Diffusion Sampler Testing at Naval Air Station 

North Island, San Diego County, California, 

November 1999 to January 2000

By DON A. VROBLESKY1 and BRIAN C. PETERS2

U.S. Geological Survey

Water-Resources Investigation 00-4182

Prepared in cooperation with the 

SOUTHWESTERN DIVISION NAVAL FACILITIES ENGINEERING COMMAND

Columbia, South Carolina

2000

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

2OHM Remediation Services Corporation
U.S. DEPARTMENT OF THE INTERIOR

BRUCE BABBITT, Secretary

U.S. GEOLOGICAL SURVEY

Charles G. Groat, Director

The use of firm, trade, and brand names in this report is for identification 

purposes only and does not constitute endorsement by the U.S. 

Geological Survey.

 

For additional information write to: Copies of this report can be purchased from

District Chief U.S. Geological Survey

U.S. Geological Survey Branch of Information Center

Stephenson Center - Suite 129 Box 25286

720 Gracern Road Denver, CO 80225-0286

Columbia, SC 29210-7651
Contents 

CONTENTS

Abstract..................................................................................................................................................................................

Introduction ...........................................................................................................................................................................

Acknowledgments .......................................................................................................................................................

Methods .................................................................................................................................................................................

Diffusion-Sampler Construction and Deployment ......................................................................................................

Collection of Pumped Ground-Water Samples............................................................................................................

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

Comparison of Diffusion-Sampler Results to Bladder-Pump Results.........................................................................

Comparison of Diffusion-Sampler Results to Peristaltic-Pump Results .....................................................................

Diffusion Samplers in Free-Phase Fuel .......................................................................................................................

Contaminant Stratification in Well Screens .................................................................................................................

Summary................................................................................................................................................................................

References .............................................................................................................................................................................

FIGURES

1. Map showing location of observation wells, Naval Air Station North Island, California ..........................................

2-9. Graphs showing:

2. Comparison of diffusion and low-flow samples in ground water at well MW-12, 

Naval Air Station North Island, California, January 2000 .................................................................................

3. Comparison of diffusion and low-flow samples in ground water at well MW-13B, 

Naval Air Station North Island, California, January 2000 .................................................................................

4. Comparison of diffusion and low-flow samples in ground water at well PW-55, 

Naval Air Station North Island, California, January 2000 .................................................................................

5. Comparison of diffusion and low-flow samples in ground water at well MW-5, Naval 

Air Station North Island, California, January 2000 ............................................................................................

6. Comparison of diffusion and low-flow samples in ground water at wells MW-68A, 

MW-68B, MW-68C, and MW-68C2, and comparison of diffusion samples from 

multiple wells to geologic log of well MW-68C, Naval Air Station North Island, California, January 2000 ...

7. Comparison of trichloroethene concentrations in diffusion and low-flow samples in ground 

water at well PW-66, Naval Air Station North Island, California, January 2000 ...............................................

8. Comparison of diffusion and low-flow samples in ground water at well PW-15, 

Naval Air Station North Island, California, January 2000 .................................................................................

9. Comparison of diffusion and low-flow samples in ground water at well MW-13A, 

Naval Air Station North Island, California, January 2000 .................................................................................

TABLES

1. Summary of well information, Naval Air Station North Island, California ................................................................

2. Sampler deployment and recovery information, Naval Air Station North Island, 

California, November 1999 to January 2000 ...............................................................................................................

3 Comparison of replicate samples collected by diffusion-sampler methodology, Naval Air 

Station North Island, California, January 2000 ...........................................................................................................

4. Comparison of replicate samples collected by low-flow methodology, Naval Air Station 

North Island, California, January 2000 .......................................................................................................................

5. Concentrations of selected chlorinated volatile organic compounds in water from diffusion 

and low-flow sampling, Naval Air Station North Island, California, January 2000 ....................................................

6. Concentrations of benzene, ethylbenzene, toluene, and total xylenes in water from diffusion 

and low-flow sampling, Naval Air Station North Island, California, January 2000 ....................................................

7. Comparison of concentrations of selected volatile organic compounds in water from 

a diffusion sampler and in water from low-flow purging using a bladder pump at 

the same depth, Naval Air Station North Island, California, January 2000 .................................................................

8. Concentrations of selected volatile organic compounds in free-phase jet fuel (JP-5) removed from 

ground water and in water from diffusion samplers deployed in a bucket containing the free-phase 

fuel, Naval Air Station North Island, California, January 2000 ..................................................................................
iv Diffusion Sampler Testing at Naval Air Station North Island, 

San Diego County, California, November 1999 to January 2000

CONVERSION FACTORS, VERTICAL DATUM, AND ABBREVIATIONS

______________________________________________________________________

Multiply By To obtain ______________________________________________________________________

Length

inch (in.) 25.4 millimeter

foot (ft) 0.3048 meter

mile (mi) 1.609 kilometer

Area

square mile (mi2) 2.590 square kilometer

Flow

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

foot squared per day (ft2

/d) 0.09294 meter squared per day

gallons per minute (gal/min) 0.06308 liter per second

gallons per day (gal/d) 0.003785 cubic meter per day

inches per year (in/yr) 25.4 millimeters per year

Volume

gallon (gal) 3.785 liter

______________________________________________________________________

Temperature: In this report, temperature is given in degrees Celsius (°C), which can be converted to degrees Fahrenheit (°F) b

following equation:

°F = (9/5 x C°) + 32

Sea Level: In this report, "sea level" refers to the National Geodetic Vertical Datum of 1929—a geodetic datum derived from 

eral adjustment of the first-order level nets of the United States and Canada, formerly called Sea Level Datum of 1929.

Chemical concentration: In this report, chemical concentration in water is expressed in metric units as milligrams per liter (mg

micrograms per liter (μg/L). 

Other units used in report:

cubic feet per day ft3/d

cubic feet per milligram ft3

/mg

degrees Celsius °C

gram g

liter L

microgram μg

micrometer μm

microliter μL

milligram mg

milliliter mL

milliliter per minute mL/min

Abbreviations used in this report:

bls - below land surface

11DCA - 1,1-dichloroethane

11DCE - 1,1-dichloroethene

cDCE - cis-1,2-dichloroethene

MCL - maximum contaminant level

PCE - tetrachloroethene

PVC - polyvinyl chloride

TCA - 1,1,1-trichloroethane

TCE - trichloroethene

USEPA - U.S. Environmental Protection Agency

USGS - U.S. Geological Survey
Introduction 

Diffusion Sampler Testing at Naval Air Station North 

Island, San Diego County, California, November 1999 t

January 2000

By Don A. Vroblesky and Brian C. Peters

ABSTRACT

Volatile organic compound concentrations 

in water from diffusion samplers were compared 

to concentrations in water obtained by low-flow 

purging at 15 observation wells at the Naval Air 

Station North Island, San Diego, California. Multiple diffusion samplers were installed in the 

wells. In general, comparisons using bladder 

pumps and diffusion samplers showed similar 

volatile organic carbon concentrations. In some 

wells, sharp concentration gradients were 

observed, such as an increase in cis-1,2-dichloroethene concentration from 100 to 2,600 micrograms per liter over a vertical distance of only 

3.4 feet. In areas where such sharp gradients were 

observed, concentrations in water obtained by 

low-flow sampling at times reflected an average 

concentration over the area of influence; however, 

concentrations obtained by using the diffusion 

sampler seemed to represent the immediate vicinity of the sampler. When peristaltic pumps were 

used to collect ground-water samples by low-flow 

purging, the volatile organic compound concentrations commonly were lower than concentrations obtained by using diffusion samplers. This 

difference may be due to loss of volatiles by 

degassing under negative pressures in the sampling lines induced while using the peristaltic 

pump, mixing in the well screen, or possible 

short-circuiting of water from an adjacent depth. 

Diffusion samplers placed in buckets of freephase jet fuel (JP-5) and Stoddard solvent from 

observation wells did not show evidence of structural integrity loss during the 2 months of 

equilibration, and volatile organic compounds 

detected in the free-phase fuel also were detect

in the water from the diffusion samplers.

INTRODUCTION

Low-density polyethylene diffusion sampler

filled with deionized water or air, have been shown 

be an inexpensive alternative sampling method for 

volatile organic compounds (VOCs) in contaminat

wells or in ground-water discharge zones beneath 

surface-water bodies (Vroblesky and others, 1996; 

Vroblesky and Robertson, 1996; Vroblesky and Hy

1997; Vroblesky and others, 1999; Gefell and othe

1999). The use of diffusion samplers in wells has g

erated substantial interest due to their capability to 

sample ground water without the need for prior we

purging. 

The Naval Air Station (NAS) North Island, i

San Diego County, California, has been used since 

1917 as an air station, harbor, and training base. Th

base is approximately 1 mile west across San Dieg

Bay from the San Diego metropolitan area (fig. 1). 

Activities at the base have resulted in ground-water 

contamination by a variety of compounds, includin

chlorinated aliphatic hydrocarbons and petroleum 

hydrocarbons. In addition, free-phase JP-5 jet fuel 

Stoddard solvent (mineral spirits) are present local

in the ground water. Stoddard solvent is a refined 

petroleum product typically used as a thinning age

for paints, coatings, waxes, printing inks, and 

adhesives; a solvent in photocopy toners and in dry 

cleaning; and as a degreaser for engine parts.

The purpose of this report is to present the fi

ings of an investigation to determine whether the u

of polyethylene deionized-water-filled diffusion 
2 Diffusion Sampler Testing at Naval Air Station North Island,

San Diego County, California, November 1999 to January 2000

San Diego Bay

MW-12

MW-5D

MW-9

MW-13A, B, C

472

Site 11

PW-66

Building 653

MW-10

S2-MW-6A

MW-68A, B, C, C2

PW-15

PW-55 379

4,000 FEET

APPROXIMATE SCALE

Site 2

1220 METERS

NAVAL AIR STATION NORTH ISLAND

SAN D

N

Figure 1. Location of observation wells, Naval Air Station North Island, California.

C

a liforni

P

a

acific Ocean

0 75 MILES

0 75 KILOMETERS

124°

124°

122°

122°

120°

120°

118°

118°

116°

116°

38°

36°

34°

40°

38°

36°

34°

40°

San Francisco

Sacramento

Los Angeles

SAN DIEGO

Study area

samplers is a viable method of sampling VOCs in 

ground water at the base. VOC concentrations in water 

obtained from diffusion samplers set at multiple levels 

in wells are compared to VOC concentrations in water 

obtained from low-flow sampling. Diffusion samplers 

were placed in 15 observation wells, and 2 samplers 

were placed in buckets of free-phase JP-5 and Stoddard solvent. 

Acknowledgments

The Department of the Navy, Southw

Division Naval Facilities Command, funded 

The fieldwork was a cooperative effort betw

U.S. Geological Survey and OHM Remedi

Services Corp. 
Methods 

METHODS

Diffusion samplers were tested in 15 wells at 

NAS North Island, California. VOC concentrations in 

water from the diffusion samplers were compared to 

VOC concentrations in water from low-flow sampling 

ports open adjacent to each diffusion sampler. Lowflow sampling was accomplished by using a peristaltic 

pump at most sites and a bladder pump at selected 

sites.

Diffusion-Sampler Construction and 

Deployment

Each diffusion sampler consisted of a 2-inchdiameter, low-density polyethylene (LDPE) tube heatsealed at both ends and containing deionized water. On 

the outside of each sampler, an LDPE mesh provided 

abrasion protection. This sampling methodology is 

patented (patent number 5,804,743) and is available 

for non-exclusive licensing from the U.S. Geological 

Survey Technology Enterprise Office, Mail Stop 211, 

National Center, 12201 Sunrise Valley Drive, Reston, 

Virginia (telephone 703 648-4450; fax 703 648-4408).

