Evaluation of Passive Diffusion Bag Samplers, 

Dialysis Samplers, and Nylon-Screen Samplers in 

Selected Wells at Andersen Air Force Base, Guam, 

March–April 2002

By Don A. Vroblesky, Manish Joshi, Jeffrey Morrell, 

and J E. Peterson

U.S. Geological Survey

Water-Resources Investigations Report 03-4157

Prepared in cooperation with the

AIR FORCE CENTER FOR ENVIRONMENTAL EXCELLENCE

Columbia, South Carolina

2003
U.S. DEPARTMENT OF THE INTERIOR

GALE A. NORTON, Secretary

U.S. GEOLOGICAL SURVEY

Charles G. Groat, Director

Use of trade, product, or firm names in this publication is for descriptive purposes only 

and does not imply endorsement by the U.S. Geological Survey.

For additional information 

write to: 

District Chief 

U.S. Geological Survey

Suite 129

720 Gracern Road

Columbia, SC 29210-7651

Copies of this report can be 

purchased from:

U.S. Geological Survey

Branch of Information Services

Box 25286

Denver, CO 80225-0286

888-ASK-USGS

Additional information about water resources in South Carolina is available on the 

internet at http://sc.water.usgs.gov
Contents III

CONTENTS

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

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

Site Description................................................................................................................................................................ 2

Purpose............................................................................................................................................................................. 4

Methods...................................................................................................................................................................................... 4

Borehole-Flowmeter Surveys........................................................................................................................................... 4

Diffusion Sampler Construction and Deployment........................................................................................................... 5

Water-Sample Collection and Diffusion-Sampler Recovery ........................................................................................... 6

Results and Discussion .............................................................................................................................................................. 9

Distribution of Ground-Water Flow in Wells................................................................................................................... 9

Comparison of Trichloroethene and Tetrachloroethene Concentrations in Passive Diffusion Bag Samples 

and Pumped Samples ................................................................................................................................................. 17

Comparison of Passive Diffusion Bag Samples to Dialysis Samples ............................................................................ 23

Comparison of Chloride in Nylon-Screen Samples, Dialysis Samples, and Pumped Samples..................................... 25

Practical Considerations for the Use of Passive Diffusion Bag Samplers in Wells at Andersen Air Force Base.......... 25

Summary and Conclusions ...................................................................................................................................................... 26

References................................................................................................................................................................................ 28

FIGURES

1. Map showing location of monitoring wells sampled at Andersen Air Force Base, Guam, March-April 2002 ................. 3

2-6. Graphs showing borehole-flowmeter data under nonpumped and pumped conditions, approximate water-yielding 

zones during pumping, and trichloroethene concentrations in dialysis samples, passive diffusion bag samples, 

and pumped samples at: 

2. Well IRP-3, Main Base, Andersen Air Force Base, Guam, April 2002..................................................................... 12

3. Well IRP-39, Main Base, Andersen Air Force Base, Guam, April 2002................................................................... 13

4. Well IRP-51, Main Base, Andersen Air Force Base, Guam, April 2002................................................................... 14

5. Well IRP-29, MARBO Annex, Andersen Air Force Base, Guam, April 2002.......................................................... 15

6. Well IRP-31, MARBO Annex, Andersen Air Force Base, Guam, April 2002.......................................................... 16

7-9. Graphs showing:

7. Comparison of trichloroethene concentrations in passive diffusion bag and dialysis samples to 

trichloroethene concentrations in pumped samples, Main Base and MARBO Annex, Andersen 

Air Force Base, Guam, April 2002 ............................................................................................................................ 21

8. Comparison of tetrachloroethene concentrations in passive diffusion bag and dialysis samples to 

tetrachloroethene concentrations in pumped samples, Main Base and MARBO Annex, Andersen 

Air Force Base, Guam, April 2002 ............................................................................................................................ 22

9. Chloride concentrations in nylon-screen, dialysis, and pumped samples at well IRP-29, MARBO Annex, 

Andersen Air Force Base, Guam, April 2002............................................................................................................ 27
IV Contents

TABLES

1. Well information, Main Base and MARBO Annex, Andersen Air Force Base, Guam, March-April 2002.........................5

2. Diffusion sampler and pumped sampling information, Main Base and MARBO Annex, Andersen Air Force Base, 

Guam, March-April 2002......................................................................................................................................................7 

3. Borehole-flowmeter data, Main Base and MARBO Annex, Andersen Air Force Base, Guam, March-April 2002 ..........10

4. Laboratory analysis of chlorinated aliphatic compounds showing detections in dialysis samples, passive diffusion 

bag samples, or pumped samples from ground water in wells, Main Base and MARBO Annex, Andersen Air Force 

Base, Guam, March-April 2002 ..........................................................................................................................................18

5. Standardized concentrations of trichloroethene and tetrachloroethene by field gas chromatography in passive 

diffusion bag samples and dialysis samples, Main Base and MARBO Annex, Andersen Air Force Base, Guam, 

April 2002 ...........................................................................................................................................................................24

6. Concentrations of chloride in nylon-screen, dialysis, and pumped samples from ground water in wells at the Main 

Base and MARBO Annex, Andersen Air Force Base, Guam, April 2002 .........................................................................26

7. Optimum deployment depths for using passive diffusion bag samplers as monitoring tools for the maximum volatile

organic compound concentration, Main Base and MARBO Annex, Andersen Air Force Base, Guam.............................27

CONVERSION FACTORS, VERTICAL DATUM, ACRONYMS, AND ABBREVIATIONS 

Chemical Concentration: In this report, chemical concentration in water is expressed in 

metric units as milligrams per liter (mg/L) or micrograms per liter (μg/L).

Sea Level: In this report, “sea level” refers to the National Geodetic Vertical Datum of 

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

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

Multiply By To obtain

Length

inch (in.) 25.4 millimeter

foot (ft) 0.3048 meter

mile (mi) 1.609 kilometer

Volume

gallon (gal) 3.785 liter

Flow

foot per day (ft/d) 0.3048 meter per day

foot per year (ft/yr) 0.3048 meter per year

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

AFB Air Force Base μ micron

AFCEE Air Force Center for Environmental Excellence mL milligram per liter

CAH chlorinated aliphatic hydrocarbon mL milliliter

EDTA ethylenediaminetetra acetic acid PDB passive diffusion bag

LDPE low-density polyethylene TCE trichloroethene

L liter PCE tetrachloroethene

MARBO Marianas Bonins USGS U.S. Geological Survey

μg microgram VOA volatile organic analysis

μg/L microgram per liter VOC volatile organic compound
Abstract 1

Evaluation of Passive Diffusion Bag Samplers, Dialysis 

Samplers, and Nylon-Screen Samplers in Selected Wells 

at Andersen Air Force Base, Guam, March–April 2002

By Don A. Vroblesky1, Manish Joshi2, Jeff Morrell3, and J E. Peterson4

1U.S. Geological Survey, Columbia, South Carolina.

2Earth Tech, San Antonio, Texas.

3EA Engineering, Science, and Technology, Inc., Yigo, Guam.

4Earth Tech, Alexandria, Virginia.

ABSTRACT 

During March-April 2002, the U.S. Geological 

Survey, Earth Tech, and EA Engineering, Science, 

and Technology, Inc., in cooperation with the Air 

Force Center for Environmental Excellence, tested 

diffusion samplers at Andersen Air Force Base, 

Guam. Samplers were deployed in three wells at 

the Main Base and two wells at Marianas Bonins 

(MARBO) Annex as potential ground-water monitoring alternatives. Prior to sampler deployment, 

the wells were tested using a borehole flowmeter to 

characterize vertical flow within each well. Three 

types of diffusion samplers were tested: passive 

diffusion bag (PDB) samplers, dialysis samplers, 

and nylon-screen samplers. The primary volatile 

organic compounds (VOCs) tested in ground water 

at Andersen Air Force Base were trichloroethene 

and tetrachloroethene. In most comparisons, 

trichloroethene and tetrachloroethene concentrations in PDB samples closely matched concentrations in pumped samples. Exceptions were in wells 

where the pumping or ambient flow produced vertical translocation of water in a chemically stratified aquifer. In these wells, PDB samplers probably 

would be a viable alternative sampling method if 

they were placed at appropriate depths. In the 

remaining three test wells, the trichloroethene or 

tetrachloroethene concentrations obtained with the 

diffusion samplers closely matched the result from 

pumped sampling. 

In all of the tests, the regenerated cellulose 

dialysis samplers produced lower VOC concentrations than the passive diffusion bag samplers and 

most of the pumped results. The source of the difference is unknown, but a possible explanation may 

be the biodegradation of the dialysis membrane 

during the 22 to 23 days of deployment. 

Chloride concentrations in nylon-screen 

samplers were compared with chloride concentrations in dialysis and pumped samples to test 

inorganic-solute diffusion into the samplers across 

a range of concentrations. The test showed that 

the results from nylon-screen samplers might have 

underestimated chloride concentrations at depths 

with elevated chloride concentrations. The reason 

for the discrepancy in this investigation is unknown, 

but may be related to nylon-screen-mesh size, 

which was smaller than that used in previous 

investigations. 
2 Evaluation of Passive Diffusion Bag Samplers, Dialysis Samplers, and Nylon-Screen Samplers in Selected Wells at Andersen 

Air Force Base, Guam, March–April 2002

INTRODUCTION 

Ground-water sampling at Andersen Air Force 

Base (AFB) (fig. 1), Guam, is complicated by the large 

depth to ground water (350 to 550 ft), necessitating the 

use of dedicated positive-displacement pumps. In addition, the pump-failure rate is high, possibly because of 

corrosion by the aquifer water. To explore alternative 

approaches for collecting ground-water samples at this 

site, EA Engineering, Science, and Technology, Inc., 

tested passive diffusion bag (PDB) samplers in wells at 

Andersen AFB in 1999 (T.L. Isakson, 2000, EA Engineering, Science, and Technology, Inc., written commun., 2000). PDB samplers were tested at single 

depths in six wells using duplicate samples. In three of 

the test wells, volatile organic compound (VOC) concentrations in the pumped and PDB samples differed 

by less than 5 μg/L. In one well, IRP-39 (fig. 1), the 

concentrations of trichloroethene (TCE) and tetrachloroethene (PCE) were about 10 μg/L higher in the PDB 

samples than in the pumped samples, which is not 

surprising considering that the pumped sample mixes 

water. EA Engineering, Science, and Technology, 

Inc., personnel expressed concern, however, because 

some compounds (acetone in some of the samples and 

benzene in samples from well IRP-51, fig. 1) were 

detected in PDB samplers, but not in the pumped samples and because concentrations of TCE in well IRP-31 

were substantially higher in the pumped samples than 

in the PDB samples. The fact that acetone was detected 

in some of the PDB samples but not in the pumped 

samples is not a concern, because acetone does not 

easily diffuse through polyethylene (Vroblesky, 2001) 

and, thus, probably represents either a component of 

the water used to fill the samplers or a laboratory contaminant. However, concern about the detection of benzene in PDB samples from well IRP-51 and the higher 

concentrations of TCE and PCE in well IRP-31 could 

be addressed by repeating the comparison using PDB 

samplers deployed at multiple depths.

