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Distribution of Ancient Carbon in Groundwater and Soil Gas from Degradation of Petroleum near the Red Hill Bulk Fuel Storage Facility, O‘ahu, Hawai‘i

Jared J. Trost, Barbara A. Bekins, Jeanne B. Jaeschke, Geoffrey N. Delin, Daniel A. Sinclair, James K. Stack · U.S. Geological Survey

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Environmental Health Program Prepared in cooperation with the U.S. Navy and the Defense Logistics Agency

Distribution of Ancient Carbon in Groundwater and Soil Gas from Degradation of Petroleum near the Red Hill Bulk Fuel Storage Facility, Oʻahu, Hawaiʻi

Scientific Investigations Report 2024–5034

U.S. Department of the Interior U.S. Geological Survey

Photograph showing Red Hill from Pearl Harbor, Oʻahu, Hawaiʻi, taken September 2022 by Jared Trost, U.S. Geological Survey.

Photograph showing U.S. Geological Survey staff sampling groundwater at a well in Oʻahu, Hawaiʻi, taken September 26, 2022, by Lhiberty Pagaduan, U.S. Geological Survey.

Photograph showing U.S. Geological Survey staff sampling soil carbon dioxide efflux in Oʻahu, Hawaiʻi, taken September 2022 by Jared Trost, U.S. Geological Survey.

Photograph showing U.S. Geological Survey staff sampling soil gas with a soil probe sampler in Oʻahu, Hawaiʻi, taken September 2022 by Geoffrey Delin, U.S. Geological Survey.

Cover.

Distribution of Ancient Carbon in Groundwater and Soil Gas from Degradation of Petroleum near the Red Hill Bulk Fuel Storage Facility, Oʻahu, Hawaiʻi By Jared J. Trost, Barbara A. Bekins, Jeanne B. Jaeschke, Geoffrey N. Delin, Daniel A. Sinclair, James K. Stack, Rylen K. Nakama, Uliʻi M. Miyajima, Lhiberty D. Pagaduan, and Isabelle M. Cozzarelli

Environmental Health Program Prepared in cooperation with the U.S. Navy and the Defense Logistics Agency

Scientific Investigations Report 2024–5034

U.S. Department of the Interior U.S. Geological Survey

U.S. Geological Survey, Reston, Virginia: 2024

For more information on the USGS—the Federal source for science about the Earth, its natural and living resources, natural hazards, and the environment—visit https://www.usgs.gov or call 1–888–392–8545. For an overview of USGS information products, including maps, imagery, and publications, visit https://store.usgs.gov/ or contact the store at 1–888–275–8747. Any use of trade, firm, or product names is for descriptive purposes only and does not imply endorsement by the U.S. Government. Although this information product, for the most part, is in the public domain, it also may contain copyrighted materials as noted in the text. Permission to reproduce copyrighted items must be secured from the copyright owner. Suggested citation: Trost, J.J., Bekins, B.A., Jaeschke, J.B., Delin, G.N., Sinclair, D.A., Stack, J.K., Nakama, R.K., Miyajima, U.M., Pagaduan, L.D., and Cozzarelli, I.M., 2024, Distribution of ancient carbon in groundwater and soil gas from degradation of petroleum near the Red Hill Bulk Fuel Storage Facility, Oʻahu, Hawaiʻi: U.S. Geological Survey Scientific Investigations Report 2024–5034, 54 p., https://doi.org/10.3133/sir20245034. Associated data for this publication: Jaeschke, J.B., Trost, J.J., Sinclair, D.A., Cozzarelli, I.M., Pagaduan, L.D., Miyajima, U.M., Nakama, R.K., Delin, G.N., Stack, J.K., and Baesman, S.M., 2023, Groundwater and soil gas data, methods, and quality assurance information for samples collected to determine ancient carbon distributions at Red Hill Bulk Fuel Storage Facility, Oʻahu, Hawaiʻi, 2022–2023: U.S. Geological Survey data release, https://doi.org/10.5066/P9TIDAA4. U.S. Geological Survey, 2024, USGS water data for the Nation: U.S. Geological Survey National Water Information System database, https://doi.org/10.5066/F7P55KJN. ISSN 2328-0328 (online)

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Acknowledgments Thanks to U.S. Navy staff for coordinating access to the site. Thanks to the AECOM groundwater sampling crews who allowed us to tag along and collect groundwater samples. Thanks to the Honolulu Board of Water Supply who allowed us to collect a sample at one of their wells (DH43) during their sampling of the well. Thanks to John (Jack) Kronen (AECOM) for field geology orientation. Thanks to Bojan Milinic and Colin Livdahl of the Upper Midwest Water Science Center who organized data and prepared figures for this report. Thanks to John Hoffmann and other staff of the Pacific Islands Water Science Center who provided administrative and technical assistance that supported successful completion of this study.

Contents Acknowledgments��iii Abstract��1 Introduction��1 Background—Application of Carbon-14 to Petroleum Spills��3 Purpose and Scope��3 Site Description��4 Facility��4 Facility Spill History��4 Geology��5 Hydrology��7 Existing Groundwater Concentration Data��7 Methods of Study��9 Groundwater��9 Groundwater Sampling Design��9 Groundwater Field and Laboratory Methods��9 Soil Gas��13 Soil Gas Sampling Design��13 Soil Gas Field and Laboratory Methods��13 Soil Probe Gas Sample Collection and Analysis��13 Soil Carbon Traps��16 Dynamic Closed Chamber Soil Carbon Dioxide Efflux Measurements��17 Petroleum and Degradation Products in Groundwater��17 Comparison of Nonvolatile Dissolved Organic Carbon to Routinely Collected Analytes��18 Bailed and Pumped Sample Comparison��19 Distribution of Petroleum Indicators��21 Ancient Carbon in Soil Carbon Dioxide��31 Carbon-14 in Soil Probe Samples��31 Soil Carbon Traps��32 Dynamic Closed Chamber Soil Carbon Dioxide Efflux��37 Summary��39 References Cited��39 Appendix 1. Carbon-14 Information��45 Appendix 2. Quality Assurance��50

Figures 1. 2.

3. 4.

5. 6.

7. 8.

9. 10.

11.

12.

13.

14.

15.

Map showing features and groundwater sampling locations near the Red Hill Bulk Fuel Storage Facility, Oʻahu, Hawaiʻi��2 Diagram showing conceptual approach for using carbon-14 to distinguish petroleum-derived carbon dioxide in soil gas and petroleum-derived nonvolatile dissolved organic carbon in groundwater from natural background sources��4 Diagram showing geology at the Red Hill Bulk Fuel Storage Facility, Oʻahu, Hawaiʻi��6 Images showing an outcrop of clinker and ʻaʻa- core sequencing, with interpreted void characteristics shown overlaying a photograph of the rock outcrop and without the photograph��7 Map showing soil gas sampling sites and types of data collected at each site��14 Graphs showing comparison of nonvolatile dissolved organic carbon concentrations with concentrations of diesel range organics and concentrations of total organic carbon in samples��19 Graphs showing comparison of bailed and pumped sample concentrations for nonvolatile dissolved organic carbon, diesel range organics, and dissolved iron��21 Graph showing correlation coefficients among analytes measured in groundwater samples that have been determined in previous studies to indicate petroleum degradation��24 Graph showing the ancient carbon contents of nonvolatile dissolved organic carbon with nonvolatile dissolved organic carbon concentrations in groundwater��25 Map showing contours of nonvolatile dissolved organic carbon concentrations in groundwater from samples collected in September 2022, January– February 2023, and April 2023 at the Red Hill Bulk Fuel Storage Facility, Oʻahu, Hawaiʻi��26 Map showing contours of ancient carbon contents of nonvolatile dissolved organic carbon concentrations in groundwater from samples collected in September 2022, January–February 2023, and April 2023 at the Red Hill Bulk Fuel Storage Facility, Oʻahu, Hawaiʻi��27 Map showing contours of diesel range organics concentrations in groundwater from samples collected in September 2022, January–February 2023, and April 2023 at the Red Hill Bulk Fuel Storage Facility, Oʻahu, Hawaiʻi��28 Map showing contours of alkalinity in groundwater from samples collected in September 2022, January–February 2023, and April 2023 at the Red Hill Bulk Fuel Storage Facility, Oʻahu, Hawaiʻi��29 Graphs showing calculated mass of ancient fossil fuel-derived carbon dioxide and assumed background carbon-14 contents for soil trap samples and tunnel air intake and exhaust samples collected in 2017 and reported as detections��36 Graph showing average dynamic closed chamber soil carbon dioxide efflux measurements made in September 2022 at the Red Hill Bulk Fuel Storage Facility, Oʻahu, Hawaiʻi��38

vii

Tables 1.

2. 3. 4. 5.

6. 7.

Summary of diesel range organics results from groundwater samples collected for the Department of the Navy or the Honolulu Board of Water Supply at sites near the Red Hill Bulk Fuel Storage Facility, Oʻahu, Hawaiʻi��8 Site information for groundwater sampling sites near the Red Hill Bulk Fuel Storage Facility, Oʻahu, Hawaiʻi��10 Summary of groundwater sampling at sites near the Red Hill Bulk Fuel Storage Facility, Oʻahu, Hawaiʻi��11 Site information for soil gas sampling sites at the Red Hill Bulk Fuel Storage Facility, Oʻahu, Hawaiʻi��15 Sample information, nonvolatile dissolved organic carbon concentrations from samples filtered through 0.22-micrometer filters and analyzed by the U.S. Geological Survey, and total organic carbon concentrations from unfiltered samples collected by AECOM��20 Table containing concentrations and percentage differences in concentrations of analytes measured in paired bailed and pumped samples��22 Compilation of soil carbon trap and cartridge results for 2017 and 2022–23 samples, literature-based atmospheric carbon-14 contents in carbon dioxide, carbon-14 contents in carbon dioxide from soil probe gas samples collected in 2022–23, and estimated reasonable ranges for background carbon-14 contents in carbon dioxide��33 Calculated masses of ancient fossil fuel-derived carbon dioxide accumulated on sorbent across a range of age-corrected background carbon-14 content values for soil trap and cartridge samplers deployed at the Red Hill Bulk Fuel Storage Facility, Oʻahu, Hawaiʻi, in 2017 and 2022–23��35

viii

Conversion Factors U.S. customary units to International System of Units.

Multiply

To obtain

Length inch (in.)

2.54

centimeter (cm)

inch (in.)

25.4

millimeter (mm)

foot (ft)

0.3048

meter (m)

mile (mi)

1.609

kilometer (km)

Area acre

4,047

square meter (m2)

acre

0.4047

hectare (ha)

acre

0.4047

square hectometer (hm2)

acre

0.004047

square kilometer (km2)

Volume gallon (gal)

3.785

liter (L)

gallon (gal)

0.003785

cubic meter (m3)

gallon (gal)

3.785

cubic decimeter (dm3)

million gallons (Mgal)

3,785

cubic meter (m3)

Flow rate inch per year (in/yr)

25.4

millimeter per year (mm/yr)

International System of Units to U.S. customary units

Multiply

To obtain

Length centimeter (cm)

0.3937

inch (in.)

millimeter (mm)

0.03937

inch (in.)

milliliter (mL)

0.033814

ounce, fluid (fl. oz)

liter (L)

33.81402

ounce, fluid (fl. oz)

liter (L)

2.113

pint (pt)

liter (L)

1.057

quart (qt)

liter (L)

0.2642

gallon (gal)

liter (L)

61.02

cubic inch (in3)

milligram (mg)

3.5274×10−5

ounce, avoirdupois (oz)

gram (g)

0.03527

ounce, avoirdupois (oz)

Volume

Mass

Temperature in degrees Celsius (°C) may be converted to degrees Fahrenheit (°F) as follows: °F = (1.8 × °C) + 32. Temperature in degrees Fahrenheit (°F) may be converted to degrees Celsius (°C) as follows: °C = (°F – 32) / 1.8.

Datums Vertical coordinate information is referenced to local mean sea level (LMSL). Horizontal coordinate information is referenced to the North American Datum of 1983 (NAD 83). Altitude, as used in this report, refers to distance above the vertical datum.

Supplemental Information Specific conductance is given in microsiemens per centimeter at 25 degrees Celsius (µS/cm at 25 °C). Concentrations of chemical constituents in water are given in either milligrams per liter (mg/L) or micrograms per liter (µg/L). Activities for carbon-14 in water and soil gas are given in percent modern carbon (pMC) or percent ancient carbon (pAC). Results for measurements of stable isotopes of an element (with symbol C) in water, solids, and dissolved constituents commonly are expressed as the relative difference in the ratio of the number of the less abundant isotope (iC) to the number of the more abundant isotope of a sample with respect to a measurement standard. Soil efflux is given in micromoles per square meter per second (µmol/m2/s).

Abbreviations Ag silver Al aluminum As arsenic B boron Ba barium Be beryllium Br bromide C carbon 14C carbon-14

Ca calcium Ce cerium Cl chloride Co cobalt CO2

carbon dioxide

Cr chromium Cu copper DOC

dissolved organic carbon

DRO

diesel range organics (synonymous with total petroleum hydrocarbons in the diesel range)

EPA

U.S. Environmental Protection Agency

F fluoride Fe iron H2SO4

sulfuric acid

HCl

hydrochloric acid

HCO3 bicarbonate HDPE

high-density polyethylene

ICP–MS

inductively coupled plasma-mass spectrometer

ICP–OES

inductively coupled plasma-optical emission spectrometer

K potassium La lanthanum Li lithium Mg magnesium Mn manganese Mo molybdenum

Na sodium Ni nickel NO3 nitrate NVDOC

nonvolatile dissolved organic carbon

Pb lead pMC

percentage modern carbon

PO4 phosphate PVC

polyvinyl chloride

Rb rubidium RBPGL

Reston Biogeochemical Processes in Groundwater Laboratory

Sb antimony Se selenium Si silicon SO4 sulfate Sr strontium τ

Kendall’s tau

Tl thallium TOC

total organic carbon

U uranium USGS

U.S. Geological Survey

V vanadium WHOI NOSAMS Woods Hole Oceanographic Institution, National Ocean Sciences Accelerator Mass Spectrometry Zn zinc

Abstract

Introduction

The groundwater below the Red Hill Bulk Fuel Storage Facility (the facility) in Oʻahu, Hawaiʻi, contains fuel compounds from past spills. This study used carbon-14 analyses to distinguish fuel-derived carbon from background carbon, along with other biodegradation indicators, to address two goals: (1) determine the extent and migration direction of groundwater affected by residual fuel below the facility and (2) determine if residual fuel locations in the subsurface could be identified by analyzing soil gas at the surface above the facility. Groundwater from 19 wells was sampled between September 2022 and April 2023. Nonvolatile dissolved organic carbon (NVDOC) from a well presumed to be unaffected by past spills contained 38 percent ancient carbon indicating a natural source of ancient carbon in the subsurface. The NVDOC concentrations and ancient carbon percentages indicate fuel biodegradation products are likely present on the north and south of Red Hill with the greatest effects at well RHMW02 near the 2014 spill site. The NVDOC concentrations are almost three times higher than diesel range organic (DRO) concentrations in groundwater from the same sites. Major ion data indicate that iron reduction is an important biodegradation process. Soil probe samples and soil carbon traps were used to determine the carbon-14 content of soil carbon dioxide. Ancient carbon from fuel biodegradation was not detected at any soil probe or carbon trap site in contrast to a 2017 study which reported ancient carbon detections. A reanalysis of the 2017 results using a range of local values for background carbon-14 indicates that ancient carbon from fuel biodegradation was probably only detected in lower tunnel exhaust system samples and not in any soil carbon trap samples. Measurements of carbon dioxide efflux with a dynamic closed chamber were highly variable. The soil gas results indicate that soil gas measurements at land surface were not useful for detecting residual fuel at the facility.

This study used information related to the fate and transport of crude oil at a spill site in Minnesota to help clarify the fate of past fuel spills at the Red Hill Bulk Fuel Storage Facility (the facility) in Oʻahu, Hawaiʻi (fig. 1). The facility has supported military operations in the Pacific since it was completed in 1943. It overlies the aquifer supplying water for the city of Honolulu and military housing. In November 2021, a fuel release at the facility resulted in residential water contamination of the Navy water system at Joint Base Pearl Harbor-Hickam, the Army’s Aliamanu Military Reservation, and Red Hill housing (Department of the Navy, 2022). Concern by the public and government agencies about the ongoing potential for contaminants from the facility to enter the water supply led to a decision to permanently shut down the facility in March 2022. At the facility, varying amounts and types of fuel have been spilled during operations (AMEC Earth and Environmental, Inc., 2002). In addition to the November 2021 spill, there were releases in May 2021 and January 2014, and evidence of releases before 2014 exists below 16 of the 20 tanks at the facility (AMEC Earth and Environmental, Inc., 2002). Although the facility is closing and the Joint Task Force-Red Hill completed its defueling mission (by removing more than 104 million gallons of fuel via gravity and all accessible residual fuel as of March 28, 2024 [U.S. Indo-Pacific Command, 2024]), the presence of fuel from past spills in the unsaturated zone above the aquifer creates a need to understand the fate of any fuel from past spills still present in the subsurface. Investigating the fate of spilled fuel commonly has two main goals. The first is to identify the locations of source areas where spilled fuel is present in the subsurface. The second is to identify the migration direction of dissolved fuel compounds and degradation products in the groundwater. Previous studies by the U.S. Geological Survey (USGS) of a crude oil spill site in Minnesota indicated that carbon dioxide (CO2) flux from biodegradation of the spilled oil is elevated at the land surface above the spilled oil (Sihota and others, 2011, 2016). The underlying crude oil source zone

eam a Str

ālaw

S. H

RHMW12A

RHMW04

y St

lle

Va lawa

Hā

RHMW11–05

Pl RHMW14–03 7 RHMW08

ni St

Ala La

t aim a

puna S

Ala Ka

PACIFIC OCEAN

Moana

i Pl

Large map extent

oa Dr

trea lu S m

lualan

i lan

1,000

2, 000 FEET

250

500 METERS

Base from U.S. Geological Survey digital data, various scales and dates Universal Transverse Mercator, zone 4 north North American Datum of 1983

1.5 1.5

Moanalua W–2

3 MILES

Oʻahu Honolulu

3 KILOMETERS

EXPLANATION Red Hill Bulk Fuel Storage Facility boundary

Approximate tunnel location

o aA Kaʻala 4,025 feet (1,227 meters)

0 0

Ala Hōkū Pl Study area

NMW24

ia Āl

tre

aP Kul

DH43

Ala ‘lolani St

RHMW09

Ala

Av e

RHMW10

RHMW19

RHMW05

Tampa Dr

of t

n atio loc nnel e t u ima cess t rox App wer ac o of l

Hill

RHP05

RHMW01R

Red

Ran

Icar

10 8 RHMW02

16 RHMW03

lau

oʻo he K

ay us W

Appro ximat of adit e location 3 tunn el

RHP04A

RHMW2254–01

a Waiu

aha

RHMW06

A' Line of section corresponding to the

geologic cross section in figure 3

RHMW08

Tunnel-access groundwater site Groundwater sampling site with identifer

Figure 1. Features and groundwater sampling locations near the Red Hill Bulk Fuel Storage Facility, Oʻahu, Hawaiʻi.

Approximate center of underground fuel storage tank with identifier

2 Ancient Carbon in Groundwater and Soil Gas from Degradation of Petroleum near the Red Hill Bulk Fuel Storage Facility

Introduction 3 at that site is roughly delineated by the area of increased CO2 efflux at the surface (Sihota and others, 2011). The CO2 from biodegrading oil is ancient and depleted in radiocarbon (carbon-14 [14C]), in contrast to CO2 from natural soil respiration, which contains modern 14C near atmospheric levels (Wozney and others, 2021). At the facility, a small number of measurements made in 2017 indicated that ancient CO2 from biodegradation of underlying spilled fuel was present at the land surface above the facility (Department of the Navy, 2019; McHugh and others, 2020). The 2017 results raised the question of whether or not it might be possible to find unknown fuel spill locations at the facility by measuring CO2 flux and the 14C content of soil CO2 at the land surface; thus, one component of this study was to measure the 14C content of soil CO2 and CO2 effluxes at the facility to determine if they could help locate spilled fuel in the subsurface. Understanding the direction of migration and biodegradation of contaminants in groundwater below the facility is complicated by the complex sequence of fractured lava flows, which make up the underlying basalt aquifer. Moreover, in some parts of the facility, the depth of the water table is more than 400 feet (ft) below land surface, making monitoring wells expensive to install. As a result, the distances between monitoring wells range from 200 to 800 ft. A groundwater sampling approach was needed to maximize information from the existing well network. The difference in spilled product dates and fuel types over the history of the facility means that past spills have differing compositions and biodegradation states. These differences make the use of a single compound problematic for tracking the effect of the spills on groundwater moving away from the facility. Consequently, monitoring of the existing well network has focused on measuring total petroleum hydrocarbons in the diesel range (also referred to as “diesel range organics [DRO]”), total petroleum hydrocarbons in the oil range (also referred to as “oil-range organics”), and a suite of hydrocarbons. Previous work by the USGS on the fate and transport of spilled crude oil has demonstrated that partial transformation products of the crude oil compounds form the largest mass fraction in the groundwater contaminant plume (Bekins and others, 2016; Podgorski and others, 2021). The total concentration of partial transformation products can be quantified by measuring the concentrations of nonvolatile dissolved organic carbon (NVDOC) in the groundwater. Results from crude oil studies indicate that concentrations of NVDOC are 3−20 times higher than DRO measured in the same wells (Bekins and others, 2016, 2020). The relatively high concentrations of NVDOC make NVDOC a useful tracer for mapping the migration of compounds from the crude-oil source zone. Thus, a second component of this study was to determine if concentrations and 14C contents of groundwater NVDOC could be used to better understand the migration direction and biodegradation potential of compounds migrating from the fuel source zones.

