Comparison of Passive Diffusion Bag Samplers

and Submersible Pump Sampling Methods for

Monitoring Volatile Organic Compounds in 

Ground Water at Area 6, Naval Air Station

Whidbey Island, Washington

Prepared in cooperation with the

DEPARTMENT OF THE NAVY, ENGINEERING FIELD ACTIVITY,

NORTHWEST NAVAL FACILITIES ENGINEERING COMMAND

U.S. GEOLOGICAL SURVEY

Water-Resources Investigations Report 02-4203
Comparison of Passive Diffusion Bag Samplers 

and Submersible Pump Sampling Methods for 

Monitoring Volatile Organic Compounds in 

Ground Water at Area 6, Naval Air Station 

Whidbey Island, Washington

By Raegan L. Huffman

Prepared in cooperation with the

DEPARTMENT OF THE NAVY

ENGINEERING FIELD ACTIVITY,

NORTHWEST NAVAL FACILITIES ENGINEERING COMMAND

Tacoma, Washington 

2002

Water-Resources Investigations Report 02-4203

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
Contents iii

CONTENTS

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

Introduction .......................................................................................................................................................... 1

Background ................................................................................................................................................. 2

Description of Study Area........................................................................................................................... 3

Study Design ........................................................................................................................................................ 6

Well Selection ............................................................................................................................................. 6

Sampler Assembly, Installation, and Recovery .......................................................................................... 6

Analytical Methods .............................................................................................................................................. 13

Quality-Control Samples............................................................................................................................. 13

Comparison of Passive Diffusion Bag Samplers and Submersible Pump Sampling Methods 

for Monitoring Volatile Organic Compounds in Short- and Long-Screened Wells ............................................ 14

Short-Screened Wells.................................................................................................................................. 14

Long-Screened Wells.................................................................................................................................. 15

Sampling Technique Cost Comparisons ..................................................................................................... 19

Summary .............................................................................................................................................................. 23

References Cited .................................................................................................................................................. 24
iv Figures

FIGURES

Figure 1. Map showing location of the Area 6 study area, Naval Air Station Whidbey Island, Washington .. 4

Figure 2. Map showing location of wells selected for diffusion sampler installation, source areas, 

approximate locations of contaminant plumes, and features in Area 6, Naval Air Station 

Whidbey Island, Washington............................................................................................................. 5

Figure 3. Graph showing comparison of selected volatile organic compound concentrations 

from ground-water samples collected with diffusion samplers and a submersible 

pump for six wells with 10-foot screened intervals in Area 6, Naval Air Station 

Whidbey Island, Washington............................................................................................................. 14

Figure 4. Graphs showing comparison of TCA and chloroethane concentrations from ground-water 

samples collected with diffusion samplers and a submersible pump for wells with 20-foot 

screened intervals in Area 6, Naval Air Station Whidbey Island, Washington................................. 16

Figure 5. Graphs showing comparison of selected volatile organic compound concentrations 

from ground-water samples collected with diffusion samplers and a submersible 

pump for wells with greater than 20-foot screened intervals in Area 6, Naval Air 

Station Whidbey Island, Washington ................................................................................................ 17

Figure 6. Cross sections showing vertical distribution of TCA concentrations in ground-water 

samples collected with the diffusion samplers and submersible pump ............................................. 20

Figure 7. Graph showing comparison of selected volatile organic compounds from ground-water 

samples collected with diffusion samplers and a submersible pump for well MW-8, with 

a 40-foot screened interval that is not indicative of laminar flow across the screened interval 

in Area 6, Naval Air Station Whidbey Island, Washington............................................................... 22
Tables v

TABLES

Table 1. Depths, altitudes, and water-level data for selected wells at Area 6, Naval Air Station 

Whidbey Island, Washington............................................................................................................. 6

Table 2. Concentrations of selected chlorinated volatile organic compounds from environmental 

and quality-control samples collected with diffusion samplers and submersible pumps 

from selected wells at Area 6, Naval Air Station Whidbey Island, Washington............................... 8

Table 3. Concentrations of all chlorinated volatile organic compounds from environmental and 

quality-control samples collected with diffusion samplers and submersible pumps from 

selected wells at Area 6, Naval Air Station Whidbey Island, Washington........................................ 9

Table 4. Concentrations of selected chlorinated volatile organic compounds in water collected 

from isolated intervals using a straddle packer in well MW-7 at Area 6, Naval Air Station 

Whidbey Island, Washington............................................................................................................. 18
vi Conversion Factors and Vertical Datum

CONVERSION FACTORS AND VERTICAL DATUM

CONVERSION FACTORS

Temperature in degrees Celsius (oC) may be converted to degrees Fahrenheit (oF) as follows:

oF=1.8 oC+32.

Temperature in degrees Fahrenheit (oF) may be converted to degrees Celsius (oC) as follows:

oC=(oF–32)/1.8.

Chemical concentrations in water are given in milligrams per liter (mg/L) or micrograms per liter 

(μg/L). Milligrams per liter is a unit expressing the solute per unit volume (liter) of water. One thousand micrograms per liter is equivalent to one milligram per liter. For concentrations less than 7,000 

mg/L, milligrams per liter is equivalent to "parts per million" and micrograms per liter is equivalent to 

"parts per billion." 

Specific conductance is given microsiemens per centimeter at 25 degrees Celsius (μS/cm at 25oC).

VERTICAL DATUM

Sea level: In this report, "sea level" refers to the National Geodetic Vertical Datum of 1929 (NGVD of 

1929)--a geodetic datum derived from a general adjustment of the first-order level nets of both the 

United States and Canada, formerly called Sea Level Datum of 1929.

Multiply By To obtain

acre 0.4047 hectare

foot (ft) 0.3048 meter

inch (in) 25.4 millimeter

mile (mi) 1.609 kilometer
Introduction 1

Comparison of Passive Diffusion Bag Samplers and 

Submersible Pump Sampling Methods for Monitoring 

Volatile Organic Compounds in Ground Water at Area 6, 

Naval Air Station Whidbey Island, Washington

By Raegan L. Huffman

ABSTRACT

Ground-water samples were collected in 

April 1999 at Naval Air Station Whidbey Island, 

Washington, with passive diffusion samplers and a 

submersible pump to compare concentrations of 

volatile organic compounds (VOCs) in water 

samples collected using the two sampling 

methods. Single diffusion samplers were installed 

in wells with 10-foot screened intervals, and 

multiple diffusion samplers were installed in wells 

with 20- to 40-foot screened intervals. The 

diffusion samplers were recovered after 20 days 

and the wells were then sampled using a 

submersible pump. VOC concentrations in the 

10-foot screened wells in water samples collected 

with diffusion samplers closely matched 

concentrations in samples collected with the 

submersible pump. Analysis of VOC 

concentrations in samples collected from the 20- 

to 40-foot screened wells with multiple diffusion 

samplers indicated vertical concentration variation 

within the screened interval, whereas the analysis 

of VOC concentrations in samples collected with 

the submersible pump indicated mixing during 

pumping. The results obtained using the two 

sampling methods indicate that the samples 

collected with the diffusion samplers were 

comparable with and can be considerably less 

expensive than samples collected using a 

submersible pump.

INTRODUCTION

Ground water contaminated with volatile organic 

compounds (VOCs) underlies many sites around the 

Nation, and monitoring of ground-water contamination 

is commonly one of the most costly elements 

associated with long-term site remediation. As 

remediation proceeds at these sites and VOC 

concentrations in ground water decrease, it is often 

beneficial to more precisely locate the remaining 

contamination to allow optimization of remediation 

strategies that may originally have been designed for 

widespread high concentration contamination. 

Therefore, methods that minimize the cost and 

maximize the usefulness of ground-water sampling are 

needed.

The purpose of this report is to compare VOC 

concentrations in ground-water samples collected using 

water-filled, low-density polyethylene passive diffusion 

bag samplers with VOC concentrations in samples 

collected using a conventional sampling method with a 

submersible pump. Comparison samples were 

collected from 11 monitoring wells at Area 6, Naval 

Air Station Whidbey Island in Washington State. The 

methods for construction, installment, and retrieval of 

diffusion samplers as described by D.A. Vroblesky and 

T.R. Campbell (U.S. Geological Survey, written 

commun., January 1999) were followed. This study 

was done by the U.S. Geological Survey in cooperation 

with the U.S. Navy. 
2 Comparison of Methods for Monitoring Volatile Organic Compounds in Ground Water at Area 6, Naval Air Station Whidbey Island, Washington

Background

The typical approach to sampling wells for 

VOCs involves using pumps or bailers to purge wells 

prior to collecting the sample. Commonly, at least three 

casing volumes of water are purged, or enough water is 

purged so that selected water-quality parameters 

stabilize. There are potential technical and economic 

shortcomings to these traditional purge and sample 

methods. Purging three or more casing volumes prior 

to sampling is sometimes unnecessary and may 

produce undesirable effects (Gibs and Imbriotta, 1990; 

Kearl and others, 1992; Powell and Puls, 1993; 

Barcelona and others, 1994). Simply lowering pumps 

or bailers into a well can significantly increase the size 

and number of colloidal particles suspended in 

borehole water (Kearl and other, 1992; Puls and others, 

1992), and purging a well can increase the radius of 

aquifer influenced by pumping which in turn can yield 

samples that are not representative of ambient ground 

water (Reilly and Gibs, 1993; Barcelona and others, 

1994; Vroblesky, 2001b). Considerable resources also 

are required to properly collect, treat, and dispose of 

contaminated purge water. When collecting a 

representative ground-water sample for VOC analysis, 

it is clearly advantageous to minimize well purging as 

much as possible.