To clarify the questions regarding the PDB results 

in wells IRP-51 and IRP-31 and to examine PDB samplers in other wells, the U.S. Geological Survey, Earth 

Tech, and EA Engineering, Science, and Technology, 

Inc., in cooperation with the Air Force Center for Environmental Excellence (AFCEE), conducted an investigation to test diffusion samplers at Andersen AFB, Guam, 

in three wells at the Main Base and two wells at Marianas Bonins (MARBO) Annex during March-April 

2002. The tested diffusion samplers were PDB samplers, 

dialysis samplers, and nylon-screen samplers. 

PDB samplers constructed of low-density 

polyethylene (LDPE) have been shown to be a costeffective alternative to conventional ground-water sampling methods for sampling VOCs (Vroblesky and 

Hyde, 1997; Parsons Engineering Science, Inc., 1999; 

Hare, 2000; McClellan AFB Environmental Management Directorate, 2000; Vroblesky and others, 2000; 

Vroblesky and Peters, 2000; Vroblesky and Petkewich, 

2000). PDB samplers are not effective, however, for 

measuring inorganic ions in ground water. 

Inorganic solutes in pore water have been measured by using a wide variety of diffusion samplers 

(Bottomly and Bayley, 1984; Ronen and others, 1986; 

Kaplan and others, 1991; Webster and others, 1998; 

Diog and Liber; 2000; Vroblesky and others, 2002, 

Vroblesky and Pravecek, 2002) that are variations of 

dialysis samplers introduced by Hesslein (1976) and 

Mayer (1976). In addition, experiments have been done 

using nylon screens as membranes (Paludan and Morris, 

1999; Vroblesky and others, 2002). The dialysis and 

nylon-screen samplers tested in this investigation are 

modeled after those used by Vroblesky and others 

(2002).

Site Description

The U.S. Territory of Guam is the largest and 

southernmost of the islands in the Marianas chain. 

Andersen AFB is in the northern part of the island. 

The two areas of the base relative to this report are the 

Main Base and MARBO Annex (fig. 1). Ground-water 

contamination by chlorinated aliphatic hydrocarbons 

(CAH) is present in the ground water. The primary contaminants of concern are TCE and PCE. In some wells, 

inorganic constituents are also of concern.

The average annual rainfall at Andersen AFB is 

approximately 100 inches, primarily during the months 

of July through November (Ward and Brookhart, 

1962). Despite the large amount of rainfall, there are no 

streams in the northern part of the island because of the 

highly permeable limestone terrane, which allows rapid 

infiltration of rainfall. Permeability in the limestone is 

controlled largely by porosity and channels that allow 

for substantial water movement. Surficial soils are thin 

to nonexistent. Hydraulic conductivity of the aquifer 

under the northern part of the island probably ranges 

between 1,000 and 5,000 ft/d, although calculations 

from the response of the water table to tidal action suggest values as high as 20,000 ft/d (Branch and others, 

1982). 
Introduction 3

1

1

3

15

16

Pacific

Ocean

Philippine

Sea

0 1 2 3 4 MILES

0 1 2 3 4 KILOMETERS

G U A M

EXPLANATION

Andersen Air Force Base property

Primary road

Secondary road

Monitoring well and well number

1

IRP-3

Northwest Field

Main Base

Pati

Point

MARBO

Annex

Harmon

Annex

Area

Shown

in Map

GUAM

Agana

Philippine Sea

Pacific

Ocean

IRP-3

IRP-39

IRP-51

IRP-31

IRP-29

13°30′

13°35′

13°40′

144°50′ 144°55′

Figure 1. Location of monitoring wells sampled at Andersen Air Force Base, Guam, March-April 2002.
4 Evaluation of Passive Diffusion Bag Samplers, Dialysis Samplers, and Nylon-Screen Samplers in Selected Wells at Andersen 

Air Force Base, Guam, March–April 2002

The surface elevation is about 450 to 550 ft 

above sea level at the Main Base and about 350 to 

400 ft above sea level at MARBO Annex. Because of 

the highly permeable nature of the limestone, the water 

table in the northern part of the island constitutes a low 

dome standing about 5 to 7 ft above sea level in the 

central part of the area and slopes gradually to sea level 

at the shore (Ward and Brookhart, 1962). Thus, the 

depth to the water table is about 450 to 550 ft beneath 

the Main Base and about 350 to 400 ft beneath 

MARBO Annex. 

The transition zone between fresh ground water 

and the underlying saltwater in northern Guam is relatively thin, and tidal mixing appears to be substantially 

less than is typical for many island aquifers (Gregg 

Ikehara, U.S. Department of Defense, oral commun., 

2003). The large depth to water complicates groundwater sampling by necessitating pumps capable of lifting hundreds of feet of head. Moreover, there is a relatively high incidence of pump failure from corrosion, 

possibly related to salinity levels.

Diffusion samplers were tested in five wells at 

the facility. The wells were IRP-3, IRP-39, and IRP-51 

at the Main Base and wells IRP-29 and IRP-31 at 

MARBO Annex (fig. 1, table 1). Although the total dissolved solids concentrations in all of these wells were 

in the range of freshwater (1 to 1,000 milligrams per 

liter), the screened interval of at least four (IRP-39, 

IRP-51, IRP-29, and IRP-31) of the five tested wells 

probably included part of the transition zone between 

fresh and saltwater. 

Purpose 

The purpose of this report is to (1) compare 

ground-water VOC concentrations obtained from 

side-by-side tests of dialysis and PDB samplers to concentrations obtained by pumped sampling in wells and 

(2) compare chloride concentrations obtained from sideby side tests of dialysis and nylon-screen samplers to 

concentrations obtained by pumped sampling. Although 

chloride is not a solute of concern at the facility, it was 

chosen as the representative solute because of the expection to see a large vertical variation in the concentration 

within the screened interval.

METHODS 

Chemical concentrations in ground water 

obtained at wells by using passive sampling methods 

(dialysis, nylon-screen, and PDB) were compared to 

concentrations obtained by using pumped sampling. 

Borehole-flowmeter results aided in the interpretation 

of the data. 

Borehole-Flowmeter Surveys

Borehole-flowmeter measurements were made in 

the screened intervals of the wells prior to deployment 

of the diffusion samplers. The measurements were 

made with a Mount Sopris HPF-2293 heat-pulse flowmeter, which is capable of quantifying vertical flow but 

is not capable of detecting horizontal flow. There is 

quantitation uncertainty in the flowmeter data presented here because the wells are screened, and the 

flowmeter cannot detect water movement through the 

sand pack outside of the well screen. The data, however, are useful in determining zones in which water is 

moving vertically in the borehole under nonpumped 

conditions and in determining which zones are contributing water to the well under pumped conditions. The 

heat-pulse flowmeter is capable of measuring flows 

ranging from 0.03 to 1.5 gal/min (Mount Sopris Instrument Company, Inc., 2001).

Borehole-flowmeter measurements were taken at 

several depths, approximately 2 to 3 ft apart, within 

each screened interval under nonpumping conditions. 

Prior to taking an initial reading at each depth, the 

probe was allowed to stabilize for at least 3 minutes 

and longer if it was suspected that water movement was 

related to movement of the probe. At least three readings were taken at each depth. Each well then 

was pumped from a shallow depth at a rate of about 

0.5 gal/min, and additional measurements were made 

at the same horizons used during nonpumping conditions. At the Main Base wells, additional measurements were taken while pumping the wells at about 

1 gal/min. In well IRP-31, a flowmeter reading was 

taken under pumping conditions within the closed 

casing of the well at a depth of 442 ft, allowing for a 

measurement of total upward flow. In this instance, 

the amount of flow was 0.38 gal/min. 

For this investigation, the flowmeter data were 

divided into the approximate percentage of contribution to the well during pumping by comparing flowmeter data from one horizon with the flowmeter data 

from the next underlying horizon. The amount of 
Methods 5

upward-flow increase between the two horizons 

divided by the amount of upward flow measured at the 

shallowest flowmeter-data point in the well indicated 

the fractional contribution of water from the zone 

between the two horizons. If one or more consecutive 

measuring points showed little or no change in flow 

(about 5 percent accuracy), then the horizons between 

the points were considered to make no measurable flow 

contribution to the pumpage. In this case, the average 

flow measured across that noncontributing interval was 

used as a comparison to shallower and deeper measurements to determine approximate relative flow contributions of the bounding zones. The amount of flow up the 

well typically does not total 100 percent of the pumpage because of (1) water movement in the annular 

space outside the well screen and (2) because the location of the water table in some wells necessitated that 

both the pump and the uppermost borehole flowmeter 

reading were within the screened interval rather than in 

the closed casing above the screen.

Diffusion Sampler Construction and 

Deployment

The PDB samplers were purchased commercially (Eon Products, Inc., Snellville, Georgia). The 

PDB samplers consisted of 4-mil-thick polyethylene 

bags attached to a bottom-discharging device, and are 

described in detail in Vroblesky (2001). Each dialysis 

sampler was constructed onsite and consisted of a 

perforated acetate or plastic pipe inside a sleeve of 

high-grade regenerated cellulose tubular dialysis membrane (Membrane Filtration Products, Inc., Seguin, 

Texas) (Vroblesky and others, 2002). The nylon-screen 

samplers each consisted of three 30-mL polyethylene 

wide-mouth bottles with a nylon-screen cloth secured 

over the openings (Vroblesky and others, 2002). 

Because the aquifer was known to be aerobic, the PDB 

samplers and dialysis samplers were filled with aerobic 

de-ionized water at the time of sampler deployment. 

The dialysis samplers were prepared from pretreated tubular regenerated cellulose dialysis membrane having a nominal molecular-weight cutoff of 

8,000 daltons, or approximately 18 angstroms pore 

size. The pretreatment was designed to remove sulfur 

compounds and residual metals. The pretreated membrane is packaged in a solution of methanol and ethylenediaminetetra acetic acid (EDTA), which is removed 

by rinsing with de-ionized water prior to use. 

To construct a dialysis sampler, the cellulose 

acetate dialysis tube was cut to a length of approximately 2 ft. The dialysis membrane was thoroughly 

washed with de-ionized water. One end of the tube was 

tied in a knot. A pipe of perforated plastic was slid into 

the dialysis tube for structural support. The sampler 

was filled with de-ionized water at the time of sampler 

deployment, and the open end of the membrane was 

tied. The assembly was slid into a length of LDPE 

mesh for abrasion protection. 

