1. (a) Groundwater Criteria Unless otherwise specified in the RBCRs, all substances in groundwater from a release shall be remediated to comply with the following, as applicable:

   1. (1) Groundwater in a GA Area Remediation of substances in groundwater in a GA area, including the portion of a groundwater plume migrating from a GB area into a GA area, shall result in the reduction of each substance to a concentration equal to or less than all of the following:

      1. (A) The background concentration, except as provided in subsection (d) of this section, concerning groundwater protection criteria;
      2. (B) Surface-water protection criteria or background concentration; and(C) Volatilization criteria.

   2. (2) Groundwater in a GB Area Except for any portion of a groundwater plume migrating from a GB area into a GA area that is subject to the requirements of subdivision (1) of this subsection, remediation of substances in groundwater in a GB area shall result in the reduction of each substance to a concentration equal to or less than:

      1. (A) (i) The surface-water protection criteria and volatilization criteria; or(ii) The background concentration; and(B) The groundwater protection criteria, where the existing use of groundwater is for drinking or other purposes, until the use of such groundwater for drinking or other purposes is permanently discontinued.

   3. (3) Groundwater Plume Discharging to a Low-Dilution Surface Water Body (A) Remediation of substances in a groundwater plume shall result in the reduction of each substance to a concentration equal to or less than the criteria set forth in subparagraph (B) of this subdivision where such plume discharges to:

      1. (i) A wetland;
      2. (ii) A tidal flat;
      3. (iii) An intermittent watercourse; or(iv) A location where the areal extent of such groundwater plume occupies more than 0.5%, or other percentage approved in writing by the commissioner, of the upstream drainage basin of the surface water body to which such plume discharges. The percentage of the upstream drainage basin occupied by such groundwater plume shall be measured from the intersection of the surface water body with such groundwater plume.
      4. (B) Each substance in a groundwater plume discharging to a low-dilution surface water body specified in subparagraph (A) of this subdivision shall be remediated to a concentration that is either:
2. (i) Equal to or less than the applicable water quality criteria or, if there are no such criteria, to criteria approved by the commissioner in accordance with subsection (i)(2) of this section; or(ii) Equal to or less than the alternative surface-water protection criteria calculated by an LEP in accordance with subsection (b)(2) of this section or approved by the commissioner in accordance with subsection (b)(3) of this section.

3. (b) Alternative Surface-Water Protection Criteria With respect to substances in groundwater for which surface-water protection criteria are specified in section 22a-134tt-App5 of the RBCRs or approved by the commissioner pursuant to subsection (i)(2) of this section, alternative surface-water protection criteria may be calculated by an LEP or approved in writing by the commissioner, pursuant to this subsection. For each substance, only one subdivision of this subsection may be used to calculate or to request commissioner approval of alternative surface-water protection criteria. In addition, the commissioner may approve an alternative method of demonstrating compliance with surface-water protection criteria under this subsection.

   1. (1) Groundwater Plume Discharge to a Watercourse (A) For a substance in a groundwater plume that discharges to an inland surface watercourse classified as AA, A, or B in the water quality standards, alternative surface-water protection criteria may be calculated. Any such calculation shall be performed by multiplying the applicable water quality criteria or, if there are no such water quality criteria, the criteria approved by the commissioner pursuant to subsection (i)(2) of this section, by a dilution factor derived from the following equation: DF=(0.25 ×Q99)/Q_plumeTermsDescriptionValueUnitsDFRelease-specific dilution factorsubstance-specificunitlessQ99Daily stream flow equal to or exceeded on 99 percent of days in a yearwaterbody specificft³/secQ_plumeAverage daily discharge of the subject groundwater plume: Q_plume = KiAcalculatedft³/secKHydraulic conductivityas measuredft/seciHydraulic gradientas measuredft/ftAArea of discharge: A = h * was measuredft²hThickness of groundwater plume at watercourse discharge areaas measuredftwWidth of groundwater plume at watercourse discharge areaas measuredft(B) For a substance in a groundwater plume that discharges to a coastal surface watercourse classified as SA or SB in the water quality standards, alternative surface-water protection criteria may be calculated. Any such calculation shall be performed by multiplying the applicable water quality criteria, or if there are no such water quality criteria, the criteria approved by the commissioner pursuant to subsection (i)(2) of this section, by a dilution factor derived from the following equation:
      >
      TermsDescriptionValueUnitsDMean depth of the watercourse at mean low tide where the groundwater plume dischargescalculatedftDFRelease-specific dilution factorsubstance-specificunitlessLDistance along which the groundwater plume intersects the watercourse discharge areacalculatedftWCross-sectional distance from one shoreline to the other for the tidally influenced watercourse under low tide conditions: (0.25*watercourse width) where the maximum value for W is 100 feetcalculatedftTDaily discharge duration0.5dayQ_plumeAverage daily discharge of the subject groundwater plume:Q_plume = KiAcalculatedft³/dayKHydraulic conductivityas measuredft/dayiHydraulic gradientas measuredft/ftAArea of discharge: A = h * was measuredft²hThickness of groundwater plume at watercourse discharge areaas measuredftwWidth of groundwater plume at watercourse discharge areaas measuredft(C) For purposes of this subdivision, no alternative surface-water protection criteria shall exceed the maximum allowable alternative surface-water protection criteria specified in the table below, which is the water quality criteria multiplied by a dilution factor calculated pursuant to subparagraph (A) or (B) of this subdivision. Distance from compliance point to nearest downgradient surface waterMaximum Allowable Alternative SWPCLess than or equal to 100 feet100 times WQCGreater than 100 feet to 200 feet200 times WQCGreater than 200 feet to 300 feet300 times WQCGreater than 300 feet to 400 feet400 times WQCGreater than 400 feet to 500 feet500 times WQCGreater than 500 feet to 600 feet600 times WQCGreater than 600 feet to 700 feet700 times WQCGreater than 700 feet to 800 feet800 times WQCGreater than 800 feet to 900 feet900 times WQCGreater than 900 feet1,000 times WQC(D) Written notice of the use of alternative surface-water protection criteria calculated by an LEP under this subdivision shall be submitted to the commissioner in accordance with section 22a-134tt-1(c) of the RBCRs and shall also include the calculation, value and basis of terms, and dilution factor used.

