where EPA is the permitting authority verifying the accuracy of the information in the report. If a successful demonstration is completed within the 90-day period, the owner or operator of the CCR unit may continue with a detection monitoring program under this section. If a successful demonstration is not completed within the 90-day period, the owner or operator of the CCR unit must initiate an assessment monitoring program as required under [§ 257.95](/cfr/40/257.95.md). The owner or operator must also include the demonstration in the annual groundwater monitoring and corrective action report required by [§ 257.90(e)](/cfr/40/257.90.md?p=e), in addition to the certification by a qualified professional engineer or approval from the Participating State Director or approval from EPA where EPA is the permitting authority. - (3) The owner or operator of a CCR unit must prepare a notification stating that an assessment monitoring program has been established. The owner or operator has completed the notification when the notification is placed in the facility's operating record as required by [§ 257.105(h)(5)](/cfr/40/257.105.md?p=h-5). - (f) The owner or operator of the CCR unit must comply with the recordkeeping requirements specified in [§ 257.105(h)](/cfr/40/257.105.md?p=h), the notification requirements specified in [§ 257.106(h)](/cfr/40/257.106.md?p=h), and the Internet requirements specified in [§ 257.107(h)](/cfr/40/257.107.md?p=h). # §257.95. Assessment monitoring program. - (a) Assessment monitoring is required whenever a statistically significant increase over background levels has been detected for one or more of the constituents listed in appendix III to this part. - (b) - (1) **Within 90 days of triggering an assessment monitoring program, and annually thereafter—** - (i) Except as provided by [paragraph (b)(1)(ii)](#b-1-ii) of this section, the owner or operator of the CCR unit must sample and analyze the groundwater for all constituents listed in appendix IV to this part. - (ii) The owner or operator of a CCR management unit must sample and analyze the groundwater for all constituents listed in appendix IV to this part no later than Monday, February 10, 2031. - (2) The number of samples collected and analyzed for each well during each sampling event must be consistent with [§ 257.93(e)](/cfr/40/257.93.md?p=e), and must account for any unique characteristics of the site, but must be at least one sample from each well. - (c) The owner or operator of a CCR unit may demonstrate the need for an alternative monitoring frequency for repeated sampling and analysis for constituents listed in appendix IV to this part during the active life and the post-closure care period based on the availability of groundwater. If there is not adequate groundwater flow to sample wells semiannually, the alternative frequency shall be no less than annual. The need to vary monitoring frequency must be evaluated on a site-specific basis. The demonstration must be supported by, at a minimum, the information specified in paragraphs [(c)(1)](#c-1) and [(2)](#c-2) of this section. - (1) **Information documenting that the need for less frequent sampling.** The alternative frequency must be based on consideration of the following factors: - (i) Lithology of the aquifer and unsaturated zone; - (ii) Hydraulic conductivity of the aquifer and unsaturated zone; and - (iii) **Groundwater flow rates.** - (2) Information documenting that the alternative frequency will be no less effective in ensuring that any leakage from the CCR unit will be discovered within a timeframe that will not materially delay the initiation of any necessary remediation measures. - (3) The owner or operator must obtain a certification from a qualified professional engineer or approval from the Participating State Director or approval from EPA where EPA is the permitting authority stating that the demonstration for an alternative groundwater sampling and analysis frequency meets the requirements of this section. The owner or operator must include the demonstration providing the basis for the alternative monitoring frequency and the certification by a qualified professional engineer or the approval from the Participating State Director or the approval from EPA where EPA is the permitting authority in the annual groundwater monitoring and corrective action report required by [§ 257.90(e)](/cfr/40/257.90.md?p=e). - (d) After obtaining the results from the initial and subsequent sampling events required in [paragraph (b)](#b) of this section, the owner or operator must: - (1) Within 90 days of obtaining the results, and on at least a semiannual basis thereafter, resample all wells that were installed pursuant to the requirements of [§ 257.91](/cfr/40/257.91.md), conduct analyses for all parameters in appendix III to this part and for those constituents in appendix IV to this part that are detected in response to [paragraph (b)](#b) of this section, and record their concentrations in the facility operating record. The number of samples collected and analyzed for each background well and downgradient well during subsequent semiannual sampling events must be consistent with [§ 257.93(e)](/cfr/40/257.93.md?p=e), and must account for any unique characteristics of the site, but must be at least one sample from each background and downgradient well; - (2) Establish groundwater protection standards for all constituents detected pursuant to paragraph [(b)](#b) or [(d)](#d) of this section. The groundwater protection standards must be established in accordance with [paragraph (h)](#h) of this section; and - (3) Include the recorded concentrations required by [paragraph (d)(1)](#d-1) of this section, identify the background concentrations established under [§ 257.94(b)](/cfr/40/257.94.md?p=b), and identify the groundwater protection standards established under [paragraph (d)(2)](#d-2) of this section in the annual groundwater monitoring and corrective action report required by [§ 