2017 Annual Groundwater Monitoring and Correction Action Report

Transcription

1 2017 Annual Groundwater Monitoring and Correction Action Report Milton R. Young Station Coal Combustion Residuals (CCR) Disposal Facility Center, ND Prepared for Minnkota Power Cooperative, Inc. December 2017

2 2017 Annual Groundwater Monitoring and Correction Action Report Milton R. Young Station Coal Combustion Residuals (CCR) Disposal Facility Center, ND Prepared for Minnkota Power Cooperative, Inc. December West Century Avenue Bismarck, ND

3 2017 Annual Groundwater Monitoring and Corrective Action Report Milton R. Young Station Coal Combustion Residuals (CCR) Disposal Facility Center, ND December 2017 Contents 1.0 Introduction Groundwater Monitoring and Corrective Action Program Groundwater Monitoring System Documentation Key Actions Completed/Problems Encountered Key Activities for Upcoming Year Analytical Results and Statistical Evaluation Documentation Key Actions Completed/Problems Encountered Key Activities for Upcoming Year References... 7 P:\Mpls\34 ND\33\ Minnkota Ash Management\WorkFiles\CCR Groundwater 2\Annual GW Monitoring and Corrective Action Report\2017 AGM&CA Report.docx i

4 List of Tables Table 1 Table 2 Table 3 Table 4 Table 5 Table 6 CCR Rule Requirements and Compliance Monitoring Well Construction Details Water Quality Results Field Blank Results Water Level Results Tukey Method Results for Outliers List of Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8 Figure 9 Figure 10 Figure 11 Site Layout CCR Unit Location April-July 2016 Groundwater Elevations October 2016 Groundwater Elevations January 2017 Groundwater Elevations March 2017 Groundwater Elevations April 2017 Groundwater Elevations May 2017 Groundwater Elevations July 2017 Groundwater Elevations August 2017 Groundwater Elevations October 2017 Groundwater Elevations List of Appendices Appendix A Appendix B Outlier Review of Background Samples Statistical Review for SSIs in 2017 Semiannual Sampling Event ii

5 1.0 Introduction Minnkota Power Cooperative, Inc. (Minnkota) owns and operates Milton R. Young Station (Facility) located about 5 miles southeast of the town of Center in west-central North Dakota. The Facility location and site layout are shown on Figure 1 and includes the Coal Combustion Residuals (CCR) management units (landfill and surface impoundment), which are shown in more detail on Figure 2. Landfill Cell 1 was closed prior to October 19, 2015; therefore it is not subject to the CCR rule requirements for groundwater monitoring and is not discussed further in this report. Landfill Cell 2 and Surface Impoundment Cell 3 are each existing CCR units that are required to comply with the provisions of the US EPA CCR Rule (40 CFR Parts 257 and 261 Disposal of Coal Combustion Residuals from Electric Utilities, 2015). Together they will be referred to as the CCR unit. The document herein is the 2017 Annual Groundwater Monitoring and Corrective Action Report (AGMCAR) required by the CCR Rule. Specific Rule requirements for the AGMCAR and demonstration of compliance are summarized in Table 1, provided at the end of this Section 1.0, and are described in more detail in Section 2.0. Table 1 CCR Rule Requirements and Compliance CCR Rule Requirements ( (e)) Annual groundwater monitoring and corrective action report (e): For existing CCR landfills and existing CCR surface impoundments, no later than January 31, 2018, and annually thereafter, the owner or operator must prepare an annual groundwater monitoring and corrective action report (AGMCAR). For new CCR landfills, new CCR surface impoundments, and all lateral expansions of CCR units, the owner or operator must prepare the initial AGMCAR no later than January 31 of the year following the calendar year a groundwater monitoring system has been established for such CCR unit as required by this subpart, and annually thereafter. For the preceding calendar year, the annual report must document the status of the groundwater monitoring and corrective action program for the CCR unit, summarize key actions completed, describe any problems encountered, discuss actions to resolve the problems, and project key activities for the upcoming year. For purposes of this section, the owner or operator has prepared the annual report when the report is placed in the facility s operating record as required by (h)(1). At a minimum, the AGMCAR must contain the following information, to the extent available: Figure of CCR unit and groundwater monitoring system (1): A map, aerial image, or diagram showing the CCR unit and all background (or upgradient) and downgradient monitoring wells, to include the well identification numbers, that are part of the groundwater monitoring program for the CCR unit; Monitoring wells installed/decommissioned (2): Identification of any monitoring wells that were installed or decommissioned during the preceding year, along with a narrative description of why those actions were taken; Compliance with CCR Rule Yes. See Section 2.0. Yes. See Section and Figure 2. No wells were installed in See Section