Background—Application of Carbon-14 to Petroleum Spills Carbon-14 is a general tracer that can be used to identify petroleum-derived carbon (C) in groundwater and in soil CO2. Carbon-14 is a radioactive isotope of C that is formed in the atmosphere and has a half-life of about 5,700 years (Woods Hole Oceanographic Institution, National Ocean Sciences Accelerator Mass Spectrometry, 2023b). Radiocarbon is continually produced in the atmosphere by interactions between energetic neutrons created by cosmic radiation and atmospheric nitrogen (Suess, 1965). In the atmosphere, 14C combines with oxygen to form 14CO2, which is then fixed by plants and algae (Tans and others, 1979). When C exchange with the atmosphere ceases because of death or senescence of photosynthetic tissues, the 14C concentration of dead organic matter declines from radioactive decay as time elapses (Larsen and others, 2018). Given enough time (about 60,000 years), plant-derived C such as that detected in fossil fuels (petroleum and coal) can become “radiocarbon dead,” being entirely depleted in 14C (Graven and others, 2017). In groundwater, plumes migrating away from petroleum fuel spills contain dissolved organic carbon (DOC) in the form of dissolved fuel compounds and partial transformation products of the fuel compounds originating in the fuel in addition to background DOC (Bekins and others, 2016). In the unsaturated zone or soil gas, plumes of CO2 from the biodegradation of petroleum fuel can exist near source areas along with CO2 from background soil respiration (Sihota and others, 2011; Wozney and others, 2021). In groundwater DOC and soil CO2, the 14C content of samples decreases as the proportion of petroleum-derived C increases (Sihota and others, 2011; Wozney and others, 2021). Samples with no petroleumderived C will typically reflect background 14C content. The primary motivations for this study were to use measurements of (1) 14C in groundwater DOC, along with other biodegradation indicators, to track migration of petroleumderived DOC away from the facility and (2) 14C in soil CO2 to identify locations at the facility where petroleum may be biodegrading in the subsurface (fig. 2).

Purpose and Scope The purpose of this report is to present results and interpretation of groundwater and soil gas samples collected in and around the facility in Oʻahu, Hawaiʻi. Samples were collected to understand the migration of petroleum-derived DOC in groundwater away from the facility and to identify locations at the facility where petroleum might be biodegrading in the subsurface.

4 Ancient Carbon in Groundwater and Soil Gas from Degradation of Petroleum near the Red Hill Bulk Fuel Storage Facility Soil gas sampled to measure 14C content of soil CO 2

Groundwater sampled to measure 14C content of NVDOC

Groundwater sample well

Soil probe

EXPLANATION [14C, carbon-14; CO2, carbon dioxide; NVDOC, nonvolatile dissolved organic carbon]

Unsaturated zone

CO 2

Organic carbon picked up by percolating water

CO 2

Soil

CO 2

Rock

CO 2

Natural background NVDOC composed of modern carbon from the surface and possibly aged carbon present in the formation CO2 and NVDOC from the petroleum source— 0-percent modern carbon and 100-percent ancient carbon

Petroleum source

Aquifer

NVDOC

Natural background CO2 from plants and soil with 14C contents near atmospheric levels— 100-percent modern carbon and 0-percent ancient carbon

NVDOC NVDOC

Aquifer

NOT TO SCALE

Figure 2. Conceptual approach for using carbon-14 to distinguish petroleum-derived carbon dioxide in soil gas and petroleum-derived nonvolatile dissolved organic carbon in groundwater from natural background sources. The carbon from petroleum is distinct from background carbon dioxide and nonvolatile dissolved organic carbon because petroleum-derived carbon is ancient and completely carbon-14 dead with 0-percent modern carbon and 100-percent ancient carbon.

Site Description The study site is on the island of Oʻahu, Hawaiʻi. The following sections describe the location and important features of the facility and the history of known spills. Short descriptions of the geology and hydrology are provided next and are followed by a description of existing groundwater concentration data used for comparison with the results from this study.

Facility The facility occupies 144 acres along Red Hill on the southwest flank of the Koʻolau Range (the eroded remnants of the Koʻolau shield volcano) 2−3 miles east of Pearl Harbor. It is flanked by Moanalua Stream valley to the southeast and South Hālawa Stream valley to the northwest. The facility contains 20 fuel tanks arranged in 2 parallel rows 100−200 ft

below the surface of Red Hill (fig. 1). The tanks were excavated into basalt rock in the early 1940s. Each tank is 245 ft high by 100 ft in diameter with a volume of 12.5 million gallons. The tanks are serviced by connecting upper, lower, and cross tunnels. The tunnel ventilation system maintains an air pressure that is lower than that in the surrounding basalt formation. As a result, some gas from the unsaturated zone flows into the tunnels (Department of the Navy, 2019). More detailed descriptions of the facility and its setting are given in other publicly available documents (Department of the Navy, 2019, 2023b).

Facility Spill History This section summarizes evidence for fuel spills documented during past investigations at the facility. During 1998−2001, core samples were collected from slant borings

Introduction 5 below each of the 20 tanks (AMEC Earth and Environmental, Inc., 2002). The cores indicated hydrocarbon in the boreholes below 16 of the 20 tanks. Hydrocarbon presence, defined as a hydrocarbon odor and an elevated photoionization detector reading, was detected at tanks 1, 2, 3, 4, 5, 6, 7, 11, 12, 13, 14, 16, 17, 18, 19, and 20; a sheen was present at tanks 1 and 13; and product was detected at tanks 6 and 11 (AMEC Earth and Environmental, Inc., 2002). Angle borings at tanks 8, 9, 10, and 15 indicated no hydrocarbon presence. Fingerprinting of fluid samples collected from cores and boreholes indicated a mixture of middle distillate fuels of varying degrees of biodegradation ranging from relatively fresh to heavily biodegraded. Taken together, these results indicate that numerous fuel spills occurred at different times and locations at the facility before 2001. The following summary of the 2014 fuel spill is based on the report from the Department of the Navy (2019). In January 2014, an estimated 27,000 gallons (gal) of Jet Propellant 8 were released during refilling of tank 5 (Department of the Navy, 2019). A Jet Propellant 8 seep was observed in the lower cross tunnel wall outside the lower part of tank 5. Soil vapor monitoring points below tank 5 and nearby tanks 3, 6, 7, 8, and 9 indicated increases in hydrocarbon vapor concentrations compared to measurements made the previous month in December 2013. Temporal variations in the hydrocarbon vapor levels below tank 5 indicate multiple migration pathways of Jet Propellant 8 from the release points on the sides of tank 5 to the tank bottom. No free product was observed in monitoring wells below the facility but exceedances of screening criteria for total petroleum hydrocarbons and (or) naphthalene were detected in the wells before and after the release. The following summary of the 2021 fuel spill is from the Department of the Navy (2022). On May 6, 2021, an estimated 20,957 gal of Jet Propellant 5 were spilled from two piping joint ruptures near tanks 18 and 20. In the immediate aftermath of the spill, an estimated 1,580 gal were recovered. Most of the remainder flowed to a sump and was pumped automatically into the fire suppression system’s aqueous film forming foam recovery pipelines. The recovered fuel flowed to a low point in the aqueous film forming foam recovery pipeline far down the facility’s lower tunnel in the area overlying Red Hill Shaft (refer to well RHMW2254–01 in fig. 1). The fuel remained there undetected for more than 6 months until November 20, 2021, when an equipment operator accidentally struck and broke an overhead valve. Consequently, the nearly 19,000 gal of fuel that had been stored in the aqueous film forming foam pipeline since May 6 spilled from the break and flowed downhill along the tunnel floor. A detailed accounting of the fuel recovered since the May 6 and November 20 spills estimates that 5,542 gal of Jet Propellant 5 were not recovered and might have entered the formation below the tunnels. The pathways of migration from the tunnel to the formation were a sump, openings in drainpipes below the floor of the tunnel that were connected to the sump, and various cracks, holes, and penetrations in the tunnel floor. The spilled fuel migrated

downward through the basalt rocks to the water infiltration tunnel for Red Hill Shaft roughly 80 ft vertically below the tunnel. The time required for the spill to reach the well is unknown but can be bracketed by two events: the first report of tainted water by a resident was on November 27, and observation of a fuel sheen on the water and stain on the wall in the Red Hill Shaft was on December 2. These two events give an upper estimate of 7–12 days migration time through the 80-ft thickness of basalt between the tunnel and the well.

Geology Most of the facility is underlain by the Koʻolau Basalt, which ranges in age from 2 to 3 million years (Ozawa and others, 2005). The far western edge of the facility lies on tuff cone deposits of the rejuvenated Honolulu Volcanics. Highly weathered basalt known as saprolite is present in the top 25–50 ft below Red Hill (fig. 3). The basalt rocks consist of individual lava flow layers containing ʻaʻā flows with clinker zones and commonly massive flow cores and pāhoehoe flows. Interflow voids, joints, and lava tubes associated with pāhoehoe flows contribute to the overall permeability of the volcanic aquifer (fig. 3, fig. 4). Based on observations from outcrops near the facility, the average dip azimuth and dip angle of the lava flows were 246 degrees (Department of the Navy, 2023a) and 2.9 degrees, respectively (Department of the Navy, 2019). The adjacent South Hālawa and Moanalua Stream valleys are underlain by alluvial valley-fill deposits and variably weathered basalt, including saprolite. Measurements of outcrops in South Hālawa, Moanalua, and Waimalu Stream valleys quantified the proportion of clinker to total ʻaʻā as 15–45 percent (Wentworth and Macdonald, 1953). Rocky outcrops on Red Hill contain numerous vertical fractures that may provide vertical flow connections across otherwise low permeability ʻaʻā flow cores (fig. 4; Beckett and others, 2022). Extensive vertical connectivity may also be inferred from the rapid transport that occurred from the tunnel floor of adit 3 to the water table about 80 ft below after the November 2021 fuel spill. Groundwater in the uncontaminated basalt aquifers of Oʻahu is relatively low in DOC with concentrations of 0.19–0.27 milligram per liter (mg/L; Chapelle and others, 2013). For reference, a literature review of uncontaminated aquifer DOC values indicated a range for other sites of 0.1–4 mg/L (Regan and others, 2017). The DOC in uncontaminated groundwater samples from Oʻahu seems to have low to no bioavailability based on the high dissolved oxygen concentrations and lack of correlation between DOC and dissolved oxygen (Chapelle and others, 2013). The Koʻolau Basalt contains organic C in paleosol layers between lava flows (Wentworth and Macdonald, 1953) that is 14C dead (Doell and Dalrymple, 1973). Addition of DOC from the paleosol layers will create a DOC pool in groundwater that is older than modern age. Paleosols may also contain pyrogenic C because lava flows engulf and burn plant matter under low oxygen conditions as they advance through forested areas (Wentworth and Macdonald, 1953).

Department of the Navy, 2019

Figure 3. Geology at the Red Hill Bulk Fuel Storage Facility, Oʻahu, Hawaiʻi (unmodified from fig. 5.2 of Department of the Navy [2019]).

6 Ancient Carbon in Groundwater and Soil Gas from Degradation of Petroleum near the Red Hill Bulk Fuel Storage Facility

NOTE: VERTICAL EXAGGERATION = 1H: 7V (APPROXIMATE)

Introduction 7

EXPLANATION Clinker

Gas blister

Contact

Vesicle

EXPLANATION Fracture

Clinker

Gas blister

Contact

Vesicle

Fracture

Figure 4. An outcrop of clinker and ʻaʻa- core sequencing, with interpreted void characteristics shown (left) overlaying a photograph of the rock outcrop and (right) without the photograph (unmodified from Beckett and others [2022]; used with permission).

Hydrology

Existing Groundwater Concentration Data

The Red Hill area is part of the southern Oʻahu groundwater flow system (Hunt, 2004). Groundwater movement is controlled by the hydraulic properties of the rocks and the spatial distribution of recharge on the Koʻolau Range, where rainfall averages as much as 276 inches per year (Giambelluca and others, 2013). Water levels in the aquifer below Red Hill are 17–20 ft above mean sea level (Nakama and others, 2022). The unsaturated zone thickness is 400–500 ft, including about 100 ft below the base of the tanks and lower tunnel. Groundwater flowing into the area is supplemented by an estimated recharge of 10–20 inches per year within the facility (Engott and others, 2017). In locations where residual fuel from past spills is present in the unsaturated zone, recharge from infiltration of rainfall provides a mechanism for transporting dissolved hydrocarbons and hydrocarbon transformation products from the unsaturated zone to the underlying aquifer. For example, infiltrating rainwater has been documented between the steel tank liners and the concrete walls (Department of the Navy, 2019). Apparent recharge dates for groundwater in four wells with age dates nearest the facility ranged from 1950s to 1980s (Hunt, 2004), indicating a travel time of 20–50 years.

Concentrations measured in water samples from wells near the facility between 2016 and 2023 are available online at the Joint Base Pearl Harbor-Hickam Safe Waters website (https://jbphh-safewaters.org/; accessed January 18, 2024). A compilation of detections of DRO for the sampled wells is listed in table 1. The number of analyzed samples and frequency of DRO detections is listed for each well by year. The highest frequency of detections was at RHMW02 where DRO was always detected. The next highest frequencies were at RHMW01R and RHMW03 at 99 and 93 percent, respectively. The lowest number of detections was at RHP05 and RHMW10 at 5 and 8 percent, respectively. Zemo and Foote (2003) previously noted that natural organic matter can contribute to elevated values of DRO. In this report, we use additional data and provide strategies to comment on the likelihood that the DRO detections came from fuel at the facility.

[n, number of results reported; f, frequency of detection; a, denotes data source is Department of the Navy (2024); --, not applicable; b, denotes data source is Honolulu Board of Water Supply (2024)]

Site short name

Data source

2016

2017

2018

2019

2020

2021

2022

2023

Total

NMW24

0.83

0.13

0.25

RHMW01R

0.98

1.00

155

0.99

RHMW02

1.00

181

1.00

RHMW03

1.00

0.96

0.98

0.71

161

0.93

RHMW04

0.50

0.40

0.28

0.44

119

0.30

RHMW05

0.25

0.57

0.50

0.13

135

0.36

RHMW06

0.38

0.15

0.19

108

0.15

RHMW08

0.60

0.55

0.25

0.69

0.29

0.37

123

0.37

RHMW09

0.50

0.29

0.25

0.37

106

0.25

RHMW10

0.20

0.25

0.17

0.08

RHMW11–05

0.25

0.43

0.31

0.11

0.24

RHMW12A

0.43

0.23

0.17

RHMW14–03

0.20

0.38

0.08

0.07

0.11

RHMW19

0.20

0.23

0.22

RHMW2254–01

0.25

0.11

0.50

0.43

113

0.28

0.09

223

0.24

RHP04A

0.28

0.11

0.19

RHP05

0.06

0.05

DH43

0.29

8 Ancient Carbon in Groundwater and Soil Gas from Degradation of Petroleum near the Red Hill Bulk Fuel Storage Facility

Table 1. Summary of diesel range organics results from groundwater samples collected for the Department of the Navy or the Honolulu Board of Water Supply at sites near the Red Hill Bulk Fuel Storage Facility, Oʻahu, Hawaiʻi.

Methods of Study 9

Methods of Study This section describes the sampling design and field and laboratory methods used in this study. Methods for 14C analyses are described in appendix 1.

Groundwater This section describes the methods used in the groundwater part of this study. The wells sampled and the sampling methods are described first and followed by a description of sample preservation methods and analytical procedures used in the field and laboratory to determine concentrations of constituents in the water.

Groundwater Sampling Design In September 2022, January to February 2023, and April 2023, 19 groundwater sites were sampled. One well was presumed to be unaffected by spills at the facility (Moanalua W–2) and was classified as a background site (fig. 1 inset, table 2, table 3). The remaining 18 sites were on or near the facility and were sampled to understand the direction of migration of dissolved groundwater plumes from spills at the facility (fig. 2). Groundwater sites were sampled by USGS personnel with assistance from field crews from consultants for the Navy (AECOM) and Honolulu Board of Water Supply (INTERA). Wells selected for sampling were (1) evenly distributed spatially around the facility, (2) routinely visited by field sampling crews, and (3) ideally open near the water table (though some exceptions to this criterion were made). Groundwater samples were analyzed for several constituents useful for distinguishing petroleum hydrocarbon groundwater plumes from unaffected groundwater. These include NVDOC (which is synonymous with DOC in this report), 14C content of NVDOC, DRO, alkalinity, pH, specific conductance, major ions, and trace metals. Dissolved iron (Fe), manganese (Mn), nitrate (NO3), sulfate (SO4), and methane are indicators of the redox state of the aquifer and useful for identifying locations where biological demand for electron acceptors is high.

Groundwater Field and Laboratory Methods Groundwater field and laboratory methods are briefly described in this section. More detailed descriptions, especially for laboratory procedures, are available in Jaeschke and others (2023) and other references as cited. Groundwater samples were collected with one of the following: a disposable bailer, a discrete interval sampler in a multilevel well (Westbay Instruments, Burnaby, British Columbia, Canada), or a pump (either a bladder pump or submersible pump; table 3). For all groundwater samples bailed in September 2022 and for wells RHMW01R, RHMW08,

RHMW09, and NMW24 bailed in January and February 2023, samples were collected with disposable Teflon bailers that were 36 inches (in.) long by 1.5 in. in diameter. All other bailed 2023 samples were collected with disposable ridge and clear per- and polyfluoroalkyl substances free AquaClear polyvinyl chloride (PVC) bailers that were 36 in. long by 1.6 in. in diameter (Pine Environmental, Glen Burnie, Maryland, United States). Bailed samples were collected from the uppermost 3–5 ft of groundwater in each well (AECOM, written commun., August 3, 2023). Wells were not purged before sample collection with bailers. At each well, bailer sample retrieval continued until enough volume was acquired for the planned analyses by USGS and AECOM. During each bailer retrieval, the bailer was kept vertical and a clamp was installed on the outlet so sample water outflow could be controlled during sample container filling. Wells RHMW14–03 and RHMW11–05 were sampled using a discrete interval sampling system (Westbay Instruments, Burnaby, British Columbia, Canada), which allows the collection of aqueous samples from multiple zones within a single borehole. The MOSDAX sampler probe contains a valve operable from the surface with a hydraulic winch, which controls the sampling operation. Four stainless steel 250-milliliter (mL) canisters (316/316L stainless steel) were linked in sequence to collect samples suspended below the probe at specified intervals (table 2, table 3). The canisters were deployed multiple times until enough sample volume was collected for the planned laboratory analyses by USGS and AECOM. Bladder pumps were used to collect regular samples at wells RHMW12A, RHP05, and DH43. The pump intake for RHMW12A was set near the middle of the well’s open interval, or about 202 ft below the water level in this well. The pump intake for RHP05 was also set near the middle of its open interval, which is about 4 ft below the water level in this well. Information on the pump intake depth for DH43 was unavailable at the time this report was prepared. At wells RHWM12A and DH43, dedicated PVC bladder pumps (model P1101HM, QED Environmental Systems, Dexter, Michigan, United States) connected to high-density polyethylene (HDPE) skip-bonded tubing were used to collect samples. At well RHP05, a dedicated stainless steel bladder pump that was 18 in. long by 1.66 in. in diameter with a polytetrafluoroethylene bladder (Geotech Environmental Equipment, Inc., Denver, Colorado, United States) connected to Teflon-lined polyethylene skip-bonded tubing was used for sample collection (AECOM, written commun., August 3, 2023). Bladder pumps were used to collect quality assurance samples for comparison with bailed samples at wells RHMW2254–01, RHMW02, and RHMW03. The pump intakes were set at about 6, 9, and 8 ft below the top of the water column at RHMW2254–01, RHMW02, and RHMW03, respectively (AECOM, written commun., August 3, 2023). At RHMW02 and RHMW03, dedicated PVC bladder pumps (model P1101M, QED Environmental Systems, Dexter, Mich.) with skip-bonded HDPE tubing were used to collect

[USGS, U.S. Geological Survey; HI, Hawaiʻi; <, less than; PVC, polyvinyl chloride; --, not available] bApproximate

Site short name

aUSGS site

identifier

aUSGS station name

bReference altitude, in feet above local mean sea level

bReference altitude

description

bWell

bHole

depth, in feet below reference

top altitude of open or screened interval, in feet above local mean sea level

bApproximate bottom altitude of open or screened interval, in feet above local mean sea level

DH43

212225157533001

3–2253–02 Moanalua DH 43, Oahu, HI

234.32

Top of casing

275

<−10

−42

Moanalua W–2

212120157535400

3–2153–11 Moanalua W–2, Oahu, HI

Approximate land surface

300

−115

−265

NMW24

212238157553001

3–2255–41 NMW24, Oahu, HI

106

Approximate land surface

109

116

−3

RHMW01R

212214157535402

3–2253–10 Red Hill RHMW01R, Oahu, HI

101.76

Top of casing

98.5

RHMW02

212216157534701

3–2253–26 Red Hill RHMW02, Oahu, HI

105.25

Mag nail in tunnel floor

103.5

RHMW03

212219157533901

3–2253–27 Red Hill RHMW03, Oahu, HI

121.62

Mag nail in tunnel floor

117

118

RHMW04

212231157532901

3–2253–28 Red Hill RHMW04, Oahu, HI

312.55

Nearby mag nail

305

320.5

RHMW05

212210157540201

3–2254–23 Red Hill RHMW05, Oahu, HI

101.78

Mag nail in tunnel floor

125

RHMW06

212226157534101

3-2253–04 Red Hill RHMW06, Oahu, HI

256.85

Mag nail in well pad

260

280

−3

RHMW08

212216157535801

3–2253–07 Red Hill RHMW08, Oahu, HI

308.95

Mag nail in well pad

309

315

RHMW09

212209157535201

3–2253–08 Red Hill RHMW09, Oahu, HI

393.11

Mag nail in well pad

397

405

RHMW10

212213157533901

3–2253–09 Red Hill RHMW10, Oahu, HI

492.92

Mag nail in well pad

494

501

492.5

−66c

−79c

RHMW11–05

212226157535002

3–2253–11 Red Hill RHMW11 (Zone 5), Oahu, HI

210.77

Land surface

290

(sampling port at −75)

RHMW12A

212230157535202

3–2253–17 Red Hill RHMW12A, Oahu, HI

238.62

Top of coupling on PVC casing

433

440

−174

−194

RHMW14–03

212221157535802

3–2253–14 Red Hill RHMW14 (Zone 3), Oahu, HI

180.23

Land surface

338

495

−140c (sampling port at −145)

−158c

RHMW19

212212157534601

3–2253–16 Red Hill RHMW19, Oahu, HI

443.16

Mag nail in well pad

445

455

−2

RHP04A

212213157542701

3–2254–13 RHP04A, Oahu, HI

157.93

Mag nail in well pad

160.26

164.50

27.67

−2.33

RHP05

212211157542401

3–2254–16 RHP05, Oahu, HI

230.28

Top of casing

234.1

238

−3

RHMW2254–01

212225157542601

3–2254–01 Red Hill Shaft (S11), Oahu, HI

100.76

Mag nail in tunnel

aData from U.S. Geological Survey (2024). Database limitations preclude the use of Hawaiian diacritical marks in U.S. Geological Survey station names. bData from AECOM and U.S. Navy (John [Jack] Kronen, written commun., January 5, 2024). cThese are multilevel monitoring wells (Westbay Instruments, Burnaby, British Columbia, Canada) that are open to the formation only at the sampling port. The top and bottom altitudes of the “open” interval are bounded by packers inside the well casing.

