View source for SVPLTR 25-0032, 2024 Annual Rgp Monitoring Report

{{Adams
| number = ML25121A290
| issue date = 04/30/2025
| title = 2024 Annual Rgp Monitoring Report
| author name = Golia R
| author affiliation = AMO Environmental Decisions, Constellation Energy Generation, LLC
| addressee name = 
| addressee affiliation = NRC/NMSS, NRC/NRR, NRC/Document Control Desk
| docket = 05000010, 05000237, 05000249
| license number = DPR-019, DPR-002, DPR-025
| contact person = 
| case reference number = SVPLTR 25-0032
| package number = ML25121A287
| document type = Environmental Monitoring Report, Letter type:SVPLTR
| page count = 1
}}

=Text=
{{#Wiki_filter:875 North Easton Road Suite 10 Doylestown, PA 18902 Geologists Hydrogeologists GIS Analysts Environmental Scientists 215-230-8282 (Phone) 215-230-8283 (Fax) www.amoed.com Dresden 2024 Summary Report - Text April 30, 2025 Constellation Energy Company, LLC Dresden Generating Station 6500 North Dresden Road Morris, IL 60450-9709 

==Subject:==
2024 Annual RGPP Monitoring Report Summary of Results and Conclusions Dresden Generating Station Morris, Illinois This letter report presents the summary of Radiologic Groundwater Protection Plan (RGPP) results for the 2024 groundwater and surface water monitoring rounds conducted at the Constellation Dresden Generating Station.
RGPP data for previous monitoring rounds is summarized in AMOs semi-annual/quarterly reports. 

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Background===
In 2006, Conestoga-Rovers & Associates (CRA) was retained by Exelon Nuclear (now Constellation Energy Generation) to perform a hydrogeologic investigation at the Dresden Generating Station to evaluate whether groundwater at or near the Station has been impacted by releases of radionuclides. Prior to performing the investigation, CRA evaluated available information concerning historic releases, as well as components, structures, and areas of the facility that have the potential to release radioactive liquid to the environment.
The results of the 2006 investigation identified that almost half of the 39 wells within the protected are showed measurable concentrations of tritium. It was concluded that the tritium in groundwater within the protected area came from historic spills from above ground tanks and leaks of underground lines within the protected area.
Groundwater samples collected outside the protected area showed no detectable tritium for 24 of the 26 wells. The two exceptions for the wells outside the protected area include wells DSP 149(R) and DSP-159-I (M).
The results of the fleet wide study for the Dresden Generating Station (the Station) are presented in the report, entitled Hydrogeologic Investigation Report, Fleetwide Assessment, Dresden Generating Station, Morris, Illinois (Conestoga-Rovers & Associates, September 2006). The referenced report also provides detailed descriptions of the Stations location, surrounding features and land use, subsurface geology and hydrogeology, and a summary of groundwater use in the area of the Station.
GHD completed three five-year update hydrogeologic investigation reports for the Station (NEI 07-07, Hydrogeologic Investigation Report, dated May 2011, December 2015, and December 2020). The reports summarized station activities since the 2006 hydrogeologic investigation, including changes at the Station that may potentially affect the RGPP, as well as RGPP sampling activities and groundwater flow. Relevant conclusions from the 2020 report are:
Tritium is not migrating off the Station at concentrations greater than the State of Illinois criteria of 200 pCi/L.
Tritium in groundwater was detected at concentrations greater than the USEPA drinking water standard.
The maximum tritium concentration at the end of 2019 was 33,850 pCi/L (MD-11). Tritium concentrations greater than the USEPA drinking water standard were limited to the B CST, south of the Unit 3 Turbine Building.
AMO ENVIRONMENTAL DECISIONS l~ ~ 1i,E~nvironmental Risk & Remediation Consultants 

2024 RGPP Monitoring Report Dresden Generating Station Dresden 2024 Summary Report - Text Page 2 of 9 AMO Environmental Decisions No gamma-radionuclides associated with licensed plant operations were detected at concentrations greater than their respective LLDs.
Select transuranics U-233/234 and U-238 were occasionally detected in several wells since 2016. The concentrations are considered background.
In 2019, Ni-63 was consistently detected in monitoring wells MW-DN-101I and MW-DN-119I. Per revision 9 of the RGPP, and to investigate Ni-63 in groundwater, the Station includes Ni-63 and Fe-55 analysis for all Source wells and all Long-Term Shutdown wells currently sampled as part of the RGPP.
In 2019, multiple Sr-90 concentrations were detected above its LLD. Sr-90 was detected in samples collected from MW-DN-105S three of the four sampling rounds in 2019. Sr-90 was also detected in DSP-108 during the second quarter 2019 RGPP sampling round.
AFE-1 remains an ongoing tritium source to groundwater. No new AFEs were identified in 2020.
Extraction well RW-DN-100S continued to withdraw tritiated water from the B CST area. Up until August/September 2019, groundwater withdrawal from RW-DN-100S was on an intermittent basis.
Continuous groundwater extraction of RW-DN-100S began in September 2019. As of December 2020, over one million gallons of groundwater was extracted from RW-DN-100S. The extracted groundwater is discharged to the Kankakee River through a permitted outfall (Outfall 002).
The next hydrogeologic investigation update is due by the end of 2025.
B Condensate Storage Tank Elevated tritium concentrations in surface water (Sewage Treatment Plant (STP) samples and RGPP surface water samples), shallow aquifer samples, and intermediate aquifer samples were detected during the 2nd quarter 2014 RGPP sampling round. The source of the tritiated groundwater was determined to be the B Condensate Storage Tank (CST) south of the Turbine Buildings. The groundwater sample collected from shallow aquifer well MD-11, which is in the immediate vicinity of the CST, had a tritium concentration of approximately 1.5 million pCi/L.
Subsequent samples collected from MD-11 have had a maximum tritium concentration of approximately 2.3 million pCi/L (June 27, 2014). The CST was taken out of service and water from the CST removed. The CST was inspected and subsequently repaired in August 2015.
A tritium monitoring plan was developed and implemented in June 2014, with weekly sampling of surface water, storm sewer water, sewer treatment plant water, shallow aquifer groundwater, and intermediate aquifer groundwater to evaluate and delineate the tritium plume. A modified tritium monitoring plan was implemented in November 2014. Based on tritium data collected, the plume was relatively small and only encompassed the area between the CST and Turbine Building.
Two groundwater extraction wells (RW-DN-100S and RW-DN-101S) were installed in January 2015 to assist in the mitigation of tritiated groundwater in the area of the CST. Aquifer testing was completed on the two extraction wells near the end of 2015. Results of the aquifer test concluded that only RW-DN-100S produced sufficient water to operate as a viable groundwater extraction well. RW-DN-100S began intermittent operation during the 1st quarter 2016 and continued operating intermittently through August 2019. In August 2019, the extraction well began pumping groundwater on a continuous basis. The extracted water is discharged to the Kankakee River through NPDES permitted Outfall 002. Overall, tritium concentrations in the area of the CST continue to decrease since the CST was repaired.
As of the end of 2024, the maximum tritium concentration in the area of the CST was approximately 5,700 pCi/L (MD-11). 