Recent investigations indicate that purging a well 

is not necessarily required to obtain a representative 

ground-water sample. Ground water can move through 

the screened portion of a borehole with little interaction 

or mixing with water in the overlying well casing 

(Robin and Gillham, 1987; Kearl and others, 1992; 

Powell and Puls, 1993; and Vroblesky and Hyde, 

1997). The studies suggested that flow across the 

screened interval of the tested wells generally was 

horizontal and laminar and representative of ambient 

ground water. Visual support of this hypothesis was 

provided using a downhole colloidal borescope to 

document advection of suspended sediment across the 

borehole (Kearl and others, 1992). Thus, in a well with 

horizontal laminar flow across the screened interval, a 

sampling device in the screened interval could be used 

to collect a representative sample while minimizing 

disturbance of the remaining borehole water.

Methods have been developed to minimize well 

purging while obtaining representative ground-water 

samples. Micro-purging and low-flow sampling with 

dedicated pumps are methods that minimally disturb 

the borehole water column by pumping at a rate slow 

enough to minimize drawdown in the borehole 

(Barcelona and others, 1994; Shanklin and others, 

1995). Another sampling method involves isolating a 

short-screened interval with an inflatable packer, and 

then purging and sampling the isolated interval 

(Kamlinsky and Wylie, 1995). Both of these methods 

reduce but do not eliminate the amount of purge water.

Diffusion samplers have the potential to 

completely eliminate well purging while obtaining 

representative ground-water samples (Kaplan and 

others, 1991; Powell and Puls, 1993; Vroblesky and 

Hyde, 1997; Vroblesky and Peters, 2000; and 

Vroblesky and Petkewich, 2000). Diffusion samplers 

rely on the diffusion of borehole solutes across various 

membranes into cells or bags filled with distilled water 

that are suspended in the borehole. The multi-layer 

passive sampler uses dialysis cells (Kaplan and others, 

1991), while other methods use simpler polyethylene 

bags (Vroblesky and Hyde, 1997; A.W. Alexander and 

T.L. Lammons , Bunnell-Lammons Engineering, Inc., 

written commun., August 1998). Field investigations of 

the latter method showed a close match between VOC 

concentrations in samples collected with diffusion 

samplers and VOC concentrations in samples collected 

using traditional purging and sampling methods 

(Vroblesky and Hyde, 1997; A.W. Alexander and T.L. 

Lammons, Bunnell-Lammons Engineering, Inc., 

written commun., August 1998; Vroblesky and Peters, 

2000; and Vroblesky and Petkewich, 2000). Vroblesky 

(2001a) prepared a protocol for the use of low-density, 

water-filled polyethylene diffusion samplers for VOCs 

in wells.
Introduction 3

In addition to minimizing well purging, there is 

often a need to obtain more information on the vertical 

distribution of VOCs in an aquifer from established 

monitoring wells. At sites characterized before the 

early 1990s, ground-water contamination commonly 

was monitored using wells with long screens that 

spanned more than one discrete zone of head or 

transmissivity. The advantage of using long-screened 

wells is to optimize the probability of intercepting 

contamination within the screened interval. The 

disadvantages are that samples provide little 

information about the vertical distribution of VOCs 

across the screened interval, and samples commonly 

represent a mixture of clean and contaminated waters 

that reflect neither the highest nor lowest contaminant 

concentrations (Reilly and Gibs, 1993). Again, the 

micro-purge and the inflatable packer sampling 

methods can be applied at different depths in a single 

long-screen well to provide data on the vertical 

distribution of VOCs, but the passive sampler 

methodology could potentially provide that 

information at a lower cost and with no well purging.

Description of Study Area

This study was conducted in April 1999, at Area 

6, Naval Air Station Whidbey, on Whidbey Island, 

Washington in the northern part of Puget Sound 

(fig. 1). The study area includes a capped 40-acre 

landfill that was used for the deposition of hazardous 

and municipal waste. The ground water beneath the 

study area is contaminated with volatile organic 

compounds (VOCs), primarily 1,1,1-trichloroethane 

(TCA), trichloroethene (TCE), cis-1, 2-dichloroethene 

(cis-DCE), 1,1-dichloroethane (DCA), 1,1-

dichloroethene (DCE), and vinyl chloride. The 

approximate extent of contamination beneath Area 6 is 

shown in figure 2.

All wells sampled were screened within the 

shallow aquifer at Area 6. The shallow aquifer beneath 

Area 6 is contained within the Vashon glacial advance 

outwash sediments. The saturated portion of the aquifer 

is composed of a fine to medium sand that gradually 

becomes finer and siltier with depth. Thin layers of 

gravel are present in the unit (Dinicola and others, 

2000).
4 Comparison of Methods for Monitoring Volatile Organic Compounds in Ground Water at Area 6, Naval Air Station Whidbey Island, Washington

122°40' 122°33'15"

48°

17'

30"

48°

20'

WHIDBEY ISLAND

Crescent

Harbor

STATE HIGHWAY 20

City of

Oak Harbor

0

0 1

1

2

2

3 MILES

3 KILOMETERS

Strait of

Juan de Fuca Dugualla

Bay

Oak

Harbor

AULT FIELD

SEAPLANE BASE

Area 6

Oak Harbor

Landfill

Naval Air Station

Whidbey Island

Seattle

Tacoma

WASHINGTON

NAS

Whidbey

Island

Port

Townsend

Seattle

WHIDBEY

ISLAND

Puget Sound

Figure 1. Location of the Area 6 study area, Naval Air Station Whidbey Island, Washington.

Modified from URS Consultants, 1993a. 
Introduction 5

0

0

1000 FEET

200 METERS

EXPLANATION

WESTERN PLUME—Predominantly A A'

TCE, TCA, and degradation

products

SOUTHERN PLUME—Predominantly

TCA and vinyl chloride

AREA 6 LANDFILL CAP

WETLAND

6-S-19

N6-38

LINE OF SECTION—Section shown

in figure 6.

BOUNDARY OF NAVAL AIR STATION

MONITORING WELL AND NO.

Well installed with diffusion sampler

Well sampled with submersible pump only

A

A'

OAK HARBOR LANDFILL

Swale

6-S-21

N6-38

PW-1

N6-37

MW-7

6-S-25

6-S-13

6-S-27

6-S-28

6-S-24

6-S-29 6-S-19

MW-8

Ault Field Road

State Highway 20

Goldie Road

48°19'30"

48°19'

122°38'30" 122°38'

T.33 N.

R.1 E.

Figure 2. Location of wells selected for diffusion sampler installation, source areas, approximate locations of contaminant plumes, and 

features in Area 6, Naval Air Station Whidbey Island, Washington
6 Comparison of Methods for Monitoring Volatile Organic Compounds in Ground Water at Area 6, Naval Air Station Whidbey Island, Washington

STUDY DESIGN

Well Selection

Eleven wells were selected for installation of 

diffusion samplers based on the results of previous 

sampling. Diffusion samplers were installed in wells 

with historical high as well as low VOC concentrations. 

Some wells with longer screened intervals also were 

selected to evaluate if more information on the vertical 

distribution of VOC contamination could be obtained 

using multiple diffusion samplers. The depths, 

altitudes, and water-level data for these selected wells 

are shown in table 1. The location of the 11 wells 

installed with diffusion samplers as well as source 

areas, contaminant plumes, and features in Area 6 are 

shown in figure 2. The areas delineating the 

contaminant plumes in figure 2 are defined by wells not 

shown on the figure and are discussed in more detail in 

Dinicola and others (2000). 

Sampler Assembly, Installation, and Recovery

The samplers were constructed by USGS 

personnel in Tacoma, Washington based on guidelines 

developed by D.A. Vroblesky and T.R. Campbell (U.S. 

Geological Survey, written commun, January 1999). 

Since this investigation, a users' guide has been 

published for the installment, recovery, data 

interpretation, and quality control and assurance of 

polyethylene based passive diffusion bag samplers 

(Vroblesky, 2001a). There were no substantial 

differences in the installation and recovery aspects 

between the draft and published protocols. 

Table 1. Depths, altitudes, and water-level data for selected wells at Area 6, Naval Air Station Whidbey Island, Washington

[USGS station identification No.: Unique number based on the latitude and longitude of the site. First six digits are latitude, next eight digits are longitude, 

and final two digits are a sequence number to uniquely identify a site. USGS, U.S. Geological Survey; –, not determined]

Well No.

(fig. 2)

USGS station 

identification No.

Altitude of the 

top of well 

(feet above mean sea 

level)

Reported total well 

depth

(feet below 

land surface)

Depth of screened 

interval 

(feet)

Water-level 

altitude, 

April 1999 

(feet above mean 

sea level)

6-S-13 481901122382601 197.82 156.5 145–155 78.55

6-S-19 481854122380901 219.37 164.5 143.5–163.5 76.18

6-S-21 481924122382602 157.74 104.5 63.5–103.5 89.15

6-S-24 481901122383002 192.56 116.5 105–115.5 81.93

6-S-25 481900122382602 197.92 126 115–125 78.64

6-S-27 481856122382601 198.58 130 120–130 78.22

6-S-28 481856122382501 198.6 155 145–155 78.2

6-S-29 181854122381401 213.14 164 144-164 76.63

MW-7 481917122382601 199.46 149 118.4–148.4 86.13

MW-8 481904122382201 205.9 162 122–162 80.28

N6-37 481921122382201 172.25 96 85.5–95.5 87.98

N6-38 – 163.85 98 79.5–89.5 88.88

PW-1 – 170.81 118.5 87.5–117.5 –
Study Design 7

A sampler was constructed by cutting an 18-inch 

length of 2-inch wide lay-flat polyethylene tubing and 

heat sealing one end. The lay-flat tubing was placed 

inside mesh tubing to help prevent the filled bag from 

rupturing. The lay-flat tubing was then filled with 

about 300 milliliters of de-ionized water and the open 

end was sealed while ensuring no air bubbles remained 

inside. An assembled sampler contained enough water 

for obtaining environmental and duplicate samples. 