10 Ancient Carbon in Groundwater and Soil Gas from Degradation of Petroleum near the Red Hill Bulk Fuel Storage Facility

Table 2. Site information for groundwater sampling sites near the Red Hill Bulk Fuel Storage Facility, Oʻahu, Hawaiʻi.

Methods of Study 11 Table 3. Summary of groundwater sampling at sites near the Red Hill Bulk Fuel Storage Facility, Oʻahu, Hawaiʻi. [Y, yes; --, no]

Year(s) of sample collection

Regular sample collection method

Background site

Site accessed through Red Hill access tunnel

Bailer-pump comparison samples collected

Field duplicate collected

DH43

2023

Pump

Moanalua W–2

2022

Pump

NMW24

2023

Bailer

RHMW01R

2022

Bailer

RHMW02

2022, 2023

Bailer

RHMW03

2022, 2023

Bailer

RHMW04

2023

Bailer

RHMW05

2022

Bailer

RHMW06

2023

Bailer

RHMW08

2022

Bailer

RHMW09

2023

Bailer

RHMW10

2023

Bailer

RHMW11–05

2023

Discrete interval sampler (Westbay System)

RHMW12A

2023

Pump

RHMW14–03

2023

Discrete interval sampler (Westbay System)

RHMW19

2023

Bailer

RHP04A

2023

Bailer

RHP05

2023

Pump

RHMW2254–01

2023

Bailer

Site short name

samples. At RHMW2254–01, a dedicated stainless steel bladder pump that was 36 in. long by 1.66 in. in diameter with a polyethylene bladder (Geotech Environmental Equipment, Inc., Denver, Colo.) connected to HDPE skip-bonded tubing was used for sample collection (AECOM, written commun., August 3, 2023). In the field at most sites, groundwater levels, specific conductance, and pH were measured according to standard USGS procedures (Cunningham and Schalk, 2011; U.S. Geological Survey, 2023). Groundwater level tapes were calibrated with a National Institute of Standards and Technology certified reference steel tape. Meters used for measuring specific conductance and pH were checked or calibrated according to standard USGS procedures (U.S. Geological Survey, 2023) and described in more detail by Jaeschke and others (2023). Specific conductance measurements were made using an Orion Star A122 instrument (Thermo Fisher Scientific, Waltham, Massachusetts, United States) or a YSI 300 instrument (Yellow Springs Instruments, Yellow Springs, Ohio, United States). Field measurements of pH were made with an Orion Star A121 instrument (Thermo Fisher Scientific,

Waltham, Mass.). Raw, unfiltered samples for methane and DRO analyses were collected into their final containers at each sampling site. Raw, unfiltered samples for all other analyses were collected into either baked 1- or 4-liter (L) amber glass bottles or 1- or 4-L HDPE bottles and immediately put on wet ice until they were processed in the laboratory. The following is a brief description of methane sample collection and analysis based on a detailed description provided in Jaeschke and others (2023). The methods used in this study are modified from Baedecker and Cozzarelli (1992). Methane analyses were only completed for samples collected in September 2022. Raw, unfiltered groundwater samples were collected into baked clear glass 25-mL vials that contained about 20 milligrams of trisodium phosphate dodecahydrate, had been purged with nitrogen gas, were capped with butyl rubber stoppers, and were partially evacuated. The trisodium phosphate dodecahydrate is a preservative that inhibits microbial activity by increasing the pH of the sample. About 2–3 mL of the water samples were injected into each sample bottle using a closed-system syringe and needle as described in Baedecker and Cozzarelli (1992). Samples were placed on wet

12 Ancient Carbon in Groundwater and Soil Gas from Degradation of Petroleum near the Red Hill Bulk Fuel Storage Facility ice immediately after collection and then stored at 4 degrees Celsius (°C) until analysis at the USGS Reston Microbiology Laboratory in Reston, Virginia. Methane concentrations were determined with a headspace method on an HP 6890 thermal conductivity detector gas chromatograph with a GS GasPro column, flame ionization detector back injection, and front detector (Agilent Technologies, Inc., Santa Clara, California, United States; described in Jaeschke and others [2023]). Samples for DRO analysis were collected into duplicate 1-L glass amber bottles provided by RTI Laboratories (Livonia, Mich.). Bottles were filled with raw, unfiltered, and unpreserved water samples. The samples were stored and shipped on wet ice as soon as possible after field collection to meet the 7-day holding time requirement. The samples were analyzed using a gas chromatograph flame ionization detector method according to U.S. Environmental Protection Agency (EPA) Validated Test Method 8015D (U.S. Environmental Protection Agency, 2003) for nonhalogenated volatile organic compounds and semivolatile organic compounds in unfiltered water. Each day after field sampling, raw water samples in field bottles (baked 1- or 4-L amber glass bottles or 1- or 4-L HDPE bottles) were filtered, transferred into final storage containers, and preserved (in some cases) for shipment to analytical laboratories. Methane and DRO samples required no laboratory processing before shipment. Each sample was first filtered through a 0.45-micron capsule filter (Pall Corporation), then through a 0.22-micron Sterivex polyethersulfone filter (Millipore Sigma) and transferred into containers for shipment to analytical laboratories. Filters were conditioned before use by running 2 L of deionized water through them. Tubing used with the peristaltic pump for filtering was cleaned before use with a 0.1 percent Alconox detergent solution, rinsed with tap water, soaked for 30 minutes in 5 percent hydrochloric acid (HCl assay of 36.5–38.0 percent), rinsed in deionized water, and finally air dried. Clean tubing and conditioned filters were used for each sample. A bottle set from each sample was shipped to the Reston Biogeochemical Processes in Groundwater Laboratory (RBPGL) in Reston, Va., on wet ice. Samples were stored at 4 °C at the laboratory until analyses were completed. The RBPGL analyzed samples for alkalinity, NVDOC, methane, fluoride (F), chloride (Cl), bromide (Br), NO3, phosphate (PO4), SO4, calcium (Ca), sodium (Na), magnesium (Mg), potassium (K), silicon (Si), strontium (Sr), aluminum (Al), Fe, Mn, boron (B), barium (Ba), lithium (Li), copper (Cu), zinc (Zn), beryllium (Be), vanadium (V), chromium (Cr), cobalt (Co), nickel (Ni), arsenic (As), selenium (Se), rubidium (Rb), molybdenum (Mo), silver (Ag), cadmium (Cd), antimony (Sb), lanthanum (La), cerium (Ce), thallium (Tl), lead (Pb), and uranium (U). Samples for analysis of major cations including Ca, Na, Mg, K, Fe, Si, Sr, Al, Mn, B, Ba, Li, Cu, and Zn were stored in acid-washed leakproof HDPE 30-mL vials (Thermo Fisher Scientific, Waltham, Mass.). The vials were filled close to the top of the shoulder, then preserved with 67–70 percent Optima

nitric acid (Fisher Scientific, Bothell, Washington, United States) to a pH of less than or equal to 2. Samples were analyzed on a Perkin Elmer Optima 4300DV inductively coupled plasma-optical emission spectrometer (ICP–OES, Perkin Elmer, Hopkinton, Mass.) following EPA Method 200.8 version 5.4 (U.S. Environmental Protection Agency, 1994). The reporting limits for the instrument were 0.05–50 mg/L (Li), 0.1–50 mg/L (Fe, Mn), 0.2–20 mg/L (B, Ba, Cu, Zn), 0.25–50 mg/L (Mg, K, Si, Sr, Al), and 0.5–200 mg/L (Ca, Na). Concentrations of trace elements including Li, Be, Al, B, Ba, V, Cr, Co, Fe, Ni, As, Cu, Mn, Zn, Se, Rb, Sr, Mo, Ag, Cd, Sb, La, Ce, Tl, Pb, and U were measured from an aliquot of the cation vial and recorded in micrograms per liter using an Agilent 7900 inductively coupled plasma-mass spectrometer (ICP–MS, Perkin Elmer, Waltham, Mass.) following EPA Method 200.8 version 5.4 (U.S. Environmental Protection Agency, 1994). The reporting limits for the instrument were 0.50–200 micrograms per liter (μg/L; Li, Be, Cr, Co, Ni, Cu, As, Tl, Pb, U), 0.50–200 μg/L (Mo, Ag, Sb), 1.00–200 μg/L (Se, La), 2.0–200 μg/L (B, Mn, Fe, Zn, Rb, Sr, Ba, Ce), and 5.00–200 μg/L (Al, V). Several cation analytes were measured on the ICP–OES and the ICP–MS. When concentrations of these analytes were greater than or equal to 500 µg/L, the ICP–OES results are reported in Jaeschke and others (2023) and in the USGS National Water Information System database (U.S. Geological Survey, 2024). When the analyte concentrations were less than 500 µg/L, the ICP–MS results are reported according to the laboratory’s reporting limits. Samples for analysis of major anions including F, Cl, Br, NO3, PO4, and SO4 were filtered into leakproof HDPE 30-mL vials (Cole-Palmer North America Vernon Hills, Illinois, United States) that were sample rinsed and filled, leaving no headspace. The six major anions were measured using ion chromatography on a Thermo Dionex ICS 1000 (Thermo Fisher Scientific, Waltham, Mass.). The method used a carbonate/bicarbonate (HCO3) eluent coupled with suppressed conductivity detection to determine inorganic anion concentrations and met the performance requirements specified in EPA Method 300.1 (U.S. Environmental Protection Agency, 1997). The minimum detection limits of the instrument were 0.013 mg/L (Cl), 0.014 mg/L (Br), 0.023 mg/L (F), 0.031 mg/L (SO4), 0.033 mg/L (NO3), and 0.063 mg/L (PO4). The reporting limit ranges were 0.10–10 mg/L (F, PO4), 0.1–50.1 mg/L (Br, NO3), and 0.10–75.1 mg/L (Cl, SO4). Values detected between the minimum detection limit and reporting limit were reported as estimated values in Jaeschke and others (2023) and the USGS National Water Information System database (U.S. Geological Survey, 2024). Alkalinity concentrations were measured on groundwater samples filtered into duplicate precleaned 40-mL clear EPA/volatile organic analysis 2000-class vials. The vials were sample rinsed, filled to the top with no headspace, and sealed with a polypropylene cap with a spectra seal polytetrafluoroethylene/silicone septa. Concentrations were recorded as milligrams of HCO3 per liter using an automatic titrator.

Methods of Study 13 Details of the field collection and analyses are described in the USGS Field Manual (Rounds and Wilde, 2012) with the modification for the normality of the acid used. Samples collected in September 2022 were titrated with 0.020N (normality) sulfuric acid (H2SO4), and samples collected in April 2023 were titrated with 0.200N H2SO4 following EPA Method 310.1 (U.S. Environmental Protection Agency, 1978). Samples were analyzed in duplicate. The reporting limits for the instrument range from 50 to 1,000 mg/L HCO3. NVDOC concentrations were measured in duplicate or triplicate on groundwater samples filtered into precleaned 20-mL amber EPA/volatile organic analysis 2000 class vials. The vials were sample rinsed and filled close to the top, leaving some headspace. The samples were acidified with trace HCl assay of 36.5–38.0 percent (Millipore Sigma, Burlington, Mass.) to a pH of less than or equal to 2 and capped. Concentrations were measured as milligrams of C per liter using a Shimadzu TOC–L Total Organic Carbon Analyzer equipped with an ASI–L Autosampler (Shimadzu Scientific Instruments, Columbia, Md.). A modified version of EPA Method 415.1 (U.S. Environmental Protection Agency, 1974) was used for determining NVDOC concentrations in samples. The method was modified as follows: (1) samples were filtered, (2) samples were acidified with HCl rather than H2SO4, (3) total organic carbon (TOC) reference stock solutions of either 100 mg/L or 1,000 mg/L (Millipore Sigma, Burlington, Mass.) were used rather than a potassium hydrogen phthalate stock solution, and (4) the lower reporting limit was 0.60 mg/L of C compared to 1.0 mg/L of C. For this study, the method detection limit was 0.20 mg/L of C and the reporting limit range was 0.60–30 mg/L of C. Carbon-14 contents of groundwater NVDOC were measured in samples filtered into duplicate 1-L baked glass amber bottles and acidified with trace HCl assay of 36.5–38.0 percent (Millipore Corporation) to a pH of less than or equal to 2. Carbon-14 analyses were completed at the Woods Hole Oceanographic Institution, National Ocean Sciences Accelerator Mass Spectrometry Facility (WHOI NOSAMS; https://www2.whoi.edu/site/nosams/). Samples were shipped on wet ice and stored at 4 °C until laboratory processing and analysis. At the laboratory, sample NVDOC was converted to CO2 (Xu and others, 2021, 2022; Xu, 2022a, b). The CO2 was then reacted with an Fe catalyst to form graphite, which was used in the analysis (Vogel and others, 1984; Pearson and others, 1997; Shah Walter and others, 2015; Elder and others, 2019; Goehring and others, 2019). A summary description of 14C analysis at WHOI NOSAMS is available through the “General Statement of 14C Procedures at the National Ocean Sciences AMS Facility: Woods Hole Oceanographic Institution” (Woods Hole Oceanographic Institution, National Ocean Sciences Accelerator Mass Spectrometry, 2023a). Refer to appendix 1 of this report for an explanation of 14C data and units.

Soil Gas This section covers the strategy and methods used for soil gas sampling and analyses. It begins with an explanation of how sample locations were chosen and continues with a description of the sampling and analysis methods.

Soil Gas Sampling Design At the facility, fluxes of CO2 depleted in 14C (ancient CO2) have been used to estimate biodegradation rates of spilled fuel below the facility (Department of the Navy, 2019; McHugh and others, 2020). In 2017, ancient CO2 was detected above tank 5 and on the southeast-facing slope of Red Hill downhill from tanks 11 and 12 (sites T2, T3, and T8 on fig. 5; Department of the Navy, 2019; McHugh and others, 2020). The presence of ancient CO2 south of the tank farm at the facility at site T8 (fig. 5) was concerning because it might indicate that spilled fuel migrated south away from the tanks in the direction of the dip of the lava flows. To investigate whether other locations had signs of underlying biodegrading fuel, a series of soil gas measurements was made over the crest of Red Hill, along the southeast-facing slope of the ridge and above the November 2021 spill areas near adit 3 (fig. 5, table 4, adit 3 shown on fig. 1). The purpose of these measurements was to replicate previous results (Department of the Navy, 2019; McHugh and others, 2020) and determine if evidence for subsurface biodegradation of fuel was present at other locations on the surface of the facility, including the area overlying adit 3, the site of the November 2021 spill (Department of the Navy, 2022). Three methods were used to evaluate the presence of ancient C in soil CO2 at land surface: (1) soil gas sample collection with soil probes for measuring 14C content of soil CO , (2) soil C traps (E-Flux, Fort Collins, 2 Colo.) for measuring soil CO2 efflux and 14C content of CO2 leaving the soil, and (3) soil CO2 efflux measurements made with a dynamic closed chamber (fig. 5, table 4).

Soil Gas Field and Laboratory Methods This section describes the sampling and analysis methods for soil gas. This study used three soil gas sampling methods. The first is a soil gas probe driven 1 ft below the surface connected to a pump. The second is a carbon trap that passively captures carbon dioxide in soil gases emitted at the land surface. The third is a dynamic closed chamber that measures the flux of carbon dioxide in soil gas exiting the land surface. These methods are described in the following sections.

Soil Probe Gas Sample Collection and Analysis Soil gas samples were collected to measure soil CO2 concentrations and the 14C content of soil CO2. Samples were collected with a soil probe based on a sampling method evaluated and refined at the National Crude Oil Spill Fate and Natural Attenuation Research Site near Bemidji, Minnesota (Wozney

T5 T22–10

lley a Va ālaw

20 FEET

4.5

Hā

aha

law

a Waiu

tre

T5 T22–10

T22–05

T22–06

T22–07

9 METERS

T22–08

T22–04 T2

A3–02

A3–03 A3–04 A3–01

T22–01 A3–06

A3–05

A3–07

A3–08

T22–02

T22–09 T3

T23–09

ay us W

Icar

Ala

Av e

T23–05 T23–02

Tampa Dr

Red

Hill

T23–06

ni St

Ala La Ala ʻlolani St

T23–08

Kul

Ala Hōkū Pl

puna S

Ala Ka

nge

u Ra

ʻola

Ko the

T23–07 T23–01

T23–10

T22–03

M a

na ad

Base from U.S. Geological Survey digital data, various scales and dates Universal Transverse Mercator, zone 4 north North American Datum of 1983

EXPLANATION

Soil carbon trap sample site—Collected only in 2022–23 Soil carbon trap sample site—Collected in 2017 but not in 2022–23

Figure 5. Soil gas sampling sites and types of data collected at each site.

la Ao

600

1,200 FEET

180

360 METERS

Dynamic closed chamber measurement site

Red Hill Bulk Fuel Storage Facility boundary Soil carbon trap sample site—Collected in 2017 and 2022–23

Data source credit note. List source of data on map

ea Str

ni Pl naluala

Moa

a alu

Soil probe gas sample site with identifer Approximate center of underground fuel storage tank

14 Ancient Carbon in Groundwater and Soil Gas from Degradation of Petroleum near the Red Hill Bulk Fuel Storage Facility

Methods of Study 15 Table 4. Site information for soil gas sampling sites at the Red Hill Bulk Fuel Storage Facility, Oʻahu, Hawaiʻi. [USGS, U.S. Geological Survey; HI, Hawaiʻi; --, no samples collected; site information from U.S. Geological Survey (2024)]

Site short name

USGS site identifier

aUSGS station name

Approximate land surface altitude, in feet above local mean sea level

Number of regular samples Dynamic closed chamber

Soil gas probe

Soil carbon trap

A3–01

212214157542302

A3–01 Red Hill, Oahu, HI

160

A3–02

212215157542302

A3–02 Red Hill, Oahu, HI

150

A3–03

212215157542301

A3–03 Red Hill, Oahu, HI

135

A3–04

212214157542101

A3–04 Red Hill, Oahu, HI

170

A3–05

212213157541603

A3–05 Red Hill, Oahu, HI

190

A3-06

212213157541602

A3–06 Red Hill, Oahu, HI

200

A3–07

212213157541701

A3–07 Red Hill, Oahu, HI

200

A3–08

212213157541601

A3–08 Red Hill, Oahu, HI

215

212217157534801

T2 Red Hill, Oahu, HI

495

T22–01

212215157535201

T22–01 Red Hill, Oahu, HI

460

T22–02

212216157535001

T22–02 Red Hill, Oahu, HI

475

T22–03

212217157534601

T22–03 Red Hill, Oahu, HI

515

T22–04

212219157534401

T22–04 Red Hill, Oahu, HI

520

T22–05

212220157534001

T22–05 Red Hill, Oahu, HI

535

T22–06

212220157534002

T22–06 Red Hill, Oahu, HI

545

T22–07

212221157533601

T22–07 Red Hill, Oahu, HI

555

T22–08

212222157533401

T22–08 Red Hill, Oahu, HI

555

T22–09

212218157534201

T22–09 Red Hill, Oahu, HI

515

T22–10

212224157534802

T22–10 Red Hill, Oahu, HI

235

T23–01

212211157535201

T23–01 Red Hill, Oahu, HI

420

T23–02

212208157534801

T23–02 Red Hill, Oahu, HI

430

T23–05

212211157534101

T23–05 Red Hill, Oahu, HI

405

T23–06

212213157533801

T23–06 Red Hill, Oahu, HI

440

T23–07

212212157534602

T23–07 Red Hill, Oahu, HI

440

T23–08

212208157534501

T23–08 Red Hill, Oahu, HI

370

T23–09

212215157534301

T23–09 Red Hill, Oahu, HI

490

T23–10

212218157533701

T23–10 Red Hill, Oahu, HI

530

212212157534701

T3 Red Hill, Oahu, HI

495

212224157534801

T5 Red Hill, Oahu, HI

235

212212157533801

T8 Red Hill, Oahu, HI

415

aDatabase limitations preclude the use of Hawaiian diacritical marks in U.S. Geological Survey station names.

and others, 2021). Stainless steel retract-a-tip soil gas sampling probes (part 210.01 at AMS Samplers, American Falls, Idaho, United States) were used to collect soil gas samples. These soil probes have an outer casing diameter of 2.2 centimeters (cm) and an inner 5.0-cm long stainless-steel screen. During installation with a slide hammer, the screened interval was protected by the outer casing. The screen was exposed after installation when the upper outer casing was pulled back

and held in place with locking pliers. The targeted soil gas sampling depth at all sites was centered at 30 cm below land surface. Sampling locations required at least 30 cm of soil for a sample to be collected; rocky areas without soil cover were not sampled. Soil gas was extracted through the exposed screen with a peristaltic pump. Fluoropolymer tubing with a 4.76-millimeter (mm) inner diameter x 6.35-mm outer diameter was used to

16 Ancient Carbon in Groundwater and Soil Gas from Degradation of Petroleum near the Red Hill Bulk Fuel Storage Facility connect the retract-a-tip sampler to the flexible tubing (MasterFlex C-Flex Ultra, 06434–15) in the pump head of the peristaltic pump. Fluorinated ethylene propylene lined Bev-A-Line tubing (6.35-mm outer diameter) was used between the pump head, pressure gage, and a final Luer-Lok fitting for connecting to sample containers. Sampling began at each location after the screen was installed, exposed to soil, and connected to a pump and tubing. The first sample collected at each site was for determining the soil CO2 concentration. A 5-L Tedlar bag (AMS Inc., American Falls, Idaho) was attached to the sample line and filled at least two-thirds full of soil gas with a pumping rate of about 600 mL per minute. These samples were stored and analyzed the same day of sample collection with an LI–8100 infrared gas analyzer (LI-COR Biosciences, Lincoln, Nebraska, United States). Next, soil gas samples for measuring the 14C content of soil CO2 were collected into prepared vials containing nitrogen gas at atmospheric pressure. Vials for soil gas sample collection were prepared at RBPGL before field sampling according to the following procedure. Each sample vial comprised a 200-mL clear serum vial (Voigt Global Distribution Inc., United States) fitted with a 20-mm butyl stopper (Bellco Glass, Pennsylvania, United States) that was held in place with an Al seal (Voigt Global Distribution Inc.). Before the stoppers were inserted into the vials, the vials were rinsed with 18 megaohm (Milli-Q) deionized water and baked at 450 degrees Fahrenheit for at least 4 hours and the stoppers were boiled in 18 megaohm (Milli-Q) deionized water for 10 minutes and then placed in a vacuum chamber for as many as 5 days to remove atmospheric gases. A crimper tool (Voigt Global Distribution Inc.) was then used to insert the stopper into the vial and emplace a seal. Each vial was then purged with at least five volumes of nitrogen gas to remove all atmospheric gases from the vial. Two needles (22 gauge or smaller and at least 2.5 cm long) were inserted through the stopper to purge the vials. One needle was pushed in as far as possible and connected to the nitrogen gas supply. The second needle served as a vent and was inserted just to the bottom of the stopper. After purging five volumes and while the gas was still flowing, both needles were removed simultaneously, so the vial remained filled with nitrogen gas at atmospheric pressure. In the field, a 3.8-cm 23-gauge needle was attached to the sample line to fill the prepared sample vials. A vent needle was inserted through the stopper and then the needle on the sample line was inserted through the stopper on a sample bottle. About five volumes of soil gas were purged through the sample bottle before removing the vent needle. The vent needle was removed while the pump was running, and the bottle was pressurized to about 25 pounds per square inch and then removed from the sample line. Silicone caulking was then used to cover the stopper and the top of the sample bottle to prevent sample leakage. A second, duplicate sample bottle was attached to the sample line, and the bottle-filling procedure was repeated. Samples were stored at ambient temperature. After sampling, the soil probe was removed from the ground.

