6. Final_2023_Annual_GW_Monitoring_Report_SA026 (RPM needs to add to AR).pdf

FINAL

2023 GROUNDWATER MONITORING REPORT

RA-O PERFORMANCE MONITORING FOR SITE SA026

– FORMER MAIN COAL STORAGE AREA

SCOTT AIR FORCE BASE, ILLINOIS

Prepared for:

AIR FORCE CIVIL ENGINEERING CENTER

2261 Hughes Avenue, Suite 155

Lackland AFB, Texas 78236-9853

Contract FA8903-14-C-0009

May 2024

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FINAL

2023 GROUNDWATER MONITORING REPORT

RA-O PERFORMANCE MONITORING FOR SITE SA026

– FORMER MAIN COAL STORAGE AREA

SCOTT AIR FORCE BASE, ILLINOIS

Prepared for:

AIR FORCE CIVIL ENGINEERING CENTER

2261 Hughes Avenue, Suite 155

Lackland AFB, Texas 78236-9853

Contract FA8903-14-C-0009

May 2024

Prepared by:

Plexus Scientific Corporation 5510 Cherokee Avenue, Suite 350

Alexandria, Virginia 22312

Final 2023 Groundwater Monitoring Report RA-O Performance Monitoring for Site SA026

Scott Air Force Base, Illinois i

TABLE OF CONTENTS

1.0 INTRODUCTION

1.1 Report Organization

1.2 Site Description and History

1.3 Previous Investigations

1.4 Site-Specific Geology

1.5 Site-Specific Hydrogeology

2.0 SUMMARY OF GROUNDWATER MONITORING FIELD ACTIVITIES

2.1 Water Level Measurements

2.2 Groundwater Sampling Activities

2.3 Investigation-Derived Waste Disposal

3.0 DATA QUALITY EVALUATION

3.1 Quality Assurance/Quality Control Sampling

3.2 Data Validation

3.3 Data Quality Assessment and Usability

3.3.1 Precision

3.3.2 Accuracy

3.3.3 Representativeness

3.3.4 Comparability

3.3.5 Completeness

3.3.6 Sensitivity

3.4 Conclusions and Recommendations

4.0 SUMMARY OF ANALYTICAL RESULTS

4.1 Zone 1 Groundwater Flow Direction and Hydraulic Gradient

4.2 Groundwater Analytical Data

4.2.1 Manganese Results

4.2.2 Sulfate Results

4.2.3 Groundwater Trend Analysis

4.2.4 Statistical Analysis

5.0 CONCLUSIONS AND RECOMMENDATIONS

6.0 REFERENCES

Scott Air Force Base, Illinois ii

LIST OF TABLES

Table 1-1 – Hydrogeologic Zones at Scott AFB Table 2-1 – Groundwater Sample Analysis Summary Table 2-2 – Summary of Depth to Water Measurements Table 2-3 – Final Groundwater Quality Parameters Table 4-1 – Calculated Hydraulic Gradients for Zone 1 Table 4-2 – Groundwater Analytical Data for the Annual 2023 Event Table 4-3 – Mann-Kendall Analyses for Manganese Table 4-4 – Mann-Kendall Analyses for Sulfate Table 4-5 – Historical Groundwater Analytical Data

LIST OF FIGURES

Figure 1-1 Scott AFB Location Map Figure 1-2 SA026 Site Location Map Figure 1-3 Site SA026 Former MCSA - Monitoring Well Network Figure 1-4 Extent of Subsurface Coal Fragments Figure 4-1 Potentiometric Surface Map - June 2023 Figure 4-2 Site SA026 Former MCSA - Estimated Manganese Plume Figure 4-3 Site SA026 Former MCSA - Estimated Sulfate Plume

LIST OF APPENDICES

Appendix A Field Forms / IDW Manifests Appendix B Laboratory Analytical Report - CD ONLY Appendix C Data Validation Report Appendix D Analytical Trend Graphs Appendix E Statistical Analysis Supporting Documentation

Scott Air Force Base, Illinois iii

ACRONYMS AND ABBREVIATIONS

% percent °C degree Celsius µg/L micrograms per liter AFB Air Force Base amsl above mean sea level bgs below ground surface btoc below top of casing COC contaminant of concern DL detection limit DO dissolved oxygen DoD Department of Defense FS Feasibility Study ft msl feet mean sea level ft/ft feet per foot GQS Groundwater Quality Standards GWE groundwater elevation HGL Hydrogeologic, Inc.

i hydraulic gradient IDW investigation-derived waste K hydraulic conductivity LCS laboratory control sample LCSD laboratory control sample duplicate LOD limit of detection LOQ limit of quantitation LUC land use control MAROS Monitoring and Remediation Optimization System MCSA Main Coal Storage Area mg/L milligrams per liter MS matrix spike mS/cm milliSiemens per centimeter MSD matrix spike duplicate MSL Mean sea level mV millivolts NRCS Natural Resources Conservation Service NTU nephelometric turbidity unit ORP oxidation reduction potential PA Preliminary Assessment Pace Pace Analytical Gulf Coast Laboratories PARCCS precision, accuracy, representativeness, comparability, completeness, and sensitivity Plexus Plexus Scientific Corporation QSM DoD Quality Systems Manual for Environmental Laboratories RA-O Remedial Action-Operation RI Remedial Investigation

Scott Air Force Base, Illinois iv

ACRONYMS AND ABBREVIATIONS (CONTINUED)

RO remediation objective RPD relative percent difference SAIC Science Applications International Corporation SDG sample delivery group SI Site Inspection SU standard units Tetra Tech Tetra Tech Inc.

U.S. United States UFP-QAPP Uniform Federal Policy-Quality Assurance Project Plan USACE U.S. Army Corps of Engineers USAF U.S. Air Force USDA U.S. Department of Agriculture USEPA U.S. Environmental Protection Agency USGS U.S. Geological Survey Vs seepage velocity η effective porosity

Scott Air Force Base, Illinois

1.0 INTRODUCTION

Plexus Scientific Corporation (Plexus) conducted performance monitoring for Environmental Restoration Program Site SA026 at Scott Air Force Base (AFB) under contract to the Air Force Civil Engineer Center, Contract Number FA8903-14-C-0009. The work was performed under the United States (U.S.) Environmental Protection Agency’s Comprehensive Environmental Response, Compensation, and Liability Act program.

The purpose of this report is to document and evaluate the results of the annual 2023 performance monitoring activities conducted at Site SA026. These activities were conducted on May 31, 2023 and between June 3 and 6, 2023. Based on the annual 2023 data set, this report also makes recommendations for future monitoring.

1.1 Report Organization

This report consists of six sections:

• Section 1.0 – Introduction: Provides a general background of the project and describes the organization and intent of this monitoring report.

• Section 2.0 – Summary of Groundwater Monitoring Field Activities: Summarizes the field activities that were completed during the sampling event.

