U.S. Department of the Interior

U.S. Geological Survey

Water-Resources Investigations Report 03-4058

Prepared in cooperation with

Department of the Navy

Engineering Field Activity, Northwest

Naval Facilities Engineering Command

science for a changing world

Estimates of Residence Time and Related Variations

in Quality of Ground Water Beneath Submarine Base

Bangor and Vicinity, Kitsap County, Washington

TOANDOS PENINSULA

SUBASE

Bangor

JEFFFERSON COUNTY

Port

Gamble

Kingston

Poulsbo

Silverdale

Seabeck

BAINBRIDGE

ISLAND

KITSAP PENINSULA

Delta

Pier

KITSAP COUNTY

PUGET

SOUND

DABOB BAY

HOOD CANAL

DYES

INLET

LIBERTY

BAY

PORT ORCHARD
Estimates of Residence Time and Related 

Variations in Quality of Ground Water Beneath 

Submarine Base Bangor and Vicinity, Kitsap 

County, Washington

By S.E. Cox

Prepared in cooperation with the

DEPARTMENT OF THE NAVY 

ENGINEERING FIELD ACTIVITY, NORTHWEST 

NAVAL FACILITIES ENGINEERING COMMAND

Tacoma, Washington

2003

Water-Resources Investigations Report 03-4058

U.S. GEOLOGICAL SURVEY
For additional information write to:

Director, Washington Water Science Center

U.S. Geological Survey

1201 Pacific Avenue – Suite 600

Tacoma, Washington 98402

http://wa.water.usgs.gov

Any use of trade, product, or firm names in this publication is for descriptive purposes only and does 

not imply endorsement by the U.S. Government.

Copies of this report can be purchased from:

U.S. Geological Survey

Information Services

Building 810

Box 25286, Federal Center

Denver, CO 80225-0286

U.S. DEPARTMENT OF THE INTERIOR

GALE A. NORTON, Secretary

U.S. GEOLOGICAL SURVEY

Charles G. Groat, Director

Suggested citation:

Cox, S.E., 2003, Estimates of residence time and related variations in quality of ground water beneath 

Submarine Base Bangor and vicinity, Kitsap County, Washington: U.S. Geological Survey WaterResources Investigations Report 03-4058, 52 p. 
Contents iii

CONTENTS

Abstract ................................................................................................................................................................ 1

Introduction .......................................................................................................................................................... 2

Purpose and Scope ...................................................................................................................................... 2

Description of Study Area........................................................................................................................... 4

Well-Numbering System............................................................................................................................. 6

Acknowledgments....................................................................................................................................... 6

Background Concepts on Age-Dating of Ground Water ..................................................................................... 7

Tritium......................................................................................................................................................... 7

Chlorofluorocarbons ................................................................................................................................... 8

Carbon-14.................................................................................................................................................... 8

Hydrogeologic System ......................................................................................................................................... 9

Vashon Till Confining Unit ........................................................................................................................ 11

Vashon Aquifer ........................................................................................................................................... 12

Upper Confining Unit and Interbeds........................................................................................................... 12

Sea-Level Aquifer and Deep Aquifer ......................................................................................................... 13

Study Methods...................................................................................................................................................... 13

Sample Collection and Processing.............................................................................................................. 14

Sample Analysis.......................................................................................................................................... 17

Estimates of Residence Time and Variations in Quality of Ground Water ......................................................... 19

Ground-Water Age Classification Using Environmental Tracers .............................................................. 19

Tritium......................................................................................................................................................... 24

Chlorofluorocarbons ................................................................................................................................... 24

Carbon-14.................................................................................................................................................... 26

Variations in Ground-Water Quality........................................................................................................... 28

Ground-Water Chemistry............................................................................................................................ 29

Organic Carbon and Carbon Isotopes ......................................................................................................... 33

Changes in Ground-Water Chemistry Along Flow Paths........................................................................... 35

Geochemical Mass-Transfer Modeling of Carbon and Estimates of Ground-Water Residence Time....... 37

Conceptual Model of Ground-Water Evolution near SUBASE Bangor..................................................... 37

NETPATH Modeling of Ground-Water Residence Time .......................................................................... 39

Variations and Distribution of Carbon-14 Estimate of Ground-Water Residence Time............................ 41

Comparison of Estimates of Ground-Water Residence Times Based on Carbon-14 and 

Numerical Ground-Water Flow Modeling ..................................................................................... 43

Summary .............................................................................................................................................................. 47

References Cited .................................................................................................................................................. 48

Appendix A.Quality-assurance data for isotope analysis of ground-water samples from wells on 

SUBASE Bangor and vicinity, Kitsap County, Washington .......................................................... 53
iv Figures

FIGURES

Figure 1. Map showing location of the study area, SUBASE Bangor and vicinity, 

Kitsap County, Washington............................................................................................................... 3

Figure 2. Diagram showing well-numbering system used in Washington ....................................................... 6

Figure 3. Schematic diagram showing conceptual model of hydrogeologic units and ground-water 

flow in the vicinity of SUBASE Bangor, Kitsap County, Washington............................................. 10

Figure 4. Map showing location of wells sampled for physical properties, dissolved constituent 

concentrations, and isotopes used to estimate residence time of ground water, and 

conceptualized ground-water flow paths, SUBASE Bangor and vicinity, 

Kitsap County, Washington............................................................................................................... 15

Figure 5. Graph showing cumulative frequency distribution of tritium concentration in 

ground water, SUBASE Bangor and vicinity, Kitsap County, Washington...................................... 24

Figure 6. Graph showing comparison of stable isotope composition (deuterium and oxygen-18) 

of ground-water samples and of non-summer (fall-spring) precipitation at Victoria, 

British Columbia, and the relation with the Modern Global Meteoric Water Line of 

Rozanski and others (1993), SUBASE Bangor and vicinity, Kitsap County, Washington............... 29

Figure 7. Trilinear diagram showing distribution of major ions in ground water by hydrogeologic 

units and by ground-water age classification, SUBASE Bangor and vicinity, 

Kitsap County, Washington............................................................................................................... 30

Figure 8. Scatter plot showing comparison of molar concentrations of calcium, organic carbon, 

and bicarbonate by hydrogeologic units in ground water beneath SUBASE Bangor 

and vicinity, Kitsap County, Washington.......................................................................................... 32

Figure 9. Histogram showing distribution of dissolved organic carbon in ground water from 

hydrogeologic units, SUBASE Bangor and vicinity, Kitsap County, Washington........................... 34

Figure 10. Scatter plot showing relation between the value of delta carbon-13 and concentrations 

of carbon-14 by age classification in dissolved inorganic carbon from ground water near 

SUBASE Bangor and vicinity, Kitsap County, Washington............................................................. 36

Figure 11. Generalized section showing distribution of estimated ground-water residence time in 

the ground-water system beneath SUBASE Bangor and vicinity, Kitsap County, Washington....... 45
Tables v

TABLES

Table 1. Median values of physical properties and concentrations of water-quality constituents in 

ground water from five hydrogeologic units, SUBASE Bangor and vicinity, Kitsap County, 

Washington ........................................................................................................................................ 5

Table 2. Location of sampled wells, well-construction data, and hydrogeologic source of water, 

SUBASE Bangor and vicinity, Kitsap County, Washington............................................................. 16

Table 3. Physical properties, concentrations of dissolved constituents, and isotope ratios in 

ground-water samples from wells near SUBASE Bangor, Kitsap County, Washington .................. 20

Table 4. Concentration of chlorofluorocarbons in ground water and corresponding model of recharge 

year and ground-water age, SUBASE Bangor and vicinity, Kitsap County, Washington ................ 25

Table 5. Age classification and concentration of environmental tracers in ground water at 

SUBASE Bangor and vicinity, Kitsap County, Washington............................................................. 27

Table 6. Mass transfers of modeled phases and measured and modeled values of carbon-13 from 

selected geochemical mass-transfer models of pre-modern ground water, SUBASE Bangor 

and vicinity, Kitsap County, Washington.......................................................................................... 42

Table 7. Estimated ground-water residence times computed from mass-balance models using a 

range of initial carbon-14 activity in Vashon aquifer and a range of carbon-14 activity in 

aquifer organic matter, SUBASE Bangor and vicinity, Kitsap County, Washington ....................... 44

Table 8. Comparison of estimates of ground-water residence time (age) based on the concentration 

of carbon-14 and numerical simulation of ground-water flow, SUBASE Bangor and vicinity, 

Kitsap County, Washington............................................................................................................... 46
vi Conversion Factors and Datums

CONVERSION FACTORS AND DATUMS

CONVERSION FACTORS

Temperature in degrees Fahrenheit (°F) may be converted to degrees Celsius (°C) as follows:

°C=(°F-32)/1.8.

Temperature in degrees Celsius (°C) may be converted to degrees Fahrenheit (°F) as follows:

°F=1.8 × °C+32.

Specific conductance is given in microsiemens per centimeter at 25 degrees Celsius 

(μS/cm at 25 °C).

Concentrations: Chemical constituents in water are given either in milligrams per liter (mg/L) or 

micrograms per liter (μg/L). Chlorofluorocarbon concentrations are given in picograms per kilogram 

of water (pg/kg). Concentrations of tritium are given in tritium units (TU). Concentrations of carbon14 are expressed as percent modern carbon (pmc). Isotopic ratios are expressed as per mil, or parts per 

thousand.

Molar concentration units (millimoles or micromoles) are used in discussion of chemical reaction 

stoichiometry. Molar concentrations are computed as mass of solute divided by formula mass weight 

of solute per liter of solution. 

DATUMS

Vertical coordinate information was referenced to the National Geodetic Vertical Datum of 1929 

(NGVD29).

Horizontal coordinate information was referenced to the North American Datum of 1927 (NAD27).

Multiply By To obtain

foot (ft) 0.3048 meter

gallon per minute (gal/min) 0.06309 liter per second

inch (in.) 2.54 centimeter

inch (in.) 25.4 millimeter

inch per year (in/yr) 2.54 centimeters per year

mile (mi) 1.609 kilometer

picoCurie per liter (pCi/L) 0.037 becquerel per liter 

square mile (mi2) 2.590 square kilometer 

tritium unit (TU) 3.2 picoCurie per liter
Abstract 1

Estimates of Residence Time and Related Variations in 

Quality of Ground Water Beneath Submarine Base 

Bangor and Vicinity, Kitsap County, Washington

By S.E. Cox

ABSTRACT

Estimates of residence time of ground water 

beneath Submarine Base Bangor and vicinity ranged 

from less than 50 to 4,550 years before present, based 

on analysis of the environmental tracers tritium, 

chlorofluorocarbons (CFCs), and carbon-14 (14C), in 

33 ground-water samples collected from wells tapping 

the ground-water system. The concentrations of 

multiple environmental tracers tritium, CFCs, and 14C 

were used to classify ground water as modern 

(recharged after 1953), pre-modern (recharged prior to 

1953), or indeterminate. Estimates of the residence 

time of pre-modern ground water were based on 

evaluation of 14C of dissolved inorganic carbon present 

in ground water using geochemical mass-transfer 

modeling to account for the interactions of the carbon 

in ground water with carbon of the aquifer sediments. 

Ground-water samples were obtained from two 

extensive aquifers and from permeable interbeds within 

the thick confining unit separating the sampled 

aquifers. Estimates of ground-water residence time for 

all ground-water samples from the shallow aquifer 

were less than 45 years and were classified as modern. 

Estimates of the residence time of ground water in the 

permeable interbeds within the confining unit ranged 

from modern to 4,200 years and varied spatially. Near 

the recharge area, residence times in the permeable 

interbeds typically were less than 800 years, whereas 

near the discharge area residence times were in excess 

of several thousand years. In the deeper aquifers, 

estimates of ground-water residence times typically 

were several thousand years but ranged from modern to 

4,550 years. These estimates of ground-water residence 

time based on 14C were often larger than estimates of 

ground-water residence time developed by particletracking analysis using a ground-water flow model. 

There were large uncertainties—on the order of 1,000-

2,000 years—in the estimates based on 14C. Modern 

ground-water tracers found in some samples from 

large-capacity production wells screened in the deeper 

aquifer may be the result of preferential ground-water 

pathways or induced downward flow caused by 

pumping stress. 

Spatial variations in water quality were used to 

develop a conceptual model of chemical evolution of 

ground water. Stable isotope ratios of deuterium and 

oxygen-18 in the 33 ground-water samples were 

similar, indicating similar climatic conditions and 

source of precipitation recharge for all of the sampled 

ground water. Oxidation of organic matter and mineral 

dissolution increased the concentrations of dissolved 

inorganic carbon and common ions in downgradient 

ground waters. However, the largest concentrations 

were not found near areas of ground-water discharge, 

but at intermediate locations where organic carbon 

concentrations were greatest. Dissolved methane, 

derived from microbial methanogenesis, was present in 

some ground waters. Methanogenesis resulted in 

substantial alteration of the carbon isotopic 

composition of ground water. 

The NETPATH geochemical model code was 

used to model mass-transfers of carbon affecting the 

14C estimate of ground-water residence time. Carbon 

sources in ground water include dispersed particulate 

organic matter present in the confining unit separating 

the two aquifers and methane present in some ground 

water. Carbonate minerals were not observed in the 

lithologic material of the ground-water system but may 

be present, because they have been found in the 

bedrock of stream drainages that contribute sediment to 

the study area. 
2 Estimates of Residence Time and Related Variations in Quality of Ground Water Beneath SUBASE Bangor and Vicinity, Kitsap County, Washington

INTRODUCTION

Naval Submarine Base Bangor (SUBASE 

Bangor) is a U.S. Navy installation of approximately 

11 mi2 (square miles) that has been in operation since 

1944. It is located along Hood Canal in Kitsap County, 

Washington (fig. 1). Ground water from a multilayered aquifer system is the principal source of water 

for SUBASE Bangor and the surrounding area. A 

steady increase in the residential population of the area 

has resulted in increased awareness of the potential for 

contamination and increased pressure for the 

development of additional ground-water supplies. 

Historical military-industrial activities at SUBASE 

Bangor have resulted in contamination of shallow 

ground water and soil at many locations within the base 

area. Contaminants include ordnance compounds, 

metals, chlorinated organics compounds, petroleum 

hydrocarbons, and pesticides. As of 2000, remediation 

and cleanup have taken place or are in progress at all of 

the previously identified contaminated locations at 

SUBASE Bangor. 

The U.S. Navy Engineering Field Activity 

Northwest (EFANW), Naval Facilities Engineering 

Command, recognized that understanding the regional 

ground-water flow system beneath SUBASE Bangor 

was important to understanding the potential 

movement of contaminants within the multi-layered 

ground-water system. In 1993, EFANW, in cooperation 

with the U.S. Geological Survey (USGS), began an 

investigation of the hydrology and water quality of 

SUBASE Bangor and its vicinity. Reports have been 

published on four aspects of the investigation: 

hydrogeology of the study area (Kahle, 1998); ambient 

quality of ground water (Greene, 1997); recharge to the 

shallow aquifer (Bidlake and Payne, 2001); and a threedimensional numerical simulation of ground-water 

flow (van Heeswijk and Smith, 2002). The study in this 

report focused on estimating the residence time of 

water at various locations in the ground-water system 

of the study area. 

Purpose and Scope

The purpose of this report is to estimate the 

residence time of ground water at locations within the 

regional ground-water system beneath SUBASE 

Bangor and vicinity. The estimates of ground-water 

residence time will provide information on the duration 

of ground-water flow between the points of recharge 

and discharge. The estimates of ground-water 

residence times were based on the concentration of 

selected environmental tracers measured in groundwater samples obtained from existing wells that were 

located along inferred flow paths between areas of 

ground-water recharge and discharge. The 

environmental tracers used to estimate ground-water 

residences times were atmospheric components that 

enter ground water as dissolved gases at the point of 

recharge. To estimate ground-water residence times, 

the concentrations of these dissolved constituents were 

measured in the ground-water samples and related to 

historical atmospheric concentrations indicative of the 

time of recharge. The results of this study were used as 

one of several parameters to calibrate a numerical 

simulation model of ground-water flow within the 

study area (van Heeswijk and Smith, 2002). 

Water samples were collected from 33 wells in 

the area to determine the concentrations of a 

combination of environmental tracers, including 

carbon-14 (14C), tritium, and chlorofluorocarbons 

(CFCs), as well as the concentrations of major ions, 

isotopic ratios of deuterium, oxygen-18 (18O), and 

carbon-13 (13C), and the physical properties 

temperature, oxidation-reduction potential (ORP), and 

specific conductance. Results of the analyses of 

environmental tracers and isotope ratios were used to 

classify the age of ground water at various locations as 

pre-modern, modern, or indeterminate. Results of the 

analysis of major ions in water samples were used to 

develop a conceptual model of water-quality variations 

along ground-water flow paths, which was then used to 

guide and constrain the geochemical model used to 

interpret the 14C data.
Introduction 3

WASHINGTON

BRITISH COLUMBIA

Figure location

Olympic

Mountains Cascade

Range

0 5 MILES

0 5 KILOMETERS

200

Base map modified from

U.S. Geological Survey digital data, 1:24,000

Universal Transverse Mercator projection,

Zone 10

400

200 200

400

400

200

400

400

200

200

400

200

200

400

600

400

400

200

400

200

400

200

400

200

400

200

400

200

400

200

400

200

200

200

200

200

200

200

200

200

200

200

200

200

200

200

200

200

200

200

200

200

200

200

600

TOANDOS PENINSULA

ISLAND

KITSAP COUNTY

COUNTY

SUBASE

Bangor

JEFFFERSON COUNTY

Port

Gamble

Kingston

Poulsbo

Silverdale

Seabeck

BAINBRIDGE

ISLAND

KITSAP PENINSULA

Delta

Pier

KITSAP COUNTY

Bremerton

PUGET

SOUND

DABOB BAY

HOOD CANAL

DYES

INLET

LIBERTYBAY

PORT ORCHARD

R.2 E.

122°44' 122°34'

R.1 W R.1 E.

T.

27

N.

T.

28

N.

T.

26

N.

T.

25

N.

T.

24

N.

EXPLANATION

PUGET SOUND LOWLAND

BOUNDARY OF SUBASE BANGOR

BOUNDARY OF STUDY AREA

TOPOGRAPHIC CONTOUR, IN FEET–

Contour interval is 200 feet. Vertical

datum is NGVD of 1929

400

47°50'

47°40'

Dogfish Creek

Clear Creek

Figure 1. Location of the study area, SUBASE Bangor and vicinity, Kitsap County, Washington.
4 Estimates of Residence Time and Related Variations in Quality of Ground Water Beneath SUBASE Bangor and Vicinity, Kitsap County, Washington

Description of Study Area

The project study area includes SUBASE Bangor 

(about 11 mi2) and roughly 65 mi2 of the adjacent area 

on the western half of the Kitsap Peninsula (fig. 1). The 

study area boundaries were selected to include 

hydrologic boundaries to be used in the numerical 

simulation of ground-water flow. The Kitsap Peninsula 

extends into Puget Sound, with Hood Canal to the west 

and Puget Sound to the north and east. Hood Canal, 

along which SUBASE Bangor is located, is a U-shaped 

fjord with steep flanks rising abruptly from the coast to 

altitudes of 200 ft above sea level or more. Inland, 

slopes are moderate and many areas are nearly flat. 

Maximum altitudes in the interior of the peninsula are 

less than 500 ft. Streams flow only a short distance 

from the interior of the peninsula before reaching the 

marine waters of Hood Canal or Puget Sound. About 

13 percent of the area is built up as urban or military 

development and about 47 percent of the study area is 

covered with coniferous and deciduous forests. The 

remaining 40 percent of the study area is covered by 

non-forest vegetation including agricultural lands and 

natural vegetative shrub cover. The geology of the 

study area is characterized by glacial and nonglacial 

sedimentary deposits forming alternating beds of more 

permeable and less permeable sediments that range in 

total thickness from 600 to 1,800 ft (Jones, 1996). 

Glacial deposits include primarily tills, outwash fluvial 

sands and gravels, and lacustrine silt-clay deposits. 

Non-glacial deposits include floodplain deposits that 

often include peat and buried soils.

Compared to the rest of the Puget Sound region, 

the Kitsap Peninsula is largely undeveloped. The 

population of the study area is concentrated in the two 

medium-sized towns of Silverdale and Poulsbo, with 

1990 populations of 7,660 and 4,848, respectively 

(U.S. Bureau of the Census, 1992). The resident 

population of SUBASE Bangor was 2,830 in 1993. 

Outside these areas, the countryside is rural and semirural, with many homes obtaining potable water from 

private wells instead of public-supply systems. From 

1970 to 1990, the population of Silverdale and Poulsbo 

increased by about 150 percent. The increase in 

population is expected to continue, with growth from 

about 39,000 inhabitants in 1990 to about 76,000 in 

2020 (Puget Sound Council of Governments, 1988; 

U.S. Bureau of the Census, 1992). The population of 

SUBASE Bangor has been projected to increase to 

6,372 in 2012, as additional residential housing is 

constructed on base (Parametrix, 1994). 

The study area has a temperate maritime climate. 

Mean annual precipitation ranges from approximately 

30 in/yr (inches per year) in the northeastern part of the 

study area to approximately 60 in/yr in the 

southwestern part (Kitsap County Ground Water 

Advisory Committee and others, 1991). Precipitation 

amounts are controlled in large part by the Olympic 

Mountains to the west and the Cascade Range to the 

east, which impede the flow of humid air masses 

generated over the Pacific Ocean. In general, 

precipitation reaches a minimum during mid-summer 

(July through August) and a maximum during the late 

fall and early winter (November through January). The 

mean monthly temperature in the study area ranges 

from approximately 39°F (degrees Fahrenheit) in 

January to 64°F in July and August (Owenby and Ezell, 

1992). At times, winter temperatures are sufficiently 

cold that several inches of snow may accumulate; 

however, snow accumulation generally is not 

significant.

 Precipitation is the source of all surface and 

ground water in the study area. Short streams flow 

from the interior of the peninsula to the Hood Canal or 

the larger drainages of Clear and Dogfish Creeks, 

which drain to Puget Sound. Most streams flow yearround and are fed by springs, aquifer discharge, and 

surface runoff following storms. Where cliffs are 

present along the coastline, springs and seeps discharge 

water directly onto the beach and into Puget Sound. 

The fraction of the annual amount of precipitation that 

infiltrates through the soil to reach the ground-water 

system is recharge. The amount of recharge varies 

spatially because of differences in the amount of 

precipitation, soil and geological characteristics, landuse practices, and vegetation. Estimated long-term 

average recharge to the shallow aquifers of the study 

area typically range from 8 to 10 in/yr, but can range 

from 0 to about 21 in/yr (Bidlake and Payne, 2001). 

Deeper aquifers are recharged by ground water from 

the overlying aquifers. Roughly 40 percent of recharge 

to the shallow aquifer passes through to recharge 

deeper aquifers (van Heeswijk and Smith, 2002). The 

direction of ground-water flow on the peninsula is 

primarily toward coastal areas, particularly in the 

deeper aquifers, however, in shallow parts of the flow 

system, ground-water flow is toward Hood Canal and 

the interior drainages of Dogfish and Clear Creeks. 