The surrounding soil was pressed into the sample probe hole, and a nail with flagging tape was inserted at the sample location to be revisited if necessary. Soil gas samples in Tedlar bags were analyzed with an LI–8100A infrared gas analyzer to determine CO2 concentrations. These CO2 concentrations were determined to ensure that the samples had enough C for 14C analysis at WHOI NOSAMS. The LI–8100A was run in “continuous” mode for determining the CO2 concentrations of soil gas. The LI–8100A “in” line was attached to a three-way Luer-Lok fitting, attached to the Tedlar sample bag. The LI–8100A pulled in ambient air until the three-way valve was turned to open the Tedlar bag. Data logging on the LI–8100A was started during the ambient air reading to record the transition to sample air. The LI–8100A recorded a concentration every second as it pumped the sample air from the bag. After the bag was nearly empty, the valve was turned so ambient air entered the LI–8100A again. After this transition, the data recording was stopped. An average CO2 concentration was calculated from the readings taken from the sample in the Tedlar bag. One of the 200-mL sample vials from each sampling location was shipped to the WHOI NOSAMS laboratory for analysis. The CO2 was extracted from each gas sample (Xu, 2022b) and reacted with an Fe catalyst to form graphite, which was used in the analysis (Vogel and others, 1984; Pearson and others, 1997; Shah Walter and others, 2015; Elder and others, 2019; Goehring and others, 2019). A summary of 14C analytical procedures used at WHOI NOSAMS is available through their document “General Statement of 14C Procedures at the National Ocean Sciences AMS Facility: Woods Hole Oceanographic Institution” (Woods Hole Oceanographic Institution, National Ocean Sciences Accelerator Mass Spectrometry, 2023a). Refer to appendix 1 of this report for an explanation of 14C data unit and interpretation.

Soil Carbon Traps Soil CO2 traps from E-Flux (Fort Collins, Colo.) were deployed during the 2022 and 2023 field sample periods to replicate and expand on soil CO2 trap measurements completed in 2017 (Department of the Navy, 2019; McHugh and others, 2020). Soil CO2 traps were deployed for at least 2 weeks to provide time-integrated average CO2 efflux measurements. The traps are designed to passively collect CO2 samples with minimal interference to soil gas respiration and transport processes. The 14C content of soil CO2 on the trap sorbent (after a trip blank correction) is used to differentiate modern background CO2 from ancient fossil fuel-derived CO2 (E-Flux, 2023a). Traps were deployed at three sites during September 28– October 12, 2022 (14 days), and at five sites during January 27– February 16, 2023 (20 days). During the 2022 sample period, traps were deployed at a background site (T5), a site with a reported detection of ancient CO2 in 2017 (T2; McHugh and others, 2020), and a site with high CO2 efflux (T22–04) measured as part of this study. During the 2023 sample period, traps were deployed at the background site T5, site T2, and three other

Petroleum and Degradation Products in Groundwater 17 locations at or near where ancient CO2 was reported in 2017 (sites T3, T8, and T23–05; fig. 5; McHugh and others, 2020). A travel blank was collected with each set of traps to correct analytical results for the trap sorbent composition (E-Flux, 2023b). After field deployment, the soil CO2 trap samples were shipped to E-Flux and analyzed to determine the mass of CO2 accumulated on each trap and apportion that mass to modern background and ancient fossil fuel components. The ancient fossil fuel fraction of the CO2 trapped on the sorbent (ffsample) was determined from the laboratory-reported 14C content (pMCsample) and an assumed background 14C content (pMCbg) according to equation 1.5 in appendix 1. The ancient fossil fuel fraction of the sample (ffsample) was then used in equation 1 to compute the mass of ancient fossil fuel CO2 on the sorbent (Department of the Navy, 2019): CO2ff=msorbent[(CO2sample×ffsample)−(CO2TB×ffTB)],(1) where

CO2ff

is ancient fossil fuel CO2 on the trap sorbent, in grams;

msorbent

is the mass of sorbent in the trap, in grams;

CO2sample

is the CO2 content on field-deployed trap sorbent, as a fraction;

ffsample

is the ancient fossil fuel fraction of the sample (calculated with eq. 1.5);

CO2TB

is the CO2 content of sorbent material determined from the travel blank, as a fraction; and

ffTB

is the ancient fossil fuel fraction of the sorbent material (calculated by applying eq. 1.5 to travel blank data).

The complete set of values from E-Flux sample reports for the variables in equations 1 and 1.5 are listed in table 1.1 in appendix 1. If equation 1 produced a negative value for a given sample, the concentration of the sample was classified by E-Flux as a nondetect. If equation 1 produced a positive value for a given sample, E-Flux reported a detection of ancient fossil fuel C and provided ancient C efflux rates in micromoles per square meter per second as CO2. The mass of ancient fossil fuel C on the trap sorbent was converted into a flux rate using the cross-sectional area of the trap, the length of the trap deployment, and the molecular weight of CO2 (Department of the Navy, 2019).

Dynamic Closed Chamber Soil Carbon Dioxide Efflux Measurements At other petroleum spill sites, the magnitude of soil CO2 effluxes overlying the source area compared to background CO2 effluxes has been used to delineate the approximate

extent of source zones (for example, Sihota and others [2011]). Furthermore, measurements of CO2 effluxes coupled with measurements of 14C content of soil CO2 can be used to separate background CO2 effluxes and petroleum-derived CO2 effluxes (Sihota and Mayer, 2012; Wozney and others, 2021). For these reasons, a field soil CO2 efflux survey was done in addition to soil gas sample collection during the September 2022 sampling period. The survey included two background sites (T5 and T22–10) and a series of sites overlying the fuel storage tanks at the facility. An LI–8100A dynamic closed CO2 flux survey chamber system equipped with an infrared gas analyzer (LI-COR Biosciences, Lincoln, Nebr.) was used for this survey. The same general field procedure described by (Sihota and others, 2011) was used and is described briefly here. PVC collars that were 20 cm in diameter by 10 cm long were installed (part 6581–044, LI-COR Biosciences, Lincoln, Nebr.). The collars were pounded at least 3 cm into the soil and vegetation and litter were removed from the soil surface within the collars. Soil CO2 efflux was measured at least 24 hours after collar installation. Two rounds of three efflux measurements were completed at each site for a total of six efflux measurements per site. These six measurements were then averaged to calculate a single efflux value for each site. A “round” of measurements at a site consisted of three consecutive 2-minute efflux measurements separated by 1 minute 20 second purges. During the 2-minute efflux measurements, the chamber was lowered onto the collar and CO2 concentrations increased within the sealed chamber-collar environment. The LI–8100A recorded CO2 concentrations every few seconds and then, at the end of the 2 minutes, calculated CO2 efflux (rate of increase of CO2 in the chamber) by fitting a linear or exponential model to the recorded CO2 concentrations. During the 1 minute 20 second purge time, the LI–8100A lifted the chamber off the collar, thereby releasing the entrapped CO2 so the next measurement could begin under ambient conditions. Soil temperature was measured with a thermocouple probe (LI-COR 8100–201), and soil moisture of the upper 5 cm of soil was measured with a Teros-10 soil moisture sensor (Meter Group, Pullman, Wash.) and recorded by the LI–8100A instrument during efflux measurements.

Petroleum and Degradation Products in Groundwater This section describes the results of sampling 19 monitoring wells in and near the facility. The goal of the sampling was to determine the migration direction of groundwater containing dissolved partial hydrocarbon oxidation products. An important focus was to measure the concentrations of partial hydrocarbon oxidation products in the groundwater by analyzing for NVDOC and the ancient C fraction of NVDOC.

18 Ancient Carbon in Groundwater and Soil Gas from Degradation of Petroleum near the Red Hill Bulk Fuel Storage Facility Recent research at the National Crude Oil Spill Fate and Natural Attenuation Research Site near Bemidji, Minn., indicates that partial hydrocarbon oxidation products (metabolites) transported by groundwater from the crude oil source are represented by about 2,000 chemical formulas (Islam and others, 2016). Plumes of benzene, toluene, ethylbenzene, xylene, and DRO are routinely delineated at petroleum spill sites, but the metabolite plumes are largely ignored (Bekins and others, 2016). Data from the Bemidji site indicate that a plume of metabolites from degradation of residual crude oil has migrated more than 1,000 ft from the source, well beyond the plumes of benzene, toluene, ethylbenzene, xylene, and DRO, which have stabilized at about 500 ft from the source (Bekins and others, 2016). The concentrations of metabolites represented by NVDOC are two to three times greater than DRO concentrations measured in samples from the same wells. The metabolite plume represents the largest electron acceptor demand of any C fraction in the groundwater plume (Bekins and others, 2016). Quantification of NVDOC in this project extends beyond previously published results on polar metabolites (Zemo and Foote, 2003; Mohler and others, 2013; Zemo and others, 2013, 2017; O’Reilly and others, 2015) because, in those studies, organics were extracted using methylene chloride, the solvent typically used for EPA Method 3510C (U.S. Environmental Protection Agency, 1996). The most polar compounds do not extract well with methylene chloride or hexane (Weisman, 1998; Zito and others, 2019). Moreover, the studies mentioned previously are based on two-dimensional gas chromatography (or GC) combined with time-of-flight mass spectrometry (or TOFMS; GC×GC−TOFMS), but many polar metabolites do not readily pass through a gas chromatography column without derivatization (Weisman, 1998). Thus, important compounds of interest may be retained in the column. We measured NVDOC using combustion, which captures all metabolites except volatiles lost during purging. Results of the NVDOC analyses include natural dissolved organic matter present in the uncontaminated aquifer. Natural organic matter can be distinguished from petroleum hydrocarbon metabolites using 14C analyses because petroleum hydrocarbon partial oxidation products contain no modern C. By analyzing for the modern C content of NVDOC to determine the fraction of NVDOC from natural organic matter, the partial hydrocarbon transformation products produced during biodegradation can also be determined; thus, NVDOC depleted in modern C can be used as a tracer for groundwater migrating from the fuel source zone. In addition to measuring NVDOC, ancient C in NVDOC, and DRO, a suite of analytes known to be altered during biodegradation of petroleum fuels in groundwater was also measured. These include major anions, cations, pH, alkalinity, and trace metals. These data are combined to help provide a picture of the direction of migration of the petroleum hydrocarbon oxidation products. The results of these analyses are presented in the next section.

Comparison of Nonvolatile Dissolved Organic Carbon to Routinely Collected Analytes A comparison of concentrations of NVDOC and DRO is shown in figure 6A. For this direct comparison of NVDOC and DRO, DRO concentrations reported in Jaeschke and others (2023) were divided by 1,000 and multiplied by 0.87 to convert from micrograms per liter into milligrams of C per liter (Zito and others, 2019). Nondetects for DRO were assigned a value of 20 μg/L (the laboratory’s limit of detection) before converting to milligrams of C per liter. The designated background well (Moanalua W–2) had an NVDOC concentration of 0.21 mg/L and DRO less than the detection limit. The NVDOC value is flagged as “estimated” by the analytical laboratory because it is less than the reporting limit but greater than the detection limit. Only well DH43 and one sample at RHMW12A had NVDOC concentrations within the range (0.19−0.27 mg/L) typical of DOC in the basalt aquifers of Oʻahu (Chapelle and others, 2013). Samples from the remaining wells all had elevated values of NVDOC compared to the background value. A linear regression through the data has a slope of 2.79 (coefficient of determination of 0.82), indicating that the NVDOC concentrations are about three times the DRO concentrations in the same wells. The NVDOC analysis method quantifies hydrocarbon oxidation products that are more polar than hydrocarbons and therefore missed in the DRO analysis (Bekins and others, 2016). Assuming no other substantial NVDOC inputs to groundwater near the facility, this result indicates that elevated NVDOC provides a measure of groundwater containing hydrocarbon oxidation products that might help to trace migration pathways of solutes away from the facility. NVDOC is operationally defined as the organic fraction passing through a 0.45-micrometer filter and typically accounts for more than 90 percent of TOC in natural groundwaters (Regan and others, 2017). In this study, samples were filtered with a 0.22-micrometer filter (to filter out particulates and microorganisms) and compared with unfiltered TOC values from the same wells (fig. 6B, table 5). For this plot, samples with nondetects for TOC were assigned a value of 0.8 mg/L, which is the laboratory limit of detection for TOC. This comparison is provided because TOC rather than NVDOC has been routinely measured as part of the facility’s monitoring. The regression line shows a strong positive linear relation (coefficient of determination of 0.82) between these variables. In general, NVDOC is expected to be lower than TOC because NVDOC samples are filtered before analysis and TOC samples are unfiltered. The slope of the relation is about 0.8, indicating, as expected, that NVDOC is about 80 percent of the TOC; however, NVDOC concentrations were greater than TOC in four of the nine samples with detections of TOC, and at low TOC values, the regression gives NVDOC values more than 100 percent of TOC. The reason for this result is unknown. NVDOC is a more sensitive analytical approach. TOC was not detected in well RHMW09 to the south of the facility, or in wells RHMW11–05 and RHMW12A, which

Petroleum and Degradation Products in Groundwater 19

A component of this study included a comparison of bailed and pumped sample concentrations at three wells. The purpose was to determine if one sampling method resulted in consistently higher analyte concentrations. The spilled fuel at the facility is a light nonaqueous phase liquid, which is less dense than water and therefore will tend to form plumes in the uppermost part of the aquifer near the water table and near the source. Bailed samples from wells near the source were hypothesized to have greater concentrations of organic constituents (NVDOC and DRO) and biodegradation indicators (Fe, alkalinity) compared to pumped samples because bailed samples were collected near the water table. At locations farther from the source, the opposite might be true because plumes often migrate deeper with distance because of the addition of recharge at the water table or the presence of downward pressure gradients. In this study, bailer samples were collected from the upper 3−5 ft below the water table at wells RHMW2254–01, RHMW02, and RHMW03, whereas the pump intakes were set deeper at about 6, 9, and 8 ft below the water table, respectively (AECOM, written commun., August 3, 2023). The shaft (RHMW2254–01) had higher DRO, NVDOC, and Fe in the bailed samples compared to the pumped samples (fig. 7, table 6). In contrast, well RHMW02 had lower DRO and NVDOC in the bailed samples compared to the pumped samples. At well RHMW03, the NVDOC and DRO results were mixed. Major ions (Al, alkalinity, B, Ba, Br, Ca, Cl, Cu, F, Fe, K, Li, Mg, Mn, Na, NO3, PO4, Si, SO4, Sr, Zn) typically had higher concentrations in bailed samples compared to pumped samples; about 70 percent of the bailed samples had higher concentrations of major ions compared to the pumped samples (table 6). At the shaft (RHMW2254–01), all detected major ion concentrations were higher in the bailed samples compared to the pumped samples. Well RHMW03 had more analytes with lower concentrations in bailed samples compared to pumped samples relative to wells RHMW2254–01 and RHMW02. In summary, the elevated NVDOC, DRO, Fe, and alkalinity concentrations in the bailed compared to the pumped samples at the shaft (RHMW2254–01) are consistent with a nearby source of light nonaqueous phase liquid. Differences in concentrations between the bailed and pumped samples were more variable at the other two wells, indicating that, in those locations, the source of light nonaqueous phase liquid is not as localized near the water table. The interpretation of RHMW03 data is discussed further with the alkalinity data in the following section.

Nonvolatile dissolved organic carbon, in milligrams of carbon per liter

Bailed and Pumped Sample Comparison

A. DRO versus NVDOC RHMW02

RHMW02

Moanalua W–2 (background site)

0.1

R =0.82 y =2.79x+0.61 0.01 0.01

0.1

Diesel range organics, in milligrams of carbon per liter 10

Nonvolatile dissolved organic carbon, in milligrams of carbon per liter

are screened below the water table; however, NVDOC was detected in these wells at concentrations of 0.41, 0.35, and 0.28 mg/L, respectively. These results indicate that NVDOC may be a better measure than TOC of the presence of hydrocarbon oxidation products.

B. TOC versus NVDOC

RHMW02

2 2

R =0.82 y =0.81x+0.14

0 0

Total organic carbon, in milligrams of carbon per liter EXPLANATION 2

[R , coefficient of determination; DRO, diesel range organics; NVDOC, nonvolatile dissolved organic carbon; TOC, total organic carbon] Nondetect for (A) DRO or (B) TOC Estimated concentration for (A) DRO or (B) TOC Concentration greater than reporting limit for (A) DRO or (B) TOC Line of best fit where y =mx +b 1:1 line

Figure 6. Comparison of nonvolatile dissolved organic carbon concentrations with (A) concentrations of diesel range organics and (B) concentrations of total organic carbon in samples.

[USGS, U.S. Geological Survey; mg/L, milligram per liter; C, carbon; J, estimated value; E, estimated value; U, nondetect value] bTotal organic

USGS site identifier

Sample date

RHMW05

212210157540201

20220927

RHMW05–20220927–1050–WG

RHMW05–WGN01B–2209WK4

Bailer

2.22

J0.63

RHMW01R

212214157535402

20220927

RHMW01R–20220927–1240–WG

RHMW01R–WGN01B–2209WK4

Bailer

1.1

2.80

RHMW02

212216157534701

20220927

RHMW02–20220927–1410–WG

RHMW02–WGN01B–2209WK4

Bailer

6.45

7.40

RHMW03

212219157533901

20220927

RHMW03–20220927–1515–WG

RHMW03–WGN01B–2209WK4

Bailer

2.74

2.20

RHMW08

212216157535801

20220928

RHMW08–20220928–1020–WG

RHMW08–WGN01B–2209WK4

Bailer

E0.56

J0.73

RHMW04

212231157532901

20230125

RHMW04–20230125–1330–WG

RHMW04–WGN01B–2301WK4

Bailer

0.74

1.20

RHMW06

212226157534101

20230125

RHMW06–20230125–1510–WG

RHMW06–WGN01B–2301WK4

Bailer

0.67

J0.9

RHMW09

212209157535201

20230123

RHMW09–20230123–1156–WG

RHMW09–WGN01B–2301WK4

Bailer

E0.41

U0.8

RHMW11–05 212226157535002

20230124

RHMW11–05–20230124–1100–WG

RHMW11–05–WGN01G–2301WK4

Discrete interval sampler (Westbay System)

E0.35

U0.8

RHMW12A

212230157535202

20230125

RHMW12A–20230125–1100–WG

RHMW12A–WGN01LF–2301WK4

Low-flow

E0.28

U0.8

RHMW19

212212157534601

20230123

RHMW19–20230123–1530–WG

RHMW19–WGN01B–2301WK4

Bailer

0.68

J0.37

RHMW14–03 212221157535802

20230216

RHMW14–03–20230216–1120–WG

RHMW14–03–WGN01G–2302WK2

Discrete interval sampler (Westbay System)

0.94

J0.45

aData from Jaeschke and others (2023). bData from Department of the Navy (2023c).

aUSGS sample lookup

bAECOM sample identifier

bSampling

aNonvolatile dissolved organic carbon, in mg/L of C

Site short name

method

carbon, in mg/L

20 Ancient Carbon in Groundwater and Soil Gas from Degradation of Petroleum near the Red Hill Bulk Fuel Storage Facility

Table 5. Sample information, nonvolatile dissolved organic carbon concentrations from samples filtered through 0.22-micrometer filters and analyzed by the U.S. Geological Survey (Jaeschke and others, 2023), and total organic carbon concentrations from unfiltered samples collected by AECOM (Department of the Navy, 2023c).

Petroleum and Degradation Products in Groundwater 21 A

1,000

RHMW02 RHMW03 RHMW2254−01

Site short name

1,000

Dissolved iron, in micrograms per liter

Diesel range organics, in micrograms per liter

Nonvolatile dissolved organic carbon, in milligrams of carbon per liter

100

RHMW02 RHMW03 RHMW2254−01

Site short name

RHMW02 RHMW03 RHMW2254−01

Site short name

EXPLANATION [ND, not detected] Bailer sample Pump sample

Figure 7. Comparison of bailed and pumped sample concentrations for (A) nonvolatile dissolved organic carbon, (B) diesel range organics, and (C) dissolved iron.