6 CCR Rule Requirements ( (e)) Monitoring data obtained under through (3): In addition to all the monitoring data obtained under through , a summary including the number of groundwater samples that were collected for analysis for each background and downgradient well, the dates the samples were collected, and whether the sample was required by the detection monitoring or assessments monitoring programs; Transitions between monitoring programs (4): A narrative discussion of any transition between monitoring programs (e.g., the date and circumstances for transitioning from detection monitoring to assessment monitoring in addition to identifying the constituent(s) detected at a statistically significant increase (SSI) over background levels); and Other required information (5): Other information required to be included in the annual report as specified in through : Detection monitoring program (d)(3): The owner or operator must obtain a certification from a qualified professional engineer (QPE) stating that the demonstration for an alternative groundwater sampling and analysis frequency meets the requirements of this section. The owner or operator must include the demonstration providing the basis for the alternative monitoring frequency and the certification by a QPE the AGMCAR required by (e). Detection monitoring program (e)(2): The owner or operator may demonstrate that a source other than the CCR unit caused the SSI over background levels for a constituent or that the SSI resulted from error in sampling, analysis, statistical evaluation, or natural variation in groundwater quality. The owner or operator must complete the written demonstration within 90 days of detecting an SSI over background levels to include obtaining a certification from a QPE verifying the accuracy of the information in the report. If a successful demonstration is completed within the 90-day period, the owner or operator of the CCR unit may continue with a detection monitoring program under this section. If a successful demonstration is not completed within the 90-day period, the owner or operator of the CCR unit must initiate an assessment monitoring program as required under The owner or operator must also include the demonstration in the AGMCAR required by (e), in addition to the certification by a QPE. Assessment monitoring program (c)(3): The owner or operator must obtain a certification from a QPE stating that the demonstration for an alternative groundwater sampling and analysis frequency meets the requirements of this section. The owner or operator must include the demonstration providing the basis for the alternative monitoring frequency and the certification by a QPE in the AGMCAR as required by (e). Assessment monitoring program (d)(3): Include the recorded concentrations required by paragraph (d)(1) of this section, identify the background concentrations established under (b), and identify the groundwater protection standards established under paragraph (d)(2) of this section in the AGMCAR required by (e). Compliance with CCR Rule Yes. See Section 2.2.1, Tables 3 5, and Figures No transition to assessment monitoring was necessary. See Section See the responses below for the other information required in through No alternative groundwater sampling frequency was used. No SSIs were detected. See Section No transition to assessment monitoring was necessary. See Section No transition to assessment monitoring was necessary. See Section

7 CCR Rule Requirements ( (e)) Assessment monitoring program (g)(3)(ii): Demonstrate that a source other than the CCR unit caused the contamination, or that the SSI resulted from error in sampling, analysis, statistical evaluation, or natural variation in groundwater quality. Any such demonstration must be supported by a report that includes the factual or evidentiary basis for any conclusions and must be certified to be accurate by a QPE. If a successful demonstration is made, the owner or operator must continue monitoring in accordance with the assessment monitoring program pursuant to this section, and may return to detection monitoring if the constituents in appendices III and IV to this part are at or below background as specified in paragraph (e) of this section. The owner or operator must also include the demonstration in the AGMCAR required by (e), in addition to the certification by a QPE. Assessment of corrective measures (a): Within 90 days of finding that any constituent listed in appendix IV to this part has been detected at a significantly significant level exceeding the groundwater protection standard defined under (h), or immediately upon detection of a release from a CCR unit, the owner or operatory must initiate an assessment of corrective measures to prevent further releases, to remediate any releases and to restore affected area to original conditions. The assessment of corrective measures must be completed within 90 days, unless the owner or operator demonstrates the need for additional time to complete the assessment of corrective measures due to site-specific conditions or circumstances. The owner or operator must obtain a certification from a QPE attesting that the demonstration is accurate. The 90-day deadline to complete the assessment of corrective measures may be extended for no longer than 60 days. The owner of operator must also include the demonstration in the AGMCAR required by (e), in addition to the certification by a QPE. Compliance with CCR Rule No transition to assessment monitoring was necessary. See Section No transition to assessment monitoring was necessary. See Section

8 2.0 Groundwater Monitoring and Corrective Action Program Section 2.0 documents the status of the groundwater monitoring and corrective action program for the CCR unit beginning when the Rule was published in April 2015 through This section has two major divisions: (2.1) Groundwater Monitoring System and (2.2) Analytical Results and Statistical Evaluation. Documentation for each division is included, as well as summaries of key actions completed, problems encountered, with resolutions, and key activities planned for Groundwater Monitoring System Documentation Figure 2 shows the two upgradient ( and ) and the four downgradient (2015-3, , , and ) monitoring wells for the CCR unit groundwater monitoring system. Also shown are two upgradient and two downgradient wells used only for water level measurements. All wells shown have well identification numbers. Table 2 provides the construction details for each well. Further details on the monitoring system, the water table aquifer, site conceptual model, release conceptual model, geologic cross sections, and logs for the CCR unit monitoring wells are included in Barr (2017a) Key Actions Completed/Problems Encountered The water table aquifer (WTA) is low-yielding (Barr, 2017a) and standard low-flow sampling techniques are not applicable (Yeskis and Zavala, 2002). As a result, some wells need to be purged as dry as practical the day before groundwater samples are collected. Furthermore, the WTA has high natural turbidity levels; turbidities were reduced to acceptable levels by frequently purging each well with its dedicated bladder pump. No CCR compliance wells were installed or decommissioned in 2017; however, well was installed in the fall of 2016 to replace an older monitoring well that produced samples having excessive turbidities. After the groundwater monitoring system was designed and constructed, and each well was developed so it could produce representative groundwater samples, the following key actions were completed through 2017: A site sampling and analysis program was completed ( (a)). A QPE certified that the groundwater monitoring system was designed and constructed (Barr, 2017a) to meet the requirements of the CCR Rule ( (f)). At least eight background samples were collected from each well in the CCR unit monitoring system by October 17, 2017; samples were analyzed for the constituents listed in Appendices III and IV of the CCR Rule ( (b)). Groundwater samples for the 2017 semiannual sampling event were collected from each well in the CCR monitoring system by October 17, 2017; samples were analyzed for constituents listed in Appendix III of the CCR Rule ( (c)). 4

