Rule 3745-525-940 | Assessment monitoring program, 40 C.F.R. 257.95.
(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 A to rule 3745-525-900 of the Administrative Code.
(B) Within ninety days of triggering an assessment monitoring program, and annually thereafter, the owner or operator of the CCR unit shall sample and analyze the groundwater for all constituents listed in appendix B to rule 3745-525-900 of the Administrative Code. The number of samples collected and analyzed for each well during each sampling event shall be consistent with paragraph (E) of rule 3745-525-920 of the Administrative Code, and shall account for any unique characteristics of the site, but shall 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 B to rule 3745-525-900 of the Administrative Code 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 shall be evaluated on a site-specific basis. The demonstration shall be supported by, at a minimum, the information specified in paragraphs (C)(1) and (C)(2) of this rule.
(1) Information documenting the need for less frequent sampling. The alternative frequency shall be based on consideration of the following factors:
(a) Lithology of the aquifer and unsaturated zone.
(b) Hydraulic conductivity of the aquifer and unsaturated zone.
(c) 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 shall obtain a certification from a qualified professional engineer stating that the demonstration for an alternative groundwater sampling and analysis frequency meets the requirements of this rule. The owner or operator shall include the demonstration providing the basis for the alternative monitoring frequency and the certification by a qualified professional engineer in the annual groundwater monitoring and corrective action report required by paragraph (E) of rule 3745-525-900 of the Administrative Code.
(D) After obtaining the results from the initial and subsequent sampling events required in paragraph (B) of this rule, the owner or operator shall do the following:
(1) Within ninety days of obtaining the results, and on at least a semiannual basis thereafter, resample all wells that were installed pursuant to the requirements of rule 3745-525-910 of the Administrative Code, conduct analyses for all parameters in appendix A to rule 3745-525-900 of the Administrative Code and for those constituents in appendix B to rule 3745-525-900 of the Administrative Code that are detected in response to paragraph (B) of this rule, 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 shall be consistent with paragraph (E) of rule 3745-525-920 of the Administrative Code and shall account for any unique characteristics of the site, but shall be at least one sample from each background and downgradient well.
(2) Establish groundwater protection standards for all constituents detected pursuant to paragraph (B) or (D) of this rule. The groundwater protection standards shall be established in accordance with paragraph (H) of this rule.
(3) Include the recorded concentrations required by paragraph (D)(1) of this rule, identify the background concentrations established under paragraph (B) of rule 3745-525-930 of the Administrative Code, and identify the groundwater protection standards established under paragraph (D)(2) of this rule in the annual groundwater monitoring and corrective action report required by paragraph (E) of rule 3745-525-900 of the Administrative Code.
(E) If the concentrations of all constituents listed in appendix A and appendix B to rule 3745-525-900 of the Administrative Code are shown to be at or below background values, using the statistical procedures in paragraph (G) of rule 3745-525-920 of the Administrative Code, for two consecutive sampling events, the owner or operator may return to detection monitoring of the CCR unit. The owner or operator shall 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 paragraph (H)(7) of rule 3745-525-50 of the Administrative Code.
(F) If the concentrations of any constituent in appendix A and appendix B to rule 3745-525-900 of the Administrative Code are above background values, but all concentrations are below the groundwater protection standard established under paragraph (H) of this rule, using the statistical procedures in paragraph (G) of rule 3745-525-920 of the Administrative Code, the owner or operator must continue assessment monitoring in accordance with this rule.
(G) If one or more constituents in appendix B to rule 3745-525-900 of the Administrative Code are detected at statistically significant levels above the groundwater protection standard established under paragraph (H) of this rule in any sampling event, the owner or operator shall prepare a notification identifying the constituents in appendix B to rule 3745-525-900 of the Administrative Code 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 paragraph (H)(8) of rule 3745-525-50 of the Administrative Code. The owner or operator of the CCR unit also shall do the following:
(1) Characterize the nature and extent of the release and any relevant site conditions that may affect the remedy ultimately selected. The characterization shall 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 rule 3745-525-950 of the Administrative Code. Characterization of the release includes the following minimum measures:
(a) Install additional monitoring wells necessary to define the contaminant plume.
(b) Collect data on the nature and estimated quantity of material released including specific information on the constituents listed in appendix B to rule 3745-525-900 of the Administrative Code and the levels at which the constituents are present in the material released.
(c) 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) of this rule.
(d) Sample all wells in accordance with paragraph (D)(1) of this rule 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) of this rule. The owner or operator has completed the notifications when the notices are placed in the facility's operating record as required by paragraph (H)(8) of rule 3745-525-50 of the Administrative Code.
(3) Within ninety days of finding that any of the constituents listed in appendix B to rule 3745-525-900 of the Administrative Code have been detected at a statistically significant level exceeding the groundwater protection standards the owner or operator shall do either of the following:
(a) Initiate an assessment of corrective measures as required by rule 3745-525-950 of the Administrative Code.
(b) 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 shall be supported by a report that includes the factual or evidentiary basis for any conclusions and shall be certified to be accurate by a qualified professional engineer. If a successful demonstration is made, the owner or operator shall continue monitoring in accordance with the assessment monitoring program pursuant to this rule, and may return to detection monitoring if the constituents in appendix A and appendix B to rule 3745-525-900 of the Administrative Code are at or below background as specified in paragraph (E) of this rule. The owner or operator shall also include the demonstration in the annual groundwater monitoring and corrective action report required by paragraph (E) of rule 3745-525-900 of the Administrative Code, in addition to the certification by a qualified professional engineer.
(4) If a successful demonstration has not been made at the end of the ninety-day period provided by paragraph (G)(3)(b) of this rule, the owner or operator of the CCR unit shall initiate the assessment of corrective measures requirements under rule 3745-525-950 of the Administrative Code.
(5) The owner or operator shall prepare a notification stating that an assessment of corrective measures has been initiated.
(H) The owner or operator of the CCR unit shall establish a groundwater protection standard for each constituent in appendix B to rule 3745-525-900 of the Administrative Code detected in the groundwater. The groundwater protection standard shall be the following:
(1) For constituents for which a maximum contaminant level (MCL) has been established under 40 C.F.R. sections 141.62 and 141.66, the MCL for that constituent.
(2) [Reserved.]
(3) For constituents for which the background level is higher than the levels identified under paragraphs (H)(1) of this rule, the background concentration.
(I) The owner or operator of the CCR unit shall comply with the recordkeeping requirements specified in paragraph (H) of rule 3745-525-50 of the Administrative Code, the notification requirements specified in paragraph (H) of rule 3745-525-60 of the Administrative Code, and the internet requirements specified in paragraph (H) of rule 3745-525-70 of the Administrative Code.
Last updated October 1, 2026 at 11:15 AM
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