• Section 3.0 – Data Quality Evaluation: Describes the data quality evaluation process used to review the collected data and the results of that evaluation.

• Section 4.0 – Summary of Analytical Results: Provides the results of the sampling and an evaluation of the results. A qualitative trend analysis and Mann-Kendall statistical trend analysis are presented for the historical data set.

• Section 5.0 – Conclusions and Recommendations: Presents the conclusions for the annual 2023 data set and recommendations for future monitoring activities.

• Section 6.0 – References: Lists the references cited in the preparation of this report.

1.2 Site Description and History

Scott AFB is in St. Clair County, 25 miles southeast of St. Louis, Missouri, in southwestern Illinois (Figure 1-1). The city of Belleville, Illinois, is located approximately six miles southwest of Scott AFB; the city of O’Fallon, Illinois, is located approximately five miles to the northwest;

and the city of Mascoutah, Illinois, is located approximately five miles to the southeast. The property comprises 3,545 acres of U.S. government-owned and easement land. Scott AFB land is used exclusively as an active military base by the U.S. Department of Defense (DoD). Airbase facilities and runways compose the largest portion of the installation, which also includes living quarters and recreational facilities. St. Clair County entered into a joint use agreement with the U.S. Air Force (USAF) at Scott AFB for a civilian air carrier airport to be built on land adjacent to the base. MidAmerica Airport was constructed in the late 1990s. The predominant land use

Scott Air Force Base, Illinois surrounding Scott AFB is agricultural, with small retail shops located near the main entrance to the base (Hydrogeologic, Inc. [HGL], 2013).

Site SA026 encompasses six acres located in the southwestern corner of Scott AFB near the intersection of Ward Drive and the Norfolk Southern Railroad Trunk Line (Figure 1-2). From the 1930s through the mid-1960s, coal was the primary energy source for Scott AFB. Scott AFB began using the Main Coal Storage Area (MCSA) after a levee was constructed along Ash Creek, which is located adjacent to the site’s western boundary (Scott AFB, 1953a, 1953b).

According to as-built drawings and aerial photographs, the Ash Creek levee was constructed between August 1952 and June 1953 (Scott AFB, 1951, 1952, 1953a; U.S. Army Corps of Engineers [USACE], 1954). Coal piles and a former railroad spur, which cut diagonally across the southeastern corner of Site SA026 and connected with the Norfolk Southern Railroad Trunk Line, were first noted in an aerial photograph dated October 29, 1953 (Scott AFB, 1953b;

USACE, 1954; U.S. Geological Survey [USGS], 1954).

From the mid-1960s through the early 1970s, Scott AFB converted to using other forms of energy, and the bulk of the coal was consumed or removed from the Site. During this time, two baseball fields were constructed on the Site. The baseball fields remained in use until Building 1990 and the associated asphalt parking lot were built in 2007 (Tetra Tech, Inc. [Tetra Tech], 2008). The layout of Site SA026, including the former rail spur, is shown on Figure 1-3.

1.3 Previous Investigations

Previous investigations conducted at Site SA026 include an initial sampling event conducted by the Air Force in 1996, a Preliminary Assessment (PA)/Site Inspection (SI; Science Applications International Corporation [SAIC], 2005), and a Basewide Due Diligence Study Investigation Report (Tetra Tech, 2008).

The 2013 Remedial Investigation (RI)/Feasibility Study (FS) determined that manganese in groundwater at the former MCSA would pose a non-cancer hazard to human receptors if the shallow groundwater were used as a potable water supply. The 2013 RI/FS detected sulfate and manganese in groundwater at concentrations greater than the Illinois Groundwater Quality Standards (GQS) of 400 milligrams per liter (mg/L) and 6,120 micrograms per liter (µg/L)1, respectively. It was estimated in 2013 that natural attenuation would reduce sulfate and manganese concentration to less than the GQSs by 2023 (HGL, 2013); however, based on current groundwater data, restoration of the aquifer will require more time than was originally estimated.

The 2014 Record of Decision selected monitored natural attenuation and land use controls (LUCs) as the final remedy. The GQSs for manganese (6,120 µg/L) and sulfate (400 mg/L) were identified as the groundwater remediation objectives (ROs). LUCs are required to prevent incompatible land and groundwater use until cleanup goals are attained (USAF, 2014).

1 6,120 µg/L represents the maximum detected background concentration.

Scott Air Force Base, Illinois

Quarterly site inspections are being conducted to ensure that the implemented land and groundwater use prohibitions are not being violated. Current and reasonably anticipated future land use is industrial/commercial use only. Annual groundwater monitoring is being conducted to evaluate remedial progress towards cleanup goal attainment (HGL, 2016).

Boring logs from the previous investigations indicate widespread presence of coal, carbon nodules, cinders, and asphalt (potentially coal fragments that were mis-identified) in the shallow subsurface at the Site. These residual materials remained in place after the coal piles were removed and appear to serve as an ongoing source of groundwater contamination. The extent of these buried materials is shown on Figure 1-4.

1.4 Site-Specific Geology

Based on soil borings completed during the RI, the surface soil at Site SA026 consists of poorly drained, high to very high water capacity, Mascoutah silty clay loam (U.S. Department of Agriculture [USDA] Natural Resources Conservation Service [NRCS], 2000). This soil type is derived from windblown loess.

Shallow subsurface soil beneath the asphalt pavement consisted of various thicknesses of fill followed by silty clay to clayey silt. The natural subsurface soil encountered at the Site consisted of a silty clay of moderate plasticity that increased in silt content and decreased in plasticity with increasing depths. Five monitoring wells were installed in the asphalt parking lot (SA26- MW002, SA26-MW003, SA26-MW004, SA26-MW007, and SA26-MW008) (Figure 1-3;

HGL, 2013).

During installation of monitoring wells SA26-MW001, SA26-MW003, and SA26-MW005, clay was encountered beneath the gravel subbase and/or shallow subsurface material. Wells SA26- MW001 and SA26-MW005 were abandoned after sampling due to construction of a temporary building for the Army Surface Deployment and Distribution Command at the Site (Tetra Tech, 2008). The near-surface natural soil consists of Mascoutah silty clay loam with 0 to 2 percent (%) slopes (USDA NRCS, 2000). The silty clay matrix contained trace amounts of fine sand and varied in hue from dark brown to grayish brown. The material was characterized as moist with moderate plasticity. Iron oxide nodules were also noted within each well boring beginning at approximately 5.5 feet below ground surface (bgs), resulting in orange mottling of the soil. Each well boring contained this silty clay loam throughout the entire soil core, except for SA26- MW005, which encountered silt beginning at 14.3 feet bgs (HGL, 2013). The current groundwater monitoring network is shown on Figure 1-3.

1.5 Site-Specific Hydrogeology

To distinguish among the different hydrogeologic zones encountered at Scott AFB, the water bearing units have been divided as shown in Table 1-1.