Most ground water within the study area discharges to 

Hood Canal.
Introduction 5

Previous regional studies of the ground-water 

quality in Kitsap County characterized the quality of 

ground water as good and suitable for most uses, 

although concentrations of iron and manganese were 

found to exceed secondary guidelines in some wells 

(Garling and others, 1965). Van Denburgh (1965) 

found that ground water from the Sea-level aquifer 

(referred to as Salmon Springs in his report) contained 

distinctly larger concentrations of potassium and 

orthophosphate than those found in near-surface glacial 

sediments. Concentrations of silica also generally were 

larger in ground water from the deeper sediments. 

The larger concentrations were attributed to longer 

periods of contact with the host rock material. More 

recently, as part of this study, Greene (1997) sampled 

136 wells to determine ambient background 

concentrations of numerous inorganic and organic 

constituents; the median concentrations of selected 

constituents from that study are listed in table 1.

Table 1. Median values of physical properties and concentrations of water-quality constituents in ground water from five hydrogeologic units, SUBASE 

Bangor and vicinity, Kitsap County, Washington

[Median concentrations are from Greene (1997) and are given in milligrams per liter, unless otherwise noted. Hydrogeologic units: Number of samples 

from each unit is noted in parentheses. Qvt, Vashon till confining unit; Qva, Vashon aquifer; QC1pi, permeable interbeds within Upper confining unit; QC1, 

Upper confining unit; QA1, Sea-level aquifer. Abbreviations: °C, degrees Celsius; μS/cm, microsiemens per centimeter at 25 degrees C; mg/L, milligrams 

per liter; –, no data]

Physical properties and 

water-quality constituents

Median values and concentrations by hydrogeologic unit

Qvt 

(3)

Qva 

(54)

QC1pi 

(34)

QC1 

(16)

QA1 

(29)

Temperature (°C) – 10.8 9.6 11.5 –

Specific conductance, field (μS/cm) 172 151 158 161 157

pH, field (units) 6.7 7.6 7.9 8.0 8.1

Dissolved oxygen 5.6 6.3 .4 .6 1.2

Alkalinity, as CaCO3 45 190 75 230 –

Hardness, as CaCO3 85 68 130 26 –

Calcium, dissolved 14 11 14 15 15

Magnesium, dissolved 10 8.0 7.8 7.8 6.8

Sodium, dissolved 5.0 4.6 5.2 6.10 5.5

Potassium, dissolved .6 .8 1.3 1.1 1.4

Bicarbonate, dissolved 97 80 92 94 96

Sulfate, dissolved 4.2 3.9 1.6 3.2 1.8

Chloride, dissolved 2.8 2.5 2.1 2.3 1.9

Fluoride, dissolved <.1 <.1 <.1 <.1 <.1

Silica, dissolved 29 28 30 30 26

Iron, dissolved .029 .010 .038 .042 .018

Manganese, dissolved <.001 .001 .038 .043 .014

Ammonium-N, dissolved .02 <.15 .04 .04 .08

Nitrite-N, dissolved <.01 <.01 <.01 <.01 <.01

Nitrate + nitrite-N, dissolved .73 .19 <.05 <.05 <.05

Phosphate-PO4, dissolved .02 .04 .08 .09 .12

Aluminum, dissolved <.01 <.01 <.01 <.01 <.01

Boron, dissolved .008 .005 .008 .005 .010

Bromide, dissolved .02 .01 .01 .02 .02

Lithium, dissolved <.004 <.004 <.004 <.004 <.004

Strontium, dissolved .093 .053 .056 .070 .061
6 Estimates of Residence Time and Related Variations in Quality of Ground Water Beneath SUBASE Bangor and Vicinity, Kitsap County, Washington

Volatile organic compounds, indicative of 

anthropogenic land-use activities, were detected in two 

of the wells sampled by Greene (1997). Localized 

studies related to cleanup of contaminated sites on 

SUBASE Bangor have documented the presence of 

anthropogenic contaminants in the shallow aquifer at 

some sites. Direct information regarding estimates of 

ground-water residence time was not found in previous 

water-quality investigations; however, the presence in 

ground water of anthropogenic contaminants related to 

land-use activities of the past 50 years indicates that the 

age of shallow ground water is less than 50 years. 

Well-Numbering System

In Washington, wells are assigned local well 

identification numbers based on their location with 

respect to the Willamette Base Line and Meridian using 

the Public Land Survey system of township, range, 

section, and 40-acre tract (fig. 2). Well number 

26N/01E-12Q01 indicates that the well is in the 

southwest quarter of the southeast quarter of section 12 

in township 26 North (N) and range 1 East (E) of the 

Willamette Base Line and Meridian. The two-digit 

sequence number (01) following the letter designation 

indicates that this was the first well inventoried by 

USGS personal in that 40-acre parcel; in situations 

where a well has been deepened, a “D” is added at the 

end of the local well number. 

Acknowledgments

The author thanks the many private well owners 

in the study area who allowed access to their wells to 

measure water levels and sample for water quality. 

Martin B. Sebren, Kitsap County Public Utilities 

District (KPUD) No. 1, provided access to KPUD wells 

for sampling and provided lithologic samples from 

wells drilled by KPUD. Arthur K. Schick, Beverly A. 

Pavlicek, and Patricia L. Kelly, all with SUBASE 

Bangor, provided data, assisted in the acquisition of 

data, and helped with field logistics.

William Steinkampf, Neil Plummer, and David 

Parkhurst provided valuable discussion during the 

interpretation of this data. 

Q

D C B A

E FGH

6 5 4 3 2 1

7

18

19

30

32 33 34 35 36

12

13

24

25

R. 1 E.

31

M L K J

NP R

Willamette Meridian

Willamette Base Line

WASHINGTON

26 N/01E-12Q01

SECTION 12

T.

26

N.

Figure 2. Well-numbering system used in Washington.
Background Concepts on Age-Dating of Ground Water 7

BACKGROUND CONCEPTS ON AGEDATING OF GROUND WATER

Nearly all ground-water recharge is derived from 

atmospheric precipitation containing dilute 

concentrations of many constituents that are present in 

the atmosphere. Several atmospherically derived 

ground-water constituents, including carbon dioxide, 

CFCs, and tritium, can function as a record of groundwater recharge. Each of these indicators can be used to 

assess ground-water age if the initial concentration is 

known and the chemical reactions and physical 

processes affecting its concentration within the groundwater system are understood and can be predicted. The 

residence time of ground water, also referred to as the 

age of ground water, typically implies the elapsed time 

between ground-water recharge and the time when the 

ground-water sample was collected. More specifically, 

ground-water residence time begins at the point when 

recharging ground waters are isolated from the earth's 

atmosphere. In relatively shallow ground-water 

systems, this typically occurs at or just below the water 

table.

The atmospheric components used as 

environmental tracers to estimate the residence time of 

ground water in this study were 14C (contained in 

carbon dioxide), tritium, and a suite of three CFCs. 

Tritium and CFCs are present in ground water largely 

as a result of human activity during the last 40 to 50 

years. Therefore, the presence of tritium and CFCs in 

ground water indicates that recharge had occurred 

within the last half-century, and these ground waters 

are referred to young or “modern.” Estimates of 

ground-water ages of older, or “pre-modern” ground 

waters can be made using 14C. Under optimal 

conditions, 14C determinations can provide estimates 

of ground-water residence times roughly between 500 

and 35,000 years. Analytical procedures are not 

routinely available to quantify tracers that could be 

used to estimate ground-water ages in the range of 50 

to 500 years (Plummer and others, 1993).

All methods that use environmental tracers to 

estimate the elapsed time between ground-water 

recharge and sample collection involve a number of 

underlying assumptions regarding both the regional or 

global input of the environmental tracers into the 

ground-water system and the physical, chemical, and 

biological processes that act on the tracer as it moves 

through the ground-water system. Estimates of groundwater age typically require extensive interpretation of 

the tracer-concentration data, and the resulting 

estimated residence time should not be considered as a 

true age but more appropriately as a “model age” 

(Plummer and others, 1993) or as a “ground-water 

mean residence time” (Clark and Fritz, 1997). In this 

report, “model age” is used to indicate the estimate of 

the average elapsed time between ground-water 

recharge and the time when the ground-water sample 

was collected, and is based on the interpretation of the 

tracer concentrations and ancillary data. 

Tritium 

Tritium, the radioactive isotope (3H) of the 

element hydrogen, is an excellent tracer of ground 

water because it is incorporated into water molecules of 

rainfall that recharges ground water, and its movement 

within the ground-water system is not restricted by 

chemical or physical processes. Tritium is continually 

produced in small quantities in the upper atmosphere 

by the interaction of cosmic rays with gaseous 

nitrogen. However, its importance as a ground-water 

tracer is due largely to the tremendous amounts of 

tritium that were produced in the atmosphere as a result 

of the above-ground testing of thermonuclear weapons 

between 1952 and 1980. The cessation of large-scale 

atmospheric testing of nuclear weapons in 1962 was 

followed by a spike in atmospheric tritium 

concentration in 1963 that was several hundred times 

larger than natural background concentrations. The 

half-life of tritium is 12.4 years, and elevated tritium 

concentrations have persisted in the atmosphere for 

many decades following the cessation of atmospheric 

nuclear weapons testing. The atmospheric 

concentration of tritium in western Washington was 

estimated to range from 3 to 5 TU (tritium units) prior 

to nuclear weapons testing (Thatcher, 1962). 

Radioactive decay over a period of 40 years would 

have reduced that concentration to about 0.3 to 0.5 TU. 
8 Estimates of Residence Time and Related Variations in Quality of Ground Water Beneath SUBASE Bangor and Vicinity, Kitsap County, Washington

Thus, the presence of tritium in ground-water samples 

at concentrations greater than 1 TU indicates that the 

ground water was recharged after the start of 

atmospheric testing of thermonuclear weapons. 

Atmospheric tritium from weapons testing (often 

referred to as bomb tritium) continues to decay, and 

tritium concentrations in present-day rainfall are still 

distinguishable from tritium concentrations in ground 

water recharged prior to the period of bomb testing. 

 The absence of tritium in ground-water samples 

clearly indicates recharge prior to the period of bomb 

testing. Such ground water is designated either as premodern or older ground water. Conversely, ground 

water containing tritium concentrations greater than 1 

TU is considered modern or young. Ground water 

containing tritium concentrations between the 

detection limit and 1 TU may be considered to have 

been recharged prior to the bomb testing period 

(Mazor, 1991) or is predominantly older water that may 

have mixed with a smaller fraction of modern ground 

water recharged after 1953 (Clark and Fritz, 1997), and 

is referred to as indeterminate in this report. Mixing 

can take place either in the aquifer along converging 

ground-water flow paths, within the well bore, as an 

artifact of well construction, or by diffusion from 

adjacent confining units (Goode, 1996). 

Chlorofluorocarbons

CFCs are a class of synthetic organic compounds 

that are thought to be entirely of anthropogenic origin, 

and when present in ground water can be used to 

estimate ground-water residence time (Plummer and 

Busenberg, 2000). Production of CFCs began in the 

1930s and their primary use was as refrigerants, but 

they also have a variety of other uses. Ultimately, CFCs 

are released to the atmosphere, where the 

concentrations of chlorotrifluoromethane (CFC-11), 

dichlorodifluoromethane (CFC-12), and 

trichloro-trifluoroethane (CFC-113) can be detected. A 

record of the atmospheric concentrations of these CFCs 

has been developed from measurements made at Niwot 

Ridge, Colo., and from CFC production records. 

Concentrations of CFC-11 and CFC-113 in the 

atmosphere have increased steadily from their earliest 

detections until peak concentrations were reached in 

1993 and 1994, respectively, whereas concentrations of 

CFC-12 were still increasing in 1994 and 1995 when 

the samples were collected for this study. CFCs in the 

atmosphere can dissolve into falling precipitation or 

into soil moisture in the unsaturated zone and thereby 

impart a signal in the ground water of the time of 

recharge. The measured concentrations of CFCs in a 

ground-water sample can be used to calculate the 

corresponding equilibrium vapor concentrations 

(using Henry's Law) that can be compared to historical 

atmospheric concentrations to determine the recharge 

date. The concentration of individual CFCs and the 

mixture of specific CFCs thus can be used to 

date some ground waters that recharged after 1940. 

Concentrations of CFCs in ground water that are larger 

than those corresponding to maximum atmospheric 

concentrations indicate additional CFC sources, such 

as landfills, abandoned refrigerators, and air 

conditioners leaking directly into the aquifer, as well as 

recharge from sanitary septic systems. Although these 

larger concentrations exceeded the range from which 

reliable estimates of ground-water residence time can 

be derived, they generally are orders of magnitude 

smaller than concentrations cited as drinking-water or 

aquatic-health guidelines. 

Carbon-14

14C is the radioactive isotope of carbon, and its 

concentration in ground water, in the form of dissolved 

inorganic carbon, has been used routinely since 1970 to 

estimate the age of ground water. 14C is produced 

continuously in the upper atmosphere by the 

interactions of nitrogen and cosmic rays. 14C-carbon 

dioxide (14CO2) can enter ground water while recharge 

water is in contact with the atmosphere, occurring 

mostly in the unsaturated zone where the gaseous 

concentration of 14CO2 is substantially increased by 

root respiration and microbial oxidation of organic 

matter. 
Hydrogeologic System 9

Once recharge water enters the aquifer at the 

water table and becomes isolated from the atmosphere 

as a result of downward flow, 14C in ground water will 

diminish due to radioactive decay at a rate of one-half 

of the remaining carbon every 5,730 years. 14C age 

estimates generally are expressed in terms of years 

before present (bp), whereas the concentration of 14C 

in ground water is expressed as percent modern carbon 

(pmc). By convention, the concentration of “modern 

carbon” is defined as 13.56 disintegrations per minute 

per gram carbon and is assigned an initial date of 1950 

(Mook, 1980; Kalin, 2000). The selection of 1950 is 

due in part to the injection of large concentrations of 

14C into the atmosphere following the atmospheric 

testing of nuclear weapons. Concentrations of 14C in 

ground water recharged after the advent of nuclear 

weapons testing in 1950 often are larger than 100 pmc 

and are often referred to as containing bomb carbon. 

A 14C ground-water age is computed from the 

half-life age equation derived from the radiometric 

decay equation written in the form: 

T = -5,730/ln2 * ln{At

14C/Ao14C}, (1)

where

Direct application of this equation involves two 

key assumptions that may in fact not be true, 

particularly for recently recharged ground water. The 

first assumption is that Ao

14C is known and has 

remained constant. The second is that carbon does not 

enter or leave ground water other than by radioactive 

decay. Because both of these assumptions often are not 

accurate, the difficulty in applying radio-carbon dating 

to ground water is in determining the extent to which 

physical, chemical, and biological processes have 

affected the 14C content of ground water in the 

upgradient (recharge) area and along the ground-water 

flow path to the sampled well.

To provide better approximations of groundwater residence time based on 14C concentrations of 

dissolved inorganic carbon, a variety of models have 

been developed to account for geochemical processes 

that affect the 14C concentrations in ground water. 

Typically, these models estimate the mass of carbonate 

and organic carbon that accumulates in ground water as 

it moves through the hydrogeologic system. Essential 

to all of these models are the assumptions relating to 

the temporal consistency of the 14C activity at the time 

of recharge and to the origin of the carbon added to or 

removed from ground water along the flow path. 

Examples of such models include those of Ingerson 

and Pearson (1964), Tamers (1967), Mook (1976), 

Wigley and others (1978, 1979), and Fontes and 

Garnier (1979). In this study, the stable isotope of 

carbon, carbon-13 (13C), and ancillary chemical data 

from the ground-water samples are used to estimate the 

extent to which chemical and microbial processes have 

affected the 14C concentration through the use of 

NETPATH, an inverse geochemical mass-transfer 

modeling approach developed by Plummer and others 

(1991, 1996). 

HYDROGEOLOGIC SYSTEM

Ground water beneath the study area is found in 

a series of aquifers composed of permeable sand and 

gravel layers separated by layers of less permeable 

deposits of silt, sand, and clay (fig. 3). The movement 

of ground water is controlled by recharge, topographic 

geometry, and the hydraulic properties of the 

sedimentary material. Generally, ground water moves 

from areas of topographic highs to topographic lows 

along the coast or stream drainages. The direction of 

ground-water flow may be upward in ground-water 

discharge zones along the coast and stream drainages. 

Typically, the direction of ground-water flow in 

permeable aquifer layers approaches horizontal, 

whereas flow in the semi-confining and confining units 

is closer to vertical. Estimates of long-term average 

ground-water recharge in most of the study area range 

from 8 to 10 in/yr (Bidlake and Payne, 2001). The 

unsaturated zone between land surface and the water 

table is typically 60 to 80 ft in the higher altitudes near 

the central part of the study area and much smaller near 

areas of ground-water discharge. 

5,730 = the half-life of 14C, in years,

At

14C = the measured 14C activity in the 

downgradient well, and

Ao

14C = the 14C activity in the upgradient 

well or recharge area.
10 Estimates of Residence Time and Related Variations in Quality of Ground Water Beneath SUBASE Bangor and Vicinity, Kitsap County, Washington

The hydrogeologic framework of the study area 

is dominated by a thick accumulation of glacial and 

non-glacial sediments that have been deposited over the 

last several hundred thousand years, resulting in a 

sequence of alternating coarse (permeable) and finegrained (less permeable) deposits that partially fill the 

regional north-south structural depression referred to as 

the Puget Sound Lowland. In the area of SUBASE 

Bangor, the thickness of these sediments is typically 

greater than 1,000 ft (Jones, 1996). Except for the 

sediments deposited by the last receding glacier, 

sediments in the study area were overridden and 

compacted by more than 3,000 ft of ice during the last 

glacial maximum (Booth and Goldstein, 1994). 

During successive periods of continental 

glaciation, glacial sediments were transported to and 

deposited within the Puget Sound Lowland by 

southward-moving glaciers and outwash streams. The 

sedimentary material originated largely from the 

metamorphic and granitic terrains of the North 

Cascades and British Columbia Coast Mountains. 

NOT TO SCALE

WEST EAST SUBASE Bangor Hood Canal Clear Creek Drainage

Qvt

QC1

QC1

QC

QC QC

QC

SEA LEVEL

QU

Qvt

Qva

Qvr Qva

QC1pi

QC1pi

QA2

QA1

Br

PERMEABLE UNITS LESS PERMEABLE UNITS

QC1 Upper confining unit

Qvr Surficial aquifer Qvt Vashon till confining unit

Qva Vashon aquifer

QA1 Sea-level aquifer

QC1pi Permeable interbeds within QC Undifferentiated confining units

Upper confining unit

QA2 Deep aquifer

CONCEPTUALIZED GROUND-WATER

FLOW PATH

Br Bedrock

QU Undifferentiated deposits

EXPLANATION

Figure 3. Conceptual model of hydrogeologic units and ground-water flow in the vicinity of SUBASE Bangor, Kitsap County, Washington.

(Modified from Kahle, 1998.)
Hydrogeologic System 11

These glacial deposits generally consist of sands and 

gravels, lacustrine silts and clay, and till. Outwash 

sand-and-gravel deposits typically are permeable and 

make excellent aquifers. In contrast, glacial tills and 

lacustrine deposits of silts and clay are much less 

permeable and act as confining units. Grain-size 

distributions in these glacial deposits are often 

heterogeneous, creating stratigraphic irregularities that 

affect the flow of ground water. Lenses of fine-grained 

sediments present in the outwash sands and gravels 

often reduce or divert the flow of ground water. 

Conversely, within the fine-grained sediment of the 

confining units are lenses of coarse-grained sediments 

of sufficient extent and permeability to provide 

quantities of ground water for domestic wells.

Non-glacial sediments were deposited in the 

Puget Sound Lowland during periods when continental 

glaciers were absent. These sediments consist largely 

of low-energy floodplain deposits, but in some areas 

may also contain sands and gravels characteristic of 

alluvial fans. The non-glacial sediments originated 

from streams and rivers draining the adjacent Olympic 

and Cascade uplands, which border the Puget Sound 

Lowland on the west and east. Near the study area, 

patterns of sedimentary cross bedding in the nonglacial sediments indicate a southwest-to-northeast 

pattern, suggesting flow from the Olympic Mountains 

(Borden, 1998). The sedimentary material from the 

Olympic Mountains was characterized as basalt, 

graywacke, and argillite, whereas andesite and 

metavolcanics were more characteristic of Cascade 

uplands (Borden and Troost, 2001). Alpine glaciers 

originating in the Cascade and Olympic Mountains are 

thought to have been most active and extended farthest 

into the Puget Sound Lowland in the period just prior to 

the arrival of each successive continental glacier. 

The description of stratigraphy of the upper half 

of this complex sequence of sediments in the Bangor 

area has been refined by the studies by Noble (1989 

and 1990), Becker (1995a), Borden (1998), and Kahle 

(1998). The stratigraphy and hydrogeologic units used 

in this report (fig. 3) are those described by Kahle 

(1998). The additional lithologic and mineralogic 

descriptions provided below are useful in 

understanding the geochemical mass-transfer models.

Vashon Till Confining Unit

 The uppermost subglacial lodgement till is 

referred to as the Vashon till confining unit (Qvt), and 

its surficial exposure covers about 71 percent of the 

study area (Kahle, 1998). Recessional outwash (Qvr, 

called the Shallow aquifer by Kahle) covers an 

additional 14 percent of the area, some of which may 

also overlay the Qvt. The Vashon till is a pebbly and 

silty sand with roughly 10 to 20 percent clay-sized 

fragments (Vanderwal, 1985). Although the 

permeability of this till is typically very low (10-7 to 

10-5 centimeters per second), more-permeable lenses 

are interspersed within the till and can yield small 

quantities of water. Thickness of the till ranges from 0 

to greater than 200 ft, but is typically 10 to 100 ft.

 Petrologic examination of rock clasts obtained 

from the Vashon till at sites throughout the Puget 

Sound Lowland indicate that nearly 60 percent of the 

clasts found in the till were of metamorphic origin, and 

the remaining clast were of granitic, volcanic, or clastic 

origins (Vanderwal, 1985). Clasts from sites near the 

Bangor study area were classified as 63 percent 

metamorphic, 14 percent clastic sedimentary rocks, 12 

percent granitic, 7 percent andesitic volcanics, 3 

percent chert, and 2 percent basaltic volcanics 

(Vanderwal, 1985). Mineralogical analyses of samples 

of the Vashon till collected from the eastern part of the 

Puget Sound Lowland by Mullineaux (1970) and 

Mullineaux and others (1964) show that carbonate 

minerals were rarely present in these samples. The siltsize fraction typically was 50 percent quartz and 40 

percent plagioclase with a trace of chlorite. The claysize fraction of Vashon till included 40 to 50 percent 

montmorillonite; 20 percent chlorite; 10 percent 

quartz; and 10 percent plagioclase. The heavy minerals 

identified in the 1/16 to 1/4 mm (millimeter) size 

fraction of these samples included pyroxene, 

amphibole (chiefly hornblende), garnet, and ironmagnesium minerals and rock fragments. In one 

sample, siderite (an iron-carbonate mineral) was 

measured as less than 5 percent of the heavy mineral 

fraction, or less than 1 percent of the total sample. 