Distribution of Petroleum Indicators A plot of Kendall’s tau (τ) correlation coefficients between analytes measured in groundwater samples in this study is shown in figure 8. These analytes have been determined in previous studies to indicate petroleum degradation (National Research Council, 2000). Data from regular field samples were included for this analysis; field blanks and duplicates were excluded. Pumped samples from pumped-bailed sample pairs were also excluded because 14C content was not measured in the pumped samples. For all analytes except DRO, nondetects were assigned the value of the reported limit in the data release (for example, a value of LT 0.5 is assigned a value of 0.5). For DRO, nondetects were assigned a value of 20 µg/L, which is the laboratory’s limit of detection. In the case of ties, Kendall’s τ is computed according to Kendall (1945). The results indicate that NVDOC correlates with percentage ancient C in NVDOC (τ=0.36) and with DRO (τ=0.52). NVDOC also correlates with Fe and Mn (τ=0.43, 0.52 respectively), consistent with biodegradation under Fe- and Mnreducing conditions. NVDOC does not correlate as strongly with either NO3, SO4, specific conductance, pH, or alkalinity (τ=−0.14, −0.15, −0.16, −0.24, 0.18 respectively), indicating that these traditional measures of biodegradation might not be useful to delineate the contaminant plume at this site. Instead, specific conductance correlates well with SO4, indicating

that mixing of groundwater with a seawater source has a larger effect on the SO4 concentration than biodegradation. The inverse correlation of pH with alkalinity is expected. In summary, the indicators that are useful for tracking the plume migration are NVDOC, percentage ancient C, Fe, and Mn. NVDOC concentrations in the samples from the wells are compared to the ancient C contents of the NVDOC in figure 9. This plot includes all regular field samples that had measurements of NVDOC and 14C; field duplicates are excluded. The NVDOC and 14C data together indicate the presence of hydrocarbon oxidation products in groundwater below the facility. At background well Moanalua W–2, the ancient C is 38.20 percent. Higher ancient C values than this are indicative of the addition of hydrocarbon oxidation products to the NVDOC pool. The highest percentage ancient C (92.99 percent) and the highest NVDOC (6.45 mg/L) were detected at well RHMW02, indicating that groundwater near this well is the most affected by a fuel source. Overall, a trend of decreasing percentage ancient C with decreasing NVDOC concentrations indicates that the hydrocarbon oxidation products are either biodegrading or mixing with uncontaminated groundwater or both. Two outliers are noteworthy. Groundwater from well RHMW05 has a relatively high NVDOC concentration of 2.22 mg/L but the ancient C is 34.95 percent, which is lower than the background value of 38.20 percent. Groundwater from this well had a DRO concentration of

[Dates given in month/day/year format; μg/L, microgram per liter; LT, less than; mg/L, milligram per liter; HCO3, bicarbonate; --, not applicable; E, estimated value; µS/cm at 25 °C, microsiemens per centimeter at 25 degrees Celsius; values with an “LT” flag were assumed to have the value listed in the table for purposes of calculating a percentage difference; data from Jaeschke and others (2023)]

Samples from RHMW02 on 1/30/2023

Analyte

Unit

Bailed sample flag

Bailed sample result, in indicated units

Samples from RHMW03 on 1/30/2023

Pumped sample result, in percent difference from bailed sample result

Bailed sample flag

Bailed sample result, in indicated units

Pumped sample result, in percent difference from bailed sample result

Samples from RHMW2254–01 on 1/26/2023 Bailed sample flag

Bailed sample result, in indicated units

Pumped sample result, in percent difference from bailed sample result

Silver (Ag)

μg/L

0.5

0.0

0.5

0.0

Aluminum (Al)

μg/L

12.8

0.0

Alkalinity

mg/L as HCO3

208

7.7

335

Arsenic (As)

μg/L

0.5

0.0

Boron (B)

μg/L

82.1

−33.1

Barium (Ba)

μg/L

18.5

−25.9

Beryllium (Be)

μg/L

0.5

0.0

Bromide (Br)

mg/L

Calcium (Ca)

μg/L

Cadmium (Cd)

μg/L

Cerium (Ce)

μg/L

Chloride (Cl)

mg/L

Cobalt (Co)

0.13

−2.7

79.5

−6.0

−23.2

0.66

3.0

180

−6.0

18.1

−12.2

11.6

−18.4

0.5

0.0

0.18

−5.6

0.4

−7.5

3.4

0.95

−7.7

−30.6

0.5

0.0

0.5

0.0

40.5

−9.4

48.4

−0.8

128

−5.5

μg/L

0.5

0.0

4.4

−46.4

0.5

0.0

Chromium (Cr)

μg/L

0.5

0.0

0.5

1.91

6.3

Copper (Cu)

μg/L

1.09

−51.4

Diesel range organics (DRO)

μg/L

100

Fluoride (F)

mg/L

Iron (Fe)

μg/L

pH (measured in field)

pH units

Specific conductance (measured in field)

μS/cm at 25 °C

235

Potassium (K)

μg/L

Lanthanum (La)

μg/L

Lithium (Li)

μg/L

Magnesium (Mg)

μg/L

23,300

Manganese (Mn)

μg/L

1,700

12,200

0.5

23,300

25,600

0.0

18.2

−11.9

0.02

0.0

−22.3

62.7

−71.3

2.69

−15.6

1.1

6.78

−0.4

7.01

−1.4

9.4

398

2.8

664

−9.2

2,380

−31.5

3,760

−5.9

2,980

−2.7

0.0

2.15

−29.8

3.85

−20

0.59

−5.1

−30.0

−31.8

1,100 0.67 1,480 6.44

210

30,300 99.8

0.5

−5.1

170

0.0 −62.9

6.3

24,600

−7.7

−33.5

0.0

22 Ancient Carbon in Groundwater and Soil Gas from Degradation of Petroleum near the Red Hill Bulk Fuel Storage Facility

Table 6. Table containing concentrations and percentage differences in concentrations of analytes measured in paired bailed and pumped samples.

Table 6. Table containing concentrations and percentage differences in concentrations of analytes measured in paired bailed and pumped samples.—Continued [Dates given in month/day/year format; μg/L, microgram per liter; LT, less than; mg/L, milligram per liter; HCO3, bicarbonate; --, not applicable; E, estimated value; µS/cm at 25 °C, microsiemens per centimeter at 25 degrees Celsius; values with an “LT” flag were assumed to have the value listed in the table for purposes of calculating a percentage difference; data from Jaeschke and others (2023)]

Samples from RHMW02 on 1/30/2023

Analyte

Unit

Bailed sample flag

Molybdenum (Mo)

μg/L

Sodium (Na)

μg/L

Nickel (Ni)

μg/L

Nitrate (NO3)

mg/L

Nonvolatile dissolved organic carbon (NVDOC)

mg/L of carbon

Lead (Pb)

Bailed sample result, in indicated units 0.5

Samples from RHMW03 on 1/30/2023

Pumped sample result, in percent difference from bailed sample result

Bailed sample flag

Bailed sample result, in indicated units

---

3.1

0.5

0.0

0.03

0.0

3.33

21.9

2.92

μg/L

0.5

0.0

0.5

Phosphate (PO4)

mg/L

0.06

0.0

0.17

Rubidium (Rb)

μg/L

2.99

−33.1

3.53

Antimony (Sb)

μg/L

0.5

0.0

3.1

Selenium (Se)

μg/L

0.0

Silicon (Si)

μg/L

35,600

−35.4

36,800

Sulfate (SO4)

mg/L

4.12

−38.6

44.7

Strontium (Sr)

μg/L

99.5

−32.9

176

Thallium (Tl)

μg/L

0.5

0.0

0.5

Uranium (U)

μg/L

0.5

0.0

0.5

Vanadium (V)

μg/L

0.5

0.0

Zinc (Zn)

μg/L

0.0

93,600

−19

Bailed sample flag LT

Bailed sample result, in indicated units 0.5 54,800

Pumped sample result, in percent difference from bailed sample result 0.0

2.8

−7.8

2.8

4.6

0.5

0.0

8.3

0.8

2.94

−11.2

−62

0.9

−57.8

0.5

0.0

29.4

0.09

0.0

−5.7

3.68

0.8

−82.3

0.5

0.0

1.4

22,200

−5.0

−4.3

19.6

−6.6

−8.5

195

−5.1

0.5

0.0

0.5

0.0

21.7

15.7

−1.9

3.1

−35.5

4.16

−51.9

Petroleum and Degradation Products in Groundwater 23

0.0 −33.5

50,500

Pumped sample result, in percent difference from bailed sample result

Samples from RHMW2254–01 on 1/26/2023

24 Ancient Carbon in Groundwater and Soil Gas from Degradation of Petroleum near the Red Hill Bulk Fuel Storage Facility EXPLANATION Alkalinity, in milligrams per liter as bicarbonate

Correlation (Kendall’s tau)

pH (measured in field, in pH units)

[DRO, diesel range organics; 14C, carbon-14; NVDOC, nonvolatile dissolved organic carbon]

Specific conductance (measured in field, in microsiemens per centimeter at 25 degrees Celsius)

1.0 0.5 0 −0.5 −1.0

Analyte

Sulfate, in milligrams per liter

Iron, in micrograms per liter Manganese, in micrograms per liter Nitrate, in milligrams per liter DRO, in milligrams per liter of carbon C content of NVDOC, in percent ancient carbon

Alkalinity, in milligrams per liter as bicarbonate

pH (measured in field, in pH units)

Specific conductance (measured in field, in microsiemens per centimeter at 25 degrees Celsius)

Sulfate, in milligrams per liter

Iron, in micrograms per liter

Manganese, in micrograms per liter

Nitrate, in milligrams per liter

DRO, in milligrams per liter of carbon

C content of NVDOC, in percent ancient carbon 14

NVDOC, in milligrams per liter of carbon

Analyte

Figure 8. Correlation coefficients among analytes measured in groundwater samples that have been determined in previous studies to indicate petroleum degradation (National Research Council, 2000).

380 µg/L, and DRO was detected at RHMW05 in 13 percent of samples collected in 2023 (table 1). Conversely, groundwater from well RHMW11–05 had a high ancient C value of 64.29 percent but a barely elevated NVDOC concentration of 0.35 mg/L. DRO values in this well were estimated concentrations of 66 and 84 µg/L. Based on the ancient C percentage, groundwater from this well could be affected by hydrocarbon oxidation products; however, the sampled interval of this well is −65 to −79 ft relative to local mean sea level or about 85−100 ft below the water table. One possible explanation for the very low NVDOC concentration is dilution and dispersion of the plume during vertical migration from the source to the sampled interval. Examining other aspects of the NVDOC

using techniques in Podgorski and others (2021) such as optical properties or ultrahigh resolution mass spectrometry could be used to determine if NVDOC matches the characteristics of the natural NVDOC or that of the hydrocarbon oxidation products. The background ancient C value of 38.20 percent is surprising because there is 0 percent ancient C at sites with shallow water tables such as the Bemidji site. The ancient C percentage of 38.20 percent corresponds to an age of 3,870 years for the background NVDOC. Such a large age is unreasonable for the transport time of NVDOC from the surface by the groundwater based on recharge dates of the 1940s to the 1980s for groundwater in this part of Oʻahu

Petroleum and Degradation Products in Groundwater 25 100

EXPLANATION 2

[R , coefficient of determination]

RHMW02

Ancient carbon content of dissolved organic carbon, in percent

Line of best fit where y =mx +b 80

RHMW11–05

RHMW03 RHMW14–03

RHMW04 RHMW10 DH43

RHP05

RHP04A NMW24

RHMW03 RHMW225–01

RHMW19 RHMW06

RHMW12A

RHMW01R

Moanalua W–2 (background site)

RHMW08

RHMW05

RHMW09

R =0.53 y =7.75x+41.68 0

0.1

Nonvolatile dissolved organic carbon, in milligrams of carbon per liter

Figure 9. Graph comparing the ancient carbon contents of nonvolatile dissolved organic carbon with nonvolatile dissolved organic carbon concentrations in groundwater.

(Hunt, 2004). Other investigators have determined that the use of DOC for estimating groundwater age is questionable for thick unsaturated zones because of the potential for old, buried soil C to be transported in recharge water (Thomas and others, 2021). A possible source of the ancient NVDOC is burned vegetation between lava flows. This hypothesis could be tested by examining the optical properties of the background NVDOC or characterizing it with ultrahigh resolution mass spectrometry (Podgorski and others, 2021). Maps showing contours of NVDOC, 14C content (percentage ancient C), DRO, and alkalinity are shown in figures 10–13. The data are combined from sample days in September 2022, January 2023–February 2023, and April 2023. Only regular field samples were used for these plots; field duplicates were excluded. Most wells were only

sampled once, but wells RHMW02 and RHMW03 were sampled in September 2022 and January 2023. For these sites, the average of the September 2022 and January 2023 samples was used for plotting each analyte except DRO in well RHMW03 (fig. 2). Only the September 2022 concentration was used for RHMW03 because the January 2023 concentration was less than detection and nondetects occur infrequently at this well (table 1). Values plotted are from samples acquired with a bailer, except for samples from RHMW11–05, RHMW14–03, DH43, RHP05 and RHMW12A. Well locations (U.S. Geological Survey, 2024) and chemical concentration data were used to interpolate a concentration surface for each analyte using the Natural Neighbor method provided in the Spatial Analyst Toolbox of ArcGIS Pro version 3.1.3

RHMW12A

RHMW04 NVDOC=0.74 mg/L

0.3

S alley wa V

Hāla

0.4 0.5

a Waiu

aha

RHMW11–05 RHMW06

0.6

0.8

RHMW14–03

ay us W

RHMW2254–01

0.8

Icar

RHP05

Tampa Dr

dA ve

RHMW19

0.5

0.4

RHMW09

DH43

tre

S lua

Moana

n ola

oa ad

ni St

Ala La

Ala Hōkū Pl

i Pl lualan

m lia

0.3

Ala ‘lolani St

puna S

Ala Ka

of t

RHMW10 0.6

0.8

RHMW05

ula

RHMW03

Hill

RHMW02

RHMW01R

K Ala

Red

‘ol e Ko

0.6

RHMW08

ang

au R

RHP04A

eam a Str

ālaw

S. H

Base from U.S. Geological Survey digital data, various scales and dates Universal Transverse Mercator, zone 4 north North American Datum of 1983

Red Hill Bulk Fuel Storage Facility boundary 0.8

Nonvolatile dissolved organic carbon, in milligrams of carbon per liter

Data source credit note. List source of data on map 0 500

EXPLANATION RHMW08

150

1,000

1,500

2,000 FEET

300

450

600 METERS

Groundwater sampling site with identifier Approximate center of underground fuel storage tank

Average of 2022 and 2023 samples

Figure 10. Contours of nonvolatile dissolved organic carbon concentrations in groundwater from samples collected in September 2022, January– February 2023, and April 2023 at the Red Hill Bulk Fuel Storage Facility, Oʻahu, Hawaiʻi.

26 Ancient Carbon in Groundwater and Soil Gas from Degradation of Petroleum near the Red Hill Bulk Fuel Storage Facility

eam a Str

ālaw

S. H

RHMW12A

40 t lley S

a wa V

Hāla

RHMW04 53.61 percent ancient carbon RHMW11–05

RHMW06

aha

a Waiu

RHMW14–03

lau

80 RHMW08

dA ve

RHMW19

RHMW01R 50

RHMW10 ni St

Ala La

RHMW09

RHMW05 Pl ula la K

Tampa Dr

Ala Hōkū Pl

la Ao

M ad

iam

Āl

ea Str

lani Pl

lua Moana

a alu

Data source credit note. List source of data on map Base from U.S. Geological Survey digital data, various scales and dates Universal Transverse Mercator, zone 4 north North American Datum of 1983

EXPLANATION

Red Hill Bulk Fuel Storage Facility boundary 50

Percentage ancient carbon-14 of dissolved organic carbon

RHMW08

500

1,000

1,500

150

300

450

2,000 FEET 600 METERS

Groundwater sampling site with identifier Approximate center of underground fuel storage tank

Average of 2022 and 2023 samples

Figure 11. Contours of ancient carbon contents of nonvolatile dissolved organic carbon concentrations in groundwater from samples collected in September 2022, January–February 2023, and April 2023 at the Red Hill Bulk Fuel Storage Facility, Oʻahu, Hawaiʻi.

Petroleum and Degradation Products in Groundwater 27

puna S

DH43

Ala ‘lolani St

Ala Ka

of t

RHMW02

Icar

RHP05

RHMW03

Hill

Ran

ay us W

RHMW2254–01

RHP04A

Red

o‘o he K

Strea

lawa

ā S. H

RHMW12A

RHMW04

alley wa V

St RHMW11–05

RHMW06

Hāla

aha

a Waiu

RHMW14–03

400 600

RHMW08

Tampa Dr

dA ve

ni St 0

RHMW09

Ala Hōkū Pl

tre

S lua

lani P analua

n ola

ia Āl

DH43

Ala ‘lolani St

puna S

of t

Ala La

ul la K

Ala Ka

Ran

RHMW10 RHMW19

RHMW05

RHMW03

RHMW01R

RHP05

Hill

Red

o‘o he K

RHMW02

ay sW aru

RHMW2254–01

RHP04A

lau

800 0 100 0 120 0 140

Data source credit note. List source of data on map Base from U.S. Geological Survey digital data, various scales and dates Universal Transverse Mercator, zone 4 north North American Datum of 1983

Red Hill Bulk Fuel Storage Facility boundary 200

EXPLANATION RHMW08

Diesel range organics concentration, in micrograms per liter

500

1,000

1,500

1 50

300

450

2,0 0 0 F E E T 600 METERS

Groundwater sampling site with identifier Approximate center of underground fuel storage tank

Average of 2022 and 2023 samples 2022 sample only

Figure 12. Contours of diesel range organics concentrations in groundwater from samples collected in September 2022, January–February 2023, and April 2023 at the Red Hill Bulk Fuel Storage Facility, Oʻahu, Hawaiʻi.

28 Ancient Carbon in Groundwater and Soil Gas from Degradation of Petroleum near the Red Hill Bulk Fuel Storage Facility

eam a Str

ālaw

S. H

RHMW12A

RHMW04

y St

alle wa V

RHMW06

RHMW11–05

140

aha

a Waiu

120

100

Hāla

160

RHMW14–03

180

200

RHP04A

RHP05

120

y Wa rus

Ica

100 120

140

RHMW02

RHMW01R

RHMW19

Tampa Dr

dA ve

Ala

RHMW10

ni St

Ala La

RHMW05

RHMW09

Kul

Ala Hōkū Pl

a alu

ea Str

ni Pl

n ola

Data source credit note. List source of data on map Base from U.S. Geological Survey digital data, various scales and dates Universal Transverse Mercator, zone 4 north North American Datum of 1983

EXPLANATION

Red Hill Bulk Fuel Storage Facility boundary 100

Alkalinity concentration, in milligrams of bicarbonate per liter

RHMW09

500

1,000

1,500

150

300

450

2,000 FEET 600 METERS

Groundwater sampling site with identifier Approximate center of underground fuel storage tank

Average of 2022 and 2023 samples

Figure 13. Contours of alkalinity in groundwater from samples collected in September 2022, January–February 2023, and April 2023 at the Red Hill Bulk Fuel Storage Facility, Oʻahu, Hawaiʻi.

Ancient Carbon in Soil Carbon Dioxide 29

luala Moana

M u

ia Āl

DH43

Ala ‘lolani St

puna S

Ala Ka

la Ko‘o

RHMW08

RHMW2254–01

f th

ill o

H Red

RHMW03 100

120

nge

u Ra

0 240 60 80 2 2 00 3

30 Ancient Carbon in Groundwater and Soil Gas from Degradation of Petroleum near the Red Hill Bulk Fuel Storage Facility (Esri, 2023). From these surfaces, concentration contour lines were created using the Contour tool in the same toolbox (Esri, 2023). A contour map of NVDOC concentrations in groundwater is shown in figure 10. The lowest value of 0.21 mg/L, measured at the Moanalua well W–2, is assumed to represent background groundwater. It falls in the range of previous values measured by Chapelle and others (2013) on Oʻahu (0.19−0.27 mg/L) and is low for natural groundwater (Regan and others, 2017). Values measured in the three blank samples were 0.20, 0.26, and 0.30 mg/L, which are in the same range as the background sample; thus, values greater than 0.3 mg/L are considered elevated. Values less than 0.3 mg/L were detected at wells DH43 (0.21, 0.23 mg/L) and RHMW12A (0.27, 0.28 mg/L). The sampled interval of RHMW12A is −174 to −194 ft relative to local mean sea level (194–215 ft below the water table); thus, the low values at RHMW12A likely reflect the natural background NVDOC. Concentrations in groundwater at all other wells exceed 0.3 mg/L with the highest at well RHMW02 (3.33, 6.45 mg/L). The second highest concentration was from well RHMW03 (2.74, 2.92). Away from the ridge, concentrations drop rapidly by a factor of 5.2 in the approximately 700 ft between RHMW03 and RHMW10. Values at the two sampled periphery wells, RHP04A and RHP05, were 0.63 and 0.38 mg/L, respectively. Examining the overall shape and extent of the contours indicates that wells on the north and south side of the ridge are elevated; however, elevated values do not extend to well DH43 on the south side or well RHMW12A on the north side.The concentrations of NVDOC in groundwater decrease to about 10 percent of the highest concentration measured under the tanks within a distance of 700 feet to the south and 1,000 feet to the north of the ridge. The NVDOC data alone indicate no clear direction of contaminant migration away from the sources associated with the facility spills. A contour map of the percentage of ancient C in NVDOC is shown in figure 11. As in figure 10, groundwater from well RHMW02 is most affected by hydrocarbon oxidation products with more than 90 percent ancient C in NVDOC. The contours in figure 11 indicate a broad south-southeast to northnorthwest pattern of migration of ancient C from RHMW02 toward wells RHMW14–03 and RHMW11–05. However, the sampled intervals of wells RHMW14–03 and RHMW11–05 are quite deep at −140 to −158 ft relative to local mean sea level (160–179 ft below the water table) and −66 to −79 ft relative to local mean sea level (86–100 ft below the water table), respectively, calling into question whether or not the elevated ancient C values measured in these wells reflect compounds from a fuel source. The samples could be analyzed by optical methods to determine if the dissolved organic C is natural or from the facility (Podgorski and others, 2021). Groundwater from wells RHMW04, RHMW10, RHP05, RHP04A, and Red Hill Shaft RHMW2254–01 have slightly elevated ancient C values of 40–50 percent. Other techniques

are needed to analyze the NVDOC from these wells to determine if the ancient C comes from biodegradation of fuel hydrocarbons. A contour map of DRO concentrations in groundwater is shown in figure 12. The lowest contour line is set to 200 µg/L. Groundwater in the four tunnel wells exceeded the reporting limit of 190–220 µg/L, with the highest values measured at well RHMW02 (2,500 µg/L in September 2022 and 1,100 µg/L in January 2023). The values drop to the south and north of the facility. As with the ancient C map (fig. 11), the contours in this figure indicate a broad south-southeast to north-northwest direction of migration of DRO from well RHMW02 toward wells RHMW14–03 and RHMW11–05, but DRO was less than detection at RHMW14–03. The contours are dominated by the high value at well RHMW02 and provide little new information. Comparing this DRO map with the NVDOC plot in figure 10 and the ancient C map in figure 11 illustrates how the lower detection level of NVDOC combined with percentage ancient C can provide greater insight into the migration directions revealing the presence of elevated NVDOC and ancient C on the south side of the ridge. The DRO results in this study compare well with the monitoring data from 2016 to 2023 summarized in table 1. The frequencies of detection of DRO in all samples from the three tunnels wells, RHMW01R, RHMW02, and RHMW03, were 0.99, 1.00, and 0.93, respectively. For RHMW05, the overall frequency of DRO detection was 0.36 with higher frequencies in 2021 and 2022 compared to other years. A contour map of carbonate alkalinity is shown in figure 13. All biodegradation reactions except fermentation produce CO2, which raises the carbonate alkalinity. The background value at Moanalua well W–2 (fig. 2) is 84.1 mg/L as HCO3. Higher values than this are considered an indicator of biodegradation, whereas lower values indicate less evidence for presence of a contaminant plume. Groundwater samples with alkalinity values less than the background alkalinity value were from wells RHMW12A, RHMW14–03, RHMW2254–01, RHMW09, RHMW10, RHMW05, and RHMW19. The elevated values on the map indicate a different pattern than the NVDOC (fig. 10) and the percentage ancient C (fig. 11). In this case, the highest values are at well RHMW03 (335 and 343 mg/L as HCO3 for bailed samples) and the second highest values are at RHMW02 (214 and 240 mg/L as HCO3 for bailed samples). These data indicate that biodegradation of fuel in the unsaturated zone above well RHMW03 results in transport to the water table of CO2. Also at this well, NVDOC was higher in the bailed sample compared to the pumped sample (fig. 7) consistent with a source of partial transformation products in the unsaturated zone. Previous studies have established that aerobic biodegradation of petroleum hydrocarbons and methane lead to increased temperatures in the vadose zone and underlying groundwater (for example, Sweeney and Ririe, 2014; Warren and Bekins, 2015; McHugh and others, 2020). Mitchell and Oki (2018) determined that the groundwater temperature in well RWMW03 was 2.4–2.5 °C warmer than RHMW02.

