LOOF_2024_Annual_Report_Part1.pdf

Old O-Field 2024 Annual Report O-Field Study Area, Operable Units One and Two

Aberdeen Proving Ground, Maryland

September 2025

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Prepared by:

Contract No.: W56ZTN-17-D-0009

Delivery Order: W56ZTN-21-F-0110

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RENOVA-SOVEREIGN JOINT VENTURE

3417 Sunset Avenue

Ocean Township, New Jersey 07712

Aberdeen Proving Ground, MD September 2025

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1. AGENCY USE ONLY (Leave blank) 2. REPORT DATE

September 2025

3. REPORT TYPE AND DATES COVERED

4. TITLE AND SUBTITLE

Old O-Field 2024 Annual Report O-Field Study Area, Operable Units One and Two

5. FUNDING NUMBERS

Contract No.

W56ZTN-17-D-0009

5. AUTHOR(S)

R. Williams/H. Cavanagh/S. Walsh

7. PERFORMING ORGANIZATION NAME(S) AND ADDRESS(ES)

ECC

1304 Governor Court, Suite 101 Abingdon, MD 21009

8. PERFORMING ORGANIZATION

REPORT NUMBER

9. SPONSORING/MONITORING AGENCY NAME(S) AND ADDRESS(ES)

Directorate of Public Works, Environmental Division

AMIM-APP-E

Aberdeen Proving Ground, Maryland 21005

10. SPONSORING/MONITORING

AGENCY REPORT NUMBER

11. SUPPLEMENTARY NOTES

12a. DISTRIBUTION/AVAILABILITY STATEMENT

Approved for Public Release, Distribution is Unlimited.

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# 260106-01

13. ABSTRACT (Maximum 200 words)

This 2024 Annual Report summarizes operations and presents the results for the performance monitoring period from January to December 2024 for the O-Field Study Area.

14. SUBJECT TERMS

O-Field Study Area, Operable Units One and Two, 2024 Annual Report

15. NUMBER OF PAGES

16. PRICE CODE

17. SECURITY CLASSIFICATION

OF REPORT

Unclassified

18. SECURITY CLASSIFICATION

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19. SECURITY CLASSIFICATION

OF ABSTRACT

Unclassified

20. LIMITATION OF ABSTRACT

i

TABLE OF CONTENTS

1.0 INTRODUCTION ..................................................................................................... 1-1

1.1 Site Location, History, and Description ............................................................ 1-1

1.2 Project Background .......................................................................................... 1-2

1.3 Purpose and Scope ........................................................................................... 1-3

2.0 PERMEABLE INFILTRATION UNIT OPERATIONS AND MAINTENANCE

AND MONITORING SUMMARY ........................................................................... 2-1

3.0 GROUNDWATER TREATMENT FACILITY AND WELL FIELD OPERATION

AND MAINTENANCE ACTIVITIES...................................................................... 3-1

3.1 Operational Hours and Staffing ........................................................................ 3-1

3.2 Routine GWTF Activities ................................................................................ 3-1

3.2.1 Bio-Monitor Experiment System .......................................................... 3-2

3.3 Routine Well Field Activities ........................................................................... 3-2

3.4 Non-Routine O&M Activities .......................................................................... 3-3

3.4.1 Power Failure, Weather Related, and Holiday Shutdowns ..................... 3-3

3.4.2 Alarm or Equipment Failure GWTF Shutdowns ................................... 3-3

3.4.3 Shutdowns Due to PIU Air Monitoring Alarms .................................... 3-3

3.4.4 Well Field Shutdowns .......................................................................... 3-4

3.4.5 Unplanned Discharges .......................................................................... 3-4

3.5 Facility Improvements ..................................................................................... 3-4

3.6 Groundwater Processed .................................................................................... 3-4

3.7 Purge Water Processed ..................................................................................... 3-4

3.8 Land Use Control ............................................................................................. 3-5

4.0 COMPLIANCE MONITORING .............................................................................. 4-1

4.1 NPDES Equivalency Monitoring...................................................................... 4-1

4.2 Process Residuals Monitoring .......................................................................... 4-2

4.3 Air Emissions .................................................................................................. 4-3

5.0 PERFORMANCE MONITORING RESULTS ........................................................ 5-1

5.1 Precipitation Amounts ...................................................................................... 5-1

5.2 Groundwater Elevations, Hydraulic Containment, and Extraction Well Operations

........................................................................................................................ 5-1

5.3 Groundwater Contaminant Monitoring ............................................................. 5-2

5.3.1 WTA Analytical Results ....................................................................... 5-3

5.3.1.1 Total VOCs .......................................................................................... 5-3

5.3.1.2 CWM (Mustard) Degradation Products................................................. 5-5

5.3.1.3 Metals .................................................................................................. 5-6

5.3.2 UCA Analytical Results ....................................................................... 5-7

5.3.2.1 Total VOCs .......................................................................................... 5-7

5.3.2.2 CWM (Mustard) Degradation Products................................................. 5-8

5.3.2.3 Metals .................................................................................................. 5-8

6.0 SUMMARY ............................................................................................................... 6-1

7.0 REFERENCES .......................................................................................................... 7-1 ii