There was no other mention of carbonate-bearing 

minerals except in the much deeper and older till 

deposit not encountered in the Bangor study area. 
12 Estimates of Residence Time and Related Variations in Quality of Ground Water Beneath SUBASE Bangor and Vicinity, Kitsap County, Washington

Vashon Aquifer

The Vashon aquifer (Qva) is composed of 

advance glacial outwash, which generally is a wellsorted deposit of gravelly sands with occasional lenses 

of fine-grained material. This unit occurs widely in the 

study area and typically is 10 to 150 ft thick, but can be 

as much as 250 ft thick. Within the study area, 

sediment grain size in the Vashon aquifer changes from 

fine to medium sands in the stratigraphically lower 

portions to coarse sands and gravels in the 

stratigraphically higher portions where foreset bedding 

is common (Deeter, 1979). The advance outwash is 

exposed at the surface in 11 percent of the study area 

where the Vashon till is absent. These windows through 

the till to the Vashon aquifer typically are along 

drainages or near-shore areas, although several are in 

the upland recharge areas (Kahle, 1998). 

The lithologic and mineral composition of the 

Vashon outwash deposits has not been well 

documented. Based on the similarity in sediment 

source areas, the composition of the Vashon till and 

outwash are expected to be similar. Major minerals 

identified in Vashon outwash, obtained from a surfaceexposure sample, include quartz and plagioclase, with 

minor fragments of tremolite, actinolite, microcline, 

epidote, and chlorite. Borden (1998) reported that the 

sands of the Vashon outwash are composed 

predominantly of quartz, with minor amounts of 

muscovite, and that lithic fragments make up less than 

30 percent of the grains. Likewise, gravel clasts are a 

mixture of felsic intrusive, dacite, andesite, and basalt 

and meta-volcanic sediments all of which were 

indicative of a northern source area. Schlichte (1968) 

reported that the mineralogical composition of a soil 

developed on the outwash was composed of roughly 44 

percent plagioclase, 26 percent potassium feldspar, 16 

percent quartz, and 14 percent heavy minerals, which 

were mostly pyroxenes and amphiboles. Mullineaux 

(1967) reported that quartz and feldspars composed 90 

percent of two samples of Vashon drift silt; and that the 

heavy-mineral content was primarily altered ironmagnesium minerals and rock fragments (35-50 

percent), pyroxene (22-45 percent), amphibole 

(hornblende; 5-25 percent), garnet (2-10 percent), and 

opaques (5-15 percent). Neither calcite nor siderite was 

found in any of 13 samples, nor was there reference to 

any other carbonate minerals.

Upper Confining Unit and Interbeds

A diverse group of generally low-permeability 

sediments beneath the Vashon glacial aquifer 

sediments separates the Vashon aquifer from the lower 

aquifers. Within the study area, Kahle (1998) classified 

this diverse group of sediments as a single 

hydrogeologic unit with the designation of QC1. The 

QC1 hydrogeologic unit is extensive, covering the 

entire study area. Thickness of the QC1 generally is 

between 100 and 300 ft, but may exceed 500 ft. The 

geologic stratigraphy within QC1 is complex and 

includes the Kitsap unit as described by Garling and 

others (1965), the Kitsap and Whidbey units as 

described by Deeter (1979), and the Lawton clay of 

Mullineaux and others (1964). The QC1 unit also 

contains discontinuous lenses or interbeds of gravelly 

material. Where mappable, Kahle (1998) classifies 

these gravelly deposits within the QC1 as permeable 

interbeds denoted as QC1pi. As mapped by Kahle 

(1998), the QC1pi is present in about 25 to 30 percent 

of the study area and lenses typically are about 30 ft 

thick but may exceed 100 ft thick (Kahle, 1998). The 

fine-grained sediments of the QC1 are not very 

permeable, yielding insufficient water for well 

construction. However, the interbedded gravels and 

sands (QC1pi) can be quite permeable and typically are 

capable of providing usable quantities of ground water 

for domestic supplies. Previous studies by Noble 

(1975a; 1975b) and Becker (1995a; 1995b) have 

designated these permeable interbeds in the southern 

part of the study area as the Semi-perched aquifer. 

The sedimentary composition of the QC1 is 

diverse, including deposits of glaciolacustrine silts and 

clay (Lawton clay) and lenses of fluvial gravelly sands. 

However, most of this unit is composed primarily of 

several non-glacial floodplain and lacustrine deposits 

of clayey silt and sands. Within the fine-grained 

sediments, lenses of silty peat and dispersed organic 

matter occur. Radiocarbon ages reported by Deeter 

(1979) from peat or woody material collected within 

the Bangor study area yield dates between 15,000 and 

greater than 40,000 years bp. Coarse-grained fluvial 

sediments within the non-glacial deposits, exposed in 

the sea cliffs along the coastal margin of SUBASE 

Bangor, are likely correlative with the permeable 

interbed hydrostratigraphic unit (QC1pi) described by 

Kahle (1998; U.S. Geological Survey, oral commun., 
Study Methods 13

2002). According to Borden (1998), these highly 

oxidized fluvial sediments are composed 

predominantly of thick-bedded to massive crossbedded sands, gravels, and silts. Cross-bedding features 

indicate that the direction of streamflow during 

deposition of these sediments was from southwest to 

northeast. Lithic fragments are composed 

predominantly of basalt, gabbro, and basaltic sandstone 

derived from the Crescent Formation of the western 

Olympic Mountains (Borden, 1998; Noble, 1990). The 

non-glacial gravels are lithologically very similar to 

gravels from the Quilecene, Dosewallips, and 

Duckabush Rivers, which drain the eastern flanks of 

the Olympic Mountains, further suggesting that the 

source for sediments in the QC1pi is likely the eastern 

Olympic Mountains. 

The basalts of the Crescent Formation are a thick 

accumulation of submarine and subaerial basalts with 

interbedded basaltic breccias, hyaloclastites, and minor 

fossiliferrous limestone (Glassley, 1973; Tabor and 

Cady, 1978). The basalts range in age from 45 to 58 

million years and are highly altered and, in some 

instances, mildly metamorphosed to prehnitepumpellyite and greenschist facies (Glassley, 1973). 

The mineralogy of basalts of the Crescent Formation 

was described by Glassley (1973, 1974) as typically 

composed of plagioclase and pyroxene (augite) with 

lesser amounts of glass, olivine (present in the basalts), 

iron-titanium oxides, and apatite. Submarine basalts 

have less-developed crystalline structure than subaerial 

basalts because of more rapid cooling, and are more 

highly altered to secondary minerals. Magnetite and 

ilmenite present in the original rocks have been 

extensively altered to hematite and sphene. Basaltic 

glass is absent, having been altered to secondary 

minerals such as chlorite, prehnite, and 

pumpellyite.The mineralogic composition of low-grade 

alteration of basaltic rocks is typically a mixture of 

prehnite, pumpellyite, chlorite, actinolite, albite, 

sphene, and minor amounts of carbonates. 

Sea-Level Aquifer and Deep Aquifer

Below the fine-grained non-glacial deposit of the 

Upper confining unit is a deep aquifer composed of 

fluvial sands and gravels of basaltic origin, referred to 

as the Sea-level aquifer (QA1; Noble, 1989; Becker, 

1995a, 1995b; and Kahle, 1998). The Sea-level aquifer 

produces large quantities of water to many municipal 

wells throughout the study area. Below the Sea-level 

aquifer is a discontinuous confining unit (QC), the 

Deep aquifer (QA2), and bedrock. Tertiary bedrock, 

which underlies the Pleistocene deposits, is estimated 

to be at depths ranging from about 600 to 1,800 ft 

below land surface, but typically is greater than 1,000 ft 

below land surface (Jones, 1996).

STUDY METHODS

The residence time of ground water was 

estimated at locations within the Bangor aquifer 

system, including areas of ground-water recharge and 

discharge. Sampling sites were concentrated in three 

general areas where conceptualized ground-water flow 

paths from areas of recharge to areas of discharge could 

be inferred from hydrologic and lithologic information 

contained in the reports by van Heeswijk and Smith 

(2002) and Kahle (1998). Residence times were 

estimated by comparing the concentrations of 

environmental tracers observed in ground-water 

samples from areas of ground-water recharge with 

those at downgradient locations within the groundwater flow system. The actual flow paths followed by 

ground water could not be identified, thus it was not 

possible to specifically identify upgradient and 

downgradient water chemistries. Variations in the range 

of common-ion concentrations observed in the Vashon 

aquifer (Qva) were small (Greene, 1997). Water-quality 

conditions representing recently recharged ground 

water were assumed to approximate uniform conditions 

within the Qva; thus, the median concentration of 

common ions in the Qva was used as the initial 

concentration in mass-transfer modeling used to 

interpret 14C estimates of ground-water residence time 

observed at downgradient locations. The selection of 

sampling points along an inferred flow path was 

constrained by the availability of existing wells, their 

location, and suitability for the collection of groundwater samples.
14 Estimates of Residence Time and Related Variations in Quality of Ground Water Beneath SUBASE Bangor and Vicinity, Kitsap County, Washington

Sample Collection and Processing

Ground-water samples were collected from 33 

wells in the study area (fig. 4). The location and wellconstruction information are listed in table 2. Five 

wells were sampled in June 1994 and the remainder 

were sampled in March and April 1995. Most of the 

sampled wells were located near three conceptualized 

ground-water flow paths (fig. 4). Most samples were 

collected from the Vashon aquifer (Qva), permeable 

interbeds in Upper confining unit (QC1pi), and the 

Sea-level aquifer (QA1). Access to the Sea-level 

aquifer was limited by the lack of suitable wells 

tapping this unit in the study area. Eight samples were 

obtained from the deeper aquifers, however, most of 

these were from large-capacity production wells. A 

single sample was obtained from a well screened only 

in the Deep aquifer (QA2), which occurs below the 

Sea-level aquifer. A second sample was obtained from 

a well open to both QA1 and QA2. Wells selected for 

sampling were primarily domestic wells that typically 

provide more discrete samples because of their shorter 

screen interval and lower pumping rates. However, 

several large municipal wells were sampled where 

more suitable wells were not available. Submersible 

pumps were temporarily installed in four test wells on 

SUBASE Bangor to obtain samples where no other 

pump system was available. 

Sample collection points were located as close to 

the wellheads as was practical and before passage 

through pressure tanks or water-treatment systems, 

following the procedures and guidelines outlined by 

Classen (1982). Water samples were collected after 

extensive flushing of the casing and well plumbing. A 

manifold was used to direct discharge from the well to 

raw and filtered sampling ports and to a fully enclosed 

flow chamber that prevented atmospheric contact with 

the water being analyzed. The flow chamber was used 

to make field measurements of specific conductance, 

pH, dissolved-oxygen concentration, and oxidationreduction potential (ORP). The ORP probe was 

calibrated using Zobell’s solution at 25°C as described 

by the American Public Health Association and others 

(1992). The dissolved-oxygen probe was calibrated 

using air-saturated water corrected to ambient 

atmospheric pressure. Duplicate dissolved-oxygen 

samples were collected for analysis by Winkler 

titration when the stabilized reading from the 

dissolved-oxygen probe indicated less than 1 mg/L of 

dissolved oxygen. Two-point bracketing calibration 

procedures were used to calibrate pH and specific 

conductance meters.

Raw and filtered samples were collected from 

sampling ports connected to the stainless steel 

manifold. Tritium, deuterium, and 18O samples were 

collected without head space from raw water 

discharged to sample bottles equipped with poly-cone 

seals. Alkalinity in samples, filtered through non-acid 

cleaned apparatus, was determined by incremental 

titration. Usually, the alkalinity titration was performed 

at the sampling sites; however, in some instances this 

titration was completed upon return to the office. 

Nutrient samples were collected in amber bottles, 

chilled to 4°C, and preserved with mercuric chloride. 

Samples of total organic carbon (TOC) and dissolved 

organic carbon (DOC) were chilled and stored at 4°C 

without additional preservatives. Procedures used to 

process samples for inorganic constituents are 

described by Wood (1981), with the exception that a 

0.1-micrometer filter was used rather than a 0.45-

micrometer filter. The 0.1-micrometer filter was used 

to reduce the potential that colloidal material might 

augment the dissolved concentrations reported by the 

laboratory and influence the results of the ensuing 

geochemical modeling. 

Methane samples, devoid of gas bubbles, were 

collected using a glass syringe and hypodermic needle 

through a butyl-rubber septum installed in the raw 

discharge line. Samples were stored in 60-mL 

(milliliter) serum bottles containing 0.1 milligram of 

mercuric chloride. Prior to sealing, the serum bottle 

was flushed with ultra-pure nitrogen before a septum 

was installed in a manner that minimized entrainment 

of atmospheric gases into the sample bottle. To collect 

a sample, an empty auxiliary syringe was inserted 

through the septum of the serum bottle and 10 cubic 

centimeters of nitrogen was removed to create a 

vacuum in the serum bottle. The needle of the 

collection syringe containing the ground-water 

methane sample then was inserted through the septum 

into the serum bottle. Through pressure equilibration, 

about 10 mL of sample in the sample-collection 

syringe was pulled into the serum bottle. At two sites, 

duplicate samples were taken to assess variability. 

Samples were packed on iced and refrigerated prior to 

analysis.
Study Methods 15

012

012

3 MILES

3 KILOMETERS

BOUNDARY OF STUDY AREA

BOUNDARY OF SUBASE

BANGOR

EXPLANATION

WELL AND NO.—Well

information is shown

in table 2

CONCEPTUALIZED GROUND

WATER FLOW PATH USED IN

GEOCHEMICAL MODELING

DYES

INLET

LIBERTY

BAY

HOOD CANAL

PORT

ORCHARD

Clear

Cre

ek

Dogfish Creek

22Q04

22Q05

27J02

27J01

35C01

17C01

20R01

18P06

30L01

33E01

32L05

5A04

32L04

32M01

31R01

6D04

36R03

1B02

12L02

12K04

12R02 7N02D1

12J01

7P02

7Q03

7K01 7J02 8L02

8L04

7J01 8Q03

8J02

9N02

Base map modified from

U.S. Geological Survey

digital data, 1:24,000

Universal Transverse Mercator projection

Zone 10

47°

46'

47°

40'

122°44' 122°38'

T.

27

N.

T.

26

N.

T.

25

N.

R.1 W. R.1 E. R.2 E.

Figure 4. Location of wells sampled for physical properties, dissolved constituent concentrations, and isotopes used to estimate 

residence time of ground water, and conceptualized ground-water flow paths, SUBASE Bangor and vicinity, Kitsap County, Washington.
16 Estimates of Residence Time and Related Variations in Quality of Ground Water Beneath SUBASE Bangor and Vicinity, Kitsap County, Washington

Table 2. Location of sampled wells, well-construction data, and hydrogeologic source of water, SUBASE Bangor and 

vicinity, Kitsap County, Washington

[Well No.: Location of wells is shown in figure 4. Latitude and Longitude: Degrees, minutes, and seconds. Altitudes are 

given in feet below NGVD29. Depths are given in feet below land surface. Abbreviations: gal/min, gallons per minute; 

–, no data]

Well No.

Altitude 

of static 

water level 

(feet)

Discharge 

rate 

(gal/min)

Latitude Longitude

Altitude

of land 

surface 

(feet)

Depth to 

top of open 

interval 

(feet)

Length of 

open interval 

(feet)

Vashon aquifer (Qva)

25N/01E-05A04 240 13 47 41 31 122 41 43 260 90 8

25N/01E-07J01 186 9 47 40 08 122 42 49 245 73 10

25N/01E-07K01 205 12 47 40 10 122 43 12 320 142 5

25N/01E-08L02 190 12 47 40 10 122 42 24 270 108 5

25N/01E-08L04 207 11 47 40 05 122 42 20 245 65 5

25N/01W-12R02 349 6 47 39 59 122 44 05 425 95 5

26N/01E-20R01 238 11 47 43 35 122 41 32 445 49 5

26N/01E-32M01 254 <.5 47 42 00 122 42 35 322 72 10

26N/01E-33E01 224 30 47 42 18 122 41 24 350 154 5

27N/01E-27J01 172 300 47 48 06 122 39 08 290 161 25

Upper confining unit (QC1)

26N/01E-17C01 288 0.8 47 45 04 122 42 10 340 131 5

27N/01E-35C01 120 8.5 47 47 34 122 38 21 375 342 5

Permeable interbeds within Upper confining unit (QC1pi)

25N/01E-07J02 80 8 47 40 19 122 42 47 285 255 5

25N/01E-07N02D1 115 27 47 40 04 122 44 01 425 343 15

25N/01E-07P02 108 15 47 40 03 122 43 31 315 292 5

25N/01E-07Q03 102 7 47 39 55 122 43 18 300 247 5

25N/01E-08J02 87 17 47 40 09 122 41 32 150 163 5

25N/01E-08Q03 90 16 47 40 00 122 42 01 245 260 5

25N/01E-09N02 69 30 47 39 59 122 41 25 60 79 5

25N/01W-12J01 115 11 47 40 07 122 44 03 425 355 5

25N/01W-12K04 53 40 47 40 12 122 44 40 220 199 5

26N/01E-30L01 77 100 47 42 45 122 43 33 325 316 25

27N/01E-22Q04 72 16 47 48 40 122 39 28 120 85 10

Sea-level aquifer (QA1)

25N/01E-06D04 31 18 47 41 31 122 44 00 294 270 –

25N/01W-01B02 16 9 47 41 30 122 44 35 70 114 5

25N/01W-12L02 2 12 47 40 18 122 44 53 30 81 5

26N/01E-18P06 76 550 47 44 24 122 43 28 175 324 60

26N/01E-32L05 57 300 47 42 02 122 42 11 290 392 0

26N/01W-36R03 11 6 47 41 47 122 44 17 205 276 5

27N/01E-22Q05 22 15 47 48 42 122 39 25 80 234 5

27N/01E-27J021 112 54 47 48 07 122 39 08 290 402 25

Deep aquifer (QA2)

26N/01E-31R012 27 100 47 41 39 122 42 53 410 512 65

26N/01E-32L04 62 2 47 42 01 122 42 11 285 532 15

1Well also may be open to Qva. Analysis of water-quality data indicated that ground water from well 

27N/01E-27J02 was likely from the Vashon aquifer. Subsequent efforts to repair well revealed that casing was broken. 2Well is screened in QA1 and QA2. 
Study Methods 17

The sample for both carbon isotopes (13C and 

14C) was collected in a 1-liter amber borosilicate bottle 

that had previously been baked at 450°C for at least 2 

hours to remove any organic carbon. Prior to collecting 

the sample, the bottles were flushed for at least 1 

minute with nitrogen gas flowing at about 5 liters per 

minute. The carbon-isotope water sample then was 

collected by inserting a flexible plastic tube from the 

filtered water port to the bottom of the bottle and 

allowing the bottle to overfill by at least three volumes 

before sealing with a poly-cone cap. Prior to shipping 

the carbon-isotope samples to the laboratory, 50 mL of 

sample was removed from each bottle and an 

equivalent volume of ammoniacal-strontium chloride 

was added to the sample below the water surface to 

precipitate the inorganic carbon in solution. 

Soil-gas samples were collected for 13C isotope 

analysis from four heavily forested locations on 

SUBASE Bangor. The gas samples were collected by 

driving a 1/4-inch pipe about 4 ft into the soil. A 

250-mL gas-sampling bulb was attached to the pipe 

using flexible plastic tubing. A hand pump was used to 

pull about 2 liters of soil gas through the gas-sampling 

bulb before it was closed. The soil-gas samples were 

sent to the USGS Isotope Laboratory in Reston, Va., for 

analysis.

CFC samples were collected in triplicate under 

ultra-pure nitrogen atmosphere and sealed in 

borosilicate glass ampules by fusing the neck closed 

using an actylene torch. Because there is a substantial 

potential for atmospheric contamination when 

measuring dissolved gases at the parts per quadrillion 

level (picograms per kilogram), three replicate samples 

were collected at each location and analyzed 

individually. The details of the CFC sample collection 

are described by Busenberg and Plummer (1992). 

Sample Analysis

Inorganic ions and nutrients were analyzed at the 

USGS National Water Quality Laboratory (NWQL) in 

Arvada, Colo., following the procedures outlined in 

Fishman and Friedman (1989). Tritium was analyzed at 

the University of Miami Tritium Laboratory in Miami, 

Fla., by gas counting following electrolytic enrichment 

utilizing procedures described by Ostlund and Dorsey 

(1977). Results of the tritium analysis were reported in 

picoCuries per liter (pCi/L) and converted to tritium 

units (TU): 3.2 pCi/L per TU unit. The isotopic ratios 

of deuterium and 18O were analyzed by mass 

spectrometry at the USGS Stable Isotope Laboratory in 

Reston, Va. (Epstein and Mayeda, 1953; Coplen and 

others, 1991). The isotope ratios were compared to 

Vienna-Standard Mean Ocean Water normalized to the 

ratio of Standard Light Antarctic Precipitation (Coplen, 

1994). Analytical uncertainty for the isotope 

measurements (two sigma or two standard deviations) 

is 0.2 ‰ (per mil, or parts per thousand) for the 

isotopic ratio of 18O and 2.0 ‰ for the isotopic ratio of 

deuterium. Methane determinations were performed by 

head-space gas chromatography using a flameionization detector with the associated analytical 

uncertainty of plus or minus 5 percent. 

Tandem accelerator mass-spectrometry analysis 

was used to analyze the carbon isotope composition of 

the ground-water samples following preparation of 

graphite targets. For the five samples collected in 1994, 

the entire procedure was performed at the University of 

Arizona Laboratory of Isotope Geochemistry in 

Tucson, Ariz. For the 20 14C samples collected in 

1995, the graphite target preparations and calculations 

of the 13C ratios were conducted at the University of 

Waterloo in Ontario, Canada, and the tandem 

accelerator mass-spectrometry analyses were 

performed at the IsoTrace Laboratory in Toronto, 

Canada. The 13C ratios were determined relative to the 

Peedee Belemnite (PDB) standard. The 14C results 

were reported as percent modern carbon (pmc) using 

14C standards from the National Institute of Standard 

Technology (NIST), oxalic acid I and oxalic acid II. 