9 2.1.3 Key Activities for Upcoming Year The following key activities for the groundwater monitoring system are planned for 2018: Wells in the CCR Groundwater Monitoring System and dedicated bladder pumps will be operated and maintained so that they perform to their design specifications ( (e)(2)). Sampling events for semiannual detection monitoring for Appendix III constituents are scheduled for April and October. Construction of CCR Cell 4 (Figure 2) has begun and will continue in The groundwater monitoring system will be expanded to monitor the new cell according to the CCR Rule. 2.2 Analytical Results and Statistical Evaluation Documentation Table 3 shows all of the analytical results and sample dates for the sampling events completed through 2017 for each of the six wells in the CCR unit groundwater monitoring system. The final sample for each well in Table 3 was collected on October 10, 2017; it is the first of the semiannual sampling events that need to be evaluated for SSIs. In Table 4 are the field blank results for the same sampling shown in Table 3. All samples were collected under the CCR detection monitoring program. The CCR Rule requires that groundwater elevations be measured in each well immediately prior to purging, and the rate and direction of groundwater flow determined each time groundwater is sampled ( (c)). All groundwater elevations are shown in Table 5. Figure 3 through Figure 11 show contours of the groundwater elevations for all multi-well sampling events, respectively. The groundwater gradient on all of these figures is generally from west to east across the CCR unit and toward the downgradient wells in the monitoring system. Gradients vary somewhat, but are generally consistent within a factor of two. On the other hand, hydraulic conductivities measured in the wells in the monitoring system vary by a factor of nearly 100 (Barr, 2017a) and therefore have a stronger influence on the estimated average groundwater velocity under the CCR unit. Given the natural variation in hydraulic conductivities at the site, the estimated average groundwater flow velocity in the WTA is about 0.02 ft/day (Barr, 2017a) for the groundwater contours shown on Figure 3 through Figure Key Actions Completed/Problems Encountered The following key actions were completed with respect to analytical results and statistical evaluation through 2017: Analytical results of the background samples were analyzed for statistical outliers by the Tukey box plot method, except for radium because the Tukey method is not compatible with the calculation used for combining radium 226 and 228. A multiplier of 1.5 of the interquartile range was used to calculate whisker length (US EPA, 2009). Only outliers with concentrations greater than detection were considered further. Of the nearly 1,000 analytical results reviewed, 13 were noted as being potential Tukey outliers (Table 6 and Appendix A); however, only one well had more than one outlier in a single sampling event. The measurements in the sample collected from 5

10 well on January 16, 2017, were responsible for 5 of the 13 outliers noted. Furthermore, cobalt was below detection (< 2.0 µg/l) for all sampling events in all wells, except for the January sampling event for well , when it was measured at 4.3 µg/l. Therefore, all measurements from the laboratory from which multiple outliers were detected for this sampling event were deleted from the background pool; the only analytical results retained from the January 2017 sampling event for well were ph, which was measured in the field, and radium 226 and 228, which were measured by a different laboratory. A replacement sample was taken from well on September 28, 2017, so that all Appendices III and IV constituents had at least eight background analytical results ( (b)). The results from the background samples were analyzed and evaluated to determine appropriate statistical evaluation methods. It was concluded that intrawell control charts are the preferred statistical method. Control charts will be used to evaluate for SSIs for each parameter, provided that the data set satisfies the statistical assumptions and requirements in the Groundwater Statistical Analysis Plan (Barr, 2017b) and the CCR Rule. A QPE certified that the selected statistical method is appropriate for evaluating the groundwater monitoring data for the CCR unit (Barr, 2017b), as required by the CCR Rule ( (f)(6)). Groundwater samples from the four downgradient CCR wells for the 2017 semiannual sampling event were analyzed for constituents listed in Appendix III of the CCR Rule and evaluated for SSIs using intrawell analyses. None of the constituents had SSIs (Appendix B); therefore, transition to an assessment monitoring program was not necessary Key Activities for Upcoming Year The following key activities for analytical results and statistical evaluation are planned for 2018: Evaluate analytical results from the 2018 semiannual detection monitoring events for SSIs according to the Groundwater Statistical Analysis Plan (Barr, 2017b). For any new wells resulting from construction of Cell 4 (Figure 2), collect and analyze samples according to the site sampling and analysis program, Groundwater Statistical Analysis Plan (Barr, 2017b), and the CCR Rule. 6

11 Barr, 2017a, Groundwater Monitoring System Certification Report, October Barr, 2017b, Groundwater Statistical Analysis Plan, Revision 1, December References US EPA, 2009, Statistical Analysis of Groundwater Monitoring Data at RCRA Facilities Unified Guidance, EPA 530-R , March US EPA, 2015, Hazardous and Solid Waste Management System; Disposal of Coal Combustion Residuals From Electric Utilities; Final Rule, Federal Register vol. 80, no. 74. Yeskis, D. and B. Zavala, 2002, Ground-Water Sampling Guidelines for Superfund and RCRA Project Managers, EPA 542-S