Scott Air Force Base, Illinois

Table 1-1 – Hydrogeologic Zones at Scott AFB

Hydrogeologic Zone Basewide Estimated Depth Range (feet bgs)1

Zone 1 (shallow clay/silt zone) 3 to 18

Zone 2 (shallow silt/sand zone) 18 to 35

Zone 3 (lower clay/silt zone) 35 to 50

Zone 4 (lower silt/sand zone) 50 to 60

1) All depths are approximate.

bgs = below ground surface

All 14 permanent monitoring well borings were terminated between 15 and 20 feet bgs (HGL, 2013). All wells were screened within the Zone 1 water-bearing unit. As described in the human health risk assessment presented in the RI Report (HGL, 2013), all metals detected in the vadose zone and saturated matrix soil samples were identified as naturally occurring background constituents; therefore, further delineation beyond hydrogeologic Zone 1 was not warranted.

Groundwater in Zone 1 is unconfined and generally encountered between 3 to 18 feet bgs at the Site. The groundwater flow direction in Zone 1 is generally from west to east. Zones 2, 3, and 4 have not been encountered during drilling activities at the Site. Based on observations from other Scott AFB sites, Zone 2 is semi-confined and is generally encountered between 18 to 35 feet bgs on average. Zone 2 is underlain by Zone 3, which consists of glacial till classified as either clay, silt, or a combination of both. Beneath the non-transmissive layer of Zone 3 is another deeper sandy/transmissive zone, or Zone 4, which is encountered at depths of approximately 50 to 60 feet bgs.

The gauging data collected during the 2013 RI/FS activities indicated that the highest groundwater elevation was measured from SA26-MW012, located along the western perimeter, while the lowest level was measured at SA26-MW013, located along the southeastern edge of the Site. Based on the groundwater elevations, the direction of groundwater flow at the Site was radial to the northeast, east, and southeast. Hydraulic gradients ranged from approximately 0.05 feet per foot (ft/ft) near well SA26-MW003 to approximately 0.002 ft/ft in the central portion of the Site.

Groundwater velocity was estimated using the formula Vs = Ki/η and the following assumptions:

• Average hydraulic conductivity value (K) of 2.6 feet/day (9.17 x 10-4 centimeters per second), based on the representative value of the Mascoutah silty clay loam (HGL, 2015).

• A hydraulic gradient (i) of 0.002 ft/ft.

• Effective porosity (η) of 0.2 based on literature values for similar soil types (silty clay).

Using these values, the seepage velocity (Vs), or velocity at which groundwater will flow through the porous space of the aquifer, for Zone 1 groundwater at Site SA026 is estimated to be 0.026 feet/day (HGL, 2015).

Scott Air Force Base, Illinois

2.0 SUMMARY OF GROUNDWATER MONITORING FIELD ACTIVITIES

This section summarizes the sampling activities for the groundwater monitoring events conducted in May and June 2023. The analytical results are discussed in Section 4.0. All field activities were conducted in accordance with the Final Uniform Federal Policy Quality Assurance Project Plan (UFP-QAPP; Plexus, 2018). Field forms documenting the sampling activities are provided in Appendix A.

All monitoring wells were inspected, gauged, purged, and sampled as part of the annual 2023 event. During inspections it was observed that SA26-MW10 was missing a lock, SA26-MW04, SA26-MW07, SA26-MW12 and SA26-MW15 were missing bolts, and SA26-MW04, SA26- MW07, SA26-MW12 and SA26-MW15 were also missing labels. No monitoring wells were reported as damaged, and all wells could be gauged. Table 2-1 lists the monitoring wells sampled. Groundwater samples were analyzed for total manganese and sulfate.

2.1 Water Level Measurements

Groundwater levels were collected from the site monitoring wells immediately prior to groundwater sampling activities. Water levels were measured from the top of the well casing using an oil/water interface probe. The depth to water was measured to the nearest 0.01 foot and recorded on the static water level record form (Appendix A). The water level meter was decontaminated between each water level reading. Groundwater elevations are presented in Table 2-2.

2.2 Groundwater Sampling Activities

After inspection and gauging, monitoring wells were purged and sampled using dedicated tubing and non-dedicated submersible bladder pumps with disposable bladders using low flow techniques. At each well, the pump inlet was placed at the approximate midpoint of the wetted well screen, the water level gauged to establish pre-purging elevation, and the pump started.

Groundwater elevation was monitored, and the flow rate was adjusted to maintain the static water level within the well to 0.3 feet of the initial elevation. A flow rate of 100 to 200 milliliters per minute was used during purging to maintain the static groundwater elevation.

During purging, water quality parameters were monitored and recorded. All groundwater monitoring parameters were measured with a calibrated water quality meter housed in a flow-through cell connected to the discharge tubing. The flow-through cell was disconnected from the monitoring well discharge tubing prior to sampling. Samples were collected when water quality parameters stabilized. Stabilization was considered complete when parameters were within parameter limits for three consecutive readings. The 2018 UFP-QAPP stabilization parameter limits are:

• Temperature: ± 1.0 degrees Celsius (°C);

• pH: ± 0.1 standard units;

Scott Air Force Base, Illinois

• Specific conductance: ± 0.01 milliSiemens per centimeter or within 3% (whichever is less);

• Oxidation-reduction potential: ± 10 millivolts or within 10% (whichever is less);

• Dissolved oxygen: ± 0.3 mg/L or within 10% (whichever is less); and

• Turbidity: ≤ 10 nephelometric turbidity units (NTU).

Turbidity was monitored using both a standalone LaMotte turbidity meter and a Horiba multiparameter water quality sonde via a flow-through cell. As the potential for sediment buildup in a flow-through cell can bias turbidity readings, the standalone LaMotte meter was used for decision making. Turbidity was not recorded above 10 NTU by either the Horiba or LaMotte devices at the time of sampling in any of the wells during the annual 2023 event. The final field groundwater quality parameters collected following purging and stabilization are presented in Table 2-3. The groundwater monitoring well purging and sampling forms are included in Appendix A.

After sample collection, all non-dedicated sampling equipment was decontaminated in accordance with the procedures specified in the 2018 UFP-QAPP. After disposing of bladders, sampling equipment (e.g., pump, filter devices) were flushed with potable water, then cleaned inside and out with laboratory-grade detergent. The detergent was applied with a scrub brush where practicable. The equipment was rinsed with potable water followed by a final rinse with distilled or de-ionized water. The equipment was then visually inspected for any remaining particles or surface film. Cleaning and rinse procedures were repeated, if necessary.

2.3 Investigation-Derived Waste Disposal

Investigation-derived waste (IDW) generated during the sampling event included:

• Purge and decontamination water generated; and

• Used personal protective equipment (e.g., nitrile/latex disposable gloves).