The samplers were constructed about 3 days prior to 

installation and were temporarily stored within a 

plastic-lined cooler.

Well depth was measured before installing a 

sampler down a well. This provided information as to 

whether sediment had accumulated at the bottom of the 

well. The distance was calculated from the bottom of 

the well to where the sampler would be placed. The 

sampler was placed in the vertical midpoint of the 

screen for 10 feet or shorter well screens. Multiple 

samplers were installed at midpoints for every 10 feet 

within the screened interval for 20 feet or longer 

screens. Sampler equilibration times vary, and a 

minimum of 14 days is suggested (Vroblesky, 2001a). 

Samplers were allowed to equilibrate for 20 days prior 

to removal.

The sampler was laid on clean plastic upon 

removal from the well. A corner was cut and the water 

gently poured into 40-mL septa vials that contained the 

preservative hydrochloric acid. The vials were filled 

without headspace, capped, placed on ice, and sent 

overnight mail to Quanterra Inc. Laboratory in Denver, 

Colorado. For multiple samplers in a well, the upper 

most sampler (shallowest) was cut open and water 

transferred first; and the deepest sampler was processed 

last.

Within a few days after removing the diffusion 

samplers, a second set of VOC samples were collected 

using a submersible pump using low-flow sampling 

methods. Samples were collected by Navy contractors 

who conduct the regular monitoring at the site. A 

submersible pump was lowered into the well about 10 

feet into the water column. The well was purged of at 

least three casing volumes of water, and ground-waterquality parameters, including pH, temperature, specific 

conductance, and turbidity were measured after every 

well volume. After three well volumes had been purged 

and water-quality parameters stabilized to within 10 

percent, the pump flow rate was reduced and VOC 

samples were collected by pouring ground water 

directly from the pump discharge line into 40-mL septa 

vials containing hydrochloric acid. The sample vials 

were placed in a cooler with ice and delivered to the 

laboratory the next morning. The submersible pump 

VOC concentrations are listed in tables 2 and 3. The 

sample depth associated with the submersible pump 

samples shown in the tables are estimated depths, 

based on the documented procedures used by the Navy 

contractors. 
8 Comparison of Methods for Monitoring Volatile Organic Compounds in Ground Water at Area 6, Naval Air Station Whidbey Island, Washington

Table 2. Concentrations of selected chlorinated volatile organic compounds from environmental and quality-control samples collected with diffusion 

samplers and submersible pumps from selected wells at Area 6, Naval Air Station Whidbey Island, Washington

[Sampling Method: DS, diffusion sample; SUB, submersible pump sample. Chemical abbreviations: TCE, Trichloroethene; TCA 1,1,1-Trichloroethane; 

cis-DCE, cis-1,2-dichloroethene; DCE, 1,1-dichloroethene; DCA, 1,1-dichloroethane. <, not detected at the given concentration; e, detected concentration is 

less than the reporting limit and is an estimated concentration; bold indicates detected concentrations; italics indicates a replicate sample]

Well No. 

(sample depth, 

in feet)

Date Sampling 

method

TCE

(μg/L)

TCA

(μg/L)

cis-DCE

(μg/L)

DCE

(μg/L)

DCA 

(μg/L)

Vinyl 

chloride 

(μg/L)

Wells with 10-foot screened intervals

6-S-13 (152.6) 04-14-99 DS <1.0 36 <1.0 5.8 65 <1.0

6-S-13 (129) 04-22-99 SUB <0.20 51 <0.20 5.5 110 <1.0

6-S-24 (115) 04-14-99 DS <1.0 10 <1.0 <1.0 <1.0 <1.0

6-S-24 (115) Replicate 04-14-99 DS <1.0 9.5 <1.0 0.76e <1.0 <1.0

6-S-24 (115) 04-22-99 SUB 0.31 9.7 <0.20 0.30 <0.20 <1.0

6-S-25 (124.3) 04-14-99 DS <20 1,800 <20 51 <20 <20

6-S-25 (124.3) Replicate 04-14-99 DS <20 1,800 <20 52 <20 <20

6-S-25 (124) 04-23-99 SUB 10 1,800 1.6 57 1.1 <1.0

6-S-27 (124.5) 04-14-99 DS <1.0 7.7 <1.0 1.8 <1.0 <1.0

6-S-27 (130) 04-20-99 SUB <0.20 2.3 <0.20 <0.20 <0.20 <1.0

6-S-28 (150.5) 04-14-99 DS <1.0 1.1 <1.0 <1.0 <1.0 <1.0

6-S-28 (130) 04-20-99 SUB <0.20 <0.50 <0.20 <0.20 <0.20 <1.0

N6-37 (91.4) 04-14-99 DS 24 4.2 <1.0 0.87e <1.0 <1.0

N6-37 (94) 04-22-99 SUB 39 14 2.1 1.1 <0.20 <1.0

Wells with 20- to 40-foot screened intervals

6-S-19 (151.1) 04-14-99 DS <1.0 11 <1.0 0.77e <1.0 2.3

6-S-19 (161.1) 04-14-99 DS <1.0 <1.0 <1.0 <1.0 <1.0 2.9

6-S-19 (153) 04-22-99 SUB <0.20 6.9 <0.20 <0.20 <0.20 1.8

6-S-19 (153) Replicate 04-22-99 SUB <0.20 7.1 <0.20 <0.20 <0.20 1.9

6-S-21 (73.2) 04-14-99 DS <2.0 240 <2.0 42 <2.0 <2.0

6-S-21 (83.2) 04-14-99 DS <1.0 15 <1.0 5.7 <1.0 <1.0

6-S-21 (93.2) 04-14-99 DS <1.0 0.87e <1.0 <1.0 <1.0 <1.0

6-S-21 (103.2) 04-14-99 DS <1.0 2.8 <1.0 <1.0 <1.0 <1.0

6-S-21 (78) 04-22-99 SUB <0.20 120 <0.20 11 <0.20 <1.0

6-S-29 (151.5) 04-14-99 DS <1.0 7.2 <1.0 0.80e 5.4 3.6

6-S-29 (161.5) 04-14-99 DS <1.0 <1.0 <1.0 <1.0 <1.0 1.5

6-S-29 (146) 04-21-99 SUB <0.20 7.4 <0.20 0.39 3.5 5.9

MW-7 (125) 04-14-99 DS 810 450 130 84 3.3e <5.0

MW-7 (135) 04-14-99 DS 940 420 110 83 <10 <10

MW-7 (145) 04-14-99 DS 0.76e <1.0 <1.0 <1.0 0.66e <1.0

MW-7 (123) 04-22-99 SUB 390 480 120 78 55 <10

MW-8 (128.5) 04-14-99 DS <1.0 6.0 <1.0 <1.0 3.8 1.9

MW-8 (138.5) 04-14-99 DS <1.0 5.9 <1.0 <1.0 3.0 2.1

MW-8 (148.5) 04-14-99 DS <1.0 6.0 <1.0 <1.0 2.8 1.4

MW-8 (158.5) 04-14-99 DS <1.0 5.3 <1.0 <1.0 2.6 1.6

MW-8 (135) 04-14-99 SUB <0.20 2.5 <0.20 <0.20 2.3 1.6

DI-B (source blank) 03-24-99 DS <0.50 <0.50 <0.50 <0.50 <0.50 <1.0

FB (field blank) 04-14-99 DS <1.0 <1.0 <1.0 <1.0 <1.0 <1.0

TRIP (trip blank) 04-14-99 DS <1.0 <1.0 <1.0 <1.0 <1.0 <1.0

SOURCE B (source blank) 04-19-99 SUB <0.20 <0.50 <0.20 <0.20 <0.20 <1.0

TB (trip blank) 04-19-99 SUB <0.20 <0.50 <0.20 <0.20 <0.20 <1.0
Study Design 9

Table 3. Concentrations of all chlorinated volatile organic compounds from environmental and quality-control samples collected with diffusion samplers 

and submersible pumps from selected wells at Area 6, Naval Air Station Whidbey Island, Washington

[Sampling Method: DS, diffusion sample; SUB, submersible pump sample. Chemical abbreviations: TCE, Trichloroethene; TCA 1,1,1-Trichloroethane; 

cis-DCE, cis-1,2-dichloroethene; DCE, 1,1-dichloroethene; DCA, 1,1-dichloroethane. <, not detected at the given concentration; e, detected concentration is 

less than the reporting limit and is an estimated concentration; bold indicates detected concentrations; italics indicates replicate sample]

Well No. 