12 Tables

13 Table 2 Monitoring Well Construction Details

14 Well Identification Number Orientation to CCR unit Borehole Name Installation Date (Month/Day/Year) Ground Surface Elevation (feet, MSL) TOR Elevation (feet above MSL) Table 2 Monitoring Well Construction Details M. R. Young Station Minnkota Power Cooperative, Inc. Constructed Depth (feet BGS) Casing Screen Interval (feet BGS) Screen Sand Pack Borehole Diameter (inches) Pump Intake from TOS (feet) CCR Monitoring Wells Upgradient UGD1 10/8/ inch PVC Sch to 193 No. 6 slotted PVC Sch silica sand Upgradient UGS1 10/9/ inch PVC Sch to 150 No. 6 slotted PVC Sch silica sand Downgradient DGS2 10/21/ inch PVC Sch to 132 No. 6 slotted PVC Sch silica sand Downgradient DGS3 10/20/ inch PVC Sch to 136 No. 6 slotted PVC Sch silica sand Downgradient DGS4 10/13/ inch PVC Sch to 168 No. 6 slotted PVC Sch silica sand Downgradient DGS5 10/6/ inch PVC Sch to 153 No. 6 slotted PVC Sch silica sand 6 19 Monitoring Wells for Water Levels Only 92-5A Upgradient Not applicable 9/4/ inch PVC SDR to 185 No. 10 slotted PVC silica sand A Upgradient Not applicable 8/31/ inch PVC SDR to No. 10 slotted PVC silica sand Downgradient Not applicable 9/8/ inch PVC SDR to No. 10 slotted PVC silica sand 4.75 Not applicable 95-4 Downgradient Not applicable 8/1/ inch PVC Sch to 145 No. 10 slotted PVC silica sand 5.25 Not applicable BGS - below ground surface MSL - mean sea level PVC - polyvinyl chloride Sch - schedule SDR - standard dimension ratio (outside diameter divided by the wall thickness) TOR - top of riser TOS - top of screen P:\Mpls\34 ND\33\ Minnkota Ash Management\WorkFiles\CCR Groundwater 2\Annual GW Monitoring and Corrective Action Report\Tables\Table 2 Monitoring Well Construction Details.xlsx

15 Table 3 Water Quality Results

16 Table 3 Water Quality Results Detection Monitoring Program Minnkota Power Cooperative, Inc. Parameter Total or Dissolved Analysis Location Location Date Sample Type Units Upgradient Background SSI Evaluation /06/ /05/2016 1/10/2017 3/07/2017 4/19/2017 5/31/2017 7/11/2017 8/15/ /10/2017 N N N N N N N N N Appendix III Constituents Boron Total Lab mg/l Calcium Total Lab mg/l Chloride NA Lab mg/l Fluoride NA Lab mg/l ph NA Field ph units Sulfate, as SO4 NA Lab mg/l Solids, total dissolved NA Lab mg/l Appendix IV Constituents Antimony Total Lab mg/l < < < < < < < Arsenic Total Lab mg/l < < 0.01 < Barium Total Lab mg/l Beryllium Total Lab mg/l < < < < < < < < Cadmium Total Lab mg/l < < < < < < < < Chromium Total Lab mg/l < < < < < < < Cobalt Total Lab mg/l < < < < < < < < Lead Total Lab mg/l < < < Lithium Total Lab mg/l < 0.1 < 0.1 < 0.1 < 0.1 < 0.1 < 0.1 < 0.1 < Mercury Total Lab mg/l < < < < < < < < Molybdenum Total Lab mg/l < 0.01 < 0.02 < Selenium Total Lab mg/l < < < < < < < < Thallium Total Lab mg/l < < < < < < < < Radium 226 NA Lab pci/l 0.3 +/ /- 0.1 ND /- 0.1 ND 0.2 +/ / ND 0.1 +/ ND 0.1 +/ ND 0.1 +/ ND -- Radium 228 NA Lab pci/l 2 +/- 3.6 ND /- 3.2 ND /- 1.5 ND /- 1.3 ND /- 2.9 ND /- 1.3 ND /- 1.6 ND /- 1.7 ND -- Radium, combined ( ) 1 NA Calc pci/l 2.3 +/- 3.6 q < /- 0.1 < / /- 1.3 q < / < 0.1 +/ < /- 1.6 < 0.1 +/ Other Constituents Temperature NA Field deg C Turbidity NA Field NTU Not analyzed/not available. N Sample Type: Normal FD Sample Type: Field Duplicate * Estimated value, QA/QC criteria not met. ND Not detected. q The combined radium result includes both detected and not detected values. 1 See note following table on Combined Radium Calculation. Page 1 of 6 12/14/2017 P:\Mpls\34 ND\33\ Minnkota Ash Management\WorkFiles\CCR Groundwater 2\Annual GW Monitoring and Corrective Action Report\Tables\Table 3 Water Quality Results_ _SFK.xlsx

17 Table 3 Water Quality Results Detection Monitoring Program Minnkota Power Cooperative, Inc. Parameter Total or Dissolved Analysis Location Location Date Sample Type Units Appendix III Constituents Boron Total Lab mg/l Calcium Total Lab mg/l Chloride NA Lab mg/l Fluoride NA Lab mg/l ph NA Field ph units Sulfate, as SO4 NA Lab mg/l Solids, total dissolved NA Lab mg/l Appendix IV Constituents Antimony Total Lab mg/l Arsenic Total Lab mg/l Barium Total Lab mg/l Beryllium Total Lab mg/l Cadmium Total Lab mg/l Chromium Total Lab mg/l Cobalt Total Lab mg/l Lead Total Lab mg/l Lithium Total Lab mg/l Mercury Total Lab mg/l Molybdenum Total Lab mg/l Selenium Total Lab mg/l Thallium Total Lab mg/l Radium 226 NA Lab pci/l Radium 228 NA Lab pci/l Radium, combined ( ) 1 NA Calc pci/l Other Constituents Temperature NA Field deg C Turbidity NA Field NTU Upgradient Background SSI Evaluation /06/ /05/2016 1/10/2017 3/07/2017 4/20/2017 5/31/2017 7/11/2017 8/15/ /10/2017 N N N N N N N N N < < < < < < < < 0.01 < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < 0.1 < 0.1 < 0.1 < 0.1 < 0.1 < 0.1 < 0.1 < < < < < < < < < < 0.01 < 0.02 < < < < < < < < < < < < < < < < < / / /- 0.1 ND /- 0.1 ND /- 0.1 ND 0.1 +/ ND 0.2 +/ / /- 4.4 ND /- 3.2 ND /- 1.5 ND 0 +/- 1.5 ND 0 +/- 1.5 ND 0.7 +/- 1.3 ND /- 1.6 ND /- 1.6 ND /- 0.1 q 0.3 +/- 0.1 q < /- 0.1 < /- 1.5 < /- 1.5 < 0.8 +/ /- 0.1 q 0.2 +/- 0.1 q Not analyzed/not available. N Sample Type: Normal FD Sample Type: Field Duplicate * Estimated value, QA/QC criteria not met. ND Not detected. q The combined radium result includes both detected and not detected values. 1 See note following table on Combined Radium Calculation. Page 2 of 6 12/14/2017 P:\Mpls\34 ND\33\ Minnkota Ash Management\WorkFiles\CCR Groundwater 2\Annual GW Monitoring and Corrective Action Report\Tables\Table 3 Water Quality Results_ _SFK.xlsx