Disposable personal protective equipment was managed as municipal waste. The liquid IDW generated during the annual 2023 event was staged in 55-gallon steel drums at the installation’s 90-day storage area (Building 3306). The IDW was picked up by Illini Environmental on October 5, 2023 for solidification and disposal in a landfill. The drums will be crushed and recycled on-site at Illini Environmental. The waste manifest forms are presented in Appendix A.

Scott Air Force Base, Illinois

Table 2-1 – Groundwater Sample Analysis Summary

Well1 Sample Sample Date Analyte2 Method Quality Control Number of Samples

SA26-MW002 SA26-MW002-060523 06/05/23

Manganese SW846 6020B

Sulfate SW846 9056A

SA26-MW003 SA26-MW003-060523 06/05/23

Manganese SW846 6020B Duplicate Sample is

SA26-MW8003-

060523

Sulfate SW846 9056A

SA26-MW004 SA26-MW004-060523 06/05/23

Manganese SW846 6020B

Sulfate SW846 9056A

SA26-MW006 SA26-MW006-060323 06/03/23

Manganese SW846 6020B

Sulfate SW846 9056A

SA26-MW007 SA26-MW007-060623 06/06/23

Manganese SW846 6020B Duplicate sample is

SA26-MW8007-

060623

Sulfate SW846 9056A

SA26-MW008 SA26-MW008-060523 06/05/23

Manganese SW846 6020B 1 Sulfate SW846 9056A

SA26-MW009 SA26-MW009-060423 06/04/23

Manganese SW846 6020B

Sulfate SW846 9056A

SA26-MW010 SA26-MW010-060423 06/04/23

Manganese SW846 6020B

Sulfate SW846 9056A

SA26-MW011 SA26-MW011-060523 06/05/23

Manganese SW846 6020B

MS/MSD 3

Sulfate SW846 9056A

SA26-MW012 SA26-MW012-060323 06/03/23

Manganese SW846 6020B

Sulfate SW846 9056A

SA26-MW013 SA26-MW013-060323 06/03/23

Manganese SW846 6020B 1 Sulfate SW846 9056A

Scott Air Force Base, Illinois

Table 2-1 – Groundwater Sample Analysis Summary

Well1 Sample Sample Date Analyte2 Method Quality Control Number of Samples

SA26-MW014 SA26-MW014-060323 06/03/23

Manganese SW846 6020B 1 Sulfate SW846 9056A

SA26-MW015 SA26-MW015-060323 06/03/23

Manganese SW846 6020B 1 Sulfate SW846 9056A

SA26-MW016 SA26-MW016-060423 06/04/23

Manganese SW846 6020B 1 Sulfate SW846 9056A

Duplicate Sample SA26-MW8003-060523 06/05/23

Manganese SW846 6020B Duplicate sample of

SA26-MW003-

060523

Sulfate SW846 9056A

Duplicate Sample SA26-MW8007-060623 06/06/23

Manganese SW846 6020B Duplicate sample of

SA26-MW007-

060623

Sulfate SW846 9056A

Equipment Blank SA26-EB-01-060423 06/04/23

Manganese SW846 6020B 1 Sulfate SW846 9056A

1) Well IDs in the Air Force database vary by well (i.e., SA26-MCSA-MW01 through SA26-MCSA-MW13, and SA26-MW014 through SA26- MW016) and are presented throughout this document using a common, consistent, simplified naming convention.

2) No field filtered manganese samples were collected in June 2023. All manganese results are unfiltered and representative of “total” concentrations.

Scott Air Force Base, Illinois

Table 2-2 – Summary of Depth to Water Measurements

Well Date Top of Casing

Elevation (feet amsl)

Ground Surface Elevation (feet amsl)

Top of Screen

Elevation (feet amsl)

Installed Total Depth

(feet bgs)

Depth to Water May

(feet btoc)

Groundwater Elevation (feet amsl)

SA26-MW002 5/31/23 440.28 440.77 434.77 16 4.7 435.58

SA26-MW003 5/31/23 438.82 439.35 423.35 16 4.13 434.69

SA26-MW004 5/31/23 440.53 440.88 423.88 17 5.26 435.27

SA26-MW006 5/31/23 441.50 441.86 436.86 15.4 6.32 435.18

SA26-MW007 5/31/23 441.36 441.80 434.80 17 8.94 432.42

SA26-MW008 5/31/23 441.34 441.70 434.70 17 6.26 435.08

SA26-MW009 5/31/23 442.78 443.20 435.20 18 7.53 435.25

SA26-MW010 5/31/23 442.84 443.20 436.20 17 7.92 434.92

SA26-MW011 5/31/23 441.73 442.20 435.20 17 7.16 434.57

SA26-MW012 5/31/23 444.24 444.60 435.60 19 8.89 435.35

SA26-MW013 5/31/23 442.18 442.40 434.40 18 7.38 434.8

SA26-MW014 5/31/23 443.49 443.82 434.82 19 8.63 434.86

SA26-MW015 5/31/23 438.55 438.88 429.88 19 3.89 434.66

SA26-MW016 5/31/23 442.46 442.78 433.78 19 7.13 435.33

amsl = above mean sea level btoc = below top of casing

Scott Air Force Base, Illinois

Table 2-3 – Final Groundwater Quality Parameters

Well Date Sampled Temp (ºC) pH

(SU)

ORP

(mV)

Specific Conductance

(mS/cm)

Turbidity

(NTU) DO

(mg/L) LaMotte Horiba

SA26-MW002 06/05/23 20.83 7.05 103 1.41 9.2 9.9 0.00

SA26-MW003 06/05/23 21.63 5.88 156 1.82 0 6.43 0.00

SA26-MW004 06/05/23 21.29 6.26 ‐45 2.8 0 1.69 0.00

SA26-MW006 06/03/23 20.33 6.26 170 1.54 0 5.38 0.00

SA26-MW007 06/06/23 23.81 6.89 99 2 0 1.54 0.00

SA26-MW008 06/05/23 18.57 6.48 144 1.39 0 2.65 0.00

SA26-MW009 06/04/23 20.13 6.81 ‐18 1.28 0 2.41 0.00

SA26-MW010 06/04/23 17.47 6.21 142 1.41 7 3.8 0.00

SA26-MW011 06/05/23 16.88 6.9 101 0.739 8.3 8.11 0.00

SA26-MW012 06/03/23 19.02 6.66 89 0.614 0 1.68 0.00

SA26-MW013 06/03/23 18.03 6.52 ‐6 1.69 3.5 0.95 0.00

SA26-MW014 06/03/23 20.49 6.8 124 0.831 6.6 3.27 0.00

SA26-MW015 06/03/23 25.47 6.89 60 3.11 0 4.89 0.00

SA26-MW016 06/04/23 19.59 6.69 143 0.494 0 1.1 0.00

°C = degrees Celsius mV = millivolts DO = dissolved oxygen ORP = oxidation-reduction potential mg/L = milligrams per liter NTU = nephelometric turbidity unit mS/cm = milliSiemens per centimeter SU = standard units

Scott Air Force Base, Illinois

3.0 DATA QUALITY EVALUATION

This section describes the validation process used to review laboratory analytical data collected during the annual 2023 event at Site SA026. The validation procedures are detailed in the 2018 UFP-QAPP with additional guidance provided by the Department of Defense Quality Systems Manual for Environmental Laboratories, Version 5.3 (QSM; DoD, 2019).