Diffusion samplers were attached to intakes 

bladder pumps by means of plastic cable ties. Attach

to each remaining diffusion sampler was a Tygon tu

extending from the sampler to land surface. The tub

was secured to the diffusion sampler and to a weigh

line at approximately 10-foot intervals by using pla

cable ties. The purpose of the tubing was to allow 

ground water to be collected adjacent to each diffus

sampler by using low-flow methodology with a per

staltic pump. 

The diffusion samplers were deployed in 15 

wells at NAS North Island during November 11, 19

(table 1). All wells were constructed of 4-inchdiameter casing. The samplers were attached by pl

tic cable ties to either a weighted line or a 1/2-inch 

(outside diameter) PVC pipe. When multiple sectio

of PVC pipe were required to reach the top of the c

ing, the sections were joined using stainless-steel 

screws. The PVC pipe was secured to the top of the 

well casing to prevent the diffusion samplers from 

shifting during the equilibration period.

Two of the sampled wells (PW-15 and PW-5

contained floating nonaqueous-phase liquid (LNAP

consisting of free-phase petroleum and Stoddard so

vent. To install diffusion samplers in these wells, a 

Table 1. Summary of well information, Naval Air Station North Island, California

[ft, feet; ft bls, feet below land surface; ft msl, feet relative to mean sea level; Elev., elevation; NM, not measured; NA, not available; TOC, top of casing; A, bladder pump attached to the diffusion sampler; B, peristaltic pump using tubing attached to individual 

diffusion samplers; C, same as B, except one depth was sampled using a bladder pump attached to a diffusion sampler; D, same as

B, except the well was resampled using a bladder pump following removal of the diffusion samplers]

Site or 

building 

designation

Well 

identifier

Depth to 

screen 

top(ft bls)

Depth to 

screen 

bottom 

(ft bls)

Saturated 

screen 

length (ft)

Depth to 

water 

(ft bls)

Elev. of 

water 

(ft msl)

Low-flow 

sampling 

method

653 MW-10 5 20.0 13.0 7.01 2.65 B

653 MW-13A 4 14.0 8.18 6.01 1.81 D

653 MW-13B 24.3 29.2 5.00 6.15 1.53 D

653 MW-13C 44.8 49.8 5.00 6.00 1.61 D

472 MW-68 C2 37 63.0 25.0 NM NA B

472 MW-68A 14 24.0 2.76 21.38 2.34 B

472 MW-68B 33 40.0 5.00 21.42 2.33 B

472 MW-68C 64.3 70.5 5.00 21.6 1.99 B

379 PW-15 20 35.0 9.94 23.34 2.61 B

379 PW-55 20 35.0 9.33 24.32 2.34 B

379 PW-66 20 35.0 10.0 25.10 2.40 B

Site 11 MW-12 30 39.7 13.7 NM NA C

Site 11 MW-5D NA 60.0 35.5 NM NA C

Site 11 MW-9 23 31.9 4.10 28.18 5.64 A

Site 2 S2-MW-6A 5 20.0 14.3 5.64 2.35 B
4 Diffusion Sampler Testing at Naval Air Station North Island,

San Diego County, California, November 1999 to January 2000

rubber cap was placed on the lower end of a section of 

2-inch-diameter PVC pipe and lowered into the well to 

a depth below the LNAPL. The top end of the pipe 

extended to land surface. A smaller diameter pipe then 

was used to pound out the rubber cap, which was 

recovered from the well along the outside of the 

2-inch-diameter pipe by means of a rope attached to 

the cap. The diffusion samplers were lowered into the 

well through the 2-inch-diameter pipe, thereby avoiding direct contact with the LNAPL. The pipe was 

secured in place to allow the diffusion sampler to be 

recovered without contact with the LNAPL. 

Collection of Pumped Ground-Water Samples

The diffusion samplers were allowed to remain 

undisturbed in the well water for 65 to 71 days 

(table 2). The wells were sampled at the time of sampler recovery using low-flow techniques. Low-flow 

sampling consisted of purging the well by means of 

using a dedicated bladder pump or a peristaltic pump 

connected to the Tygon tubing that had been attached 

to each of the diffusion samplers prior to deployment. 

Purging was done at a rate of 120 milliliters per minute 

until measurements of pH, water temperature, and specific conductance stabilized. In general, purging 

involved about 20 minutes of pumping and removal of 

less than 1 gallon of water from each sampling port. 

Decontamination of equipment was not required 

because each sampling interval had dedicated tubing.

A variety of methods were used to retrieve the 

diffusion samplers and to low-flow sample the well. 

The first method of sample retrieval involved recovering the diffusion sampler from the well immediately 

following low-flow sampling by using a bladder pump 

from the depth at which the diffusion sampler had 

equilibrated (well MW-9 only). A second method 

involved using a peristaltic pump to low-flow sample 

ground water adjacent to each of the diffusion samplers by means of the dedicated Tygon tubing attached 

to each diffusion sampler. The depths were low-flow 

sampled beginning with the shallowest and proceeding 

to the deepest. In some wells (MW-5 and MW-12), 

one of the depths was sampled using a dedicated bladder pump while the remaining depths were sampled 

using a bladder pump attached to dedicated tubing. 

Two wells (MW-13A and MW-13B) were low-flow 

sampled by using a peristaltic pump, the diffusion 

samplers were recovered, a bladder pump was inserted 

into each well, and the wells were then immediately 

resampled by low-flow methodology using t

pump.

The diffusion samplers were recovere

wells by means of the attached weighted lin

pipe. The samplers were cut open, and the w

slowly decanted into glass vials pretreated w

chloric acid. The water samples were sent to 

laboratory for analysis by using Environmen

tection Agency Method 8260B (U.S. Enviro

Protection Agency, 1999). Replicate sample

lected from approximately 10 percent of the 

sites. In general, both diffusion samples and 

samples compared well with their respective 

samples (tables 3 and 4).

RESULTS AND DISCUSSION

VOC concentrations in water obtained 

fusion samplers were similar to concentratio

obtained by using low-flow sampling metho

most of the tested wells (tables 5 and 6, resp

As will be shown, most concentration differ

between the two sampling methods probably 

attributed to VOC degassing during peristalt

sampling or to in-well mixing.

Comparison of Diffusion-Sampler Re

Bladder-Pump Results

Tests showing the most direct compar

between diffusion sampling and low-flow sa

were in wells where a bladder pump was us

flow sample. The test producing the least am

well-water disturbance was in well MW-9 w

fusion sampler was recovered immediately f

low-flow sampling using a bladder pump fro

same depth. Concentrations of 1,1-dichloroe

(1,1-DCE) and trichloroethene (TCE) obtain

the diffusion sampler agreed well (12 and 3 

difference, respectively) with those obtained 

bladder pump (table 7). The difference is ab

same as the differences (approximately 12 p

1,1-DCE and TCE concentrations measured 

cate samples collected by using a dedicated 

pump at well MW-5D (table 4). Thus, 12 pe

within the sample-collection variability for 

and TCE. Agreement between the methods w

for tetrachloroethene (PCE) concentrations. 

concentration in water from the diffusion sa

21 percent lower than the concentration in w
Comparison of Diffusion-Sampler Results to Bladder-Pump Results 

Table 2. Sampler deployment and recovery information, Naval Air Station North Island, California, November 1999 to Janu

2000

[repl, replicate sample; NA, not applicable; *, low-flow bladder-pump sample; #, data from OHM Remediation Services Corporation (2000)]

Site or 

building 

designation

Well 

identifier

Sampling 

interval 

identifier

Low-flow 

sample 

laboratory 

identifier

Diffusionsampler 

laboratory 

identifier

Depth to 

diffusionsampler 

center 

(ft bls)

Date 

installed

Date 

recovered

Numbe

days 

diffusi

sample

were 

wells

653 MW-10 A 779679-0091 779679-0099 7.75 11/12/99 1/18/00 67

653 MW-10 B 779679-0092 779679-0100 9.15 11/12/99 1/18/00 67

653 MW-10 C 779679-0093 779679-0101 11.1 11/12/99 1/18/00 67

653 MW-10 D 779679-0094 779679-0102 13.1 11/12/99 1/18/00 67

653 MW-10 E 779679-0095 779679-0103 15.1 11/12/99 1/18/00 67

653 MW-10 F 779679-0096 779679-0104 17.1 11/12/99 1/18/00 67

653 MW-10 G 779679-0097 779679-0105 18.8 11/12/99 1/18/00 67

653 MW-10 G repl 779679-0098 NA 18.8 11/12/99 1/18/00 67

653 MW-13A A 779679-0030 779679-0042 6.50 11/10/99 1/17/00 68

653 MW-13A B 779679-0031 779679-0043 7.95 11/10/99 1/17/00 68

653 MW-13A C 779679-0032 779679-0044 9.35 11/10/99 1/17/00 68

653 MW-13A D 779679-0033 779679-0045 10.9 11/10/99 1/17/00 68

653 MW-13A E 779679-0034 779679-0046 12.4 11/10/99 1/17/00 68

653 MW-13A*# NA NA NA NA NA 1/17/00 NA

653 MW-13B A 779679-0035 779679-0047 24.8 11/10/99 1/17/00 68

653 MW-13B B 779679-0036 779679-0048 26.1 11/10/99 1/17/00 68

653 MW-13B C 779679-0037 779679-0049 27.5 11/10/99 1/17/00 68

653 MW-13B*# NA NA NA NA NA 1/17/00 NA

653 MW-13C A 779679-0038 779679-0054 45.4 11/10/99 1/17/00 68

653 MW-13C B 779679-0039 779679-0055 46.6 11/10/99 1/17/00 68

653 MW-13C B repl 779679-0041 NA 46.6 11/10/99 1/17/00 68

653 MW-13C C 779679-0040 779679-0056 48.0 11/10/99 1/17/00 68

653 MW-13C*# NA NA NA NA NA 1/17/00 NA

472 MW-68A A 779679-0023 779679-0025 21.7 11/9/99 1/17/00 69

472 MW-68A B 779679-0024 779679-0026 23.0 11/9/99 1/17/00 69

472 MW-68B A 779679-0016 779679-0020 34.5 11/9/99 1/17/00 69

472 MW-68B B 779679-0017 779679-0021 37.0 11/9/99 1/17/00 69

472 MW-68B B repl 779679-0018 NA 37.0 11/9/99 1/17/00 69

472 MW-68B C 779679-0019 779679-0022 38.5 11/9/99 1/17/00 69

472 MW-68C A 779679-0027 779679-0050 56.0 11/9/99 1/17/00 69

472 MW-68C B 779679-0028 779679-0051 57.5 11/9/99 1/17/00 69

472 MW-68C C 779679-0117 779679-0116 59.0 11/9/99 1/19/00 71
6 Diffusion Sampler Testing at Naval Air Station North Island,

San Diego County, California, November 1999 to January 2000

Table 2. Sampler deployment and recovery information, Naval Air Station North Island, California, November 1999 

2000—Continued

[repl, replicate sample; NA, not applicable; *, low-flow bladder-pump sample; #, data from OHM Remediation Services Corporation (2000)]

Site or 

building 

designation

Well 

identifier

Sampling 

interval 

identifier

Low-flow 

sample 

laboratory 

identifier

Diffusionsampler 

laboratory 

identifier

Depth to 

diffusionsampler 

center 

(ft bls)