18 Table 3 Water Quality Results Detection Monitoring Program Minnkota Power Cooperative, Inc. Parameter Total or Dissolved Analysis Location Location Date Sample Type Units Appendix III Constituents Boron Total Lab mg/l Calcium Total Lab mg/l Chloride NA Lab mg/l Fluoride NA Lab mg/l ph NA Field ph units Sulfate, as SO4 NA Lab mg/l Solids, total dissolved NA Lab mg/l Appendix IV Constituents Antimony Total Lab mg/l Arsenic Total Lab mg/l Barium Total Lab mg/l Beryllium Total Lab mg/l Cadmium Total Lab mg/l Chromium Total Lab mg/l Cobalt Total Lab mg/l Lead Total Lab mg/l Lithium Total Lab mg/l Mercury Total Lab mg/l Molybdenum Total Lab mg/l Selenium Total Lab mg/l Thallium Total Lab mg/l Radium 226 NA Lab pci/l Radium 228 NA Lab pci/l Radium, combined ( ) 1 NA Calc pci/l Other Constituents Temperature NA Field deg C Turbidity NA Field NTU Downgradient Background SSI Evaluation /06/ /04/2016 1/16/2017 3/07/2017 4/18/2017 5/31/2017 7/11/2017 8/15/2017 9/28/ /10/2017 N N N N N N N N N N * * < < < < < 0.01 < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < 0.1 < 0.1 < 0.1 < 0.1 < 0.1 < 0.1 < 0.1 < 0.1 < < < < < < < < < < < 0.01 < 0.02 < < < < < < < < < < < < < < < < < / / /- 0.1 ND 0.4 +/ / /- 0.1 ND / ND /- 0.1 ND 0.2 +/ / /- 3.1 ND /- 1.9 ND 0.5 +/- 1.2 ND /- 3 ND /- 1.6 ND 1.5 +/- 1.6 ND /- 1.6 ND 0.6 +/- 1.8 ND / /- 3.1 q < / /- 1.2 q 0.2 +/- 0.1 q < /- 0.1 < /- 1.6 < / /- 1.8 q Not analyzed/not available. N Sample Type: Normal FD Sample Type: Field Duplicate * Estimated value, QA/QC criteria not met. ND Not detected. q The combined radium result includes both detected and not detected values. 1 See note following table on Combined Radium Calculation. 2 Five statistical outliers (Tukey method) were found for the January 2017 sample for As a result only values for ph and radium were retained in the background dataset. Page 3 of 6 12/14/2017 P:\Mpls\34 ND\33\ Minnkota Ash Management\WorkFiles\CCR Groundwater 2\Annual GW Monitoring and Corrective Action Report\Tables\Table 3 Water Quality Results_ _SFK.xlsx

19 Table 3 Water Quality Results Detection Monitoring Program Minnkota Power Cooperative, Inc. Parameter Total or Dissolved Analysis Location Location Date Sample Type Units Appendix III Constituents Boron Total Lab mg/l Calcium Total Lab mg/l Chloride NA Lab mg/l Fluoride NA Lab mg/l ph NA Field ph units Sulfate, as SO4 NA Lab mg/l Solids, total dissolved NA Lab mg/l Appendix IV Constituents Antimony Total Lab mg/l Arsenic Total Lab mg/l Barium Total Lab mg/l Beryllium Total Lab mg/l Cadmium Total Lab mg/l Chromium Total Lab mg/l Cobalt Total Lab mg/l Lead Total Lab mg/l Lithium Total Lab mg/l Mercury Total Lab mg/l Molybdenum Total Lab mg/l Selenium Total Lab mg/l Thallium Total Lab mg/l Radium 226 NA Lab pci/l Radium 228 NA Lab pci/l Radium, combined ( ) 1 NA Calc pci/l Other Constituents Temperature NA Field deg C Turbidity NA Field NTU Downgradient SSI Background Evaluation /06/ /05/2016 1/11/2017 3/07/2017 4/20/2017 5/31/2017 7/11/2017 8/15/ /10/2017 N N N N N N N N N < < < < < < < < < < 0.01 < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < 0.1 < 0.1 < 0.1 < 0.1 < 0.1 < 0.1 < 0.1 < < < < < < < < < < 0.01 < 0.02 < < < < < < < < < < < < < < < < < / /- 0.1 ND / ND 0.2 +/ / /- 0.1 ND 0.1 +/ ND /- 0.1 ND /- 3.9 ND 0.9 +/- 3.1 ND 0.3 +/- 1.4 ND /- 1.4 ND /- 1.4 ND /- 1.4 ND 0.6 +/- 1.6 ND 0.5 +/- 1.5 ND /- 0.1 q < /- 3.1 < / /- 1.4 q 0.2 +/- 0.1 q < /- 0.1 < 0.7 +/- 1.6 < / Not analyzed/not available. N Sample Type: Normal FD Sample Type: Field Duplicate * Estimated value, QA/QC criteria not met. ND Not detected. q The combined radium result includes both detected and not detected values. 1 See note following table on Combined Radium Calculation. Page 4 of 6 12/14/2017 P:\Mpls\34 ND\33\ Minnkota Ash Management\WorkFiles\CCR Groundwater 2\Annual GW Monitoring and Corrective Action Report\Tables\Table 3 Water Quality Results_ _SFK.xlsx