(sample depth, 

in feet)

Date Sampling 

method

Bromodichloromethane 

(μg/L)

Bromoform 

(μg/L)

Bromomethane 

(μg/L)

Carbon 

tetrachloride 

(μg/L)

Chlorobenzene 

(μg/L)

Dibromochloromethane 

(μg/L)

Chloroethane 

(μg/L)

Wells with 10-foot screened intervals

6-S-13 (152.6) 04-14-99 DS <1.0 <5.0 <5.0 <1.0 <2.0 <1.0 8.5

6-S-13 (129) 04-22-99 SUB <0.20 <0.50 <2.0 <0.20 <0.50 <0.20 17

6-S-24 (115) 04-14-99 DS <1.0 <5.0 <5.0 <1.0 <2.0 <1.0 <5.0

6-S-24 (115) Replicate 04-14-99 DS <1.0 <5.0 <5.0 <1.0 <2.0 <1.0 <5.0

6-S-24 (115) 04-22-99 SUB <0.20 <0.50 <2.0 <0.20 <0.50 <0.20 <2.0

6-S-25 (124.3) 04-14-99 DS <20 <100 <100 <20 <40 <20 <100

6-S-25 (124.3) Replicate 04-14-99 DS <20 <100 <100 <20 <40 <20 <100

6-S-25 (124) 04-23-99 SUB <0.20 <0.50 <2.0 1.8 <0.50 <0.20 <2.0

6-S-27 (124.5) 04-14-99 DS <1.0 <5.0 <5.0 <1.0 <2.0 <1.0 <5.0

6-S-27 (130) 04-20-99 SUB <0.20 <0.50 <2.0 <0.20 <0.50 <0.20 <2.0

6-S-28 (150.5) 04-14-99 DS <1.0 <5.0 <5.0 <1.0 <2.0 <1.0 1.5e

6-S-28 (130) 04-20-99 SUB <0.20 <0.50 <2.0 <0.20 <0.50 <0.20 <2.0

N6-37 (91.4) 04-14-99 DS <1.0 <5.0 <5.0 <1.0 <2.0 <1.0 <5.0

N6-37 (94) 04-22-99 SUB <0.20 <0.50 <2.0 <0.20 <0.50 <0.20 <2.0

N6-38 04-22-99 SUB <1.0 <2.5 <10 <1.0 <2.5 <1.0 <10

Wells with 20- to 40-foot screened intervals

6-S-19 (151.1) 04-14-99 DS <1.0 <5.0 <5.0 <1.0 <2.0 <1.0 28

6-S-19 (161.1) 04-14-99 DS <1.0 <5.0 <5.0 <1.0 <2.0 <1.0 4.6e

6-S-19 (153) 04-22-99 SUB <0.20 <0.50 <2.0 <0.20 <0.50 <0.20 <2.0

6-S-19 (153) Replicate 04-22-99 SUB <0.20 <0.50 <2.0 <0.20 <0.50 <0.20 <2.0

6-S-21 (73.2) 04-14-99 DS <2.0 <10 <10 <2.0 <4.0 <2.0 <10

6-S-21 (83.2) 04-14-99 DS <1.0 <5.0 <5.0 <1.0 <2.0 <1.0 <5.0

6-S-21 (93.2) 04-14-99 DS <1.0 <5.0 <5.0 <1.0 <2.0 <1.0 <5.0

6-S-21 (103.2) 04-14-99 DS <1.0 <5.0 <5.0 <1.0 <2.0 <1.0 <5.0

6-S-21 (78) 04-22-99 SUB <0.20 <0.50 <2.0 <0.20 <0.50 <0.20 <2.0

6-S-29 (151.5) 04-14-99 DS <1.0 <5.0 <5.0 <1.0 <2.0 <1.0 28

6-S-29 (161.5) 04-14-99 DS <1.0 <5.0 <5.0 <1.0 <2.0 <1.0 7.8

6-S-29 (146) 04-21-99 SUB <0.20 <0.50 <2.0 <0.20 <0.50 <0.20 <2.0

MW-7 (125) 04-14-99 DS <5.0 <25 <25 <5.0 <10 <5.0 <25

MW-7 (135) 04-14-99 DS <10 <50 <50 <10 <20 <10 <50

MW-7 (145) 04-14-99 DS <1.0 <5.0 <5.0 <1.0 <2.0 <1.0 <5.0

MW-7 (123) 04-22-99 SUB <2.0 <0.50 <20 <2.0 <5.0 <2.0 <2.0

MW-8 (128.5) 04-14-99 DS <1.0 <5.0 <5.0 <1.0 <2.0 <1.0 19

MW-8 (138.5) 04-14-99 DS <1.0 <5.0 <5.0 <1.0 <2.0 <1.0 22

MW-8 (148.5) 04-14-99 DS <1.0 <5.0 <5.0 <1.0 <2.0 <1.0 21

MW-8 (158.5) 04-14-99 DS <1.0 <5.0 <5.0 <1.0 <2.0 <1.0 20

MW-8 (135) 04-14-99 SUB <0.20 <0.50 <2.0 <0.20 <0.50 <0.20 <2.0

PW-1 04-19-99 SUB <0.20 <0.50 <2.0 <0.20 <0.50 <0.20 <2.0

DI-B (source blank) 03-24-99 DS <1.0 <5.0 <5.0 <0.50 <2.0 <1.0 <5.0

FB (field blank) 04-14-99 DS <1.0 <5.0 <5.0 <1.0 <2.0 <1.0 <5.0

TRIP (trip blank) 04-14-99 DS <1.0 <5.0 <5.0 <1.0 <2.0 <1.0 <5.0

SOURCE B (source blank) 04-19-99 SUB <0.20 <0.50 <2.0 <0.20 <0.50 <0.20 <2.0

TB (trip blank) 04-19-99 SUB <0.20 <0.50 <2.0 <0.20 <0.50 <0.20 <2.0
10 Comparison of Methods for Monitoring Volatile Organic Compounds in Ground Water at Area 6, Naval Air Station Whidbey Island, Washington

Table 3. Concentrations of all chlorinated volatile organic compounds from environmental and quality-control samples collected with diffusion samplers 

and submersible pumps from selected wells at Area 6, Naval Air Station Whidbey Island, Washington—Continued

Well No. 

(sample depth.

in feet)

Date Sampling 

method

Chloroform

(μg/L)

Chloromethane 

(μg/L)

1,2-Dichlorobenzene 

(μg/L)

1,3-Dichlorobenzene 

(μg/L)

1,4-Dichlorobenzene 

(μg/L)

DCA 

(μg/L)

1,2-Dichloroethane 

(μg/L)