257.90(e)](/cfr/40/257.90.md?p=e). - (e) If the concentrations of all constituents listed in appendices III and IV to this part are shown to be at or below background values, using the statistical procedures in [§ 257.93(g)](/cfr/40/257.93.md?p=g), for two consecutive sampling events, the owner or operator may return to detection monitoring of the CCR unit. The owner or operator must prepare a notification stating that detection monitoring is resuming for the CCR unit. The owner or operator has completed the notification when the notification is placed in the facility's operating record as required by [§ 257.105(h)(7)](/cfr/40/257.105.md?p=h-7). - (f) If the concentrations of any constituent in appendices III and IV to this part are above background values, but all concentrations are below the groundwater protection standard established under [paragraph (h)](#h) of this section, using the statistical procedures in [§ 257.93(g)](/cfr/40/257.93.md?p=g), the owner or operator must continue assessment monitoring in accordance with this section. - (g) If one or more constituents in appendix IV to this part are detected at statistically significant levels above the groundwater protection standard established under [paragraph (h)](#h) of this section in any sampling event, the owner or operator must prepare a notification identifying the constituents in appendix IV to this part that have exceeded the groundwater protection standard. The owner or operator has completed the notification when the notification is placed in the facility's operating record as required by [§ 257.105(h)(8)](/cfr/40/257.105.md?p=h-8). The owner or operator of the CCR unit also must: - (1) Characterize the nature and extent of the release and any relevant site conditions that may affect the remedy ultimately selected. The characterization must be sufficient to support a complete and accurate assessment of the corrective measures necessary to effectively clean up all releases from the CCR unit pursuant to [§ 257.96](/cfr/40/257.96.md). Characterization of the release includes the following minimum measures: - (i) Install additional monitoring wells necessary to define the contaminant plume(s); - (ii) Collect data on the nature and estimated quantity of material released including specific information on the constituents listed in appendix IV of this part and the levels at which they are present in the material released; - (iii) 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)(1)](#d-1) of this section; and - (iv) Sample all wells in accordance with [paragraph (d)(1)](#d-1) of this section to characterize the nature and extent of the release. - (2) 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 with [paragraph (g)(1)](#g-1) of this section. The owner or operator has completed the notifications when they are placed in the facility's operating record as required by [§ 257.105(h)(8)](/cfr/40/257.105.md?p=h-8). - (3) Within 90 days of finding that any of the constituents listed in appendix IV to this part have been detected at a statistically significant level exceeding the groundwater protection standards the owner or operator must either: - (i) Initiate an assessment of corrective measures as required by [§ 257.96](/cfr/40/257.96.md); or - (ii) Demonstrate that a source other than the CCR unit caused the contamination, or that the statistically significant increase resulted from error in sampling, analysis, statistical evaluation, or natural variation in groundwater quality. Any such demonstration must be supported by a report that includes the factual or evidentiary basis for any conclusions and must be certified to be accurate by a qualified professional engineer or approval from the Participating State Director or approval from EPA where EPA is the permitting authority. If a successful demonstration is made, the owner or operator must continue monitoring in accordance with the assessment monitoring program pursuant to this section, and may return to detection monitoring if the constituents in Appendix III and Appendix IV of this part are at or below background as specified in [paragraph (e)](#e) of this section. The owner or operator must also include the demonstration in the annual groundwater monitoring and corrective action report required by [§ 257.90(e)](/cfr/40/257.90.md?p=e), in addition to the certification by a qualified professional engineer or the approval from the Participating State Director or the approval from EPA where EPA is the permitting authority. - (4) If a successful demonstration has not been made at the end of the 90 day period provided by [paragraph (g)(3)(ii)](#g-3-ii) of this section, the owner or operator of the CCR unit must initiate the assessment of corrective measures requirements under [§ 257.96](/cfr/40/257.96.md). - (5) The owner or operator must prepare a notification stating that an assessment of corrective measures has been initiated. - (h) The owner or operator of the CCR unit must establish a groundwater protection standard for each constituent in appendix IV to this part detected in the groundwater. The groundwater protection standard shall be: - (1) For constituents for which a maximum contaminant level (MCL) has been established under §§ [141.62](/cfr/40/141.62.md) and [141.66](/cfr/40/141.66.md) of this title, the MCL for that constituent; - (2) **For the following constituents—** - (i) Cobalt 6 micrograms per liter (µg/l); - (ii) Lead 15 µg/l; - (iii) Lithium 40 µg/l; and - (iv) **Molybdenum 100 µg/l.** - (3) For constituents for which the background level is higher than the levels identified under paragraphs [(h)(1)](#h-1) and [(h)(2)](#h-2) of this section, the background concentration. - (i) The owner or operator of the CCR unit must comply with the recordkeeping requirements specified in [§ 257.105(h)](/cfr/40/257.105.md?p=h), the notification requirements specified in [§ 257.106(h)](/cfr/40/257.106.md?p=h), and the Internet requirements specified in [§ 257.107(h)](/cfr/40/257.107.md?p=h).