Ancient Carbon in Soil Carbon Dioxide 31 Likewise, McHugh and others (2020) measured temperatures about 2 °C higher at RHMW03 than RHMW02. These observations of increased temperatures support the conclusion from the alkalinity data that there is aerobic biodegradation of fuel in the unsaturated zone above well RHMW03. Samples from both periphery wells, RHP04A and RHP05, provide evidence of increased alkalinity consistent with biodegradation. Alkalinity at Red Hill Shaft RHMW2254–01 is not elevated. Groundwater from well DH43 had elevated alkalinity but no other clear signs of the presence of hydrocarbon oxidation products based on the NVDOC concentrations and ancient carbon percentage. Petroleum hydrocarbons in the diesel and oil range were detected at well DH43 in 2022 on February 23 (2.53 mg/L), March 6 (1.83 mg/L), and May 5 (0.46–0.06 mg/L) (Honolulu Board of Water Supply, 2024). These concentrations decreased with time from greater than 2 mg/L in February to less than 0.5 mg/L in May. The decreasing trend is consistent with the lack of evidence for fuel contamination by the time of sampling on April 11, 2023, in this study.

Ancient Carbon in Soil Carbon Dioxide In this section, results from soil probe gas samples, soil C trap samples, and dynamic closed chamber measurements of soil CO2 efflux at the facility are discussed. Data that are the basis for this discussion are primarily from Jaeschke and others (2023) and the USGS National Water Information System database (U.S. Geological Survey, 2024) unless otherwise referenced. A detailed discussion of 14C units and approaches for data interpretation is in appendix 1. For discussions of 14C in soil and atmospheric CO2, 14C contents are referenced to the absolute international standard for the base year 1950 (Stuiver and Polach, 1977). Carbon-14 data from WHOI NOSAMS were first converted from conventional percentage modern C (pMCsample) to ∆14C notation using equation 1.1 in appendix 1, where ∆14C notation reports sample 14C content relative to the absolute international standard for the base year of 1950 (Stuiver and Polach, 1977). To keep language consistent in this report (though it is not the typical 14C convention), the atmospheric ∆14C values from Graven and others (2017) and the soil ∆14C values were converted into an absolute percentage modern notation, which is corrected for age since 1950 (pMCage-corr) using equation 1.2 in appendix 1. A subset of soil 14C contents in CO2 from soil probe samples in conventional percentage modern (pMCsample), ∆14C per mil, and absolute (age-corrected) percentage modern (pMCage-corr) notations are listed in table 7 (columns beginning with “soil probe sample”).

Carbon-14 in Soil Probe Samples All but two soil gas samples at the facility had 14C age-corrected percentage modern values higher than annual average atmospheric 14C during the study period (Jaeschke and others, 2023). The annual average atmospheric 14C was estimated to be about 99 and 98 percent modern in 2022 and 2023, respectively (table 7). These values were estimated with equation 1.6 in appendix 1. Equation 1.6 is a linear regression equation fit to annual average atmospheric 14C values for 2005–15 from Graven and others (2017). Samples with 14C contents greater than atmospheric 14C indicate that ancient fossil fuel-derived CO2 is not present in detectable quantities in soil gas at land surface. Two samples at site T3 (fig. 5), a regular sample and a field duplicate sample, had 14C contents (97.85 and 97.35 percent modern, age corrected) slightly less than the estimated annual average atmospheric 14C of 98 percent modern in 2023. This difference is too small to confidently classify the T3 results as a detection of ancient C because of variability in atmospheric 14C and measurement error. During 2020, 12 samples of atmospheric CO2 were collected at Mauna Loa Observatory and analyzed for 14C content (about 200 miles from the facility). These samples varied by about 1 percent modern (10 per mil); similar annual ranges in atmospheric 14C were observed at stations in La Jolla, Calif.; Samoa; and the South Pole (Graven and others, 2022). This atmospheric variation in 14C, coupled with the laboratory measurement error (0.2 percent modern), and the standard deviation of the two samples at site T3 (0.35 percent modern) indicates that the 14C contents of CO2 at site T3 are not distinguishable from atmospheric 14C contents and are therefore not classified as detections of ancient C. The average 14C content of CO2 in soil gas samples (including regular and duplicate samples) at the facility was 100.43 percent modern (age corrected), which is about 2 percent higher than average atmospheric 14C contents in 2022 and 2023. Because the 14C of soil CO2 is generally higher than atmospheric 14C at the facility, it indicates that a substantial part of the soil CO2 is produced from biodegradation of soil organic matter containing “bomb” 14C deposited in the soil since the 1950s and early 1960s. After peaking in the late 1960s, atmospheric 14C contents have been declining (Graven and others, 2017). Between June 2017 and June 2023, atmospheric 14C contents decreased from about 101 to 98 percent modern (age corrected) according to equation 1.6. Positive 14C values (values of ∆14C greater than 0 or percentage modern values greater than 100) of soil CO2 indicate “bomb” 14C whereas negative 14C values indicate CO2 that is derived from a soil C pool with an average turnover time long enough to reflect radioactive decay of cosmogenic 14C (Wang and others, 2000).

32 Ancient Carbon in Groundwater and Soil Gas from Degradation of Petroleum near the Red Hill Bulk Fuel Storage Facility The 14C contents of CO2 in soil probe samples collected at the facility in 2022 and 2023 varied by almost 6 percent, from 97.35 to 103.06 percent modern (age corrected by applying equation 1.1 and 1.2 in appendix 1 to 14C data in Jaeschke and others [2023]). The wide range of soil 14C values is likely the result of variability across sample sites in soil moisture, temperature, and vegetation types. These are characteristics that are known to affect root respiration rates (Raich and Tufekcioglu, 2000). The sites sampled at the facility had different vegetation types, ranging from grass covered to scrub forest, to forested. Surface soil temperatures were variable during sample collection, ranging from about 23 to 36 °C for samples collected in September 2022 (Jaeschke and others, 2023). Soil moisture in the upper 10 cm of soil also varied substantially, from about 5 to 31 percent, during the September 2022 sample collection (Jaeschke and others, 2023). Soil temperature and moisture were not measured during the January 2023 sample collection, but samples were collected at different times of day and some sites were rarely exposed to direct sunlight because of their position on slopes.

Soil Carbon Traps In 2022 and 2023, 8 traps were deployed at 6 sites at the facility (fig. 5). No detections of ancient fossil fuel-derived CO2 were reported by the laboratory for any of these trap samples (table 7; Jaeschke and others, 2023). These results are consistent with the soil probe samples and support the conclusion that no detectable ancient fossil fuel-derived CO2 was present in soil at the locations sampled for this study; however, the 2022–23 trap results differ from 2017 reported detections at sites T1, T2, T3, and T8 (Department of the Navy, 2019; McHugh and others, 2020). Detections of ancient fossil fuelderived C were also reported for tunnel air intake samples and upper and lower tunnel air exhaust samples collected in 2017 (table 7; Department of the Navy, 2019; McHugh and others, 2020). The mass of ancient fossil fuel CO2 trapped on the sorbent material (CO2 ff )for each of these samples was calculated by equation 1 using analytical data measured in the laboratory. The values used for these calculations are provided in table 1.1 in appendix 1 and Jaeschke and others (2023). The reported masses of ancient fossil fuel-derived CO2 (CO2 ff ) for 2017 trap samples were near zero (0.002–0.085 gram, table 7), which is the operational "detection limit" of equation 1. Positive CO2 ff values from equation 1 are classified as detections, but CO2 ff values that are less than or equal to zero are classified as nondetects. Nondetects are represented as “ND” in table 7, table 8, and table 1.1 in appendix 1. The calculated CO2 ff values from equation 1 that are less than 0 are shown below the zero line in figure 14A and B. Positive CO2 ff values are shown as numeric values in table 7, table 8, and table 1.1 in appendix 1 and shown above the zero line in figure 14A and B. The laboratory provided ancient C efflux rates in micromoles per square meter per second (µmol/m2/s) for all

samples classified as detections. In the following discussion, the sensitivity of classifying results as a detection or nondetect from equation 1 is examined. Equation 1 corrects sample results for the CO2 content and 14C composition of the trap sorbent from the travel blank (table 1.1 in appendix 1). Equation 1 relies on the variable ffsample, which is the fossil fuel fraction of a sample calculated according to equation 1.5 in appendix 1. Equation 1.5 relies on an assumed value of age-corrected background C content (pMCbg). As pMCbg for a given sample and travel blank combination increases, the calculated ancient fossil fuel CO2 mass also increases (table 8, fig. 14). Therefore, for samples near the reporting limit, classification of results as detections by equation 1 is sensitive to the assumed age-corrected background 14C content value (pMC ). bg E-Flux assumed that age-corrected background CO2 from natural soil respiration processes (pMCbg) is equal to the atmospheric 14C content (Department of the Navy, 2019; Jaeschke and others, 2023). Under this assumption, E-Flux used a fixed value of 102 for pMCbg for the 2022–23 samples (Jaeschke and others, 2023) based on literature values (Cerling and others, 2016; Larsen and others, 2018). E-Flux assumed a fixed value of 105 for pMCbg for the 2017 samples (Department of the Navy, 2019) also based on a literature value available at the time of sample analysis (Hua and others, 2013). E-Flux’s approach is typical in that literature-based annual average 14C values are considered to be representative of conditions over very large areas, such as the entire northern or southern hemisphere (Graven and others, 2017, 2020). However, this study’s soil probe field data and other comprehensive published compilations of atmospheric 14C data (Graven and others, 2017, 2020) indicate the age-corrected background 14C values used by E-Flux were likely high and indicate the trap results could be reevaluated using more reasonable values for background 14C content. Evaluating possible ancient fossil fuel CO2 detections across a range of reasonable pMCbg values is a careful approach that provides more context for classifying sample results as detections compared to evaluating possible detections at a single literature value. For the following evaluations, samples are considered to have likely detections when equation 1 produces positive CO2 ff values across the entire site-specific reasonable range of pMCbg values listed in table 7 and table 8 and shown on figure 14. Each sample was evaluated by plugging in the age-corrected background 14C contents (pMCbg) listed in table 8 into equation 1.5 and then using the resulting ffsample values in equation 1 along with the reported sample values in table 1.1 in appendix 1. Reasonable ranges for age-corrected background 14C contents in CO2 (pMCbg) are from published atmospheric 14C data and from soil probe samples collected in this study (table 7). The 14C content of atmospheric CO2 is trending down through time (Graven and others, 2017, 2022). Data from this study demonstrate that 14C contents of soil CO2 are variable across the facility. In 2022 and 2023, the average age-corrected atmospheric 14C was 98 to 99 percent modern (eq. 1.6 in

Table 7. Compilation of soil carbon trap and cartridge results for 2017 and 2022–23 samples (Department of the Navy, 2019; McHugh and others, 2020; Jaeschke and others, 2023), literature-based atmospheric carbon-14 contents in carbon dioxide, carbon-14 contents in carbon dioxide from soil probe gas samples collected in 2022–23, and estimated reasonable ranges for background carbon-14 contents in carbon dioxide (background percentage modern carbon). [CO2, carbon dioxide; CO2 ff , ancient fossil fuel CO2 on the trap sorbent; µmol/m2/s, micromole per square meter per second; 14C, carbon-14; ∆14C, sample 14C content relative to the absolute international standard with a base year of 1950 and sample activity corrected for age and isotopic fractionation; --, no data available; ND, not detected]

Literature-based atmospheric data

E-Flux reported results

Sample year

Site

aE-Flux sample type

aFossil-

fuel CO2 (grams; CO2 ff)

aNonaque-

aBackground 14C

fuel CO2 efflux (μmol/ m2/s)

ous phase liquid loss rate (gallons per acre per year)

in CO2 used in sample report, age-corrected (percentage modern carbon)

bAnnual

Soil probe sample results dSoil probe

cAnnual average sample 14C atmospheric average in CO2, as 14C in CO , atmospheric reported by 2 14C in CO , age-corrected laboratory 2 (percentage-corrected (percentage modern (∆14C, per mil) age modern carbon) carbon)

gEstimated

reasonable range of eSoil probe 14 background sample C sample 14C 14C in CO , in CO2, age2 in CO2, agecorrected age-corrected corrected (percent(percent(∆14C, per age modern age modern mil) carbon) carbon) fSoil probe

Soil trap

0.002

0.0

105

101

101–103

2017

Soil trap

0.02

0.0

105

101

101–103

2022

Soil trap

102

−14

101.18

3.0

100.30

99–101

2023

Soil trap

102

−19

102.30

14.0

101.40

98–101.40

2017

Soil trap

0.01

0.0

105

101

101–103

2023

Soil trap

102

−19

98.72

−21.5

97.85

98–100

2022

Soil trap

102

−14

100.19

−6.8

99.32

99–101

2023

Soil trap

102

−19

101.27

3.8

100.38

98–100.38

2017

Soil trap

0.06

0.1

105

101

101–103

2023

Soil trap

102

−19

101.65

7.6

100.76

98–100.76

2022

T22–04

Soil trap

102

−14

101.34

4.6

100.46

99–101

2023

T23–05

Soil trap

102

−19

102.14

12.4

101.24

98–101.24

2017

Tunnel air intake day 1

Cartridge

0.033

105

101

100–102

2017

Tunnel air intake day 2

Cartridge

105

101

100–102

Ancient Carbon in Soil Carbon Dioxide 33

2017

[CO2, carbon dioxide; CO2 ff , ancient fossil fuel CO2 on the trap sorbent; µmol/m2/s, micromole per square meter per second; 14C, carbon-14; ∆14C, sample 14C content relative to the absolute international standard with a base year of 1950 and sample activity corrected for age and isotopic fractionation; --, no data available; ND, not detected] Literature-based atmospheric data

E-Flux reported results

average atmospheric 14C in CO , 2 age-corrected (∆14C, per mil)

sample 14C in CO2, as reported by laboratory (percentage modern carbon)

sample 14C in CO2, agecorrected (∆14C, per mil)

sample 14C in CO2, agecorrected (percentage modern carbon)

gEstimated reasonable range of background 14C in CO , 2 age-corrected (percentage modern carbon)

bAnnual

Sample year

Site

aNonaque-

aBackground 14C

aFossil-

sample type

fuel CO2 (grams; CO2 ff)

fuel CO2 efflux (μmol/ m2/s)

ous phase liquid loss rate (gallons per acre per year)

aE-Flux

in CO2 used in sample report, age-corrected (percentage modern carbon)

average atmospheric 14C in CO , 2 age-corrected (percentage modern carbon)

Soil probe sample results dSoil probe

cAnnual

eSoil probe

fSoil probe

2017

Upper tunnel air exhaust day 1

Cartridge

0.022

105

101

100–102

2017

Upper tunnel air exhaust day 2

Cartridge

0.037

105

101

100–102

2017

Lower tunnel air exhaust day 1

Cartridge

0.09

105

101

100–102

2017

Lower tunnel air exhaust day 2

Cartridge

0.08

105

101

100–102

aValues are from Jaeschke and others (2023). The 2017 samples were originally reported in either Department of the Navy (2019) or McHugh and others (2020). . bValues in this column are calculated by equation 1.6 in appendix 1 and converted to percentage modern carbon notation with equation 1.2 in appendix 1. cValues in this column are calculated by equation 1.6 in appendix 1. dValues in this column are from Jaeschke and others (2023) and correspond to the variable pMC

sample as used in equations 1.1 and 1.3 in appendix 1.

eValues in this column are from Jaeschke and others (2023), converted to ∆14C notation with equation 1.1 in appendix 1. fValues in this column are from Jaeschke and others (2023), converted to ∆14C notation with equation 1.1, and then converted to percentage modern notation with equation 1.2 in appendix 1. gValues in this column correspond to the variable pMC in equations 1.4 and 1.5 in appendix 1. For soil trap samples, the lower limit of the reasonable range is the literature-based annual average atmobg spheric 14C in CO2 and the upper limit is 2 percent higher or a soil probe sample’s age-corrected soil 14C in CO2 (if it is more than 2 percent higher than atmospheric 14C in CO2); for cartridge samples on tunnel air intake and exhaust, the reasonable range is plus or minus 1 percent from the literature-based annual average atmospheric 14C in CO2.

34 Ancient Carbon in Groundwater and Soil Gas from Degradation of Petroleum near the Red Hill Bulk Fuel Storage Facility

Table 8. Calculated masses of ancient fossil fuel-derived carbon dioxide accumulated on sorbent across a range of age-corrected background carbon-14 content values for soil trap and cartridge samplers deployed at the Red Hill Bulk Fuel Storage Facility, Oʻahu, Hawaiʻi, in 2017 and 2022–23. [14C, carbon-14; CO2, carbon dioxide; CO2 ff, ancient fossil fuel CO2 on the trap sorbent; pMCbg, background 14C content; ND, not detected]

Sample year

Site

aEstimated reasonable range of E-Flux age-corrected sample type background 14C in CO2 (pMCbg)

cCalculated ancient fossil fuel CO (CO ), in grams, at different pMC values 2 2 ff bg bProbable

detection

pMCbg=99

pMCbg=100

pMCbg=101

dpMC =102 bg

pMCbg=103

pMCbg=104

epMC =105 bg

Soil trap

101–103

0.002

2017

Soil trap

101–103

0.017

2022

Soil trap

99–101

2023

Soil trap

98–101.40

0.022

0.045

0.066

2017

Soil trap

101–103

0.003

0.014

2023

Soil trap

98–100

0.011

0.023

0.034

2022

Soil trap

99–101

2023

Soil trap

98–100.38

0.021

0.045

2017

Soil trap

101–103

0.014

0.036

0.057

2023

Soil trap

98–100.76

0.009

2022

T22-04

Soil trap

99–101

0.012

2023

T23-05

Soil trap

98–101.24

0.015

0.040

2017

Tunnel air intake day 1

Cartridge

100–102

0.010

0.022

0.033

2017

Tunnel air intake day 2

Cartridge

100–102

2017

Upper tunnel air exhaust day 1

Cartridge

100–102

0.010

0.022

2017

Upper tunnel air exhaust day 2

Cartridge

100–102

0.002

0.014

0.025

0.037

2017

Lower tunnel air exhaust day 1

Cartridge

100–102

Yes

0.007

0.021

0.034

0.047

0.060

0.073

0.085

2017

Lower tunnel air exhaust day 2

Cartridge

100–102

Yes

0.010

0.025

0.039

0.054

0.067

0.081

aValues in this column correspond to the variable pMC in equations 1.4 and 1.5 in appendix 1. For soil trap samples, the lower limit of the reasonable range is the literature-based annual average atmobg spheric 14C in CO2 and the upper limit is 2 percent higher or a soil probe sample’s age-corrected soil 14C in CO2 (if it is more than 2 percent higher than atmospheric 14C in CO2); for cartridge samples on tunnel air intake and exhaust, the reasonable range is plus or minus 1 percent from the literature-based annual average atmospheric 14C in CO2. See table 7. bA probable detection for a sample is defined as a positive mass (CO ) calculated from equation 1 throughout the entire estimated reasonable range of background 14C in CO (pMC ). 2 ff 2 bg cAncient fossil fuel CO (CO ) values were calculated with equations 1 and 1.5 using the pMC values in this table and values for each sample available in table 1.1 in appendix 1. 2 2 ff bg dValues in this column for samples collected in 2022 and 2023 are reported in Jaeschke and others (2023). eValues in this column for samples collected in 2017 are reported in Department of the Navy (2019) or McHugh and others (2020).

Ancient Carbon in Soil Carbon Dioxide 35

2017

36 Ancient Carbon in Groundwater and Soil Gas from Degradation of Petroleum near the Red Hill Bulk Fuel Storage Facility A. Soil trap samples EXPLANATION Reasonable range of pMCbg values based on this study’s soil gas samples and Graven and others (2017).

0.10

[pMCbg, background percentage modern carbon, age corrected]

0.06

T1 soil trap T2 soil trap T3 soil trap T8 soil trap

0.02 0.01 0.002

Reported values (Department of the Navy, 2019; McHugh and others, 2020)

0.05

Detection

Calculated ancient fossil fuel carbon dioxide, in grams

Nondetect

−0.05

−0.10 98

100

101

102

103

104

105

106

B. Air intake and exhaust samples

EXPLANATION

Reasonable range of pMCbg values based on this study’s soil gas samples and Graven and others (2017).

0.10

Tunnel air intake day 1 Tunnel air intake day 2 Lower tunnel air exhaust day 1 Lower tunnel air exhaust day 2 Upper tunnel air exhaust day 1 Upper tunnel air exhaust day 2

0.09 0.08

0.05 0.037 0.033

Reported values (Department of the Navy, 2019; McHugh and others, 2020)

0.022 Detection

Nondetect

−0.006

−0.05

−0.10 98

100

101

102

103

104

105

106

Background carbon-14 content of carbon dioxide, age-corrected, in percent modern carbon

Figure 14. Calculated mass of ancient fossil fuel-derived carbon dioxide (CO2 ff, eq. 1) and assumed background carbon-14 contents, age-corrected (pMCbg) for (A) soil trap samples and (B) tunnel air intake and exhaust samples collected in 2017 and reported as detections (Department of the Navy, 2019; McHugh and others, 2020).