   2. (2) Aquifer Dilution (A) Alternative surface-water protection criteria may be calculated in accordance with subparagraph (B) of this subdivision, provided that:

      1. (i) The portion of the groundwater plume for which such alternative criteria are calculated is at least 500 feet from the nearest downgradient surface water; and(ii) A dilution ratio for such groundwater plume is calculated pursuant to the following equation, and such ratio is equal to or greater than 5: DR = RC/DCTermsDescriptionValueunitsDRRelease-specific dilution ratiocalculatedunitlessRCGroundwater concentration of a substance within the release areaas measuredug/LDCGroundwater concentration no more than 50 feet downgradient from the location where the RC was collectedas measuredug/L(B) For substances in a groundwater plume that comply with subparagraph (A) of this subdivision, alternative surface-water protection criteria shall be calculated by multiplying the surface-water protection criteria, or if applicable the water quality criteria, by the dilution factor identified in the following table: Distance to nearest downgradient surface waterDilution factorGreater than 500 feet to 600 feet5Greater than 600 feet to 700 feet6Greater than 700 feet to 800 feet7Greater than 800 feet to 900 feet8Greater than 900 feet to 1,000 feet9Greater than 1,000 feet10(C) Written notice of the use of alternative surface-water protection criteria calculated by an LEP under this subparagraph shall be submitted to the commissioner in accordance with section 22a-134tt-1(c) of the RBCRs and shall also include the calculation, value and basis of terms, and dilution factor used.

   3. (3) Commissioner Approval The commissioner may approve or deny in writing a request for a release-specific alternative surface-water protection criteria or an alternative method of demonstrating compliance with surface-water protection criteria. No request under this subdivision shall be approved until it is demonstrated to the commissioner’s satisfaction that such alternative criteria or alternative method for demonstrating compliance will protect all existing and proposed uses of surface water and is protective of human health and the environment. A request for such approval shall be submitted to the commissioner in accordance with section 22a-134tt-1(c) of the RBCRs. Upon receipt of such request, the commissioner shall specify which of the following shall be provided to the commissioner:

      1. (A) The Q99 stream flow rate of the surface water body into which the subject groundwater plume discharges;
      2. (B) The identification of other surface water or groundwater discharges to the surface water body within one-half mile of the areal extent of the subject groundwater plume;
      3. (C) A report on the instream water quality into which the subject groundwater plume discharges, including assessment and use attainment information in the most current integrated water quality report and any applicable total maximum daily loads; and(D) The flow rate of the subject groundwater plume that discharges to the surface water body and the extent and degree of mixing of such discharge in such surface water.

4. (c) Volatilization Criteria (1) Volatilization Criteria for Groundwater (A) Residential Volatilization Criteria Unless otherwise specified in this subsection, each volatile organic substance in groundwater shall be remediated to a concentration that is equal to or less than the residential volatilization criteria for groundwater.

   1. (B) Industrial/Commercial Volatilization Criteria Each volatile organic substance in groundwater may be remediated to a concentration that is equal to or less than the industrial/commercial volatilization criteria for groundwater, provided that the subject area above the groundwater polluted with volatile organic substances:

5. (i) Is not used for residential activity;

   1. (ii) Has limited access only to those individuals working at or temporarily visiting for industrial/commercial activity; and(iii) An EUR is in effect for the subject area or the entire parcel, which restriction shall:

   2. (I) Prohibit residential activity;

      1. (II) Require compliance with clause (ii) of this subparagraph.
   3. (C) Applicability of Volatilization Criteria Subdivision (1) of this subsection shall apply to:

6. (i) Volatile organic substances, other than volatile petroleum substances, within 30 feet or less of the ground surface and within 30 feet or less of the lowest portion of a building under which groundwater is polluted with such substances; and(ii) Volatile petroleum substances, within 10 feet or less of the ground surface and within 10 feet or less of the lowest portion of a building under which groundwater is polluted with such substances.

   1. (2) Alternative Demonstration of Compliance with Volatilization Criteria for Groundwater (A) Soil Vapor Below a Building For volatile organic substances in groundwater, remediation to the volatilization criteria specified in subdivision (1) of this subsection shall not be required if the concentration of such substances in soil vapors below a building is equal to or less than:

      1. (i) The residential volatilization criteria for soil vapor; or(ii) The industrial/commercial volatilization criteria for soil vapor, provided the requirements of subdivision (1)(B) of this subsection are satisfied.
      2. (B) Concentrations at the Water Table For volatile organic substances in groundwater, remediation to the volatilization criteria specified in subdivision (1) of this subsection shall not be required if the substances in groundwater exceeding volatilization criteria are not at the water table and all of the laboratory analytical results from sampling the concentration of such substances at the water table, as seasonally demonstrated by groundwater monitoring representative of the uppermost portion of the water column are equal to or less than:

7. (i) The residential volatilization criteria for groundwater; or(ii) The industrial/commercial volatilization criteria for groundwater, provided the requirements of subdivision (1)(B) of this subsection are satisfied.