2024 RGPP Monitoring Report Dresden Generating Station Dresden 2024 Summary Report - Text Page 3 of 9 AMO Environmental Decisions MW-DN-119I Nickel 63 Hard-to-detect radionuclide Nickel-63 was detected at a concentration over 50 pCi/L in a sample collected during the 2nd quarter 2017. An investigation into the source of the Nickel-63 was completed and additional samples were collected from MW-DN-119I and surrounding wells. Results and recommendations of the evaluation are included in AMOs Evaluation of Nickel -63 detections in MW-DN-119I Update (March 28, 2018). Hard-to-detects (Fe-55 and Ni-63) are currently analyzed annually to monitor concentrations in the area of MW-DN-119I.
As of the end of 2024, Ni-63 was not detected in the sample collected from MW-DN-119I.
Current RGPP Summary Dresden Generating Station has 61 wells (twenty Background wells, twenty Source wells, six Mid-Field wells, ten Long-Term Shutdown wells, and five perimeter wells), that are part of the Station RGPP (EN-DR-408-4160 Revision 10). Figure 1a shows the shallow aquifer RGPP sample locations and Figure 1b shows the intermediate aquifer RGPP sample locations.
RGPP sampling at the Station is performed by ATI, under contract to Constellation. Laboratory testing is performed by Teledyne Brown Engineering. The laboratory data, field data, and depth to water readings are uploaded to the RACER website, which is a data repository for the RGPP sampling rounds. The uploaded data is used by AMO for quarterly RGPP reporting.
Gross-Alpha Alert Level At Dresden Generating Station, gross-alpha (dissolved and suspended fractions) was analyzed annually from 2011 through 2019. In 2020, gross-alpha data was evaluated to establish an Alert Level for the dissolved and suspended gross-alpha fractions. The gross alpha data was evaluated by looking at the average concentration for each gross-alpha fraction for each well. Statistical outlier results were considered during the gross-alpha evaluation. An outlier is a value that is significantly higher or lower than most of the results, that can skew the results and not reflect the true dataset. Therefore, outlier results are not factored into the average gross-alpha concentrations. Outliers were established using methods an online website such as Statisticshowto.com. Additional websites identified similar statistical models for removing outlier data.
Procedure EN-DR-408-4160 (Revision 9) established an Alert Level of three times the ongoing average gross-alpha concentration for each RGPP monitoring well that had gross-alpha analyzed more than one time and that will continue to be monitored for during future RGPP sampling rounds. Note that in 2024, the Alert Level changed from three times the ongoing average to three times the ongoing standard deviation. According to the EN-DR-408-4160 (Revision 10), samples from the eighteen Source designated sample points and ten Long-Term Shutdown designated wells will be analyzed once every two years for gross alpha dissolved and suspended fractions in the future. The Alert Level will be able to account for fluctuations in naturally occurring alpha activity in the area of wells, while identifying a result that may be indicative of a potential release. Beginning in 2021, select transuranics were analyzed if a gross alpha concentration exceeded the Alert Level in a particular well, to ensure that the Alert Level is conservative enough to detect whether licensed material could be present in groundwater. If the results of the select transuranics analysis showed no unusual activity, the gross-alpha result that triggered the select transuranics analysis, was incorporated into the ongoing average concentration for that well.
Table 1 provides a gross-alpha (dissolved and suspended) results summary as well as the average concentration and Alert Level for each well. Gross-alpha analysis was most recently performed on samples collected from Long-Term Shutdown and Source designated wells during the 2nd quarter 2023 RGPP sampling round. Note that a sample could not be collected from Long-Term Shutdown well MW-DN-117I because the well was inaccessible in 2023. Gross-alpha detections did not exceed the Alert Level in samples collected in 2023. Per the RGPP, all Long-Term Shutdown and Source designated wells will have gross-alpha analysis performed again in 2025. 

2024 RGPP Monitoring Report Dresden Generating Station Dresden 2024 Summary Report - Text Page 4 of 9 AMO Environmental Decisions Tritium Dresden Generating Station has 61 monitoring wells that are sampled for tritium. Samples collected from Long-Term Shutdown and Source designated wells are analyzed for tritium quarterly; samples collected from Mid-Field designated wells are analyzed for tritium semi-annually; and samples collected from the Perimeter and Background designated wells are analyzed for tritium annually.
Gamma-Radionuclides Gamma-radionuclide analysis has been performed on RGPP samples (quarterly to annually) at Dresden Generating Station since 2006. This extensive sampling and analysis produced over 18,400 data records for the Station. Station-related gamma-radionuclides have not been detected at concentrations greater than their respective LLDs, in RGPP samples submitted to the vendor laboratory since 2006. Therefore, in the 2020 RGPP, gamma-radionuclide analysis frequency was reduced from annual to every two years.
Samples collected from all wells were most recently analyzed for gamma-radionuclides during the 2nd quarter 2023 RGPP sampling round. Note that a sample could not be collected from Long-Term Shutdown well MW-MW-DN-106S, MW-DN-108I, and DN-117I because the wells were inaccessible in 2023. Station-related gamma radionuclides were not detected at concentrations greater than their respective LLDs in the samples collected in 2023. All wells will have gamma-radionuclide analysis performed again in 2025.
Select Transuranics Select transuranics analysis is procedurally required annually for RGPP sample locations that were identified as Elevated designated wells in the historic EN-DR-408-4160 revisions and continued additional evaluation is warranted. At Dresden Generating Station, these monitoring wells include MW-DN-124S, MW-DN-124I, and MD-
: 11. Additionally, the current RGPP requires select transuranics analysis if a gross alpha concentration exceeds the Alert Level in a particular well, there is an unexpected increase in tritium activity, or if a non-tritium licensed material result exceeds the High Level as established by the RGPP.
Select transuranics analysis was performed on former Elevated designated wells MD-11, MW-DN-124S, and MW-DN-124I, during the 2nd quarter 2024 RGPP sampling round. Select Transuranics were not detected at concentrations greater than their respective LLDs in the samples collected during the 2nd quarter 2024 RGPP sampling round. Table 2 provides a summary of select transuranics results (U-233/234 and U-238) since 2006.
Hard-to-Detects (Fe-55 and Ni-63)
Hard-to-detect analysis (Fe-55 and Ni-63) is procedurally required annually for RGPP sample locations that were identified as Elevated designated wells in the historic EN-DR-408-4160 revisions and continued additional evaluation is warranted, as well as Long-Term Shutdown designated wells. Wells previously designated as Elevated include MW-DN-124S, MW-DN-124I, and MD-11. As part of the current EN-DR-408-4160, hard-to-detect analysis is required on samples collected from Source designated wells once every 5 years, starting in 2021.
Additionally, hard-to-detect analyses is required if there is an unexpected increase in tritium activity, or if a non-tritium licensed material result exceeds the High Level as established by the RGPP.
In 2024, samples collected from the nine Long-Term Shutdown designated wells, one former Elevated designated well, and two Source designated well were analyzed for hard-to-detects (Fe-55 and Ni-63). Fe-55 and Ni-63 were not detected in the samples collected during the 2nd quarter 2024 RGPP sampling round.
Sr-89 and Sr-90 Sr-89 and Sr-90 have been an annual procedurally required analysis on Detection, Long-Term Shutdown, and Elevated designated wells since sample point designations became part of the RGPP in 2010. The current EN-DR-408-4160 states that Sr-89 and 90 analyses should be performed annually for Source and Long-Term Shutdown 

2024 RGPP Monitoring Report Dresden Generating Station Dresden 2024 Summary Report - Text Page 5 of 9 AMO Environmental Decisions designated sample locations. If a positive result is reported, samples collected from the wells with Sr-89 and Sr-90 detections will be analyzed quarterly to evaluate the activity in the area of the well. In 2024, samples were collected from the eighteen Source designated wells, nine Long-Term Shutdown designated wells, and one Mid-Field designated well (former Elevated designation) were analyzed for Sr-89 and Sr-90. Sr-90 was detected in the sample collected from MW-DN-105S (3.1 pCi/L) and DSP-108 (2.67 pCi/L). Sr-89 and Sr-90 were not detected in any of the other samples collected in 2024.
Precipitation Recapture Dresden Generating Station is a Boiling Water Reactor (BWR) generating station. The RGPP requires BWR generating stations to sample precipitation on a semi-annual basis. The RGPP states that a minimum of eight samples should be collected from within the protected area in a manner that surrounds the Turbine Building and Reactor Building as well as ancillary structures that could vent tritiated vapor to the atmosphere.
In 2024, four sample rounds were completed in February, May, August, and November to evaluate if tritium was present in the atmosphere at the Station. Three onsite samples were collected in February; nine onsite samples were collected during the May 2024 sampling; eight onsite samples were collected during the August 2024 sampling; and ten onsite samples were collected during the November 2024 sampling round. A summary of 2024 precipitation recapture results is presented in Table 3 and sample locations are depicted on Figure 3. A summary of historic precipitation recapture results is provided in Appendix A.
Tritium was detected in one or more samples during each of the four sampling rounds completed in 2024. The highest tritium concentrations were reported during the February 2024 precipitation recapture sampling round with detected tritium concentrations ranging between 734 pCi/L (FW-1) and 820 pCi/L (FW-3).
Summary of 2024 RGPP Sampling Rounds February 2024 RGPP Sampling Round Activities (1st Quarter 2024)
Data Summary A total of 30 groundwater samples were collected during the 1st quarter 2024 sampling round. A sample was not collected from MW-DN-117I due to the well being inaccessible during the 1st quarter 2024. Per the RGPP, the Background, Perimeter, and Mid-Field designated wells were not sampled during the 1st quarter 2024 RGPP sampling round. All samples were analyzed for tritium.
Tritium was detected in eight shallow aquifer samples with a maximum tritium concentration of 11,700 pCi/L (RW-DN-101S). Tritium was detected in seven intermediate aquifer samples with a maximum tritium concentration of 1,560 pCi/L (DSP-122).
The tritium concentration in MW-DN-111S averaged 412 pCi/L since the inception of the RGPP in 2006 through the 4th quarter 2019. The tritium concentration in MW-DN-111S increased from approximately 1,000 pCi/L to almost 3,500 pCi/L between the 4th quarter 2019 and 1st quarter 2020. The tritium concentration in the area of this well has been fluctuating between 1,470 pCi/L and 5,530 pCi/L since the 1st quarter 2020. The 1st quarter 2024 RGPP tritium result for this well was 8,560 pCi/L. The Station reviewed documents and performed an assessment of potential tritium sources in the area of MW-DN-111S and did not find any potential sources. The increased tritium activity in this well could be due to historic plumes migrating around the building structures.
The tritium concentration in MW-DN-141S increased from 2,910 pCi/L to 4,430 pCi/L between the 3rd and 4th quarter 2022 RGPP sampling rounds and shows an increasing tritium concentration trend since the beginning of 2022. The 1st quarter 2024 tritium result is similar to those reported in late 2022, at 2,840 pCi/L. It was recommended that the Station evaluate SSCs in the area of MW-DN-141S for potential sources of the increased 