Ancient Carbon in Soil Carbon Dioxide 37 appendix 1, based on data from Graven and others [2017]) and the average 14C of soil CO2 from soil probe samples was 100.43 percent modern (age-corrected), or about 2 percent higher than atmospheric 14C. Therefore, 2022–23 samples were evaluated over a reasonable pMCbg range of 98–101. In some cases, a soil probe sample had a 14C content more than 2 percent greater than the average atmospheric value, so the soil probe sample concentration was set as the upper limit to the reasonable range rather than 101 (table 7, table 8). Assuming the 14C of soil CO2 in 2017 was also, on average, about 2 percent higher than annual average atmospheric 14C, a reasonable pMCbg range of 101–103 is appropriate for evaluating the 2017 samples. Evaluation of the 2022–23 samples across the pMCbg range of 98–101 still indicates no detectable ancient fossil-fuel derived CO2 for all samples (table 8). The reevaluation of reported ancient fossil fuel 14C results from the 2017 samples collected at the facility (Department of the Navy, 2019; McHugh and others, 2020) is listed in table 8 and figure 14A and B. Each line in figure 14A and B represents one field sample being evaluated over a range of age-corrected pMCbg values. The gray shading on figure 14A and B shows the reasonable range of age-corrected background 14C content (pMCbg) values (x-axis) over which the 2017 samples were evaluated. The reasonable ranges do not overlap the background 14C content of 105 percent modern, which is the value used by E-Flux in sample reports (Department of the Navy, 2019). When the pMCbg value is 105, all four soil trap samples (T1, T2, T3, T8) are classified as detections (above the zero line), as was reported previously (fig. 14A); however, within the reasonable range of pMCbg values, none of the samples’ calculated ancient CO2 masses are entirely greater than zero. Therefore, according to the metrics proposed in this report, none of the 2017 soil trap samples are classified as detections because none of the samples are always positive across the reasonable range of pMCbg values (fig. 14A and B). Furthermore, when pMCbg is set to 105 for the 2022–23 samples, the range of calculated ancient fossil fuel CO2 masses for the 2022–23 samples overlaps with the calculated masses for the 2017 samples (table 8). This is further evidence that the analytical results for the soil trap samples are similar from the two studies and the detections of ancient C reported from the 2017 samples were affected by the selection of a high agecorrected background 14C value. In 2017, cartridges were used to collect CO2 from the tunnel air intake and exhaust systems (Department of the Navy, 2019; McHugh and others, 2020). These cartridges were not placed on soil so evaluating the trap results over a range of possible atmospheric 14C contents was more appropriate than evaluating trap results over a range of 14C from soil CO2. The average atmospheric value in 2017 was about 101 percent modern (age-corrected). Previous studies have determined that atmospheric 14C varies by about 1 percent modern (10 per mil) within 1 year at the Mauna Loa Observatory and other stations

(Graven and others, 2022); therefore, the exhaust samples were evaluated over a pMCbg range of 100–102 percent modern (table 8, fig. 14B). Both lower tunnel exhaust cartridge samples were classified as detections because the calculated ancient fossil fuel CO2 mass was always greater than zero over the reasonable range of age-corrected pMCbg values (fig. 14B, table 8). No other tunnel intake or upper tunnel exhaust samples were classified as detections because they were not always positive over the reasonable range of age-corrected background 14C values (table 8, fig. 14B). In conclusion, only the lower tunnel exhaust samples from 2017 are classified as detections using a method that accounts for reasonable ranges of 14C contents of background CO2. All other intake, exhaust, and soil trap samples collected in 2017 and 2022–23 are not classified as detections.

Dynamic Closed Chamber Soil Carbon Dioxide Efflux Soil CO2 effluxes measured with a dynamic closed chamber were highly variable at the facility, ranging from site average values of 1.34 to 7.72 μmol/m2/s (fig. 15). As previously discussed, none of the sites sampled in 2022–23 had detectable ancient C in soil CO2; therefore, the variability in measured soil CO2 effluxes only represents variability in natural soil respiration rather than variability caused by mixtures of natural soil respiration and petroleum biodegradation. The variability in natural soil respiration at the facility is large compared to variability in measured soil CO2 effluxes at the well-documented Bemidji site. At the Bemidji site, the magnitude of soil CO2 effluxes has been used to distinguish sampling locations unaffected by petroleum biodegradation from “affected” locations where petroleum biodegradation is occurring (Sihota and others, 2011). At the Bemidji site, 30 years after a crude oil spill occurred, the average CO2 efflux at unaffected locations was 3.29 µmol/m2/s compared to an average of 5.89 µmol/m2/s at affected locations where oil was degrading (Sihota and others, 2011). The individual efflux measurements at affected and unaffected locations were also distinct. The effluxes ranged from 2.63 to 4.45 µmol/ m2/s at the unaffected locations and from 5.21 to 7.12 µmol/ m2/s at the affected locations (Sihota and others, 2011). The range of natural soil respiration effluxes observed at the facility (6.38 µmol/m2/s) exceeds the range of mixed natural respiration and petroleum degradation effluxes observed at the Bemidji site (4.49 µmol/m2/s). Because of the inherent variability in natural soil respiration at the facility, a substantial increase in CO2 efflux from petroleum biodegradation would be needed to distinguish natural and contaminant effluxes based solely on the magnitude of fluxes. The magnitude of soil CO2 effluxes alone could not be used to estimate natural source zone depletion rates at the facility.

S. Hālawa Stream

1.39 µmol/m2/s

T22–10 1.34 µmol/m2/s

T22–08

ay sW

T22–07

ru Ica

T22–06 T22–05

6.17 µmol/m2/s

4.86 µmol/m2/s

6.81 µmol/m2/s

4.03 µmol/m2/s

T22–04

T22–09

7.72 µmol/m2/s T2

T22–03

4.71 µmol/m2/s

2.27 µmol/m2/s

4.06 µmol/m2/s

T22–02 T22–01

2.01 µmol/m2/s

1.7 µmol/m2/s

ni St

Ala La

Data source credit note. List source of data on map Base from U.S. Geological Survey digital data, various scales and dates Universal Transverse Mercator, zone 4 north North American Datum of 1983

Soil carbon dioxide efflux, in micromoles per square meter per second (µmol/m2/s) 7.72 1.34

EXPLANATION Red Hill Bulk Fuel Storage Facility boundary T2

Dynamic closed chamber sampling site with identifier

200 50

400 100

600 150

800 FEET 200 METERS

Approximate center of underground fuel storage tank

Figure 15. Average dynamic closed chamber soil carbon dioxide efflux measurements made in September 2022 at the Red Hill Bulk Fuel Storage Facility, Oʻahu, Hawaiʻi.

38 Ancient Carbon in Groundwater and Soil Gas from Degradation of Petroleum near the Red Hill Bulk Fuel Storage Facility

References Cited 39

Summary This study had two goals. The first was to provide information helpful to determine the direction of migration of fuel compounds and biodegradation products in the groundwater below the Red Hill Bulk Fuel Storage Facility (the facility). The second was to determine whether or not surface measurements of carbon dioxide efflux can help to locate fuel source zones in the underlying unsaturated zone. To determine the direction of migration of fuel-related compounds in groundwater, a total of 19 wells were sampled. These included one well known to be unaffected by contamination that served as a background well. The groundwater analyses included nonvolatile dissolved organic carbon (NVDOC), ancient carbon in NVDOC, and diesel range organics (DRO). In addition, a suite of analytes known to be altered during biodegradation of petroleum fuels in groundwater, including major anions, cations, pH, alkalinity, and trace metals, was measured. The results indicate that NVDOC correlates with ancient carbon, indicating that concentrations of NVDOC elevated to greater than background originate from a fuel source. The NVDOC concentrations are almost three times higher than DRO values in the same wells, demonstrating that DRO analyses quantify only a fraction of the compounds migrating from the fuel source zones. The NVDOC concentrations and ancient carbon data indicate that groundwater from well RHMW02 has the highest concentrations of partial transformation products from fuel. The ancient carbon data indicate partial transformation products are present in wells on the north and south sides of the ridge. The NVDOC concentrations in groundwater decrease to about 10 percent of the highest concentration measured under the tanks within a distance of 700 feet to the south and 1,000 feet to the north of the ridge, indicating biodegradation, dilution, or both. Further analyses of the organic carbon may help determine if biodegradation is important. Optical methods could be applied to determine if increased oxidation of the NVDOC with distance occurs during biodegradation. These measurements would also help to distinguish ancient natural organic matter in the unaffected aquifer from NVDOC migrating from fuel sources. In addition, a few puzzling cases could be investigated further, such as the elevated NVDOC with low ancient carbon in groundwater from well RHMW05 and the small concentration of ancient carbon at RHMW11–05. The carbon-14 content of soil carbon dioxide in samples collected with a soil probe were determined at 28 sites overlying the facility and the adit 3 tunnel. The modern and ancient fossil fuel components of soil carbon dioxide efflux were determined from soil carbon traps deployed at six sites overlying the tank farm. Bulk soil carbon dioxide efflux was measured with a dynamic closed chamber at 12 sites overlying the tank farm.

Ancient carbon from biodegradation of fuels was not detected in any of the soil probe or carbon trap samples above the facility. Soil carbon trap results were evaluated using an approach that accounts for variability in the background carbon-14 content of carbon dioxide. Calculations that used reasonable ranges of background carbon-14 contents were key to determining whether or not soil carbon trap results near the reporting limit should be classified as detections of ancient fossil-fuel-derived carbon dioxide. Using this approach, a reanalysis of the 2017 carbon trap data indicates that the only probable detections of ancient carbon in 2017 were in samples from the lower tunnel exhaust system. Bulk measurements of soil carbon dioxide efflux with a dynamic closed chamber were highly variable across the site and could not be used to delineate areas potentially affected by fuel biodegradation. Overall, soil gas results indicate that discrete soil gas measurements at land surface were not useful for detecting biodegradation of residual fuel in the unsaturated zone at the facility.

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44 Ancient Carbon in Groundwater and Soil Gas from Degradation of Petroleum near the Red Hill Bulk Fuel Storage Facility Xu, L., Roberts, M.L., Elder, K.L., Hansman, R.L., Gagnon, A.R., and Kurz, M.D., 2022, Radiocarbon in dissolved organic carbon by UV oxidation—An update of procedures and blank characterization at NOSAMS: Radiocarbon, v. 64, no. 1, p. 195–199, accessed December 19, 2023, at https://doi.org/10.1017/RDC.2022.4. Xu, L., Roberts, M.L., Elder, K.L., Kurz, M.D., McNichol, A.P., Reddy, C.M., Ward, C.P., and Hanke, U.M., 2021, Radiocarbon in dissolved organic carbon by UV oxidation—Procedures and blank characterization at NOSAMS: Radiocarbon, v. 63, no. 1, p. 357–374, accessed December 19, 2023, at https://doi.org/10.1017/ RDC.2020.102. Zemo, D.A., and Foote, G.R., 2003, The technical case for eliminating the use of the TPH analysis in assessing and regulating dissolved petroleum hydrocarbons in ground water: Groundwater Monitoring & Remediation, v. 23, no. 3, p. 95–104, accessed December 19, 2023, at https://doi.org/10.1111/j.1745-6592.2003.tb00687.x.

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Appendix 1. Carbon-14 Information 45

Appendix 1. Carbon-14 Information Unit Definitions “Modern” carbon is defined as 95 percent of the radiocarbon concentration in 1950 of the National Bureau of Standards oxalic acid I (Standard Reference Material 4990B, OX-I) normalized to δ carbon-13 (13C) of Vienna Pee Dee Belemnite equal to −19 per mil (Olsson, 1970). δ13C is the ratio of 13C to carbon-12 (12C) of the sample compared to the ratio of 13C to 12C of the reference material. Results from the Woods Hole Oceanographic Institution, National Ocean Sciences Accelerator Mass Spectrometry, laboratory are calculated using this internationally agreed upon definition. The definition is equivalent to an absolute 1950 carbon-14 (14C)/12C ratio of 1.176 plus or minus 0.010×10−12 (Karlen and others, 1965). All results are normalized to −25 per mil using the δ13C Vienna Pee Dee Belemnite of the sample (Woods Hole Oceanographic Institution, National Ocean Sciences Accelerator Mass Spectrometry, 2023). Carbon-14 contents of samples are reported as deviations from “modern.” Percentage modern carbon (pMC) is a measurement of the deviation of the 14C/12C ratio, normalized to a δ13C of −25 per mil to account for isotopic fractionation (Woods Hole Oceanographic Institution, National Ocean Sciences Accelerator Mass Spectrometry, 2023). To compare laboratory-reported values in units of pMC directly to atmospheric data (Graven and others, 2017, 2020, 2022), the laboratory data were converted to ∆14C values, which are defined as the relative difference between the sample and the absolute international standard with a base year of 1950 (Stuiver and Polach, 1977). Carbon-14 values given in ∆14C notation are corrected for age and isotopic fractionation in contrast to 14C values in pMC notation, which are only corrected for isotopic fractionation. Carbon-14 contents were converted from pMC to ∆14C notation according to Woods Hole Oceanographic Institution, National Ocean Sciences Accelerator Mass Spectrometry (2023): Δ 14 C=[ (pM Csample   / 100 ) × e  λ(1950−Yc  ) −1]×1, 000, (1.1) where ∆14C is sample 14C content relative to the absolute international standard with a base year of 1950 and sample activity corrected for age and isotopic fractionation (Stuiver and Polach, 1977); pMCsample

is sample 14C content relative to the “modern” standard corrected for isotopic fractionation (Woods Hole Oceanographic Institution, National Ocean Sciences Accelerator Mass Spectrometry, 2023);

is 1/8,267, or the inverse of the true average life of 14C (Woods Hole Oceanographic Institution, National Ocean Sciences Accelerator Mass Spectrometry, 2023); and

is the year of sample collection.

The ∆14C notation is the typical convention for reporting age-corrected values that are referenced to the absolute international standard with a base year of 1950 (Stuiver and Polach, 1977), but for consistency among 14C data discussions in this report, all 14C values are presented in pMC notation. Values that have been age corrected according to equation 1.1 are converted back to pMC notation using equation 1.2: pMCage-corr=100+(Δ14C/10),(1.2) where pMCage-corr

∆14C

is sample 14C content relative to the absolute international standard with a base year of 1950 14C with sample activity corrected for age and isotopic fractionation (Stuiver and Polach, 1977), in percent modern notation, and is as defined previously.

In this report, all pMC values are only corrected for isotopic fractionation unless age correction is also specified. And finally, the 14C contents of some samples are converted from pMC to percentage ancient carbon according to the following equation: pACsample =100–pMCsample ,(1.3) where pACsample pMCsample

is 14C content as percentage ancient carbon and is 14C content as percentage modern carbon, as previously defined.

Data Interpretation Understanding how much petroleum-derived carbon depleted in 14C relative to background carbon exists in environmental samples requires direct measurements or assumptions of background 14C contents. Conceptually, the background and petroleum-derived parts of samples are related by a two-component mass balance (Avery and others, 2006):

46 Ancient Carbon in Groundwater and Soil Gas from Degradation of Petroleum near the Red Hill Bulk Fuel Storage Facility pMCsample=ffsample×pMCff+(1−ffsample)×pMCbg,(1.4) where pMCsample

is the measured 14C content reported by the laboratory, in percent modern carbon;

ffsample

is the petroleum, or fossil fuel, fraction of the sample;

pMCff

is the 14C content of the petroleum-derived fraction of the sample, in percent modern carbon; and

pMCbg

is the 14C content of the background fraction of the sample, in percent modern carbon.

In equation 1.4, pMCff equals 0 because petroleum-derived carbon is depleted in 14C; therefore, the equation simplifies to the following: ffsample=1–(pMCsample/pMCbg).(1.5) This equation illustrates that the background percentage modern carbon is important for quantifying the fraction of petroleum-derived carbon in an environmental sample. In this report, equation 1.5 was applied to soil carbon dioxide (CO2) trap samples with age-corrected values for pMCbg in order to distinguish between petroleum-derived CO2 and CO2 from background soil respiration. The pMCsample, pMCbg, and ffsample values for the samples collected in 2017, 2022, and 2023 and data values from E-Flux laboratory reports that were used in equation 1 to calculate the mass of ancient fossil fuel CO2 in soil trap and cartridge samples are listed in table 1.1 and Jaeschke and others (2023). Groundwater dissolved organic carbon (DOC) can have a background 14C content that is much different from modern atmospheric 14C. Modern-aged DOC from plant and soil organic matter at the land surface is transported to groundwater in recharge. In thick unsaturated zones, such as those at the facility, infiltrating recharge water may also incorporate older organic carbon present deeper in the formation. As a result, 14C contents of background groundwater DOC in geologic settings like the facility can be much older than modern age (Thomas and others, 2021). The 14C content of background soil CO2 is generally close to atmospheric 14C contents and fluctuates seasonally from variations in root respiration and soil organic matter decomposition (Dörr and Münnich, 1986; Wang and others, 2000).

Atmospheric 14C nearly doubled in the 1950s and 1960s from nuclear weapons testing and has since been declining because of radioactive decay, mixing with other reservoirs, and burning of 14C-depleted fossil fuels (Graven and others, 2017). In addition to these atmospheric changes, the 14C content of soil CO2 at a given location varies depending on the relative contributions of root respiration and soil organic matter decomposition to soil CO2. Generally, when plant roots are actively respiring during the growing season, 14C of soil CO2 nearly reaches atmospheric levels, whereas in dormant seasons, soil CO2 is more depleted in 14C (Dörr and Münnich, 1986). The 14C depletion results from a decreasing effect of root respiration and an increasing contribution of microbial decomposition of soil organic matter (Dörr and Münnich, 1986; Wang and others, 2000). Soil moisture and temperature conditions during the warm season can also affect rates of root respiration and soil organic matter decomposition (Wang and others, 2000). The atmospheric 14C content during soil CO2 sample collection at the facility varied from an annual average ∆14C value of about 9 per mil in 2017 to about −19 per mil in 2023. These age-corrected values (∆14Cpred) were estimated from the following linear regression equation: Δ14Cpred=−4.68Y+9,451.35,(1.6) where

is decimal year (for example, 2015.5 corresponds to around July 2, 2015) and

4.68 and 9,451.35 are coefficients from a linear regression, which related ∆14C to year for the period of 2005.5 to 2015.5 using published atmospheric ∆14C annual average values for tropical regions (Graven and others, 2017). The coefficient of determination for this regression fit was 0.995. The value predicted from equation 1.6 for June 2020 (−4.6 per mil) was within 10 per mil of all observed values at the Mauna Loa Observatory in 2020 (Graven and others, 2022). The predicted values (∆14Cpred) from equation 1.6 were then converted to age-corrected pMC values of about 101 for 2017, 99 for 2022, and 98 for 2023 with equation 1.2. These values represent the background atmospheric 14C for the soil trap sampling events discussed in this report.

Table 1.1. Data values from E-Flux sample reports (Department of the Navy, 2019; Jaeschke and others, 2023) used in equations 1 and 1.5 to calculate the mass of ancient fossil fuel carbon dioxide in soil trap and cartridge samples deployed at the Red Hill Bulk Fuel Storage Facility, Oʻahu, Hawaiʻi, in 2017 and 2022–23. [ID, identifier; 14C, carbon-14; CO2, carbon dioxide; ND, not detected; a, denotes data source is appendix B in Department of the Navy (2019); b, denotes data source is Jaeschke and others (2023)]

aBackground 14C

content in CO2 Data

Sample

source

year

Site

E-Flux

used in E-Flux

sample

report (pMCbg in

type

eq. 1.5), age corrected, in percent modern

2017

PHHI–R1–

Dry sorbent mass (msorbent in eq. 1), in grams

bAverage

CO2 content of sample sorbent (CO2 sample in eq. 1), as a fraction

14C content

of sample as reported from laboratory (pMCsample in eq. 1.5), in percent modern

bAverage CO 2

content of travel blank sorbent (CO2 TB in eq. 1), as a fraction

14C content of

travel blank as reported from laboratory (used as pMCsample in eq. 1.5), in percent modern

bFossil fuel

fraction of the sample (ffsample in eqs. 1 and 1.5), as a fraction

b, cFossil fuel

fraction of the travel blank (ffTB in equation 1 and computed as ffsample in eq. 1.5), as a fraction

dAncient

Ancient

fossil fuel

CO2 in

sample

(calculated

reported

by eq. 1), in

by E-Flux,

grams

in grams

Soil trap

105

41.937

0.0248

89.9

0.0092

64.6

0.144

0.385

0.0016

e0.00

Soil trap

105

43.589

0.0756

99.6

0.0092

64.6

0.052

0.385

0.0165

0.02

Soil trap

102

41.67

0.0341

92.75

0.0155

75.71

0.0907

0.2577

−0.0376

Soil trap

102

42.84

0.0675

96.86

0.0127

74.57

0.0504

0.2689

−0.0006

Soil trap

105

41.747

0.0366

93.9

0.0092

64.6

0.106

0.385

0.0143

0.01

Soil trap

102

41.93

0.0421

93.79

0.0127

74.57

0.0805

0.2689

−0.0011

Soil trap

102

41.99

0.0342

92.46

0.0155

75.71

0.0935

0.2577

−0.0334

Soil trap

102

43.20

0.0695

97.88

0.0127

74.57

0.0404

0.2689

−0.0263

Soil trap

105

45.130

0.0597

96.6

0.0092

64.6

0.080

0.385

0.0571

0.06

Soil trap

102

42.59

0.0477

96.44

0.0127

74.57

0.0545

0.2689

−0.0347

Soil trap

102

44.27

0.0786

98.87

0.0155

75.71

0.0307

0.2577

−0.0701

Soil trap

102

42.89

0.0753

98.56

0.0127

74.57

0.0337

0.2689

−0.0376

Cartridge

105

4.877

0.2557

100.8

0.0091

65.3

0.040

0.378

0.0331

0.03

Cartridge

105

4.817

0.2362

104.0

0.0091

65.3

0.009

0.378

−0.0061

CO2–04 a

2017

PHHI–R1– CO2–07

2022

10231–R1– CO2–01

2023

10231–R2– CO2–01

2017

PHHI–R1– CO2–02

2023

10231–R2– CO2–02

2022

10231–R1– CO2–03

2023

10231–R2– CO2–05

2017

PHHI–R1– CO2–08

2023

10231–R2– CO2–04

2022

T22–04

10231–R1– CO2–02

2023

T23–05

10231–R2– CO2–03

2017

Tunnel air

PHHI–C1–

intake

CO2–05

day 1 a

2017

Tunnel air

PHHI–C1–

intake

CO2–06

day 2

Appendix 1. Carbon-14 Information 47

deployed at the Red Hill Bulk Fuel Storage Facility, Oʻahu, Hawaiʻi, in 2017 and 2022–23.—Continued [ID, identifier; 14C, carbon-14; CO2, carbon dioxide; ND, not detected; a, denotes data source is appendix B in Department of the Navy (2019); b, denotes data source is Jaeschke and others (2023)]

aBackground 14C

content in CO2 Data

Sample

source

year

Site

E-Flux sample ID

E-Flux

used in E-Flux

sample

report (pMCbg in

type

eq. 1.5), age corrected, in percent modern

2017

Upper tunnel

PHHI–C1–

air exhaust

CO2–01

Dry sorbent mass (msorbent in eq. 1), in grams

bAverage

CO2 content of sample sorbent (CO2 sample in eq. 1), as a fraction

14C content

of sample as reported from laboratory (pMCsample in eq. 1.5), in percent modern

bAverage CO 2

content of travel blank sorbent (CO2 TB in eq. 1), as a fraction

14C content of

travel blank as reported from laboratory (used as pMCsample in eq. 1.5), in percent modern

bFossil fuel

fraction of the sample (ffsample in eqs. 1 and 1.5), as a fraction

b, cFossil fuel

fraction of the travel blank (ffTB in equation 1 and computed as ffsample in eq. 1.5), as a fraction

dAncient

Ancient

fossil fuel

CO2 in

sample

(calculated

reported

by eq. 1), in

by E-Flux,

grams

in grams

Cartridge

105

4.858

0.2592

101.8

0.0091

65.3

0.031

0.378

0.0217

0.02

Cartridge

105

4.882

0.2540

100.5

0.0091

65.3

0.043

0.378

0.0366

0.04

Cartridge

105

5.005

0.2841

97.4

0.0091

65.3

0.072

0.378

0.0853

f0.09

Cartridge

105

5.101

0.3029

98.3

0.0091

65.3

0.064

0.378

0.0810

g0.08

day 1 a

2017

Upper tunnel

PHHI–C1–

air exhaust

CO2–02

day 2 a

2017

Lower tunnel

PHHI–C1–

air exhaust

CO2–03

day 1 a

2017

Lower tunnel

PHHI–C1–

air exhaust

CO2–04

day 2 aReported as a fraction in E-Flux sample reports but listed here as a percentage as in Jaeschke and others (2023). bReported as a percentage in E-Flux sample reports but listed here as a fraction as in Jaeschke and others (2023). cEquation 1.5 was used to calculate ff , where ff TB TB is synonymous with ffsample and pMCsample is the reported value of the travel blank from the laboratory, and pMCbg is the same as was used for the field sample. dIn some cases, the 2017 reported data had fewer decimal places than the 2022–23 data. Higher precision estimates (that at least matched the 2022–23 data precision) were used for pMC sample , ffsample , and ffTB to calculate the values shown in this column. Estimated higher precision values, when rounded, were equivalent to the reported values in this table. eThis is the value in the E-Flux report in appendix B in Department of the Navy (2019); however, McHugh and others (2020) report a value of 0.002 gram for this sample. fThe value 0.09 is the value in the E-flux report in appendix B in Department of the Navy (2019); however, McHugh and others (2020) report a value of 0.081 gram for this sample. gThe value 0.08 is the value in the E-flux report in appendix B in Department of the Navy (2019); however, McHugh and others (2020) report a value of 0.085 gram for this sample.