   1. (3) Exemption from Volatilization Criteria for Groundwater through Vapor Mitigation For volatile organic substances in groundwater beneath an existing building, remediation to the volatilization criteria for groundwater specified in subdivision (1) of this subsection shall not be required, provided that:

      1. (A) Measures to prevent the migration of volatile organic substances into any overlying building have been implemented and submitted to the commissioner in accordance with section 22a-134tt-1(c) of the RBCRs. The submittal shall also include:

8. (i) A brief description of the measures implemented to control the migration of such volatile organic substances into any overlying building;

   1. (ii) A demonstration of the effectiveness of such control measures;
   2. (iii) The plan for monitoring the effectiveness of such control measures over time and maintaining such control measures in good condition; and(iv) A map showing all existing buildings, the areal extent of the groundwater plume, and the location of such control measures;
   3. (B) The commissioner deems the measure proposed under subparagraph (A) of this subdivision acceptable and such measures have been and continue to be implemented and monitored; and(C) An EUR, or other permanent control measures approved in writing by the commissioner, is or will be in effect for the subject area, which restriction or control measure shall:

9. (i) Prohibit removal of any building above such volatile organic substances in groundwater; and(ii) Require compliance with:

   1. (I) Control measures deemed acceptable by the commissioner under subparagraphs (A) and (B) of this subdivision; and(II) Any condition specified by the commissioner in the approval of such permanent control measures under this subparagraph.

   2. (4) Alternative Release-Specific Volatilization Criteria and Alternative Method of Demonstrating Compliance with Volatilization Criteria With respect to volatile organic substances in groundwater or soil vapor for which volatilization criteria are specified in sections 22a-134tt-App6 or 22a-134tt-App7 of the RBCRs or approved by the commissioner pursuant to subsection (i)(3) of this section, the commissioner may approve or deny in writing a request for a release-specific alternative volatilization criteria. In addition, the commissioner may approve or deny in writing an alternative method of determining compliance with such criteria.

      1. (A) A request for approval of alternative volatilization criteria or for an alternative method of demonstrating compliance with volatilization criteria shall be submitted to the commissioner in accordance with section 22a-134tt-1(c) of the RBCRs, and shall also include:

10. (i) A description of the distribution and concentration of volatile organic substances in groundwater or soil vapor beneath any overlying building;

    1. (ii) A description of any site-specific conditions, including, but not limited to, the value of all terms used and the source of any release-specific values.
    2. (B) No request under subparagraph (A) of this subdivision shall be approved unless such request demonstrates to the commissioner’s satisfaction that such criteria or alternative method of determining compliance is protective of human health and will ensure that volatile organic substances in groundwater or soil vapor do not accumulate in the air of any building at a concentration which:

11. (i) For any carcinogenic substance, creates a risk to human health in excess of a 10^-6 excess lifetime cancer risk level, and, for any non-carcinogenic substance, does not exceed a hazard index of 1; and(ii) For a groundwater plume or soil vapor polluted with 10 or more volatile organic substances, does not exceed a cumulative excess cancer risk level of 10^-5 for carcinogenic substances, and for non-carcinogenic substances with the same target organ, the cumulative hazard index does not exceed 1.

    1. (C) Any approval of the commissioner under this subdivision, may require that an EUR is or will be in effect for the subject area, which restriction shall enumerate and require compliance with any conditions specified by the commissioner when issuing such approval.

    2. (5) Exemption from Volatilization Criteria for Groundwater Through a No Build Restriction For volatile organic substances in groundwater, remediation to the applicable volatilization criteria specified in subdivision (1) of this subsection shall not be required if the following conditions are satisfied:

       1. (A) The water table is less than 30 feet below the ground surface;
       2. (B) No building exists over the groundwater polluted with such substances at a concentration above applicable volatilization criteria;
       3. (C) One of the following has been satisfied:

12. (i) An EUR is in effect for the subject area, which restriction shall;

    1. (I) Prohibit construction of a building at the subject area; and(II) Require compliance with subparagraph (B) of this subdivision;

       1. (ii) The commissioner has approved in writing a request demonstrating that no building can reasonably be expected to be constructed over the subject groundwater; or(iii) The commissioner has approved in writing a request demonstrating that natural attenuation or other methods of remediation will, within 5 years, reduce the concentration of volatile organic substances in such groundwater to a concentration equal to or less than:
    2. (I) Residential volatilization criteria; or(II) The industrial/commercial volatilization criteria, in which case subdivision (1)(B) of this subsection shall apply; and(D) For any volatile organic substances, other than volatile petroleum substances, that exceed the applicable volatilization criteria within 30 feet of any part of a building, the potential for a vapor intrusion pathway into such building shall be thoroughly evaluated. If such evaluation identifies a vapor intrusion pathway into such building, compliance with subdivision (3) of this subsection shall be required.