Environmental samples were analyzed by Pace Analytical Gulf Coast Laboratories (Pace) (formerly Gulf Coast Analytical Laboratories) of Baton Rouge, Louisiana, a DoD Environmental Laboratory Accreditation Program certified laboratory (Certificate # 74960). Data from the annual 2023 event are presented in one sample delivery group (SDG) identified by Pace as SDG 223060710. Samples were analyzed for total manganese (SW-846 Method 6020B) and sulfate (SW-846 Method 9056A). The laboratory report is presented in Appendix B.

3.1 Quality Assurance/Quality Control Sampling

The following field quality assurance/quality control samples were collected to ensure that the measurement systems were maintained within prescribed limits and the sample results were of acceptable quality:

• Two field duplicate samples were collected. One duplicate was collected from SA26- MW003 on June 5, 2023, and another duplicate was collected from SA26-MW007 on June 6, 2023;

• Matrix spike (MS)/matrix spike duplicate (MSD) samples were collected from SA26- MW011 on June 5, 2023; and

• One equipment blank was collected on June 4, 2023. It was collected at the end of the sampling day by running deionized water over and through the bladder pump used for sampling after the pump was decontaminated.

The field duplicates, MS/MSD samples, and equipment blank were analyzed for sulfate (SW-846 Method 9056A) and total manganese (SW-846 Method 6020B).

3.2 Data Validation

Plexus completed a 100% validation review of the analytical data package. The validation of the laboratory analytical data package consisted of examination and checks for the compliance of sample receipt conditions, sample characteristics, confirmation of the analytical results with the associated lab records, and fulfillment of the data quality objectives. The data validation report is presented in Appendix C.

3.3 Data Quality Assessment and Usability

Data quality was assessed in terms of precision, accuracy, representativeness, comparability, completeness, and sensitivity (PARCCS).

Scott Air Force Base, Illinois

3.3.1 Precision

Precision was evaluated using the relative percent difference (RPD) to determine the reproducibility of field duplicate samples, MS/MSD, laboratory control/laboratory control duplicate (LCS/LCSD) and laboratory duplicate samples. RPDs were calculated when both the parent and duplicate results exceeded the limit of detection (LOD). All precision indicators were within acceptable parameters. No data qualifiers were applied, and no systemic trends or biases were observed.

3.3.2 Accuracy

Accuracy was evaluated by reviewing the surrogate recoveries, MS/MSD recoveries, LCS/LCSD recoveries, and initial and continuing calibration recoveries. The accuracy indicators were within acceptable parameters with the exception that all sample results were biased low and qualified as “J-” due to higher than expected sample receipt temperature when samples were received by the laboratory.

3.3.3 Representativeness

Representativeness was evaluated by reviewing sample documentation to determine if samples were collected as required by the 2018 UFP-QAPP and evaluating equipment blanks for contamination. All samples were collected according to the procedures outlined in the 2018 UFP-QAPP and QSM (DoD, 2019). Manganese and sulfate were not detected at a concentration greater than the LOD in the equipment blank. The equipment blank results were non-detected and rejected due to temperature above the acceptable limit. All representativeness indicators are within acceptable parameters.

3.3.4 Comparability

Comparability was evaluated by ensuring that the data set collected during the investigation event is comparable or agrees with the data set collected during previous sampling events. A review of the sampling, preparation, and analytical methods was performed to verify consistency between events. The samples were collected, prepared, and analyzed in accordance with the methodologies presented in the 2018 UFP-QAPP and QSM (DoD, 2019) and are considered comparable.

3.3.5 Completeness

Completeness was calculated as the ratio of usable data to all analytical data collected. For completeness requirements, usable results are all results not qualified with an “R” (rejected data) qualifier during data validation. The completeness goal, as defined in the 2018 UFP-QAPP, is 90% for each parameter. The following equation was used to calculate analytical completeness:

% Analytical Completeness = (number of non-rejected results/number of reported results) * 100

Scott Air Force Base, Illinois

Per the UFP-QAPP (Plexus, 2018), the analytical completeness goal for this sampling event is 90%. Equipment blank SA26-EB-060423 results were qualified as rejected, “R”. The calculated analytical completeness attained is 94%, and the analytical completeness goal was met.

3.3.6 Sensitivity

Sensitivity was evaluated by comparing the reporting limits to the project action limits. The instrument or method should provide an accurate analyte concentration that is not greater than the applicable standard and/or screening level. The reporting requirement for the QSM is to report compound results at three levels (LOQ, LOD, and detection limit [DL]). As required by QSM protocol, all compounds, which are qualitatively identified at concentrations below their respective LOQ but above the DL, must been marked with “J” qualifiers to indicate that they are quantitative estimates. Non-detect results are required to be reported to the LOD. No compounds were detected at concentrations below their respective LOQ but above their DLs during the annual 2023 event. All non-detect results were reported to their LODs.

Several samples required dilution following initial analysis for total manganese and sulfate. The dilutions were necessary due to elevated levels of target analytes in the samples. The corresponding reporting limits have been adjusted accordingly. All results were reported as detections; therefore, data quality from a sensitivity perspective was not affected. Other results were run at a 1x dilution and LODs/LOQs conform to the requirements in the 2018 UFP-QAPP.

3.4 Conclusions and Recommendations

The data collected at Site SA026 as part of the annual 2023 event were evaluated using the PARCCS data quality indicators. The samples were received at the laboratory at an excessive temperature; therefore, the results are considered biased low and qualified as “J-”. The data were otherwise found to be of good quality and are usable for environmental decision-making.

Scott Air Force Base, Illinois

Scott Air Force Base, Illinois

4.0 SUMMARY OF ANALYTICAL RESULTS

This section summarizes the hydrogeologic observations and analytical results from the annual 2023 event.

4.1 Zone 1 Groundwater Flow Direction and Hydraulic Gradient

During the annual 2023 event, all 14 monitoring wells at Site SA026 were gauged before sample collection activities. The resulting depth to water data were used to generate a potentiometric surface. The overall flow directions were consistent with those observed during the RI and with previous annual sampling events. Groundwater flows onto the Site from the west. It then bifurcates to the northeast and southeast as it passes through the Site. A depression in the potentiometric surface remains evident at monitoring well SA26-MW003. This depression is consistent with the subsurface stratigraphy shown on the cross-section figures presented in the RI Report (HGL, 2013), which show a depression in the vicinity of SA26-MW003. According to the RI Report, a map included in the 2005 PA/SI report identified a former drain and culvert in the immediate vicinity of SA26-MW003. It is possible that a remnant of this former drainage system is causing a localized groundwater depression near SA26-MW003. The groundwater potentiometric surface for June 2023 is presented on Figure 4-1.