Date 

installed

Date 

recovered

472 MW-68C2 A 779679-0166 779679-0181 37.2 11/11/99 1/20/00 

472 MW-68C2 B 779679-0169 779679-0182 39.1 11/11/99 1/20/00 

472 MW-68C2 B repl NA 779679-0183 39.1 11/11/99 1/20/00 

472 MW-68C2 C 779679-0171 779679-0184 40.5 11/11/99 1/20/00 

472 MW-68C2 D 779679-0173 779679-0185 42.0 11/11/99 1/20/00 

472 MW-68C2 E 779679-0176 779679-0186 44.1 11/11/99 1/20/00 

472 MW-68C2 F 779679-0178 779679-0187 46.0 11/11/99 1/20/00 

472 MW-68C2 G 779679-0180 779679-0188 47.8 11/11/99 1/20/00 

472 MW-68C2 H 779679-0179 779679-0189 49.8 11/11/99 1/20/00 

472 MW-68C2 I 779679-0177 779679-0190 51.9 11/11/99 1/20/00 

472 MW-68C2 J 779679-0174 779679-0191 53.9 11/11/99 1/20/00 

472 MW-68C2 J repl 779679-0175 NA 53.9 11/11/99 1/20/00 

472 MW-68C2 K 779679-0172 779679-0192 55.5 11/11/99 1/20/00 

472 MW-68C2 L 779679-0170 779679-0193 57.5 11/11/99 1/20/00 

472 MW-68C2 M 779679-0168 779679-0194 59.5 11/11/99 1/20/00 

472 MW-68C2 M repl NA 779679-0195 59.5 11/11/99 1/20/00 

472 MW-68C2 N 779679-0167 779679-0196 61.5 11/11/99 1/20/00 

379 PW-15 A 779679-0083 779679-0089 25.4 11/13/99 1/19/00 

379 PW-15 B 779679-0084 779679-0118 27.1 11/13/99 1/19/00 

379 PW-15 B repl NA 779679-0119 27.1 11/13/99 1/19/00 

379 PW-15 C 779679-0085 779679-0156 28.5 11/13/99 1/19/00 

379 PW-15 D 779679-0086 779679-0157 30.2 11/13/99 1/19/00 

379 PW-15 E 779679-0087 779679-0158 31.7 11/13/99 1/19/00 

379 PW-15 E repl NA 779679-0159 31.7 11/13/99 1/19/00 

379 PW-15 F 779679-0088 779679-0164 33.1 11/13/99 1/19/00 

379 PW-55 A 779679-0077 779679-0109 27.1 11/13/99 1/19/00 

379 PW-55 B 779679-0078 779679-0110 28.9 11/13/99 1/19/00 

379 PW-55 B repl NA 779679-0114 28.9 11/13/99 1/19/00 

379 PW-55 C 779679-0079 779679-0111 30.6 11/13/99 1/19/00 

379 PW-55 D 779679-0080 779679-0112 31.9 11/13/99 1/19/00 

379 PW-55 E 779679-0081 779679-0113 33.1 11/13/99 1/19/00 

379 PW-55 E repl 779679-0082 779679-0115 33.1 11/13/99 1/19/00 

379 PW-66 A 779679-0106 779679-0145 25.5 11/10/99 1/18/00 

379 PW-66 B 779679-0107 779679-0146 27.3 11/10/99 1/18/00 

379 PW-66 B repl NA 779679-0151 27.3 11/10/99 1/18/00 
Comparison of Diffusion-Sampler Results to Bladder-Pump Results 

379 PW-66 C 779679-0073 779679-0147 29.1 11/10/99 1/18/00 69

379 PW-66 D 779679-0108 779679-0148 30.8 11/10/99 1/18/00 69

379 PW-66 E 779679-0074 779679-0149 32.3 11/10/99 1/18/00 69

379 PW-66 F 779679-0075 779679-0150 33.9 11/10/99 1/18/00 69

379 PW-66 F repl NA 779679-0152 33.9 11/10/99 1/18/00 69

Site 11 MW-12 A 779679-0006 779679-0012 30.5 11/13/99 1/17/00 65

Site 11 MW-12 B 779679-0007 779679-0013 32.1 11/13/99 1/17/00 65

Site 11 MW-12 C 779679-0008 779679-0014 33.7 11/13/99 1/17/00 65

Site 11 MW-12* D 779679-0009 779679-0057 35.1 11/13/99 1/17/00 65

Site 11 MW-12* D repl NA 779679-0060 35.1 11/13/99 1/17/00 65

Site 11 MW-12 E 779679-0010 779679-0058 36.9 11/13/99 1/17/00 65

Site 11 MW-12 F 779679-0011 779679-0059 38.5 11/13/99 1/17/00 65

Site 11 MW-5D A 779679-0121 779679-0128 50.8 11/12/99 1/18/00 67

Site 11 MW-5D B 779679-0122 779679-0129 52.3 11/12/99 1/18/00 67

Site 11 MW-5D C 779679-0123 779679-0130 54.2 11/12/99 1/18/00 67

Site 11 MW-5D C repl NA 779679-0134 54.2 11/12/99 1/18/00 67

Site 11 MW-5D* D 779679-0124 779679-0131 55.75 11/12/99 1/18/00 67

Site 11 MW-5D D repl 779679-0125 NA 55.75 11/12/99 1/18/00 67

Site 11 MW-5D E 779679-0126 779679-0132 57.4 11/12/99 1/18/00 67

Site 11 MW-5D F 779679-0127 779679-0133 59.0 11/12/99 1/18/00 67

Site 11 MW9* NA 779679-0154 779679-0155 31 11/12/99 1/19/00 68

Site 2 S2-MW6A A 779679-0062 779679-0135 6.5 11/13/99 1/18/00 66

Site 2 S2-MW6A B 779679-0063 779679-0136 7.85 11/13/99 1/18/00 66

Site 2 S2-MW6A C 779679-0064 779679-0137 9.2 11/13/99 1/18/00 66

Site 2 S2-MW6A D 779679-0065 779679-0138 10.6 11/13/99 1/18/00 66

Site 2 S2-MW6A E 779679-0066 779679-0139 11.95 11/13/99 1/18/00 66

Site 2 S2-MW6A F 779679-0067 779679-0140 13.3 11/13/99 1/18/00 66

Site 2 S2-MW6A G 779679-0068 779679-0141 14.65 11/13/99 1/18/00 66

Site 2 S2-MW6A H 779679-0069 779679-0142 16.05 11/13/99 1/18/00 66

Site 2 S2-MW6A I 779679-0070 779679-0143 17.5 11/13/99 1/18/00 66

Site 2 S2-MW6A J 779679-0071 779679-0144 18.95 11/13/99 1/18/00 66

Site 2 S2-MW6A J repl 779679-0072 NA 18.95 11/13/99 1/18/00 66

Table 2. Sampler deployment and recovery information, Naval Air Station North Island, California, November 1999 to Janu

2000—Continued

[repl, replicate sample; NA, not applicable; *, low-flow bladder-pump sample; #, data from OHM Remediation Services Corporation (2000)]

Site or 

building 

designation

Well 

identifier

Sampling 

interval 

identifier

Low-flow 

sample 

laboratory 

identifier

Diffusionsampler 

laboratory 

identifier

Depth to 

diffusionsampler 

center 

(ft bls)

Date 

installed

Date 

recovered

Numb

of day

diffusi

sample

were 

wells
8 Diffusion Sampler Testing at Naval Air Station North Island,

San Diego County, California, November 1999 to January 2000

Table 3. Comparison of replicate samples collected by diffusion-sampler methodology, Naval Air Station North Isla

California, January 2000

[repl, replicate sample; ft bls, feet below land surface; (μg/L, micrograms per liter; J, estimated value; U, value was below the analytical quan

11DCA, 1,1-dichloroethane; 11DCE, 1,1-dichloroethene; cDCE, cis-1,2-dichloroethene; TCE, trichloroethene]

Well 

identifier

and 

(depth code)

Depth to diffusion sampler

center 

(ft bls)

Site or building designation

11DCA

(μg/L)

11DCE

(μg/L)

cDCE

(μg/L)

Ethylbenzene

(μg/L)

TCE

(μg/L)

Vinyl 

chloride(μg/

L)

MW-12 (D) 35.1 Site 11 86 J 1,500 100 100 U 1,800 100 U 

MW-12 (D-repl) 35.1 Site 11 89 J 1,500 110 100 U 1,700 100 U 

MW-5D (C) 54.2 Site 11 170 2,800 E 61 50 U 930 50 U 

MW-5D (C repl) 54.2 Site 11 170 2,900 E 61 50 U 930 50 U 

MW-68C2 (B) 39.1 472 2,500 U 4,100 1,000 J 2,500 U 47,000 2,500 U 

MW-68C2 (B repl) 39.1 472 5,000 U 4,300 J 960 J 5,000 U 52,000 5,000 U 

MW-68C2 (M) 59.5 472 500 U 350 J 500 U 500 U 7,000 500 U 

MW-68C2 (M repl) 59.5 472 500 U 360 J 500 U 500 U 6,800 500 U 

PW-15 (B) 27.1 379 52 8 130 15 7 72 

PW-15 (B repl) 27.1 379 54 8 130 17 5 J 75 

PW-15 (E) 31.7 379 500 U 500 U 1,900 500 U 5,500 500 U 

PW-15 (E repl) 31.7 379 500 U 500 U 1,900 500 U 5,600 500 U 

PW-55 (B) 28.9 379 2,500 U 2,500 U 6,500 2,500 U 39,000 2,500 U 

PW-55 (B repl) 28.9 379 2,500 U 2,500 U 6,700 2,500 U 36,000 2,500 U 

PW-55 (E) 33.1 379 2,500 U 2,500 U 6,300 2,500 U 33,000 2,500 U 

PW-55 (E repl) 33.1 379 2,500 U 2,500 U 6,100 2,500 U 31,000 2,500 U 

PW-66 (B) 28.9 379 500 U 500 U 3,400 500 U 9,000 500 U 

PW-66 (B repl) 28.9 379 500 U 500 U 3,200 500 U 9,200 500 U 

PW-66 (F) 33.1 379 5 U 130 5 U 5 U 13 5 U 

PW-66 (F repl) 33.1 379 5 U 120 5 U 5 U 18 5 U 

obtained using the bladder pump (table 7). The reason 

for the difference in tetrachloroethene concentrations 

is not known. 

The data from well MW-5 (site 11) show that 

the diffusion samplers performed favorably. At well 

MW-5, where a bladder pump was used to obtain 

water adjacent to a diffusion sampler and where peristaltic pumps were used at the other depths, the difference between the TCE concentration in water from the 

adjacent diffusion sampler and the average concentration (300 μg/L) in water from the bladder pump was 

relatively small (17-percent difference) (table 7). 

Moreover, the higher TCE concentration in water from 

the diffusion sampler compared to the concentration in 

water from the bladder pump implies that the sample 

collected by the diffusion method was more discrete 

than the sample collected by using the bladder pump.