    3. (6) Exemption from Volatilization Criteria Through Indoor Air Monitoring For volatile organic substances in groundwater, remediation to the applicable volatilization criteria specified in subdivision (1) of this subsection shall not be required for groundwater underlying an existing building, provided a request is approved pursuant to subparagraph (A) of this subdivision. No request under subparagraph (A) of this subdivision shall be approved unless such request demonstrates to the commissioner’s satisfaction that the conditions in the building overlying volatile organic substances in groundwater are protective of human health and the environment.

       1. (A) A request in accordance with this subdivision shall be submitted to the commissioner in accordance with section 22a-134tt-1(c) of the RBCRs, and shall also include:

13. (i) The acknowledgement and consent of the owner of the building for which approval of the air monitoring program is sought; and(ii) An indoor air monitoring program and measures to control the level of any such volatile organic substances in the air of the subject building, including, but not limited to:

    1. (I) A description of the distribution and concentration of volatile organic substances beneath the building;

       1. (II) Any measures to be taken;
       2. (III) The location of proposed monitoring points;
       3. (IV) The proposed frequency of monitoring;
    2. (V) The parameters to be monitored; and(VI) The actions to be taken in the event such monitoring indicates that selected parameters are exceeded.
    3. (B) The commissioner may approve or deny in writing a request submitted under this subdivision. Approval of any indoor air monitoring program pursuant to this subdivision shall require that an ELUR is or will be in effect for the subject area, which restriction shall require compliance with the indoor air monitoring program approved by the commissioner in writing, including any conditions imposed by the commissioner when approving such program.
    4. (7) For the purposes of this subsection, “building” means any structure enclosed by a roof and walls that is capable of accumulating vapors from the subsurface.

14. (d) Groundwater Protection Criteria (1) Exemption from Attaining Background Concentration in a GA Area For substances in groundwater in a GA area, remediation to the background concentration shall not be required if the concentration of each substance in a groundwater plume is equal to or less than the groundwater protection criteria and 1 of the following conditions exist:

    1. (A) (i) A public water supply distribution system is available within 200 feet of the parcel on which the release area is located, within 200 feet of all adjacent parcels, and within 200 feet of any parcel within the areal extent of the groundwater plume;

       1. (ii) Such groundwater plume is not located in an aquifer protection area; and(iii) Such groundwater plume is not located within the area of influence of any public drinking water supply well;
    2. (B) Prior to any soil or groundwater remediation, the groundwater plume is a diminishing state groundwater plume; or(C) Each substance in groundwater is remediated to a concentration equal to or less than the groundwater protection criteria, and further reduction of the concentrations of such substances to the background concentration cannot be achieved using sound engineering and hydrogeologic remediation practices.
    3. (2) Alternative Groundwater Protection Criteria With respect to substances in groundwater for which groundwater water protection criteria are specified in section 22a-134tt-App4 of the RBCRs, or approved by the commissioner pursuant to subsection (i)(1) of this section, alternative groundwater protection criteria may be calculated by an LEP pursuant to subdivision (3) of this subsection or approved in writing by the commissioner pursuant to subdivision (4) or (5) of this subsection.

    4. (3) LEP Calculation of Alternative Groundwater Protection Criteria (A) For a substance in groundwater located in an area designated on the department’s “Potential Alternative Groundwater Protection Criteria Map” in section 22a-134tt-App-10 of the RBCRs, alternative groundwater protection criteria may be calculated by an LEP, in accordance with subparagraph (B) or (C) of this subdivision, as applicable, provided that:

       1. (i) Written notice of the use of alternative groundwater protection criteria is submitted to the commissioner in accordance with section 22a-134tt-1(c) of the RBCRs, and any such notice includes:

       2. (I) The alternative groundwater protection criteria calculation in accordance with subparagraph (B) or (C) of this subdivision; and(II) Documentation demonstrating compliance with the requirements of this subdivision, including, but not limited to, a water supply well receptor survey;

          1. (ii) Any alternative groundwater protection criteria shall not exceed:

       3. (I) 100 times the groundwater protection criteria specified in section 22a-134tt-App4 of the RBCRs or approved by the commissioner in accordance with subsection (i)(1) of this section; and(II) The residential volatilization criteria for groundwater specified in section 22a-134tt-App6 of the RBCRs or approved by the commissioner in accordance with subsection (i)(3) of this section;

          1. (iii) No public or private drinking water supply well is present on any subject parcel within or adjacent to the areal extent of the portion of the subject groundwater plume in which a substance exceeds the background concentration;
          2. (iv) A public water supply distribution system is available within 500 feet downgradient and 200 feet in any direction of the subject groundwater plume;
          3. (v) All releases to soil that constitute a source of pollution resulting in the subject groundwater plume have been remediated so there is no longer an ongoing source in soil impacting groundwater;
          4. (vi) No alternative pollutant mobility criteria is used for the same substance for which an alternative groundwater protection criteria is used;
          5. (vii) The subject groundwater plume is a diminishing state groundwater plume; and(viii) The alternative groundwater protection criteria being calculated is not used for any portion of the subject groundwater plume located in bedrock unless approved by the commissioner in accordance with subdivision (5) of this subsection.