2024 RGPP Monitoring Report Dresden Generating Station Dresden 2024 Summary Report - Text Page 6 of 9 AMO Environmental Decisions tritium activity and sample MW-DN-141S on a monthly basis to further evaluate the tritium concentration in the area of the well.
Tritium concentrations in samples collected from wells (other than MD-11) used to monitor the CST leak have decreased to less than 2,000 pCi/L, indicating the extent of the CST leak is confined to a small geographic area south of the Turbine Building.
Water Elevations All groundwater sample locations, with the exception of MW-DN-117I, had depth to water measurements collected during the 1st quarter 2024 sampling round. The 1st quarter 2024 groundwater elevation data was compared to the 1st quarter 2023 sampling round to evaluate if changes in groundwater elevations occurred that may have an effect on groundwater flow direction. The variations in groundwater elevations have no significant effect on groundwater flow direction. Based on comparison of groundwater elevations, the wells sampled effectively monitored groundwater conditions at the Station.
May 2024 RGPP Sampling Round Activities (2nd Quarter 2024)
Data Summary A total of 58 groundwater samples were collected during the 2nd quarter 2024 sampling round. Samples were not collected from MW-DN-106S, MW-DN-108I, and MW-DN-117I due to inaccessibility or well damage during the 2nd quarter 2024. All samples were analyzed for tritium. The samples collected from Long-Term Shutdown designated wells were also analyzed for hard-to-detects (Fe-55 and Ni-63) and Sr-89/90. Source designated wells were also analyzed for Sr-89/90. Samples collected from mid-field designated well MW-DN-124I; and source designated wells MD-11 and MW-DN-124S were also analyzed for select transuranics and hard-to-detects (Fe-55 and Ni-63).
Tritium was detected in eleven shallow aquifer samples with a maximum tritium concentration of 18,500 pCi/L (RW-DN-101S). Tritium was detected in Thirteen intermediate aquifer samples with a maximum tritium concentration of 1,610 pCi/L (DSP-107).
Elevated tritium activity in the area of MW-DN-111S continued during the 2nd quarter 2024 RGPP sampling round.
The 2nd quarter 2024 RGPP tritium result for MW-DN-111S was 6,850 pCi/L. The increased tritium activity in this well could be due to historic plumes migrating around the building structures.
Tritium concentrations in samples collected from wells (other than MD-11) used to monitor the CST leak have generally decreased to less than 1,000 pCi/L, indicating the extent of the CST leak is confined to a small geographic area south of the Turbine Building.
While the tritium concentration in MW-DN-141S has been decreasing since the end of 2023, concentrations remained elevated in the 2nd quarter 2024. Due to the continued elevated tritium concentrations, it was recommended that the Station evaluate SSCs in the area of MW-DN-141S for potential sources of the increased tritium activity and sample MW-DN-141S on a monthly basis to further evaluate the tritium concentration in the area of the well.
Select transuranics analysis was performed on MD-11, MW-DN-124S, and MW-DN-124I, during the 2nd quarter 2024 RGPP sampling round. Select Transuranics were not detected at concentrations greater than their respective LLDs in the samples collected during the 2nd quarter 2024 RGPP sampling round.
Ni-63 has historically been detected in samples collected from MW-DN-119I and MW-DN-101I. Ni-63 was not detected in any of the samples collected during the 2nd quarter 2024 RGPP sampling round. 

2024 RGPP Monitoring Report Dresden Generating Station Dresden 2024 Summary Report - Text Page 7 of 9 AMO Environmental Decisions Sr-90 has historically been detected in samples collected from MW-DN-105S and DSP-108. However, Sr-90 was not detected in the samples collected from these wells during the 2nd quarter 2024 RGPP sampling round. Sr-90 was also not detected in the other samples collected during the 2nd quarter 2024 RGPP sampling round.
Water Elevations All groundwater sample locations had depth to water measurements collected during the 2nd quarter 2024 sampling round. The 2nd quarter 2024 sampling round groundwater elevation data was compared to the 2nd quarter 2023 sampling round to evaluate if changes in groundwater elevations occurred that may have an effect on groundwater flow direction. The variations in groundwater elevations have no significant effect on groundwater flow direction.
Based on comparison of groundwater elevations, the wells sampled effectively monitored groundwater conditions at the facility.
August 2024 RGPP Sampling Round Activities (3rd Quarter 2024)
Data Summary A total of 31 groundwater samples were collected during the 3rd quarter 2024 sampling round. A sample was not collected from MW-DN-117I due to inaccessibility. All samples were analyzed for tritium. Tritium was detected in eight shallow aquifer samples with a maximum concentration of 6,420 pCi/L (MW-DN-111S). Tritium was detected in seven intermediate aquifer samples with a maximum concentration of 1,370 pCi/L (DSP-122).
Elevated tritium activity in the area of MW-DN-111S continued during the 3rd quarter 2024 RGPP sampling round.
The 3rd quarter 2024 RGPP tritium result for MW-DN-111S was 6,420 pCi/L. The increased tritium activity in this well could be due to historic plumes migrating around the building structures.
Elevated tritium activity in the area of MW-DN-141S continued during the 3rd quarter 2024 RGPP sampling round.
The tritium concentration increased from 1,910 pCi/L to 2,590 pCi/L between the 2nd and 3rd quarter 2024 RGPP sampling rounds. While tritium concentrations are lower than those reported in 2023 it was recommended that the Station evaluate SSCs in the area of MW-DN-141S for potential sources of the increased tritium activity and sample MW-DN-141S on a monthly basis to further evaluate the tritium concentration in the area of the well.
Tritium concentrations in samples collected from wells (other than MD-11) used to monitor the CST leak have generally decreased to less than 1,000 pCi/L, indicating the extent of the CST leak is confined to a small geographic area south of the Turbine Building.
Water Elevations All groundwater sample locations had depth to water measurements collected during the 3rd quarter 2024 sampling round. The 3rd quarter 2024 sampling round groundwater elevation data was compared to the 3rd quarter 2023 sampling round to evaluate if changes in groundwater elevations occurred that may have an effect on groundwater flow direction. The variations in groundwater elevations have no significant effect on groundwater flow direction.
Based on comparison of groundwater elevations, the wells sampled effectively monitored groundwater conditions at the facility.
October 2024 RGPP Sampling Round Activities (4th Quarter 2024)
Data Summary A total of 35 groundwater samples were collected during the 4th quarter 2024 sampling round. A sample was not collected from MW-DN-117I due to the well being inaccessible at the time of the 4th quarter 2024 RGPP sampling.
All samples were analyzed for tritium. Tritium was detected in nine shallow aquifer samples with a maximum concentration of 5,700 pCi/L (MD-11). Tritium was detected in seven intermediate aquifer samples with a maximum concentration of 1,620 pCi/L (MW-DN-114I). 