A comparison between diffusion samp

bladder pump sample at well MW-12 showe

TCE concentration in water from the diffusio

was similar to the TCE concentration in wat

the bladder pump (1,800 and 2,100 μg/L, re

tively); however, the cis-1,2-dichloroethene 

concentration in water from the diffusion sam

substantially lower (78 percent) than the con

in water from the bladder pump (table 7 and 

This difference may be due to in-well mixin

flow sampling in a chemically stratified part 

screened interval. Data from diffusion samp

that the VOC concentrations substantially in

with depth over a distance of only 3.4 ft and 

bladder pump was positioned at a transition 

between two depths of differing concentratio

(table 5 and fig. 2). The bladder pump was s
Comparison of Diffusion-Sampler Results to Bladder-Pump Results 

Table 4. Comparison of replicate samples collected by low-flow methodology, Naval Air Station North Island, California, 

January 2000

[repl, replicate sample; *, sample collected by using bladder pump - low-flow samples without * were collected by using a peristaltic pump; #, data fro

OHM Remediation Services Corp. (2000); ft bls, feet below land surface; (μg/L, micrograms per liter; J, estimated value; U, value was below the analy

quantitation limit; 11DCA, 1,1-dichloroethane; 11DCE, 1,1-dichloroethene; cDCE, cis-1,2 dichloroethene; TCE, trichloroethene]

Well 

Identifier and (depth 

code)

Depth to 

diffusion 

sampler 

center 

(ft bls)

Site or building

designation

11DCA 

(μg/L)

11DCE 

(μg/L)

cDCE 

(μg/L)

Ethylbenzene 

(μg/L)

TCE 

(μg/L)

Vinyl 

chloride 

(μg/L)

Total 

xylenes 

(μg/L)

MW-10 (G) 18.8 653 5 U 0 J 5 U 5 U 6 5 U 3 J

MW-10 (G repl) 18.8 653 5 U 5 U 1 J 5 U 9 5 U 5 U

MW-13B*# 26 653 5 U 5 U 3,100 5 U 5 U 1,600 5 U

MW-13B*# (repl) 26 653 5 U 5 U 3,200 5 U 5 U 1,400 5 U

MW-13C (B) 46.6 653 5 U 5 U 3 J 5 U 5 U 5 U 5 U

MW-13C (B repl) 46.6 653 5 U 5 U 2 J 5 U 5 U 5 U 5 U

MW-5D (D)* 55.7 Site 11 51 760 23 J 25 U 320 25 U 25 U

MW-5D (D repl)* 55.7 Site 11 44 670 22 J 25 U 280 25 U 25 U

MW-68C2 (J) 53.9 472 2,500 U 2,500 J 2,500 U 2,500 U 38,000 2,500 U 2,500 U

MW-68C2 (J repl) 53.9 472 2,500 U 2,600 2,500 U 2,500 U 38,000 2,500 U 2,500 U

MW-68B (B) 37.0 472 5,000 U 4,400 J 5,000 U 5,000 U 34,000 5,000 U 5,000 U

MW-68B (B repl) 37.0 472 5,000 U 4,900 J 5,000 U 5,000 U 33,000 5,000 U 5,000 U

PW-55 (E) 33.1 379 2,500 U 2,500 U 5,500 2,500 U 29,000 2,500 U 2,500 U

PW-55 (E repl) 33.1 379 2,500 U 2,500 U 5,700 2,500 U 29,000 2,500 U 2,500 U

S2-MW-6A (J) 18.9 Site 2 5 U 5 U 5 U 5 U 5 U 5 U 5 U

S2-MW-6A (J repl) 18.9 Site 2 5 U 5 U 5 U 5 U 5 U 5 U 5 U

following low-flow sampling from three overlying 

depths using a peristaltic pump; thus, the concentration interface potentially shifted upward toward the 

bladder pump intake. It is possible that in-well mixing 

was more pronounced for cDCE than for TCE because 

there was a greater percentage of change in concentrations with depth for cDCE than for TCE. The cDCE 

concentration increased by a factor of 26 (100 to 

2,600 μg/L) over a depth of 3.4 feet, whereas TCE 

increased by only a factor of 4.6 over the same depth 

interval (1,700 to 7,800 μg/L) (fig. 2). The VOC concentration data indicate that in well MW-12, the diffusion samplers collected point samples of ground water, 

whereas the bladder pump either collected water from 

a greater radius of influence or from water induced up 

the well bore by low-flow sampling at shallower 

depths.

Wells MW-13A and MW-13B were tested us

diffusion samplers and low-flow sampling with a p

staltic pump. Following sample collection with the 

peristaltic pump, the diffusion samplers were recov

ered and the wells were sampled by using a bladde

pump (bladder-pump data from OHM Remediation 

Services Corporation, 2000). The data show that at 

well MW-13A, the cDCE and vinyl chloride conce

trations in water obtained using the bladder pump 

were within the concentration ranges for water 

obtained from diffusion samplers that bracketed th

depth interval of the bladder pump intake (table 7)

well MW-13B, the cDCE concentration also was 

within the range measured in those diffusion sampl

bracketing the depth of the bladder pump intake 

(table 7 and fig. 3). Although vinyl chloride concen

tions differed between the two methods by 16 to 
Diffusion Sampler Testing at Naval Air Station North Island,San Diego County, California, November 1999 to January 2000

Island, California, January 2000

[μg/L, micrograms per liter; D, sample was diluted; U, value was below the analytical quantitation limit; J, estimated value; NA, not applicable; E, the detected result is between the samplespecific estimated quantitation and the method detection limit; *, sample collected by using bladder pump; #, data from OHM Remediation Services Corporation (2000)]

Well Depth 

(feet)

1,1-Dichloroethane 

(μg/L)

1,1-Dichloroethene 

(μg/L)

cis-1,2-Dichloroethene

(μg/L)

Tetrachloroethene

(μg/L)

Trichloroethene

(μg/L)

Vinyl chloride

(μg/L)

Diffusion Low flow Diffusion Low flow Diffusion Low flow Diffusion Low flow Diffusion Low flow Diffusion Low flow

MW-5D 50.8 260 200 1,500 1,900 D 66 62 50 U 25 U 690 660 50 U 25 U

MW-5D 52.3 260 210 3,600 4,300 D 120 J 63 250 U 50 U 1,200 1,100 250 U 50 U

MW-5D 54.2 170 95 J 3,200 D 1,400 61 36 J 50 U 100 U 930 590 50 U 100 U

MW-5D* 55.8 65 51 1,500 D 760 27 23 J 5 U 25 U 510 D 320 5 U 25 U

MW-5D 57.4 50 U 20 460 360 D 50 U 11 50 U 5 U 160 120 50 U 5 U

MW-5D 59.0 50 U 6 190 94 10 J 6 50 U 5 U 55 36 50 U 5 U

MW-9* 27.6 270 270 4,000 3,500 250 U 250 U 260 330 3,300 3,200 250 U 250 U

MW-10 7.8 5U 5U 5U 2J 5 U 5 U 5 U 5 U 5 U 30 5 U 5 U

MW-10 9.2 5U 5U 5U 1J 5 U 5 U 5 U 5 U 5 U 18 5 U 5 U

MW-10 11.2 5U 5U 5U 1J 1 J 5 U 5 U 5 U 5 U 17 5 U 5 U

MW-10 13.2 5U 5U 5U 1J 5 U 5 U 5 U 5 U 5 U 13 5 U 5 U

MW-10 15.2 5U 5U 5U 0J 5 U 5 U 5 U 5 U 5 U 10 5 U 5 U

MW-10 17.2 5U 5U 5U 0J 5 U 5U 5U 5 U 5 U 9 5 U 5U

MW-10 18.9 5U 5U 5U 0J 5 U 5U 5U 5 U 5 U 6 5 U 5U

MW-12 30.5 94 J 73 1,500 970 D 99 J 77 100 U 4 J 1,700 1,400 D 100 U 5 U

MW-12 32.2 91 J 52 1,500 510 D 96 J 57 100 U 2 J 1,700 800 D 100 U 5 U

MW-12 33.7 91 J 87 1,500 780 D 93 J 140 100 U 2 J 1,900 960 D 100 U 5 U

MW-12* 35.1 86 J 260 1,500 2,200 100 450 100 U 100 U 1,800 2,100 100 U 100 U

MW-12 37.0 230 890 2,600 3,700 500 1,500 100 U 500 U 2,400 3,800 100 U 500 U

MW-12 38.5 1,600 1,800 8,800 7,900 2,600 3,000 500 U 500 U 7,800 7,600 500 U 500 U
Comparison of Diffusion-Sampler Results to Bladder-Pump Results 11

specific estimated quantitation and the method detection limit; *, sample collected by using bladder pump; #, data from OHM Remediation Services Corporation (2000)]

Well Depth 

(feet)

1,1-Dichloroethane 

(μg/L)

1,1-dichloroethene 

(μg/L)

Cis-1,2-dichloroethene

(μg/L)

Tetrachloroethene

(μg/L)

Trichloroethene

(μg/L)

Vinyl chloride

(μg/L)

Diffusion Low flow Diffusion Low flow Diffusion Low flow Diffusion Low flow Diffusion Low flow Diffusion Low flow

MW-13A 6.5 5 U 5 U 5 U 5 U 39 47 5 U 5 U 5 U 5 U 4 J 6

MW-13A 8.0 5 U 5 U 5 U 5 U 78 46 5 U 5 U 5 U 5 U 9 6

MW-13A 9.4 5 U 5 U 5 U 5 U 77 47 5 U 5 U 5 U 5 U 9 6

MW-13A 10.9 5 U 5 U 5 U 5 U 74 53 5 U 5 U 5 U 5 U 8 7

MW-13A 12.4 5 U 5 U 5 U 5 U 46 55 5 U 5 U 5 U 5 U 5 7

MW-13A*# 12.0 NA 5 U NA 5 U 61 NA 5 U NA 5 U NA 7 

MW-13B 24.9 5 U 5 U 4 J 4 J 3,100 D 2,600 D 5 U 5 U 4 J 5 1,900 D 1,900 D

MW-13B 26.2 5 U 5 U 4 J 5 U 2,600 D 2,600 D 5 U 5 U 4 J 6 2,000 D 1,600 D

MW-13B 27.6 5 U 5 U 5 J 5 J 2,700 D 2,900 D 5 U 5 U 8 7 2,400 D 1,700 D

MW-13B*# 26.0 NA 5 U NA 5 U NA 3,100 NA 5 U NA 5 U NA 1,400

MW-13C 45.5 5U 5 U 5U 5 U 2J 5U 5U 5U 5U 5U 5U

MW-13C 46.7 5U 5 U 5U 5 U 5U 3J 5U 5U 5U 5U 5U 5U

MW-13C 48.1 5U 5 U 5U 5 U 5U 2J 5U 5U 5U 5U 5U 5U

MW-13C*# 46.0 NA 5 U NA 5 U NA 1 J NA 5 U NA 5 U NA 5 U

MW-68A 21.7 7 J 4 J 25 U 5 U 140 81 7 J 2 J 570 320 D 25 U 5 U

MW-68A 23.0 50 U 5 J 50 U 5 U 160 87 50 U 1 J 730 190 50 U 5 U

MW-68B 34.5 85 J 5,000 U 5,800 4,700 J 87 J 5,000 U 93 J 5,000 U 49,000 D 28,000 250 U 5,000 U

MW-68B 37.0 5,000 U 5,000 U 7,700 4,400 J 5,000 U 5,000 U 5,000 U 5,000 U 62,000 34,000 5,000 U 5,000 U

MW-68B 38.5 5,000 U 5,000 U 8,300 5,000 J 5,000 U 5,000 U 5,000 U 5,000 U 130,000 62,000 5,000 U 5,000 U

MW-68C 56.0 50 U 50 U 20 J 50 U 50 U 50 U 50 U 50 U 1,400 680 50 U 50 U

MW-68C 57.5 100 U 50 U 100 U 10 J 100 U 50 U 100 U 50 U 2,700 880 100 U 50 U

MW-68C 59.0 250 U 50 U 250 U 50 U 250 U 50 U 250 U 50 U 4,100 1,100 250 U 50 U
Diffusion Sampler Testing at Naval Air Station North Island,San Diego County, California, November 1999 to January 2000