Table 1. Well information, Main Base and MARBO Annex, Andersen Air Force Base, Guam, March-April 2002

[TOC, top of casing; ft, feet; MLLW, mean lowest low water; BLS, below land surface; BTOC, below top of casing; all wells were 

4-inch diameter PVC]

Well

Elevation 

of TOCa

(ft relative 

to MLLW)

Sounded 

depth of 

well 

(ft below 

TOC)

Reported 

depth to 

well 

bottoma

(ft BLS)

Height 

of stand 

pipe 

(ft)

Screen 

length 

(ft)

Screened 

interval 

(ft BTOC)

Depth to 

water at 

time of 

recovery 

(ft BTOC)

Elevation of the 

water table at 

time of sampler 

recovery 

(ft relative to 

MLLW)

Saturated 

screened 

interval at 

time of 

sampler 

recovery 

(ft)

Main Base

IRP-3 559.79 581.74 584 2.1 41 545.1 - 586.1 556.18 3.61 30

IRP-39 556.96 629.22 625 2.8 20 607.8 - 627.8 553.41 3.55 20

IRP-51 459.46 510.22 507 1.8 20 588.8 - 508.8 458.52 .94 20

MARBO Annex

IRP-29 383.13 481.44 479 2.4 20 461.4 - 481.4 377.74 5.39 20

IRP-31 363.64 465.92 465 2.1 20 447.1 - 467.1 358.25 5.39 20

aData from Dames and Moore (2001).
6 Evaluation of Passive Diffusion Bag Samplers, Dialysis Samplers, and Nylon-Screen Samplers in Selected Wells at Andersen 

Air Force Base, Guam, March–April 2002

To prepare a nylon-screen sampler, a 2- by 2-in. 

section of nylon screen was secured by holding it in 

place over the jar opening and screwing the open-top 

cap onto the jar and screen. The screen-opening size 

used in this investigation was 48 μ. This is a smaller 

size than that used in a previous successful field test 

(125 and 250 μ) at Fort Worth, Texas (Vroblesky and 

others, 2002). Each sampler consisted of two such jars 

held in a sleeve of 2-in-diameter flexible LDPE mesh, 

giving a total of approximately 50 to 60 mL of available water. The jars were oriented horizontally in the 

4-in-diameter well screens, with the openings facing 

opposite directions. Webster and others (1998) found 

that vials oriented with the membrane facing downward failed to equilibrate with saltwater after 60 hours 

because density differences eliminated the tendency for 

saline convection to develop within the samplers. Vials 

oriented with the membrane facing upward or to the 

side equilibrated much faster (85 percent equilibration 

in 15 hours) than samplers oriented downward; however, samplers oriented with the membrane facing 

upward equilibrated more slowly than samplers 

oriented with the membrane facing sideways. 

The diffusion samplers were deployed at Andersen AFB in three wells at the Main Base and in two 

wells at MARBO Annex (table 1). Deployment of the 

samplers consisted of attaching the samplers to a 

weighted support line and lowering them into the well. 

A PDB sampler was attached to a dialysis sampler at 

each targeted horizon. Each well consisted of at least 

seven targeted horizons (table 2). Three days following 

initial deployment, the samplers were removed from 

wells IRP-3, IRP-29, and IRP-51, the depths were 

adjusted for better vertical coverage, and the samplers 

were redeployed in wells. In IRP-29, nylon-screen 

samplers were added. In IRP-3, the adjustment 

included attaching additional PDB samplers and redeploying them. The samplers were out of the water less 

than 45 minutes at each well.

Some uncertainty is associated with the depths of 

the upper two PDB samplers in well IRP-3. In the original deployment, the upper PDB sampler was positioned at a depth of 556 ft to the center of the sampler, 

which was partly above the water table at a depth of 

556.79 ft. The close match in concentration between 

samples IRP-3A and IRP-3B indicates that sampler 

IRP-3A almost certainly was not above the water table. 

A probable scenario is that the weight of sampler 

IRP-3A suspended above the water table caused the 

rope to stretch, allowing the PDB sampler to become 

immersed. Thus, samplers IRP-3A and IRP-3B 

probably represent similar depths at the top of the 

water table. 

Water-Sample Collection and 

Diffusion-Sampler Recovery

Ground-water samples were collected by pumping the wells at Andersen AFB, Guam. The wells were 

purged at a rate of approximately 0.5 gal/min until the 

tubing volume was purged (about 7 gal), followed by a 

minimum of 14 gal to purge the well volume. During 

pumping, field readings of temperature, pH, specific 

conductance, turbidity, dissolved oxygen, redox, and 

chlorides were taken every 3 to 4 minutes. If after purging the 14 gal of casing water by pumping, the field 

properties had not stabilized, then the pumping was 

continued until stabilization was achieved. Stabilization meant that the field properties had three consecutive sets of readings, all within defined ranges. Water 

levels were monitored during pumping, but drawdowns 

typically were slight. Ground-water samples were collected after field properties stabilized. The pumped 

ground-water samples were collected between 3 and 8 

days following retrieval of the diffusion samplers from 

the well (table 2). 

Samples were analyzed for chloride by method 

E300.0 (U.S. Environmental Protection Agency, 1983, 

1992). Because of the limited sample volumes available from the nylon-screen samplers, a minimum of 

15 mL was analyzed for chloride. 

Water from the dialysis and PDB samplers was 

analyzed for TCE and PCE in the field by gas chromatography (SRI 8610 gas chromatograph with photoionization detection). Based on the results of the field gas 

chromatography, water from diffusion samples collected at selected horizons was sent to a commercial 

laboratory for VOC analysis using Environmental Protection Agency Method 8260B (U.S. Environmental 

Protection Agency, 1999). In general, the selected horizons represented the depths of highest concentrations 

as detected with the field gas chromatography. The laboratory results were used to obtain an adjustment factor 

with which to standardize the results from the gas chromatograph in the field. All field gas chromatography 

results for a particular well were uniformly adjusted by 

the percentage difference between the field result and 

the laboratory result for the coanalyzed depth in that 

well. Thus, the field gas chromatography results are 

reported as “standardized.” The standardized values 

should be considered to be estimated concentrations.
Methods 7

Table 2. Diffusion sampler and pumped sampling information, Main Base and MARBO Annex, Andersen Air Force Base, Guam, March-[ft, feet; ft BTOC, feet below top of casing; ft BLS, feet below land surface; # depth uncertain because of probable shifting of samplers; ---, data not collect

which monitoring data are routinely collected]

Well 

number

Sample 

identifier

Diffusion samples Pumped samples Num

Distance 

from well 

bottom to 

sampler 

center 

(ft)

Depth to 

sampler 

center 

(ft BTOC)

Diffusion 

sampler 

deployment 

date

Diffusion 

sampler 

recovery 

date

Days of 

diffusionsampler 

equilibration

Pumped 

sample 

depth 

(ft BLS)

Pumped 

sample 

depth 

(ft BTOC)

Pumped 

sampling 

date

Passive 

diffusion 

bag 

sample

Main Base

IRP-3 IPR-3A 24.5# 556.5# 3/11/02 4/3/02 23 --- --- --- 1 

IPR-3B 24# 557# 3/11/02 4/3/02 23 --- --- --- 1 IPR-3C 23.3 557.7 3/14/02 4/3/02 20 --- --- --- 1 

IPR-3D 21.3 559.7 3/11/02 4/3/02 23 558.5 560.6 4/11/02 1 

IPR-3E 18.3 562.7 3/11/02 4/3/02 23 560.5 562.6 4/11/02 1 

IPR-3F 16.8 564.2 3/14/02 4/3/02 20 --- --- --- 1 

IPR-3G 15.3 565.7 3/11/02 4/3/02 23 564* 566.1* 4/11/02 1 IPR-3H 13.3 567.7 3/11/02 4/3/02 23 --- --- --- 1 

IPR-3I 11.3 569.7 3/11/02 4/3/02 23 --- --- --- 1 

IPR-3J 7.3 573.7 3/11/02 4/3/02 23 --- --- --- 1 

IPR-3K 3.3 577.7 3/11/02 4/3/02 23 --- --- --- 1 

IRP-39 IRP-39A 17.3 611.2 3/11/02 4/2/02 22 610 612.9 4/9/02 1 

IRP-39B 12.3 616.2 3/11/02 4/2/02 22 611* 613.8* 4/9/02 1 

IRP-39C 9.3 619.2 3/11/02 4/2/02 22 --- --- --- 1 

IRP-39D 7.3 621.2 3/11/02 4/2/02 22 --- --- --- 1 

IRP-39E 4.5 624.0 3/11/02 4/2/02 22 --- --- --- 1 

IRP-39F 2.7 625.9 3/11/02 4/2/02 22 --- --- --- 1 

IRP-39G 1.2 627.2 3/11/02 4/2/02 22 --- --- --- 1 

IRP-51 IRP-51A 18.9 490.6 3/11/02 4/2/02 22 490* 491.8* 4/10/02 1 

IRP-51B 16.9 492.6 3/11/02 4/2/02 22 491.5 493.3 4/10/02 1 IRP-51C 14.9 494.6 3/11/02 4/2/02 22 --- --- --- 1 

IRP-51D 12.9 496.6 3/11/02 4/2/02 22 --- --- --- 1 

IRP-51E 10.9 498.6 3/11/02 4/2/02 22 --- --- --- 1 

IRP-51F 6.9 502.6 3/11/02 4/2/02 22 503.5 505.3 4/10/02 1 

IRP-51G 2.9 506.6 3/11/02 4/2/02 22 --- --- --- 1 
8 Evaluation of Passive Diffusion Bag Samplers, Dialysis Samplers, and Nylon-Screen Samplers in Selected Wells at Andersen 

Air Force Base, Guam, March–April 2002 Marbo Annex IRP-29 IRP-29A 18.8 461.9 3/13/02 4/1/02 19 --- --- --- --- 

IRP-29A 18.3 462.4 3/10/02 4/1/02 22 --- --- --- 1 

IRP-29B 16.3 464.4 3/10/02 4/1/02 22 --- --- --- 1 IRP-29C 14.8 465.9 3/13/02 4/1/02 19 463 465.4 4/4/02 --- IRP-29C 14.3 466.4 3/10/02 4/1/02 22 --- --- --- 1 