2024 RGPP Monitoring Report Dresden Generating Station Dresden 2024 Summary Report - Text Page 8 of 9 AMO Environmental Decisions Elevated tritium activity in the area of MW-DN-111S continued during the 4th quarter 2024 RGPP sampling round.
The 4th quarter 2024 RGPP tritium result for MW-DN-111S was 5,570 pCi/L. The increased tritium activity in this well could be due to historic plumes migrating around the building structures.
Elevated tritium activity in the area of MW-DN-141S continued during the 4th quarter 2024 RGPP sampling round. The tritium concentration increased from 2,590 pCi/L to 2,970 pCi/L between the 3rd and 4th quarter 2024 RGPP sampling rounds. While tritium concentrations are lower than those reported in 2023 it was recommended that the Station evaluate SSCs in the area of MW-DN-141S for potential sources of the increased tritium activity and sample MW-DN-141S on a monthly basis to further evaluate the tritium concentration in the area of the well.
Tritium concentrations in samples collected from wells (other than MD-11) used to monitor the CST leak have generally decreased to less than 1,000 pCi/L, indicating the extent of the CST leak is confined to a small geographic area south of the Turbine Building.
Water Elevations All sampled groundwater locations had depth to water measurements collected during the 4th quarter 2024 sampling round. Groundwater elevations and groundwater flow direction for the shallow aquifer are provided on Figure 2a and groundwater elevations and groundwater flow direction for the intermediate aquifer are provided on Figure 2b.
Based on the groundwater flow depicted on figures 2a and 2b, the wells sampled effectively monitored groundwater conditions at the facility.
2025 RGPP Sample Locations Samples could not be collected from MW-DN-106S, MW-DN-108I, and MW-DN-117I in 2024 due to inaccessibility and/or well damage. Not being able to sample these wells and assess data associated with the area of these wells is considered a data gap. Therefore, these wells should be repaired and made accessible to sampling crews to complete the RGPP.
Summary of 2024 RGPP Conformance The Station did not conform with its RGPP in 2024 with respect to RGPP sampling protocol because water levels and samples were not collected from one Background designated well, one Perimeter designated well, and one Long Term Shutdown well. These wells have not been accessible for over two years.
Conclusions Based on the review of the data collected during the 2024 RGPP sampling rounds AMO concludes:
The Station continued to implement the tritium monitoring plan for the B CST. The tritium concentrations in the area of the CST showed a decreasing trend at the Station through 2024. While the tritium concentration in MD-11 decreased from its maximum reported tritium concentration of approximately 2.29 million pCi/L, an elevated concentration persists in the area of the CST. However, tritium concentrations in samples collected from wells (other than MD-11) used to monitor the CST leak have generally decreased to less than 1,000 pCi/L, indicating the extent of the CST leak is confined to a small geographic area south of the Turbine Building.
The tritium concentration in MW-DN-111S averaged 412 pCi/L since the inception of the RGPP in 2006 through the 4th quarter 2019. The tritium concentration in MW-DN-111S increased from approximately 1,000 pCi/L to almost 3,500 pCi/L between the 4th quarter 2019 and 1st quarter 2020. The tritium concentration in the area of this well has been fluctuating between 1,470 pCi/L and 5,530 pCi/L since the 

2024 RGPP Monitoring Report Dresden Generating Station Dresden 2024 Summary Report - Text Page 9 of 9 AMO Environmental Decisions 1st quarter 2020. Tritium concentrations in samples collected from MW-DN-111S showed a decreasing trend in 2024. As of the end of October 2024, the tritium concentration in MW-DN-111S was 5,570 pCi/L.
The increased tritium activity in this well is likely due to historic plumes migrating around the building structures.
The tritium concentration in samples collected from MW-DN-141S ranged between 1,910 pCi/L (May 2024) and 2,970 pCi/L (October 2024).
Hard-to-detects (Fe-55 and Ni-63), select transuranics, and Sr-89/90 were not detected at concentrations greater than their respective LLDs in the samples collected during the 2nd quarter 2024 RGPP sampling round.
Based on recapture tritium results, shallow groundwater could potentially be affected by precipitation recapture.
Samples were not collected from MW-DN-106S, MW-DN-108I, and MW-DN-117I in 2024 due to inaccessibility and/or well damage. Not being able to sample these wells and assess data associated with the area of these wells is considered a data gap.
Based on the evaluation of groundwater flow direction, the wells sampled effectively monitored groundwater conditions at the facility.
Please call me at 215-230-8282 if you have questions.
Respectfully, AMO Environmental Decisions Ralph T. Golia, P.G.
attachments Principal Hydrogeologist File 

Dresden Generating Station Constellation Energy Company Table 1 Summary of Gross-Alpha Results 2021 2023 Feb Mar Jun Dec Mar May Jun Mar Jun Jul May Jun Jun Nov May Jun Aug Oct Feb May Nov Feb Jun Sep Nov May Dec May Jun DSP-105 1.71 4.0577 5.14 0.611 1.15 3.06 1.9 2.5 1.79 1.31 1.39 DSP-106 1.39 2.7094 4.17 1.04 0.744 2.84 1.61 1.77 1.53 1.07 1.1 1.5 2.16 DSP-107 1.72 4.0696 5.17 1.05 0.847 1.03 2.96 1.74 2.72 2.73 1.17 1.21 1.35 2.14 DSP-108 3.91 9.9450 11.73 1.05 1.37 7.87 12.4 5.79 2.95 3.84 4.71 3.2 4.59 3.74 DSP-122 5.04 9.9852 15.11 6.93 3.91 4.27 DSP-123 2.00 3.7347 6.00 0.893 1.99 1.71 2.45 2.81 2.63 1.7 1.86 1.95 5.29 11.4 DSP-124 3.37 10.4560 10.11 0.91 3.58 5.62 DSP-125 8.35 16.4507 25.05 4.93 9.1 6.84 6.81 35.4 12.6 10.7 5.11 9.6 6.41 11.4 MD-11 1.21 1.9594 3.62 6.17 0.977 1.22 1.67 1.22 1.21 0.978 0.996 1.59 0.978 1.24 MW-DN-101-I 2.83 6.5892 8.48 2.39 1.25 2.32 1.26 3.05 4.81 4.6 1.86 3.14 3.6 MW-DN-101-S 4.42 11.7113 13.26 6.2 1.54 5.96 4.33 8.7 6.55 4.28 3.3 1.55 1.78 MW-DN-102-I 2.30 6.7215 6.89 0.675 1.46 1.29 3.03 4.08 2.63 13.8 4.46 0.758 MW-DN-102-S 19.59 44.9566 58.78 9.44 13.9 15.6 19.9 28.3 51.8 35.2 20.2 14.2 MW-DN-104-S 6.40 16.9854 19.20 2.44 7.55 9.21 MW-DN-105-S 5.39 8.8428 16.16 6.2 4.57 MW-DN-106-S
#DIV/0!
#DIV/0!
#DIV/0!
1.42 MW-DN-107-S 5.71 19.2653 17.13 6.37 9.86 0.895 MW-DN-108-I 1.53 3.0601 4.58 1.39 1.13 0.828 1.73 1.87 2.22 3.35 MW-DN-109-I 3.32 8.9309 9.97 1.04 0.499 0.936 3.81 4.29 4.02 3.79 3.71 6.06 5.07 MW-DN-109-S 5.10 11.4540 15.31 3.74 2.74 4.01 1.97 6.52 5.93 5.15 5.17 6.57 9.23 MW-DN-111-S 0.97 1.6391 2.92 0.816 1.13 MW-DN-113-I 2.31 6.6897 6.93 0.485 0.531 3.87 1.54 1.53 8.9 3.91 3.66 2.95 MW-DN-113-S 2.24 4.0151 6.71 2.34 1.76 2.56 2.08 1.45 3.02 3.16 2.1 1.65 MW-DN-114-S 1.72 4.2656 5.16 1.12 2.32 MW-DN-115-S 3.13 4.3604 9.39 3.42 2.84 MW-DN-116-I 3.01 5.8624 9.04 3.31 1.64 3.01 4.16 3.77 3.79 1.68 2.74 MW-DN-116-S 2.95 7.0515 8.85 2.53 3.55 1.15 5.21 4.83 3.82 1.57 2.08 1.97 2.79 MW-DN-117-I 1.06 1.5277 3.19 1
1.24 0.884 1.13 MW-DN-118-S 1.57 4.7390 4.70 0.745 1.24 1.84 0.897 4.81 2.34 0.551 1.11 1.41 3.97 MW-DN-119-I 3.39 6.9550 10.17 1.86 3.62 2.42 3.18 4.44 28.9 6.25 2.95 3.85 2.24 3.29 2.53 4.03 MW-DN-119-S 2.78 6.4375 8.34 2.35 1.55 4.23 4.95 7.23 1.57 3.03 2.98 1.44 2.92 MW-DN-122-I
#DIV/0!
#DIV/0!
#DIV/0!
1.41 MW-DN-124-I 3.70 8.9513 11.11 2.13 2
3.35 9.99 4.06 5.33 7.19 3.74 4.15 3.99 1.09 MW-DN-124-S 4.07 8.7647 12.21 2.63 1.71 4.74 5.76 5.77 6.35 3.72 2.96 4.26 2.8 MW-DN-125-S 3.03 7.8080 9.09 2.62 1.83 4.83 1.38 3.63 30 5.32 1.6 MW-DN-126-S 6.47 19.9177 19.40 11.5 12.7 13.1 6.66 4.16 6.85 1.56 3.46 2.5 2.18 MW-DN-127-S 2.45 8.6690 7.35 2.1 2.36 5.27 1.09 2.03 5.89 0.476 0.393 MW-DN-134-S 2.78 6.1589 8.33 1.65 2.62 3.65 3.77 4.38 1.06 2.88 2.21 MW-DN-135-S 2.48 5.2802 7.44 2.81 4.2 1.64 1.7 3.21 2.06 1.5 2.71 MW-DN-136-S 5.24 12.2922 15.72 2.31 3.28 4.51 6.46 7.85 3.65 3.27 8.84 4.16 8.06 MW-DN-137-S 4.88 11.5010 14.63 8.52 1.58 4.9 5.57 6.65 5.46 3.43 2.89 MW-DN-140-S 3.43 11.9437 10.28 6.59 1.1 2.59 MW-DN-141-S 1.01 2.1690 3.02 0.837 0.769 2.08 1.33 1.12 0.78 0.722 0.852 0.757 1.89 MW-DN-142-S 4.56 10.2241 13.67 7.27 2.98 4.31 3.66 MW-DN-143-S 3.10 6.5062 9.31 2.16 4.71 3.06 2.48 MW-DN-144-S 3.66 6.7243 10.97 4.17 4.76 3.27 2.43 RW-DN-100-S 5.45 9.1835 16.35 4.57 6.33 RW-DN-101-S 3.48 11.9653 10.44 1.48 5.48 ALERT LEVEL (Hist Avg)
Well Average
(-Outliers)
Dresden SITE Well ID 2012 2013 2014 2015 2017 2018 2016 2019 Gross Alpha - Dissolved Results ALERT LEVEL (STDEV -
Outliers) 2011 Results in pCi/L Page 1 of 2 AMO Environmental Decisions