FIGURES

Figure 1 Location of Old O-Field at US Army Garrison Aberdeen Proving Ground

Figure 2 Old O-Field Site and Features

Figure 3 2024 Permeable Infiltration Unit Survey and Historical Subsidences

Figure 4 Non-Planned/Planned GWTF Shutdowns 2024

Figure 5 Non-Planned/Planned Well Field Shutdowns 2024

Figure 6 2024 “Normal” versus Measured Precipitation

Figure 7 WTA Hydrograph for Wells PM-1, MW-01, and OF-83R January to December

Figure 8 Old O-Field Sampling Locations

Figure 9 2024 Semi-Annual WTA TVOC Sampling Results

Figure 10 2024 Semi-Annual WTA TCWM Sampling Results

Figure 11 2024 Semi-Annual WTA Arsenic Sampling Results

Figure 12 2024 Semi-Annual UCA TVOC Sampling Results

Figure 13 2024 Semi-Annual UCA TCWM Sampling Results

TABLES

Table 1 PIU Survey Elevation Summary

Table 2 BME System Alarms

Table 3 2024 Old O-Field Monthly Influent and Effluent Concentrations

Table 4 2024 Old O-Field Summary of Influent and Effluent Detected Concentrations

Table 5 Average Metals Removal Efficiencies

Table 6 Quantities of Removed Process Residuals and Universal Wastes

Table 7 2024 1st and 2nd Semi-Annual Sampling Results and Historical Results WTA Total

VOC Concentrations

Table 8 2024 1st and 2nd Semi-Annual Sampling Results and Historical Results WTA CWM

(Mustard) Degradation Product Concentrations

Table 9 2024 1st and 2nd Semi-Annual Sampling Results and Historical Results WTA

Selected Metal Concentrations

Table 10 2024 1st and 2nd Semi-Annual Sampling Results and Historical Results UCA Total

VOC Concentrations

Table 11 2024 1st and 2nd Semi-Annual Sampling Results and Historical Results UCA CWM

(Mustard) Degradation Product Concentrations

Table 12 2024 1st and 2nd Semi-Annual Sampling Results and Historical Results UCA

Selected Metal Concentrations iii

APPENDICES

Appendix A Log of Significant Activities for CY 2024

Appendix B 2024 PIU Subsidence Repair Technical Memorandum

Appendix C Monthly Activity Reports

Appendix D Acceptance Reports for Treatment of Offsite Purge Water

Appendix E Quarterly Discharge Monitoring Reports

Appendix F Process Residuals (Waste) Characterization Results

Appendix G WTA and UCA 2024 Groundwater Elevation Contour Maps

Appendix H 2024 1st Semi-Annual Sampling Event Analytical Results

Appendix I 2024 2nd Semi-Annual Sampling Event Analytical Results

Appendix J Historical Concentration Plots Total VOCs and CWM (Mustard) Degradation

Products iv

ACRONYMS AND ABBREVIATONS

μg/L micrograms per liter

% percent

APG Aberdeen Proving Ground

BME Bio-Monitor Experiment

BQL below quantitation limit

BTAG Biological Technical Assistance Group

CWM chemical warfare material

CY calendar year

DEVCOM Combat Capabilities Development Command

DO dissolved oxygen

EA Edgewood Area

ECC Environmental Chemical Corporation

ESD Explanation of Significant Differences

GAC granular activated carbon

GES groundwater extraction system gpm gallons per minute

GWTF Groundwater Treatment Facility

IDM investigative derived material

LUCs Land Use Controls

MiniCAMS Miniature Continuous Air Monitoring Systems

NPDES National Pollutant Discharge Elimination System

O&M operations and maintenance

OU Operable Unit pH hydrogen ion concentration

PIU Permeable Infiltration Unit

QA Quality Assurance

QC Quality Control

ROD Record of Decision

RSJV Renova-Sovereign Joint Venture

SCADA Supervisory Control and Data Acquisition

TCLP Toxic Characteristic Leaching Procedure

TCWM total chemical warfare material

TeCA 1,1,2,2-tetrachloroethane

TVOC total volatile organic compounds

UCA upper confined aquifer

U.S. United States

USEPA United States Environmental Protection Agency

UVOX ultraviolet oxidation

UXO unexploded ordinances

VOC volatile organic compound

WTA water table aquifer

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1.0 INTRODUCTION

The United States (U.S.) Army Garrison Aberdeen Proving Ground (APG), Directorate of Public

Works Environmental Division has tasked Renova-Sovereign Joint Venture (RSJV) to operate and maintain the Old O-Field Groundwater Treatment Facility (GWTF) and Permeable Infiltration

Unit (PIU) in the Edgewood Area (EA), APG, Maryland. The RSJV assumed control of operations in July 2021 under contract number W56ZTN-17-D-0009. RSJV teaming partner Environmental

Chemical Corporation (ECC) oversees the maintenance and operation activities of the Old O-Field

GWTF and PIU. This annual report summarizes operations and presents the results for the performance monitoring period from January to December 2024.

1.1 Site Location, History, and Description

The O-Field Study Area is located within the EA peninsula of APG (Figure 1). The Old O-Field former waste disposal site is bordered by Watson Creek Road to the west, Watson Creek to the north and east, and a drainage swale and New O-Field to the south. The GWTF is located west of the former disposal site, between Watson Creek Road and the Gunpowder River. Groundwater at the Old O-Field flows primarily east-northeast, and discharges to Watson Creek (Figure 2).