Wells with 10-foot screened intervals

6-S-13 (152.6) 04-14-99 DS <1.0 <5.0 <2.0 <2.0 0.66e 65 <1.0

6-S-13 (129) 04-22-99 SUB <0.20 <1.0 <0.50 <0.50 <0.50 110 <0.20

6-S-24 (115) 04-14-99 DS <1.0 <5.0 <2.0 <2.0 <2.0 <1.0 <1.0

6-S-24 (115) Replicate 04-14-99 DS <1.0 <5.0 <2.0 <2.0 <2.0 <1.0 <1.0

6-S-24 (115) 04-22-99 SUB <0.20 <1.0 <0.50 <0.50 <0.50 <0.20 <0.20

6-S-25 (124.3) 04-14-99 DS <20 <100 <40 <40 <40 <20 <20

6-S-25 (124.3) Replicate 04-14-99 DS <20 <100 <40 <40 <40 <20 <20

6-S-25 (124) 04-23-99 SUB <0.20 <1.0 <0.50 <0.50 <0.50 1.1 <0.20

6-S-27 (124.5) 04-14-99 DS <1.0 <5.0 <2.0 <2.0 <2.0 <1.0 <1.0

6-S-27 (130) 04-20-99 SUB 0.87 <1.0 <0.50 <0.50 <0.50 <0.20 <0.20

6-S-28 (150.5) 04-14-99 DS <1.0 <5.0 <2.0 <2.0 <2.0 <1.0 <1.0

6-S-28 (130) 04-20-99 SUB <0.20 <1.0 <0.50 <0.50 <0.50 <0.20 <0.20

N6-37 (91.4) 04-14-99 DS <1.0 <5.0 <2.0 <2.0 <2.0 <1.0 <1.0

N6-37 (94) 04-22-99 SUB <0.20 <1.0 <0.50 <0.50 <0.50 <0.20 <0.20

N6-38 (85) 04-22-99 SUB <1.0 <5.0 <2.5 <2.5 <2.5 <1.0 <1.0

Wells with 20- to 40-foot screened intervals

6-S-19 (151.1) 04-14-99 DS <1.0 2.3e <2.0 <2.0 <2.0 <1.0 <1.0

6-S-19 (161.1) 04-14-99 DS <1.0 <5.0 <2.0 <2.0 0.70e <1.0 <1.0

6-S-19 (153) 04-22-99 SUB <0.20 <1.0 <0.50 <0.50 <0.50 <0.20 <0.20

6-S-19 (153) Replicate 04-22-99 SUB <0.20 <1.0 <0.50 <0.50 <0.50 <0.20 <0.20

6-S-21 (73.2) 04-14-99 DS <2.0 <10 <4.0 <4.0 <4.0 <2.0 <2.0

6-S-21 (83.2) 04-14-99 DS <1.0 <5.0 <2.0 <2.0 <2.0 <1.0 <1.0

6-S-21 (93.2) 04-14-99 DS <1.0 <5.0 <2.0 <2.0 0.67e <1.0 <1.0

6-S-21 (103.2) 04-14-99 DS <1.0 <5.0 <2.0 <2.0 1.0e <1.0 <1.0

6-S-21 (78) 04-22-99 SUB <0.20 <1.0 <0.50 <0.50 <0.50 <0.20 <0.20

6-S-29 (151.5) 04-14-99 DS <1.0 3.1e <2.0 <2.0 <2.0 5.4 <1.0

6-S-29 (161.5) 04-14-99 DS <1.0 2.5e <2.0 <2.0 0.85e <1.0 <1.0

6-S-29 (146) 04-21-99 SUB <0.20 <1.0 <0.50 <0.50 <0.50 3.5 <0.20

MW-7 (125) 04-14-99 DS 3.7e <25 <10 <10 <10 3.3e <5.0

MW-7 (135) 04-14-99 DS <10 <50 <20 <20 <20 <10 <10

MW-7 (145) 04-14-99 DS <1.0 <5.0 <2.0 <2.0 0.79e 0.66e <1.0

MW-7 (123) 04-22-99 SUB <2.0 <10 <5.0 <5.0 <5.0 55 <2.0

MW-8 (128.5) 04-14-99 DS <1.0 <5.0 <2.0 <2.0 <2.0 3.8 <1.0

MW-8 (138.5) 04-14-99 DS <1.0 <5.0 <2.0 <2.0 0.45e 3.0 <1.0

MW-8 (148.5) 04-14-99 DS <1.0 <5.0 <2.0 <2.0 <2.0 2.8 <1.0

MW-8 (158.5) 04-14-99 DS <1.0 <5.0 <2.0 <2.0 0.81e 2.6 <1.0

MW-8 (135) 04-14-99 SUB <0.20 <1.0 <0.50 <0.50 <0.50 2.3 <0.20

PW-1 04-19-99 SUB <0.20 0.55 <0.50 <0.50 <0.50 4.3 1.1

DI-B (source blank) 03-24-99 DS <0.50 4.4e <2.0 <2.0 <2.0 <0.50 <1.0

FB (field blank) 04-14-99 DS <5.0 <5.0 <2.0 <2.0 <2.0 <1.0 <1.0

TRIP (trip blank) 04-14-99 DS <5.0 <5.0 <2.0 <2.0 <2.0 <1.0 <1.0

SOURCE B (source blank) 04-19-99 SUB <1.0 <1.0 <0.50 <0.50 <0.50 <0.20 <0.20

TB (trip blank) 04-19-99 SUB <1.0 <1.0 <0.50 <0.50 <0.50 <0.20 <0.20
Study Design 11

Table 3. Concentrations of all chlorinated volatile organic compounds from environmental and quality-control samples collected with diffusion samplers 

and submersible pumps from selected wells at Area 6, Naval Air Station Whidbey Island, Washington—Continued

Well No. 

(sample depth, 

in feet)

Date Sampling 

method

DCE

(μg/L)

cis-DCE

(μg/L

trans-1,2- 

Dichloroethene 

(μg/L)

1,2-Dichloropropane 

(μg/L)

cis-1,3- 

Dichloropropene 

(μg/L)

trans-1,3- 

dichloropropene 

(μg/L)

Trichlorofluoromethane 

(μg/L)

Wells with 10-foot screened intervals

6-S-13 (152.6) 04-14-99 DS 5.8 <1.0 <1.0 <1.0 <2.0 <1.0 <5.0

6-S-13 (129) 04-22-99 SUB 5.5 <0.20 <0.20 <0.20 <0.20 <0.20 <0.50

6-S-24 (115) 04-14-99 DS <1.0 <1.0 <1.0 <1.0 <2.0 <1.0 <5.0

6-S-24 (115) Replicate 04-14-99 DS 0.76e <1.0 <1.0 <1.0 <2.0 <1.0 <5.0

6-S-24 (115) 04-22-99 SUB 0.30 <0.20 <0.20 <0.20 <0.20 <0.20 <0.50

6-S-25 (124.3) 04-14-99 DS 51 <20 <20 <20 <40 <20 <100

6-S-25 (124.3) Replicate 04-14-99 DS 52 <20 <20 <20 <40 <20 <100

6-S-25 (124) 04-23-99 SUB 57 1.6 <0.20 <0.20 <0.20 <0.20 <0.50

6-S-27 (124.5) 04-14-99 DS 1.8 <1.0 <1.0 <1.0 <2.0 <1.0 <5.0

6-S-27 (130) 04-20-99 SUB <0.20 <0.20 <0.20 <0.20 <0.20 <0.20 <0.50

6-S-28 (150.5) 04-14-99 DS <1.0 <1.0 <1.0 <1.0 <2.0 <1.0 1.5e

6-S-28 (130) 04-20-99 SUB <0.20 <0.20 <0.20 <0.20 <0.20 <0.20 <0.50

N6-37 (91.4) 04-14-99 DS 0.87e <1.0 <1.0 <1.0 <2.0 <1.0 <5.0

N6-37 (94) 04-22-99 SUB 1.1 2.1 <0.20 <0.20 <0.20 <0.20 <0.50

N6-38 (85) 04-22-99 SUB 38 <1.0 <1.0 <1.0 <1.0 <1.0 <2.5

Wells with 20- to 40-foot screened intervals

6-S-19 (151.1) 04-14-99 DS 0.77e <1.0 <1.0 <1.0 <2.0 <1.0 5.8

6-S-19 (161.1) 04-14-99 DS <1.0 <1.0 <1.0 <1.0 <2.0 <1.0 1.8e

6-S-19 (153) 04-22-99 SUB <0.20 <0.20 <0.20 <0.20 <0.20 <0.20 5.4

6-S-19 (153) Replicate 04-22-99 SUB <0.20 <0.20 <0.20 <0.20 <0.20 <0.20 5.4

6-S-21 (73.2) 04-14-99 DS 42 <2.0 <2.0 <2.0 <4.0 <2.0 <10

6-S-21 (83.2) 04-14-99 DS 5.7 <1.0 <1.0 <1.0 <2.0 <1.0 <5.0

6-S-21 (93.2) 04-14-99 DS <1.0 <1.0 <1.0 <1.0 <2.0 <1.0 <5.0

6-S-21 (103.2) 04-14-99 DS <1.0 <1.0 <1.0 <1.0 <2.0 <1.0 <5.0

6-S-21 (78) 04-22-99 SUB 11 <0.20 <0.20 <0.20 <0.20 <0.20 <0.50

6-S-29 (151.5) 04-14-99 DS 0.80e <1.0 <1.0 <1.0 <2.0 <1.0 4.3e

6-S-29 (161.5) 04-14-99 DS <1.0 <1.0 <1.0 <1.0 <2.0 <1.0 <5.0

6-S-29 (146) 04-21-99 SUB 0.39 <0.20 <0.20 <0.20 <0.20 <0.20 4.8

MW-7 (125) 04-14-99 DS 84 130 <5.0 <5.0 <10 <5.0 <25

MW-7 (135) 04-14-99 DS 83 110 <10 <10 <20 <10 <50

MW-7 (145) 04-14-99 DS <1.0 <1.0 <1.0 <1.0 <2.0 <1.0 <5.0

MW-7 (123) 04-22-99 SUB 78 120 <2.0 <2.0 <2.0 <2.0 <5.0

MW-8 (128.5) 04-14-99 DS <1.0 <1.0 <1.0 <1.0 <2.0 <1.0 12

MW-8 (138.5) 04-14-99 DS <1.0 <1.0 <1.0 <1.0 <2.0 <1.0 14

MW-8 (148.5) 04-14-99 DS <1.0 <1.0 <1.0 <1.0 <2.0 <1.0 13

MW-8 (158.5) 04-14-99 DS <1.0 <1.0 <1.0 <1.0 <2.0 <1.0 9.6

MW-8 (135) 04-14-99 SUB <0.20 <0.20 <0.20 <0.20 <0.20 <0.20 4.8

PW-1 04-19-99 SUB 10 64 <0.20 <0.20 <0.20 <0.20 <0.50

DI-B (source blank) 03-24-99 DS <1.0 <1.0 <1.0 <1.0 <2.0 <1.0 <5.0

FB (field blank) 04-14-99 DS <1.0 <1.0 <1.0 <1.0 <2.0 <1.0 <5.0

TRIP (trip blank) 04-14-99 DS <1.0 <1.0 <1.0 <1.0 <2.0 <1.0 <5.0

SOURCE B (source blank) 04-19-99 SUB <0.20 <0.20 <0.20 <0.20 <0.20 <0.20 <0.50

TB (trip blank) 04-19-99 SUB <0.20 <0.20 <0.20 <0.20 <0.20 <0.20 <0.50
12 Comparison of Methods for Monitoring Volatile Organic Compounds in Ground Water at Area 6, Naval Air Station Whidbey Island, Washington

Table 3. Concentrations of all chlorinated volatile organic compounds from environmental and quality-control samples collected with diffusion samplers 

and submersible pumps from selected wells at Area 6, Naval Air Station Whidbey Island, Washington—Continued

Well No. 