IRP-29D 12.8 467.9 3/13/02 4/1/02 19 --- --- --- --- IRP-29D 12.3 468.4 3/10/02 4/1/02 22 --- --- --- 1 

IRP-29E 8.8 471.9 3/13/02 4/1/02 19 --- --- --- --- IRP-29E 8.3 472.4 3/10/02 4/1/02 22 --- --- --- 1 

IRP-29F 4.8 475.9 3/13/02 4/1/02 19 --- --- --- --- IRP-29F 4.3 476.4 3/10/02 4/1/02 22 475* 477.4* 4/4/02 1 

IRP-29G 1.8 478.9 3/13/02 4/1/02 19 --- --- --- --- IRP-29G 1.3 479.4 3/10/02 4/1/02 22 --- --- --- 1 

IRP-31 IRP-31A 18.3 446.9 3/10/02 4/1/02 22 447 449.1 4/4/02 2 

IRP-31B 15.3 449.9 3/10/02 4/1/02 22 --- --- --- 2 IRP-31C 12.3 452.9 3/10/02 4/1/02 22 --- --- --- 1 

IRP-31D 9.3 455.9 3/10/02 4/1/02 22 --- --- --- 1 

IRP-31E 6.3 458.9 3/10/02 4/1/02 22 456* 458.1* --- 2 

IRP-31F 3.3 461.9 3/10/02 4/1/02 22 --- --- --- 1 

IRP-31G 1.3 463.9 3/10/02 4/1/02 22 --- --- --- 1 

Table 2. Diffusion sampler and pumped sampling information, Main Base and MARBO Annex, Andersen Air Force Base, Guam, March-[ft, feet; ft BTOC, feet below top of casing; ft BLS, feet below land surface; # depth uncertain because of probable shifting of samplers; ---, data not collect

which monitoring data are routinely collected]

Well 

number

Sample 

identifier

Diffusion samples Pumped samples Num

Distance 

from well 

bottom to 

sampler 

center 

(ft)

Depth to 

sampler 

center 

(ft BTOC)

Diffusion 

sampler 

deployment 

date

Diffusion 

sampler 

recovery 

date

Days of 

diffusionsampler 

equilibration

Pumped 

sample 

depth 

(ft BLS)

Pumped 

sample 

depth 

(ft BTOC)

Pumped 

sampling 

date

Passive 

diffusion 

bag 

sample
Results and Discussion 9

Duplicate samples were collected from approximately 10 percent of the sampling sites. In general, both 

diffusion samples and pumped samples compared well 

with their respective duplicate samples. All samples and 

corresponding duplicate samples at concentrations less 

than 5 μg/L differed by less than 1 μg/L. At concentrations greater than 10 μg/L, the samples and corresponding duplicates differed by a relative percentage 

difference of 0 to 13.3 percent, with an average relative 

percentage difference of 5.2 percent.

RESULTS AND DISCUSSION 

The test wells at Andersen AFB Main Base and 

MARBO Annex are characterized by both hydraulic 

and chemical differences along the screened intervals. 

The following sections discuss hydraulic results 

obtained from borehole-flowmeter tests and the distribution and comparison of chemical concentrations in 

the diffusion samplers and pumped samples.

Distribution of Ground-Water Flow in Wells

 Vertical flow was detected by the heat-pulse 

flowmeter under nonpumping conditions in all of the 

test wells (table 3; figs. 2A, 3A, 4A, 5A, and 6A), 

indicating differences in head along the length of the 

screened intervals. The direction of flow was upward in 

the wells at MARBO Annex and a mixture of upward 

and downward in the wells at the Main Base. Nearly all 

of the vertical flow detected under nonpumping conditions, however, was at amounts less than the quantitation limit of the borehole flowmeter (0.03 gal/min). 

Thus, there is uncertainty in the evaluation of vertical 

flow under nonpumping conditions at most locations. 

Exceptions are in wells IRP-3 and IRP-39, in which 

downward flow near the bottoms of the wells was 

detected at rates greater than the minimum quantitation 

limit for the borehole flowmeter (figs. 2A and 3A, 

respectively). The downward movement of water near 

the base of wells IRP-3 and IRP-39 indicates some 

degree of in-well mixing under nonpumping conditions. 

The lower-than-quantifiable vertical flow rates in the 

remaining wells may represent actual movement of 

water or may be an artifact of the method used. 

A variety of factors influence vertical movement 

of water in wells at Andersen AFB and probably influence solute mixing in the wells. Part of the vertical 

movement under nonpumping conditions probably is in 

response to tides. The wells at the Main Base have not 

been tested for tidal efficiency, which is the ratio of 

well-water level range during a tidal cycle to the tidal 

range. An investigation, however, in wells at MARBO 

Annex in 1995 showed that the tidal efficiency ranged 

between 0.7 to 3.9 percent in wells (Jeff Morrell, EA 

Engineering, Science, and Technology, Inc., written 

commun., 2002), with water-level responses of 0.5 to 

3 in. A well near well IRP-29 (approximately 1.5 miles 

from the shoreline had a tidal efficiency of 3.1 percent. 

Well IRP-31 (approximately 2.5 miles from the shoreline) had a tidal efficiency of 3.4 percent. These 

responses indicate that tidal movement causes some 

degree of ground-water fluctuation even 2.5 miles 

inland. Although these water-level responses are small, 

the very high aquifer hydraulic conductivity [probably 

between 1,000 to 5,000 ft/d and possibly as high as 

20,000 ft/d (Branch and others, 1982)] suggests that 

even small water-level changes can indicate water 

movement. The fact that the wells at the Main Base 

used in this investigation had a lower water elevation 

and were closer to the shoreline than the wells at 

MARBO Annex, implies that the test wells at the Main 

Base also probably are influenced by tides. Thus, the 

direction of ambient water movement in these wells 

may change with the tides, and the chemical concentrations may represent some degree of mixing. Rainfall 

infiltration may be an additional influence on vertical 

fluctuations in the ground water at this site. Additional 

water-level changes in the wells occur from barometric 

changes, as indicated by the high barometric efficiency 

(about 95 to 100 percent in wells at MARBO Annex; 

Jeff Morrell, EA Engineering, Science, and Technology, Inc., written commun., 2002). 

In well IRP-3, the predominant zone of inflowing water during pumping was at a depth below the top 

of casing of about 573 ft (fig. 2C). This depth approximately coincides with the depth where downward flow 

begins under nonpumping conditions (fig. 2A). The 

downward flow implies that water enters the well at a 

depth between 571 and 577 ft under nonpumping conditions. This downward flow appears to exit the borehole at a depth of about 578 to 579 ft (fig. 2A). Despite 

this downward flow under nonpumping conditions, the 

apparent exit zone did not appear to contribute water to 

the well under pumping conditions. One explanation is 

that the pumping may have reduced the amount of 

downward flow to that horizon, making it appear to be 

a nonflowing zone. 
10 Evaluation of Passive Diffusion Bag Samplers, Dialysis Samplers, and Nylon-Screen Samplers in Selected Wells at Andersen 

Air Force Base, Guam, March–April 2002

Table 3. Borehole-flowmeter data, Main Base and MARBO Annex, Andersen Air Force Base, Guam, March-April 2002 

[ft below TOC, feet below top of casing: gal/min, gallons per minute; negative values under nonpumping conditions indicate downward 

flow; ---, data not available; *, pumping rate was 0.34 gallons per minute]

Well 

number

Depth of 

measurement 

(ft below TOC)

Vertical flow 

under nonpumping 

conditions 

(gal/min)

Upward flow 

(gal/min) 

when pumped 

at about 

0.5 gal/min

Upward flow 

(gal/min) 

when pumped 

at about 

1.0 gal/min

Estimated 

depth of 

contribution 

(ft below TOC)

Approximate 

percent of 

contribution 

when pumped 

at 0.5 gal/min

Approximate 

percent of 

contribution 

when pumped 

at 1.0 gal/min

Main Base

IRP-3 556 0.01 0.54 1.16 557 30 23

558 0 0.38 0.89 559 21 34

560 0.01 0.24 0.5 561 0 7

562 0.01 0.15 0.42 563 0 3

564 0.02 0.22 0.21 565 0 0

566 0.02 0.27 0.38 567 0 6

568 0.01 0.01 0.31 569 0 3

570 0.02 0.26 0.28 571 9 3

572 -0.03 0.21 0.25 573 26 13

574 -0.05 0.07 0.01 575 6 5

576 -0.08 0.04 0.04 577 7 3

578 -0.08 0 0 579 0 0

580 0 0 0 580 0 0

582 0 0 0 581 0 0

IRP-39 605 0.02 0.64 1.45 606 18 11

607 0.02 0.5 1.29 608 0 9

609 0.02 0.53 1.16 610 0 0

611 0 0.5 1.16 612 0 8

613 0 0.56 1.04 614 0 9

615 0 0.53 0.87 616 16 0

617 -0.04 0.42 0.95 618 36 23

619 0.01 0.19 0.6 620 0 0

621 -0.02 0.17 0.56 622 0 17

623 -0.04 0.09 0.33 624 0 8

625 0.02 0.18 0.22 626.5 28 15

IRP-51 487 0 0.87 1.45 488 8 0

489 0 0.8 1.45 490 18 20

491 0 0.64 1.16 492 9 8

493 0 0.56 1.04 494 10 12
Results and Discussion 11

495 0.01 0.47 0.87 496 10 5

497 0 0.38 0.8 498 24 14

499 0.02 0.17 0.6 500 0 9

501 0.01 0.19 0.47 502 13 17

503 0.01 0.08 0.22 504 0 6

505 -0.01 0.08 0.14 506 7 6

507 0 0.02 0.06 507.5 2 4

MARBO Annex

IRP-29 460 0.01 0.44 --- 461 20 ---

462 0.01 0.35 --- 463 11 ---

464 0.01 0.3 --- 465 27 ---

466 0.01 0.18 --- 467 20 ---

468 0 0.09 --- 469 0 ---

470 0 --- --- 471 0 ---

472 0.01 0.09 --- 473 0 ---

474 0.01 0.09 --- 475 0 ---

476 0.02 0.09 --- 477 5 ---

478 0 0.07 --- 479 7 ---

480 0 0.04 --- 480.5 9 ---

IRP-31 444 0 0.38* --- 445 34 ---

446 0 0.25* --- 447 18 ---

448 0 0.18* --- 449 5 ---

450 0 0.16* --- 451 3 ---

452 0.02 0.15* --- 453 8 ---

454 0.01 0.12* --- 455 3 ---

456 0.02 0.11* --- 457 0 ---

458 0 0.1* --- 459 11 ---

460 0.01 0.06* --- 461 8 ---

462 0.02 0.03* --- 463 3 ---

464 0 0.02* --- 465 5 ---

Table 3. Borehole-flowmeter data, Main Base and MARBO Annex, Andersen Air Force Base, Guam, March-April 2002 

(Continued)

[ft below TOC, feet below top of casing: gal/min, gallons per minute; negative values under nonpumping conditions indicate downward 

flow; ---, data not available; *, pumping rate was 0.34 gallons per minute]

Well 

number

Depth of 

measurement 

(ft below TOC)

Vertical flow 

under nonpumping 

conditions 

(gal/min)

Upward flow 

(gal/min) 

when pumped 

at about 

0.5 gal/min

Upward flow 

(gal/min) 

when pumped 

at about 

1.0 gal/min

Estimated 

depth of 

contribution 

(ft below TOC)