During the 1940s and 1950s, chemical warfare agents, munitions, contaminated equipment, and miscellaneous hazardous wastes were disposed of in approximately 35 unlined pits and trenches at the Old O-Field site. Decontamination and cleanup efforts occurred intermittently from 1949 through the early 1970s. In 1949, more than 1,000 barrels of decontaminating agent were applied to the field to neutralize mustard agent spread across the site as a result of several spontaneous detonations of disposed munitions. The decontaminating agent contained approximately 95 percent (%) 1,1,2,2-tetrachloroethane (TeCA). In 1953, the field was soaked with fuel oil, ignited, and allowed to burn, in an attempt to detonate or deactivate materials and munitions buried at the

Old O-Field disposal site. Due to historical operations, groundwater downgradient of the Old O-

Field disposal site contains multiple contaminants detected during sampling events, including:

• Degradation products of mustard agent: 1,4-dithiane, 1,4-oxathiane, and thiodiglycol;

• Metals including arsenic, iron, copper, and zinc;

• Chlorinated aliphatic hydrocarbons including: TeCA and its degradation products, 1,2-dichloroethane, chloroform, tetrachloroethene, trichloroethene, cis-1,2-dichloroethene, trans-1,2-dicholoroethene, and vinyl chloride; and

• Aromatic and nitroaromatic compounds including benzene and chlorobenzene.

Two aquifers have been identified underlying Old O-Field, the water table aquifer (WTA) and the upper confined aquifer (UCA). Both aquifers are recharged primarily by vertical infiltration of precipitation within the Old O-Field area. A groundwater divide for the WTA lies directly west and adjacent to Watson Creek Road (Figure 2). Groundwater along the western side of this divide discharges to the Gunpowder River, whereas groundwater along the eastern portion of the divide flows beneath the Old O-Field source area and discharges to Watson Creek. The WTA and UCA are divided by an upper confining unit that is comprised of an average four feet thick, silt and clay layer that is discontinuous within areas of Old O-Field. This allows for communication between the two aquifer units where the confining layer is discontinuous. The UCA aquifer primarily exhibits an upward gradient and discharges into the WTA at these discontinuous areas, downgradient of the extraction system. Groundwater flow in the aquifers beneath Old O-Field is

Aberdeen Proving Ground, MD September 2025

1-2 made additionally complex because of tidal effects from the Gunpowder River and Watson Creek.

In addition, a large phragmites marsh south of the well field has a pronounced effect on the observed groundwater elevations of the WTA during the summer growing season.

1.2 Project Background

An interim remedy for groundwater, designated as Operable Unit (OU) 1 under the Comprehensive

Environmental Response, Compensation, and Liability Act, was selected in an interim action

Record of Decision (ROD), signed in 1991 by the U.S. Army and U.S. Environmental Protection

Agency (USEPA) (U.S. Army, 1991). Under the interim ROD, construction of the groundwater extraction system (GES) and GWTF began in 1993 to mitigate the potential environmental risks to aquatic and terrestrial ecosystems in the area. The Old O-Field GWTF and GES began operations in April 1995. Explanations of Significant Difference (ESD) to the OU1 interim ROD were signed in 1998 and 2004 to document changes in operations, addition of treatment systems, reductions in compliance monitoring frequency, and to allow treatment of investigation derived material (IDM) water from other APG areas for treatment (U.S. Army, 2004).

The GWTF was designed to operate at a maximum influent flow rate of 30 gallons per minute

(gpm), but it has been modified to allow operation up to 50 gpm. GWTF treatment processes include metals precipitation, volatile organic compounds (VOCs) destruction using ultraviolet oxidation (UVOX) system, and VOC removal using carbon adsorption. The VOCs destruction and removal processes are also effective in treating chemical agent degradation products in the extracted groundwater. Over the years of operation, major improvements to the GWTF have included:

• Cleaning and resurfacing of the clarifier;

• Replacement of pumps, controls, impellers, dissolved oxygen (DO) meters, hydrogen ion concentration (pH) probes, and analyzers throughout the plant;

• Addition of pressure transducers to the cartridge filter system;

• Installation of a National Pollutant Discharge Elimination System (NPDES) auto sampler;

• Addition of a static mixer to the hydrogen peroxide injection line for the UVOX system;

• Major programming updates to automate systems and alarm functions through use of the

Supervisory Control and Data Acquisition (SCADA) system;

• Replacement of the polymer batch system;

• Addition of bulk chemical storage with automated hoppers; and

• Replacement of the automated brush cleaning system for the UVOX system with an automated acid cleaning system.

The initial configuration of the GES utilized 11 active extraction wells, but it has been modified over years of operations to utilize up to 15 active extraction wells. Major upgrades to the conveyance line and extraction equipment have increased the well field efficiency and improved the variability of flow rates from extraction. Additional GES improvements include an upgrade to double-containment and added leak detection abilities. Currently, a total of eight extraction wells

(EX-3A, EX-4A, EX-8A, MW4-3A, PM-2R, PM-3A, PM-4, and PM-5) are operated within the northeastern and eastern portions of the well field, downgradient of the source area (Figure 2).

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This operational approach was implemented in June 2003 in order to maximize groundwater extraction and control in the area of highest contaminant levels. Only extraction wells screened in

WTA are used, to prevent potential contaminant migration into the UCA (U.S. Army, 2004).