       4. (B) For volatile organic substances, the following equation shall be used to calculate alternative groundwater protection criteria in accordance with this subparagraph:
          >
          TermsDescriptionValueUnitsAlternative GWPCCriteria in groundwater as alternative to groundwater protection criteriacalculatedµg/LTACTarget Indoor Air Concentration as approved by the commissioner in accordance with section 22a-134tt-App8 of the RBCRssubstance-specificµg/m³fFraction of substance concentration volatilized0.5unitlessHVHouse Volume1,000m³ERAir exchange rate per day, as a time weighted average134times per dayMCMixing coefficient0.33noneWFRWater Flow Rate3,183L/day(C) For semi-volatile organic substances, inorganic substances and pesticides, the following equation shall be used to calculate alternative groundwater protection criteria in accordance with this subparagraph: Alternative GWPC = WSF x RSC x DEC x UCFTermsDescriptionValueUnitsAlternative GWPCCriteria in groundwater as alternative to groundwater protection criteriacalculatedµg/LWSFWater to soil concentration factor, based upon accumulation of arsenic in soil0.02(mg/L)/(mg/kg)RSCRelative source contribution to account for other background contributions t in soil0.2unitlessDECResidential direct exposure criteria in section 22a-134tt-App2 of the RBCRs or criteria approved by the commissioner pursuant to section 22a-134tt-9(b)(7) of the RBCRsSubstance Specificmg/kgUCFUnit Conversion Factor1,000µg/mg(4) Commissioner Approval of Alternative Groundwater Protection Criteria Not In Mapped Areas For a substance in groundwater that is not located in an area designated on the department’s “Potential Alternative Groundwater Protection Criteria Map” in section 22a-134tt-App10 of the RBCRs, the commissioner may approve or deny in writing a request for an alternative groundwater protection criteria pursuant to this subparagraph. A request for such alternative groundwater protection criteria shall be submitted to the commissioner in accordance with section 22a-134tt-1(c) of the RBCRs. No request shall be approved unless such request demonstrates to the commissioner’s satisfaction:

          1. (A) Compliance with the requirements of clauses (i) to (viii), inclusive, of subdivision (3)(A) of this subsection;
          2. (B) Calculation of proposed alternative groundwater protection criteria in accordance with subparagraphs (B) and (C) of subdivision (3) of this subsection, as applicable; and(C) Compliance with clause (i) or (ii) of this subparagraph:

15. (i) Documentation from a public or private water company subject to regulation by the Department of Public Health demonstrating that public drinking water is available in the area where the subject groundwater plume is located, including a public water service area map on file with the Department of Public Health indicating that public water is available. This clause can be used only if;

    1. (I) A public water supply distribution system has become available to any parcel within or adjacent to the areal extent of the portion of the groundwater plume not previously included on the department’s “Potential Alternative Groundwater Protection Criteria Map” in section 22a-134tt-App10 of the RBCRs; and(II) The subject groundwater plume is not located in an aquifer protection area or in an aquifer suitable for development of a public water supply.

       1. (ii) As a result of stratified drift aquifer conditions where the subject groundwater plume is located:
    2. (I) The aquifer is not suitable for development of a public water supply due to the hydrogeology, depth, saturated thickness of the surficial materials or other hydrogeologic factors(II) There is less than 20 feet of saturated sand or sand and gravel in such aquifer or pumping more than 15 gallons per minute from such aquifer is not sustainable for public water use; and(III) A cross-sectional map is provided showing the nature and distribution of surficial materials in such aquifer.

    3. (5) Commissioner Approval of Alternative Groundwater Protection Criteria Where Any Portion of a Plume Is In Bedrock For a substance in groundwater that is located in an area designated on the department’s “Potential Alternative Groundwater Protection Criteria Map” in section 22a-134tt-App10 of the RBCRs, and where the portion of the groundwater plume is located in bedrock. A request for such alternative groundwater protection criteria shall be submitted to the commissioner in accordance with section 22a-134tt-1(c) of the RBCRs. No request shall be approved unless such request includes a map showing the horizontal and vertical extent of the bedrock groundwater plume that exceeds or could be expected to exceed the groundwater protection criteria and demonstrates to the commissioner’s satisfaction:

       1. (A) Compliance with the requirements of clauses (i) to (vii), inclusive, of subdivision (3)(A) of this subsection; and(B) That the groundwater plume that exceeds the groundwater protection criteria will not pose a risk to human health and the environment.

16. (e) Technical Impracticability Variance Groundwater may be eligible for a variance from compliance with the surface-water protection criteria or the groundwater protection criteria if the commissioner determines that compliance with such criteria is technically impracticable. No request for a variance shall be approved unless such request demonstrates to the commissioner’s satisfaction that the requirements of this subsection have been satisfied.

    1. (1) Request for Technical Impracticability Variance (A) A request for a technical impracticability variance shall be submitted to the commissioner in accordance with section 22a-134tt-1(c) of the RBCRs, and shall also include:

       1. (i) The substance and its concentration in the groundwater plume for which a variance is sought;
       2. (ii) A map showing the horizontal and vertical extent of the groundwater plume that exceeds or could be expected to exceed surface-water protection criteria or groundwater protection criteria;
       3. (iii) A demonstration of compliance with the soil standards in section 22a-134tt-9 of the RBCRs, and unless it is demonstrated that remediation of soil is technically impracticable, that polluted soil is not contributing to the groundwater plume;
       4. (iv) Laboratory analytical results of all representative sampling before, during, and after the implementation of such actions and a description of all actions to remediate the groundwater plume;
       5. (v) A feasibility study for achieving compliance with the criteria for which a variance is sought that evaluates remediation methods and demonstrates that achieving compliance with such criteria in a reasonable timeframe is technically impracticable;
       6. (vi) A demonstration that the subject groundwater plume is in a steady-state or is a diminishing state groundwater plume, or that the subject groundwater plume is hydraulically controlled;
       7. (vii) A map and description of the proposed TI zone, including the identification of existing groundwater withdrawals and potential for future withdrawal of groundwater on parcels within and adjacent to the proposed TI zone, and a demonstration that such withdrawals will not induce movement of the subject groundwater plume into uncontaminated areas or adversely affect the protectiveness of the proposed variance;
       8. (viii) A study to determine the risks posed by the polluted groundwater that would remain if a variance was granted. If such study shows a risk or a potential risk to human health or the environment, a contingency plan to eliminate or minimize such risk shall be included;
       9. (ix) Measures for long-term monitoring, operation, maintenance, and reporting, to ensure that the selected remedy remains effective in its protectiveness. Such measures shall:

       10. (I) Demonstrate through groundwater monitoring that the groundwater plume is not increasing in size or concentration, or otherwise migrating in a manner that would alter the risk assumptions of clause (viii) of this subparagraph;

           1. (II) Confirm that unacceptable risks to human health and the environment do not occur and if such risks do occur, contingency actions will be taken to abate such risks, including, but not limited to, changes in land use; and(III) Demonstrate through monitoring that any proposed operation and maintenance controls are working properly and remain effective; and(x) The type and estimated amount of financial assurance to be posted in accordance with the requirements of section 22a-134tt-7(c) of the RBCRs.
       11. (B) Based upon the information submitted in accordance with subparagraph (A) of this subdivision, the commissioner shall indicate, in writing, either that a groundwater plume does not qualify for a variance under this subsection, or alternatively, that the information specified in subdivision (2) of this subsection shall be submitted and may include conditions the commissioner deems appropriate to protect public health and the environment.

    2. (2) Additional Information to be Submitted Upon Request After submission of the information required in this subdivision, the commissioner may approve or deny in writing a request for a technical impracticability variance. Unless otherwise specified by the commissioner, the following information shall be submitted within 120 days of a request for such information by the commissioner. The information shall be submitted to the commissioner in accordance with section 22a-134tt-1(c) of the RBCRs, and shall also include:

       1. (A) A demonstration that public notice has been provided in accordance with section 22a-134tt-7(d) of the RBCRs;
       2. (B) A certification that written notice of the extent and degree of such pollution allowed to remain in place has been provided to each owner of record of each parcel within the TI zone, at the address for such owner on the last-completed grand list of the municipality where the parcel is located, and to the Director of Health of the municipality or municipalities in which the TI zone is located;
       3. (C) If the commissioner has specified that an ELUR is required, the acknowledgement and consent from the owner of each parcel in the TI zone to such variance;
       4. (D) A demonstration that financial assurance has been obtained in accordance with section 22a-134tt-7(c) of the RBCRs; and(E) A demonstration, as specified by the commissioner in the written request for information under this subdivision, that either an ELUR is in effect on each parcel in the TI zone or other permanent control measure is in place. Any ELUR or other permanent control measure shall:

17. (i) Require compliance with the plan and measures specified in clauses (viii) and (ix) of subdivision (1)(A) of this subsection;

    1. (ii) Include conditions the commissioner deems appropriate to protect public health and the environment;
    2. (iii) In addition to any requirement in the EUR regulations, require the preparation of a report every 5 years, which reviews the implementation and effectiveness of the variance approved by the commissioner, including, but not limited to, the impact of the use of groundwater on parcels adjacent to the TI zone. Such reports shall be maintained by the parcel owner who is requesting such variance until the technical impracticability variance is no longer required under this subsection and shall be provided to the commissioner upon request; and(iv) In addition, for a variance from compliance with the groundwater protection criteria:
    3. (I) Prohibit the use of groundwater for drinking or other purposes; and(II) Prohibit the withdrawal of groundwater, unless a withdrawal has been approved in writing by the commissioner.

18. (f) Conditional Exemption for Incidental Sources Compliance with the groundwater criteria specified in subsection (a) of this section is not required for the following substances in groundwater under the circumstances described in this subsection:

    1. (1) Trihalomethanes or any other substance within drinking water released from a public water supply distribution system; or(2) Metals, petroleum hydrocarbons, or semi-volatile organic substances, provided such substances are the result of:

       1. (A) An incidental release due to the normal operation of motor vehicles, not including refueling, repair or maintenance of a motor vehicle; or(B) Normal paving and maintenance of a consolidated bituminous concrete surface provided such bituminous concrete surface has been maintained for its intended purpose.

19. (g) Conditional Exemption for Groundwater Polluted with Pesticides Compliance with the groundwater criteria specified in subsection (a) of this section is not required for pesticides in groundwater resulting from the application of pesticides at the release area, provided that:

    1. (1) A determination has been made that such pesticides are present solely as a result of the application of pesticides;
    2. (2) Compliance with the soil standards in section 22a-134tt-9 of the RBCRs has been achieved for any release of pesticides;
    3. (3) The nature and approximate extent of pesticides in the groundwater has been evaluated;
    4. (4) Potable water supply wells on the parcel where pesticides are in groundwater have been sampled and any exposure pathway to drinking water in such wells is eliminated or mitigated to the extent necessary to protect human health;
    5. (5) A potable water supply well receptor survey identifying surrounding drinking water uses has been conducted;
    6. (6) With respect to the parcel for which a demonstration of compliance with the RBCRs is being made, if pesticides in the groundwater on such parcel exceed the groundwater criteria notice is recorded on the municipal land records identifying such exceedance;
    7. (7) If pesticides applied at a parcel, for which a demonstration of compliance with the RBCRs is being made, are present in groundwater on other parcels at concentrations exceeding the groundwater criteria, best efforts have been made to ensure that an EUR has been placed which provides notice that pesticides in groundwater on such affected parcels exceeds the groundwater criteria. A certification stating such best efforts have been made shall be submitted with the notice required under subdivision (8) of this section; and(8) Notice of compliance with the requirements of this subsection, including all documents demonstrating such compliance, is submitted to the commissioner in accordance with section 22a-134tt-1(c) of the RBCRs, and is also submitted to the Director of Health of the municipality in which such pesticides in groundwater are located.