The isotopic ratios of deuterium, 18O, and 13C 

are expressed in delta notation as δD, δ18O, and δ13C 

and are reported in units of per mil. Samples with 

isotopic ratios greater than the standard have positive 

delta values and are referred to as “heavy” or 

“enriched” relative to the standard. Conversely, 

samples with isotopic ratios less than the standard have 

negative delta values and are referred to as “light” or 

"depleted." Additional discussion of isotopic ratios can 

be found in reports by Clark and Fritz (1997) and Cook 

and Herczeg (2000).
18 Estimates of Residence Time and Related Variations in Quality of Ground Water Beneath SUBASE Bangor and Vicinity, Kitsap County, Washington

Analysis of CFCs were performed at the USGS 

Chlorofluorocarbon Laboratory in Reston, Va., using 

purge-and-trap gas chromatography with an electroncapture detector as described by Busenberg and 

Plummer (1992). The results are reported as picograms 

per kilogram water (pg/kg). The reported detection 

limit for CFC analysis is 1 pg/kg with an associated 

uncertainty of 50 percent near the detection level; 

above 50 pg/kg the analytical uncertainty was plus or 

minus 3 percent (Ekwurzel and others, 1994). The 

model recharge year was calculated using the 

procedures described by Busenberg and Plummer 

(1992) and a recharge temperature of 9°C. The 

recharge temperature was selected on the basis of 

measurements of dissolved nitrogen and argon in three 

ground-water samples and the seasonal average mean 

daily temperature for the Bremerton Weather station 

(near the study area) for the major recharge months of 

October through May. If CFC concentrations measured 

in the ground-water samples were greater than 

maximum reported global atmospheric concentrations 

of these compounds prior to the time of sample 

collections, then the concentration data were deemed 

unsuitable for estimating the residence time of ground 

water and were labeled as “Concentrations exceed 

dateable range.” The maximum northern hemisphere 

atmospheric concentrations, measured at Niwot Ridge, 

Colo., are reported as 294 pg/kg for CFC-11; 570 pg/kg 

for CFC-12; and 92 pg/kg for CFC-113 (Eurybiades 

Busenberg, U.S. Geological Survey, written commun., 

1998). 

As a check for the occurrence of contamination 

of CFC samples during collection or analysis, water 

samples were collected from two domestic wells, 

25N/01W-01B02 and 12L02 (see fig. 4 for locations), 

which were expected to be devoid of CFCs. The wells 

were located near Hood Canal where discharging 

ground water was expected to be pre-modern. The 

concentrations of tritium and 14C in samples from these 

wells were less than 0.3 TU and 80 pmc, respectively, 

indicating pre-modern ground waters. CFCs were not 

detectable in the sample from well 25N/01W-01B02, 

demonstrating that the procedures and equipment used 

to collect and analyze the CFC samples were noncontaminating. Materials used in well construction and 

plumbing may have been the source of small 

concentrations of CFC-11 (2.7-3.0 pg/kg) and 

CFC-113 (4.8-6.5 pg/kg) that were detected in the 

sample from well 25N/1W-12L02. In the plumbing 

system of well 12L02, a small section of PVC pipe was 

present ahead of the sampling point, whereas the 

plumbing system ahead of the sampling point in well 

25N/01W-01B02 was constructed entirely of 

galvanized pipe. Similarly, well 26N/01E-17C01, 

which was a 2-inch monitoring well constructed 

entirely of PVC, produced ground-water samples that 

contained low concentrations of all three CFCs but was 

classified as pre-modern based on tritium and 14C data. 

Although the use of PVC and other plastics are 

demonstrated to be non-contaminating for many 

organic compounds that are analyzed at the parts per 

billion concentration level or greater, the presence of 

plastics and rubber components in well systems to be 

sampled for dateable concentrations of CFCs (4 to 5 

orders of magnitude smaller than parts per billion) is 

not recommended because of potential sample 

contamination (L.N. Plummer and Eurybiades 

Busenberg, U.S. Geological Survey, written commun., 

notes on procedures for dating young waters, 1994). 

The wells sampled in this study, particularly wells 

sampled for CFCs, generally were domestic wells 

containing pumps and casing components constructed 

of materials that were not well documented and may 

have potential for low-level contamination of CFC 

samples. CFC contamination from well construction or 

plumbing material was considered a possibility in 

ground-water samples that contained low 

concentrations (less than 25 pg/kg) of CFCs or CFC 

concentrations that generated model recharge years that 

varied by more than 15 years for the different CFC 

compounds. 

The physical properties and analytical results of 

chemical analyses were evaluated for internal and 

external consistency. The common-ion, ORP, and 

dissolved-oxygen data for well 25N/01E-05A04 were 

judged to be anomalous with respect to other wells 

tapping the Vashon aquifer. Information obtained after 

this well was sampled indicated that the well is located 

downgradient of the contaminant plume mapped during 

the remedial investigation of the OU8 contamination 

site (E.A. Engineering, Science, and Technology, 

2000). That investigation concluded that microbial 

degradation of organic contaminants within the plume 

was extensive. Because microbial degradation of 
Estimates of Residence Time and Variations in Quality of Ground Water 19

organic contaminants can lead to reducing conditions 

and elevated bicarbonate concentrations like those in 

samples from well 25N/01E-05A04, it was highly 

probable that the water samples from well 5A04, 

although not contaminated, were affected by 

upgradient land-use activities. All data for this well 

were included in data tables. However, the dissolvedconstituents data were excluded from consideration of 

the natural variations in the water chemistry of recently 

recharged ground water in the Vashon aquifer (Qva). 

Blanks and replicate samples were submitted as 

part of the Quality Assurance (QA) program to assess 

sampling bias and analytical variability. About 15 

percent of the samples collected for this investigation 

were QA samples. With the exception of the CFC data 

discussed above, results of the QA data indicated the 

absence of a general bias and low analytical variability, 

and as such, the data do not need to be qualified for this 

interpretation. Quality-assurance data for carbon 

isotope data are tabulated in Appendix A (at back of 

report) and are discussed where the results affect 

interpretation of the environmental data. 

ESTIMATES OF RESIDENCE TIME AND 

VARIATIONS IN QUALITY OF GROUND 

WATER 

Estimates of ground-water residence time were 

determined from the concentrations of environmental 

tracers measured in samples of ground water collected 

at selected locations within the ground-water flow 

system beneath SUBASE Bangor and vicinity. 

Concentrations of environmental tracers were used to 

estimate ground-water residence time because the 

concentration measured in the sample can be related to 

atmospheric concentrations that were present at the 

time of ground-water recharge. In the analysis of the 

differences in tracer concentrations observed between 

recharge areas and downgradient sampling points, 

ground-water transport of environmental tracers was 

characterized as advective flow alone, without 

consideration of the influences of dispersion or 

diffusion. 

The measured concentrations of environmental 

tracers in the ground-water samples initially were used 

to classify the ground waters as either modern 

(recharged after 1953), pre-modern (recharged prior to 

1953), or indeterminate. In ground-water samples that 

were determined to be pre-modern, and hence older 

than about 42 years, a radiometric ground-water age 

based on the concentrations of 14C in dissolved 

inorganic carbon in the ground water was used to 

estimate the ground-water residence time. The 

geochemical model NETPATH was used to refine the 

14C estimates of ground-water age by accounting for 

mass transfers of carbon that occur within the groundwater flow system and that affected the 14C 

concentration of the sample ground water. Analysis of 

the spatial distribution of δ13C ratios, along with 

concentration data for common ions and other 

constituents, was used to develop a conceptual model 

of geochemical processes that alter the chemistry of 

ground water within the aquifer system present beneath 

SUBASE Bangor. This conceptual model was used to 

constrain and select the mineral phases included in the 

NETPATH model. The stable isotopes of the groundwater samples (oxygen and hydrogen) showed that 

ground water beneath SUBASE Bangor was recharged 

under similar climatic and geographic conditions. 

Physical properties of the water samples (temperature, 

ORP, and specific conductance) and concentrations of 

dissolved constituents and isotope ratios were 

determined for ground-water samples from 33 wells in 

the study area (table 3). Additional information 

regarding ambient concentrations of inorganic and 

organic constituents in the ground water in the study 

area is available in Greene (1997). 

Ground-Water Age Classification Using 

Environmental Tracers 

The tritium, CFC, and 14C data are discussed 

before the general ground-water chemistry so that 

general ground-water age relations can be used in the 

discussion of water-quality variations. In this report, 

the presence or absence of tritium and CFC is used to 

distinguish which of the 33 samples contained modern 

ground water and would not be included for 

determining 14C model ages for ground water. The 

chemical characteristic of ground water that contained 

modern tracers were used to characterize recently 

recharged ground water and used as the starting 

solution in developing the geochemical model 

describing the chemical changes occurring in ground 

water as it moved through the aquifer system. 
20 Estimates of Residence Time and Related Variations in Quality of Ground Water Beneath SUBASE Bangor and Vicinity, Kitsap County, Washington

Table 3. Physical properties, concentrations of dissolved constituents, and isotope ratios in ground-water samples from wells near SUBASE Bangor, 

Kitsap County, Washington

[Well No.: Location of wells is shown in figure 4. Bicarbonate: E, estimated. Abbreviations: °C, degrees Celsius; mV, millivolts; μS/cm, microsiemens per 

centimeter at 25 °C; μg/L, micrograms per liter; TU, tritium units; pmc, percent modern carbon; <, less than; >, greater than; –, no data]

Well

No.

Sample 

date

Temperature 

(°C)

pH

(standard 

units)

Oxidation 

reduction 

potential 

(ORP) (mV)

Specific 

conductance

(μS/cm)

Dissolved

oxygen

(mg/L)

Calcium

(mg/L)

Magnesium

(mg/L)

Vashon aquifer (Qva)

25N/01E-05A04 07-01-94 10.5 8.3 -180 303 0.2 32 16

25N/01E-07J01 04-19-95 10.1 7.2 >165 105 8.0 8.7 5.7

25N/01E-07K01 03-17-95 8.7 6.9 190 211 5.0 12 16

25N/01E-08L02 03-15-95 9.8 8.3 55 104 8.6 7.6 6.3

25N/01E-08L04 03-11-95 10.1 6.9 150 104 6.2 9.6 4.5

25N/01W-12R02 03-22-95 9.6 6.6 >115 116 8.4 11 5.5

26N/01E-20R01 04-18-95 9.4 7.9 245 110 6.4 6.9 7.2

26N/01E-32M01 04-21-95 10.6 7.2 195 146 5.9 11 9.0

26N/01E-33E01 03-24-95 10.2 7.2 65 183 8.4 13 11

27N/01E-27J01 03-23-95 10.1 7.3 110 184 6.5 14 12

Upper confining unit (QC1)

26N/01E-17C01 04-20-95 11.1 8.4 -230 157 <0.1 14 6.4

27N/01E-35C01 03-23-95 9.0 8.6 -150 132 <.1 16 5.8

Permeable interbeds in Upper confining unit (QC1pi)

25N/01E-07J02 03-20-95 9.6 7.6 -150 253 <0.1 26 12

25N/01E-07N01D1 03-21-95 9.6 7.8 140 144 3.9 13 7.5

25N/01E-07P02 03-16-95 9.2 7.6 70 158 3.4 13 9.7

25N/01E-07Q03 03-17-95 9.0 7.4 150 162 3.4 13 11

25N/01E-08J02 03-14-95 9.6 7.6 -180 204 .0 23 5.8

25N/01E-08Q03 03-15-95 9.5 8.1 -190 225 .1 23 6.7

25N/01E-09N02 03-20-95 10.9 7.8 -165 209 .0 19 9.1

25N/01W-12J01 03-16-95 9.3 8.1 100 137 9.7 12 6.9

25N/01W-12K04 03-22-95 9.3 7.8 85 121 7.2 12 5.9

26N/01E-30L01 03-24-95 8.7 8.2 -370 160 .2 13 8.8

27N/01E-22Q04 04-18-95 8.5 8.4 -210 184 .4 20 8.1

Sea-level aquifer (QA1)

25N/01E-06D04 06-29-94 9.7 7.7 -165 231 0.0 28 7.4

25N/01W-01B02 04-19-95 9.4 7.8 -140 165 .2 19 5.8

25N/01W-12L02 03-20-95 9.0 8.2 125 114 6.5 13 3.9

26N/01E-18P06 03-24-95 9.9 8.0 -140 154 <.1 12 8.6

26N/01E-32L05 03-24-95 9.6 8.2 – 150 .1 16 6.7

26N/01W-36R03 07-01-94 10.6 7.8 -35 154 – 18 6.1

27N/01E-22Q05 04-18-95 9.7 8.3 -95 154 .2 20 3.7

27N/01E-27J021 03-23-95 10.2 7.3 90 218 1.9 18 13

Deep aquifer (QA2)

26N/01E-31R012 06-30-94 9.6 7.8 -175 178 .1 20 6.6

26N/01E-32L04 06-28-94 10.4 8.2 -205 149 0.0 15 6.1

1Well also may be open to Qva. Analysis of water-quality data indicated that ground water from well 

27N/01E-27J02 was likely from the Vashon aquifer. Subsequent efforts to repair well revealed that casing was broken. 2Well is screened in QA1 and QA2. 
Estimates of Residence Time and Variations in Quality of Ground Water 21

Table 3. Physical properties, concentrations of dissolved constituents, and isotope ratios in ground-water samples from wells near SUBASE Bangor, 

Kitsap County, Washington — Continued

[Well No.: Location of wells is shown in figure 4. Bicarbonate: E, estimated. Abbreviations: °C, degrees Celsius; mV, millivolts; μS/cm, microsiemens per 

centimeter at 25 °C; μg/L, micrograms per liter; TU, tritium units; pmc, percent modern carbon; <, less than; >, greater than; –, no data]

Well

No.

Sodium

(mg/L)

Potassium

(mg/L)

Chloride

(mg/L)

Sulfate

(mg/L)

Dissolved inorganic carbon Silica

(mg/L)

Strontium

(mg/L)

Barium 

(μg/L)

Aluminum

(μg/L) Bicarbonate

(mg/L)

Carbonate

(mg/L)

Vashon aquifer (Qva)

25N/01E-05A04 6.1 2.2 4.2 13 183 0.0 27 140 14 <10

25N/01E-07J01 3.5 0.4 2.2 1.6 60 .0 25 44 3 <10

25N/01E-07K01 5.1 1.0 6.9 2.3 106 .0 39 58 5 <10

25N/01E-08L02 3.6 .5 2.7 0.8 59 .0 28 33 3 <10

25N/01E-08L04 4.2 .4 2.4 2.4 56 .0 24 50 <2 <10

25N/01W-12R02 4.1 .4 3.0 3.4 63 .0 25 49 2 <10

26N/01E-20R01 4.0 .8 2.8 3.5 65 .0 29 37 <2 <10

26N/01E-32M01 4.7 .6 2.0 2.7 84 .0 32 61 3 <10

26N/01E-33E01 6.1 1.4 6.1 3.3 101 .0 30 65 3 <10

27N/01E-27J01 5.6 1.0 2.7 5.8 101 .0 29 80 3 <10

Upper confining unit (QC1)

26N/01E-17C01 6.9 4.1 1.7 4.7 91 0.0 30 88 12 <10

27N/01E-35C01 7.0 1.9 2.7 3.3 77 .0 32 60 5 50

Permeable interbeds in Upper confining unit (QC1pi)

25N/01E-07J02 7.1 1.7 1.4 <0.1 166 0.0 47 110 21 <10

25N/01E-07N01D1 4.5 .7 1.8 1.4 89 .0 25 47 <2 10

25N/01E-07P02 4.4 .5 2.4 2.0 93 .0 32 47 4 <10

25N/01E-07Q03 4.5 .7 2.7 1.7 92 .0 30 51 3 <10

25N/01E-08J02 4.7 .8 1.2 1.8 124 .0 42 140 12 <10

25N/01E-08Q03 10 1.6 1.2 1.0 142 .0 39 130 14 <10

25N/01E-09N02 8.1 2.1 1.2 1.1 128 .0 35 89 7 <10

25N/01W-12J01 4.3 1.1 1.8 1.5 71 .0 25 45 <2 <10

25N/01W-12K04 3.8 .5 2.2 2.2 72 .0 23 49 <2 <10

26N/01E-30L01 5.6 1.0 2.1 .4 E103 .0 25 56 5 <10

27N/01E-22Q04 5.5 3.4 2.1 .2 120 .0 36 93 12 <10

Sea-level aquifer (QA1)

25N/01E-06D04 7.9 1.3 1.4 0.9 149 0.0 37 130 5 <10

25N/01W-01B02 6.7 .5 1.3 .1 109 .0 25 78 6 <10

25N/01W-12L02 4.0 .5 1.7 .9 77 .0 22 56 <2 20

26N/01E-18P06 5.6 1.7 1.9 3.2 89 .0 27 55 4 <10

26N/01E-32L05 5.1 1.5 1.6 2.4 92 .0 30 76 4 <10

26N/01W-36R03 4.7 .4 1.6 1.2 98 .0 22 65 4 <10

27N/01E-22Q05 6.5 1.8 2.0 3.2 92 .0 20 160 5 10

27N/01E-27J021 6.5 1.2 3.6 9.1 115 .0 29 100 3 <10

Deep aquifer (QA2)

26N/01E-31R012 5.5 1.1 1.3 .4 110 .0 35 90 6 <10

26N/01E-32L04 4.6 1.4 1.5 3.0 93 0.0 27 72 3 <10

1Well also may be open to Qva. Analysis of water-quality data indicated that ground water from well 

27N/01E-27J02 was likely from the Vashon aquifer. Subsequent efforts to repair well revealed that casing was broken. 2Well is screened in QA1 and QA2.
22 Estimates of Residence Time and Related Variations in Quality of Ground Water Beneath SUBASE Bangor and Vicinity, Kitsap County, Washington

Table 3. Physical properties, concentrations of dissolved constituents, and isotope ratios in ground-water samples from wells near SUBASE Bangor, 

Kitsap County, Washington — Continued

[Well No.: Location of wells is shown in figure 4. Bicarbonate: E, estimated. Abbreviations: °C, degrees Celsius; mV, millivolts; μS/cm, microsiemens per 

centimeter at 25 °C; μg/L, micrograms per liter; TU, tritium units; pmc, percent modern carbon; <, less than; >, greater than; –, no data]

Well No. Bromide

(μg/L)

Nitrate as 

nitrogen

(mg/L)

Ammonia 

as nitrogen

(mg/L)

Organic 

nitrogen

(mg/L)

Total 

organic 

carbon

(mg/L)

Dissolved 

organic 

carbon

(mg/L)

Methane

(mg/L)

Phosphate

(mg/L)

Boron

(μg/L)

Iron

(μg/L)

Vashon aquifer (Qva)

25N/01E-05A04 0.06 <0.05 0.04 <0.2 0.6 0.3 – 0.03 <10 49

25N/01E-07J01 <.01 .41 <.015 <.2 1.0 .2 – .02 <10 <3

25N/01E-07K01 .03 2.0 <.015 <.2 – .4 – .04 <10 14

25N/01E-08L02 .02 .25 <.015 <.2 – .3 0.04 .03 <10 12

25N/01E-08L04 <.01 .32 <.015 <.2 – .3 – .02 <10 <3

25N/01W-12R02 <.01 .16 <.015 <.2 1.2 .3 – .02 10 <3

26N/01E-20R01 <.01 .10 <.015 <.2 .3 .2 – .05 <10 <3

26N/01E-32M01 .02 .75 <.015 <.2 3.5 .3 – .03 <10 10

26N/01E-33E01 .03 1.0 <.015 <.2 .7 .2 – .04 <10 <3

27N/01E-27J01 .02 .84 <.015 <.2 .9 .5 – .04 <10 <3

Upper confining unit (QC1)

26N/01E-17C01 0.02 <0.05 0.14 <0.2 1.4 0.4 – 0.12 30 93

27N/01E-35C01 .02 <.05 .04 <.2 .5 .4 0.04 .10 <10 13

Permeable interbeds in Upper confining unit (QC1pi)

25N/01E-07J02 <0.01 <0.05 1.6 1.8 – 1.8 23 0.81 30 1,500

25N/01E-07N01D1 .02 .20 <.015 <.2 – .2 – .08 <10 <3

25N/01E-07P02 .02 .47 <.015 <.2 – .3 – .05 20 22

25N/01E-07Q03 .02 .60 <.015 <.2 – .6 <.04 .05 20 <3

25N/01E-08J02 <.01 <.05 2.5 2.6 – 1.7 22 1.40 10 800

25N/01E-08Q03 <.01 <.05 1.6 1.7 – 1.8 44 .76 50 650

25N/01E-09N02 <.01 <.05 1.4 1.5 – 1.1 16 .93 30 310

25N/01W-12J01 .02 .25 <.015 <.2 – .2 – .08 <10 3

25N/01W-12K04 <.01 .50 <.015 <.2 .4 .2 – .04 20 <3

26N/01E-30L01 .02 <.05 .16 <.2 2.0 .3 .93 .17 <10 86

27N/01E-22Q04 <.01 <.05 .20 .2 3.2 1.5 – .22 10 150

Sea-level aquifer (QA1)

25N/01E-06D04 <0.01 <0.05 1.3 1.3 1.6 2.0 – 1.50 30 380

25N/01W-01B02 <.01 <.05 .32 .3 2.6 1.8 – .33 10 650

25N/01W-12L02 .01 .06 .02 <.2 – <.1 – .10 <10 <3

26N/01E-18P06 .02 <.05 .14 .3 .6 .2 – .12 10 55

26N/01E-32L05 .01 <.05 .17 <.2 .4 .4 0.30 .24 10 25

26N/01W-36R03 .01 .10 .02 <.2 .1 .8 – .10 <10 12

27N/01E-22Q05 <.01 <.05 .14 <.2 .4 .2 – .12 20 9

27N/01E-27J021 .03 1.2 <.015 <.2 .6 .3 .07 .04 <10 10

Deep aquifer (QA2)

26N/01E-31R012 <0.01 <0.05 1.0 1.0 1.2 2.0 – 0.82 10 320

26N/01E-32L04 .01 <.05 .23 .2 .4 .3 – .30 <10 99

1Well also may be open to Qva. Analysis of water-quality data indicated that ground water from well 

27N/01E-27J02 was likely from the Vashon aquifer. Subsequent efforts to repair well revealed that casing was broken. 2Well is screened in QA1 and QA2.
Estimates of Residence Time and Variations in Quality of Ground Water 23

Table 3. Physical properties, concentrations of dissolved constituents, and isotope ratios in ground-water samples from wells near SUBASE Bangor, 

Kitsap County, Washington — Continued

[Well No.: Location of wells is shown in figure 4. Bicarbonate: E, estimated. Abbreviations: °C, degrees Celsius; mV, millivolts; μS/cm, microsiemens per 

centimeter at 25 °C; μg/L, micrograms per liter; pmc, percent modern carbon; <, less than; >, greater than; –, no data]

Well No.