Under a separate interim action ROD (U.S. Army, 1994), a PIU was constructed over the Old O-

Field former disposal area (designated as the Source Area, OU2) to mitigate potential exposure to chemical warfare material (CWM), unexploded ordnance, and other hazardous materials. The PIU is a 5- to 14-foot-thick sand and gravel cover that allows infiltration and percolation of precipitation to flush contamination toward the GES. The cover also serves to prevent the migration of contamination to the surface and mitigate explosive events by “self-healing” the cover after the explosion and dissipating the energy. In 2005, an ESD for OU2 was issued to explain that during construction of the PIU five automatic continuous environmental monitoring units were in place around the perimeter of Old O-Field to monitor for potential releases of low-level toxic chemicals (U.S. Army, 2005). The use of the environmental monitoring units continued after construction replacing the subsurface air monitoring system, which was not commissioned due to concerns regarding moisture in the subsurface interfering with their detection effectiveness. These older automatic continuous environmental monitoring units were subsequently replaced by three

Miniature Continuous Air Monitoring Systems (MiniCAMS). The system was also modified to monitor for mustard and phosgene instead of mustard and nerve agents. The MiniCAMS operate and record data continuously. The units are checked and calibrated every workday (excluding weekends and holidays) by Combat Capabilities Development Command (known as DEVCOM) personnel who operate the systems in support of APG. Non-utilization of the existing sprinkler system for amendment application and the addition of an auxiliary subsurface trickling system to deliver liquid treatments to the PIU’s subsurface to expedite degradation of munition casings was defined in the 2005 ESD (U.S. Army, 2005). The trickling system has not been used to date because bench-scale studies indicated that the addition of subsurface amendments did not significantly expedite degradation of munition casings and use of the system would form preferential pathways for vapor migration.

1.3 Purpose and Scope

The operations and maintenance (O&M) and the performance activities of the Old O-Field site are conducted in accordance with, and to meet the requirements of, the interim action ROD for OU1

– Old O-Field Groundwater, the interim action ROD for OU2 – Source Area, the ESD documents for OU1 and OU2, and the O-Field Study Area Groundwater Treatment Facility O&M Manual

(ECC, 2016).

This report is intended to summarize and document the activities conducted by the O&M contractors during calendar year (CY) 2024, including operating and maintaining the GWTF, GES, and PIU and conducting performance monitoring activities in accordance with project requirements. The interim action RODs, the ESDs, and the O&M manual define the requirements.

Section 2 of the report includes a summary of the PIU O&M activities and observations. Section

3 discusses the O&M activities associated with the GWTF and well field. Section 4 presents the plant compliance monitoring results. The performance monitoring results are summarized and discussed in Section 5. Section 6 provides an overall operations summary. Finally, Section 7 includes references used in this report.

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2.0 PERMEABLE INFILTRATION UNIT OPERATIONS AND MAINTENANCE

AND MONITORING SUMMARY

The purpose of the PIU is to control the risks associated with exposure to CWM and other chemicals within the Old O-Field surface and subsurface soil by covering the site with non-flammable materials, minimizing the air flow to the surface, preventing erosion and stabilizing the soil, providing a blast resistant layer on top of the ordnance, and providing a barrier to mitigate surface exposure to CWM in the event of an underground release.

In order to protect the integrity of the PIU, Old O-Field operations personnel inspected the PIU and completed periodic maintenance tasks as per the O&M manual (ECC, 2016). On a weekly basis, walk down inspections of the surface of the PIU were conducted for any signs of subsidence.

The inspections were conducted to document new subsidences and changes to existing subsidences, which occur due to breakdown and settling of buried materials within the source area.

During the growing season, the perimeter of the PIU was maintained to prevent encroachment of plant growth onto the cover area. The PIU sprinkler system was activated at least once per quarter

(except during winter months) and typically once per month to confirm operation of the pump system and sprinkler heads. Sprinkler tests for CY 2024 were successfully conducted on 18 April, 3 June, 27 June, 25 July, 29 August, and 17 September. All systems were confirmed to be operational during each test event. The PIU sprinkler system pump motor was exercised weekly and the sprinkler system piping visually inspected for leaks or cracking (all piping was found in good order during 2024). On 25 June 2024, the nozzles were cleaned and inspected, and the pivot joints were lubricated on the PIU sprinkler heads. The nozzle connection on sprinkler #9 was also repaired on 25 June 2024. The sprinkler system was drained and winterized on 30-31 October

2024 (Appendix A).

The 2024 annual topographic survey of the PIU was performed on 13 January 2025 by a licensed

Maryland land surveyor. The survey was originally scheduled for December 2024 but was delayed due to weather conditions. Ground surface elevations were recorded at 86 grid locations across the

PIU. Additional feature markers were tracked by the surveyor but were not used in the actual monitoring of the PIU surface. Table 1 provides a comparison of the 2024 surveyed (conducted

13 January 2025) elevations to the 2023 and 2003 topographic surveyed elevations. All elevations are reported in feet using the North American Vertical Datum 83. The 2003 survey results are provided as a baseline. The 2023 results are provided for comparison of the previous year’s survey data. The topographic contour map for 2024 is presented as Figure 3. Comparison of the data assists in detecting evidence of subsidences. Several small unactionable depressions are noted by on Figure 3 with solid yellow circles. One area of interest on the PIU cap is located where

Subsidence A was repaired and is starting to reappear. The area was outlined for observation in

September 2017, but the subsidence is currently too shallow for measurements. This area will continue to be monitored for changes.

Figure 3 summarizes the location and details of subsidences and repairs that have occurred within the PIU surface. The operations personnel through visual observations during periodic inspections marked and tracked each subsidence. Repairs of a subsidence are initiated when a monitored subsidence is of a significant size and depth that potentially could compromise the integrity of the

PIU (ECC, 2016). The last PIU repairs were completed in December 2014. In 2022, subsidence

F was marked and measured approximately 7 feet in diameter and 16 inches deep. In 2023, subsidence F increased to 8.5 feet in diameter and 3 feet deep. Between 16 and 18 September

Aberdeen Proving Ground, MD September 2025

2-2

2024, subsidence F was repaired. The 2024 PIU Subsidence Repair Technical Memorandum is provided in Appendix B.