The hydraulic gradient was calculated across the northern and southern portions of the Site.

SA026-MW009/SA026-MW015 approximates the gradient for the northern portion. The gradient for the southern portion is approximated by SA026-MW012/SA026-MW013. The hydraulic gradients presented in Table 4-1 for these well pairs were calculated using the following formula:

i = (h2 - h1)/d

Where: i = hydraulic gradient (feet of head per foot of distance) h1 = upgradient head (water level in feet) h2 = downgradient head (water level in feet) d = distance between wells (length in feet)

Table 4-1 – Calculated Hydraulic Gradients for Zone 1

Well #1 Well #1 GWE (h1) (feet MSL) Well #2 Well #2 GWE

(h2) (feet MSL)

Distance Between Wells

(d) (feet)

Horizontal Gradient (i) (feet/foot)

MW009 435.25 MW015 434.66 623.30 < 0.01

MW012 435.35 MW013 434.8 647.48 <0.01

feet MSL = feet mean sea level GWE = groundwater elevation

The hydraulic gradient (i) was estimated to be less than 0.01 ft/ft across the Site. These results are consistent with the historically measured gradient.

Scott Air Force Base, Illinois

4.2 Groundwater Analytical Data

The total manganese and sulfate results from the annual 2023 event are compared to the Site SA026 groundwater ROs in Table 4-2. The ROs for groundwater at Site SA026 were established by the Record of Decision for Site SA-26 (USAF, 2014).

Table 4-2 – Groundwater Analytical Data for the Annual 2023 Event

Sample Location

Sample Date

Sample Type Manganese (µg/L) Sulfate (mg/L)

Analytical Method SW846 6020B 9056A

Groundwater Remediation Objective 6,120 400

SA26-MW002 6/5/2023 Normal 2,800 J- 412 J-

SA26- MW003

6/5/2023 Normal 11,000 J- 1,040 J-

6/5/2023 Duplicate 10,300 J- 1,030 J-

SA26-MW004 6/5/2023 Normal 13,500 J- 302 J-

SA26-MW006 6/3/2023 Normal 715 J- 420 J-

SA26-MW007

6/6/2023 Normal 11,700 J- 877 J-

6/6/2023 Duplicate 12,800 J- 884 J-

SA26-MW008 6/5/2023 Normal 43 J- 160 J-

SA26-MW009 6/4/2023 Normal 1,680 J- 537 J-

SA26-MW010 6/4/2023 Normal 388 J- 463 J-

SA26-MW011 6/5/2023 Normal 45.5 J- 28.9 J-

SA26-MW012 6/3/2023 Normal 127 J- 212 J-

SA26-MW013 6/3/2023 Normal 2,240 J- 57.5 J-

SA26-MW014 6/3/2023 Normal 111 J- 206 J-

SA26-MW015 6/3/2023 Normal 776 J- 118 J-

SA26-MW016 6/4/2023 Normal 39.8 J- 81.7 J-

Shaded and bolded values denote an exceedance of the groundwater remediation objectives.

All data is reported to the LOD (See Appendix B).

µg/L = micrograms per liter mg/L = milligrams per liter

1) Manganese results are unfiltered and represent total concentrations.

2) Sample analysis performed by Pace Analytical Gulf Coast, Baton Rouge, Louisiana.

3) Manganese and sulfate results were qualified as “J-” during data validation due to sample temperatures at time of receipt by laboratory.

4.2.1 Manganese Results

During the annual 2023 event, total manganese exceeded the RO of 6,120 µg/L in 3 of 14 monitoring wells. The RO exceedances were observed in SA26-MW003 (11,000 µg/L [10,300 µg/L in the duplicate sample]), SA26-MW004 (13,500 µg/L), and SA26-MW007 (11,700 µg/L

Scott Air Force Base, Illinois

[12,800 µg/L in the duplicate sample]), which is historically consistent with the long-term groundwater monitoring data set. The total manganese RO exceedances and a depiction of the total manganese plume are presented on Figure 4-2.

4.2.2 Sulfate Results

Sulfate exceeded the RO of 400 mg/L in 6 of 14 monitoring wells during the annual 2022 event.

Exceedances were observed in SA26-MW002, SA26-MW003, SA26-MW006, SA26-MW007, SA26-MW009, and SA26-MW010. The exceedances ranged from 412 mg/L in SA26-MW002 to 1,040 mg/L (1,030 mg/L in the duplicate sample) in SA26-MW003. The groundwater sulfate data for the annual 2023 event are generally consistent with the historical data set. Sulfate has slightly exceeded the RO at SA26-MW006 on three occasions (June 2018, June 2020, and, now, June 2023). SA26-MW008 and SA26-MW0012 exceeded the sulfate RO prior to 2015; since this time, sulfate has only exceeded the RO in samples collected from these wells once (SA26- MW008 in June 2022). SA26-MW004 has not exceeded the RO since it was slightly exceeded in June 2018. The sulfate RO exceedances and a depiction of the sulfate plume are presented on Figure 4-3.

4.2.3 Groundwater Trend Analysis

The annual 2023 event was the ninth time that all 14 wells at the Site have been sampled during the same event. While at least eight rounds of monitoring data are of sufficient quantity to determine whether a monitoring well network can be optimized using the Air Force’s Monitoring and Remediation Optimization System (MAROS) software, MAROS software was not utilized as the expansion or reduction of the monitoring well network at the Site was not an objective of this evaluation. The groundwater plume is being contained, consistent with the remedial action objectives of the Final Record of Decision (USAF, 2014), and containment of the plume is being demonstrated through the monitoring of the existing well network. In place of MAROS software, the Mann-Kendall Toolkit from GSI Environmental (GSI, 2012), which provides comparable functionality to the Mann-Kendall Statistics portion of the MAROS software, was used to statistically evaluate the total manganese and sulfate concentration trends in groundwater, as detailed in Section 4.2.4 below. Additionally, analytical results were plotted to compare concentrations at each well and evaluate how concentrations have changed since 2015. These trend graphs are presented in Appendix D.

Qualitative trend analysis of the historical groundwater results at SA026 indicates that concentrations have remained consistent during recent sampling events, with minor fluctuations.

A notable exception is the total manganese and sulfate concentrations at SA26-MW003. Last year, the total manganese concentration decreased to 6,020 µg/L from an all-time high of 17,500 µg/L in 2021. The sulfate concentration also decreased to 683 mg/L last year from 1,010 mg/L in 2021. While the concentrations observed last year are more in line with concentrations detected

Scott Air Force Base, Illinois in 2019 and 2020, in 2023 SA26-MW003 again exhibited an increase in both total manganese (11,000 µg/L) and sulfate (1,040 mg/L).