Manganese

(μg/L)

Tritium

(tritium 

units)

Delta

carbon-13

(per mil)

Delta 

deuterium

(per mil)

Delta 

oxygen-18

(per mil)

Carbon-14

(pmc)

Carbon-14 

age 

(years)

Tritium 

age 

(years)

CFC age 

(years)

Vashon aquifer (Qva)

25N/01E-05A04 100 13 -21.0 -78.9 -11.1 88 <45 <45 –

25N/01E-07J01 <1 4.7 -21.1 -74.9 -10.5 117 <45 <45 Modern

25N/01E-07K01 2 17 – -77.2 -10.6 – – <45 Modern

25N/01E-08L02 1 7.2 -20.3 -77.1 -10.8 115 <45 <45 Modern

25N/01E-08L04 3 3.4 -21.9 -75.1 -10.4 115 <45 <45 Modern

25N/01W-12R02 1 4.1 -21.4 -70.2 -10.4 119 <45 <45 Modern

26N/01E-20R01 <1 14 -18.2 -78.3 -11.1 101 <45 <45 –

26N/01E-32M01 <1 6.2 -24.0 -78.2 -10.8 116 <45 <45 Modern

26N/01E-33E01 <1 8.8 – -78.2 -10.9 – – <45 Modern

27N/01E-27J01 <1 5.3 -21.7 -78.5 -11.0 101 <45 <45 Modern

Upper confining unit (QC1)

26N/01E-17C01 53 <0.1 -17.40 -79.0 -11.2 60 1,840-2,990 <45 Pre-modern

27N/01E-35C01 33 .2 -18.70 -78.9 -11.2 62 1,900-3,080 <45 –

Permeable interbeds in Upper confining unit (QC1pi)

25N/01E-07J02 270 <0.1 -12.4 -77.7 -10.8 58 50-510 >45 –

25N/01E-07N01D1 <1 5.6 -21.6 -76.5 -10.9 89 – <45 –

25N/01E-07P02 <1 7.5 -22.1 -77.7 -10.9 101 <45 <45 Modern

25N/01E-07Q03 <1 9.1 – -74.3 -10.8 – – <45 –

25N/01E-08J02 360 1.0 -10.5 -78.5 -11.0 43 50-1,700 >45 Pre-modern

25N/01E-08Q03 280 <.1 -6.80 -78.7 -11.1 47 920-4,550 >45 –

25N/01E-09N02 91 .2 -15.0 -78.5 -11.0 42 2,130-4,500 >45 –

25N/01W-12J01 <1 8.4 -21.5 -76.4 -11.0 69 – <45 Modern

25N/01W-12K04 <1 12 -20.4 -78.3 -11.0 86 <45 <45 –

26N/01E-30L01 50 3.8 -21.8 -79.4 -11.2 69 – <45 –

27N/01E-22Q04 94 <.1 -21.1 -77.7 -11.0 81 – >45 –

Sea-level aquifer (QA1)

25N/01E-06D04 440 <0.1 -18.9 -79.2 -11.2 40 330-2,480 >45 –

25N/01W-01B02 72 .3 -13.8 -81.9 -11.4 39 2,750-4,550 >45 Pre-modern

25N/01W-12L02 1 .1 -20.8 -77.4 -11.0 78 – >45 Pre-modern

26N/01E-18P06 67 7.5 -21.8 -80.3 -11.3 84 – <45 –

26N/01E-32L05 31 .2 -20.7 -78.1 -11.1 77 50-1,040 >45 –

26N/01W-36R03 <1 <.1 -20.7 -78.8 -11.3 75 50-450 >45 –

27N/01E-22Q05 11 <.1 -18.4 -80.1 -11.2 71 1240-1,480 >45 –

27N/01E-27J021 <1 6.6 -21.2 -76.8 -11.1 96 – <45 –

Deep aquifer (QA2)

26N/01E-31R012 180 <0.1 -14.7 -78.9 -11.2 51 180-2,120 >45 –

26N/01E-32L04 28 .4 -20.3 -79.2 -11.2 72 250-1,510 >45 –

1Well also may be open to Qva. Analysis of water-quality data indicated that ground water from well 

27N/01E-27J02 was likely from the Vashon aquifer. Subsequent efforts to repair well revealed that casing was broken. 2Well is screened in QA1 and QA2.
24 Estimates of Residence Time and Related Variations in Quality of Ground Water Beneath SUBASE Bangor and Vicinity, Kitsap County, Washington

Tritium

Tritium concentrations in ground water from the 

Bangor area ranged from less than 0.1 to 17 TU 

(table 3). The laboratory reporting limit for the tritium 

analysis was 0.1 TU with a standard error of 0.1 to 1.3 

TU. Ground-water samples with concentrations less 

than 0.4 TU are considered to contain little, if any, 

bomb tritium, indicating that ground water in these 

samples was recharged prior to 1953. When the tritium 

data are plotted to show the cumulative frequency 

distribution (fig. 5), a prominent break in the 

distribution occurs above concentrations of 1 TU, the 

level above which the presence of bomb tritium is 

clearly indicated (Mazor, 1991). Tritium concentrations 

between 0.4 and 1.0 TU were considered to fall in a 

range where a clear distinction between modern and 

pre-modern ground water could not be assigned based 

on tritium data alone. The reported tritium 

concentration for wells 25N/01E-08J02 and 26N/01E32L04 (1.0 and 0.4 TU, respectively) indicate that low 

concentrations of tritium are likely present in the 

ground-water samples. Although these data may be 

interpreted to mean that ground water from these wells 

recharged in the period just before the start of nuclear 

weapons testing, a more likely explanation is that the 

samples are a mixture of predominantly tritium-free

Figure 5. Cumulative frequency distribution of tritium concentration in 

ground water, SUBASE Bangor and vicinity, Kitsap County, Washington.

pre-modern ground water and a small fraction of 

modern ground water (on the order of 5 percent) 

containing bomb tritium. This interpretation is 

supported by CFC and 14C data, which are discussed 

later in this section. Similar minor mixing was 

observed in ground-water samples from the terrace 

regions of Oklahoma by Busenberg and Plummer 

(1992). 

Chlorofluorocarbons

Concentrations of CFCs were measured in 

ground-water samples from 14 wells and ranged from 

less than detection limits to 45,000 pg/kg (table 4). The 

CFC data indicated that 10 of the 14 wells sampled 

contained predominantly modern ground water, 

whereas ground water in the other four wells was 

predominantly pre-modern. Use of the CFC data to 

refine the estimates of the ground-water residence time 

of modern ground water was confounded due to several 

causes. Concentrations of CFCs exceeded atmospheric 

equilibrium levels in samples from about 50 percent of 

the wells sampled. In several of the other wells, there 

was apparent contamination during sampling or 

analysis. Lastly, when concentration data were within 

the dateable range for more than one CFC, widely 

divergent model ages were produced. 

In 7 of 14 wells sampled, the concentration of at 

least one CFC compound exceeded the concentration 

attributable to equilibration with the maximum 

atmospheric concentrations for the northern 

hemisphere. Model recharge years could not be 

calculated from these data, which are listed in table 4 as 

“CEDR, or concentration exceeds dateable range.” 

CFC-12 showed the highest incidence of excessive 

concentrations, occurring in five wells, where as 

excessive concentrations of CFC-113 and CFC-11 

occurred in four and two wells, respectively. Local 

sources of CFCs that can create such conditions in 

ground water include refrigeration equipment, airconditioners, aerosol spray cans, plastic containers and 

sewage effluent. 

0

0

5

10

15

20

20 40 60 80 100

CUMULATIVE FREQUENCY OF TRITIUM SAMPLES, IN PERCENT

TRITIUM CONCENTRATION,

IN TRITIUM UNITS (TU)
Estimates of Residence Time and Variations in Quality of Ground Water 25

Table 4. Concentration of chlorofluorocarbons in ground water and corresponding model of recharge year and ground-water age, SUBASE 

Bangor and vicinity, Kitsap County, Washington

[Well No.: Location of wells are shown in figure 4. Concentration: CFC, chlorofluorocarbon. Model recharge year: CEDR, concentration of CFC 

exceeds dateable range; SLLC, suspected low-level contamination. Concentrations and model recharge years in parentheses exceed relativepercent-difference limits. Abbreviations: pg/kg, picograms per kilogram; >, greater than; <, less than]

Well No.

Concentration (pg/kg) Model recharge year Tritium 

(tritium 

units)

Estimated 

groundwater age 

(years)

CFC-11 CFC-12 CFC-113 CFC-11 CFC-12 CFC-113

Vashon aquifer (Qva)

25N/01E-07J01 171 233 12.2 1969 1982 1974 4.6 Modern

175 238 (36.3) 1969 1982 (1981)

170 239 14.0 1969 1982 1974

25N/01E-07K01 1.5 37.0 (2.9) 1950 1963 1963 17 Modern

0.8 35.5 .0 1948 1963 <1955

1.2 40.1 .0 1949 1963 <1955

25N/01E-08L02 31.5 133 5.8 1960 1974 1968 7.1 Modern

32.8 136 8.0 1960 1974 1970

40.2 157 8.3 1961 1975 1970

25N/01E-08L04 539 41,200 136 1981 CEDR CEDR 3.4 Modern

520 41,100 (102) 1980 CEDR (1991)

534 44,900 138 1980 CEDR CEDR

25N/01W-12R02 419 470 55 1976 CEDR 1985 4.0 Modern

421 466 41.5 1976 CEDR 1982

(751) (694) (80.8) (1988) CEDR 1988

26N/01E-32M01 183 177 5,520 1970 1976 CEDR 6.2 Modern

191 175 5,990 1970 1976 CEDR

195 182 6,180 1970 1977 CEDR

26N/01E-33E01 392 990 20.5 1975 CEDR 1977 8.6 Modern

393 1,010 19.2 1975 CEDR 1976

(756) (1,570) 25.0 (1988) CEDR 1978

27N/01E-27J01 4,690 3,600 42.3 CEDR CEDR 1982 5.2 Modern

4,650 3,550 36.4 CEDR CEDR 1981

9,450 4,420 59.0 CEDR CEDR 1985

Upper confining unit (QC1)

26N/01E-17C01 12.5 1.7 (26.7) SLLC SLLC SLLC <0.1 Pre-modern

7.7 8.2 11.9 SLLC SLLC SLLC

7.0 0.0 16.4 SLLC SLLC SLLC

Permeable interbeds in Upper confining unit (QC1pi)

25N/01E-07P02 (2,840) (388) (90.5) CEDR (>1992) (1989) 7.4 Modern

105 189 .0 1966 1978 <1955

164 256 .0 1969 1983 <1955

25N/01E-08J02 1.5 .0 6.4 SLLC <1940 SLLC 1.0 Pre-modern

.0 .0 .0 <1945 <1940 <1955

1.4 .0 .0 SLLC <1940 <1955

25N/01W-12J01 2.2 343 4.7 SLLC 1991 SLLC 8.3 Modern

1.8 343 3.5 SLLC 1991 SLLC

1.6 (384) 6.6 SLLC (1992) SLLC

Sea-level aquifer (QA1)

25N/01W-01B02 0.0 0.0 0.0 <1945 <1940 <1955 <0.3 Premodern

.0 .0 .0 <1945 <1940 <1955

.0 .0 .0 <1945 <1940 <1955

25N/01W-12L02 3.0 .0 6.5 SLLC <1940 SLLC .1 Pre-modern

2.7 .0 4.8 SLLC <1940 SLLC

(4.7) (5.0) (28.8) SLLC SLLC SLLC
26 Estimates of Residence Time and Related Variations in Quality of Ground Water Beneath SUBASE Bangor and Vicinity, Kitsap County, Washington

Sampling contamination also may have 

confounded use of CFC data in several wells. Small 

concentrations of CFCs, including CFC-113, which 

was not widely present in the atmosphere prior to 1955, 

were measured in a sample each, from wells 

25N/01W-12L02 and 26N/01E-17C01. Both of these 

wells contained 0.1 TU or less and less than 80 pmc 

of 14C (table 3), clearly indicating the samples were 

pre-modern and that the presence of CFC in the sample 

was from either contamination or mixing. The presence 

of CFC in the blank test samples from well 

25N/01W-12L02, discussed earlier in the section 

“Study Methods,” demonstrates the presence of 

contaminants from either well construction materials or 

procedural problems during sampling or analysis. CFC 

concentrations less than 25 pg/kg were considered 

ambiguous with respect to classification of groundwater age unless the calculated model ages for the three 

CFCs were within 5 years. 

Lastly, in the few wells, such as 25N/01E-8L02, 

which were aerobic and contained concentrations of all 

three CFCs that were within the range of dateable 

concentrations, the corresponding model ages were 

highly variable, further indicating uncertainty in CFC 

model ages. 

Carbon-14

Concentrations of 14C in the 30 ground-water 

samples from the Bangor area ranged from 39 to 119 

pmc (table 3). 14C concentrations in eight wells were 

greater than 100 pmc, indicating that the sample 

contained modern water that was recharged during or 

after the period of thermonuclear weapons testing. 

Bomb carbon also may be present in ground-water 

samples with concentrations less than 100 pmc, as 

indicated by the presence of tritium at concentrations 

above 1 TU in samples that had 14C concentrations 

between 80 to 100 pmc. 

Concentrations of 14C in samples from the 

Vashon aquifer ranged from 88 to 119 pmc and 

concentrations in seven of eight samples were greater 

than 100 pmc, indicating that ground water in the 

Vashon aquifer has recharged after the initiation of 

thermonuclear weapons testing. This conclusion is 

consistent with tritium and CFC data. The sample in 

which the 14C concentration was 88 pmc contained 13 

TU of tritium, indicating modern ground water. The 

range of 14C concentrations were similar in samples 

from the Upper confining unit and the deeper aquifers. 

Concentrations of 14C ranged from 42 to 101 pmc in 

the Upper confining unit and permeable interbeds and 

from 39 to 96 pmc in the Sea-level and Deep aquifers. 

Smaller 14C concentrations indicate either older ground 

water, more chemically evolved ground water, or some 

combination of both. 

Concentrations of tritium, CFCs, and 14C were 

used to classify the age of ground-water samples 

collected in the study area as modern, pre-modern, or 

indeterminate (table 5). The primary criterion for 

classifying a sample as modern ground water was 

concentrations of tritium greater than 1 TU, 

concentrations of CFCs greater than 25 pg/kg, and 

concentrations of 14C greater than 100 pmc. Premodern ground water was characterized by nondetectable or trace concentrations of CFCs (less than 

25 pg/kg) and tritium (0.4 TU or less) and 14C 

concentrations less than 85 pmc. When tracer 

concentration data were within the above ranges, the 

data were considered unambiguous indicators of the 

presence of either modern or premodern ground water. 

Interpretation of ground-water age classification was 

considered uncertain if concentrations of any one of the 

environmental tracers was in these ranges: tritium, 

0.4-1.0 TU; 14C, 85-100 pmc; CFCs, less than 

25 pg/kg. In instances where this occurred, the 

classification of ground-water age was based on the 

other tracer data and the ambiguous data were noted in 

table 5. Indeterminate ground waters were 

characterized as ground waters containing 

unambiguous indicators of both modern and premodern environmental tracers, such as in well 

25N/01W-12J01, which contained 8.5 TU of tritium 

and 69 pmc of 14C, indicating a mixture of recently 

recharged and pre-modern ground water.
Estimates of Residence Time and Variations in Quality of Ground Water 27

Table 5. Age classification and concentration of environmental tracers in ground 

water at SUBASE Bangor and vicinity, Kitsap County, Washington

[Well No.: Location of wells are shown in figure 4. Hydrogeologic unit: Qva, Vashon 

aquifer; QC1, Upper confining unit; QC1pi, permeable interbeds within Upper confining 

unit; QA1, Sea-level aquifer; QA2, Deep aquifer. CFC recharge: CFC, 

chlorofluorocarbon. Bold type with V-code indicates near detection level concentrations of 

some CFCs detected in ground-water samples, which coincided with inconsistent model 

recharge dates; measured concentrations believed to result from leaching of CFCs from 

materials used in well construction or plumbing. Abbreviations: pmc, percent modern 

carbon; –, not measured]

Well No. Hydrogeologic 

unit

Tritium

(tritium units)

Carbon-14

(pmc)

CFC recharge 

modern/

pre-modern

Modern

25N/01E-05A04 Qva 13 188 –

25N/01E-07J01 Qva 4.7 117 Modern

25N/01E-07K01 Qva 17 – Modern

25N/01E-08L02 Qva 7.2 115 Modern

25N/01E-08L04 Qva 3.4 115 Modern

25N/01W-12R02 Qva 4.1 119 Modern

26N/01E-20R01 Qva 14 101 –

26N/01E-32M01 Qva 6.2 116 Modern

26N/01E-33E01 Qva 8.8 – Modern

27N/01E-27J01 Qva 5.3 101

27N/01E-27J022 Qva, QA1 6.6 196 –

25N/01E-07P02 QC1pi 7.5 101 Modern

25N/01E-07Q03 QC1pi 9.1 – –

25N/01E-07N02D01 QC1pi 5.6 189 –

25N/01W-12K04 QC1pi 12 286 –

Pre-Modern

26N/01E-17C01 QC1 <0.1 60 Vpre-modern

27N/01E-35C01 QC1 .2 62 –

25N/01E-07J02 QC1pi <.1 58 –

25N/01E-08J02 QC1pi 11 43 Vpre-modern

25N/01E-08Q03 QC1pi <.1 47 –

25N/01E-09N02 QC1pi .2 42 –

27N/01E-22Q04 QC1pi <.1 81 –

25N/01E-06D04 QA1 <.1 40 –

25N/01W-01B02 QA1 .3 39 Pre-modern

25N/01W-12L02 QA1 .1 78 Vpre-modern

27N/01E-22Q05 QA1 <.1 71 –

26N/01E-32L05 QA1 .2 77 –

26N/01W-36R03 QA1 <.1 75 –

25N/01E-31R013 QA1, QA2 <.1 51 –

26N/01E-32L04 QA2 1.4 72 –

Indeterminate

25N/01W-12J01 QC1pi 8.4 69 Modern

26N/01E-30L01 QC1pi 3.8 69 –

26N/01E-18P06 QA1 7.5 84 –

1Ambiguous indicator concentration, classification not possible without additional 

information. 2Well also may be open to Qva. Analysis of water-quality data indicated that ground 

water from well 27N/01E-27J02 was likely from the Vashon aquifer. Subsequent efforts to 

repair well revealed that casing was broken. 3Well is screened in QA1 and QA2.

All ground-water samples from the 

Vashon aquifer (Qva) contained tritium at 

concentrations ranging from 3.4 to 17 TU, 

suggesting that ground water in the Vashon 

aquifer was largely recharged after 1953 

(table 5). The presence of CFCs in all 

samples from Vashon aquifer wells further 

supports this conclusion (table 4), as do the 

14C data, in which seven of eight samples 

were greater than 100 pmc (table 3). The 

multiple lines of evidence, tritium, CFC, and 

14C, clearly indicate that ground water in the 

Vashon aquifer recharged after 1953.

Modern ground waters also were 

present in deeper hydrogeologic units at 

several locations in the Bangor area. Water in 

six wells in the QC1pi unit had tritium 

concentration greater than 1 TU, although 

only four of those wells (25N/01E-7P02, 

7Q03, 7N02D1, and 25N/01W-12K04) were 

classified as having modern ground waters 

based on supporting 14C and CFC data. 

Water in wells 25N/01W-12J01 and 

26N/01E-30L01 in the QC1pi unit, which 

also had concentrations of tritium greater 

than 1 TU, contained concentrations of 14C 

at 69 pmc and were thus classified as 

indeterminate. Water from two deeper wells 

(27N/01E-27J02 and 26N/01E-18P06), 

which were both screened in the QA1 

aquifer, produced ground water 

characteristic of modern water, suggesting 

very rapid recharge deep into the aquifer 

system. However, for both wells alternate 

explanations are equally plausible. In well 

27N/01E-27J02, which had a reported screen 

depth of 402 ft below land surface and was 

classified as a Sea-level aquifer well, the 

tracer concentrations and overall groundwater chemistry closely resembled well 

water from the nearby (within 100 ft) 

shallow well 27N/01E-27J01, suggesting 

that a preferential pathway was allowing 

shallow ground water to move rapidly to the 

deeper well 27N/01E-27J02. Subsequent 

maintenance work on well 27N/01E-27J02 

by KPUD revealed a broken casing that 

permitted ground water to move between the 

aquifers both within the well bore and 

around the outside of the casing (Martin 
28 Estimates of Residence Time and Related Variations in Quality of Ground Water Beneath SUBASE Bangor and Vicinity, Kitsap County, Washington

Sebren, Kitsap County Public Utility District, written 

commun., 2002). The nearly identical chemistry of 

water in wells 27N/01E-27J02 and 27J01, which was 

screened only in the Qva, indicated that ground water 

from 27N/01E-27J02 should be classified as modern. 

In contrast, the overall chemistry of water in samples 

from Sea-level aquifer well 26N-01E-18P06 were 

characteristic of pre-modern ground water from the 

deeper aquifer units, but also had substantial 

concentrations of tritium (7.5 TU) and 14C (84 pmc). 

This well is a large-capacity production well (500 

gal/min) and is part of a well field of six to eight similar 

wells. The presence of modern water in this well, as 

evidenced by high tritium concentrations, can be 

explained by either increased downward flow induced 

by a substantial increase in the downward hydraulic 

head gradient produced by the pumping wells or by 

leaky well construction. Data from this well could not 

be readily classified as modern or pre-modern and thus 

was classified as indeterminate. 

Samples from seven wells from QC1 and QC1pi 

had either no detectable or only trace concentrations of 

tritium and concentrations of 14C less than 85 pmc. The 

concentrations of CFCs measured in four of these wells 

were either non-detectable or at trace levels attributable 

to materials used in well construction or the pump and 

water discharge lines. These wells were classified as 

pre-modern ground water (table 5). Pre-modern 

ground-water samples from the QC1 and QC1pi 

generally were collected either near discharge areas or 

at greater depths in the upland areas. Water samples 

from eight wells tapping the Sea-level aquifer (QA1) 

and Deep aquifer (QA2) were classified as pre-modern, 

having no detectable concentrations of tritium and 

concentrations of 14C less than 85 pmc (table 5). CFCs 

were not detected in well 25N/01W-01B02, and the 

trace concentrations in well 25N/01W-12L02 were 

attributable to materials used in well construction or the 

pump and water discharge lines. 

Variations in Ground-Water Quality

The oxygen and hydrogen isotopic composition 

of ground water from the SUBASE Bangor area ranged 

from –11.4 to –10.4 ‰ for δ18O and from –81.9 to 

–70.2 ‰ for delta deuterium. The isotope data plot as a 

single group (fig. 6) slightly offset from the global 

meteoric water line of Rozanski and others (1993). The 

data generally plot within the range of winter-spring 

precipitation samples collected at the Global Network 

of Isotopes in Precipitation site at Victoria, British 

Columbia (International Atomic Energy Agency, 

2001). The Victoria isotope data were collected mostly 

from 1975 to 1982 at a station located near sea level 

about 60 miles northwest of the Bangor study area. All 

of the ground-water samples plot within or near the 

range of modern precipitation, indicating that they 

were recharged under climatic conditions very similar 

to present day conditions and thus implying an upper 

limit for the age of the ground-water samples as postglacial, or less than about 10,000 years. 

Although the ground-water isotope data plot as a 

single group, slight differences are apparent between 

the different hydrogeologic units. Differences in the 

median concentrations of δ18O from the hydrogeologic 

units are about 0.2 ‰ and are not large enough to 

signify distinctly different recharge areas within the 

irregular geography of the Puget Sound region. The 

observed variation in δ18O in study wells tapping the 

Vashon aquifer (Qva) was about 0.7 ‰, which is 

several times larger than differences between 

hydrogeologic units. Variations in δ18O due to 

differences in altitude of precipitation typically are 

about 0.2 to 0.5 ‰ per 330 ft of change in altitude 

(Clark and Fritz, 1997). Measurements of δ18O in snow 

taken from different altitudes on Blue Glacier in the 

Olympic Mountains indicate a gradient of about 0.5 ‰ 

per 330 ft elevation (Sharp and others, 1960). 