California, January 2000Continued

[μg/L, micrograms per liter; D, sample was diluted; U, value was below the analytical quantitation limit; J, estimated value; NA, not applicable; E, the detected result is between the sample-specific 

estimated quantitation and the method detection limit; *, sample collected by using bladder pump; #, data from OHM Remediation Services Corporation (2000)]

Well Depth 

(feet)

1,1-Dichloroethane 

(μg/L)

1,1-Dichloroethene 

(μg/L)

cis-1,2-Dichloroethene

(μg/L)

Tetrachloroethene

(μg/L)

Trichloroethene

(μg/L)

Vinyl chloride

(μg/L)

Diffusion Low flow Diffusion Low flow Diffusion Low flow Diffusion Low flow Diffusion Low flow Diffusion Low flow

MW-68C2 37.3 1,000 U 500 U 2,400 1,200 490 J 360 J 1,000 U 500 U 19,000 9,100 1,000 U 500 U

MW-68C2 39.1 2,500 U 2,500 U 4,100 3,400 1,000 J 2,500 U 2,500 U 2,500 U 47,000 34,000 2,500 U 2,500 U

MW-68C2 40.5 5,000 U 2,500 U 5,400 2,700 5,000 U 2,500 U 5,000 U 2,500 U 84,000 39,000 5,000 U 2,500 U

MW-68C2 42.1 10,000 U 2,500 U 14,000 2,800 10,000 U 2,500 U 10,000 U 2,500 U 200,000 46,000 10,000 U 2,500 U

MW-68C2 44.2 10,000 U 2,500 U 7,800 J 3,600 10,000 U 2,500 U 10,000 U 2,500 U 110,000 54,000 10,000 U 2,500 U

MW-68C2 46.1 10,000 U 1,000 U 7,500 J 1,200 10,000 U 1,000 U 10,000 U 1,000 U 110,000 17,000 10,000 U 1,000 U

MW-68C2 47.9 10,000 U 5,000 U 7,400 J 4,300 J 10,000 U 5,000 U 10,000 U 5,000 U 110,000 55,000 10,000 U 5,000 U

MW-68C2 49.9 10,000 U 2,500 U 7,200 J 4,400 10,000 U 2,500 U 10,000 U 2,500 U 100,000 53,000 10,000 U 2,500 U

MW-68C2 52.0 2,500 U 2,500 U 3,000 2,800 2,500 U 2,500 U 2,500 U 2,500 U 42,000 42,000 2,500 U 2,500 U

MW-68C2 53.9 1,000 U 2,500 U 1,100 2,500 J 1,000 U 2,500 U 1,000 U 2,500 U 14,000 38,000 1,000 U 2,500 U

MW-68C2 55.6 500 U 1,000 U 600 1,000 500 U 1,000 U 500 U 1,000 U 8,800 14,000 500 U 1,000 U

MW-68C2 57.5 500 U 500 U 450 J 710 500 U 500 U 500 U 500 U 7,300 9,100 500 U 500 U

MW-68C2 59.5 500 U 500 U 350 J 920 500 U 500 U 500 U 500 U 7,000 11,000 500 U 500 U

MW-68C2 61.5 500 U 500 U 280 J 740 500 U 500 U 500 U 500 U 6,500 11,000 500 U 500 U

PW-15 25.4 45 53 4 J 12 42 200 E 5 U 2 J 4 J 15 82 66

PW-15 27.1 52 52 75 22 130 850 D 1 J 8 7 92 72 29 .

PW-15 28.5 73 J 77 J 36 J 66 J 1,500 2,200 100 J 250 U 180 2,500 100 U 250 U

PW-15 30.2 97 J 500 U 250 U 500 U 2,900 1,600 59 J 500 U 3,000 4,700 250 U 500 U

PW-15 31.8 500 U 500 U 500 U 500 U 1,900 1,800 500 U 500 U 5,500 5,800 500 U 500 U

PW-15 33.2 500 U 500 U 500 U 500 U 2,400 2,100 120 J 130 J 7,500 7,300 500 U 500 U

PW-55 27.1 2,500 U 2,500 U 2,500 U 2,500 U 7,300 5,700 2,500 U 2,500 U 39,000 31,000 2,500 U 2,500 U

PW-55 28.9 2,500 U 2,500 U 2,500 U 2,500 U 6,500 5,900 2,500 U 2,500 U 39,000 32,000 2,500 U 2,500 U

PW-55 30.6 2,500 U 2,500 U 2,500 U 2,500 U 6,600 5,900 2,500 U 2,500 U 38,000 34,000 2,500 U 2,500 U
Comparison of Diffusion-Sampler Results to Bladder-Pump Results 13

estimated quantitation and the method detection limit; *, sample collected by using bladder pump; #, data from OHM Remediation Services Corporation (2000)]

Well Depth 

(feet)

1,1-Dichloroethane 

(μg/L)

1,1-Dichloroethene 

(μg/L)

cis-1,2-Dichloroethene

(μg/L)

Tetrachloroethene

(μg/L)

Trichloroethene

(μg/L)

Vinyl chloride

(μg/L)

Diffusion Low flow Diffusion Low flow Diffusion Low flow Diffusion Low flow Diffusion Low flow Diffusion Low flow

PW-55 31.9 2,500 U 2,500 U 2,500 U 2,500 U 6,800 5,300 2,500 U 2,500 U 38,000 29,000 2,500 U 2,500 U

PW-55 33.1 2,500 U 2,500 U 2,500 U 2,500 U 6,300 5,500 2,500 U 2,500 U 33,000 29,000 2,500 U 2,500 U

PW-66 25.5 1,000 U 500 U 1,000 U 38 J 2,000 1,600 1,000 U 599 U 17,000 13,000 1,000 U 500 U

PW-66 27.3 500 U 500 U 500 U 500 U 3,400 1,000 500 U 500 U 9,000 6,400 500 U 500 U

PW-66 29.1 50 U 500 U 38 J 500 U 23 J 500 U 50 U 500 U 770 9,800 50 U 500 U

PW-66 30.8 25 U 500 U 49 500 U 25 U 500 U 25 U 500 U 180 5,600 25 U 500 U

PW-66 32.3 5 U 500 U 72 500 U 5 U 500 U 5 U 500 U 48 6,200 5 U 500 U

PW-66 33.9 5 U 500 U 130 500 U 5 U 500 U 1 J 500 U 13 6,000 5 U 500 U

S2-MW-6A 6.5 5 U 5 U 5 U 5 U 5U 5U 5 U 5 U 5 U 5 U 5 U 5 U

S2-MW-6A 7.9 5 U 5 U 5 U 5 U 5U 5U 5 U 5 U 5 U 2 U 5 U 5 U

S2-MW-6A 9.2 5 U 5 U 5 U 5 U 5U 5

S2-MW-6A 10.6 5 U 5 U 5 U 5 U 5U 5U 5 U 5 U 2 J 2 J 5 U 5 U

S2-MW-6A 12.0 5 U 5 U 5 U 5 U 5U 5U 5 U 5 U 5 U 2 J 5 U 5 U

S2-MW-6A 13.3 5 U 5 U 5 U 5 U 5U 5U 5 U 5 U 1 J 5 U 5 U 5 U

S2-MW-6A 14.7 5 U 5 U 5 U 5 U 5U 5U 5 U 5 U 5 U 2 J 5 U 5 U

S2-MW-6A 16.1 5 U 5 U 5 U 5 U 5U 5U 5 U 5 U 5 U 2 J 5 U 5 U

S2-MW-6A 17.5 5 U 5 U 5 U 5 U 5U 5U 5 U 5 U 5 U 2 J 5 U 5 U

S2-MW-6A 19.0 5U 5U 5U 5 U 5 U 5 U 5 U 5 U 5 U 5U 5U 5U
14 Diffusion Sampler Testing at Naval Air Station North Island,

San Diego County, California, November 1999 to January 2000

Table 6. Concentrations of benzene, ethylbenzene, toluene, and total xylenes in water from diffusion and low-flow 

sampling, Naval Air Station North Island, California, January 2000

[μg/L, micrograms per liter; U, value was below the analytical quantitation limit; J, estimated value; NA, not applicable; *, sample collected 

using bladder pump; #, data from OHM Remediation Services Corporation (2000)]

Well Depth

(feet)

Benzene 

(μg/L)

Ethylbenzene 

(μg/L)

Toluene 

(μg/L)

Total xylenes 

(μg/L)

Diffusion Low flow Diffusion Low flow Diffusion Low flow Diffusion Low flow

MW-5D 50.8 50 U 25 U 50 U 25 U 50 U 25 U 50 U 25 U

MW-5D 52.3 250 U 50 U 250 U 50 U 250 U 50 U 250 U 50 U

MW-5D 54.2 50 U 100 U 50 U 100 U 50 U 100 U 50 U 100 U

MW-5D* 55.8 5 U 25 U 5 U 25 U 5 U 25 U 5 U 25 U

MW-5D 57.4 50 U 5 U 50 U 5 U 50 U 5 U 50 U 5 U

MW-5D 59.0 50 U 5 U 50 U 5 U 50 U 5 U 50 U 5 U

MW-9* 27.6 250 U 250 U 250 U 250 U 250 U 250 U 250 U 250 U

MW-10 7.8 5 U 5 U 5 U 5 U 5 U 5 U 5 U 5 U

MW-10 9.2 5 U 5 U 5 U 5 U 5 U 5 U 5 U 5 U

MW-10 11.2 5 U 5 U 5 U 5 U 5 U 5 U 5 U 5 U

MW-10 13.2 5 U 5 U 5 U 5 U 5 U 5 U 1 J 5 U

MW-10 15.2 5 U 5 U 5 U 5 U 5 U 5 U 5 U 5 U

MW-10 17.2 5 U 5 U 5 U 5 U 5 U 5 U 5 U 5 U

MW-10 18.9 5 U 5 U 5 U 5 U 5 U 5 U 5 U 2.5 J

MW-12 30.5 100 U 5 U 100 U 5 U 100 U 5 U 100 U 5 U

MW-12 32.2 100 U 5 U 100 U 5 U 100 U 5 U 100 U 5 U

MW-12 33.7 100 U 5 U 100 U 5 U 100 U 5 U 100 U 5 U

MW-12* 35.1 100 U 100 U 100 U 100 U 100 U 100 U 100 U 100 U

MW-12 37.0 100 U 500 U 100 U 120 U 100 U 500 U 100 U 360 U

MW-12 38.5 500 U 500 U 500 U 500 U 500 U 500 U 500 U 500 U

MW-13A 6.5 5 U 5 U 5 U 5 U 5 U 5 U 5 U 5 U

MW-13A 8.0 5 U 5 U 5 U 5 U 5 U 5 U 5 U 5 U

MW-13A 9.4 5 U 5 U 5 U 5 U 5 U 5 U 5 U 5 U

MW-13A 10.9 5 U 5 U 5 U 5 U 5 U 5 U 5 U 5 U

MW-13A 12.4 5 U 5 U 5 U 5 U 5 U 5 U 5 U 5 U

MW-13A*# 12.0 NA 5 U NA 5 U NA 5 U NA 

MW-13B 24.9 9 5 5 U 5 U 5 U 5 U 5 U 5 U

MW-13B 26.2 5 4 J 5 U 5 U 5 U 5 U 5 U 5 U

MW-13B 27.6 1 J 4 J 5 U 5 U 1 J 5 U 5 U 5 U

MW13B*# 26.0 NA 5 U NA 5 U NA 5 U NA 5 U

MW-13C 45.5 5 U 5 U 5 U 5 U 5 U 5 U 5 U 5 U

MW-13C 46.7 5 U 5 U 5 U 5 U 5 U 5 U 5 U 5 U
Comparison of Diffusion-Sampler Results to Bladder-Pump Results 