Approximate 

percent of 

contribution 

when pumped 

at 0.5 gal/min

Approximate 

percent of 

contribution 

when pumped 

at 1.0 gal/min
12 Evaluation of Passive Diffusion Bag Samplers, Dialysis Samplers, and Nylon-Screen Samplers in Selected Wells at Andersen 

Air Force Base, Guam, March–April 2002

Vertical flow in wellbore

under nonpumping

conditions, in gallons

per minute

Upward flow under

pumping conditions,

in gallons per minute

Trichloroethene

concentration, in

micrograms per liter

Approximate

percentage of flow

entering the well in

response to shallow

pumping

-0.1 0.0 0.1 0.00 0.25 0.50 0.75 0 10 20 30 40 20 40 60 80 100

Depth below top of casing, in feet

550

555

560

565

570

575

580

585

Down

flow

Up

flow

A. B. C. D.

EXPLANATION

Results when pumping at about 0.5 gallon per minute

Results when pumping at about 1.0 gallon per minute

Flowrates which are less than flowmeter quantitation limits

Flowmeter investigation depths

Approximate depths of inflow determination

Laboratory analysis: Passive diffusion bag sample

Laboratory analysis: Dialysis sample

Laboratory analysis: Pumped sample

Field analysis: Passive diffusion bag sample

Field analysis: Dialysis sample

Figure 2. Borehole-flowmeter data under nonpumped and pumped conditions, approximate water-yielding zones during 

pumping, and trichloroethene concentrations in dialysis samples, passive diffusion bag samples, and pumped samples at 

well IRP-3, Main Base, Andersen Air Force Base, Guam, April 2002.
Results and Discussion 13 Figure 3. Borehole-flowmeter data under nonpumped and pumped conditions, approximate water-yielding zones during pumping, an

concentrations in dialysis samples, passive diffusion bag samples, and pumped samples at well ell IRP-39, Main Base, Andersen Air April 2002.

Vertical flow in wellbore

under nonpumping

conditions, in gallons

per minute

Upward flow under

pumping conditions,

in gallons per minute

Trichloroethene

concentration, in

micrograms per liter

Approximate

percentage of flow

entering the well in

response to shallow

pumping

-0.1 0.0 0.1 0.0 0.5 1.0 2.0 1.5 0 10 20 30 40 50 10 15 20 25 30

Depth below top of casing, in feet

600605610615620625630

Down

flow

Up

flow

A. B. C. D.

EXPLANATION

Results when pumping at about 0.5 gallon per minuteResults when pumping at about 1.0 gallon per minuteFlowrates which are less than flowmeter quantitation limitsFlowmeter investigation depthsApproximate depths of inflow determination

Laboratory analysis: Passive diffus

Laboratory analysis: Dialysis sampLaboratory analysis: Pumped samField analysis: Passive diffusion ba

Field analysis: Dialysis sample

0 
14 Evaluation of Passive Diffusion Bag Samplers, Dialysis Samplers, and Nylon-Screen Samplers in Selected Wells at Andersen 

Air Force Base, Guam, March–April 2002

Vertical flow in wellbore

under nonpumping

conditions, in gallons

per minute

Upward flow under

pumping conditions,

in gallons per minute

Trichloroethene

concentration, in

micrograms per liter

Approximate

percentage of flow

entering the well in

response to shallow

pumping

-0.1 0.0 0.1 0.0 0.5 1.0 2.0 1.5 0 5 10 15 20 25 30 0 5 10 15 20 25

Depth below top of casing, in feet

485

490

495

500

505

510

Down

flow

Up

flow

A. B. C. D.

EXPLANATION

Results when pumping at about 0.5 gallon per minute

Results when pumping at about 1.0 gallon per minute

Flowrates which are less than flowmeter quantitation limits

Flowmeter investigation depths

Approximate depths of inflow determination

Laboratory analysis: Passive diffusion bag sample

Laboratory analysis: Dialysis sample

Laboratory analysis: Pumped sample

Field analysis: Passive diffusion bag sample

Field analysis: Dialysis sample

Figure 4. Borehole-flowmeter data under nonpumped and pumped conditions, approximate water-yielding zones during 

pumping, and trichloroethene concentrations in dialysis samples, passive diffusion bag samples, and pumped samples at 

well ell IRP-51, Main Base, Andersen Air Force Base, Guam, April 2002.
Results and Discussion 15

Vertical flow in wellbore

under nonpumping

conditions, in gallons

per minute

Upward flow while

pumping at

approximately

0.5 gallon per minute

Tetrachloroethene

concentration, in

micrograms per liter

Approximate

percentage of flow

entering the well while

pumping at approximately

0.5 gallon per minute

-0.1 0.0 0.1 0.0 0.2 0.4 0.6 0 5 10 15 20 25 30 02468

Depth below top of casing, in feet

455

460

465

470

475

480

485

Down

flow

Up

flow

A. B. C. D.

EXPLANATION

Flowrates which are less than flowmeter quantitation limits

Flowmeter investigation depths

Approximate depths of inflow determination

Laboratory analysis: Passive diffusion bag sample

Laboratory analysis: Dialysis sample

Laboratory analysis: Pumped sample

Field analysis: Passive diffusion bag sample

Figure 5. Borehole-flowmeter data under nonpumped and pumped conditions, approximate water-yielding zones during 

pumping, and trichloroethene concentrations in dialysis samples, passive diffusion bag samples, and pumped samples at 

well ell IRP-29, MARBO Annex, Andersen Air Force Base, Guam, April 2002.
16 Evaluation of Passive Diffusion Bag Samplers, Dialysis Samplers, and Nylon-Screen Samplers in Selected Wells at Andersen 

Air Force Base, Guam, March–April 2002

Vertical flow in wellbore

under nonpumping

conditions, in gallons

per minute

Upward flow while

pumping at

approximately

0.5 gallon per minute

Trichloroethene

concentration, in

micrograms per liter

Approximate

percentage of flow

entering the well while

pumping at approximately

0.5 gallon per minute

-0.1 0.0 0.1 0.0 0.1 0.2 0.3 0.4 0 10 20 30 40 0 100 200 300

Depth below top of casing, in feet

440

445

450

455

460

465

470

Down

flow

Up

flow

A. B. C. D.

Typical

pumped-sample

collection depth

EXPLANATION

Flowrates which are less than flowmeter quantitation limits

Flowmeter investigation depths

Approximate depths of inflow determination

Laboratory analysis: Passive diffusion bag sample

Laboratory analysis: Dialysis sample

Laboratory analysis: Pumped sample

Figure 6. Borehole-flowmeter data under nonpumped and pumped conditions, approximate water-yielding zones during 

pumping, and trichloroethene concentrations in dialysis samples, passive diffusion bag samples, and pumped samples at 

well ell IRP-31, MARBO Annex, Andersen Air Force Base, Guam, April 2002.
Results and Discussion 17

A decrease in upward flow under pumping 

conditions also was observed at some horizons, such 

as at a depth of 564 ft (fig. 2B). In some cases, small 

decreases in flow may be due to instrument noise, but 

because the decrease was observed at 564 ft under 

pumping conditions of both 0.5 and 1 gal/min, the 

decrease likely is related to factors outside the well 

screen. One probable explanation is that the decrease 

represents a zone of widened borehole outside the 

casing, such as a dissolution feature or a fracture that 

straddled the borehole-flowmeter diverter, causing the 

appearance of water loss by allowing flow around the 

diverter. The dissolution feature or fracture may not be 

water-yielding, or the amount of water inflowing from 

the zone may be small relative to the loss of water by 

leakage around the diverter. For the purposes of this 

investigation, such zones are not considered to be 

major contributors of water to the well under pumping 

conditions, although there is some uncertainty in this 

determination.

The borehole-flowmeter data collected under 

pumping conditions indicate the zones within the 

borehole that transmit water. The borehole-flowmeter 

data collected at the Main Base showed that water was 

entering the boreholes at several horizons in response 

to pumping (wells IRP-3, IRP-39, and IRP-51; figs. 2B, 

3B, and 4B, respectively). In well IRP-51, the amount 

of flow entering the well at 0.5 gal/min was more uniform along the screen length (fig. 4C) than at wells 

IRP-3 and IRP-39, where the inflow zones appeared to 

be more localized (figs. 2C and 3C, respectively). In 

well IRP-39, the predominant zone of inflowing water 

was at a depth of 618 ft, with contributing zones at 606 ft 

and 621 to 625 ft (fig. 3C). 

At MARBO Annex in wells IRP-29 and IRP-31, 

the vertical flow under nonpumping conditions was at 

amounts below the quantitation limits of the borehole 

flowmeter (figs. 5A and 6A, respectively), but several 

horizons yielded water under pumping conditions 

(figs. 5B and 6B, respectively). Borehole-flowmeter 

tests in IRP-29 while pumping showed that the screened 

interval encompassed two distinct water-yielding depths 

(about 461 to 467 ft and about 477 to 480 ft) separated 

by a zone of relatively low yield (about 469 to 475 ft) 

(fig. 5C). Of the two relatively high-yielding zones, the 

shallowest zone (about 461 to 467 ft) appears to provide most of the water during pumping. 

In well IRP-31 at MARBO Annex, inflow to the 

well during pumping is predominantly through the 

upper part of the screened interval at depths of about 

445 to 447 ft (fig. 6C). In this well, the predominant 

inflow depth is slightly shallower than the uppermost 

diffusion sampler. 

Comparison of Trichloroethene and 

Tetrachloroethene Concentrations in 

Passive Diffusion Bag Samples and 

Pumped Samples

A number of chlorinated aliphatic compounds 

were found in ground water from wells tested at the 

Main Base and MARBO Annex of Andersen AFB 

(table 4); however, the primary compounds were TCE 

and PCE. In most comparisons, TCE and PCE concentrations in PDB samples closely matched concentrations in pumped samples (figs. 7 and 8, respectively). 

Exceptions were in well IRP-31, where the shallowest 

TCE concentrations were lower in the diffusion samplers than in the pumped sample (fig. 7), and in well 

IRP-39, where the TCE and PCE concentrations were 

higher in the diffusion samplers than in the pumped 

samples (figs. 7 and 8, respectively). As will be discussed, these differences probably are related to vertical translocation of water by the pump or ambient flow 

during sampling in a chemically stratified aquifer. Both 

wells IRP-31 (fig. 6D) and IR-39 (fig. 3D) showed 

stratification of TCE, with higher concentrations near 

the top than the bottom of the screened interval. 

Substantial stratification of TCE was observed 

in well IRP-31. The TCE concentration was about 211 

to 218 μg/L at a depth of 446.9 ft and only 20 μg/L 

at a depth of 463.9 ft, based on PDB-sampler results 

(fig. 6D, table 4). The upward increasing concentration 

in well IRP-31 implies that there may be higher concentrations at shallower depths than the uppermost 

zone sampled by the PDB samplers (fig. 6D). Because 

during pumping, most of the water in this well is 

derived from a horizon shallower than the PDB samplers (fig. 6C), it is probable that the PDB samples 

represent local concentrations, and the pumped sample 

primarily represents water derived from a more contaminated zone at a depth of about 444 to 446 ft, 

slightly shallower than the PDB samplers (fig. 6D). 