Ground waters characterized as pre-modern 

appear to have stable isotope ratios of δ18O that are 

slightly more depleted, about 0.5 ‰, than ground 

waters characterized as modern, suggesting that these 

ground waters were recharged under slightly cooler 

climatic conditions. This difference is not nearly as 

large as differences observed by Gonfiantini and others 

(1974) and Hendry and Wassenaar (1999) between 

ground waters recharged during the present climatic 

regime and ground waters recharged during the 

Pleistocene glacial climatic regime. The more-depleted 

isotope ratios of the pre-modern ground water from the 

Bangor study area may be the result of recharge during 

slightly cooler times, such as when the climatic 

conditions were similar to the Little Ice Age of the late 

1800s. An alternative explanation may be that small 

amounts of Pleistocene ground water containing 

depleted δ18O have been retained within the finegrained sediments of the QC1pi and are slowly 

diffusing into ground water flowing through this unit. 
Estimates of Residence Time and Variations in Quality of Ground Water 29

Similar slightly depleted δ18O ratios have been 

observed in ground water from aquifers beneath the 

pre-Vashon confining unit (analgous to the QC1 of this 

report) in other parts of the Puget Sound region 

(Stephen Cox, U.S. Geological Survey, unpub. data, 

2002). 

Ground-Water Chemistry

Concentrations of dissolved constituents in 33 

ground-water samples from the Bangor study area were 

characterized as dilute. In wells unaffected by land-use 

activities, the specific conductance of ground water 

ranged from 105 to 253 μS/cm (microsiemens per 

centimeter). Concentrations of dissolved constituents 

were smallest in the upland recharge areas, where 

specific conductance of ground water was about 120 

μS/cm, and increased in samples collected from 

downgradient locations. Based on their major-ion 

chemistry, these ground waters were classified as 

predominantly calcium-magnesium/bicarbonate 

ground water. Calcium and magnesium together make 

up more than 80 percent of the cations in solution, with 

calcium generally present in larger concentrations than 

magnesium, particularly in wells downgradient from 

the recharge area. Bicarbonate makes up more than 95 

percent of the anions present in ground-water samples. 

The distribution of major ions in ground water from the 

Vashon aquifer, the Upper confining unit and 

permeable interbeds, and the Sea-level and Deep 

aquifers-were plotted on a trilinear diagram (fig. 7A). 

The distributions of cations and anions plot in 

overlapping regions, indicating similarity in the 

chemical composition of ground water in these 

hydrogeologic units. The distribution of common ions 

in these ground waters and their relations with groundwater residence time are consistent with ground waters 

that have a similar source of recharge and undergo 

modest chemical evolution of the major-ion 

composition as ground water moves along a flow path. 

However, the distribution of cations suggests there may 

be a subtle difference between ground water from the 

Vashon aquifer (Qva) and deeper (QA1 and QA2)

-90

-85

-80

-75

-70

-65

-60

-55

-50

-12.5 -12 -11.5 -11 -10.5 -10 -9.5 -9 -8.5

Vashon aquifer (Qva)

HYDROGEOLOGIC UNIT

Upper confining unit (QC1) and

permeable interbeds within the Upper confining unit (QC1pi)

Sea-level (QA1) and Deep (QA2) aquifers

Precipitation, fall – spring,

Victoria, British Columbia

DELTA DEUTERIUM, PER MIL

DELTA OXYGEN-18, PER MIL

Global Meteoric Water Line

Figure 6. Comparison of stable isotope composition (deuterium and oxygen-18) of ground-water samples and of nonsummer (fall-spring) precipitation at Victoria, British Columbia, and the relation with the Modern Global Meteoric Water Line 

of Rozanski and others (1993), SUBASE Bangor and vicinity, Kitsap County, Washington.
30 Estimates of Residence Time and Related Variations in Quality of Ground Water Beneath SUBASE Bangor and Vicinity, Kitsap County, Washington

 aquifers. The apparent difference may be an artifact of 

the limited number of samples from each 

hydrogeologic unit, or may be due to slight changes in 

the chemical composition of ground water that 

typically result from its interaction with the 

surrounding aquifer material. 

Chemical differences in the distribution of major 

ions were more clearly visible when the major-ion 

distributions in ground-water samples were grouped on 

the basis of ground-water age classification (fig. 7B). In 

most ground waters that were characterized as modern, 

the magnesium fraction of cations was greater than 

40 percent, whereas in pre-modern samples the 

magnesium fraction was never greater than 40 percent. 

Indeterminate ground waters plotted at intermediate 

positions on the trilinear diagram. The distribution of 

major ions by age classification shows a pattern of 

ground-water evolution in which the composition of 

major ions in older ground waters is increasingly 

dominated by calcium and bicarbonate. Differences in 

the chemical composition of ground water are more 

likely a function of the length of time that ground water 

is in contact with the aquifer material than of the 

occurrence of ground water within a specific 

hydrogeologic unit. 

CATIONS ANIONS %meq/L

Na+K HCO3+CO3 Cl

Mg SO4

Ca

Calcium (Ca) Chloride (Cl)

Sulfate (SO4) + Chloride (Cl)

Calcium (Ca) + Magnesium (Mg)

Sodium (Na) + Potassium (K)

Sulfate (SO4

Magnesium (Mg)

)

80

60

40

20

80

60

40

20

20 40 60 80

80

60

40

20

40

60

80

80 60 40 20

20

40

60

80

60

40

20

Carbonate (CO3) + Bicarbonate (HCO3)

20

40

60

80

20

40

60

80

20

80

Qva-Vashon aquifer

Upper confining unit (QC1) and

Permeable interbeds in

Upper confining unit (QC1pi)

Sea-level aquifer (QA1) and

Deep aquifer (QA2)

A. Distribution of major ions by hydrogeologic units.

EXPLANATION

MAJOR IONS BY HYDROGEOLOGIC UNIT—

Well information is shown in table 2

Figure 7. Distribution of major ions in ground water by hydrogeologic units and by ground-water age classification, SUBASE Bangor and vicinity, Kitsap 

County, Washington.
Estimates of Residence Time and Variations in Quality of Ground Water 31

The common ions that show the largest range in 

concentration were calcium and bicarbonate. A plot of 

molar concentrations of calcium and bicarbonate in 

samples from the 33 wells (fig. 8) shows a linear 

pattern in which the concentration of bicarbonate is 

consistently about four times larger than the 

concentration of calcium. The four to one ratio of the 

concentration of bicarbonate to calcium is maintained 

in samples from different hydrogeologic units as well 

as in the sample from well 25N/01E-5A04 where landuse activities are believed to have affected the overall 

chemistry of ground water near that area. The 

consistency in the ratio of bicarbonate to calcium 

suggests a similar source material or mechanism 

for the presence of these constituents. 13C isotope 

data indicate that the dissolution of calcite, a common 

calcium-carbonate mineral, is not the source 

of these ions. Samples with the largest and smallest 

concentrations of calcium and bicarbonate were 

both obtained from wells tapping the Qva, although 

aquifer conditions were considered to be quite 

different in each case. Concentrations were diluted in 

samples from wells located in areas where recently 

recharged ground water could be expected.

Figure 7.—Continued.

Modern

Pre-modern

Indeterminate

EXPLANATION

MAJOR IONS BY GROUND-WATER

AGE CLASSIFICATION—

is shown in table 5

Well information

CATIONS ANIONS

Na+K HCO3+CO3 Cl

Mg SO4

Ca

Calcium (Ca) Chloride (Cl)

Sulfate (SO4) + Chloride (Cl)

Calcium (Ca) + Magnesium (Mg)

Sodium (Na) + Potassium (K)

Sulfate (SO4

Magnesium (Mg)

)

80

60

40

20

80

60

40

20

20 40 60 80

80

60

40

20

20

40

60

80

80 60 40 20

20

40

60

80

80

60

40

20

Carbonate (CO3) + Bicarbonate (HCO3)

20

40

60

80

20

40

60

80

B. Distribution of major ions by ground-water age classification.

PERCENTAGE OF TOTAL

MILLIEQUIVALENTS PER LITER
32 Estimates of Residence Time and Related Variations in Quality of Ground Water Beneath SUBASE Bangor and Vicinity, Kitsap County, Washington

Vashon aquifer (Qva)

HYDROGEOLOGIC UNIT

Upper confining unit (QC1) and

permeable interbeds within Upper confining unit (QC1pi)

Sea-level (QA1) and Deep (QA2) aquifers

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1 1.5 2 2.5 3 3.5

CONCENTRATION OF CALCIUM, IN MILLIMOLES

0.5

0

20

40

60

80

100

120

140

160

180

1 1.5 2 2.5 3 3.5

CONCENTRATION OF BICARBONATE, IN MILLIMOLES

CONCENTRATION OF ORGANIC CARBON, IN MICROMOLES

0 0.5

Figure 8. Comparison of molar concentrations of calcium, organic carbon, and bicarbonate by hydrogeologic units in ground 

water beneath SUBASE Bangor and vicinity, Kitsap County, Washington.
Estimates of Residence Time and Variations in Quality of Ground Water 33

Concentrations were highest in the sample from well 

25N/01E-5A04, which was located downgradient of a 

location where ground-water contamination was found, 

indicating that land-use activities may have 

substantially altered the shallow ground-water 

chemistry. Concentrations of calcium and bicarbonate 

were often high in samples from wells tapping the 

QC1pi that were located close to the area of recharge. 

Concentrations were often smaller in many wells 

located in what were believed to be downgradient flowpath positions (screened in deeper aquifers or located 

near ground-water discharge areas), indicating that the 

ground-water chemistry data cannot be characterized as 

a generalized progressive change along the inferred 

ground-water flow paths. 

Organic Carbon and Carbon Isotopes

Calculating the model ages of pre-modern 

ground water based on the radioactive decay of 14C can 

be straightforward if initial carbon activity is well 

known and radioactive decay is the only process 

responsible for decreasing 14C activity. However, 

ground water from the Bangor area shows a significant 

increase in carbon as ground water moves through the 

ground-water system, hence the source and activity of 

the added carbon must be assessed in order to estimate 

14C model ages for these ground waters. Constituents 

in ground water that are important in understanding the 

evolution of ground water and the addition of carbon 

include several different forms of carbon in solution, 

the concentration of major ions, and the value of the 

stable isotope ratio of 13C. Carbon species measured in 

ground water included inorganic carbon, organic 

carbon, and dissolved methane. Inorganic carbon 

includes both carbonate and bicarbonate ions in 

solution (filtered samples) and is referred to as 

dissolved inorganic carbon (DIC). Only bicarbonate 

ions were measured in the ground-water samples from 

the Bangor area. Non-purgeable organic carbon was 

measured in solution (filtered samples) as dissolved 

organic carbon (DOC). For about 60 percent of the 

sites, additional unfiltered samples also were analyzed 

for total organic carbon (TOC). Dissolved methane was 

measured in selected samples. The sum of all dissolved 

carbon species (inorganic, organic, and methane) is 

referred to as total dissolved carbon (TDC). Isotope 

ratios of 13C and 14C were measured only on the DIC 

fraction (bicarbonate) of ground-water samples. 

In addition to DIC, other forms of carbon present 

in ground water beneath SUBASE Bangor included 

organic carbon and dissolved methane gas. Methane, 

derived from microbial activity or light hydrocarbon 

gases, is commonly present in ground water of reduced 

geochemical aquifer systems (Hem, 1985). Organic 

carbon, typically present in all natural waters, generally 

is found at much smaller concentrations than 

bicarbonate carbon, but can have a substantial effect on 

the overall ground-water chemistry because of its 

influence on the solubility of trace elements, potential 

to participate in redox reactions, and use as a source of 

carbon and energy to microbially mediated processes 

that can greatly alter the chemistry of ground water 

(Hem, 1985). TOC and DOC may act as reactive 

intermediates in the degradation of sedimentary 

organic matter to bicarbonate. In samples analyzed for 

DOC and TOC, concentrations of TOC typically were 

two to three times larger than concentrations of DOC, 

indicating that the amount of TOC present in these 

ground waters often was slightly larger than the amount 

of DOC but generally of the same order of magnitude. 

DOC is a better measure of chemically reactive forms 

of carbon in solution than TOC, which also includes 

large colloidal carbon molecules, carbon fragments, 

and microbial detritus that are often recalcitrant 

(Thurman, 1985). 

 Concentrations of DOC in the Vashon 

aquifer (Qva) typically ranged from 0.2 to 0.6 mg/L 

(fig. 9). Concentrations of DOC in the permeable 

interbeds (QC1pi) and in the Sea-level aquifer (QA1) 

were bimodal, with about one-half to two-thirds 

of the samples having concentrations similar to 

those in the Vashon aquifer. Most of the remaining 

samples had DOC concentrations from 1.5 to 2.0 mg/L. 

A similar bimodal distribution in DOC concentrations 

was observed in 34 samples from the QC1pi by 

Greene (1997), although the maximum DOC 

concentration was slightly larger (3.1 mg/L). Most 

samples with large DOC concentrations were in the 

permeable interbeds of the Upper confining unit, 

which was reported to contain interbedded lenses of 

peat and disperse organic material in some of the silty 

deposit (Deeter, 1979). These findings are consistent 

with other studies in which larger concentrations of 

dissolved organic carbon were often found in ground 

water from aquifers containing kerogen and other 

forms of buried organic matter (Thurman, 1985).
34 Estimates of Residence Time and Related Variations in Quality of Ground Water Beneath SUBASE Bangor and Vicinity, Kitsap County, Washington

Concentrations of organic nitrogen and ammonia in 

ground waters of the SUBASE Bangor area also 

typically were larger in ground water with larger DOC 

concentrations.

In 6 of 10 ground-water samples analyzed for 

dissolved methane, the reported concentrations were 

greater than 0.07 mg/L, the maximum level attributable 

to atmospheric equilibration, indicating a methane 

source within the aquifer system. Concentrations of 

methane in the 10 samples ranged from less than 0.04 

to 44 mg/L (table 3), with the largest concentrations 

observed in samples from the QC1pi. Ground-water 

samples with large concentrations (greater than 

10 mg/L) of methane also had concentrations of DOC 

greater than 1.0 mg/L. Bacterial methanogenesis is 

suspected because of the relative abundance of organic 

carbon reported in some of the hydrogeologic units in 

which there was no evidence of hydrocarbon deposits 

such as coal or petroleum. Microbial methanogenesis 

can result in significant fractionation of the isotope 

distribution of carbon constituents dissolved in ground 

water (Games and Hayes, 1976; Grossman, 1997). 

Methane was observed in similar-aged glacial 

sediments in Ontario, Canada, where Aravena and 

others (1995) found that bacterial methanogenesis had 

a substantial effect on the estimated age of ground 

water based on 14C data, as did Barker and others 

(1979). 

Values of δ13C for DIC measured in ground 

water can provide valuable information on the 

extent to which microbial and geochemical processes 

affect 14C concentrations in the ground water. 

Values of δ13C for DIC measured in ground-water 

samples from 30 wells near SUBASE Bangor ranged 

from –24.0 to –6.80 ‰, although concentrations 

of 14C ranged from 39 to 119 pmc (table 3). Analysis 

of replicate samples indicated analytical uncertainties 

of about 0.5 ‰ for δ13C and 1 pmc for 14C. 

. 

0

2

3

4

5

6

7

8

9

10

11

12

13

14

15

1

0 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 0.2

CONCENTRATION OF DISSOLVED ORGANIC CARBON, IN MILLIGRAMS PER LITER

NUMBER OF SAMPLES WITH DISSOLVED ORGANIC

CARBON IN CONCENTRATION CLASSIFICATION

Vashon aquifer (Qva)

HYDROGEOLOGIC UNIT

Upper confining unit (QC1) and

permeable interbeds within Upper confining unit (QC1pi)

Sea-level (QA1) and Deep (QA2) aquifers

Figure 9. Distribution of dissolved organic carbon in ground water from hydrogeologic units, SUBASE Bangor and vicinity, Kitsap 

County, Washington.
Estimates of Residence Time and Variations in Quality of Ground Water 35

The δ13C values of four samples of soil gas collected 

from heavily forested areas of SUBASE Bangor ranged 

from –21.6 to –20.6 ‰. The δ13C ratio of the ground 

waters characterized as modern ranged from –24 to –

18.2 ‰ with a median value of –21.2 ‰, consistent 

with the δ13C value in soil gas. The range of δ13C 

values present in modern ground waters of the Bangor 

area is typical of non-carbonate aquifers systems where 

root respiration and the oxidation of soil organic 

material is the source of carbon present in ground water 

(Pearson and Friedman, 1970; Clark and Fritz, 1997). 

The δ13C ratio of ground water that was characterized 

as pre-modern ranged from –21 to –6.8 ‰, indicating 

that enrichment of δ13C was occurring in some ground 

waters downgradient of the Qva.

In 7 of the 30 samples, δ13C was heavier than 

–18 ‰ (less negative than –18‰). Methanogenesis and 

carbonate mineral dissolution are processes that can 

enrich the δ13C (cause the value to become less 

negative) of DIC incorporated into ground water from 

soil organic-matter sources. Typical δ13C ratios for 

carbonate minerals range from –7 to 0 ‰ (Mook, 1980) 

and the extent of enrichment depends on the amount of 

carbonate dissolved. Chemical speciation of groundwater samples from the Bangor area indicates that 

dissolution of calcite was thermodynamically favorable 

in all ground waters except from well 27N/01E-35C01, 

and thus if calcite was present in the aquifer sediments, 

enriched values of δ13C in DIC (greater than –15 ‰) 

should have been more prevalent. 

During methanogenesis, bacteria fractionate 

carbon, enriching the δ13C of DIC and generating 

highly depleted δ13C (more negative) in the methane 

that is formed (Rosenfeld and Silverman, 1959; Barker 

and Fritz, 1981; and Grossman, 1997). Biogenic 

methane typically contains δ13C in the range of –55 to 

–90 ‰ (Deines, 1980). Aravena and others (1995) 

evaluated ground-water ages in a methanogenic-glacial 

aquifer in southern Ontario that also contained 

carbonate minerals, and found that the DIC in the aged 

ground waters ranged from –14 to +3 ‰. All groundwater samples from the Bangor study area with δ13C 

values greater than –15 ‰ also contained DOC and 

methane at concentrations greater than 1 mg/L. 

The concentration of 14C measured in groundwater samples from 29 wells ranged from 39 to 119 

pmc. The occurrence of 14C at concentrations greater 

than 100 pmc indicates the presence of 14C produced 

by thermonuclear-weapons testing. In ground-water 

samples that contained less than 100 pmc of 14C, the 

concentrations of 14C and 13C vary in a consistent 

manner such that ground water with diminished 14C 

concentrations is associated with enriched δ13C 

(fig. 10), suggesting that the mechanisms affecting the 

values of these two isotope concentrations are linked, 

as in bacterial methanogenesis.

Estimates of the bacterial fractionation of 14C 

resulting from methanogenesis typically are twice that 

of 13C (Plummer and others, 1996), thus, the effect of 

bacterial methanogenesis will be to increase the 

apparent age of ground water if the age of the carbon 

being reduced by methanogenesis is older than the 

carbon present in the ground water. Organic matter 

present in the Bangor aquifer system has been 

determined to range from 13,000 to greater than 40,000 

years old (Deeter, 1979). Thus, additional DIC in 

ground water of the Bangor area produced by 

methanogenic bacteria that are utilizing organic matter 

containing partially decayed 14C from the aquifer will 

substantially affect the apparent age of ground water 

based on the content of 14C in DIC in ground water. 

Geochemical mass-balance modeling can be used to 

estimate the amount of additional DIC present in 

ground water due to microbial methanogenesis. 

Changes in Ground-Water Chemistry Along Flow 

Paths

The composition of dilute ground water typically 

results from mineral dissolution and chemical 

alterations brought on by the interaction of the ground 

water with the aquifer sediments, and results in the 

accumulation within ground water of dissolved 

constituents as the water moves along its flow path. If 

dissolved concentrations rise to exceed mineral 

saturation levels, then precipitation may occur. 

Comparisons of the differences in the chemical and 

physical properties of ground-water samples collected 

near the recharge and discharge areas of the SUBASE 

Bangor study area indicate that the chemical evolution 

of ground water can be characterized by increases in 

the concentrations of dissolved constituents and the 

transition from oxidizing to reducing conditions. The 

largest increases in the concentrations of dissolved 

constituents were for calcium and bicarbonate, with 

more modest increases in the concentrations of silica, 

sodium, potassium, DOC, iron, manganese, and 

orthophosphate. Oxidizing conditions were common 

throughout the recharge area, where the concentrations
36 Estimates of Residence Time and Related Variations in Quality of Ground Water Beneath SUBASE Bangor and Vicinity, Kitsap County, Washington

of dissolved oxygen typically were greater than 5 mg/L 

and the value of ORP was commonly greater than 

150 mV (millivolts). Oxidizing conditions rapidly gave 

way to reducing conditions in the Upper confining unit 

QC1, as indicated by decreasing concentrations of 

dissolved oxygen and nitrate and decreasing ORP, 

typically to less than –150 mV, and increasing 

concentrations of iron and manganese. At some 

locations, diminished sulfate concentrations and the 

presence of methane indicated more extreme reducing 

conditions. Other changes that were common in some 

downgradient wells were increases in the 

concentrations of organic carbon and organic nitrogen 

and decreases in the concentrations of nitrate and 

chloride. Concentrations of environmental tracers also 

were decreasing at sampling sites downgradient of the 

recharge area. Concentrations of 14C typically were 

greater than 100 pmc in the recharge area and were 

generally less than 70 pmc in samples from wells 

tapping deeper hydrogeologic units. Likewise, 

enrichment of δ13C was observed only at downgradient 

sites.

The most chemically evolved ground waters 

were those collected from wells tapping the permeable 

interbeds (QC1pi) or those that moved through the 

QC1pi to more distant points along the ground-water 

flow path. The most chemically evolved ground waters 

are likely related to the presence of organic carbon. 

Elevated concentrations of calcium and bicarbonate 

were coincident with elevated concentrations of DOC. 

For instance, wells 25N/01E-6D04, 7J02, 8J02, and 

8Q03, which all had larger concentrations of calcium 

and bicarbonate than wells at greater distances along 

the flow path from the recharge area, also had larger 

concentrations of DOC. Microbial decomposition of 

organic material within the aquifer may have a 

substantial effect on the major-ion chemistry in ground 

water.