In 2019, the average sulfate concentration (389.31 mg/L) at SA026 fell below the RO for the first time since annual sampling of all wells began in 2015. Average sulfate concentrations have remained below the RO of 400 mg/L since, with an average sulfate concentration of 351.08 mg/L in 2023. In 2023, sulfate exceeded the RO at SA026-MW006 (420 mg/L) for the first time since 2020; SA026-MW006 is located in the southwestern corner of the Site near the base boundary. In 2023, sulfate returned to concentrations below the RO at SA026-MW008 (160 mg/L) after an exceedance was observed in that well (554 mg/L) for the first time since sampling began in 2015. Overall, sulfate concentrations have been below the RO in 6 of 14 wells at the Site since 2015.

4.2.4 Mann-Kendall Statistical Analysis

For this report, the Mann-Kendall Toolkit was used to statistically evaluate the total manganese and sulfate concentration trends in groundwater concentration trends at all 14 wells (SA26- MW002, SA26-MW003, SA26-MW004, and SA26-MW006 through SA26-MW016) from 2015 to 2023. The worksheets associated with the Mann-Kendall Toolkit analyses and associated outputs are presented in Appendix E. The results of the Mann-Kendall analyses for total manganese are presented in Table 4-3, and the results of the Mann-Kendall analyses for sulfate are presented in Table 4-4. The historical data set is presented in Table 4-5.

Table 4-3 – Mann-Kendall Analyses for Total Manganese

Well Coefficient of Variation

Mann-Kendall Statistic Confidence Factor Concentration

Trend

SA26-MW002 0.64 23 99.1% Increasing

SA26-MW003 0.39 -9 79.2% Stable

SA26-MW004 0.24 -26 99.7% Decreasing

SA26-MW006 0.48 -1 50.0% Stable

SA26-MW007 0.18 -8 76.2% Stable

SA26-MW008 1.74 2 54.0% No Trend

SA26-MW009 0.57 -6 69.4% Stable

SA26-MW010 0.42 -24 99.4% Decreasing

SA26-MW011 0.40 -14 91.0% Prob. Decreasing

SA26-MW012 0.60 -10 82.1% Stable

SA26-MW013 0.18 -10 82.1% Stable

SA26-MW014 0.94 24 99.4% Increasing

Scott Air Force Base, Illinois

Table 4-3 – Mann-Kendall Analyses for Total Manganese

Well Coefficient of Variation

Mann-Kendall Statistic Confidence Factor Concentration

Trend

SA26-MW015 0.47 4 61.9% No Trend

SA26-MW016 0.83 -26 99.7% Decreasing

Conclusions of the Mann-Kendall Toolkit analysis for total manganese are summarized as follows:

• Probably Decreasing – one monitoring well: SA26-MW011.

• Decreasing – three monitoring wells: SA26-MW004, SA026-MW010, and SA26-

MW016.

• No Trend – two monitoring wells: SA26-MW008 and SA26-MW015.

• Stable – six monitoring wells: SA26-MW003, SA26-MW006, SA26-MW007, SA26-

MW009, SA26-MW012, and SA26-MW013.

• Probably Increasing – none.

• Increasing – two monitoring wells: SA026-MW002 and SA26-MW014.

All areas of the plume are stable, shrinking, or not increasing (no trend) with two exceptions.

The total manganese concentration at SA26-MW002 is increasing, but remains well below the RO of 6,120 µg/L. This well is located between the northern and southern portions of the plume.

Over the last four annual events concentrations at SA26-MW002 have ranged between 2,540 µg/L (2020) to 3,470 µg/L (2022). The total manganese concentration at SA26-MW014 is increasing. This well is located at the downgradient edge of the southern portion of the plume.

The concentration of total manganese at SA26-MW014 (111 µg/L) was more than an order of magnitude less than the RO (6,120 µg/L) during the annual 2023 event. It should be noted that neither of these wells represent plume migration in an off-base direction.

Table 4-4 – Mann-Kendall Analyses for Sulfate

Well Coefficient of Variation

Mann-Kendall Statistic Confidence Factor Concentration

Trend

SA26-MW002 0.45 14 91.0% Prob. Increasing

SA26-MW003 0.33 -18 96.2% Decreasing

SA26-MW004 0.15 -22 98.8% Decreasing

SA26-MW006 0.27 12 87.0% No Trend

SA26-MW007 0.09 2 54.0% No Trend

Scott Air Force Base, Illinois

Table 4-4 – Mann-Kendall Analyses for Sulfate

Well Coefficient of Variation

Mann-Kendall Statistic Confidence Factor Concentration

Trend

SA26-MW008 0.44 -18 96.2% Decreasing

SA26-MW009 0.10 -12 87.0% Stable

SA26-MW010 0.28 -31 >99.9% Decreasing

SA26-MW011 0.29 -18 96.2% Decreasing

SA26-MW012 0.17 -23 99.1% Decreasing

SA26-MW013 0.26 -26 99.7% Decreasing

SA26-MW014 0.18 -10 82.1% Stable

SA26-MW015 0.25 -12 87.0% Stable

SA26-MW016 0.30 -18 96.2% Decreasing

Conclusions of the Mann-Kendall Toolkit analysis for sulfate are summarized as follows:

• Probably Decreasing – none.

• Decreasing – eight monitoring wells: SA26-MW003, SA26-MW004, SA26-MW008, SA26-MW010, SA26-MW011, SA26-MW012, SA26-MW013, and SA26-MW016.

• No Trend – two monitoring wells: SA26-MW006 and SA26-MW007.

• Stable – three monitoring wells: SA26-MW009, SA26-MW014, and SA26-MW015.

• Probably Increasing – one monitoring well: SA26-MW002.

• Increasing – none.

All areas of the plume are stable, shrinking, or not increasing (no trend) with one exception. The sulfate concentration at SA26-MW002 is probably increasing. This well is located between the northern and southern portions of the plume. More recent data show that sulfate concentration increases are stabilizing. Over the last six annual events concentrations at SA26-MW002 have ranged between 411 mg/L (2018) to 532 mg/L (2020). The sulfate concentration at SA26- MW002 in 2023 was 412 mg/L. It should be noted that increasing sulfate concentrations at SA26-MW002 does not represent plume migration.