Therefore, it is not surprising that the uppermost PDB 

sample TCE concentration is slightly lower than the 

adjacent pumped sample. 
18 Evaluation of Passive Diffusion Bag Samplers, Dialysis Samplers, and Nylon-Screen Samplers in Selected Wells at Andersen 

Air Force Base, Guam, March–April 2002

Table 4. Laboratory analysis of chlorinated aliphatic compounds showing detections in dialysis samples, passive diffusion bag samples, 

ground water in wells, Main Base and MARBO Annex, Andersen Air Force Base, Guam, March-April 2002 

[μg/L, micrograms per liter; PDB, passive diffusion bag sample; <, less than; two numbers separated by a comma indicate a sample and duplicate; F, the 

positively identified, but the associated numerical value was below the reporting limit; J, the analyte was positively identified, the quantitation is an estima

outside the calibration limits or other Air Force Center for Environmental Excellence acceptance criteria were not met; ---, data not collected or not applica

indicate detected concentrations that were not accompanied by data qualifiers]

Well 

number

Sample 

identifier

1,1,2-Trichloroethane (μg/L) 1,1-Dichloroethene (μg/L) Carbon tetrachlo

Dialysis PDB Pumped Dialysis PDB Pumped Dialysis PDB 

Main Base

IRP-3 IRP3C --- <1 <1 --- <1.2 <1.2 --- 2.82F 

IRP3D <1 <1 <1 <1.2 <1.2 <1.2 1.52F 3 

IRP3E --- --- <8, <8 --- --- <8, <8 --- --- 

IRP-39 IRP39A <1, <1 <1 <1, <1 <1.2, <1.2 <1.2 <1.2, <1.2 0.59F, 0.68F 0.93F 

IRP39B --- --- <1, <1 --- --- <1, <1 --- --- 

IRP-51 IRP51A <1 <1 <1, <1 <1.2 <1.2 <1, <1 <2.1 <2.1 

IRP51B --- --- <1 --- --- <1.2 --- --- 

IRP51F <1 <1 <1 <1.2 <1.2 <1.2 <2.1 <2.1 

Marbo Annex

IRP-29 IRP29A <1 <1 <1 <1.2 <1.2 <1.2 0.35F 0.61F 

IRP29F --- --- <1, <1 --- --- <1, <1 --- --- 

IRP-31 IRP31A 1 1.88, 2.02 2 2 1.7, 2.1 2 <2.1 <2.1, <2.

IRP31B 1 1.85, 1.97 --- 1 1.9, 2.3 --- <2.1 <2.1, <2.IRP31C 0.8F 1 --- 1F 2 --- <2.1 <2.1 

IRP31D 0.37F 0.8F, 0.7F 0.8, 0.9 0.4F 0.8F, 0.9F 1.5, <10 <2.1 <2.1, <2.

IRP31E 0.29F 0.3F --- 0.4F 0.6F --- <2.1 <2.1 

IRP31F <1 0.2J, 0.2F --- <1.2 0.3F, 0.3J --- <2.1 <2.1, <2.

IRP31G <1 <1 --- <1.2 <1.2 --- <2.1 <2.1 
Results and Discussion 19

Well 

number

Sample 

identifier

Chloroform (μg/L) Chloromethane (μg/L) cis-1,2-Dichloroet

Dialysis PDB Pumped Dialysis PDB Pumped Dialysis PDB 

Main Base

IRP-3 IRP3C --- 0.8F 0.6 --- <1.3 <1.3 --- 4.38F 

IRP3D 0.6 0.7 0.6 0.25F 0.28F 0.23F 2.8 4.1 

IRP3E --- --- 0.6, 0.6 --- --- <8, <8 --- --- 

IRP-39 IRP39A 0.2F, 0.2F 0.3 0.3F, 0.3F <1.3, <1.3 <1.3 <1.3, <1.3 0.49F, 0.54F 0.65F 

IRP39B --- --- 0.2J, 0.3J <1, <1 --- --- 

IRP-51 IRP51A 0.2F 0.2F <1, <1 <1.3 <1.3 <1, <1 <1.2 <1.2 

IRP51B --- --- 0.2F --- --- 0.29F --- --- 

IRP51F 0.2F 0.2F 0.2F <1.3 <1.3 0.47F <1.2 <1.2 

Marbo Annex

IRP-29 IRP29A 0.28F 0.28F 0.4 <1.3 0.3F 0.3F <1.2 <1.2 

IRP29F --- --- <1, <1 --- --- <1, <1 --- --- 

IRP-31 IRP31A 0.5 0.6, 0.5 0.7 0.23F <1.3, <1.3 0.41F <1.2 <1.2, <1

IRP31B 0.4 0.6, 0.6 --- 0.45F <1.3, <1.3 --- <1.2 <1.2, <1

IRP31C 0.3F 0.5 --- <1.3 <1.3 --- <1.2 <1.2 

IRP31D 0.1F 0.3F, 0.3F 0.3, 0.3 0.24F 0.31F, <1.3 <10, <10 <1.2 <1.2, <1

IRP31E 0.2F 0.2F --- <1.3 <1.3 --- <1.2 <1.2 

IRP31F 0.1F 0.1F, 0.1F --- <1.3 <1.3, <1.3 --- <1.2 <1.2, <1

IRP31G <0.3 <0.3 --- <1.3 <1.3 --- <1.2 <1.2 

Table 4. Laboratory analysis of chlorinated aliphatic compounds showing detections in dialysis samples, passive diffusion bag samples, 

ground water in wells, Main Base and MARBO Annex, Andersen Air Force Base, Guam, March-April 2002 (Continued) 
20 Evaluation of Passive Diffusion Bag Samplers, Dialysis Samplers, and Nylon-Screen Samplers in Selected Wells at Andersen 

Air Force Base, Guam, March–April 2002 Well number Sample identifier Methylene chloride (μg/L) Trichloroethene (μg/L) Tetrachloroethe

Dialysis PDB Pumped Dialysis PDB Pumped Dialysis PDB 

Main Base IRP-3 IRP3C --- <0.3 <0.3 --- 86 83 --- 4 

IRP3D <0.3 <0.3 <0.3 71 82 82 2 3 

IRP3E --- --- 0.4, <8 --- --- 107, 102 

IRP-39 IRP39A <0.3, <0.3 <0.3 <0.3, <0.3 19, 20 28 19, 19 23, 23 34 

IRP39B --- --- <1, <1 --- --- 20, 21 --- --- 

IRP-51 IRP51A <0.3 <0.3 <1, <0.3J 12 19 20, 19 0.3F 0.7F 

IRP51B --- --- <0.3 --- --- 19 

IRP51F <0.3 <0.3 <0.3 13 19 19 0.3F 0.6F 

Marbo Annex

IRP-29 IRP29A <0.3 <0.3 <0.3 0.19F 0.31F 0.98F 1.92 5.64 

IRP29F --- --- <1, <1 --- --- 1.1, 1.1 --- --- 

IRP-31 IRP31A 0.18F <0.3, <0.3 <0.3 156 218, 211 267 0.63F 1.4F, 1.2

IRP31B <0.3 <0.3, <0.3 --- 144 204, 226 --- 0.7F 1.1F, 1.0

IRP31C 0.21F <0.3 --- 89.64J 149 --- 0.3F 0.6F 

IRP31D 0.2F <0.3, <0.3 <10, <10 43 57, 63 153.1, 149.7 <1.4 0.3J, 0.2

IRP31E <0.3 <0.3 --- 33 37 --- <1.4 0.2F 

IRP31F <0.3 <0.3, <0.3 --- 21 32, 28 --- <1.4 <1.4, <1.

IRP31G <0.3 <0.3 --- 9 20 --- <1.4 <1.4 

Table 4. Laboratory analysis of chlorinated aliphatic compounds showing detections in dialysis samples, passive diffusion bag samples, 

ground water in wells, Main Base and MARBO Annex, Andersen Air Force Base, Guam, March-April 2002 (Continued) 
Results and Discussion 21

The TCE concentration in well IRP-31 at the 

depth from which pumped samples typically are collected (about 458 ft) was higher in the pumped samples 

(150 to 153 μg/L) than in the PDB samples (57 to 63 

μg/L), as was the case in the 1999 investigation by EA 

Engineering, Science, and Technology, Inc. (359.3 to 

466.8 μg/L in the pumped samples and 37 to 149.7 μg/L 

in the PDB samples) (T.L. Isakson, EA Engineering, 

Science, and Technology, Inc., written commun., 

2000). The vertical concentration and flowmeter profiles in the well shows that most of the water during 

pumping is derived from a shallower zone having 

higher TCE concentrations than the typical pumpedsample collection depth (fig. 6D). Therefore, the most 

probable explanation for the difference is that the 

pumped sample represents higher concentration water 

from a shallower horizon transported downward in 

response to pumping. A less probable, but possible, 

alternative explanation is that upward flowing water in 

the borehole under ambient conditions may have 

diluted water in contact with the PDB samples below a 

depth of about 453 ft. There is some uncertainty, however, in attributing the difference to upward flowing 

water because the amount of potentially upward flowing water is so small that it is less than the quantitation 

limit of the borehole flowmeter, and may in fact be an 

artifact of measurement (fig. 6A). 

Regardless, it appears that the typical pumping 

depth in well IRP-31 is deeper than the zone of maximum contamination and maximum yield, and in the 

shallower, more contaminated part of the well screen, 

the PDB and pumped-sample concentrations more 

closely correspond (fig. 6D). At a depth of 446.9 ft, the 

TCE concentration in the pumped sample was 267 μg/L, 

Trichloroethene concentration in pumped samples,

in micrograms per liter

0 50 100 150 200 250 300

Trichloroethene concentration in passive diffusion ba

g and

dialysis samples, in micro

grams per liter

0

50

100

150

200

250

300

Passive diffusion bag sample

Dialysis sample

Sample

IRP-31A

Sample

IRP-39A

1:1 Correspondence

Figure 7. Comparison of trichloroethene concentrations in passive diffusion bag and dialysis 

samples to trichloroethene concentrations in pumped samples, Main Base and MARBO Annex, 

Andersen Air Force Base, Guam, April 2002.
22 Evaluation of Passive Diffusion Bag Samplers, Dialysis Samplers, and Nylon-Screen Samplers in Selected Wells at Andersen 

Air Force Base, Guam, March–April 2002

and the average TCE concentration in the PDB samples 

was 214 μg/L. Moreover, it is highly probable that the 

PDB samples would more closely correspond to the 

pumped sample if they were placed at a depth of about 

445 ft, corresponding to the zone of maximum water 

movement into the well during pumping. Therefore, 

PDB samplers probably are a viable alternative sampling method for well IRP-31 if the samplers are placed 

at an appropriate depth.