20 Table 3 Water Quality Results Detection Monitoring Program Minnkota Power Cooperative, Inc. Parameter Total or Dissolved Analysis Location Location Date Sample Type Units Appendix III Constituents Boron Total Lab mg/l Calcium Total Lab mg/l Chloride NA Lab mg/l Fluoride NA Lab mg/l ph NA Field ph units Sulfate, as SO4 NA Lab mg/l Solids, total dissolved NA Lab mg/l Appendix IV Constituents Antimony Total Lab mg/l Arsenic Total Lab mg/l Barium Total Lab mg/l Beryllium Total Lab mg/l Cadmium Total Lab mg/l Chromium Total Lab mg/l Cobalt Total Lab mg/l Lead Total Lab mg/l Lithium Total Lab mg/l Mercury Total Lab mg/l Molybdenum Total Lab mg/l Selenium Total Lab mg/l Thallium Total Lab mg/l Radium 226 NA Lab pci/l Radium 228 NA Lab pci/l Radium, combined ( ) 1 NA Calc pci/l Other Constituents Temperature NA Field deg C Turbidity NA Field NTU Downgradient Background SSI Evaluation /05/ /04/2016 1/11/2017 3/08/2017 4/19/2017 5/30/2017 7/12/2017 8/15/ /10/2017 N N N N N N FD N N N * < < < < < < < < < < < < < 0.01 < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < 0.1 < 0.1 < 0.1 < 0.1 < 0.1 < 0.1 < 0.1 < 0.1 < < < < < < < < < < < < 0.01 < 0.01 < 0.02 < < < < < < < < < < < < < < < < < < < /- 0.1 ND 0.3 +/ / ND 0.2 +/ /- 0.1 ND 0.3 +/ / ND /- 0.1 ND 0.1 +/- 0.1 ND /- 1.2 ND 4.7 +/ /- 1.6 ND 0.9 +/- 1.5 ND /- 1.5 ND /- 1.5 ND 0.2 +/- 1.3 ND /- 1.6 ND /- 1.6 ND -- < 0.1 +/ /- 3 < 0.1 +/ /- 1.5 q < 0.1 +/ /- 0.1 q < 0.3 +/- 1.3 < /- 0.1 < 0.1 +/ Not analyzed/not available. N Sample Type: Normal FD Sample Type: Field Duplicate * Estimated value, QA/QC criteria not met. ND Not detected. q The combined radium result includes both detected and not detected values. 1 See note following table on Combined Radium Calculation. Page 5 of 6 12/14/2017 P:\Mpls\34 ND\33\ Minnkota Ash Management\WorkFiles\CCR Groundwater 2\Annual GW Monitoring and Corrective Action Report\Tables\Table 3 Water Quality Results_ _SFK.xlsx

21 Table 3 Water Quality Results Detection Monitoring Program Minnkota Power Cooperative, Inc. Parameter Total or Dissolved Analysis Location Location Date Sample Type Units Appendix III Constituents Boron Total Lab mg/l Calcium Total Lab mg/l Chloride NA Lab mg/l Fluoride NA Lab mg/l ph NA Field ph units Sulfate, as SO4 NA Lab mg/l Solids, total dissolved NA Lab mg/l Appendix IV Constituents Antimony Total Lab mg/l Arsenic Total Lab mg/l Barium Total Lab mg/l Beryllium Total Lab mg/l Cadmium Total Lab mg/l Chromium Total Lab mg/l Cobalt Total Lab mg/l Lead Total Lab mg/l Lithium Total Lab mg/l Mercury Total Lab mg/l Molybdenum Total Lab mg/l Selenium Total Lab mg/l Thallium Total Lab mg/l Radium 226 NA Lab pci/l Radium 228 NA Lab pci/l Radium, combined ( ) 1 NA Calc pci/l Other Constituents Temperature NA Field deg C Turbidity NA Field NTU Downgradient SSI Background Evaluation /28/2016 1/11/2017 3/09/2017 4/20/2017 5/30/2017 6/15/2017 7/12/2017 8/16/ /10/2017 N N N FD N N N N N FD N < < < < < < < < < < < < < < < < < < 0.01 < 0.01 < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < 0.1 < 0.1 < 0.1 < 0.1 < 0.1 < 0.1 < 0.1 < 0.1 < 0.1 < < < < < < < < < < < < < 0.02 < 0.01 < < < < < < < < * < < < < < < < < < < < < /- 0.1 ND 0.1 +/ ND 0.4 +/ / / / ND 0.1 +/- 0.1 ND 0.1 +/- 0.1 ND 0.1 +/- 0.1 ND /- 0.1 ND /- 2.9 ND /- 1.6 ND 0.2 +/- 1.5 ND /- 1.6 ND 0.3 +/- 1.3 ND /- 1.5 ND -2 +/- 1.6 ND /- 1.6 ND /- 1.6 ND /- 1.5 ND -- < 2.7 +/- 2.9 < 0.1 +/ /- 1.5 q 0.3 +/- 1.6 q 0.5 +/- 1.3 q < 0.1 +/ < 0.1 +/- 0.1 < 0.1 +/- 0.1 < 0.1 +/- 0.1 < / Not analyzed/not available. N Sample Type: Normal FD Sample Type: Field Duplicate * Estimated value, QA/QC criteria not met. ND Not detected. q The combined radium result includes both detected and not detected values. 1 See note following table on Combined Radium Calculation. Page 6 of 6 12/14/2017 P:\Mpls\34 ND\33\ Minnkota Ash Management\WorkFiles\CCR Groundwater 2\Annual GW Monitoring and Corrective Action Report\Tables\Table 3 Water Quality Results_ _SFK.xlsx