(sample depth, 

in feet)

Date Sampling 

method

Methylene 

chloride 

(μg/L)

1,1,2,2- 

Tetrachloethene 

(μg/L)

Tetrachloroethene 

(μg/L)

TCA 

(μg/L)

1,1,2-Trichloroethane 

(μg/L)

TCE

(μg/L)

Vinyl 

chloride 

(μg/L)

Wells with 10-foot screened intervals

6-S-13 (152.6) 04-14-99 DS 0.53e <1.0 <1.0 36 <1.0 <1.0 <1.0

6-S-13 (129) 04-22-99 SUB <5.0 <0.20 <0.20 51 <0.20 <0.20 <1.0

6-S-24 (115) 04-14-99 DS <5.0 <1.0 <1.0 10 <1.0 <1.0 <1.0

6-S-24 (115) Replicate 04-14-99 DS <5.0 <1.0 <1.0 9.5 <1.0 <1.0 <1.0

6-S-24 (115) 04-22-99 SUB <5.0 <0.20 <0.20 9.7 <0.20 0.31 <1.0

6-S-25 (124.3) 04-14-99 DS <100 <20 <20 1,800 <20 <20 <20

6-S-25 (124.3) Replicate 04-14-99 DS <100 <20 <20 1,800 <20 <20 <20

6-S-25 (124) 04-23-99 SUB <5.0 <0.20 <0.20 1,800 <0.20 10 <1.0

6-S-27 (124.5) 04-14-99 DS <5.0 <1.0 <1.0 7.7 <1.0 <1.0 <1.0

6-S-27 (130) 04-20-99 SUB <5.0 <0.20 <0.20 2.3 <0.20 <0.20 <1.0

6-S-28 (150.5) 04-14-99 DS <5.0 <1.0 <1.0 1.1 <1.0 <1.0 <1.0

6-S-28 (130) 04-20-99 SUB <5.0 <0.20 <0.20 <0.50 <0.20 <0.20 <1.0

N6-37 (91.4) 04-14-99 DS <5.0 <1.0 <1.0 4.2 <1.0 24 <1.0

N6-37 (94) 04-22-99 SUB <5.0 <0.20 <0.20 14 <0.20 39 <1.0

N6-38 04-22-99 SUB <25 <1.0 <1.0 260 <1.0 18 <5.0

Wells with 20- to 40-foot screened intervals

6-S-19 (151.1) 04-14-99 DS <5.0 <1.0 <1.0 11 <1.0 <1.0 2.3

6-S-19 (161.1) 04-14-99 DS <5.0 <1.0 <1.0 <1.0 <1.0 <1.0 2.9

6-S-19 (153) 04-22-99 SUB <5.0 <0.20 <0.20 6.9 <0.20 <0.20 1.8

6-S-19 (153) Replicate 04-22-99 SUB <5.0 <0.20 <0.20 7.1 <0.20 <0.20 1.9

6-S-21 (73.2) 04-14-99 DS 0.75e <2.0 <2.0 240 <2.0 <2.0 <2.0

6-S-21 (83.2) 04-14-99 DS 0.43e <1.0 <1.0 15 <1.0 <1.0 <1.0

6-S-21 (93.2) 04-14-99 DS <5.0 <1.0 <1.0 0.87e <1.0 <1.0 <1.0

6-S-21 (103.2) 04-14-99 DS <5.0 <1.0 <1.0 2.8 <1.0 <1.0 <1.0

6-S-21 (78) 04-22-99 SUB <5.0 <0.20 <0.20 120 <0.20 <0.20 <1.0

6-S-29 (151.5) 04-14-99 DS 0.41e <1.0 <1.0 7.2 <1.0 <1.0 3.6

6-S-29 (161.5) 04-14-99 DS <5.0 <1.0 <1.0 <1.0 <1.0 <1.0 1.5

6-S-29 (146) 04-21-99 SUB <5.0 <0.20 <0.20 7.4 <0.20 <0.20 5.9

MW-7 (125) 04-14-99 DS 5.4e <5.0 5.3 450 <5.0 810 <5.0

MW-7 (135) 04-14-99 DS <50 <10 <10 420 <10 940 <10

MW-7 (145) 04-14-99 DS <5.0 <1.0 <1.0 <1.0 <1.0 0.76e <1.0

MW-7 (123) 04-22-99 SUB <50 <2.0 <2.0 480 2.3 390 <10

MW-8 (128.5) 04-14-99 DS 0.88e <1.0 <1.0 6.0 <1.0 <1.0 1.9

MW-8 (138.5) 04-14-99 DS 0.78e <1.0 <1.0 5.9 <1.0 <1.0 2.1

MW-8 (148.5) 04-14-99 DS 0.39e <1.0 <1.0 6.0 <1.0 <1.0 1.4

MW-8 (158.5) 04-14-99 DS <5.0 <1.0 <1.0 5.3 <1.0 <1.0 1.6

MW-8 (135) 04-14-99 SUB <5.0 <0.20 <0.20 2.5 <0.20 <0.20 1.6

PW-1 04-19-99 SUB <5.0 <0.20 <0.20 200 0.74 148 <1.0

DI-B (source blank) 03-24-99 DS <5.0 <1.0 <0.50 <0.50 <1.0 <0.50 <1.0

FB (field blank) 04-14-99 DS <5.0 <1.0 <1.0 <1.0 <1.0 <1.0 <1.0

TRIP (trip blank) 04-14-99 DS 0.87e <1.0 <1.0 <1.0 <1.0 <1.0 <1.0

SOURCE B (source blank) 04-19-99 SUB <5.0 <0.20 <0.20 <0.20 <0.20 <0.20 <1.0

TB (trip blank) 04-19-99 SUB <5.0 <0.20 <0.20 <0.20 <0.20 <0.20 <1.0
Analytical Methods 13

ANALYTICAL METHODS

Both sample sets were sent to commercial 

laboratories for analysis using U.S. Environmental 

Protection Agency (EPA) method 601. Although the 

same EPA analytical methods were performed on both 

sample sets, the submersible pump samples had lower 

detection limits because they were sent to a different 

laboratory for analysis. Due to the high VOC 

concentrations at the site, samples required dilution at 

both laboratories for quantification. The laboratory that 

performed the analyses on the samples collected with 

the diffusion sampler diluted samples to obtain 

quantification for one analyte and quantified the 

remainder of the analytes of interest in the same diluted 

sample. The laboratory that performed the analyses on 

the pumped samples only quantified high concentration 

analytes in diluted samples, and quantified other 

analytes in undiluted samples from the same well.

Quality-Control Samples

When using a new sampling method, such as 

diffusion sampling, it is necessary to know if quality 

assurance and control results are within acceptable 

ranges and how they compare with the quality 

assurance and control results of low-flow sampling 

using a submersible pump. Quality-control samples 

submitted to the laboratories included field blanks, trip 

blanks, and source blanks to measure possible 

contamination and bias; as well as replicate samples to 

measure variability. Concentrations of the six 

compounds of primary interest (TCE, TCA, cis-DCE, 

DCE, DCA, and vinyl chloride) in environmental and 

quality-control samples collected with the diffusion 

samplers and the submersible pump are shown in 

table 2. Concentrations of all analytes in the analysis 

are shown in table 3. 

A total of five blanks, two trip blanks, a field-trip 

blank, and two source blanks were collected from both 

sampling methods. Trip blanks are used to determine 

whether external VOCs are contaminating the sample 

due to handling and/or analytical processes not 

associated with field processing. Trip blanks for both 

sampling methods were water-filled vials supplied by 

the laboratory that were stored and transported with 

other bottles used for collecting the environmental 

samples and were then submitted for analysis with the 

environmental samples. A field blank was collected 

from a diffusion sampler that was stored and 

transported with the field diffusion samplers from the 

time of sampler construction to the time of sampler 

recovery. A field blank is a blank solution that is 

subject to all aspects of the sample collection, field 

processing, preservations, transportation, and 

laboratory handling. The water from the field blank 

was poured from the diffusion sampler into 40-mL 

vials at the time of sampler recovery and submitted for 

analysis with the environmental samples. Source 

blanks were collected from both sampling methods and 

are aliquots of blank water that are analyzed to 

determine the presence of background VOCs. 

Concentrations of the compounds of interest were not 

detected in any blank samples for both sampling 

methods.

Replicate samples provide information needed to 

estimate the variability of concentrations determined 

from the sample-processing and analytical method, and 

to evaluate the consistency of quantifying target VOCs. 

A replicate sample for diffusion samplers consisted of 

two separate sets of VOC vials filled from the same 

diffusion sampler. Two sets of diffusion sampler 

replicate samples were collected, and concentration 

differences in those samples ranged from 0 to 5 percent 

as measured by relative percentage of difference. 

Concentration differences for the pump replicate 

sample ranged from 0 to 5.4 percent as measured by 

relative percentage of difference. The data set was not 

modified based on these results. The results of the 

quality-control data from the diffusion samplers were 

acceptable and the relative percentages of differences 

using the diffusion sampler are comparable to those 

using the submersible pump. 
14 Comparison of Methods for Monitoring Volatile Organic Compounds in Ground Water at Area 6, Naval Air Station Whidbey Island, Washington

COMPARISON OF PASSIVE DIFFUSION 

BAG SAMPLERS AND SUBMERSIBLE 

PUMP SAMPLING METHODS FOR 

MONITORING VOLATILE ORGANIC 

COMPOUNDS IN SHORT- AND LONGSCREENED WELLS

VOC concentrations in water samples collected 

from the 10-foot screened wells with diffusion 

samplers generally were similar to concentrations in 

water samples collected with the submersible pump, 

which was consistent with previous study results 

(Vroblesky and Hyde, 1997; Vroblesky and Peters, 

2000; Vroblesky and Petkewich, 2000; Vroblesky and 

others, 2000). Most differences in concentrations 

between the two sampling methods can likely be 

attributed to the mixing of chemically stratified water 

in the well. Diffusion samplers also indicated vertical 

stratification of VOC contamination in wells with longscreened intervals. 

Short-Screened Wells

Six of the 11 wells selected for diffusion sampler 

installation were wells with 10-foot screened intervals 

(table 1). VOC concentrations of the primary 

compounds of interest (TCE, TCA, cis-DCE, DCE, 

DCA and vinyl chloride) in samples collected using the 

diffusion samplers and a submersible pump are shown 

in table 2. 

VOC concentrations in ground-water samples 

collected using the diffusion sampler and a submersible 

pump were comparable for the wells with 10-foot 

screened intervals (table 2). VOC concentrations of the 

compounds of interest from ground-water samples 

collected with a submersible pump compared to 

concentrations from samples collected with the 

diffusion samplers are shown in figure 3. The mean 

absolute difference of detected concentrations between 

the two sampling methods was only 7.7 μg/L with a 

bias of 6.5 μg/L. 