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3.0 GROUNDWATER TREATMENT FACILITY AND WELL FIELD OPERATION

AND MAINTENANCE ACTIVITIES

The GWTF is part of a pump and treat system that includes a network of extraction wells and a pipeline system to transport extracted groundwater to the plant. The treatment plant employs metals removal and VOC destruction and removal processes. Process monitoring guides operational control of the treatment plant performance, while effluent monitoring (see Section 4) governs discharge of the treated effluent to the Gunpowder River, as per the GWTF’s NPDES equivalency requirements.

Both routine and non-routine O&M of the GWTF and well field were completed during CY 2024.

A log of significant activities is presented in Appendix A and monthly reports generated during

CY 2024 are presented in Appendix C. Routine O&M includes actions necessary for operation of the treatment processes (e.g., chemical filling, process monitoring, etc.) and maintenance (e.g., pump servicing, preventive maintenance of compressors and generators, line and vessel cleaning, etc.). Non-routine O&M includes repair of items that have failed (e.g., generators, compressors, heating, ventilation, and air conditioning units, etc.) and responding to alarm conditions (e.g., high or low pH, high tank levels, etc.).

3.1 Operational Hours and Staffing

During CY 2024, the GWTF was staffed five days per week, eight hours per day, with occasional off-hours response for system alarms or weather/power related issues. The plant and well field remained operational during unmanned hours Monday through Friday, during weekends, and most holidays, except during planned or unplanned shutdowns.

The SCADA system initiates alarms and telephone notifications (via an auto dialer) in response to treatment process parameters (including flow, pH, tank levels, and effluent discharge parameters) outside of established operational ranges. The SCADA system will shut down the treatment system when selected alarm conditions are not corrected or acknowledged. The GWTF and well field can run autonomously for approximately two days, without the need for key functions performed onsite by the operations team. The SCADA system, in conjunction with the plant operator’s capability to remotely access the computer controls, enables safe and effective operation of the GWTF 24 hours/7 days per week.

3.2 Routine GWTF Activities

During CY 2024, facility inspections were conducted on a daily basis when the treatment system was operational. Process parameters were continuously recorded via the SCADA system and stored on a system database. Data parameters recorded were as follows: temperature, DO, groundwater storage tank levels, process flow rates, process pH readings, discharge flow rates, and other water quality parameters. Daily equipment checks were recorded on the daily check sheet and daily facility activities were recorded in the operations logbook. Refer to Appendix A for the significant O&M activities that occurred during CY 2024.

The GWTF operated continuously seven days per week during the CY 2024, with the exception of planned shutdowns (e.g., holidays, replacing spent carbon filters, equipment maintenance, etc.)

and unplanned shutdowns (e.g., severe weather conditions, PIU air monitoring alarms, and equipment failures), which are summarized in Figure 4. The treatment system operated within discharge parameters throughout CY 2024 (see Section 4). Treated effluent was directed to one

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3-2 of two effluent storage tanks (T-13 and T-14). Effluent was then pumped from the storage tanks to the outfall located in the Gunpowder River.

3.2.1 Bio-Monitor Experiment System

A side-stream of the GWTF effluent was monitored prior to discharge using an inline ventilatory bio-monitoring system, known as the Bio-Monitor Experiment (BME) System. The BME System was designed by the U.S. Army Center for Environmental Health Research, located at Fort Detrick, Maryland. The system used bluegill sunfish (Lepomis macrochirus) as test organisms to detect conditions in the post plant process effluent that could contribute to biological stress in the receiving discharge waters. The bluegill sunfish are placed in the bio-monitoring chambers for active monitoring via the computerized system. The operations staff monitored the fish responses by online tracking information displayed on a computer screen in the GWTF control room. Alarm programming in the SCADA system was updated during 2010 to provide notifications to operations personnel if the bio-monitoring parameters generated an alarm condition during unmanned operational periods. Throughout the year, the operations staff maintained the fish supplied by Blue Sources personnel for use in the bio-monitoring system and periodically changed the fish in the active monitoring chambers as directed. Under normal conditions, the fish served as online monitors for a period of three weeks.

BME System alarms resulted in three discharge stoppages (16 May, 7 October, and 29 December) during CY 2024. Section 3.4.2 summarizes the amount of downtime resulting from the BME

System alarms. The GWTF discharge stoppages were caused by erratic water quality parameters and/or faulty DO probe. No fish mortalities occurred during CY 2024. Table 2 summarizes the

BME system alarms.

3.3 Routine Well Field Activities

The GES ran consistently throughout CY 2024, with the exception of planned shutdowns (e.g., regular O&M, replacing well pumps, cleaning discharge, suction lines, etc.) and unplanned shutdowns (e.g., weather and significant treatment system equipment maintenance or repair).

Operations staff conducted daily well field inspections on staffed operations days. These inspections included recording flow meter readings, pump operation, and pump air pressure on the extraction well maintenance sheet. Groundwater level surveys were conducted monthly during

CY 2024.

Periodic maintenance of the extraction wells required turning off individual pumping wells or the entire extraction well field. The high volume of solids accumulated in the suction lines, pumps, flow meters, discharge lines, T-18 (groundwater extraction system) tank, and T-18 discharge line required frequent short-term shutdowns to clean and remove solids accumulation from equipment and pipelines. The discharge lines were flushed on a weekly basis with compressed air to remove accumulated solids (Appendix C).