22 Combined Radium Calculation 12/13/2017 Combining Ra-226 and Ra-228 Results After individually verifying results as detected or ND and addressing any blanks contamination, calculate as detailed below: Both results detected add the numerical results and combine the uncertainties as follows: Where: U = Uncertainty for the associated radium isotope Both results ND add the numerical results and combine the uncertainties as per equation above. Report the ND combined result as less than (<). One result detected and the other result ND add the numerical results and combine the uncertainties as per equation above. Qualify the combined result q. The q qualifier states The combined radium result includes both detected and not detected values. Negative results are considered ND. Replace with zero when adding numerical results together and do not combine the counting uncertainty of a negative result. Report only the detected result and uncertainty. If both results are negative, report as < 0. Examples Ra ± 0.20 detected, Ra ± 0.30 detected = 1.0 ± 0.36 Ra ± 0.20 detected, Ra ± 0.30 ND = 1.0 ± 0.36 with q qualifier Ra ± 0.20 ND, Ra ± 0.30 ND = < 1.0 ± 0.36 Ra ± 0.20 detected, Ra ± 0.30 = 0.5 ± 0.20 with q qualifier Ra ± 0.20, Ra ± 0.30 = < 0

23 Table 4 Field Blank Results

24 Parameter Total or Dissolved Analysis Location Location Date Sample Type Units Table 4 Field Blank Results Detection Monitoring Program Minnkota Power Cooperative, Inc. QC QC QC QC QC QC QC 1/13/2017 3/09/2017 4/20/2017 5/31/2017 7/12/2017 8/24/ /10/2017 Field Blank Field Blank Field Blank Field Blank Field Blank Field Blank Field Blank Appendix III Constituents Boron Total Lab mg/l < 0.1 < 0.1 < 0.1 < 0.1 < 0.1 < 0.1 < 0.1 Calcium Total Lab mg/l < 1 < 1 < 1 < 1 < 1 < 1 < 1 Chloride NA Lab mg/l < 1 < 1 < 1 < 1 < 1 < 1 < 1 Fluoride NA Lab mg/l < 0.1 < 0.1 < 0.1 < 0.1 < 0.1 < 0.1 < 0.1 ph NA Lab ph units Sulfate, as SO4 NA Lab mg/l < 5 < 5 < 5 < 5 < 5 < 5 < 5 Solids, total dissolved NA Lab mg/l < 5 < 10 < 10 < 10 < 10 < 10 < 10 Appendix IV Constituents Antimony Total Lab mg/l < < < < < < Arsenic Total Lab mg/l < < < < < 0.01 < Barium Total Lab mg/l < < < < < < Beryllium Total Lab mg/l < < < < < < Cadmium Total Lab mg/l < < < < < < Chromium Total Lab mg/l < < < < < < Cobalt Total Lab mg/l < < < < < < Lead Total Lab mg/l < < < < < < Lithium Total Lab mg/l < 0.1 < 0.1 < 0.1 < 0.1 < 0.1 < Mercury Total Lab mg/l < < < < < < Molybdenum Total Lab mg/l < < < < 0.01 < 0.02 < Selenium Total Lab mg/l < < < < < < Thallium Total Lab mg/l < < < < < < Radium 226 NA Lab pci/l / ND / ND 0.3 +/ /- 0.1 ND 0.1 +/ ND / ND Radium 228 NA Lab pci/l -1 +/- 0.6 ND /- 1.4 ND /- 2.8 ND /- 1.5 ND /- 1.6 ND 0.5 +/- 2.3 ND Radium, combined ( ) 1 NA Calc pci/l < /- 0.6 < / /- 2.8 q < /- 0.1 < 0.1 +/ < / Not analyzed/not available. ND Not detected. q The combined radium result includes both detected and not detected values. 1 See note following table on Combined Radium Calculation. Page 1 of 1 12/14/2017 P:\Mpls\34 ND\33\ Minnkota Ash Management\WorkFiles\CCR Groundwater 2\Annual GW Monitoring and Corrective Action Report\Tables\Table 4 Field Blank Results_ _SFK.xlsx