Table 6. Concentrations of benzene, ethylbenzene, toluene, and total xylenes in water from diffusion and low-flow 

sampling, Naval Air Station North Island, California, January 2000—Continued

[μg/L, micrograms per liter; U, value was below the analytical quantitation limit; J, estimated value; NA, not applicable; *, sample collected b

using bladder pump; #, data from OHM Remediation Services Corporation (2000)]

Well Depth

(feet)

Benzene 

(μg/L)

Ethylbenzene 

(μg/L)

Toluene 

(μg/L)

Total xylenes 

(μg/L)

Diffusion Low flow Diffusion Low flow Diffusion Low flow Diffusion Low flow

MW-13C 48.1 5 U 5 U 5 U 5 U 5 U 5 U 5 U 5 U

MW-13C*# 46.0 NA 5 U NA 5 U NA 5 U NA 5 U

MW-68A 21.7 25 U 5 U 25 U 5 U 25 U 5 U 25 U 5 U

MW-68A 23.0 50 U 5 U 50 U 5 U 50 U 5 U 50 U 5 U

MW-68B 34.5 250 U 5,000 U 250 U 5,000 U 250 U 5,000 U 250 U 5,000 U

MW-68B 37.0 5,000 U 5,000 U 5,000 U 5,000 U 5,000 U 5,000 U 5,000 U 5,000 U

MW-68B 38.5 5,000 U 5,000 U 5,000 U 5,000 U 5,000 U 5,000 U 5,000 U 5,000 U

MW-68C 56.0 50 U 50 U 50 U 50 U 50 U 50 U 50 U 50 U

MW-68C 57.5 100 U 50 U 100 U 50 U 100 U 50 U 100 U 50 U

MW-68C 59.0 250 U 12 J 250 U 50 U 250 U 50 U 250 U 50 U

MW-68C2 37.3 1,000 U 500 U 1,000 U 500 U 1,000 U 500 U 1,000 U 500 U

MW-68C2 39.1 2,500 U 2,500 U 2,500 U 2,500 U 2,500 U 2,500 U 2,500 U 2,500 U

MW-68C2 40.5 5,000 U 2,500 U 5,000 U 2,500 U 5,000 U 2,500 U 5,000 U 2,500 U

MW-68C2 42.1 10,000 U 2,500 U 10,000 U 2,500 U 10,000 U 2,500 U 10,000 U 2,500 U

MW-68C2 44.2 10,000 U 2,500 U 10,000 U 2,500 U 10,000 U 2,500 U 10,000 U 2,500 U

MW-68C2 46.1 10,000 U 1,000 U 10,000 U 1,000 U 10,000 U 1,000 U 10,000 U 1,000 U

MW-68C2 47.9 10,000 U 5,000 U 10,000 U 5,000 U 10,000 U 5,000 U 10,000 U 5,000 U

MW-68C2 49.9 10,000 U 2,500 U 10,000 U 2,500 U 10,000 U 2,500 U 10,000 U 2,500 U

MW-68C2 52.0 2,500 U 2,500 U 2,500 U 2,500 U 2,500 U 2,500 U 2,500 U 2,500 U

MW-68C2 53.9 1,000 U 2,500 U 1,000 U 2,500 U 1,000 U 2,500 U 1,000 U 2,500 U

MW-68C2 55.6 500 U 1,000 U 500 U 1,000 U 500 U 1,000 U 500 U 1,000 U

MW-68C2 57.5 500 U 500 U 500 U 500 U 500 U 500 U 500 U 500 U

MW-68C2 59.5 500 U 500 U 500 U 500 U 500 U 500 U 500 U 500 U

MW-68C2 61.5 500 U 500 U 500 U 500 U 500 U 500 U 500 U 500 U

PW-15 25.4 4 J 2 J 16 9 7 3 J 75 28

PW-15 27.1 3 J 3 J 15 3 J 5 J 5 U 52 7

PW-15 28.5 100 U 250 U 100 U 250 U 100 U 250 U 100 U 250 U

PW-15 30.2 250 U 500 U 250 U 500 U 250 U 500 U 250 U 500 U

PW-15 31.8 500 U 500 U 500 U 500 U 500 U 500 U 500 U 500 U

PW-15 33.2 500 U 500 U 500 U 500 U 500 U 500 U 500 U 500 U

PW-55 27.1 2,500 U 2,500 U 2,500 U 2,500 U 2,500 U 2,500 U 2,500 U 2,500 U

PW-55 28.9 2,500 U 2,500 U 2,500 U 2,500 U 2,500 U 2,500 U 2,500 U 2,500 U

PW-55 30.6 2,500 U 2,500 U 2,500 U 2,500 U 2,500 U 2,500 U 2,500 U 2,500 U
16 Diffusion Sampler Testing at Naval Air Station North Island,

San Diego County, California, November 1999 to January 2000

20 percent, the concentrations obtained using the diffusion samplers were slightly higher than those concentrations obtained using the bladder pump. The 

concentrations obtained using the diffusion samplers 

in well MW-13B were slightly higher, but similar to 

the concentrations obtained using the peristaltic pump 

(fig. 3). Concentrations of toluene and total xylenes 

were present in water obtained from both the diffusion 

samplers and the peristaltic pump (fig. 3); toluene and 

total xylenes were not detectable (less than 5 μg/L) in 

water from the bladder pump. The data suggest that 

the diffusion samplers performed equally well with the 

bladder pump in wells MW-13A and MW-13B for 

cDCE. The higher concentrations of vinyl chloride, 

toluene, and total xylenes in water from the diffusion 

samplers relative to water from the bladder pump indicate that the diffusion samplers obtained more discrete 

samples from these wells; however, disturbing the well 

water by using the peristaltic pump and removing the 

diffusion samplers prior to sampling with th

pump may have induced mixing and affecte

ity of the water sampled by the bladder pum

Comparison of Diffusion-Sampler Re

Peristaltic-Pump Results

The remaining comparisons between diffusi

pler and low-flow sampler methods utilized 

diffusion-sampling and low-flow sampling p

within screened intervals. At most depths, lo

sampling was conducted by using peristaltic 

contrast to bladder pumps, using peristaltic 

some wells potentially could cause degassin

ples during recovery, which could result in u

mating actual VOC concentrations. Thus, VO

concentrations in water obtained using peris

Table 6. Concentrations of benzene, ethylbenzene, toluene, and total xylenes in water from diffusion and lo

flow sampling, Naval Air Station North Island, California, January 2000—Continued

[μg/L, micrograms per liter; U, value was below the analytical quantitation limit; J, estimated value; NA, not applicable; *, sample coll

by using bladder pump; #, data from OHM Remediation Services Corporation (2000)

Well Depth

(feet)

Benzene 

(μg/L)

Ethylbenzene 

(μg/L)

Toluene 

(μg/L)

Total xylenes 

(μg/L)

Diffusion Low flow Diffusion Low flow Diffusion Low flow Diffusion Low fl

PW-55 31.9 2,500 U 2,500 U 2,500 U 2,500 U 2,500 U 2,500 U 2,500 U 2,500 U

PW-55 33.1 2,500 U 2,500 U 2,500 U 2,500 U 2,500 U 2,500 U 2,500 U 2,500 U

PW-66 25.5 1,000 U 500 U 1,000 U 500 U 1,000 U 500 U 1,000 U 500 U

PW-66 27.3 500 U 500 U 500 U 500 U 500 U 500 U 500 U 500 U

PW-66 29.1 50 U 500 U 50 U 500 U 50 U 500 U 50 U 500 U

PW-66 30.8 25 U 500 U 25 U 500 U 25 U 500 U 25 U 500 U

PW-66 32.3 5 U 500 U 5 U 500 U 5 U 500 U 5 U 500 U

PW-66 33.9 5 U 500 U 5 U 500 U 5 U 500 U 5 U 500 U

S2-MW-6A 6.5 5 U 5 U 5 U 5 U 5 U 5 U 5 U 5 U

S2-MW-6A 7.9 5 U 5 U 5 U 5 U 5 U 5 U 5 U 5 U

S2-MW-6A 9.2 5 U 5 U 5 U 5 U 5 U 5 U 5 U 5 U

S2-MW-6A 10.6 5 U 5 U 5 U 5 U 5 U 5 U 5 U 5 U

S2-MW-6A 12.0 5 U 5 U 5 U 5 U 5 U 5 U 5 U 5 U

S2-MW-6A 13.3 5 U 5 U 5 U 5 U 5 U 5 U 5 U 5 U

S2-MW-6A 14.7 5 U 5 U 5 U 5 U 5 U 5 U 5 U 5 U

S2-MW-6A 16.1 5 U 5 U 5 U 5 U 5 U 5 U 5 U 5 U

S2-MW-6A 17.5 5 U 5 U 5 U 5 U 5 U 5 U 5 U 5 U

S2-MW-6A 19.0 5 U 5 U 5 U 5 U 5 U 5 U 5 U 5 U
Comparison of Diffusion-Sampler Results to Peristaltic-Pump Results 

Table 7. Comparison of concentrations of selected volatile organic compounds in water from a diffusion 

sampler and in water from low-flow purging using a bladder pump at the same depth, Naval Air Station North 

Island, California, January 2000

[*, average percent difference; -, concentration measured in diffusion sampler was lower than concentration measured in low-flow

sample]

Constituent

Diffusion samples Low-flow bladder-pump samples

Percent 

difference

Depth, in feet 

below land 

surface

Concentration, 

in micrograms 

per liter

Depth, in feet 

below land 

surface

Concentration, 

in micrograms 

per liter

Well MW-9

1,1-Dichloroethene 

(1,1-DCE)

31 4,000 31 3,500 2.0

Tetrachloroethene (PCE) 31 260 31 330 -21.0

Trichloroethene (TCE) 31 3,300 31 3,200 3.0

Well MW-5

Trichloroethene (TCE) 55.75 360 55.75 280, 320 17*

Well MW-12

cis-1,2-Dichloroethene 

(cDCE) 

35.1 100 35.1 450 -78

Trichloroethene (TCE) 35.1 1,800 35.1 2,100 -14

Well MW-13A

cis-1,2-Dichloroethene 

(cDCE) 10.9 - 12.4 46 - 74 12 61 Within range

Vinyl chloride 10.9 - 12.4 5 - 8 12 7.4 Within range

Well MW-13B

cis-1,2-Dichloroethene 

(cDCE) 24.85 - 26.15 3,100 - 2,600 26 3,100 Within range

Toluene 24.85 - 26.15 9 26 <5 Not applicable

Total xylenes 24.85 - 26.15 111 - 110 26 <5 Not applicable

Vinyl chloride 24.85 - 26.15 1,900 - 2,000 26 1,600 18*

pumps may be representative of concentrations in 

ground water at some wells but may underestimate 

actual concentrations in ground water at other wells. 

Moreover, when multiple depths within a screened 

interval are purged using low-flow methods, there is a 

potential for each low-flow sampling event to disturb 

the equilibrated water column. If the pumping rate 

during low-flow sampling is low enough to prevent 

drawdown in the well, then all of the pumped water is 

replaced by ground water from the aquifer; however, 

the zone of influence contributing water to the well 

may not be adjacent to the pump. Thus, in a chemically stratified screened interval where multiple depth 

intervals are sequentially sampled, water entering the 

well screen from early low-flow samplings may influence concentrations obtained in later samplings as a 

result of vertical transport and mixing in the well 

screen. Despite these uncertainties, the use of 

multiple-level low-flow sampling methods using 

peristaltic pumps sometimes can provide an estima

of contaminant vertical distribution in the screened 

interval, which can be used as a comparison for the 

diffusion samplers. 