0

20

40

60

80

100

120

140

-25 -20 -15 -10 -5

DELTA CARBON-13, PER MIL

CONCENTRATION OF CARBON-14, IN PERCENT MODERN CARBON

Modern

Pre-modern

Indeterminate

GROUND WATER

Figure 10. Relation between the value of delta carbon-13 and concentrations of carbon-14 by age classification in dissolved 

inorganic carbon from ground water near SUBASE Bangor and vicinity, Kitsap County, Washington.
Estimates of Residence Time and Variations in Quality of Ground Water 37

Geochemical Mass-Transfer Modeling of Carbon 

and Estimates of Ground-Water Residence Time

Mass-transfer modeling is a method of 

accounting for changes in the chemical quality of 

ground water along a flow path. Measured differences 

in water chemistry at different locations in the groundwater flow system are accounted for by chemical 

reactions likely to occur in solution and with minerals 

of specific elemental compositions thought to be 

present in the aquifer. Chemical reactions simulated in 

mass-transfer modeling include dissolutionprecipitation of mineral phases, ion-exchange, 

oxidation-reduction, or gas-exchange. Pairs of samples 

with different water chemistries were used to represent 

ground water from different positions in the flow path. 

The results of this type of modeling typically lead to 

multiple solutions. Unrealistic solutions can be 

eliminated by using information on chemical variations 

in ground water, the thermodynamic solubilities of 

aqueous species and minerals, and the composition of 

solid phases within the aquifer. The model also can 

calculate and predict the isotopic composition of DIC 

in the ground water resulting from specified masstransfers, which can be used to simulate the interaction 

of ground water with the surrounding aquifer material 

through specific geochemical reactions that fractionate 

the specific element. This type of modeling provides a 

method of testing different possibilities for the 

chemical evolution of ground water, and has been 

useful in determining the mass transfer of carbon 

needed to improve estimates of ground-water residence 

time based on 14C concentrations in the DIC of ground 

water. Potential sources of carbon in the aquifer of the 

Bangor area include oxidation of organic matter and 

the dissolution of carbonate minerals. Potential sources 

of calcium and silica include weathering of silicate and 

mafic minerals. Potential sinks for dissolved carbon 

include precipitation of carbonate minerals and the 

microbial production of methane.

The modeling procedure used follows the 

theoretical framework for carbon mass transfer and 

isotope evolution in natural waters described by Wigley 

and others (1978; 1979), implemented through the 

geochemical model NETPATH developed by Plummer 

and others (1994; 1996). NETPATH accounts for the 

mass balance of carbon and other constituents by 

dissolution, precipitation, cation exchange, and 

oxidation-reduction reactions. Within NETPATH, the 

WATEQF subroutine calculates aqueous speciation of 

elements in solution and the thermodynamic stability 

of mineral phases (Plummer and others, 1976). 

Rayleigh distillation equations for fractionating 

isotopes are used. NETPATH has been used 

successfully to estimate ground-water residence times 

in chemically and hydrologically complex aquifer 

systems where processes such as oxidation of organic 

matter and outgassing of carbon dioxide are occurring 

(Aravena and others, 1995; Hinkle, 1995). 

Conceptual Model of Ground-Water Evolution 

near SUBASE Bangor

The selection of mineral phases and chemical 

constraints used in the NETPATH model was based on 

a conceptual model of the chemical evolution of 

ground water in the glacial aquifers and non-glacial 

confining units in the Puget Sound Lowland. This 

conceptual model was based on information about 

variations in the chemical composition of ground 

water, the composition of aquifer material, and 

previous geochemical studies in the Puget Sound 

Lowland, including the work of Dethier (1977), 

Johnson (1975),Wildrick (1976), Drever and Hurcomb 

(1986), and Postma and Brockenhuus-Schack (1987). 

The foundation of this conceptual geochemical model 

is that frequent precipitation containing dilute 

concentrations of major ions and charged with 

dissolved oxygen and carbon dioxide reacts with 

largely unweathered minerals in sediments deposited 

during Pleistocene glaciation. The dissolution of 

soluble minerals such as plagioclase and biotite results 

in the dilute ground-water solution found in the Qva. 

The chemical composition of ground water in the Qva 

develops within the time frame of modern ground 

water (10 to 50 years) and provides the starting solution 

for ground waters that continue to evolve chemically in 

deeper hydrogeologic units. As the flow of ground 

water proceeds away from the recharge areas, there is 

an increase in concentrations of carbon (both DIC and 

DOC), calcium, and magnesium and, to a smaller 

extent, silica, iron, and ammonia, and a decrease in 

concentrations of dissolved oxygen, nitrate, and 

sulfate. In the Upper confining unit (QC1), prominent 

geochemical processes included the weathering of 

basalt mineral phases and the oxidation of organic 

carbon. In some instances, the reduction of carbon 

dioxide led to the formation of methane via microbial 
38 Estimates of Residence Time and Related Variations in Quality of Ground Water Beneath SUBASE Bangor and Vicinity, Kitsap County, Washington

methanogenesis. Overall, the concentrations of 

dissolved constituents typically were dilute. Formation 

of mineral phases by precipitation reactions from 

solution was limited to secondary clay mineral phases. 

Basaltic material in the QC1 is often weathered 

to the extent that olivine and glass phases have been 

altered to chlorite and other secondary minerals 

(Glassley, 1973). General descriptions of basalt 

weathering indicate that after glass and olivine, the 

minerals pyroxene and plagioclase are the most 

susceptible to weathering (Colman, 1982; and Eggleton 

and others, 1987). Although the weathering of Crescent 

Formation basalts has not been well characterized, 

studies of the weathering of Columbia River Basalts 

demonstrate the alteration of pyroxene to smectite 

(Hearn and others, 1985; and McKinley, 1990). 

The weathering of plagioclase and pyroxenes to 

kaolinite or smectite is suggested by the molar ratio of 

sodium to calcium and the ratios of bicarbonate to 

silica found in the ground water of the Vashon aquifer, 

which are similar to many other natural waters where 

these reactions have been studied (Garrels and 

Mackenzie, 1967; and Drever, 1988). Smectite, 

montmorillonite, and kaolinite were weathering 

products identified in glacial sediments of the Puget 

Sound region and of the Cascade foothills (Wildrick, 

1976) and would be consistent with this type of silicate 

weathering. Evidence of the dissolution of calcite was 

reported for alpine environments of the Cascade Range 

by Dethier (1977) and Drever and Hurcomb (1986), but 

has not been reported in sediments from the Puget 

Sound Lowland (Mullineaux, 1961; Schlichte, 1968; 

Johnson, 1975; and Wildrick, 1976). 

The increase in both calcium and bicarbonate 

measured along the inferred ground-water flow path 

beneath SUBASE Bangor is a common pattern found 

in ground waters. Often, this pattern is the result of the 

dissolution of calcite or other calcium-carbonate 

minerals. This explanation may not be appropriate in 

the ground-water system of the Puget Lowland, 

although Drever and Hurcomb (1986) assumed the 

presence of calcite to explain chemical evolution of 

waters in glacial sediments of the North Cascade 

Mountains. Calcite was not observed in the 

geochemical and mineralogic studies of glacial 

sediments of the Puget Lowland (Mullineaux, 1961; 

Wildrick, 1976; and Detheir, 1977) and the δ13C value 

of DIC indicates that calcite or other marine carbonates 

are not a significant source of DIC in ground water of 

the Bangor aquifer system. Other sources of calcium, 

such as plagioclase, are widely present in these 

sediments and they are relatively soluble in dilute 

ground water, and bicarbonate is a primary product of 

the oxidation of organic matter. 

Organic matter present in the aquifer material 

can be oxidized and fermented, leading to the 

formation of bicarbonate. The occurrence of microbial 

methanogenesis within the aquifer system is indicated 

by the presence of methane in ground-water samples 

that characteristically have low ORPs and elevated 

concentrations of DIC, DOC, and enriched δ13C. The 

effects of microbial methanogenesis on the value of 

δ13C of DIC are large: fractionation factors range from 

–40 to –75 ‰ depending on metabolic pathway and 

temperature (Grossman, 1997). The fractionation factor 

for 14C is estimated to be twice that of δ13C, thus a 

small amount of methanogenic activity in ground water 

can have a substantial effect on the apparent 14C age of 

ground water as well as the value of δ13C. 

In this study, ground-water samples with small 

14C concentrations have substantially larger amounts of 

total carbon than those with 14C concentrations near 

100 pmc. The major source of additional carbon in the 

SUBASE Bangor ground-water system is believed to 

be the oxidation or fermentation of sedimentary 

organic material. Deeter's (1979) examination of the 

glacial deposits of the Kitsap Peninsula showed that 

organic material commonly is found in the fine-grained 

interglacial deposits. Organic material also has been 

noted in many well drillers' reports from the area. The 

increase in concentrations of DOC, nitrogen, and 

ammonia with decreasing 14C concentrations is 

consistent with the oxidation of organic material. 

Microbial oxidation of organic material has been 

shown to occur deep within aquifers and to result in the 

increase of bicarbonate concentrations along groundwater flow paths (Chapelle and Knobel, 1985; Chapelle 

and others, 1987; McMahon and Chapelle, 1991; and 

Murphy and others, 1992). 
Estimates of Residence Time and Variations in Quality of Ground Water 39

NETPATH Modeling of Ground-Water Residence 

Time

To provide more reliable estimates of the 

residence time of pre-modern ground waters based on 

the concentration of 14C in DIC, NETPATH 

simulations were used to model the geochemical 

interactions that affect the concentration and isotopic 

composition of DIC in ground water as it flows 

between the point of recharge and the point at which 

the sample was collected. The NETPATH model 

calculates the 14C concentration at the downgradient 

well by modifying the 14C concentration found in the 

upgradient well for chemical reactions occurring along 

the flow path, and not for radioactive decay. The 

calculated activity is referred to as the “non-decay 14C 

concentration.” The ratio of the 14C concentration 

measured in the sample to the non-decay 14C 

concentration is utilized in the radioactive decay 

equation to calculate ground-water residence time. 

Multiple NETPATH simulations were run to evaluate 

the sensitivity of the modeling results to uncertainty in 

14C concentrations of the initial solution and the 

organic material found in the aquifer sediments. 

Mass-transfer modeling using NETPATH was 

applied to water chemistry reported for 14 

downgradient wells in which environmental tracer data 

indicated that the ground water could be characterized 

as pre-modern (table 5). A mass-transfer model was not 

developed for well 25N/01W-12L02 because the DIC 

concentration in this sample was small, the water 

contained dissolved oxygen, and the general chemistry 

resembled recently recharged ground water. To the 

degree possible, the location of these wells was 

concentrated in localized areas to provide a crosssectional view of the distribution of ground-water 

residence times. The NETPATH simulations were 

carried out on paired sets of water chemistries from 

samples representing an upgradient and a downgradient 

location in the ground-water system. The upgradient 

conditions for all NETPATH simulations were 

represented by the median concentrations of 

ground-water constituents found in wells tapping 

modern water in the Vashon aquifer (table 5; well 

25N/01E-5A04, which was judged to be anomalous, 

was not used). The median cation and anion 

concentrations for these nine wells were within a few 

of percent of the median concentrations for the 54 

wells from the Vashon aquifer sampled as part of the 

ambient water-quality part of the broader study at 

SUBASE Bangor (Greene, 1997). The charge balance 

for the chemical analysis (difference between the sum 

of median values for anions and cations) was 2.34 

percent for the 9 wells and 1.75 percent for the 54 

wells, which was acceptable. For the aqueous 

speciation modeling, the charge balance was reduced to 

zero by adjusting the concentration of bicarbonate. 

A lack of extensive data on the mineralogical 

composition of glacial sediments limited the extent to 

which a conceptual geochemical model of the chemical 

evolution within those sediments could be developed. 

A specific concern for the correction of 14C estimates 

of ground-water residence time is the apparent lack of 

carbonate minerals in glacial sediments in the Puget 

Sound Lowland. Of the mineralogical and chemical 

analysis reported by previous investigators, only one 

reported the presence of siderite, an iron-carbonate 

mineral, as a minor component in one sample. 

Constituents used to constrain the NETPATH 

model for chemical evolution of downgradient wells 

included the concentrations of carbon, calcium, 

sodium, iron, sulfur, and silica and redox state. The 

following phases were available to the NETPATH 

modeling process, but only seven phases (equal to the 

number of constraints) could be included in any 

specific version of the models developed. Mineral 

phases included pyroxene (augite), chlorite, pyrite, 

smectite, mafic montmorillinite, calcite, goethite, and 

gypsum. Non-mineral phases include organic matter as 

CH2O and carbon dioxide and methane gases. Anion 

exchange of two sodium ions for one calcium ion could 

also be used as a model phase. The mineral phase 

gypsum, which is not known to occur in these aquifer 

sediments, was included to provide a source of sulfate 

ions required in models for three wells. The source of 

the sulfate observed in ground water from the deeper 

hydrogeologic units is not known. Possible 

explanations include pyrite oxidation, as suggested by 

Tesoriero and others (2000), or the fine-grained 

deposits of the adjacent confining unit, as described by 

Chapelle and McMahon (1991).

 With the exception of smectite and chlorite, the 

stoichiometry of the mineral phases was default values 

contained in the NETPATH code. Smectite, a mafic 

montmorillinite, contains a larger fraction of calcium 

than the default mafic montmorillinite. The 

stoichiometry of smectite used here was derived from 

weathered basalts of the Columbia River Basalt Group 

(Hearn and others, 1985). The analysis of chlorite by 

Glassley (1973) indicated that iron made up about 40 

percent of the cations in mineral formula of chlorite in 

basalts of the Crescent Formation. Chlorite was 
40 Estimates of Residence Time and Related Variations in Quality of Ground Water Beneath SUBASE Bangor and Vicinity, Kitsap County, Washington

assigned a stoichiometry of (Mg3.5,Fe1.5)

Al2Si3O10(OH)8. The NETPATH mass-balance model 

computed the amounts of each phase required to either 

dissolve, precipitate, or exchange in order to match the 

chemical changes observed between the modern 

ground water, as represented by the median 

concentrations from wells tapping the Qva, and the premodern water, from the 14 downgradient wells. The 

thermodynamic validity of the dissolution-precipitation 

reactions was checked within the WATEQF subroutine 

by examining the saturation index calculated for 

mineral phases at the downgradient well.

Other carbon isotopic data needed in the masstransfer modeling were either measured during this 

study or taken from published values. Carbonate 

minerals were considered an active phase in three of 

the models, in which case the isotope values for calcite 

were δ13C = 0 ‰ and 14C activity = 0 pmc (Clark and 

Fritz, 1997). With the apparent absence of carbonate 

minerals in the soils and unsaturated zone, the δ13C 

value in the recharge ground water is assumed to be 

that found in soil gas. The δ13C of four samples of soil 

gas ranged from –21.6 to –20.6 ‰. A value of –21.0 ‰ 

was used in all carbon mass-transfer models. The δ13C 

of organic matter in the aquifer was assumed to be 

–25.0 ‰, which is a commonly used value for plant 

matter (Mook, 1980). Methane also was generated in 9 

of 14 of the mass-transfer models. The δ13C of 

methane from ground water of the study area was not 

measured and was assigned a value of –70 ‰, based on 

13C analysis of biogenic methane found in glacial-drift 

deposits (Deines, 1980; Arevena and others, 1995). The 

resulting fractionation factor for δ13C from the 

methanogenic conversion of δ13C from –25 to –70 ‰ 

was calculated to be 1.0541. 

The modeling technique utilized by NETPATH 

will find all possible models utilizing the phases that 

satisfy the model constraints, and as such NETPATH 

can generate numerous hypothetical models. Models 

that violate geochemical constraints, such as 

precipitation of a phase in which the aqueous 

concentrations were not saturated, were eliminated 

from consideration. The primary check on the 

suitability of models involving the mass transfer of 

carbon was a comparison of model-calculated values of 

δ13C to the values of δ13C measured in the 

downgradient wells. 

In general, the overall reactions that were 

modeled by NETPATH to represent the geochemical 

evolution of ground water between the recharge areas 

and the sampled well were the oxidation of organic 

matter, the dissolution of pyroxene (augite) and 

chlorite, and the precipitation of smectite, 

montmorillinite, goethite, pyrite, and the exchange of 

calcium for sodium ions. In 60 percent of the wells, the 

production of methane was modeled. The modeled 

mass transfers that occurred between the recharge area 

and well 25N/01W-01B02 could be written in the 

following manner:

MedQva(dissolved) + 0.82 CH20 + 0.82 pyroxene 

 + 0.06Na2X ⇒ 0.28 methane + 0.43 smectite 

 + 0.06 goethite + 0.02 pyrite +0.06 CaX 

 + Well 1B02(dissolved), (2)

where:

MedQva(dissolved) and Well 1B02(dissolved) 

represent the dissolved constituents present in the 

initial and final waters, respectively. The reaction 

coefficients are in millimoles (mmoles) per kilogram of 

water. For mass balance of carbon between ground 

water from the Vashon aquifer and well 25N/01W01B02, 1.41 mmoles of carbon are present in the initial 

ground water of MedQva, to which is added 0.82 

mmole of carbon from CH2O through the oxidation of 

organic material. With the production of 0.28 mmole of 

methane, 1.95 mmoles of inorganic carbon remains in 

the ground water sampled from well 25N/01W-01B02. 

Uncertainty relating to the silicate mineral phases led 

to several modeled solutions. However, the estimates of 

ground-water residence time were not sensitive to the 

silicate phases utilized in the model and estimates of 

ground-water residence time varied by only a few 

percent under the various silicate mineral scenarios. 

MedQva(dissolved) = median concentration of 

dissolved constituent in the 

Vashon aquifer,

Well 1B02(dissolved) = concentration of dissolved 

constituents in well 

25N/01W-01B02,

Na2X = sodium exchange site on 

solid phases, and

CaX = calcium exchange site on 

solid phases.
Estimates of Residence Time and Variations in Quality of Ground Water 41

Selected results of the NETPATH modeling that 

represent the geochemical evolution between the 

recharge area and 14 downgradient sampling locations 

are shown in table 6. The value of δ13C of ground 

water DIC was not used as a model constraint in the 

construction of NETPATH models and was allowed to 

change on the basis of the geochemical reaction 

involving carbon. The primary criterion for the 

selection of models representing mass transfers of 

carbon and the concurrent effect to 14C was the 

accuracy in the model-predicted δ13C compared to 

measured δ13C. The model that included the oxidation 

of organic carbon and methanogenesis was found to 

satisfy the basic mineral and water-quality constraints 

for all ground waters modeled; however, 

methanogenesis was invoked to model mass transfers at 

only nine sites. The values of δ13C predicted by 9 of 

the 14 mass-transfer models were within 1 ‰, which is 

considered a good match. Analytical variability in the 

measurement of δ13C is about 0.5 ‰ and measurement 

of δ13C in three sets of duplicate ground-water samples 

varied from 0.3 to 0.6 ‰ (Appendix A). The maximum 

difference in the model-predicted value of δ13C and the 

measured value was 2.5 ‰. 

The calculated value of δ13C of DIC was very 

sensitive to the amount of methane generated. The 

largest difference in the modeled and measured values 

of δ13C of DIC for methanogenic models was 2.3 ‰ 

for well 25N/01E-8Q03. Some of the discrepancy may 

be related to uncertainty in the methane analysis. The 

quality-assurance data for the methane analysis were 

limited to replicate samples, which showed little 

variation but could not be used to assess bias in the 

analysis. For the five wells with large measured 

methane concentrations, the model-calculated quantity 

of methane was typically about one-half or less than 

the measured amount. Whether this indicates an 

additional source of methane, inaccurate analysis, or 

inappropriate modeling could not be determined. 

However, when the model for well 25N/01E-8Q03 was 

run without the methane present in the downgradient 

solution, the difference between the modeled and 

measured values of δ13C of DIC was 1.3 ‰. 

Variations and Distribution of Carbon-14 Estimate 

of Ground-Water Residence Time

After the NETPATH models were developed that 

fit geochemical constraints, ground-water residence 

time based on 14C concentrations were estimated. A 

series of model runs were performed to evaluate the 

effects of uncertainty in two important model input 

parameters that could not be well constrained: the 

initial concentration of 14C in the ground water of the 

recharge area and the concentration of 14C in the 

organic material present in the QC1 that was the source 

of additional carbon in ground water. 

The range of concentration of 14C measured in 

modern ground water from the recharge area was large, 

from 86 to 119 pmc and undoubtedly affected by the 

14C generated by the testing of thermonuclear weapons 

and thus not representative of 14C concentrations 

present at the time pre-modern ground waters were 

recharged. The presumption that 14C activity of the 

recharge was 100 percent modern carbon may not be 

realistic as the oxidation of old carbon within soils can 

generate soil CO2 in which the 14C activity is less than 

modern (Clark and Fritz, 1997). Likewise, pediogenic 

carbonates and kerogen incorporated in glacial till 

(Vogel, 1967; Keller, 1991) also could affect the 

concentration of 14C without affecting the value of 

δ13C. Coal and shale from bedrock overridden by 

moving glaciers are the reported sources of the kerogen 

found in till by Keller (1991). These sources of carbon 

are not extensive in the Puget Sound region, although 

they are found in some areas. Vogel (1967) assigned an 

initial 14C concentration in a glacial aquifer of 85 pmc 

to account for additional DIC incorporated into 

recharging ground waters from carbonate minerals in 

the unsaturated zone. Preliminary estimates of groundwater residence times using data from downgradient 

wells of this study and Vogel’s initial 14C concentration 

of 85 pmc resulted in negative estimates of ground 

water residence time in some wells. Thus, using 85 

pmc for the initial activity produced overestimations of 

the amount of DIC dilution in the initial ground waters 

at some wells but not others. Kalin (2000) reported that 

oxidation of Holocene organic matter resulted in 14C 

activity from 88 to 92 pmc in recently recharged 

ground water which also contained tritium. 
42 Estimates of Residence Time and Related Variations in Quality of Ground Water Beneath SUBASE Bangor and Vicinity, Kitsap County, Washington

Table 6. Mass transfers of modeled phases and measured and model-calculated values of carbon-13 from selected geochemical mass-transfer models of 

pre-modern ground water, SUBASE Bangor and vicinity, Kitsap County, Washington

[Well No.: Location of wells is shown in figure 4. Phases: Mass transfer units are in millimoles per liter. Values in parentheses indicate concentration in solution. 

Hydrogeologic units: QC1, Upper confining unit; QC1pi: permeable interbeds within Upper confining unit; QA1, Sea-level aquifer; QA2, Deep aquifer.

Abbreviations: –, phase not part of model]

Methanogenic models

Hydrogeologic unit and well No. 

Phase QC1 QC1pi QA1 QA1, QA2

26N/01E17C0125N/01E07J0225N/01E08J0225N/01E08Q0325N/01E09N0225N/01E06D0425N/01W01B0227N/01E22Q0526N/01E31R011

Ca/Na exchange 0.062 0.084 0.019 0.226 0.108 0.074 0.063 0.061 0.035

Goethite -.767 -2.33 -.168 -5.06 -.993 -.059 -.072 -.122

CH2O 2.45 1.52 3.76 1.83 1.49 .816 .175 .935

CH4 gas -.036 (-1.44) -.663 (-2.75) (-1.00) -.213 -.282 -.067 -.333

Pyrite – -.022 -.012 -.017 -.016 -.21 -.021 .005 -.02

Calcite – .578 – – – – – – –

Chlorite .362 1.09 .88 2.24 .476

Augite – – .958 2.45 1.09 .327 .819 .901 .789

Smectite -.284 -.798 -.429 -3.03 -.851 – -.434 -.499 -.373

Mafic montmorillinite – – – – – -1.29 – – –

SO4, gypsum .005 – – – – .384 – – –

Comparison of carbon-13 measured in samples and calculated from mass-balance modeling

δ13C, measured, per 

mil

-17.4 -12.4 -10.5 -6.8 -15 -18.7 -13.8 -18.4 -14.7

δ13C, model 

calculated, per mil

-17.9 -10.4 -10.1 -4.5 -15.4 -18.7 -15.2 -19.3 -14.4

Non-methanogenic models

Hydrogeologic unit and well No.