0.1

1

10

100

1,000

10,000

0.1 1 10 100 1,000 10,000

TCE, DCE, AND DCA CONCENTRATIONS, IN MICROGRAMS PER LITER,

FOR SAMPLES COLLECTED WITH DIFFUSION SAMPLERS

TCE, DCE, AND DCA CONCENTRATIONS, IN MICROGRAMS PER LITER,

FOR SAMPLES COLLECTED WITH SUBMERSIBLE PUMP

1:1 ratio line

MEAN ABSOLUTE DIFFERENCE = 7.7 MICROGRAM/LITER

BIAS = 6.5 MICROGRAM/LITER

1_

n · (|vocDF- voc Mean Absolute Difference = PS|) 1_

n · (vocDF- voc Bias = PS)

Figure 3. Comparison of selected volatile organic compound concentrations from ground-water samples 

collected with diffusion samplers and a submersible pump for six wells with 10-foot screened intervals in 

Area 6, Naval Air Station Whidbey Island, Washington.
Passive Diffusion Bag Samplers and Submersible Pump Sampling Methods 15

A Rank-Sum Test (Wilcoxon rank sum) was 

used to determine if there were significant differences 

between the two data sets. The null hypothesis for this 

test is that the probability of a x value (diffusion 

sampler) being higher than any given y value 

(submersible pump) is one-half. That is, if both groups 

of data are from the same population, an observation 

from either group could be expected to be higher than 

that from the other about one-half of the time. A high p 

value of 0.94 was obtained from the test therefore the 

above null hypothesis applies. The diffusion samplers 

generally provided results similar to pumped samples 

in wells with short-screened intervals (10 feet or less), 

which is consistent with previous study results 

(Vorblesky and Hyde, 1997; A.W. Alexander and T.L. 

Lammons, Bunnell-Lammons Engineering, Inc., 

written commun., August 1998; Vroblesky and Peters, 

2000; and Vroblesky and Petkewich, 2000).

However, TCA and DCA concentrations in the 

water sample collected with the submersible pump 

from well 6-S-13 were considerably higher than the 

TCA and DCA concentrations in water samples 

collected with the diffusion sampler as were TCE, TCA 

and cis-DCE concentrations in water samples from 

well N6-37. A possible explanation for the differences 

is that purging induced flow from a more contaminated 

zone of the aquifer into the well bore; whereas, the 

diffusion samplers do not affect the well bore. 

Alternatively, the well may be characterized by 

contaminant stratification. Vroblesky and Peters (2001) 

found cis-DCE concentration changes in wells of 2,500 

μg/L over a vertical distance of 3.4 feet, and TCE 

concentration changes of 7,300 to 17,500 μg/L over a 

vertical distance of 5 feet. Down-hole flow-meter 

testing and multiple diffusion samplers would be 

needed to further explore the differences.

Long-Screened Wells

Multiple diffusion samplers were installed in 5 of 

the 11 wells at 20- to 40-foot screen intervals (table 2). 

Multiple diffusion samplers were installed in these 

wells to obtain a better understanding of the vertical 

distribution of VOC contamination at the study site. As 

long as there is laminar flow across the screened 

interval in the wells, diffusion samplers can quantify 

vertical stratification of VOC contaminants (Kearl and 

others, 1992; Reilly and LeBlanc, 1998). 

Concentrations of TCA and chloroethane in 

water samples collected with the diffusion samplers 

and a submersible pump from wells 6-S-19 and 6-S-29 

with 20-foot screened intervals are shown in figure 4. 

Two diffusion samplers were installed in both of these 

wells at different depths within the screened interval. 

Concentrations of TCA and chloroethane were 

consistently high in water samples collected with the 

diffusion samplers toward the top of the aquifer. TCA 

concentrations in water samples from well 6-S-29 were 

7.2 μg/L in the sample collected with the shallow 

diffusion sampler (installed at 151.5 feet); <1.0 μg/L in 

the sample collected with the diffusion sampler 

installed 10 feet deeper (161.5 feet); and 7.4 μg/L in 

the sample collected with the submersible pump at a 

depth of about 146 feet. Chloroethane concentrations 

ranged from 28 μg/L in the water sample collected with 

the shallow diffusion sampler to 7.8 μg/L in the water 

sample collected with the deeper diffusion sampler. 
16 Comparison of Methods for Monitoring Volatile Organic Compounds in Ground Water at Area 6, Naval Air Station Whidbey Island, Washington

Figure 4. Comparison of TCA and chloroethane concentrations from ground-water samples collected with diffusion samplers 

and a submersible pump for wells with 20-foot screened intervals in Area 6, Naval Air Station Whidbey Island, Washington.

Well 6-S-29

Screened Interval

144-164 feet

140

145

150

155

160

165

140

145

150

155

160

165

SAMPLE DEPTH, IN FEET

BELOW LAND SURFACE

0 5 10 15 20 25 30 0 5 10 15 20 25 30

Well 6-S-19

Screened Interval

143.5-163.5 feet

CONTAMINANT CONCENTRATION, IN MICROGRAMS PER LITER

EXPLANATION

TCA

Chloroethane

TCA

Chloroethane

CONTAMINANT CONCENTRATION IN SAMPLES

COLLECTED WITH DIFFUSION SAMPLERS

CONTAMINANT CONCENTRATION IN SAMPLES

COLLECTED WITH SUBMERSIBLE PUMP
Passive Diffusion Bag Samplers and Submersible Pump Sampling Methods 17

The results are similar for well 6-S-19, with the 

samples collected with the diffusion samplers showing 

high concentrations of TCA and chloroethane near the 

top of the aquifer. The TCA concentration from the 

sample collected with the submersible pump showed 

considerably less contamination and appears to 

represent a mixture of water from the shallower and 

deeper part of the screened interval. TCA and 

chloroethane concentrations within the screened 

interval were generally underestimated in samples 

collected with the submersible pump and did not show 

a vertical distribution of contamination like the samples 

collected with the diffusion samplers. 

The vertical distribution of contamination in 

wells 6-S-21 and MW-7 with screened-intervals of 40 

and 30 feet are shown in figure 5. Four diffusion 

samplers were installed in well 6-S-21 at 73.2, 83.2, 

93.2, and 103.2 feet. The TCA concentrations ranged 

from 240 μg/L in the shallowest sample to 2.8 μg/L in 

the deepest and DCE concentrations ranged from 42 to 

<1.0 μg/L. The TCA concentration in the 

corresponding sample collected with the submersible 

pump was 120 μg/L and the DCE concentration was 11 

μg/L. Three diffusion samplers were installed in the 

screened interval at 125, 135, and 145 feet in well MW7. TCE concentrations in samples collected with the

CONTAMINANT CONCENTRATION, IN MICROGRAMS PER LITER

EXPLANATION EXPLANATION

1,1-DCE

TCA

1,1-DCE

TCA

CONTAMINANT CONCENTRATION IN SAMPLES

COLLECTED WITH DIFFUSION SAMPLERS

CONTAMINANT CONCENTRATION IN SAMPLES

COLLECTED WITH SUBMERSIBLE PUMP

TCE

TCA

TCE

TCA

CONTAMINANT CONCENTRATION IN SAMPLES

COLLECTED WITH DIFFUSION SAMPLERS

CONTAMINANT CONCENTRATION IN SAMPLES

COLLECTED WITH SUBMERSIBLE PUMP

SAMPLE DEPTH, IN FEET BELOW LAND SURFACE

SAMPLE DEPTH, IN FEET

BELOW LAND SURFACE

Well 6-S-21

Screened Interval

63.5-103.5 feet

0 50 100 150 200 250 300 0 200 400 600 800 1,000

80

85

90

75

70

95

100

105

Well MW-7

Screened Interval

118.4-148.4 feet

125

130

135

120

140

145

150

Figure 5. Comparison of selected volatile organic compound concentrations from ground-water samples collected with diffusion samplers 

and a submersible pump for wells with greater than 20-foot screened intervals in Area 6, Naval Air Station Whidbey Island, Washington.
18 Comparison of Methods for Monitoring Volatile Organic Compounds in Ground Water at Area 6, Naval Air Station Whidbey Island, Washington

diffusion samplers were 810 μg/L from the 

shallowest sample and 0.76 μg/L from the deepest 

sample and TCE concentrations ranged from 450 to 

<1.0 μg/L. TCE and TCA concentrations were 390 and 

480 μg/L in the corresponding sample collected with 

the submersible pump. Concentrations of DCE, TCE, 

and TCA from the water samples collected with the 

submersible pump from these two wells appear to 

represent an integrated sample of water from the entire 

screened interval.

For comparison to the diffusion sampler results, 

an inflatable straddle-packer was placed down well 

MW-7 in June 1998 to preferentially sample an 18-inch 

interval of the long screen. Samples were collected 

with a submersible pump from three depth intervals - 

123, 126, and 136 feet. The results of the straddlepacker data are shown in table 4. The packer results, 

like the diffusion samplers, and unlike the samples 

collected with the submersible pump indicate vertical 

stratification of contamination. Although the packer 

was used to preferentially sample the screen at certain 

intervals, the wells were purged and sampled with a 

pump allowing water to move freely toward the pump 

through the sand or gravel screen pack through zones 

not adjacent to the packed interval, resulting in a 

sample that represents an integration of different water 

types from outside the borehole (Vorbelsky and Hyde, 

1997). Although the packer results showed a better 

vertical resolution than the single submersible pump 

sample, the packer would not be as effective as the 

diffusion samplers in discriminating the vertical 

distribution of contaminants because it does not 

actually isolate a horizon. Whereas, the concentrations 

in water samples collected using diffusion samplers 

represent the immediate vicinity of the sampler.