Dresden Generating Station Constellation Energy Company Table 1 Summary of Gross-Alpha Results 2021 2023 Feb Mar Jun Dec Mar May Jun Mar Jun Jul May Jun Jun Nov May Jun Aug Oct Feb May Nov Feb Jun Sep Nov May Dec May Jun DSP-105 0.86 1.6990 2.59 0.82 0.793 0.63 0.923 0.599 0.617 1.13 1.39 DSP-106 0.69 1.4498 2.07 0.809 0.793 0.63 0.923 0.599 0.617 1.13 4.28 0.367 0.346 DSP-107 0.60 1.4761 1.79 0.345 0.349 0.361 0.63 0.918 4.74 0.618 1.13 0.896 0.367 0.346 DSP-108 0.68 1.4799 2.04 0.348 0.361 0.851 0.63 0.933 0.605 0.619 1.14 0.897 1.83 0.432 DSP-122 2.08 7.1817 6.25 0.245 2.4 3.6 DSP-123 0.66 1.4235 1.99 0.614 0.347 0.601 1.9 0.923 0.608 0.617 1.16 0.719 0.369 1.74 DSP-124 0.80 1.2818 2.40 0.616 0.912 0.872 DSP-125 1.68 3.5783 5.03 1.28 0.66 1.69 1.9 0.892 2.88 2.21 1.65 3.72 1.84 1.75 MD-11 0.66 1.1995 1.98 0.639 0.711 0.777 0.347 0.822 0.624 0.844 0.898 0.628 0.366 0.6 MW-DN-101-I 0.78 1.7349 2.34 0.78 0.267 1.24 0.923 1.04 0.62 1.14 0.719 0.717 0.347 MW-DN-101-S 1.88 5.1353 5.63 1.12 0.695 1.24 0.962 3.41 13.55 1.73 3.82 2.14 1.77 MW-DN-102-I 1.02 3.3470 3.05 2
0.495 0.496 0.63 0.359 0.361 2.33 1.73 0.752 MW-DN-102-S 2.82 7.6781 8.45 3.58 1.8 1.88 0.63 2.14 4.99 3.8 1.37 5.16 MW-DN-104-S 3.45 11.7380 10.35 0.62 3.59 6.14 MW-DN-105-S 6.84 20.6710 20.52 3.58 10.1 MW-DN-106-S
#DIV/0!
#DIV/0!
#DIV/0!
1.17 MW-DN-107-S 3.40 13.0167 10.20 2.5 6.96 0.742 MW-DN-108-I 2.12 11.2784 6.37 0.64 0.781 0.608 1.24 1.15 8.33 36.3 MW-DN-109-I 1.07 2.7943 3.22 0.502 0.604 1.24 0.51 0.357 1.84 1.6 1.48 3.56 1.52 MW-DN-109-S 1.62 4.8092 4.87 0.396 0.503 1.24 0.508 2.05 1.84 1.6 1.48 3.56 3.04 MW-DN-111-S 0.57 0.7791 1.70 0.517 0.617 MW-DN-113-I 2.70 11.8613 8.09 1.18 0.499 1.3 1.21 0.361 20.18 1.85 7.89 7.27 MW-DN-113-S 4.70 19.8243 14.10 0.649 1.63 0.446 2.47 3.24 15.7 7.59 8.62 1.94 MW-DN-114-S 0.77 1.4579 2.31 0.931 0.606 MW-DN-115-S 0.85 1.7410 2.55 1.06 0.64 MW-DN-116-I 0.70 1.5728 2.11 1.02 0.503 1.24 0.503 0.374 0.623 0.627 0.726 MW-DN-116-S 0.77 1.4963 2.31 0.69 0.502 1.24 0.506 0.746 1.02 0.871 0.747 3.35 0.608 MW-DN-117-I 0.82 1.6274 2.46 0.807 0.491 0.831 1.15 MW-DN-118-S 0.72 1.2529 2.15 0.622 0.491 1.79 0.511 0.938 0.809 0.862 0.892 1.66 0.605 MW-DN-119-I 0.91 1.8339 2.74 0.62 1.03 2.83 0.515 0.912 2.78 0.85 0.501 0.981 1.54 1.03 0.849 1.22 MW-DN-119-S 2.35 8.0503 7.06 0.622 0.557 1.24 0.509 2.38 3.73 4.28 5.52 4.07 0.616 MW-DN-122-I
#DIV/0!
#DIV/0!
#DIV/0!
3.2 MW-DN-124-I 1.21 3.4084 3.63 0.345 0.491 0.665 1.21 1.28 1.73 2.78 1.5 1.5 4.33 0.613 MW-DN-124-S 1.83 5.9504 5.50 0.356 0.49 1.21 1.28 2.41 2.87 3.46 0.982 4.4 0.889 MW-DN-125-S 1.14 2.7651 3.43 0.362 0.798 1.21 1.94 0.739 2.87 1.51 1.44 MW-DN-126-S 1.81 3.5834 5.42 1.33 1.5 1.21 1.29 1.79 2.77 1.5 2.57 4.54 2.31 MW-DN-127-S 0.92 1.7664 2.77 0.817 0.488 1.21 1.34 0.731 0.815 0.862 1.13 MW-DN-134-S 0.72 1.3220 2.15 0.925 0.513 0.657 0.345 0.721 0.807 0.868 0.886 MW-DN-135-S 0.75 1.4555 2.25 1.08 0.538 0.657 0.345 0.721 0.843 0.932 0.884 MW-DN-136-S 1.64 5.5701 4.92 0.4 0.545 0.657 0.346 2.55 1.76 1.36 1.43 4.33 3.01 MW-DN-137-S 1.41 3.8084 4.24 1.25 0.645 1.1 0.351 2.5 2.61 1.42 1.44 MW-DN-140-S 1.20 2.1319 3.59 1.49 0.869 1.23 MW-DN-141-S 0.84 1.5436 2.52 0.973 0.513 1.24 0.504 0.894 0.83 1.03 0.884 0.909 0.608 MW-DN-142-S 1.16 2.6527 3.49 2.62 0.591 1.47 1.43 MW-DN-143-S 1.26 2.6054 3.78 0.819 1.81 1.43 0.982 MW-DN-144-S 1.89 4.7607 5.66 3.23 1.85 1.44 1.02 RW-DN-100-S 13.84 44.2173 41.52 6.68 21 RW-DN-101-S 1.05 1.7026 3.14 0.89