In most of the observation wells, the vertical 

concentration gradients obtained using the diffusio

sampler and low-flow sampler methods were simil

However, in several cases, the concentrations in wa

obtained by using the peristaltic pump were lower th

the concentrations in water obtained by using the d

fusion samplers (figs. 4, 5, and 6). An example of t

is TCE concentrations measured in water from wel

MW-68A, MW-68B, and MW-68C. TCE concentra

tions were approximately 43 to 73 percent lower in 

water samples collected by using low-flow samplin

methods and peristaltic pumps than in samples collected by the diffusion samplers. This substantial d

ference in concentrations between the two methods 

expected if VOCs were lost by degassing as a resul
18 Diffusion Sampler Testing at Naval Air Station North Island,

San Diego County, California, November 1999 to January 2000

0 2,000 4,000 6,000 8,000 10,000

30

32

34

36

38

40

0 1,000 2,000 3,000

30

32

34

36

38

40

0 2,000 4,000 6,000 8,000 10,000

30

32

34

36

38

40

J

J

J

0 400 800 1,200 1,600 2,000

30

32

34

36

38

40

DEPTH BELOW TOP OF CASING, IN FEET DEPTH BELOW TOP OF CASING, IN FEET 

DEPTH BELOW TOP OF CASING, IN FEET DEPTH BELOW TOP OF CASING, IN FEET 

1,1-DICHLOROETHANE CONCENTRATION,

IN MICROGRAMS PER LITER

1,1-DICHLOROETHENE CONCENTRATION,

IN MICROGRAMS PER LITER

cis-1,2-DICHLOROETHENE CONCENTRATION,

IN MICROGRAMS PER LITER

TRICHLOROETHENE CONCENTRATION,

IN MICROGRAMS PER LITER

DIFFUSION SAMPLE

LOW-FLOW PERISTALTIC-

 PUMP SAMPLE

LOW-FLOW BLADDER-PUMP

 SAMPLE

EXPLANATION

Figure 2. Comparison of diffusion and low-flow samples in ground water at well MW-12,

Naval Air Station North Island, California, January 2000.
Comparison of Diffusion-Sampler Results to Peristaltic-Pump Results 

using peristaltic pumps or if mixing in the well screens 

occurred during pumping. The vertical concentration 

distribution between the two methods implies that the 

VOC concentrations measured in water from diffusion 

samplers reflected the vertical distribution of contaminants in the aquifer adjacent to the screened interval 

more accurately than the peristaltic-pump sampling.

Further comparison of TCE concentration data 

from the two sampling methods indicates that diffusion sampling provides a point sample, whereas 

sequential low-flow sampling of multiple horizons 

within a single well screen can induce mixing. In general, the vertical sequence of low-flow sampling in the 

wells began with the shallowest depth interval and 

ended with the deepest interval. In well PW-66, TCE 

data show that concentrations in water collected with a 

diffusion sampler were highest in the shallowest sampled depth, and then decreased sharply over the 5-ft 

depth interval below this shallowest depth (fig. 7). 

Although the highest TCE concentration ob

low-flow sampling also was at the shallowe

it was approximately 24 percent lower than 

centration obtained from the corresponding 

sampler, and the vertical stratification was l

defined. These data suggest that as low-flow 

with a peristaltic pump progressed vertical

ward, the pumping gradually mixed the TC

nated water from the shallowest sampling d

water from deeper intervals, thus obscuring 

nal contaminant stratification (fig. 7). 

A similar effect can be seen in the da

wells MW-12 and PW-15 (figs. 2 and 8). A

wells, the shallowest interval was relatively 

inated. The comparison between diffusion 

and low-flow samples at this shallowest de

a relatively close match between cDCE and 

centrations. However, as sampling progress

vertically downward toward the interface o

CONCENTRATION, IN MICROGRAMS PER LITER

1 10 100 1,000 10,000

24

25

26

27

28

EXPLANATION

DEPTH BELOW TOP OF CASING, IN FEET 

LOW-FLOW

BLADDERPUMP SAMPLE

DIFFUSION

SAMPLE

LOW-FLOW

PERISTALTICPUMP SAMPLE

NOT DETECTED

NOT DETECTED

cis-1,2-DICHLOROETHENE

TOLUENE

TOTAL XYLENES

VINYL CHLORIDE

Figure 3. Comparison of diffusion and low-flow samples in ground water at

well MW-13B, Naval Air Station North Island, California, January 2000.
20 Diffusion Sampler Testing at Naval Air Station North Island,

San Diego County, California, November 1999 to January 2000

stratified contamination, the low-flow sample concentrations generally increased higher than the diffusionsample concentrations, which is to be expected if the 

zone of influence for the low-flow pumping captured 

the more contaminated ground water in the well. In 

general, the data suggest that diffusion sampling provides a more precise delineation of the contaminant 

stratification within the screened interval than lowflow sampling.

Insight into the use of diffusion samplers in a 

chemically stratified screened interval can be observed 

in the data from wells at the MW-68 cluster (figs. 6D 

and 6E). Unlike the other wells, two peristaltic pumps 

were used to low-flow sample well MW-68C2. Starting simultaneously from both the uppermost and the 

lowermost sample depths, sampling progressed 

sequentially toward the center of the 25-ft screened 

interval. Results from both the diffusion samples and 

the low-flow samples showed that the uppermost and 

lowermost parts of the screened interval were relatively uncontaminated. Concentration data from the 

diffusion samples show that substantially hi

concentrations occurred between depths of a

mately 40 to 50 ft, with a sharp peak at abou

(fig. 6D). Thus, the first water pulled into th

screen from both ends of the screen was rela

uncontaminated. As the low-flow sampling p

toward the center of the screened interval, th

tion between concentrations obtained from t

sion samples began to differ substantially fr

obtained by low-flow sampling (fig. 6D). Be

depths of approximately 40 to 50 ft, TCE co

tions from low-flow sampling were approxim

to 84 percent lower than TCE concentration

fusion samplers; additionally, the low-flow s

data did not indicate a TCE peak concentrat

depth of 42 ft as shown by the diffusion samp

A probable explanation for the concentratio

ences between the two methods is that initia

tively uncontaminated water was pumped in

screened interval, thus mixing the ground w

well and diluting concentrations of TCE. As 

0 10,000 20,000 30,000 40,000 50,000

26

27

28

29

30

31

32

33

34

DEPTH BELOW TOP OF CASING, IN FEET 

CONCENTRATION, IN MICROGRAMS PER LITER

EXPLANATION

DIFFUSION

SAMPLE

LOW-FLOW

SAMPLE

cis-1,2-DICHLOROETHENE

TRICHLOROETHENE

Figure 4. Comparison of diffusion and low-flow samples in ground water at

well PW-55, Naval Air Station North Island, California, January 2000.
Comparison of Diffusion-Sampler Results to Peristaltic-Pump Results 

0 50 100 150 200 250 300

50

52

54

56

58

60

0 2,000 4,000 6,000

50

52

54

56

58

60

0 20 40 60 80 100 120 140

50

52

54

56

58

60

0 400 800 1,200

50

52

54

56

58

60

U

U

U

U

DEPTH BELOW TOP OF CASING, IN FEET DEPTH BELOW TOP OF CASING, IN FEET 

DEPTH BELOW TOP OF CASING, IN FEET 

DEPTH BELOW TOP OF CASING, IN FEET 

DIFFUSION SAMPLE

LOW-FLOW PERISTALTIC-

 PUMP SAMPLE

LOW-FLOW BLADDER-PUMP

 SAMPLE

VALUE WAS BELOW THE ANALYTICAL

 QUANTITATION LIMIT

EXPLANATION

Figure 5. Comparison of diffusion and low-flow samples in ground water at

well MW-5, Naval Air Station North Island, California, January 2000.

1,1-DICHLOROETHANE

CONCENTRATION, IN

MICROGRAMS PER LITER

1,1-DICHLOROETHENE

CONCENTRATION, IN

MICROGRAMS PER LITER

cis-1,2-DICHLOROETHENE

CONCENTRATION, IN

MICROGRAMS PER LITER

TRICHLOROETHENE

CONCENTRATION,

IN MICROGRAMS PER LITER
Diffusion Sampler Testing at Naval Air Station North Island,San Diego County, California, November 1999 to January 2000

MW-68 well cluster

25

30

35

40

45

50

55

60

65

70

Diffusion

Samples

MW-68C

Well Log

Sand

Clay

Sand

Silt

MW-68A

22

23

24

MW-68B

33

34

35

36

37

38

39

40

41

MW-68C

56

58

60

62

MW-68C2

40

45

50

55

60

65

70

A. D. B. C. E.

0 500 1,000 0 60,000 120,000 0 2,000 4,000 0 100,000 200,000 0 100,000 200,000

DEPTH BELOW TOP OF CASING, IN FEET 

TRICHLOROETHENE CONCENTRATION, IN MICROGRAMS PER LITER

Figure 6. Comparison of diffusion and low-flow samples in ground water at wells (A) MW-68A, (B) MW-68B, (C) MW-68C, and

(D) MW-68C2, and (E) comparison of diffusion samples from multiple wells to geologic log of well MW-68C, Naval Air Station

North Island, California, January 2000.

DIFFUSION

 SAMPLE

LOW-FLOW

 SAMPLE

DEDICATED

 PUMP

 SAMPLE

DIFFUSION

 SAMPLE

LOW-FLOW

 SAMPLE

DEDICATED

 PUMP

 SAMPLE

DIFFUSION

 SAMPLE

LOW-FLOW

 SAMPLE

DEDICATED

 PUMP

 SAMPLE

DIFFUSION

 SAMPLE

LOW-FLOW

 SAMPLE

MW68C2

MW68A

MW68B

MW68C
Comparison of Diffusion-Sampler Results to Peristaltic-Pump Results 

0 2,000 4,000 6,000 8,000 10,000 12,000 14,000 16,000 18,000

24

26

28

30

32

34

36

DIFFUSION SAMPLE

LOW-FLOW PERISTALTIC

 PUMP SAMPLE

DEPTH BELOW TOP OF CASING, IN FEET 

TRICHLOROETHENE CONCENTRATION, IN MICROGRAMS PER LITER

Figure 7. Comparison of trichloroethene concentrations in diffusion and

low-flow samples in ground water at well PW-66, Naval Air Station

North Island, California 2000.

0 2,000 4,000 6,000 8,000

24

26

28

30

32

34

0 500 1,000 1,500 2,000 2,500 3,000 3,500

24

26

28

30

32

34

EXPLANATION

DIFFUSION SAMPLE

LOW-FLOW SAMPLE

cis-1,2-DICHLOROETHENE

CONCENTRATION, IN

MICROGRAMS PER LITER

TRICHLOROETHENE CONCENTRATION,

IN MICROGRAMS PER LITER

DEPTH BELOW TOP OF CASING, IN FEET 

DEPTH BELOW TOP OF CASING, IN FEET 

Figure 8. Comparison of diffusion and low-flow samples in ground water at

well PW-15, Naval Air Station North Island, California, January 2000.
24 Diffusion Sampler Testing at Naval Air Station North Island,

San Diego County, California, November 1999 to January 2000

TCE concentrations were lowered in ground water collected from subsequently sampled depths. Additional 

VOC losses by degassing during the use of peristaltic 

pumps probably resulted in further concentration differences between the two sampling methods.