Table 4. Concentrations of selected chlorinated volatile organic compounds in water collected from 

isolated intervals using a straddle packer in well MW-7 at Area 6, Naval Air Station Whidbey Island, 

Washington

[Chemical Abbreviations: TCE, trichloroethene; TCA, 1.1.1-trichloroethane; cis-DCE, cis-1,1-dichloroethene; DCE, 1,1-

dichloroethene; DCA, 1,1-dichloroethane. μg/L, micrograms per liter; <, not detected at the given concentration; e, detected 

concentration is less than the reporting limit and is an estimate concentration]

Well No. 

(sample depth, 

in feet)

TCE

(μg/L)

TCA

(μg/L)

cis-DCE

(μg/L)

DCE

(μg/L)

DCA

(μg/L)

Vinyl 

chloride 

(μg/L)

MW-7 (123) 1,000 820 160 36 4.5 <25

MW-7 (126) 570 420 170 38 5.1e <25

MW-7 (136) 650 440 120 57 140 <25
Passive Diffusion Bag Samplers and Submersible Pump Sampling Methods 19

The analysis of VOC concentrations in water 

samples collected with diffusion samplers generally 

provides a better understanding of the vertical 

distribution of contaminants in the aquifer. Figure 6 is a 

generalized cross section that illustrates the differences 

in vertical distribution of TCA in the aquifer that could 

be inferred from the VOC data collected with the 

diffusion samplers and submersible pump. The single 

concentrations in samples collected with the 

submersible pump infer that the concentration is 

distributed across the entire screened interval, which 

spans 40 feet for well 6-S-21 and 30 feet for well MW7. Whereas, a different distribution of contamination is 

inferred based on multiple concentrations in samples 

collected from the diffusion samplers. 

In contrast to results from other wells, analysis of 

VOC concentrations in samples collected with the 

diffusion samplers for well MW-8 (a 40-foot screen 

well) did not show a clear vertical distinction of VOC 

contamination (see figure 7 and table 2). The results 

may be indicative of vertical flow within the screened 

interval where contaminants are entering the well near 

the top or bottom of the screen, flowing vertically with 

in the screen under a hydraulic gradient and exiting the 

well at the opposite end. Concentration changes are 

not apparent because the measurements are at different 

points along the pipe flow. In a 40-foot screen, it is 

almost certain that there is vertical flow in the well 

because of the large potential to connect zones of 

differing hydraulic head. A down-hole flow meter 

could be used in this well to indicate the primary 

source water zones. If the zone of low hydraulic head 

from the well is within the contaminated horizon then 

water samples from the diffusion samplers as well as 

the submersible pump would be inadequate because the 

contaminated horizon does not contribute water to the 

well under static conditions, therefore contamination 

concentrations in the water samples would be 

underestimated or not detected (Reilly and Leblanc, 

1998; Vroblesky, 2001). Instead, water from other 

horizons with higher hydraulic head will flow into the 

contaminated horizon by way of the well screen. 

Although pumping draws inflow from the 

contaminated zone, most of that inflow will represent 

the residual water from other horizons.

Sampling Technique Cost Comparisons

The materials cost for the construction of a 

diffusion sampler were about $2 per sampler. Materials 

included nylon parachute cord, polyethylene tubing, 

mesh tubing, and stainless steel weights. A reusable 

heat sealer was purchased at cost of $80; the item is a 

one-time purchase needed to construct the diffusion 

sampler. For this study site, construction required one 

person 4 hours for 24 samplers, and a two-person crew 

8 hours for installation and another 4 hours for retrieval 

of the samplers. About six wells (12 samplers) were 

sampled per-person day, and the total purge water 

collected for disposal was a little over 1 gallon. 

In comparison, the ability to collect a sample 

using a submersible pump requires a much larger onetime purchase of a submersible pump (about $5,000) 

and a generator, which can be either rented or 

purchased. At this study site, an average of 2.5 wells 

were sampled per person-day and the total purge water 

collected for disposal was about 200 gallons. The use 

of diffusion samplers is clearly more cost effective. If 

diffusion samplers were to be used again at this site, the 

re-installation of the samplers would be faster because 

the desired placement of samplers is known.
20 Comparison of Methods for Monitoring Volatile Organic Compounds in Ground Water at Area 6, Naval Air Station Whidbey Island, Washington

0

0

100 500 FEET 200 300 400

20 40 60 80 100 METERS

VERTICAL SCALE GREATLY EXAGGERATED

480

120 260

225

N-6-38

(163.85)

260

N-6-38

(163.85)

50

55

60

65

70

75

80

85

90

95

100

150

160

170

180

190

200

210

Land surface

6-S-21

(157.7)

PW-1

(170.81)

MW-7

(199.46) VERTICAL DISTRIBUTION OF TCA FROM PUMP SAMPLES

300

400

200

WL

89.15

WL

88.88 WL

86.13

? ?

? ?

A A'

ALTITUDE, IN FEET ABOVE SEA LEVEL

FEET

EXPLANATION

LINE OF EQUAL TCA CONCENTRATION—

Dashed where approximately located.

Interval, 100 micrograms per liter

WELL—Number is TCA concentration,

in micrograms per liter

Well No.

(Altitude of the top of the well,

in feet above mean sea level)

Water-level altitude, April 1999,

in feet above mean sea level

200

Figure 6. Vertical distribution of TCA concentrations in ground-water samples collected with the diffusion samplers 

and submersible pump.
Passive Diffusion Bag Samplers and Submersible Pump Sampling Methods 21

0

0

100 500 FEET 200 300 400

20 40 60 80 100 METERS

VERTICAL SCALE GREATLY EXAGGERATED

225

260

N-6-38

(163.85)

240

50

60

70

80

90

100

150

160

170

180

190

200

210

450

420

2.8 21.0

Land surface

6-S-21

(157.4)

PW-1

(170.81)

MW-7

(199.46)

15

0.87

VERTICAL DISTRIBUTION OF TCA FROM DIFFUSION SAMPLES

300

400

200

? ?

A A'

ALTITUDE, IN FEET ABOVE SEA LEVEL

FEET

Figure 6.—Continued.
22 Comparison of Methods for Monitoring Volatile Organic Compounds in Ground Water at Area 6, Naval Air Station Whidbey Island, Washington

0 1 2 3 4 5 6 7

CONTAMINANT CONCENTRATION,

IN MICROGRAMS PER LITER

EXPLANATION

TCA

DCA

Vinyl chloride

TCA

DCA

Vinyl chloride

CONTAMINANT CONCENTRATION IN SAMPLES

COLLECTED WITH DIFFUSION SAMPLERS

CONTAMINANT CONCENTRATION IN SAMPLES

COLLECTED WITH SUBMERSIBLE PUMP

Well MW-8

Screened Interval

122-162 feet

135

130

125

140

145

150

155

160

SAMPLE DEPTH, IN FEET BELOW LAND SURFACE

Figure 7. Comparison of selected volatile organic compounds from ground-water samples collected with diffusion samplers and a 

submersible pump for well MW-8, with a 40-foot screened interval that is not indicative of laminar flow across the screened interval in 

Area 6, Naval Air Station Whidbey Island, Washington. 
Summary 23

SUMMARY

Ground-water samples were collected in April 

1999 at Naval Air Station Whidbey Island, 

Washington, with passive diffusion samplers and a 

submersible pump to compare concentrations of 

volatile organic compounds (VOCs) in water samples 

collected using the two sampling methods. Single 

diffusion samplers were installed in six wells with 10-

foot screened intervals, and multiple diffusion samplers 

were installed in five wells with 20- to 40-foot screened 

intervals. The samplers were recovered after 20 days, 

and the wells were then sampled using a submersible 

pump.

For the 10-foot screened wells, contaminant 

concentrations in samples collected using the passive 

diffusion samplers closely matched contaminant 

concentrations using the submersible pump. The mean 

absolute difference of detected concentrations was 7.7 

μg/L. For the long-screen wells (screen length greater 

than 10 feet), the analysis of VOC concentrations in 

samples collected with multiple diffusion samplers 

indicated vertical concentration variations within the 

screened interval, whereas the analysis of VOC 

concentrations in samples collected with the 

conventional submersible pump indicated mixing 

during pumping. VOC data collected using diffusion 

samplers also indicated that contaminant stratification 

was present in some wells. TCA concentrations in one 

well ranged from 240 to 15 μg/L over a vertical 

distance of about 10 feet. In this and other wells where 

concentration stratification was observed, the 

concentration in the samples collected with the 

submersible pump appears to represent a mixing of 

waters with differing concentrations, whereas the 

concentrations in samples collected with the diffusion 

samplers represent localized concentrations. However, 

where vertical flow may be apparent within the 

screened interval such as the data indicate from well 

MW-8, a borehole flow meter should be used to 

determine what horizon borehole water is coming 

from, and to determine if samples collected with 

diffusion samplers as well as samples collected with 

submersible pumps would be representative of 

contaminant concentrations in the aquifer. 

An advantage of the diffusion sampling method 

over the traditional submersible pump method includes 

less overall time and money for collection of samples 

and minimal wastewater. In addition, diffusion 

samplers have an advantage over the pump method in 

evaluating the stratification of VOCs in wells because 

diffusion samplers can collect multiple samples with 

little added time over the time needed for collection of 

one sample. Overall, the data indicate that the use of 

diffusion samplers provided an effective less expensive 

alternative sampling method to the purge-and-sample 

approach used at this site.
24 Comparison of Methods for Monitoring Volatile Organic Compounds in Ground Water at Area 6, Naval Air Station Whidbey Island, Washington

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Huffman WRIR 02-4203 Comparison of Methods for Monitoring Volatile Organic Compounds in Ground Water,

Area 6, Naval Air Station Whidbey Island, WA