===1.2 Explanation===
2.83 Historic data outlier removed from the calculation of the average concentration that was used to calculate the Alert Level.
3.35 Alert Level Exceedance where select transuranics were analyzed and found to be less than their respective LLDs. The result is now used in generating the Alert Level.
3.56 Alert Level Exceedance However, the result is ND and less than LLD Dresden Well Average
(-Outliers)
ALERT LEVEL (Hist Avg)
SITE Well ID 2019 2018 2014 2015 2016 Gross Alpha - Suspended Results ALERT LEVEL (STDEV -
Outliers) 2017 2011 2012 2013 Results in pCi/L Page 2 of 2 AMO Environmental Decisions

Dresden Generating Station Constellation Energy Company Table 2 Summary of U-233/234 and U238 Results 2014 2021 2022 2023 2024 Feb Mar Jun Dec Mar Jun Mar Jun Jun Jun Nov May Oct Feb May Nov Jan Feb Jun Oct Nov Mar May Aug Dec Mar Jul Nov May Jun Jun May DSP-107 0.09023 DSP-122 0.1733 DSP-123 0.1647 DSP-124 0.03502 DSP-125 0.1329 0.08067 MD-11 0.05616 0.1496 0.1019 0.03347 0.1252 0.1154 0.1121 0.04995 0.1377 0.1474 0.1156 0.1418 0.07021 0.0272 MW-DN-101-I 0.3894 0.05872 0.4567 0.2605 0.527 0.4477 0.2788 0.5173 0.2971 MW-DN-102-I 0.5784 MW-DN-102-S 0.1116 MW-DN-104-S 0.8506 MW-DN-106-S 1.091 MW-DN-107-S 0.371 0.9135 MW-DN-108-I 0.3799 MW-DN-111S 0.03651 MW-DN-113-I 0.09059 MW-DN-113-S 0.544 MW-DN-116-S 0.07296 MW-DN-119-I 0.8408 0.09179 0.1428 0.0229 0.0217 0.04698 0.1045 0.1441 0.1718 0.1187 0.08836 0.06477 MW-DN-122-I 0.324 MW-DN-124-I 0.05192 0.06465 0.08076 0.1292 0.143 0.08868 0.1273 0.104 0.1055 0.03858 0.1186 0.1395 0.04893 0.1451 0.07568 MW-DN-124-S 0.05753 0.9742 0.1876 0.7096 0.03498 0.113 0.02586 0.1175 0.1191 0.1802 0.092303 0.07651 0.07268 RW-DN-100S 0.1454 RW-DN-101S 0.05042 SW-DN-101 0.4082 SW-DN-102 0.441 SW-DN-103 0.6737 SW-DN-104 0.7946 SW-DN-105 0.553 SW-DN-106 0.489 2014 2021 2022 2023 2024 Feb Mar Jun Dec Mar Jun Mar Jun Jun Jun Nov May Oct Feb May Nov Jan Feb Jun Oct Nov Mar May Aug Dec Mar Jul Nov May Jun Jun May DSP-107 0.07626 DSP-122 0.1605 DSP-123 0.0743 DSP-124 0.06065 DSP-125 0.1879 0.0433 MD-11 0.07942 0.1058 0.09531 0.05797 0.1252 0.1233 0.1068 0.06118 0.1124 0.1575 0.03103 0.07612 0.05733 0.07166 MW-DN-101-I 0.1488 0.08303 0.1215 0.1775 0.2164 0.1499 0.1993 0.124 0.1755 MW-DN-102-I 0.1066 MW-DN-102-S 0.1116 MW-DN-104-S 0.4353 MW-DN-106-S 0.845 MW-DN-107-S 0.4338 0.6638 MW-DN-108-I 0.2105 MW-DN-111S 0.06802 MW-DN-113-I 0.06406 MW-DN-113-S 0.2991 MW-DN-116-S 0.07296 MW-DN-119-I 0.4422 0.1124 0.08746 0.04265 0.0217 0.08136 0.08333 0.1556 0.1403 0.1346 0.1141 0.1295 MW-DN-122-I 0.3512 MW-DN-124-I 0.1465 0.07465 0.08076 0.0914 0.1891 0.05121 0.2437 0.1644 0.08823 0.122 0.08389 0.1801 0.04893 0.1451 0.1993 MW-DN-124-S 0.04069 0.3889 0.1532 0.2626 0.1399 0.04273 0.1274 0.06283 0.1191 0.1472 0.09203 0.1803 0.07268 RW-DN-100S 0.1781 RW-DN-101S 0.05042 SW-DN-101 0.5516 SW-DN-102 0.5302 SW-DN-103 0.4086 SW-DN-104 0.4812 SW-DN-105 0.3978 SW-DN-106 0.5952 Notes:
1 - If a sample was re-analyzed on a particular date, only the highest concentration is noted.
2018 2017 Dresden 2020 2019 2016 2015 2013 2012 Station Well ID 2011 U-233/234 Results 2018 2019 2020 Dresden 2013 2015 2016 2017 Station Well ID 2011 2012 U-238 Results Results in pCi/L Page 1 of 1 AMO Environmental Decision

Dresden Generating Station Constellation Energy Company Table 3 Summary of 2024 Precipitation Results Sample Location Sample Date Directional Sector Result Qual FW-11 2/27/2024 ESE 187 U
FW-3 2/28/2024 NNW 820
+
FW-1 2/28/2024 NW 734
+
FW-13 5/28/2024 S
190 U
FW-5 5/29/2024 NE 191 U
FW-14 5/30/2024 N
231
+
FW-1 5/30/2024 NW 615
+
FW-2 5/30/2024 NNE 249
+
FW-3 5/30/2024 NNW 567
+
FW-10 5/30/2024 E
190 U
FW-12 5/31/2024 SSE 187 U
FW-11 5/31/2024 ESE 189 U
FW-11 8/15/2024 ESE 190 U
FW-13 8/15/2024 S
186 U
FW-1 8/15/2024 NW 291
+
FW-14 8/15/2024 N
221
+
FW-2 8/15/2024 NNE 196 U
FW-10 8/15/2024 E
192 U
FW-12 8/15/2024 SSE 188 U
FW-5 8/15/2024 NE 189 U
FW-12 11/26/2024 SSE 182 U
FW-4 11/26/2024 SW 177 U
FW-13 11/26/2024 S
186 U
FW-1 11/26/2024 NW 519
+
FW-14 11/26/2024 N
340
+
FW-2 11/26/2024 NNE 245
+
FW-3 11/26/2024 NNW 390
+
FW-10 11/26/2024 E
179 U
FW-11 11/26/2024 ESE 185 U
FW-5 11/26/2024 NE 182 U
Explanation:
U - Tritium not detected at a concentration greater than the laboratory detection limit.
+ - Tritium detected at a Concentration greater than the laboratory detection limit.
 - All results presented in pCi/L.
2024 Summary of Precipitation Tritium Results/ 2024 Summary Page 1 of 1 AMO Environmental Decisions

$1
$1
$1
$1 DSP-159S MW-DN-122-S MW-DN-144-S MW-DN-143-S MW-DN-142-S MW-DN-135-S MW-DN-137-S MW-DN-136-S MW-DN-134-S
$1
$1
$1
$1 MD-11 RW-DN-100-S MW-DN-106-S MW-DN-103-S MW-DN-124-S MW-DN-114-S MW-DN-140-S MW-DN-115-S MW-DN-111-S MW-DN-125-S MW-DN-141-S MW-DN-119-S MW-DN-118-S MW-DN-116-S MW-DN-126-S MW-DN-107-S MW-DN-102-S MW-DN-101-S MW-DN-105-S MW-DN-104-S MW-DN-113-S MW-DN-110-S MW-DN-109-S MW-DN-112-S RW-DN-101-S MW-DN-127-S Figure 1a RGPP Sample Locations Shallow Aquifer Constellation Energy Corporation Dresden Generating Station