Phase QC1 QC1pi QA1 QA2

27N/01E35C127N/01E22Q426N/01E32L526N/01W36R326N/01E32L4

Ca/Na exchange 0.068 0.027 0.022 0.009 0.009

Goethite -.119 -.401 -.129 .02 -.092

CH2O .082 .649 .129 .197 .135

CH4 gas – – – – –

Pyrite -.005 -.147 -.009 -.016 -.006

Calcite -.127 – .123

Chlorite . .243 .032 .047

Augite .799 – .462 .199 .351

Smectite -.392 -.161 -.255 -.129 -.208

SO4, gypsum – .252 –

Comparison of 13C measured in samples and calculated from mass-balance modeling

δ13C, measured, per mil -18.7 -21.1 -20.7 -20.7 -20.3

δ13C, model calculated, 

per mil

-21.2 -22.1 -21.3 -19.8 -21.4

1Well is screened in QA1 and QA2. 
Estimates of Residence Time and Variations in Quality of Ground Water 43

When the concentration of 14C and the value of δ13C 

for the 33 wells are plotted (fig. 10), there is an 

apparent change in slope and the distribution of modern 

and pre-modern ground water near 80 pmc. Because a 

single initial concentration of 14C was not readily 

indicated from the data, model simulations were run 

using three values for the initial 14C activity: 80, 85, 

and 92 pmc. Uncertainty also was present in the 14C 

activity of the dispersed organic matter present within 

the aquifer sediments. The concentration of 14C in 

organic matter present within the peat material 

obtained from the Upper confining unit (QC1) ranged 

from roughly 2 to 15 pmc (Deeter, 1979) and provides 

a likely range of 14C activity present throughout the 

sediments that make up the hydrogeologic units tapped 

by the downgradient wells. Multiple simulations were 

run using 14C concentrations of 2, 10, and 15 pmc.

A matrix showing the estimates of ground-water 

residence time calculated using different values of the 

14C activity in the recharge water and aquifer organic 

matter is shown in table 7. Estimates of ground-water 

residence time varied most in the Upper confining unit, 

where estimates ranged from modern to more than 

4,550 years bp. The younger-aged waters were 

restricted to the upgradient recharge area, whereas the 

older-aged waters (on the order of thousands of years) 

were found in both upgradient and downgradient 

locations.

Many ground waters with shorter residence times 

were from wells near the area of recharge, and those 

with longer residence times were from wells either 

deeper in the ground-water flow system or near the area 

of ground-water discharge. The spatial distribution is 

shown in figure 11, which is a composite of groundwater residence times that were estimated near the 

southern end of SUBASE Bangor. The large residence 

times of water found in wells tapping the Upper 

confining unit near Clear Creek drainage (a groundwater discharge zone) are explained by the fact that this 

ground water previously may have been in deeper parts 

of the flow system, such as the Sea-level aquifer, and is 

moving upward as it discharges. Residence times of 

ground waters in the Sea-level aquifer generally are on 

the order of thousands of years. However, residence 

times at several locations were only several hundred 

years old to modern. The shorter residence times may 

be explained by intensive pumping at large production 

wells such as the SUBASE Bangor production well 

(26N/01E-18P01) that may cause increased downward 

flow of ground water, resulting in a mixture of modern 

and pre-modern ground water.

Comparison of Estimates of Ground-Water 

Residence Times Based on Carbon-14 and 

Numerical Ground-Water Flow Modeling

The 14C estimates of ground-water residence 

time were developed to provide an independent 

constraint that could be used to help calibrate the 

ground-water flow model developed by van Heeswijk 

and Smith (2002). At 12 selected wells, van Heeswijk 

and Smith estimated ground-water residence times 

using the calibrated flow model with the particletracking module MODPATH to trace the paths of 600 

hypothetical water particles from a well to the recharge 

area. The 12 wells were identified as having premodern water, based on environmental tracer data. The 

resulting flow-modeled estimates of ground-water 

residence time for all particles ranged from 16 to 2,359 

years, and the median residence time of the 600 

particles modeled for each well ranged from about 100 

to 500 years (table 8).

Estimates of ground-water residence time 

derived from the geochemical and numerical flow 

modeling were both less than 5,000 years. The 

minimum residence times estimated using 14C-dating 

techniques exceeded the median residence times 

simulated with the flow model for 5 of the 12 simulated 

sites. Most of the maximum residence times simulated 

with the flow model were significantly less than the 

maximum residence times estimated using the 14Cdating techniques. Therefore, the 14C estimates provide 

an upper limit on the age of ground water in the flow 

system. 
44 Estimates of Residence Time and Related Variations in Quality of Ground Water Beneath SUBASE Bangor and Vicinity, Kitsap County, Washington

Table 7. Estimated ground-water residence times computed from mass-balance models using a range of initial carbon-14 activity in Vashon aquifer and 

a range of carbon-14 activity in aquifer organic matter, SUBASE Bangor and vicinity, Kitsap County, Washington

[Abbreviations: 14C, carbon-14; pmc, percent modern carbon]

Well No.

Assigned 14C activity 

in organic matter in 

aquifer (pmc)

Estimated ground-water residence time for 

assigned initial 14C activity (years) Range of estimated ground-water 

residence time (years) 92 pmc 85 pmc 80 pmc

Upper confining unit (QC1)

26N/01E-17C01 Model does not 

utilize organic C

2,990 2,350 1,840 1,840 to 2,990

27N/01E-35C01 15 3,080 2,440 1,940 1,900 to 3,080

10 3,070 2,430 1,920

2 3,050 2,410 1,900

Permeable interbeds within Upper confining unit (QC1pi)

25N/01E-07J02 15 510 41 -330 50 to 510

10 -310 -830 -1,240

2 -1,610 -2,220 -2,710

25N/01E-08J02 15 1,700 1,180 760 50 to 1,700

10 1,210 650 210

2 350 -270 -770

25N/01E-08Q03 15 4,550 4,110 3,760 920 to 4,550 

10 3,550 3,060 2,670

2 2,010 1,400 920

25N/01E-09N02 15 4,500 3,970 3,560 2,130 to 4,500

10 4,040 3,480 3,040

2 3,250 2,630 2,130

27N/01E-22Q04 15 -975 -1,570 -2,040 All models result in futuristic dates and are 

invalid for estimating 14C age of ground 

water

10 -1,170 -1,780 -2,270

2 -1,490 -2,130 -2,630

Sea-level aquifer (QA1)

25N/01E-06D04 15 2,480 1,940 1,500 330 to 2,480

10 2,110 1,540 1,080

2 1,470 850 330

25N/01W-01B02 15 4,550 4,000 3,540 2,750 to 4,550

10 4,550 3,720 3,240

2 3,890 3,250 2,750

27N/01E-22Q05 15 1,480 850 340 120 to 1,480 

10 1,420 790 280

2 1,330 690 120

26N/01E-32L05 15 1,040 400 -100 50 to 1,040

10 1,010 370 -140

2 960 320 -190

26N/01E-36R03 15 450 -180 -680 50 to 450 

10 410 -220 -730

2 340 -300 -810

Deep aquifer (QA2)

26N/01E-31R011 15 2,120 1,540 1,090 180 to 2,120

10 1,820 1,220 750

2 1,320 690 180

26N/01E-32L04 15 1,510 870 370 250 to 1,510

10 1,490 860 350

2 1,420 780 250

1Well is screened in QA1 and QA2. 
Estimates of Residence Time and Variations in Quality of Ground Water 45

800

400

200

600

400

200

600

800

400

200

600

400

200

600

SEA LEVEL

25N/01W-01B02

25N/01E-06D0426/N01E-31R01

26N/01E-32L04

26N/-01E-32L05

9N2

Qvr

QC1pi

QC

QA2

Qva 15-50

QC1pi

15-1,700

QA1

QU

Qvt

QC1

Qvt Qvt

QC1pi 3,480

QC

1540 3,720

1,220

370

860

SEA LEVEL

FEET FEET

Water table

EXPLANATION

Qvr SURFICIAL AQUIFER

0 0.5 1 MILE

VERTICAL EXAGGERATION × 10

Qvt VASHON TILL CONFINING UNIT

Qva VASHON AQUIFER

QC1 UPPER CONFINING UNIT

QC1pi PERMEABLE INTERBEDS WITHIN UPPER CONFINING UNIT

QA1 SEA-LEVEL AQUIFER

QC UNDIFFERENTIATED CONFINING UNITS

QA2 DEEP AQUIFER

QU UNDIFFERENTIATED DEPOSIT

WELL NO.

STATIC WATER LEVEL IN WELL

SAMPLED FOR ESTIMATE OF

RESIDENCE TIME

SCREENED INTERVAL

ESTIMATE OF GROUND-WATER

RESIDENCE TIME, IN YEARS 1,541

25N/01E-06D4

WEST EAST

Figure 11. Distribution of estimated ground-water residence time in the ground-water system beneath SUBASE Bangor and 

vicinity, Kitsap County, Washington. 

Individual estimates are based on initial 14C activity of 85 percent modern carbon (pmc) and 14C activity of aquifer organic 

matter of 10 pmc (see table 7). Section based on hydrogeologic section F-F' of Kahle (1998, pl. 3). Ground-water residence times 

for Qva and QC1pi projected from other locations.
46 Estimates of Residence Time and Related Variations in Quality of Ground Water Beneath SUBASE Bangor and Vicinity, Kitsap County, Washington

The residence times simulated with the groundwater flow model were consistent with tritium and CFC 

concentration data—the median simulated residence 

times were all greater than 50 years. The minimum 

residence times simulated for some particles arriving at 

wells 25N/01E-06D04 and 26N/01E-32L05 were 32 

and 16 years, respectively, indicating that some modern 

water may be present in these wells. However, the 

minimum flow-modeled estimates may represent only 

a small percentage of the water in each well, hence the 

presence of modern environmental tracers would likely 

be small and may not be detectable. 

The discrepancies between the 14C and groundwater flow model estimates of ground-water residence 

time likely resulted from multiple factors, including 

uncertainties related to geochemical processes and 

measurements, as well as uncertainties related to the 

flow-model representation of the hydrologic system. 

Uncertainties in the numerical simulation of groundwater flow include the conceptualization of the groundwater flow system, vertical and horizontal 

discretization of the model grid, simulated aquifer and 

confining unit properties such as porosities and vertical 

and horizontal hydraulic conductivities, and simulated 

ground-water recharge. In their simulation, van 

Heeswijk and Smith (2002) used values for effective 

porosity of till = 0.15; sand and gravel = 0.3; and clay 

and silt = 0.2 that they considered to be the largest 

appropriate for the hydrogeologic units of the Bangor 

area and that increased their estimated of ground-water 

residence time. It is possible that some of the flow 

paths simulated by the particle-tracking software do not 

accurately represent the actual flow paths of water 

particles that were sampled. This may explain large 

discrepancies between flow-modeled and 14C-modeled 

ages estimated for wells 25N/01W-01B02 and 

25N/01E-09N02, which are located near regional 

discharge locations. Within the flow model, the particle 

paths to these wells may have originated from nearby 

recharge areas rather than following deeper regional 

Table 8. Comparison of estimates of ground-water residence time (age) based on the concentration 

of carbon-14 and numerical simulation of ground-water flow, SUBASE Bangor and vicinity, Kitsap 

County, Washington

[Modified from van Heeswijk and Smith (2002)]

Well No.

 Estimate of ground water residence time, in years

Range based 

on 14C

Based on numerical ground-water flow modeling

Median Minimum Maximum

Upper confining unit (QC1)

27N/01E-35C01 1,900-3,080 104 41 168

Permeable interbeds within the Upper confining unit (QC1pi)

25N/01E-07J02 50-510 163 106 199

25N/01E-08J02 50-1,700 219 175 361

25N/01E-08Q03 920-4,550 235 175 407

25N/01E-09N02 2,130-4,500 237 190 359

Sea-level aquifer (QA1)

25N/01E-06D04 330-2,480 103 32 212

25N/01W-01B02 2,750-4,550 101 54 160

26N/01E-32L05 50-1,040 211 16 428

26N/01E-36R03 50-450 97 71 392

27N/01E-22Q05 120-1,480 399 242 2,359

Deep aquifer (QA2)

26N/01E-31R011 180-2,120 296 182 661

26N/01E-32L04 250-1,510 478 360 1,816

1Well is screened in QA1 and QA2.
Summary 47

ground-water flow paths that are indicated by the 

evolved ground-water quality observed in the samples 

from these wells. Additionally, near-stagnant or lowvelocity parts of the flow system may not be adequately 

simulated by the numerical flow model and may 

explain the discrepancy between the flow-modeled and 

14C-modeled ages in well 25N/01E-08Q03. The 

limitations of the ground- water flow model are 

discussed in more detail by van Heeswijk and Smith 

(2002). Uncertainty in the isotope data can result in 

large variability in 14C model results, as demonstrated 

by the data in this report (table 7). 

In their simulation, van Heeswijk and Smith 

(2002) used values for effective porosity of till = 0.15; 

sand and gravel = 0.3; and clay and silt = 0.2 that they 

considered to be the largest appropriate for the 

hydrogeologic units of the Bangor area and that 

resulted in upper limits of residence times that could be 

simulated with their numerical flow model. Despite 

simulating upper limits of residence times, the modelsimulated values generally are smaller than the 14C 

values. It is possible that some of the flow paths 

simulated by the particle-tracking software do not 

accurately represent the actual flow paths of water 

particles that were sampled, particularly near regional 

ground-water discharge areas where ground water flow 

lines converge. This may explain large discrepancies 

between flow-modeled and 14C-modeled ages 

estimated for wells 25N/01W-01B02 and 25N/01E09N02, which are located near regional discharge 

locations. Within the flow model, the particle paths to 

these wells may have originated from nearby recharge 

areas rather than following deeper regional groundwater flow paths that are indicated by the evolved 

ground-water quality observed in the samples from 

these wells. Additionally, near-stagnant or low-velocity 

parts of the flow system may not be adequately 

simulated by the numerical flow model and may 

explain the discrepancy between the flow-modeled and 

14C-modeled ages observed in well 25N/01E-8Q03. 

The limitations of the ground-water flow model are 

discussed in more detail by van Heeswijk and Smith 

(2002). 

Uncertainty in the 14C estimates of ground-water 

residence time are often on the order of 1,000 years, in 

large part due to uncertainty in the estimate of the 

initial 14C activity of recently recharged ground water 

(Kalin, 2000). Information about the mineralogy of the 

aquifer sediments in the Bangor area is very limited 

and undoubtedly incomplete. Thus, the selection of 

phases used in the NETPATH model might be 

improved with additional information. Likewise, 

NETPATH was only able to model a limited number of 

phases, and it is likely that in glacial sediments with 

heterogeneous source areas there are more than seven 

chemically reactive phases in the ground-water system. 

Diffusion in ground-water systems that contain 

substantial confining units also may reduce the 

concentration of 14C in ground water, resulting in a 

bias toward larger estimates of ground-water residence 

time, as suggested by Sanford (1997) and Bethke and 

Johnson (2002). In ground-water systems that contain 

many confining units, recently recharged ground water 

containing large concentrations of 14C may leave the 

aquifer by diffusion into adjacent confining units; 

likewise, at downgradient locations ground water that 

is depleted in 14C may defuse into the aquifer. Both 

processes would diminish the 14C content of ground 

water, resulting in an over-estimate of ground-water 

residence times. 

Although differences between estimates of 

ground-water residence times based on the 

geochemical models of 14C and numerical simulation 

of ground-water flow can be large, the results do 

confirm that travel times to the stratigraphically deeper 

sections of the aquifer system on and near SUBASE 

Bangor are on the order of hundreds to thousands of 

years. The use of environmental tracers provides 

additional information in instances where there is rapid 

movement of ground water to stratigraphically deeper 

units along routes that bypass portions of the aquifer 

system, such as in well 27N/01E-27J02.

SUMMARY

The U.S. Geological Survey, in cooperation 

with the U.S. Navy, estimated the residence time of 

ground water at different locations within the groundwater system in the vicinity of Naval Submarine Base 

(SUBASE) Bangor. Water samples were collected

 from 33 wells for analysis of selected environmental 

tracers, inorganic constituents, and carbon species. 

Estimates of ground-water residence time were 

based on concentrations of 14C, tritium, and 

chlorofluorocarbons. This work is part of a larger study 

to understand the regional ground-water flow system at 

SUBASE Bangor and vicinity. 
48 Estimates of Residence Time and Related Variations in Quality of Ground Water Beneath SUBASE Bangor and Vicinity, Kitsap County, Washington

The ground-water system is composed of 

alternating coarse and fine-grained deposits, mostly of 

glacial and inter-glacial origin. The shallower aquifer 

(Vashon aquifer) is composed of glacial outwash sand 

and is beneath a discontinuous surficial till deposit. The 

deeper Sea-level and Deep aquifers are fluvial sand and 

gravel deposit separated from the shallow aquifer by a 

thick layer of fine-grained interglacial material that in 

places contain lenses or interbeds of coarse material 

that yield usable quantities of ground water. 

The concentration of carbon increased in ground 

water along ground-water flow paths, indicating that 

additional carbon was being incorporated into solution 

from the aquifer matrix. The carbon present within the 

aquifer material will affect the 14C activity of ground 

water and thus affect the estimate of ground-water 

residence time. Carbon-13 ratios indicate that the 

source of the additional carbon is dispersed organic 

carbon present primarily in the confining unit 

separating the two aquifers. Dissolved methane was 

present in some ground water at concentrations larger 

than atmospheric concentrations in more than one-half 

of the samples analyzed. The source of the methane is 

the microbial decomposition of organic matter. The 

additional carbon in the form of methane reduces the 

activity of 14C in ground water, resulting in uncorrected 

estimates of residence time that are substantially larger 

than the actual ground-water residence time. 

 Geochemical modeling of the mass transfer of 

carbon and carbon isotopes, using the NETPATH code, 

was used to estimate ground-water residence times 

based on 14C concentrations. The modeling also 

accounted for the interaction of carbon in solution with 

carbon present in the aquifer material. The overall 

reactions that were modeled were the oxidation of 

organic matter with the production of methane, the 

dissolution of silicate minerals and the precipitation of 

goethite, and the ion exchange of calcium for sodium. 

Ground-water residence times based on 14C were 

estimated for 14 locations in the ground-water flow 

system and ranged from modern to about 4,550 years 

before present. 

 Tritium concentrations were used to detect the 

presence of modern ground water and to identify water 

samples that were a mixture of modern and pre-modern 

ground water. Three of the samples analyzed contained 

both modern and pre-modern waters. Mixed ground 

water is believed to result from large pumping stresses 

that may have increased downward movement of 

younger water into lower aquifers, resulting in a 

mixture of relatively young and old waters. 

The shortest residence times are found largely 

near the area of recharge, whereas longer residence 

times are in water from wells either deeper in the 

ground-water flow system or near the area of groundwater discharge. 

At selected wells where estimates of groundwater residence times also had been estimated by 

particle-tracking analysis using a ground-water flow 

model, estimates of the residence time of ground water 

based on the analysis of 14C were often larger. At 

upgradient locations close to recharge areas, estimates 

of residence time based on analysis of 14C were in the 

range of 50 to 500 years. However, for wells located 

near regional ground-water discharge areas, estimates 

of ground-water residence time based on analysis of 

14C were often in the range of 2,000 to 4,500 years and 

were as much as 10 times larger or more than estimates 

derived from a ground-water flow model.

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Appendix A 53

Appendix A. Quality-assurance data for isotope analysis of ground-water samples from wells on SUBASE Bangor and vicinity, Kitsap County, Washington

[Data as reported by analyzing laboratory and not rounded. NH4-SrCl2: 50 milliliters added to sample in the file prior to sending to laboratory. Water: Water 

only sent to laboratory. Powder: Powder precipitate of SrCO3 prepared in Reston laboratory and then sent to analyzing laboratory. AMS, Accelerator Mass 

Spectrometer; MS, mass spectrometer. δ13C, delta carbon-13; pCi/L, picoCuries per liter; NH4-SrCl2, ammoniacal-strontium-chloride. —, no data]

Well No. 

Carbon-14 AMS Carbon-13 AMS

Carbon-13 MS

NH4-SrCl2 Water Powder NH4-SrCl2 Water Powder

(percent modern carbon) (δ13C, per mil)

25N/01E-06D04 – 40.81±0.32 – – -19.3 – -19.2

– 39.94±0.32 – – -18.6 – -18.9

25N/01E-07J01 117.18±0.75 – – -21.09 – – –

25N/01E-07N02D1 68.72±0.48 63.03±0.47 66.97±0.46 -21.64 -22.44 -22.05 -21.76

25N/01E-12J01 – 66.97±0.52 70.15±0.46 -21.60 -21.31 -21.69 -21.37

26N/01E-17C01 – 59.06±0.44 60.47±0.39 – -18.06 -17.64 -17.47

26N/01E-18P06 83.99±0.58 78.63±0.57 82.01±0.50 -21.75 -20.57 -21.41 -21.19

26N/01E-30L01 68.79±0.52 66.99±0.49 66.15±0.57 -21.75 -21.80 -21.58 -21.23

70.39±0.50 – – -21.10 – – –

26N/01E-32M01 116.15±0.74 – – -24.1 – – –

27N/01E-35C01 61.62±0.48 – – -18.64 – – –

62.02±0.46 – – -18.92 – – –

Well No. Tritium

(pCi/L)

Deuterium

(δ2H, per mil)

Oxygen-18

(δ18O, per mil)

25N/01E-06D04 <0.3±0.6 -79.20 -11.20

00.4±0.6 -79.10 -11.27

25N/01E-07J01 15.5±1.1 -74.9 -10.53

16.6±1.1 – –

25N/01E-07N02D1 18.0±1.2 -76.5 -10.91

25N/01E-12J01 27.0±1.2 -76.4 -10.99

26N/01E-17C01 <0.3±0.6 -79.0 -11.25

26N/01E-18P06 24.0±1.6 -80.3 -11.28

26N/01E-30L01 12.0±0.08 -79.4 -11.23

26N/01E-32M01 20.4±1.3 -78.2 -10.81

21.4±1.4 – –

27N/01E-35C01 0.7±0.6 -78.9 -11.21
54 Estimates of Residence Time and Related Variations in Quality of Ground Water Beneath Submarine Base Bangor and Vicinity, Kitsap County, Washington
Estimates of Residence Time and Related Variations in Quality of Ground Water

Beneath Submarine Base Bangor and Vicinity, Kitsap County, Washington

S.E. Cox USGS-WRIR 03-4058

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