All the extraction wells are redeveloped as necessary based on extraction well performance determined by a significant decline in the pumping rate (ECC, 2016). In CY 2024, six (6) extraction wells were redeveloped (EX-3A [three times], EX-8A [two times], PM-2R [two times], PM-3A [two times], PM-4A, and PM-5).

The flow data from each well was recorded and tracked through the SCADA system and well field inspection. The data collected was analyzed to guide the redevelopment, reconditioning, or

Aberdeen Proving Ground, MD September 2025

3-3 replacement of pumps and flow meters as a result of solids buildup. Flow meters and pumps removed from the wells were cleaned, serviced as necessary, and shelved for reuse. Suction lines were cleaned and pulled based upon daily monitoring of individual well flow.

3.4 Non-Routine O&M Activities

The following sections summarize the non-routine shutdowns of the treatment systems during CY

2024.

3.4.1 Power Failure, Weather Related, and Holiday Shutdowns

The GWTF experienced approximately 198 hours of shutdowns due to power failures, equipment maintenance, alarms, and/or holiday/scheduled shutdowns during CY 2024. Virtually all the power outage shutdowns were weather related, approximately 86.5 hours, comprising 43.7% of the shutdowns (Figure 4). No planned shutdowns (extended holidays and scheduled shutdowns) or severe weather (e.g., hurricanes, tropical storms, snowstorms, etc.) related shutdowns occurred in CY 2024.

Standby power via an onsite 300-kilowatt emergency generator is available to power critical systems during electric service outages. During a power failure, the plant systems shut down and discharge is stopped. The emergency generator continues to power the well field for tank fill operations and some of the plant emergency systems (ECC, 2016).

3.4.2 Alarm or Equipment Failure GWTF Shutdowns

The SCADA system was programmed to monitor selected treatment system process variables and initiate treatment system shutdown in response to alarm conditions. Monitored variables included process flow rates and pH values, tank levels, the effluent discharge parameters (pH, temperature, and DO), and the BME system alarm condition.

Alarm generated shutdowns occurred on 16 occasions during the reporting period, approximately

75 hours or 37.9% of the total non-planned/non-routine shutdown hours (Figure 4). The majority of the alarms resulted from issues with the following systems and processes: BME, UVOX, pH levels, low flow rates, and high/low water levels in the T-13 and T-14 tanks. BME alarm shutdowns occurred on three occasions during the reporting period, approximately 13.9 hours or

7% of the total non-planned/non-routine shutdown hours (refer to Section 3.2.1). Equipment maintenance shutdowns occurred on 13 occasions during the reporting period, accounting for approximately 22.4 hours or 11.3% of the shutdown hours (Figure 4).

3.4.3 Shutdowns Due to PIU Air Monitoring Alarms

The treatment plant operators follow a set protocol when a PIU air monitoring alarm occurs. When an alarm occurs during the daytime shift (07:00 to 16:00), the operators contact Range Control to confirm whether DEVCOM air monitoring personnel are onsite at the Old O-Field PIU to complete calibrations. If DEVCOM personnel are confirmed by Range Control to be onsite, no further action by the operators is required. If the alarm occurs during other operational shifts or the presence of the DEVCOM personnel could not be confirmed, the operators evacuate the site and rely upon the SCADA system alarms to automatically shut down the GWTF. No PIU system alarms occurred in CY 2024.

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3.4.4 Well Field Shutdowns

The well field shutdowns are divided into five categories:

1. repairs (planned shutdowns to make equipment/system repairs);

2. alarms (non-planned shutdowns due to system alarms);

3. power failures (non-planned shutdowns due to base power outages);

4. holiday/scheduled (planned shutdowns for extended holidays and scheduled outages); and

5. severe storms (planned shutdowns according to weather forecast).

During CY 2024, the well field was operational for 99.6% of the year (Figure 5). No system repairs generated shutdowns in CY 2024. Alarm generated shutdowns occurred on eight occasions for a total of 30.7 hours (78.6%), due to high levels in the T-1 and T-2 (equalization) tanks and one occurrence of a leak detection in the conveyance line. Power failures occurred once for a total of approximately 8.4 hours (21.4%) during CY 2024. No planned/scheduled shutdowns or weather related shutdowns occurred in CY 2024. A Hurricane/Storm Preparedness Plan was implemented at Old O-Field in 2012 for forecasted severe weather (ECC, 2012).

3.4.5 Unplanned Discharges

In CY 2024, no unplanned discharges of treated effluent water occurred.

3.5 Facility Improvements

Replacement offshore wells CWP-16R and CWP-17R were installed in September and October

2024. Appendix A contains the log of these activities.

3.6 Groundwater Processed

Extracted groundwater totaled 14,015,251 gallons during CY 2024. The average monthly extracted volume for the year was 1,167,938 gallons, with a monthly maximum of 1,296,341 gallons in May, and a monthly minimum of 1,006,743 gallons in December. The average monthly extraction flow rates ranged from 22.6 gpm in December to 29.2 gpm in April, with an annual average of 26.7 gpm (Appendix C).

Tank levels in the T-13 and T-14 tanks drove discharge flow rates typically in the range of 25 to

40 gpm with an annual average of approximately 26.9 gpm. A minimum of 9,000 to 25,000 gallons of treated effluent were maintained in one of the effluent storage tanks to supply the split effluent stream for the BME System. The effluent was treated via recirculation to a DO above five parts per million to prevent suffocation of the fish and to meet effluent discharge requirements.