Explanation:
Shallow Aquifer RGPP Monitoring Location

===Background===
$1 Long-Term Shutdown Mid-Field Perimeter Source 0
1,000 500 Feet 0
800 400 Feet I 
/4 

$1
$1
$1
$1
$1
!$1 DSP-154 DSP-147 DSP-126 DSP-150 DSP-148 DSP-159M MW-DN-122-I
$1
$1
$1
$1
$1
$1 DSP-126 DSP-107 DSP-106 DSP-124 DSP-123 DSP-108 DSP-122 DSP-125 DSP-149R MW-DN-103-I MW-DN-124-I MW-DN-114-I MW-DN-101-I MW-DN-115-I MW-DN-109-I MW-DN-116-I MW-DN-117-I MW-DN-119-I MW-DN-112-I MW-DN-108-I Figure 1b RGPP Sample Locations Intermediate Aquifer Constellation Energy Corporation Dresden Generating Station

Explanation:
Intermediate Aquifer RGPP Monitoring Location

===Background===
$1 Long-Term Shutdown Mid-Field Perimeter Source 0
1,000 500 Feet 0
800 400 Feet m
I I 
~ --

508 512 510 506 502 504 510 508 512 506 506 502 504 MW-DN-115-S 509.90 MW-DN-114-S 508.30 MW-DN-102-S 512.70 MW-DN-127-S 511.23 MW-DN-107-S 513.31 MW-DN-141-S 508.46 MW-DN-140-S 507.78 MW-DN-126-S 511.68 MW-DN-125-S 511.81 MW-DN-124-S 511.68 MW-DN-119-S 506.57 MW-DN-118-S 508.16 MW-DN-116-S 504.96 MW-DN-113-S 513.75 MW-DN-112-S 512.66 MW-DN-111-S 510.96 MW-DN-110-S 509.76 MW-DN-109-S 509.27 MW-DN-106-S 504.37 MW-DN-105-S 512.05 MW-DN-104-S 507.67 MW-DN-103-S 507.79 MW-DN-101-S 505.05 1 Cribhouse 505.35 2/3 Discharge 507.58 2/3 Cribhouse 501.98 Explanation:
October 2024 RGPP Shallow Aquifer Monitoring Locations October 2024 Shallow Aquifer Groundwater Elevation Contours Inferred Groundwater Elevation Contour Groundwater Elevation Contour Shallow Aquifer Estimated Flow Direction 508.45 - Groundwater elevation with respect to mean sea level Figure 2a 4th Quarter 2024 (October) RGPP Groundwater Elevations and Water Elevation Contours Surface Water and Shallow Aquifer Constellation Energy Corporation Dresden Generating Station

0 1,000 Feet
[RI y
0 c:, 
=
c:, 
= 
= D 0 
= 
= 

508 512 506 510 510 508 512 506 DSP-126 512.20 DSP-150 506.11 DSP-148 507.36 DSP-125 512.31 DSP-124 512.66 DSP-123 504.65 DSP-122 507.94 DSP-108 506.63 DSP-107 506.79 DSP-106 509.01 MW-DN-124-I 511.45 MW-DN-119-I 506.49 MW-DN-116-I 504.44 MW-DN-115-I 509.39 MW-DN-114-I 512.64 MW-DN-112-I 511.54 MW-DN-109-I 509.83 MW-DN-103-I 506.69 MW-DN-101-I 504.31 DSP-149 (R) 505.37 Explanation:
October 2024 Intermediate Aquifer Monitoring Location Groundwater Elevation Contour Inferred Groundwater Elevation Contour Intermediate Aquifer Estimated Groundwater Flow Direction 508.45 - Groundwater elevation with respect to mean sea level Figure 2b 4th Quarter 2024 (October) RGPP Groundwater Elevations and Water Elevation Contours Intermediate Aquifer Constellation Energy Corporation Dresden Generating Station

0 1,000 Feet
[RI 0
c:, 
=
c:, 
= 
= D 0 
= 
= 

FW-5 FW-3
<200 - 820 FW-2
<200 - 249 FW-1
<200 - 734 FW-4 FW-11 FW-10 FW-14
<200 - 340 FW-13 FW-12 Figure 3 2024 Precipitation Recapture Sample Locations Constellation Energy Corporation Dresden Generating Station Explanation:
2024 Precipitation Recapture Sample Locations Result <200 pCi/L Result >200 pCi/L 404 - Tritium concentration in pico-curies per liter (pCi/L).
- Precipitation sampling completed in February, May, August, and November in 2024.

0 1,000 Feet
[RI c:, 
= 
=
0 0
c:, 
&#xa2; c:, 
= D 
= 
= 

Dresden Generating Station Constellation Energy Company Appendix A Summary of 2011 - 2024 Precipitation Sample Tritium Results Sample ID Date Directional Sector Result Qual Units RB-1 7/28/2011 NW 400
+
pCi/L RB-10 7/28/2011 E
630
+
pCi/L RB-11 7/28/2011 ESE 300
+
pCi/L RB-12 7/28/2011 SSE 100 U
pCi/L RB-2 7/28/2011 NNE 630
+
pCi/L RB-3 7/28/2011 NNW 200 U
pCi/L RB-4 7/28/2011 SW 100 U
pCi/L RB-5 7/28/2011 NE 100 U
pCi/L RB-6 7/28/2011 ENE 200 U
pCi/L RB-7 7/28/2011 SE 200 U
pCi/L RB-8 7/28/2011 S
100 U
pCi/L RB-9 7/28/2011 SSW 100 U
pCi/L RB-1 10/21/2011 NW 300
+
pCi/L RB-10 10/21/2011 E
0 U
pCi/L RB-11 10/21/2011 ESE 200
+
pCi/L RB-12 10/21/2011 SSE 100 U
pCi/L RB-2 10/21/2011 NNE 300
+
pCi/L RB-3 10/21/2011 NNW 300
+
pCi/L RB-4 10/21/2011 SW 400
+
pCi/L RB-5 10/21/2011 NE 300
+
pCi/L RB-6 10/21/2011 ENE 200 U
pCi/L RB-7 10/21/2011 SE 200 U
pCi/L RB-8 10/21/2011 S
100 U
pCi/L RB-9 10/21/2011 SSW 0
U pCi/L RB-1 1/11/2012 NW 400
+
pCi/L RB-10 1/11/2012 E
300
+
pCi/L RB-11 1/11/2012 ESE 100 U
pCi/L RB-12 1/11/2012 SSE 300
+
pCi/L RB-2 1/11/2012 NNE 600
+
pCi/L RB-3 1/11/2012 NNW 600
+
pCi/L RB-4 1/11/2012 SW 500
+
pCi/L RB-5 1/11/2012 NE 400
+
pCi/L RB-6 1/11/2012 ENE 300
+
pCi/L RB-7 1/11/2012 SE 400
+
pCi/L RB-8 1/11/2012 S
300
+
pCi/L RB-9 1/11/2012 SSW 100 U
pCi/L RB-1 5/23/2012 NW 191 U
pCi/L RB-10 5/23/2012 E
199 U
pCi/L RB-11 5/30/2012 ESE 168 U
pCi/L RB-12 5/30/2012 SSE 167 U
pCi/L FW-1 6/6/2013 NW 161 U
pCi/L FW-10 6/7/2013 E
160 U
pCi/L FW-11 6/13/2013 ESE 169 U
pCi/L FW-12 6/14/2013 SSE 168 U
pCi/L FW-1 5/29/2014 NW 194 U
pCi/L FW-10 5/30/2014 E
191 U
pCi/L FW-11 5/30/2014 ESE 194 U
pCi/L FW-12 5/30/2014 SSE 196 U
pCi/L FW-1 6/1/2015 NW 190 U
pCi/L FW-10 6/2/2015 E
188 U
pCi/L FW-11 6/3/2015 ESE 182 U
pCi/L FW-12 6/8/2015 SSE 175 U
pCi/L FW-1 06/07/2016 NW 181 U
pCi/L FW-10 06/01/2016 E
183 U
pCi/L FW-11 06/01/2016 ESE 181 U
pCi/L FW-12 06/01/2016 SSE 182 U
pCi/L FW-1 05/15/2017 NW 177 U
pCi/L FW-10 05/23/2017 E
177 U
pCi/L FW-11 05/17/2017 ESE 175 U
pCi/L FW-12 05/24/2017 SSE 178 U
pCi/L FW-1 06/12/2018 NW 193 U
pCi/L 2024 Summary of Precipitation Tritium Results/ 2011 - 2024 Tritium Data Page 1 of 3 AMO Environmental Decisions