25 Combined Radium Calculation 12/13/2017 Combining Ra-226 and Ra-228 Results After individually verifying results as detected or ND and addressing any blanks contamination, calculate as detailed below: Both results detected add the numerical results and combine the uncertainties as follows: Where: U = Uncertainty for the associated radium isotope Both results ND add the numerical results and combine the uncertainties as per equation above. Report the ND combined result as less than (<). One result detected and the other result ND add the numerical results and combine the uncertainties as per equation above. Qualify the combined result q. The q qualifier states The combined radium result includes both detected and not detected values. Negative results are considered ND. Replace with zero when adding numerical results together and do not combine the counting uncertainty of a negative result. Report only the detected result and uncertainty. If both results are negative, report as < 0. Examples Ra ± 0.20 detected, Ra ± 0.30 detected = 1.0 ± 0.36 Ra ± 0.20 detected, Ra ± 0.30 ND = 1.0 ± 0.36 with q qualifier Ra ± 0.20 ND, Ra ± 0.30 ND = < 1.0 ± 0.36 Ra ± 0.20 detected, Ra ± 0.30 = 0.5 ± 0.20 with q qualifier Ra ± 0.20, Ra ± 0.30 = < 0

26 Table 5 Water Level Results

27 Table 5 Water Level Results Detection Monitoring Program Minnkota Power Cooperative, Inc. Location Sample Type Purge Date Water Level Before Purge Top of Casing Elevation Groundwater Elevation /5/ /4/ /9/ /6/ Upgradient Background 4/18/ /30/ /10/ /14/ SSI Evaluation 10/9/ /5/ /4/ /9/ /6/ Upgradient Background 4/17/ /30/ /10/ /14/ SSI Evaluation 10/9/ /5/ /3/ /9/ /6/ Background 4/17/ Downgradient /30/ /10/ /14/ /27/ SSI Evaluation 10/9/ /5/ /4/ /10/ /6/ Downgradient Background 4/17/ /30/ /10/ /14/ SSI Evaluation 10/9/ /5/ /4/ /11/ /8/ Downgradient Background 4/19/ /30/ /12/ /15/ SSI Evaluation 10/10/ of 2 12/14/2017 P:\Mpls\34 ND\33\ Minnkota Ash Management\WorkFiles\CCR Groundwater 2\Annual GW Monitoring and Corrective Action Report\Tables\Table 5 Water Level Results_ _SFK.xlsx

28 Table 5 Water Level Results Detection Monitoring Program Minnkota Power Cooperative, Inc. Location Sample Type Purge Date Water Level Before Purge Top of Casing Elevation Groundwater Elevation /28/ /11/ /9/ /20/ Downgradient Background 5/30/ /15/ /12/ /16/ SSI Evaluation 10/10/ /7/ Downgradient 5/31/ /11/ A 6/9/ A 10/6/ A 1/12/ A 3/8/ A Upgradient 4/19/ A 5/31/ A 7/11/ A 8/24/ A 10/10/ A 5/5/ A 10/5/ A 1/13/ A 3/8/ A Upgradient 4/17/ A 5/31/ A 7/10/ A 8/14/ A 10/9/ /7/ Downgradient 5/31/ /11/ of 2 12/14/2017 P:\Mpls\34 ND\33\ Minnkota Ash Management\WorkFiles\CCR Groundwater 2\Annual GW Monitoring and Corrective Action Report\Tables\Table 5 Water Level Results_ _SFK.xlsx

29 Table 6 Tukey Method Results for Outliers

30 Table 6 Tukey Method Results for Outliers Detection Monitoring Program Minnkota Power Cooperative, Inc. Well Location Date Constituent Upgradient 7/6/2017 Total Dissolved Solids 1/11/2017 ph Upgradient 4/20/2017 Fluoride 1/16/2017 Barium 1/16/2017 Calcium Downgradient 1/16/2017 Chloride 1/16/2017 Chromium 1/16/2017 Lead Downgradient 1/11/2017 Calcium Downgradient 1/11/2017 Boron 10/28/2016 Total Dissolved Solids Downgradient 4/20/2017 Chloride 8/16/2017 Sulfate as SO4 Yellow shading highlights sample with multiple outliers noted by Tukey method.

31 Figures

32 Figure 1 Site Layout

33 Barr Footer: ArcGIS , :28 File: I:\Projects\34\33\1014\Maps\Reports\Minnkota\GW_Monitoring_Certification\Figure 1 Site Layout.mxd User: MRQ RD 23 SW ST 24TH ST SW Property Boundary Nelson Lake Closed Cell Location Existing Cell Location Ha g el C r e e k 24 k Cree tte Bu re ua Sq 1/ 2 ST SW Proposed Cell Location Cell 1 35TH AVE SW Cell 2 Cell 3 Cell 4 ;! N 0 MERCER COUNTY OLIVER COUNTY MORTON COUNTY MCLEAN COUNTY 625 1,250 Feet SHERIDAN COUNTY SITE LAYOUT M.R. Young Station Center, North Dakota Minnkota Power Cooperative, Inc. Site Location BURLEIGH COUNTY Service Layer Credits: Copyright: 2013 National Geographic Society, i-cubed FIGURE 1

34 Figure 2 CCR Unit Location

35 Barr Footer: ArcGIS , :53 File: I:\Projects\34\33\1014\Maps\Reports\Minnkota\GW_Monitoring_Certification\Figure 2 Landfill Area.mxd User: MRQ #* 92-5A Cell #* 95-4 #* #* Monitoring Well For Water Level Only ") Downgradient Monitoring Well!( Upgradient Monitoring Well Closed Landfill Area Landfill Area CCR Unit Note: * Cell 4 is proposed !(!( Cell ") 92-6A #* ") Cell 3 Cell 4* ") ")!;N Feet CCR UNIT LOCATION M.R. Young Station Center, North Dakota Minnkota Power Cooperative, Inc. FIGURE 2