20. (h) Applying the Groundwater Criteria Compliance with the standards for groundwater in this section, or standards specified in section 22a-134tt-9 of the RBCRs that refer to or require groundwater monitoring, shall be based upon groundwater monitoring conducted in compliance with this subsection.

    1. (1) Groundwater monitoring shall be capable of determining:

       1. (A) The conceptual site model for the release is valid;
       2. (B) The background concentration at the nearest location upgradient of and unaffected by the release;
       3. (C) The effectiveness of any soil remediation to prevent the pollution of groundwater by substances from the release area;
       4. (D) The effectiveness of any measures to render soil environmentally isolated;
       5. (E) The effectiveness of any remediation to eliminate or minimize any risks to human health and the environment associated with each release being remediated, including, but not limited to, any risks identified during remediation or identified in any risk assessment conducted in accordance with subsection (e)(1) of this section;
       6. (F) Whether the concentration of a substance in groundwater is equal to or less than the applicable groundwater criteria for such substance;
       7. (G) Whether a groundwater plume in a GB area interferes with any existing use of groundwater, including, but not limited to, a drinking water supply or an industrial, agricultural, or commercial use of groundwater; and(H) The effectiveness of monitored natural attenuation to achieve compliance with groundwater criteria within a reasonable timeframe.

    2. (2) Pre-requisites for Determining Compliance with Groundwater Criteria The groundwater samples that will be used in determining compliance with an applicable criteria for a substance shall be collected after:

       1. (A) All active remediation of soil and groundwater conducted to achieve compliance with pollutant mobility criteria and the applicable groundwater criteria for such substance have been concluded, other than natural attenuation of a groundwater plume or the recording of an EUR;
       2. (B) The aquifer is no longer subject to the transient effects on hydraulic head attributable to withdrawal from or injection to groundwater for the purpose of remediation, or other effects due to site redevelopment or remediation;
       3. (C) Any changes to the geochemistry induced by remedial actions or monitoring well construction methods that might influence the concentration of such substance have stabilized and equilibrium geochemical conditions are established; and(D) The groundwater plume is a diminishing state groundwater plume.

    3. (3) Determining Compliance with Groundwater Criteria With the exception of monitoring conducted in accordance with subparagraph (B)(ii) or (C)(ii) of this subdivision, when determining compliance with applicable groundwater criteria for substances, a minimum of 4 sampling events shall be performed which reflect seasonal variability on a quarterly basis, provided that all sampling events used to demonstrate compliance are performed within 2 years prior to the most current sampling event used to determine compliance, and shall comply with this subdivision.

       1. (A) Determining Compliance with Groundwater Protection Criteria or the Background Concentration Compliance with the groundwater protection criteria or the background concentration for each substance in groundwater is achieved when sampling locations used for compliance are representative of the subject groundwater plume, and either:

21. (i) All laboratory analytical results for such substance at all sampling locations are equal to or less than the groundwater protection criteria or the background concentration, whichever is applicable; or(ii) The 95 percent upper confidence level of the arithmetic mean of a statistically representative sampling data set consisting of all laboratory analytical results for such substance for no less than 12 consecutive monthly samples, calculated individually for each sampling location, is equal to or less than the groundwater protection criteria or the background concentration, whichever is applicable.

    1. (B) Determining Compliance with Surface-Water Protection Criteria or Water Quality Criteria Compliance with the surface-water protection criteria for each substance groundwater is achieved when sampling locations are representative of the subject groundwater plume, and either:

22. (i) For sample locations in that portion of such groundwater plume which is upgradient of the area at which such groundwater discharges to the receiving surface water body:

    1. (I) All laboratory analytical results for such substance are less than or equal to the surface-water protection criteria or, if applicable, the water quality criteria; or(II) 95 percent upper confidence level of the arithmetic mean of a statistically representative sampling data set consisting of all laboratory analytical results for such substance for no less than 12 consecutive monthly samples, calculated individually for each sampling location, is equal to or less than the surface-water protection criteria or, if applicable, the water quality criteria; or(ii) The 95 percent upper confidence level of the arithmetic mean of a statistically representative sampling data set consisting of all laboratory analytical results for such substance in the entire groundwater plume, collected to reflect seasonal variability on a quarterly basis, is equal to or less than the surface-water protection criteria or, if applicable, water quality criteria.

    2. (C) Determining Compliance with Volatilization Criteria (i) Compliance with volatilization criteria for each substance in groundwater is achieved when the sampling is representative of the subject groundwater plume and all laboratory analytical results for such substance are equal to or less than the applicable volatilization criteria for groundwater.