3.7 Purge Water Processed

Purge water generated during routine groundwater sampling activities at Old O-Field was drained from drums into the plant sump and processed through the plant. Approximately 321 gallons of purge water collected during Old O-Field groundwater sampling activities and well redevelopment were processed in CY 2024.

In addition, approximately 684 gallons of purge/development water were processed in the plant during CY 2024 from the following study area’s sampling activities:

• Nike

• Maxwell Point

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• J-Field

• New O-Field

The treatment approval and acceptance paperwork are included in Appendix D.

3.8 Land Use Control

While not specified in the interim action RODs and ESDs for Old O-Field, land use controls

(LUCs) are being implemented by the U.S. Army that are unique to OU1 and OU2. LUCs monitored included:

• Prohibiting use of extracted groundwater for consumption, agricultural, or irrigation;

• Prohibiting activities that would impact the landfill cap (or cover system) and drainage system;

• Prohibiting excavation on the landfill cap or cover system;

• Prohibiting installation of utility system lines throughout the site;

• Restricting construction of buildings that may interfere with the landfill cap or cover system;

• Restricting plantings that would interfere with the landfill cap or cover system (i.e., roots that penetrate the cap or cover system); and

• Restricting vehicular traffic.

The site is monitored and surveyed constantly by the onsite GWTF staff as part of the plant O&M activities. There was no evidence of any infringements of the above listed LUCs during 2024 and all physical barriers maintained to restrict access to the site.

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4.0 COMPLIANCE MONITORING

The Old O-Field GWTF compliance monitoring program is conducted in accordance with the Old

O-Field interim RODs for OU1 and OU2 and the NPDES equivalency requirements. During CY

2024, the compliance monitoring was comprised of monthly sampling and analysis of plant influent/effluent, two chronic toxicity monitoring events using plant effluent, and semi-annual groundwater sampling and analysis. In addition, the treated effluent waters are monitored by the

BME system for acutely toxic conditions and are continuously monitored during discharge via the

SCADA system to confirm that temperature, DO, and pH parameters are within acceptable ranges.

4.1 NPDES Equivalency Monitoring

The SCADA system provided continuous online monitoring of effluent temperature, pH, and DO to meet NPDES equivalency requirements for discharge of the treated effluent to the Gunpowder

River. No exceedance of the temperature requirement (less than 90 degrees Fahrenheit), DO requirement (greater than 5 milligrams per Liter), or pH requirement (between 6.5 and 8.5) occurred during CY 2024.

The temperature, pH, and DO results were documented in quarterly Discharge Monitoring Reports submitted to Maryland Department of the Environment as part of the NPDES equivalency requirements (Appendix E).

The NPDES equivalency documentation established requirements for monthly sampling and analysis of the treated GWTF effluent. Samples were analyzed for nine metals (aluminum, arsenic, barium, copper, iron, lead, mercury, nickel, and zinc), VOCs, mustard agent degradation products

(1,4-dithiane, 1,4-oxathiane, and thiodiglycol), total suspended solids, and turbidity. The influent and effluent monthly monitoring results for the GWTF are presented in Table 3. Table 4 presents a summary of all sample detections compared to discharge parameters for each compound. The average metals removal efficiencies for the nine monitored metals are provided in Table 5.

The majority of the treated effluent analytical results met established limits throughout CY 2024, with the exception of zinc. Zinc exceeded the established limits four times throughout CY 2024

(January at 374 micrograms per liter [µg/L], May at 4,420 µg/L, September at 564 µg/L, and

November at an average concentration of 462 µg/L [from two separate sampling results of 850 μg/L and 74 μg/L]). The 30-day average limit of zinc (310 μg/L) was exceeded three times (10

January, 11 September, and November). The 1-day maximum limit (1,020 μg/L) was exceeded once (8 May). The May 2024 effluent results were not representative of the true effluent concentrations at the time of sample collection, and was likely the result of a contaminated sample bottle (refer to Appendix C for more details). In all four exceedances, the effluent zinc concentrations were higher than the influent zinc concentrations. Influent zinc concentrations were all consistent with historical values. Following an evaluation of the treatment system processes, a correlation was identified between the acid washing frequency of the UVOX system and the effluent zinc exceedances (refer to Appendix E for additional details). The following corrective measures were implemented to mitigate future excursions:

• Acid washing of the UVOX sleeves has been integrated into the plant’s monthly maintenance schedule; and

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• The pH set point of the metals removal system was reduced from 10 to 9.7 on 25 November

2024 to optimize zinc removal and maintain removal efficiency of additional metals contaminants (a pH of 9.1 is optimal for zinc removal).

The December 2024 effluent met discharge requirements with zinc results at 92.1 μg/L and 84.2 μg/L.

All other treated effluent analytical results met the established limits throughout CY 2024. The measured effluent total VOC concentrations were less than the maximum criterion of 100 µg/L, with an average measured concentration of 16 µg/L for CY 2024.

A total of ten VOC constituents were detected in at least six of the monthly influent samples (Table

4). The highest detected influent VOC concentration was TeCA at 790 µg/L. The average influent total VOC concentration for CY 2024 was 1,301 µg/L.