Dresden Generating Station Constellation Energy Company Appendix A Summary of 2011 - 2024 Precipitation Sample Tritium Results Sample ID Date Directional Sector Result Qual Units FW-10 06/12/2018 E
193 U
pCi/L FW-11 06/12/2018 ESE 196 U
pCi/L FW-12 06/02/2018 SSE 196 U
pCi/L FW-1 5/28/2019 NW 188 U
pCi/L FW-10 5/28/2019 E
181 U
pCi/L FW-11 5/28/2019 ESE 186 U
pCi/L FW-12 5/28/2019 SSE 187 U
pCi/L FW-1 11/12/2020 NW 207
+
pCi/L FW-10 11/12/2020 E
170 U
pCi/L FW-11 11/12/2020 ESE 175 U
pCi/L FW-12 11/12/2020 SSE 276 U
pCi/L FW-11 3/8/2021 ESE 182 U
pCi/L FW-10 3/8/2021 E
187 U
pCi/L FW-1 3/9/2021 NW 404
+
pCi/L FW-4 3/11/2021 SW 180 U
pCi/L FW-12 3/11/2021 SSE 186 U
pCi/L FW-2 3/11/2021 NNE 184 U
pCi/L FW-3 3/11/2021 NNW 182 U
pCi/L FW-5 3/11/2021 NE 182 U
pCi/L FW-11 8/10/2021 ESE 169 U
pCi/L FW-5 8/10/2021 NE 169 U
pCi/L FW-10 8/11/2021 E
161 U
pCi/L FW-2 8/11/2021 NNE 176 U
pCi/L FW-3 8/11/2021 NNW 421
+
pCi/L FW-1 8/12/2021 NW 177 U
pCi/L FW-4 8/12/2021 SW 176 U
pCi/L FW-12 8/12/2021 SSE 173 U
pCi/L FW-4 11/8/2021 SW 193 U
pCi/L FW-5 11/8/2021 NE 177 U
pCi/L FW-12 11/9/2021 SSE 187 U
pCi/L FW-11 11/9/2021 ESE 181 U
pCi/L FW-10 11/9/2021 E
186 U
pCi/L FW-2 11/9/2021 NNE 192
+
pCi/L FW-3 11/9/2021 NNW 239
+
pCi/L FW-1 11/10/2021 NW 215
+
pCi/L FW-1 3/15/2022 NW 229
+
pCi/L FW-10 3/15/2022 E
195 U
pCi/L FW-11 3/15/2022 ESE 193 U
pCi/L FW-12 3/15/2022 SSE 175 U
pCi/L FW-2 3/15/2022 NNE 360
+
pCi/L FW-3 3/15/2022 NNW 589
+
pCi/L FW-4 3/15/2022 SW 171 U
pCi/L FW-5 3/16/2022 NE 172 U
pCi/L FW-1 6/7/2022 NW 735
+
pCi/L FW-10 6/7/2022 E
204
+
pCi/L FW-11 6/7/2022 ESE 173 U
pCi/L FW-12 6/7/2022 SSE 182
+
pCi/L FW-2 6/7/2022 NNE 377
+
pCi/L FW-3 6/7/2022 NNW 394
+
pCi/L FW-4 6/7/2022 SW 470
+
pCi/L FW-5 6/6/2022 NE 229
+
pCi/L FW-1 7/27/2022 NW 418
+
pCi/L FW-10 7/27/2022 E
196 U
pCi/L FW-11 7/26/2022 ESE 194 U
pCi/L FW-12 7/28/2022 SSE 195 U
pCi/L FW-2 7/27/2022 NNE 234
+
pCi/L FW-3 7/27/2022 NNW 266
+
pCi/L FW-4 7/27/2022 SW 195 U
pCi/L FW-5 7/25/2022 NE 196 U
pCi/L FW-1 11/16/2022 NW 1,860
+
pCi/L FW-10 11/16/2022 E
176 U
pCi/L 2024 Summary of Precipitation Tritium Results/ 2011 - 2024 Tritium Data Page 2 of 3 AMO Environmental Decisions

Dresden Generating Station Constellation Energy Company Appendix A Summary of 2011 - 2024 Precipitation Sample Tritium Results Sample ID Date Directional Sector Result Qual Units FW-11 11/16/2022 ESE 242
+
pCi/L FW-12 11/16/2022 SSE 230
+
pCi/L FW-2 11/16/2022 NNE 902
+
pCi/L FW-3 11/16/2022 NNW 1,330
+
pCi/L FW-4 11/16/2022 SW 353
+
pCi/L FW-5 11/16/2022 NE 191 U
pCi/L FW-4 3/15/2023 SW 212
+
pCi/L FW-12 3/15/2023 SSE 281
+
pCi/L FW-1 3/15/2023 NW 332
+
pCi/L FW-2 3/15/2023 NNE 218
+
pCi/L FW-3 3/15/2023 NNW 422
+
pCi/L FW-10 3/15/2023 E
196 U
pCi/L FW-5 3/15/2023 NE 198 U
pCi/L FW-11 3/16/2023 ESE 193 U
pCi/L FW-5 9/18/2023 NE 197 U
pCi/L FW-4 9/20/2023 SW 264
+
pCi/L FW-11 9/21/2023 ESE 195 U
pCi/L FW-10 9/21/2023 E
198 U
pCi/L FW-12 9/21/2023 SSE 197 U
pCi/L FW-2 9/22/2023 NNE 189 U
pCi/L FW-3 9/22/2023 NNW 188 U
pCi/L FW-1 9/22/2023 NW 369
+
pCi/L FW-5 12/5/2023 NE 190 U
pCi/L FW-4 12/6/2023 SW 191 U
pCi/L FW-1 12/6/2023 NW 619
+
pCi/L FW-2 12/7/2023 NNE 524
+
pCi/L FW-3 12/7/2023 NNW 914
+
pCi/L FW-10 12/7/2023 E
184 U
pCi/L FW-11 12/7/2023 ESE 189 U
pCi/L FW-12 12/7/2023 SSE 191 U
pCi/L FW-11 2/27/2024 ESE 187 U
pCi/L FW-3 2/28/2024 NNW 820
+
pCi/L FW-1 2/28/2024 NW 734
+
pCi/L FW-13 5/28/2024 S
190 U
pCi/L FW-5 5/29/2024 NE 191 U
pCi/L FW-14 5/30/2024 N
231
+
pCi/L FW-1 5/30/2024 NW 615
+
pCi/L FW-2 5/30/2024 NNE 249
+
pCi/L FW-3 5/30/2024 NNW 567
+
pCi/L FW-10 5/30/2024 E
190 U
pCi/L FW-12 5/31/2024 SSE 187 U
pCi/L FW-11 5/31/2024 ESE 189 U
pCi/L FW-11 8/15/2024 ESE 190 U
pCi/L FW-13 8/15/2024 S
186 U
pCi/L FW-1 8/15/2024 NW 291
+
pCi/L FW-14 8/15/2024 N
221
+
pCi/L FW-2 8/15/2024 NNE 196 U
pCi/L FW-10 8/15/2024 E
192 U
pCi/L FW-12 8/15/2024 SSE 188 U
pCi/L FW-5 8/15/2024 NE 189 U
pCi/L FW-12 11/26/2024 SSE 182 U
pCi/L FW-4 11/26/2024 SW 177 U
pCi/L FW-13 11/26/2024 S
186 U
pCi/L FW-1 11/26/2024 NW 519
+
pCi/L FW-14 11/26/2024 N
340
+
pCi/L FW-2 11/26/2024 NNE 245
+
pCi/L FW-3 11/26/2024 NNW 390
+
pCi/L FW-10 11/26/2024 E
179 U
pCi/L FW-11 11/26/2024 ESE 185 U
pCi/L FW-5 11/26/2024 NE 182 U
pCi/L 2024 Summary of Precipitation Tritium Results/ 2011 - 2024 Tritium Data Page 3 of 3 AMO Environmental Decisions}}