Scott Air Force Base, Illinois

Table 4-5 – Historical Groundwater Analytical Data

Sample Location

Sample Date

Sample Type

Manganese (µg/L)

Manganese (Filtered) (µg/L)

Sulfate (mg/L)

Analytical Method SW846 6020B 9056A

Groundwater Remediation Objective 6,120 6,120 400

SA26-MW002

11/15/2006 Normal 20,200 -- 1,060 J

11/18/2010 Normal 3,310 3,220 J 382

11/18/2010 Duplicate 3,250 2,400 J 394

6/3/2015 Normal 772 2.5 U 170

6/23/2016 Normal 1,300 J 1,000 J 370

6/19/2017 Normal 250 21 Q 23 MI

6/19/2017 Duplicate 300 13 27 MI

6/13/2018 Normal 343 266 411

6/19/2019 Normal 2,470 1,520 485

6/19/2019 Duplicate 2,540 1,670 497

7/1/2020 Normal 2,540 1,020 532

7/8/2021 Normal 2,960 -- 495

6/6/2022 Normal 3,470 -- 469

SA26- MW003

11/16/2006 Normal 2,800 -- 1,180

11/17/2010 Normal 2,070 2,280 773

6/3/2015 Normal 15,300 12,000 1,450

6/23/2016 Normal 15,000 J 15,000 J 1,600

6/19/2017 Normal 15,000 D 14,000 D 1,400 D

6/12/2018 Normal 16,600 15,600 1,430

6/19/2019 Normal 10,500 9,760 862

7/1/2020 Normal 3,940 3,820 554

7/1/2020 Duplicate 4,010 3,970 562

7/7/2021 Normal 17,500 -- 1,010

6/6/2022 Normal 6,020 -- 683

6/6/2022 Duplicate 5,970 -- 700

SA26-MW004

11/15/2006 Normal 5,120 -- 793 J

11/17/2010 Normal 16,200 14,900 584

6/4/2015 Normal 21,400 J 20,300 371

6/23/2016 Normal 22,000 J 19,000 J 380

Scott Air Force Base, Illinois

Table 4-5 – Historical Groundwater Analytical Data

Sample Location

Sample Date

Sample Type

Manganese (µg/L)

Manganese (Filtered) (µg/L)

Sulfate (mg/L)

Analytical Method SW846 6020B 9056A

Groundwater Remediation Objective 6,120 6,120 400

SA26-MW004

6/23/2016 Duplicate 20,000 J 20,000 J 380

6/19/2017 Normal 20,000 D 19,000 D 370 D

6/12/2018 Normal 19,800 18,600 409

6/19/2019 Normal 16,600 15,800 354

6/19/2019 Duplicate 15,900 15,800 362

7/1/2020 Normal 11,100 10,900 244

7/7/2021 Normal 14,900 -- 352

7/7/2021 Duplicate 14,400 -- 350

6/7/2022 Normal 12,900 -- 310

SA26-MW006

1/30/2008 Normal 3,060 -- --

11/17/2010 Normal 2,380 2,520 229

11/17/2010 Duplicate 2,550 2,330 235

6/4/2015 Normal 439 J 354 187

6/22/2016 Normal 880 J 480 J 260

6/19/2017 Normal 850 640 Q 380 D

6/14/2018 Normal 460 366 410

6/19/2019 Normal 221 193 366

6/29/2020 Normal 460 335 500

7/7/2021 Normal 1,080 -- 314

6/3/2022 Normal 332 -- 302

SA26-MW007

11/18/2010 Normal 16,600 14,200 1,180

6/4/2015 Normal 17,700 J 15,900 835

6/23/2016 Normal 13,000 J 10,000 J 880

6/16/2017 Normal 17,000 D 17,000 D 1,000 D

6/12/2018 Normal 10,600 10,100 1,060

6/12/2018 Duplicate 11,100 9,990 1,100

6/19/2019 Normal 18,800 17,200 996

6/30/2020 Normal 17,600 17,800 883

7/7/2021 Normal 13,800 -- 922

Scott Air Force Base, Illinois

Table 4-5 – Historical Groundwater Analytical Data

Sample Location

Sample Date

Sample Type

Manganese (µg/L)

Manganese (Filtered) (µg/L)

Sulfate (mg/L)

Analytical Method SW846 6020B 9056A

Groundwater Remediation Objective 6,120 6,120 400

7/7/2021 Duplicate 12,600 -- 930

SA26-MW007 6/7/2022 Normal 12,300 -- 912

6/7/2022 Duplicate 14,000 -- 915

SA26-MW008

11/17/2010 Normal 362 395 532

6/3/2015 Normal 59.6 19.1 324

6/23/2016 Normal 83 J 50 J 360

6/19/2017 Normal 100 43 Q 310 D

6/13/2018 Normal 31.5 8.52 280

6/18/2019 Normal 38.3 6.06 191

6/30/2020 Normal 94.9 J 31.6 199

7/7/2021 Normal 59.2 -- 171

6/3/2022 Normal 849 -- 554

SA26-MW009

11/18/2010 Normal 753 778 545

6/3/2015 Normal 2,390 1,690 698

6/22/2016 Normal 1,800 J 1,500 J 640

6/16/2017 Normal 5,500 1,800 Q 580 D

6/13/2018 Normal 579 149 530

6/19/2019 Normal 2,910 2,770 677

6/26/2020 Normal 1,970 1,950 678

6/26/2020 Duplicate 1,980 1,940 680

7/6/2021 Normal 1,880 -- 608

6/6/2022 Normal 2,530 -- 589

SA26-MW010

3/21/2011 Normal 577 576 745 M

6/4/2015 Normal 811 J 407 658

6/22/2016 Normal 690 J 550 J 650

6/16/2017 Normal 800 670 650 D

6/12/2018 Normal 523 466 647

6/19/2019 Normal 699 492 563

6/29/2020 Normal 464 415 592

Scott Air Force Base, Illinois

Table 4-5 – Historical Groundwater Analytical Data

Sample Location

Sample Date

Sample Type

Manganese (µg/L)

Manganese (Filtered) (µg/L)

Sulfate (mg/L)

Analytical Method SW846 6020B 9056A

Groundwater Remediation Objective 6,120 6,120 400

SA26-MW010

7/6/2021 Normal 652 -- 532

6/7/2022 Normal 58.1 -- 172

SA26-MW011

3/21/2011 Normal 138 125 62.8 M

6/4/2015 Normal 52.3 UJ 33.8 58.1

6/22/2016 Normal 140 J 130 J 65

6/15/2017 Normal 150 100 70

6/14/2018 Normal 94.6 49.1 67.2

6/18/2019 Normal 103 80.4 42.6

6/30/2020 Normal 74.1 47.6 37.5

7/6/2021 Normal 98 -- 39.9

6/2/2022 Normal 66.1 -- 45.2

SA26-MW012

3/21/2011 Normal 246 238 477 M

3/21/2011 Duplicate 239 243 556 M

6/4/2015 Normal 258 J 138 307

6/22/2016 Normal 160 J 130 J 290

6/19/2017 Normal 280 180 Q 330 D

6/14/2018 Normal 92.2 76.5 319

6/19/2019 Normal 39.1 24.8 293

6/29/2020 Normal 88.8 64.4 283

7/7/2021 Normal 91.1 -- 212

6/6/2022 Normal 91.3 -- 228

SA26-MW013

3/21/2011 Normal 520 484 121 M

6/3/2015 Normal 2,400 1,820 115

6/23/2016 Normal 2,200 J 2,100 J 100

6/16/2017 Normal 1,700 1,700 81 MI

6/14/2018 Normal 1,900 1,940…