Well IRP-39 also showed contaminant stratification, with the higher concentrations of TCE and PCE at 

a depth of 611.2 ft than at 627.2 ft (fig. 3D and 3E). In 

this case, however, the pumped TCE and PCE concentrations (19 and 21.5 μg/L, respectively) at the shallowest sampling depth were lower than the concentrations 

in the adjacent PDB sampler (28 and 34 μg/L, respectively). Most of the pumped water in well IRP-39 

appears to enter the well at a depth of about 618 ft 

(fig. 3C). Therefore, the pumped samples from depths 

of 612.9 and 613.8 primarily represent water from a 

depth of about 618 ft, which contains slightly lower 

TCE and PCE concentrations than at the pumping 

depth. The small difference between methods (only 

9 μg/L for TCE and 12.5 μg/L for PCE) implies that 

the use of PDB samplers is a viable sampling alternative for well IRP-39.

In the remaining three test wells (IRP-3, IRP-51, 

and IRP-29), the TCE or PCE concentrations obtained 

with the diffusion samplers closely matched the results 

from pumped sampling (figs. 2D, 4D, and 5D, respectively). The wells appeared to contain less contaminant 

stratification than in wells IRP-31 and IRP-39, possibly 

contributing to the closer match between PDB samples 

and pumped samples than in wells IRP-31 and IRP-39. 

0 10 20 30 40

0

10

20

30

40

Passive diffusion bag sample

Dialysis sample

Sample IRP-39A

1:1 Correspondence

Tetrachloroethene concentration in pumped samples,

in micrograms per liter

Tetrachloroethene concentration in passive diffusion ba

g and

dialysis samples, in micro

grams per liter

Figure 8. Comparison of tetrachloroethene concentrations in passive diffusion bag and dialysis 

samples to tetrachloroethene concentrations in pumped samples, Main Base and MARBO 

Annex, Andersen Air Force Base, Guam, April 2002.
Results and Discussion 23

No benzene was detected in PDB or pumped samples 

from well IRP-51, in contrast to an earlier test by EA 

Engineering Science Inc. (T.L. Isakson, EA Engineering, Science, and Technology, Inc., written commun., 

2000). 

The analytical results from well IRP-29 demonstrate the ability of PDB samplers to accurately reflect 

low concentrations (less than 7 μg/L) of PCE. The 

PCE concentrations in pumped and PDB samples 

differed by less than 1 μg/L at a depth of about 465 ft 

in the most productive part of the screened interval 

(fig. 5D). Although there is some uncertainty in terms 

of laboratory variations at these low concentrations, the 

close agreement implies a close correlation between 

pumped- and PDB-sample results.

In addition, PCE concentrations in well IRP-29 

obtained with the PDB samplers appear to reflect zones 

of water production. The highest PCE concentration 

(fig. 5D) is associated with the zone showing the greatest 

percentage of flow entering the well during pumping 

(fig. 5C). The lowest PCE concentrations are found in 

the middle of the screened interval adjacent to zones 

showing little or no water inflow during pumping. The 

PCE concentration is slightly increased near the bottom 

of the well screen adjacent to a zone showing a higher 

degree of water inflow than near the middle of the well 

screen. These data also are consistent with the PCE 

concentration from pumped sampling at a depth of 

477.4 ft, which was higher than the standardized field 

analysis of PCE from a PDB sampler at about the same 

depth (fig. 5D). The pumped sample from 477.4 ft 

depth probably represents downward movement of 

water in the wellbore from the productive horizon near 

the shallower pumped sample. This would explain why 

the pumped samples are similar in concentration 

despite the apparent change in concentration indicated 

by the PDB samplers. In this well, it appears that the 

PCE concentrations in PDB samplers represent the 

slight concentration changes with depth and differ by 

less than 5 μg/L from concentrations in low-flow 

samples from corresponding depths.

The close match between PDB sample and 

pumped sample results shows that PDB samples are 

a viable alternative sampling method to the existing 

method of pumped sampling in the test wells at Andersen AFB, Guam. The data also show that, because of 

contaminant stratification, placement of PDB samplers 

in the screened interval at an arbitrary depth can produce 

results that do not represent the zone of highest concentrations. As a general guide to sampler placement in 

wells at Andersen AFB, VOC concentrations in four 

out of the five test wells were highest in the shallowest 

tested horizon (table 5). 

Comparison of Passive Diffusion Bag 

Samples to Dialysis Samples

In all of the side-by-side tests, the regenerated 

cellulose dialysis samplers produced lower VOC concentrations than the PDB samplers (figs. 2D, 3D, 4D, 

5D, and 6D) and in most cases, underestimated the 

pumped-sample results (figs. 7 and 8). The source of 

the difference is unknown, but a possible explanation is 

related to the biodegradation of the dialysis membrane. 

Carignan (1984) examined several types of dialysis 

membranes for suitability in lakebed studies. He found 

that raw cellulose membranes rapidly degraded in lakebed sediments, and the degradation created a local 

nutrient demand resulting in high methane and dissolved inorganic carbon concentrations and low dissolved reactive phosphorus and ammonium. He also 

noted marked deformation of cellulose acetate membranes, as did Martens and Klump (1980) and Hopner 

(1981). 

A previous investigation of regenerated cellulose 

samplers in wells showed that in an anaerobic petroleum hydrocarbon-contaminated aquifer, marked degradation was observed on several of the membranes, as 

evidenced by discoloring (Vroblesky and Pravecek, 

2002). Despite the discoloring, the concentrations of 

VOCs appeared similar to those in the PDB samplers. 

In the present investigation, however, the VOC concentrations in the degraded regenerated cellulose dialysis 

samplers were consistently lower than in the PDB 

samplers. 

This investigation differed from the previous 

investigation in the type of contaminant examined and 

in the length of time the samplers were deployed. The 

previous investigation was in anaerobic water with a 

high availability of oxidizable organic carbon, and the 

primary contaminants were petroleum hydrocarbons. 

In the present investigation, the aquifer was aerobic 

with an extremely low concentration of oxidizable 

organic carbon, and the primary contaminants were 

chlorinated solvents. It is possible that in the organic 

carbon-limited aquifer of northern Guam, the cellulose 

membrane may have provided sufficient organic carbon 

to create local environments that were more conducive 
24 Evaluation of Passive Diffusion Bag Samplers, Dialysis Samplers, and Nylon-Screen Samplers in Selected Wells at Andersen 

Air Force Base, Guam, March–April 2002

Table 5. Standardized concentrations of trichloroethene and tetrachloroethene by field gas 

chromatography in passive diffusion bag samples and dialysis samples, Main Base and MARBO 

Annex, Andersen Air Force Base, Guam, April 2002

[μg/L, micrograms per liter; ---, sample not analyzed or not collected; J, the analyte was positively identified, the 

quantitation is an estimate because it is ouside the calibration limits or other Air Force Center for Environmental 

Excellence acceptance criteria were not met; two values separated by a comma indicate a sample and duplicate]

Well 

number

Trichlorothene in 

passive diffusion 

bag samples, 

in μg/l

Trichlorothene in 

dialysis samples, 

in μg/L

Tetrachlorothene in 

passive diffusion 

bag samples, 

in μg/L

Tetrachlorothene in 

dialysis samples, 

in μg/L

Main Base

IPR-3A 87 60 5J 3J

IPR-3B 87 50 6 2J

IPR-3C 86 --- 4J ---

IPR-3D 86 57 4J 2J

IPR-3E 82 50 3J 2J

IPR-3F 76, 71 --- 3J, 3J ---

IPR-3G 71 54 3J 2J

IPR-3H 70 50 3J 1J

IPR-3I 71 48 3J 1J

IPR-3J 60 48 3J 1J

IPR-3K 64 48 2J 1J, 1J

IRP-39A 28 21 34 20

IRP-39B 25 17 25 15

IRP-39C 23 15 22 12

IRP-39D 20 16 15 13

IRP-39E 16 --- 9 ---

IRP-39F 16 12 8 6

IRP-39G 13 11 6 3

IRP-51A 19 13 <6 <6

IRP-51B 18 7J <6 <6

IRP-51C 16 8 <6 <6

IRP-51D 16 9 <6 <6

IRP-51E 18 12 <6 <6

IRP-51F 19 14 <6 <6

IRP-51G 15 12 <6 <6

MARBO Annex

IRP-29A --- --- 6 ---

IRP-29B --- --- 4 ---

IRP-29C --- --- 3 ---

IRP-29D --- --- 1 ---

IRP-29E --- --- 1 ---

IRP-29F --- --- 1 ---

IRP-29G --- --- 2 ---

IRP-31A 218 --- --- ---

IRP-31B 196 --- --- ---

IRP-31C 149 --- --- ---

IRP-31D 76 --- --- ---

IRP-31E 50 --- --- ---

IRP-31F 37 --- --- ---

IRP-31G 27 --- --- ---
Results and Discussion 25

to TCE and PCE degradation than in the aquifer, resulting in decreased concentrations. Although no elevated 

concentrations of dehalogenation byproducts (such as 

cis-1,2-dichloroethene or vinyl chloride) were 

observed in dialysis samples relative to PDB and 

pumped samples, these compounds would not be 

expected to persist in the aerobic ground water of 

Guam. In addition, the samplers in the previous investigation were left in place for only 14 days, whereas the 

samplers in the present investigation were left in place 

for 22 to 23 days. The extra time the samplers were 

deployed during the present investigation may have 

allowed for increased effects from sampler degradation, resulting in anomalously low concentrations. 

The observation by Carignan (1984) that membrane 

degradation can affect water chemistry indicates that 

microbial activity on the membrane surface can affect 

sampling results. 

Comparison of Chloride in Nylon-Screen 

Samples, Dialysis Samples, and Pumped 

Samples

Chloride concentrations in nylon-screen samplers 

were compared with chloride concentrations in dialysis 

samples to examine the ability of the samplers to provide 

concentrations of inorganic solutes. Although chloride is 

not a solute of concern at the facility, it was chosen as 

the representative solute because a large vertical variation in the concentration within the screened interval 

was expected. The results showed both nylon-screen 

and dialysis samplers were capable of determining the 

depth of chloride stratification in well IRP-29, however, 

the nylon-screen samplers produced slightly lower 

chloride concentrations than the corresponding dialysis 

samplers at depths with elevated chloride concentrations 

(table 6, fig. 9). The chloride concentration (188.3 mg/L) 

measured in the pumped sample from well IRP-29 

from a depth of 477.4 ft was between the concentrations detected in the nearby nylon-screen samples 

(114.3 mg/L at 1.5 ft shallower and 227.7 mg/L at 1.5 ft 

deeper) and dialysis samples (188.8 mg/L 1 ft deeper), 

making it unclear whether the dialysis sample or the 

nylon-screen sample provided the more accurate result. 