48 Ancient Carbon in Groundwater and Soil Gas from Degradation of Petroleum near the Red Hill Bulk Fuel Storage Facility

Appendix 1. Carbon-14 Information 49

References Cited Avery, G.B., Jr., Willey, J.D., and Kieber, R.J., 2006, Carbon isotopic characterization of dissolved organic carbon in rainwater—Terrestrial and marine influences: Atmospheric Environment, v. 40, no. 39, p. 7539–7545. [Also available at https://doi.org/10.1016/j.atmosenv.2006.07.014.] Department of the Navy, 2019, Conceptual site model, investigation and remediation of releases and groundwater protection and evaluation, Red Hill Bulk Fuel Storage Facility, Joint Base Pearl Harbor-Hickam, Oʻahu, Hawaiʻi: Fort Belvoir, Va., Defense Logistics Agency Energy, prepared by AECOM Technical Services, Inc., [variously paged], accessed December 19, 2023, at https://www.epa.gov/sites/ default/files/2019-07/documents/red_hill_conceptual_site_ model_20190630-redacted.pdf. Dörr, H., and Münnich, K.O., 1986, Annual variations of the 14C content of soil CO2: Radiocarbon, v. 28, no. 2A, p. 338–345. [Also available at https://doi.org/10.1017/ S0033822200007438.] Graven, H., Allison, C.E., Etheridge, D.M., Hammer, S., Keeling, R.F., Levin, I., Meijer, H.A.J., Rubino, M., Tans, P.P., Trudinger, C.M., Vaughn, B.H., and White, J.W.C., 2017, Compiled records of carbon isotopes in atmospheric CO2 for historical simulations in CMIP6: Geoscientific Model Development, v. 10, no. 12, p. 4405–4417. [Also available at https://doi.org/10.5194/gmd-10-4405-2017.] Graven, H., Keeling, R.F., and Rogelj, J., 2020, Changes to carbon isotopes in atmospheric CO2 over the industrial era and into the future: Global Biogeochemical Cycles, v. 34, no. 11, article e2019GB006170, 21 p. [Also available at https://doi.org/10.1029/2019GB006170.] Graven, H., Keeling, R.F., and Xu, X., 2022, Radiocarbon dating—Going back in time: Nature, v. 607, no. 7919, 1 p., accessed September 15, 2023, at https://doi.org/10.1038/ d41586-022-01954-y. Jaeschke, J.B, Trost, J.J., Polite, B.F., Sinclair, D.A., Cozzarelli, I.M, Pagaduan, L.D., Miyajima, U.M., Nakama, R.K., Delin, G.N., Stack, J.K., and Baesman, S.M., 2023, Groundwater and soil gas data, methods, and quality assurance information for samples collected to determine ancient carbon distributions at Red Hill, Bulk Fuel Storage Facility, Oʻahu, Hawaiʻi 2022–2023: U.S. Geological Survey data release, accessed December 19, 2023, at https://doi. org/10.5066/P9TIDAA4. Karlen, I., Olsson, I.U., Kallberg, P., and Kilicci, S., 1965, Absolute determination of the activity of two 14C dating standards: Arkiv Geofysik., v. 4, no. 22, p. 265–471.

McHugh, T., Newell, C., Strasert, B., Stanley, C., Johnson, J., Henderson, T., Roff, D., and Narusawa, J., 2020, Direct aerobic NSZD of a basalt vadose zone LNAPL source in Hawaii: Journal of Contaminant Hydrology, v. 235, article 103729, 7 p., accessed December 19, 2023, at https://doi.org/10.1016/j.jconhyd.2020.103729. Olsson, I.U., 1970, The use of oxalic acid as a standard, in Olsson, I.U., ed., Radiocarbon variations and absolute chronology: Proceedings of the 12th Noel symposium, New York, John Wiley and Sons, 17 p. Stuiver, M., and Polach, H.A., 1977, Discussion reporting of 14C data: Radiocarbon, v. 19, no. 3, p. 355–363. [Also available at https://doi.org/10.1017/S0033822200003672.] Thomas, J.M., Hershey, R.L., Fereday, W., and Burr, G., 2021, Using carbon-14 of dissolved organic carbon to determine groundwater ages and travel times in aquifers with low organic carbon: Applied Geochemistry, v. 124, article 104842, 17 p., accessed March 1, 2024, at https://doi.org/ 10.1016/j.apgeochem.2020.104842. Wang, Y., Amundson, R., and Niu, X.-F., 2000, Seasonal and altitudinal variation in decomposition of soil organic matter inferred from radiocarbon measurements of soil CO2 flux: Global Biogeochemical Cycles, v. 14, no. 1, p. 199–211. [Also available at https://doi.org/10.1029/1999GB900074.] Woods Hole Oceanographic Institution, National Ocean Sciences Accelerator Mass Spectrometry, 2023, Radiocarbon data and calculations: Woods Hole Oceanographic Institution web page, accessed October 16, 2023, at https://www2.whoi.edu/site/nosams/calculations- and-reporting-of-results/.

50 Ancient Carbon in Groundwater and Soil Gas from Degradation of Petroleum near the Red Hill Bulk Fuel Storage Facility

Appendix 2. Quality Assurance Field Blank Samples Three field blank samples were collected during groundwater sampling at wells RHMW03, RHMW08, and RHP05. Most analytes were not detected in field blank samples, although a few detections that are described in this appendix were notable (table 2.1). For the purposes of the discussion in this appendix, concentrations of analytes with LT flags were assigned the value of the reported limit for calculating summary statistics; for example, an analyte result with a reported concentration of LT 0.5 was assigned a numeric value of 0.5 for calculation of the median. Field samples described in this section include regular field samples and field duplicates (sample_type equal to “REGULAR” or “FIELD DUP” in Jaeschke and others [2023]). The field blank collected at RHMW03 had detectable concentrations of copper and sodium. Copper was only detected in about 25 percent of the field samples, and the copper concentration (0.55 microgram per liter [μg/L]) in the RHMW03 field blank was within the range of copper concentrations of regular field samples (0.51–1.11 μg/L). Sodium was detected in all nonblank field samples, and the sodium concentration (686 μg/L) in the RHMW03 blank was substantially less than the concentration in any regular field sample (minimum of 32,300 μg/L). The field blank collected at RHMW08 had detectable concentrations of arsenic, barium, iron, and zinc. Arsenic was detected in about 68 percent of field samples, and the arsenic concentration of this field blank (0.81 μg/L) is near the lower end of the range of field sample concentrations (0.66–9.2 μg/L). Barium was detected in all field samples, and the barium concentration of this field blank (11.7 μg/L) is greater than the median concentration (10.0 μg/L) of the

measured field sample concentrations. Iron was detected in 82 percent of field samples, and the iron concentration of this field blank (7.39 μg/L) is greater than the median concentration (4.55 μg/L) of the measured field sample concentrations. Zinc was detected in 64 percent of field samples, and the zinc concentration (68.6 μg/L) of this field blank is greater than the zinc concentration of all field samples, except for samples collected at well DH43, which had zinc concentrations of about 80 μg/L. The field blank collected at RHP05 had detectable concentrations of sodium (507 μg/L), diesel range organics (DRO; estimated value of 71 μg/L), nitrate (estimated value of 0.07 mg/L), and sulfate (estimated value of 0.04 mg/L). The sodium concentration of this blank (507 μg/L) was substantially less than the sodium concentration in any regular field sample (minimum of 32,300 μg/L). The DRO, nitrate, and sulfate concentrations were all low and flagged as estimated values because they were greater than the minimum detection level but less than the reporting level (Jaeschke and others, 2023). These analytes were frequently detected in nonblank field samples (DRO, 74 percent; nitrate, 86 percent; and sulfate, 100 percent) and generally at higher concentrations than reported in the blank samples. Nonvolatile dissolved organic carbon (NVDOC) was detected in every sample, including the field blanks. Low concentrations of NVDOC were measured in all three field blanks, ranging from 0.20 to 0.30 milligram per liter (mg/L) of carbon. The blank NVDOC concentrations were generally lower than NVDOC concentrations in regular field samples, which ranged from 0.21 to 6.45 mg/L. Five field sample NVDOC concentrations from three sites (DH43, Moanalua W–2, and RHMW12A) overlapped with the blank NVDOC concentrations. RHMW12A is a deep well (table 2) and Moanalua W–2 was presumed to be a background well.

Appendix 2. Quality Assurance 51 Table 2.1. Results from field blank samples collected at the Red Hill Bulk Fuel Storage Facility, Oʻahu, Hawaiʻi. [Dates given in month/day/year format; HST, Hawaiʻi-Aleutian standard time; μg/L, microgram per liter; mg/L, milligram per liter; HCO3, bicarbonate; μS/ cm at 25 °C, microsiemens per centimeter at 25 degrees Celsius; LT, less than; ND, not determined; --, no data or not applicable; E, estimated value; data from Jaeschke and others (2023)]

Analyte

Unit

Field blank collected at site RHMW03 on 1/30/2023 at 17:52 HST

Field blank collected at site RHMW08 on 9/28/2022 at 10:22 HST

Field blank collected at site RHP05 on 1/27/2023 at 10:52 HST

Flag

Result

Flag

Result

Flag

Result

Silver (Ag)

μg/L

0.5

Aluminum (Al)

μg/L

5.0

Alkalinity

mg/L as HCO3

Arsenic (As)

μg/L

0.5

0.81

0.5

Boron (B)

μg/L

2.0

Barium (Ba)

μg/L

2.0

11.7

2.0

Beryllium (Be)

μg/L

0.5

Bromide (Br)

μg/L

0.01

Calcium (Ca)

μg/L

Cadmium (Cd)

μg/L

0.5

Cerium (Ce)

μg/L

2.0

Methane (CH4)

mg/L

Chloride (Cl)

mg/L

0.01

Cobalt (Co)

μg/L

0.5

Chromium (Cr)

μg/L

0.5

Copper (Cu)

μg/L

0.55

0.5

Diesel range organics (DRO)

μg/L

Fluoride (F)

mg/L

0.02

Iron (Fe)

μg/L

2.0

7.4

2.0

pH (measured in field)

pH units

7.67

Specific conductance (measured in field)

μS/cm at 25 °C

Potassium (K)

μg/L

250

Lanthanum (La)

μg/L

1.0

Lithium (Li)

μg/L

0.5

Magnesium (Mg)

μg/L

Manganese (Mn)

μg/L

Molybdenum (Mo)

μg/L

Sodium (Na)

μg/L

686

500

507

n-Eicosane C20 (laboratory surrogate in DRO analyses)

Percent

95.2

103

90.9

Nickel (Ni)

μg/L

0.5

Nitrate (NO3)

mg/L

0.03

0.07

Nonvolatile dissolved organic carbon (NVDOC)

mg/L of carbon

0.30

0.20

0.26

Lead (Pb)

μg/L

0.5

Phosphate (PO4)

mg/L

0.06

Rubidium (Rb)

μg/L

2.0

Antimony (Sb)

μg/L

0.5

Selenium (Se)

μg/L

1.0

500

200

250

2.0

0.5

500

190

250

2.0

0.5

0.01 500

250 2.0 0.5

52 Ancient Carbon in Groundwater and Soil Gas from Degradation of Petroleum near the Red Hill Bulk Fuel Storage Facility Table 2.1. Results from field blank samples collected at the Red Hill Bulk Fuel Storage Facility, Oʻahu, Hawaiʻi.—Continued [Dates given in month/day/year format; HST, Hawaiʻi-Aleutian standard time; μg/L, microgram per liter; mg/L, milligram per liter; HCO3, bicarbonate; μS/ cm at 25 °C, microsiemens per centimeter at 25 degrees Celsius; LT, less than; ND, not determined; --, no data or not applicable; E, estimated value; data from Jaeschke and others (2023)]

Analyte

Unit

Field blank collected at site RHMW03 on 1/30/2023 at 17:52 HST

Field blank collected at site RHMW08 on 9/28/2022 at 10:22 HST

Field blank collected at site RHP05 on 1/27/2023 at 10:52 HST

Flag

Result

Flag

Result

Flag

250

Silicon (Si)

μg/L

Sulfate (SO4)

mg/L

0.03

Squalene (laboratory surrogate in DRO analyses)

Percent

93.5

Strontium (Sr)

μg/L

2.0

Thallium (Tl)

μg/L

0.5

Uranium (U)

μg/L

0.5

Vanadium (V)

μg/L

0.5

Zinc (Zn)

μg/L

2.0

Field Duplicate Samples Variability between regular-duplicate sample pairs was evaluated by calculating the relative percentage difference according to the following equation:

v 1 + v 2 RPD=( v 1−v 2)/ (_   ×100, 2 ) where

RPD

is the relative percentage difference,

is the reported value of the regular field sample, and

is the reported value of the field duplicate sample.

(2.1)

Field duplicate soil gas samples were collected at sites T2, T3, T5, and A3–07. Four sample pairs were analyzed for ancient carbon (14C) content of CO2, and four sample pairs were analyzed in the field for CO2 concentration. All the relative differences between regular samples and field duplicates were less than 15 percent (table 2.2). Field duplicate groundwater samples were collected at wells RHMW08, RHMW11–05, RHMW12A, and DH43. Detections and concentrations were in reasonable agreement for most of the regular-duplicate sample pair comparisons. Sample pairs with split detections/nondetections or relative differences greater than 15 percent are discussed. Only two split detections/nondetections were observed in the regular-duplicate sample pairs: aluminum from RHMW08 (regular sample: 5.72 μg/L; duplicate: less than 5.0 μg/L) and antimony from DH43 (regular sample: less than 0.5 μg/L; duplicate: 0.52 μg/L). In both cases, the detected concentration was very near the

0.03

Result 250

0.04

91.3

2.0

0.5

68.6

2.0

119

detection limit. Nondetects in paired regular and field duplicate samples were reported in 67 cases. In all other instances, the analyte was detected in the field duplicate and regular sample. These detected concentrations are the basis for the following discussion and summarized in table 2.2. Five analytes (NVDOC, DRO, phosphate, iron, and ancient carbon content of NVDOC [NVDOC_14C]) each had one instance of a regular and field duplicate sample having a relative difference of greater than 15 percent. The regular and field duplicate concentrations of NVDOC from well RHMW08 were 0.56 mg/L and 0.87 mg/L, respectively. These concentrations straddle the laboratory reporting level of 0.60 mg/L. The concentration of 0.56 mg/L is reported as an estimated value because it is less than the reporting level of the laboratory (Jaeschke and others, 2023). Three analytes from the regular-duplicate pair of samples at well RHWMW11–05 had relative differences greater than 15 percent: DRO, phosphate, and iron. The DRO concentrations (66 and 84 μg/L) were low-level estimated concentrations that were less than the reporting level but greater than the detection level of the laboratory (Jaeschke and others, 2023). The regular and field duplicate concentrations of phosphate were 0.48 mg/L and 0.58 mg/L, respectively. The regular and field duplicate concentrations of iron were 6.53 μg/L and 15.3 μg/L, respectively. The relative difference between these two concentrations (80.3 percent) was the largest in the study and anomalous for iron. All other regular-duplicate sample pairs had a relative difference of less than 15 percent for iron. The regular and field duplicate concentrations of carbon-14 (14C) content in NVDOC from well DH43 were 52.23 percent and 66.26 percent, respectively, with a relative difference of 23.7 percent. The other three field duplicate samples for 14C content of NVDOC (parameter NVDOC_14C in Jaeschke and others, 2023) had relative difference values of less than 5 percent. Field pH and specific conductance are not included in table 2.2 because they were not independently measured in the regular and field duplicate samples.

Appendix 2. Quality Assurance 53 Table 2.2. Results from field duplicate samples collected at the Red Hill Bulk Fuel Storage Facility, Oʻahu, Hawaiʻi. [μg/L, microgram per liter; mg/L, milligram per liter; HCO3, bicarbonate; 14C, carbon-14; δ13C, isotopic ratio of 13C to 12C of the sample compared to the ratio of the Vienna Pee Dee Belemnite standard; results are only included for samples when analytes were detected in the regular and duplicate sample pair; silver, beryllium, cadmium, cerium, methane, cobalt, copper, lanthanum, nickel, thallium, and uranium did not have any paired detections and therefore are not included in this table; data from Jaeschke and others (2023)]

Analyte

Unit

Sample medium

Count of field duplicates

Absolute value of relative percentage difference Minimum

Median

Maximum

Aluminum (Al)

μg/L

Groundwater

0.3

Alkalinity

mg/L as HCO3

Groundwater

2.7

3.8

8.4

Arsenic (As)

μg/L

Groundwater

3.4

5.4

13.9

Boron (B)

μg/L

Groundwater

0.6

2.9

6.2

Barium (Ba)

μg/L

Groundwater

0.0

2.0

5.0

Bromide (Br)

μg/L

Groundwater

0.0

2.15

11.8

Calcium (Ca)

μg/L

Groundwater

0.0

0.7

2.2

Chloride (Cl)

μg/L

Groundwater

0.0

0.1

2.3

14C content of CO 2

Percent modern carbon

Soil gas

0.1

0.4

0.5

Carbon dioxide (CO2)

Percent

Soil gas

0.0

7.1

δ 13C of CO2

Per mil

Soil gas

0.3

0.7

2.1

Chromium (Cr)

μg/L

Groundwater

0.5

0.8

2.0

Diesel range organics (DRO)

μg/L

Groundwater

6.8

15.4

24.0

Fluoride (F)

mg/L

Groundwater

Iron (Fe)

μg/L

Groundwater

8.6

11.1

80.3

Potassium (K)

μg/L

Groundwater

0.4

1.5

3.0

Lithium (Li)

μg/L

Groundwater

1.1

1.2

1.3

Magnesium (Mg)

μg/L

Groundwater

0.0

0.4

0.5

Manganese (Mn)

μg/L

Groundwater

0.7

Molybdenum (Mo)

μg/L

Groundwater

4.8

5.0

5.5

Sodium (Na)

μg/L

Groundwater

0.3

1.6

2.5

Nitrate (NO3)

mg/L

Groundwater

2.6

6.2

Nonvolatile dissolved organic carbon (NVDOC)

mg/L of carbon

Groundwater

3.6

11.2

43.4

14C content of

Percent modern carbon

Groundwater

1.4

3.7

23.7

δ 13C of NVDOC

Per mil

Groundwater

0.1

3.8

11.0

Lead (Pb)

μg/L

Groundwater

1.5

Phosphate (PO4)

μg/L

Groundwater

8.75

18.9

Rubidium (Rb)

μg/L

Groundwater

0.4

Antimony (Sb)

μg/L

Groundwater

4.65

9.3

Selenium (Se)

μg/L

Groundwater

5.2

Silicon (Si)

μg/L

Groundwater

0.3

0.5

1.0

Sulfate (SO4)

mg/L

Groundwater

0.7

0.8

1.9

Strontium (Sr)

μg/L

Groundwater

0.0

1.1

4.6

Vanadium (V)

μg/L

Groundwater

0.0

0.2

0.4

Zinc (Zn)

μg/L

Groundwater

0.5

4.2

13.1

NVDOC

54 Ancient Carbon in Groundwater and Soil Gas from Degradation of Petroleum near the Red Hill Bulk Fuel Storage Facility

Reference Cited Jaeschke, J.B, Trost, J.J., Polite, B.F., Sinclair, D.A., Cozzarelli, I.M, Pagaduan, L.D., Miyajima, U.M., Nakama, R.K., Delin, G.N., Stack, J.K., and Baesman, S.M., 2023, Groundwater and soil gas data, methods, and quality assurance information for samples collected to determine ancient carbon distributions at Red Hill, Bulk Fuel Storage Facility, Oʻahu, Hawaiʻi 2022–2023: U.S. Geological Survey data release, accessed December 19, 2023, at https://doi. org/10.5066/P9TIDAA4.

For more information about this publication, contact: Director, USGS Upper Midwest Water Science Center 2280 Woodale Drive Mounds View, MN 55112 763–783–3100 For additional information, visit: https://www.usgs.gov/centers/ umid-water Publishing support provided by the Rolla Publishing Service Center

Trost and others—Ancient Carbon in Groundwater and Soil Gas from Degradation of Petroleum near the Red Hill Bulk Fuel Storage Facility—SIR 2024–5034

ISSN 2328-0328 (online) https://doi.org/10.3133/sir20245034

Distribution of Ancient Carbon in Groundwater and Soil Gas from Degradation of Petroleum near the Red Hill Bulk Fuel Storage Facility, O‘ahu, Hawai‘i

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