Metals removal efficiencies ranged from -0.3% removal of lead to 100% removal of mercury and nickel during CY 2024. Specific metals removal efficiencies were consistent with historical removal efficiencies and were within the NPDES equivalency requirements (Table 5). The May

2024 removal efficiencies were excluded from Table 5 due to the discrepancy in the sample (refer to Appendix C for more details).

Chronic toxicity monitoring was conducted in the third and fourth quarters of CY 2024. The results of both events indicated no evidence of toxicity from the treated effluent (Appendix E).

The BME system continuously monitors the treated effluent for contaminant concentrations at acute toxicity levels (Table 2).

4.2 Process Residuals Monitoring

Compliance monitoring for process residuals conducted at Old O-Field during CY 2024 was comprised of an annual sampling and analysis of spent liquid phase granular activated carbon

(GAC), process and tank sludge, spent cartridge filters, and spent vapor phase GAC. The vapor phase GAC is replaced on a semi-annual basis and the lead liquid phase GAC is replaced approximately every six months (dependent upon compliance monitoring results and operating parameters (ECC, 2016).

The process residual samples were analyzed for hazardous waste and toxicity characteristics as per the Resource Conservation and Recovery Act and preparations using the Toxicity Characteristic

Leaching Procedure (TCLP). The analyses performed included TCLP semi-volatiles, TCLP pesticides, TCLP herbicides, TCLP metals, TCLP volatiles, thiodiglycol, flash point, reactive cyanide and sulfide, pH, and percent solids.

All samples of the process residuals met the established criteria for disposal as non-hazardous waste throughout CY 2024, as documented in Appendix F. Quantities of wastes disposed in CY

2024 are listed in Table 6. APG’s disposal contractor handled and disposed Old O-Field’s process residual waste. In addition, universal waste (lime strainer basket cleaning) was removed from the treatment facility and properly disposed of in CY 2024 (Table 6).

Purge water generated during routine groundwater sampling activities at Old O-Field was drained from drums into the GWTF plant sump and processed through the plant (Section 3.7).

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4.3 Air Emissions

Emissions of VOCs from the Old O-Field GWTF and GES are controlled via vapor phase GAC treatment. The following tanks are vented for emissions controls:

• T-18 – Groundwater Extraction System tank

• T-1 and T-2 – Equalization tanks

• T-9A – Re-pump tank

• T-5 – Sludge holding tank

• T-8 – Filtrate sump

• T-10 and T-11 – Intermediate holding tanks

The filter press room has an active vapor control system that captures fugitive emissions from the filter press room using a centrifugal blower to deliver the captured VOCs to two 200-pound activated carbon units. Both the secondary and active 55-gallon GAC units were changed out in

October 2024.

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5.0 PERFORMANCE MONITORING RESULTS

The interim ROD of the Old O-Field OU1 specified that a groundwater monitoring plan shall be developed and implemented during the interim response action to ensure that hydraulic control of the plume of contamination emanating from Old O-Field towards Watson creek is maintained.

Specifically, an inward and upward gradient within the plume must exist to mitigate the discharge of contaminated groundwater to Watson creek. Information necessary for this determination includes:

• horizontal and vertical hydraulic gradients in the groundwater between Old O-Field and

Watson creek;

• horizontal and vertical contaminant concentration gradients in groundwater between Old

O-Field and Watson Creek;

• changes in contaminant concentration or distribution over time;

• effects of tidal influence on the plume capture zone; and

• effects of any modifications to the original interim response action.

The current Performance Monitoring Plan was implemented in 2004 and is detailed in the GWTF

O&M Manual (ECC, 2016).

5.1 Precipitation Amounts

Precipitation amounts are recorded on a regular basis from a rain gauge located at the GWTF.

Significant precipitation events or extended periods of multiple precipitation events tend to impact groundwater elevations, which potentially effects the GES operations. Figure 6 depicts the monthly measured precipitation amounts recorded at Old O-Field compared to the “normal” average rainfall amounts for the area as measured at Phillips Airfield, APG.

For CY 2024, rainfall measured at Old O-Field totaled approximately 34.8 inches, approximately

10 inches less than the “normal” for Phillips Airfield of 44.85 inches. Rainfall measured at the

GWTF was below the normal in February, April, May, June, July, September, October, November, and December. January and August had rainfall well above normal and March and May rainfall were close to the average amounts at Phillips Airfield.

For CY 2024, measurable snowfall was observed in January, February, and December (9.1 inches,

4.4 inches, and 0.1 inches, respectively). Trace amounts of snow was observed in November. The measured snowfall for CY 2024 was below the historical monthly averages.

5.2 Groundwater Elevations, Hydraulic Containment, and Extraction Well Operations

In order to comply with the requirements of the interim ROD, monitoring and assessment of the well field performance are necessary to evaluate containment of the contaminated groundwater.

As per the Performance Monitoring Plan, water level measurements will be collected monthly from existing WTA monitoring and extraction wells and UCA monitoring wells. The monthly water level data collected from the WTA is used to create groundwater elevation contour maps to assess hydraulic containment and performance of the extraction system. Elevations collected in the UCA wells are presented on well field maps but are not contoured due to the flat lateral gradient in the UCA. The UCA is not actively pumped by the GES. The monthly groundwater elevation maps for both the WTA and UCA are provided in Appendix G.

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Figure 7 depicts a hydrograph for CY 2024 with groundwater elevations from three (3) monitoring wells representing the northern, southern, and western (PM-1, MW-01, and OF-83R) portions of the well field. Normal seasonal changes in the groundwater typically depict groundwater elevation highs in April and groundwater elevation lows in October of the year.