The reason for the discrepancy is unknown. Previous 

investigations in Minnesota and Texas showed close 

matches between chloride concentrations in nylonscreen and pumped samples (Vroblesky and others, 

2002). 

One difference in methods between the historical 

and the present investigation is screen-mesh size. The 

mesh size used in the present investigation (47 μ was 

substantially smaller than that used in the previous 

investigation (125 and 250 μ). To determine whether 

mesh size could be a factor in the results of the present 

investigation, the mesh sizes were compared under laboratory conditions in a saltwater solution. The results of 

the investigation showed that after 13 days of equilibration 

in constantly stirred water containing 73,300 mg/L of 

chloride, a dialysis sampler produced 72,400 mg/L, and 

a nylon-screen sampler with a 125-μ mesh produced 

73,400 mg/L, whereas a nylon-screen sampler with a 

47-μ mesh produced only 60,700 mg/L. Thus, screen 

size may be a factor affecting equilibration, and the 

nylon-screen samplers at well IRP-29 may have underestimated the chloride concentrations.

Practical Considerations for the Use of 

Passive Diffusion Bag Samplers in Wells at 

Andersen Air Force Base

There are substantial practical differences 

between pumped sampling and passive diffusion bag 

sampling at Andersen AFB. The time onsite per well is 

about 2 to 2.5 hours with pumped sampling and about 

1 hour with diffusion sampling using multiple diffusion 

samplers. Less time would be required for diffusion 

sampling once a target horizon was determined and that 

horizon was targeted with only one or two PDB samplers. When the pumped sampling approach is used at 

the site with a portable pump, the pump and equipment 

must be decontaminated between wells by pumping 

30 gal of carbon-filtered water with detergent and 30 gal 

of carbon-filtered water through the system. The pump 

must then be scrubbed, which requires about 1.5 hours, 

including transport to the decontamination station. The 

method requires periodic rinsate blanks to verify the 

quality of the decontamination procedure. PDB samplers are disposable and require no decontamination. 

In addition, there is substantially more wastewater produced in pumped sampling than in diffusion sampling. 

The large depth to ground water (350 to 550 ft) at 

Andersen AFB limits the available conventional sampling tools to positive-displacement pumps; however, 

the pump-failure rate is high because of corrosion by 

the aquifer water. The pumps and associated air compressor are not needed with PDB sampling. Moreover, 

the PDB samplers allow collection of samples from 

more discrete horizons than with pumped sampling.
26 Evaluation of Passive Diffusion Bag Samplers, Dialysis Samplers, and Nylon-Screen Samplers in Selected Wells at Andersen 

Air Force Base, Guam, March–April 2002

The pumping approach does have some advantages 

over PDB sampling. Pumps allow water samples to 

be collected for a variety of contaminants other than 

VOCs. At the present time (2002), diffusion sampling 

has been extensively tested only in relation to VOC 

sampling. In addition, for this investigation, three trips 

to the site were required to install and recover the PDB 

samplers. The first trip involved flowmeter testing, the 

second involved deployment, and the third trip was for 

sampler recovery; however, these trips were for initial 

setup only. If PDB sampling were used as a long-term 

monitoring option, then once the deployment depth 

was determined, future sampling events would involve 

only a single trip to the wells for sampler recovery, at 

which time a new sampler could be deployed and left in 

place until the next sampling event. Table 7 lists suggested placement depths of PDB samplers as monitoring tools for wells examined in this investigation. For 

application of diffusion samplers in others wells, optimum 

diffusion-sampler placement within the screened interval 

would need to be determined by an initial vertical profile 

using multiple diffusion samplers. 

SUMMARY AND CONCLUSIONS 

The test wells at Andersen AFB and MARBO 

Annex are characterized by both hydraulic and chemical differences along the screened intervals. Small 

amounts of vertical flow were found in all of the test 

wells, indicating differences in head along the length of 

the screened intervals, but the flow typically was less 

than the quantitation limit of the borehole flowmeter. 

Exceptions are in wells IRP-3 and IRP-39, where 

downward flow near the bottoms of the wells was 

detected at rates above the minimum quantitation limit 

for the borehole flowmeter. 

The primary VOC contaminants in wells tested 

at Andersen AFB and MARBO Annex were TCE and 

PCE. In most comparisons, TCE and PCE concentrations in PDB samples closely matched concentrations 

in pumped samples. Exceptions were in wells where 

pumping or ambient flow may have produced vertical 

translocation of water in a chemically stratified aquifer 

(wells IRP-31 and IRP-39). In well IRP-39, the concentrations in the PDB samples were slightly higher 

(by only 9 μg/L for TCE and 12.5 μg/L for PCE) than 

the pumped sample, indicating that the PDB samplers 

are a viable ground-water-sampling option for well 

IRP-39. 

Table 6. Concentrations of chloride in nylon-screen, 

dialysis, and pumped samples from ground water in wells 

at the Main Base and MARBO Annex, Andersen Air Force 

Base,Guam, April 2002

[<, less than; two numbers separated by a comma indicate a 

sample and duplicate; ---, data not collected or not applicable]

Well 

number

Chloride, in milligrams per liter

Nylon-screen 

sample

Dialysis 

sample

Pumped 

sample

Main Base

IRP3C --- --- 30.2

IRP3D --- 28.78 30.7

IRP3E --- 28.95 ---

IRP3G --- 27.85 ---

IRP3H --- 28.58 ---

IRP3I --- 29.19 ---

IRP3J --- 29.04 ---

IRP3K --- 27.15 ---

IRP39A --- 16.25J 127.4, 166.2J

IRP39B --- 67.3 ---

IRP39C --- 115.4 ---

IRP39D --- 134.8 ---

IRP39E --- 159.5 ---

IRP39F --- 172.8 ---

IRP39G --- 178.4 ---

IRP51A --- 99.8 390.2

IRP51B --- 99.5 ---

IRP51C --- 104.3 ---

IRP51D --- 106.3 ---

IRP51E --- 122.3 ---

IRP51F --- 308.5 588.3

IRP51G --- 628.5 ---

MARBO Annex

IRP29A 36.44 36.32, 36.23 38.36

IRP29B --- 35.95 ---

IRP29C 35.45 35.27 ---

IRP29D 83.33 117.2 ---

IRP29E 103.1 144.3 ---

IRP29F 114.3 188.8, 188.1 188.3

IRP29G 222.7 440.4, 432 ---

IRP31A --- 144.7 133.8

IRP31B --- 140.5, 140.5 ---

IRP31C --- 168.4 ---

IRP31D --- 211 ---

IRP31E --- 250.1 ---

IRP31F --- 305.3 ,302.5 222.8

IRP31G --- 342.7 ---
Summary and Conclusions 27

Chloride concentration, in milligrams per liter

0 100 200 300 400 500

Depth below top of casing, in feet

460

465

470

475

480

485

 Nylon-screen sample

 Dialysis sample

 Pumped sample

Figure 9. Chloride concentrations in nylon-screen, dialysis, and pumped samples at well IRP-29, 

MARBO Annex, Andersen Air Force Base, Guam, April 2002.

Table 7. Optimum deployment depths for using passive diffusion bag samplers as 

monitoring tools for the maximum volatile organic compound concentration, Main Base 

and MARBO Annex, Andersen Air Force Base, Guam

[ft, feet; ft BTOC, feet below top of casing; ft BLS, feet below land surface}

Well 

number

Suggested passive diffusion bag sampler 

deployment information Depth at which 

monitoring data are 

routinely collected 

(ft BTOC)

Distance from well 

bottom to sampler 

center (ft)

Depth to 

sampler center 

(ft BTOC)

Main Base

IRP-3 23.3 559.0 566.1

IRP-39 17.3 611.9 613.8

IRP-51 18.9 491.5 491.8

MARBO Annex

IRP-29 18.3 463.4 477.4

IRP-31 19.2 446.0 458.1
28 Evaluation of Passive Diffusion Bag Samplers, Dialysis Samplers, and Nylon-Screen Samplers in Selected Wells at Andersen 

Air Force Base, Guam, March–April 2002

The TCE concentration in well IRP-31 at the 

depth from which pumped samples typically are collected was higher in the pumped samples than in the 

PDB samples, as in the 1999 investigation by EA 

Engineering, Science, and Technology, Inc. Because 

the highest TCE concentrations and the source of 

most of the pumped water is shallower than the typical 

sampling depth in well IRP-31, the most probable 

explanation for the difference is that the PDB samples 

represent local concentrations and the pumped sample 

represents downward movement of more contaminated 

water. The PDB and pumped-sample concentrations 

more closely correspond in the shallower, more contaminated part of the well screen, near the zone of maximum pumpage contribution. Therefore, PDB samplers 

probably are a viable alternative sampling method for 

well IRP-31, if the samplers are placed at an appropriate 

depth.

In the remaining three test wells (IRP-3, IRP-29, 

and IRP-51), the TCE or PCE concentrations obtained 

with the PDB samplers closely matched the result from 

pumped sampling. These three wells appeared to contain less contaminant stratification than wells IRP-31 

and IRP-39, possibly contributing to the closer match 

between PDB samples and pumped samples from the 

wells compared to wells IRP-31 and IRP-39. In well 

IRP-29, the PDB samplers appeared to accurately 

represent aquifer PCE concentrations at low levels 

(less than 7 μg/L).

The close match between PDB sample and 

pumped sample results shows that PDB samples are a 

viable sampling alternative to the existing method of 

pumped sampling in the test wells at Andersen AFB, 

Guam. The data indicate that placement of PDB samplers in the screened interval at an arbitrary depth can 

produce results that do not represent the zone of highest concentrations. As a general guide to sampler placement in wells at Andersen AFB, VOC concentrations 

in four out of the five test wells were highest in the 

shallowest tested horizon. 

In all of the side-by-side tests, the regenerated 

cellulose dialysis samplers produced lower VOC concentrations than the PDB samplers, and in most cases, 

underestimated the pumped results. The source of the 

difference is unknown, but the samplers were deployed 

for a longer time (22 to 23 days) than in a previous 

investigation (14 days), possibly allowing biodegradation 

of the dialysis membrane to influence the contaminant 

concentration. 

The comparison of chloride concentrations in 

nylon-screen samplers to chloride concentrations in 

dialysis and pumped samples showed both nylonscreen and dialysis samplers were capable of determining the depth of chloride stratification in well IRP-29; 

however, the nylon-screen samples showed lower chloride concentrations than the dialysis samples at several 

depths. The reason for the discrepancy in this investigation is unknown but may be related to nylon-screenmesh size. 

REFERENCES 

Bottomly, E.Z., and Bayley, I.L., 1984, A sediment porewater sampler used in root zones studies of the submerged macrophyte, Myriophyllum spicatum: 

Limnology and Oceanography, v. 29, p. 671-673.

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