       1. (ii) Compliance with volatilization criteria for each substance in soil vapor is achieved when the sampling is representative of the subject soil vapor, including during the heating and cooling seasons, and the results of all laboratory analytical results for such substance are equal to or less than the applicable volatilization criteria for soil vapor.
    3. (D) Alternative Methods to Determine Compliance with the Groundwater Criteria The commissioner may approve or deny in writing a request for an alternative to the methods prescribed in this subdivision to determine compliance with an applicable groundwater criteria. Such proposed alternative methods may be based upon emerging technologies and approaches for which guidance, a standard, or an industrial code has been published by a regulatory agency, governmental advisory group, or other recognized professional organization. A request under this subdivision shall be submitted to the commissioner in accordance with section 22a-134tt-1(c) of the RBCRs, and shall include any information the commissioner deems necessary to evaluate such request. Any approval by the commissioner may specify conditions necessary to protect human health and the environment.
23. (i) Additional Polluting Substances (1) Groundwater Protection Criteria for Additional Polluting Substances (A) Any substance in groundwater for which a groundwater protection criterion is not specified in section 22a-134tt-App4 of the RBCRs, shall be remediated to the background concentration or to criteria obtained pursuant to this subdivision. A request under this subdivision shall be submitted to the commissioner in accordance with section 22a-134tt-1(c) of the RBCRs, and shall also include:

24. (i) A proposed risk-based groundwater protection criteria for each substance calculated in accordance with section 22a-134tt-App8 of the RBCRs;

    1. (ii) The laboratory reporting limit for each substance;
    2. (iii) A description of the organoleptic properties of each substance; and(iv) Any information about the health effects such substance may cause due to exposure not accounted for in the proposed risk-based groundwater protection criteria.
    3. (B) The commissioner may approve or deny in writing a request made under subparagraph (A) of this subdivision. No request shall be approved unless it is demonstrated to the commissioner’s satisfaction that the requirements of this subdivision have been satisfied and that the proposed groundwater protection criteria will be protective of human health and the environment.
    4. (C) Unless prohibited in writing by the commissioner, criteria approved by the commissioner pursuant to subparagraph (B) of this subdivision may be the subject of a request for alternative criteria under subsection (d)(2) of this section.

    5. (2) Surface-Water Protection Criteria for Additional Polluting Substances (A) Any substance in groundwater for which a surface-water protection criterion is not specified in section 22a-134tt-App5 of the RBCRs or for which there are no water quality criteria, shall be remediated to the background concentration or to criteria obtained pursuant to this subdivision. A request under this subdivision shall be submitted to the commissioner in accordance with section 22a-134tt-1(c) of the RBCRs, and shall also include:

       1. (i) A proposed risk-based surface-water protection criteria for each substance calculated in accordance with section 22a-134tt-App8 of the RBCRs;
       2. (ii) The laboratory reporting limit for each substance;
       3. (iii) A description of the bioaccumulative properties of each substance; and(iv) Any information about the ecological effects each substance may cause due to exposure not accounted for in the proposed risk-based surface-water protection criteria.
       4. (B) The commissioner may approve or deny in writing a request made under subparagraph (A) of this subdivision. No request shall be approved unless it is demonstrated to the commissioner’s satisfaction that the requirements of this subdivision have been satisfied and that the proposed surface-water protection criteria will be protective of human health and the environment.
       5. (C) Unless prohibited in writing by the commissioner, criteria approved by the commissioner pursuant to subparagraph (B) of this subdivision, may be the subject of a request for alternative criteria under section 22a-134tt-10(b) of the RBCRs.

    6. (3) Volatilization Criteria for Additional Polluting Substances (A) Any substance in groundwater for which a volatilization criterion is not specified in section 22a-134tt-App6 or 22a-134tt-App7 of the RBCRs, shall be remediated to the background concentration or to criteria obtained pursuant to this subdivision. Such request may include target indoor air concentrations and volatilization criteria to apply to such substances in groundwater or soil vapor. A request under this subdivision shall be submitted to the commissioner in accordance with section 22a-134tt-1(c) of the RBCRs, and shall also include:

       1. (i) A risk-based target indoor air concentration or volatilization criteria for each substance calculated in accordance with section 22a-134tt-App8 of the RBCRs;
       2. (ii) The laboratory reporting limit for each substance;
       3. (iii) A description of the odor threshold of each substance; and(iv) Any information about the health effects each substance may cause due to exposure not accounted for in the proposed risk-based volatilization criteria.
       4. (B) Such volatilization criteria shall ensure that such target indoor air concentrations will not be exceeded above the polluted groundwater.
       5. (C) The commissioner may approve or deny in writing a request made under subparagraph (A) of this subdivision. No request shall be approved unless it is demonstrated to the commissioner’s satisfaction that the requirements of this subdivision have been satisfied and that the proposed volatilization criteria will be protective of human health and the environment.
       6. (D) Unless prohibited in writing by the commissioner, criteria approved by the commissioner pursuant to subparagraph (C) of this subdivision, may be the subject of a request for alternative criteria under section 22a-134tt-10(c)(4) of the RBCRs.
25. (j) Additional Remediation of Groundwater Nothing in the RBCRs shall preclude the commissioner from taking any action authorized by chapter 446k of the Connecticut General Statutes necessary to prevent or abate pollution, or to prevent or abate any threat to human health or the environment. If the presence of any substance impairs the aesthetic quality of any groundwater which is or can reasonably be expected to be a source of water for drinking or other uses, additional remediation shall be conducted in order to reduce the concentration of such substance to a concentration appropriate for such use.

(Effective March 1, 2026)