TCE concentration data in diffusion samplers 

collected from wells MW-68B and MW-68C and concentration data in diffusion samplers collected from 

adjacent well MW-68C2 support the vertical distribution indicated by the diffusion samplers in well 

MW-68C2 (figs. 6B, 6C, and 6D). Diffusion samplers 

from well MW-68C2 indicate that the lowest concentrations in the screened interval are below a depth of 

approximately 55 ft, and the detected concentrations 

are similar to those from the same depth in the adjacent well MW-68C (fig. 6E). 

Similarly, diffusion samplers from wells 

MW-68C2 and MW-68B both indicate TCE concentrations increasing with depth between approximately 

35 and 40 ft (fig. 6E). The TCE concentrations in diffusion samples from well MW-68B are higher than 

those from the corresponding depth in well MW-68C2 

(fig. 6E). The reasons for the concentration difference 

between wells MW-68C2 and MW-68B are not 

known; however, two explanations can be postulated. 

One explanation is that the contaminant concentrations in well MW-68C2 may have been shifted downward as a result of a vertical hydraulic gradient within 

the well. Water-level measurements are not shown for 

well MW-68C2 because they would reflect only compositing across the screened interval; however, evidence for such a hydraulic gradient can be seen in the 

water-level data for wells MW-68B and MW-68C. The 

water level in well MW-68B is 0.34 ft higher than the 

water level in well MW-68C, indicating a net downward hydraulic gradient between the two depths (table 

1). Water levels remeasured in March 2000 confirmed 

the hydraulic gradient. Because well MW-68C2 is 

only about 5 ft from wells MW-68B and MW-68C, 

and because the screened interval of well MW-68C2 

hydraulically connects the depths sampled by wells 

MW-68B and MW-68C, the probability is high that 

there also is a downward hydraulic gradient within 

well MW-68C2. An alternative explanation is that 

lithologic heterogeneities in the screened zone place 

the contamination at slightly different depths in different wells. Evidence for such heterogeneity is the clay 

layer at a depth of 37.5 to 40 ft in well MW-68C 

(driller's log, Richard Wong, OHM Remediation, written commun., 2000). Despite the uncertainty regarding 

concentration differences between wells, the 

samplers appear to have been successful in a

mately locating the zone of highest concentr

between the depths of 37 to 52 ft (fig. 6E).

VOC concentrations in water collecte

well MW-13A varied less and generally wer

for peristaltic pump sampling compared to d

sampling (fig. 9). Following low-flow sampl

a peristaltic pump, well MW-13A was imme

resampled by low-flow sampling using a bla

pump. Although subject to the same mixing 

as the peristaltic pump, the bladder pump ha

potential for volatilization loss than the peri

pump, and thus, probably provides a more r

tive sample than the peristaltic pump. The c

tions of cDCE and TCE in water obtained u

flow sampling methods with a bladder pump 

mated the average of concentrations obtaine

from the diffusion samplers directly above a

the bladder pump (fig. 8). These findings su

data obtained by using the diffusion sampler

depth-specific VOC concentrations while th

from low-flow sampling represented a mixin

waters in well MW-13A.

In well MW-10, low-flow peristaltic-p

pling detected low concentrations (30 μg/L 

TCE, whereas diffusion sampling detected n

(table 5). This difference in concentrations i

because the potential for volatilization loss u

peristaltic pump usually results in underestim

ambient concentrations, while diffusion sam

capable of producing representative samples 

low (less than 20 μg/L) concentrations. Acc

historical data (OHM Remediation Services 

tion, 2000), TCE has never previously been d

well MW-10 (sampling dates July 1998, Ma

June 1999, and September 1999). Furthermo

mpling of the well using low-flow methodol

multiple horizons in February 2000 also sho

TCE was not present. Thus, it seems that the 

samplers accurately reflected VOC concentr

ground water; the source of low TCE concen

found in water obtained from low-flow, peri

pump sampling is unknown, but may repres

cross-contamination source not related to loc

water.

Wells S2-MW-06A and MW-13C con

detectable VOCs (less than 5 μg/L) in water 

either the diffusion samples or from the low

samples. Thus, the construction materials us
Contaminant Stratification in Well Screens 

diffusion samplers did not contribute contaminants to 

the water.

Diffusion Samplers in Free-Phase Fuel

The diffusion samplers deployed in buckets containing free-phase JP-5 and Stoddard solution from 

wells MW-11 and PW-17 did not show evidence of 

structural integrity loss during the 2 months of equilibration. The VOCs detected in the free-phase fuel also 

were detected in the water from the diffusion samplers 

(table 8). The VOC concentrations in water from the 

diffusion samplers were lower than the VOC concentrations in the fuel; however, this is to be expected 

because the first is an aqueous solution and the second 

is an organic solvent concentration. The diffusion samplers provided an alternative method for showing that 

the free-phase fuel in ground water from well MW

also contained TCE (table 5).

Contaminant Stratification in Well Screen

The data from this investigation show that 

stantial stratification of VOCs can be present with

10-ft well screen. At four observation wells (MW

MW-5, PW-66, and PW-15), the data showed a sh

layering of VOCs within the screened interval (fig

5, 7, and 8). The diffusion-sampler data show tha

vertical change in TCE concentrations over a dist

of about 5 ft was approximately 17,500 μg/L in w

PW-66, approximately 7,300 μg/L in well PW-15

approximately 5,900 μg/L in well MW-12. At we

MW-5, the 1,1-DCE concentration changed by 

3,410 μg/L, and the TCE concentration changed 

0 20 40 60 100 80

6

7

8

9

10

11

12

13

Diffusion sample

not completely

submerged

EXPLANATION

LOW-FLOW

BLADDERPUMP SAMPLE

DIFFUSION

SAMPLE

LOW-FLOW

PERISTALTICPUMP SAMPLE

cis-1,2-DICHLOROETHENE

VINYL CHLORIDE

DEPTH BELOW TOP OF CASING, IN FEET 

CONCENTRATION, IN MICROGRAMS PER LITER

Figure 9. Comparison of diffusion and low-flow samples in ground water well

MW-13A, Naval Air Station North Island California, January 2000.
26 Diffusion Sampler Testing at Naval Air Station North Island,

San Diego County, California, November 1999 to January 2000

1,145 μg/L over a vertical distance of about 7 ft 

(fig. 5). The concentrations decreased with depth at 

some wells [MW-5 and PW-66 (figs. 5 and 7, respectively)] and increased with depth at others [MW-12 

and PW-15 (figs. 2 and 8, respectively)].

The presence of contaminant stratification in 

well screens has importance for ground-water sampling. In an environment with a sharp concentration 

gradient, small disturbances in the water column can 

obscure the stratification. Thus, small amounts of mixing during low-flow sampling can result in large variations in VOC concentrations from pumped samples. 

In addition, the potential for stratification is an 

important consideration when selecting a sampling 

depth. For example, the data indicate that if the dedicated bladder pump at well MW-12 had been set about 

3 ft deeper, the pump would have been in contact with 

water containing approximately 6,000 μg/L more TCE 

than was present at the original sampling depth. If the 

dedicated bladder pump at well MW-5 had been set 

about 3 ft shallower, the pump would have been in 

contact with water containing approximately 690 μg/L 

higher concentrations of TCE. This consideration is 

even more important for diffusion samplers, which 

sample only the water in the immediate vicinity of the 

sampler. Therefore, when using diffusion samplers in a 

well where chemical stratification is suspected within 

the screened interval, multiple diffusion samplers can 

be used to at least initially delineate the stra

Analytical costs during such an investigation 

minimized by using field gas chromatograph

delineate the stratification and to select parti

ples for more detailed laboratory analyses. 

SUMMARY

The ground-water VOC concentration

by using water-filled polyethylene diffusion 

were compared to the ground-water VOC co

tions obtained by using low-flow sampling m

with a peristaltic pump and dedicated bladd

in observation wells at Naval Air Station No

California. Comparisons of VOC concentrat

obtained by using bladder pumps and diffus

plers showed a generally good correlation. C

tions of 1,1-dichloroethene (1,1-DCE) and 

trichloroethene (TCE) in ground water obtai

well MW-9 obtained using the diffusion sam

agreed well (12 and 3 percent difference, res

with those samples obtained using the bladd

At well MW-5, the TCE concentration in wa

the diffusion sampler was higher than in wa

the bladder pump, implying that the sample 

by the bladder pump may have underestima

concentrations as a result of mixing. Similar

Table 8. Concentrations of selected volatile organic compounds in free-phase jet fuel (JP-5) removed from ground 

in water from diffusion samplers deployed in a bucket containing the free-phase fuel, Naval Air Station North Island

January 2000

[μg/L, micrograms per liter; J, estimated value; U, value was below the analytical quantitation limit]

Sample 

source

1,1-Dichloroethane 

(μg/L)

1,1-Dichloroethene 

(μg/L)

cis-1,2-Dichloroethene 

(μg/L)

Tetrachloroethene 

(μg/L)

Trichloroet

(μg/L)

Diffusion 

sampler 

water

Freephase 

fuel

Diffusion 

sampler 

water

Freephase 

fuel

Diffusion 

sampler 

water

Free-phase 

fuel

Diffusion 

sampler 

water

Free-phase 

fuel

Diffusion 

sampler 

water

Fr

Free product 

from well 

PW-17

4 J 5,000 U 5 U 5,000 U 3.9 J 5,000 U 5 U 5,000 U 2 J 

Free product 

from well 

MW-11

10 U 5,000 U 10 U 5,000 U 10 U 5,000 U 7 J 4,300 J 65 

Vinyl chloride

(μg/L)

Benzene 

(μg/L)

Ethylbenzene 

(μg/L)

Toluene 

(μg/L)

Total xyle

(μg/L)

Diffusion 

sampler 

wate

Freephase 

fuel

Diffusion 

sampler 

water

Freephase fuel

Diffusion 

sampler 

water

Free-phase 

fuel

Diffusion 

sampler 

water

Free-phase 

fuel

Diffusion 

sampler 

water

Fr

Free product 

from well 

PW-17

5 U 5,000 U 5,000 U 70 21,000 112 1,100 J 350 10

Free product 

from well 

MW-11

10 U 5,000 U 10 U 5,000 U 13 5,700 10 U 5,000 U 120 4
References 

higher concentrations of vinyl chloride, toluene, and 

total xylenes in water from the diffusion samplers in 

wells MW-13A and MW-13B compared to water from 

the bladder pump imply that the concentrations 

obtained by the bladder pump may have underestimated actual concentration as a result of mixing in 

these wells. Concentration differences between the 

diffusion sampling and bladder-pump sampling methods were noted in samples from well MW-12, and 

probably are related to mixing in a chemically stratified part of the screened interval. The findings of this 

investigation suggest that diffusion samplers provide a 

viable sampling alternative for VOCs in ground water 

in most tested wells at NAS North Island. 

Comparisons of volatile organic compound 

(VOC) concentrations in water obtained by using diffusion samplers to concentrations obtained by lowflow sampling using a peristaltic pump were used to 

gain information on the vertical distribution of contamination in the wells. In several wells, the probable 

effects of mixing or volatization during pumping 

resulted in lower VOC concentrations in water 

obtained by using the peristaltic pump compared to 

concentrations obtained by using the diffusion samplers; however, the data from the low-flow sampling 

supported the vertical VOC stratification identified by 

using the diffusion samplers.

Substantial VOC stratification was observed in 

the screened intervals of several observation wells 

(MW-12, MW-5, PW-15, and PW-66). The diffusionsampler data show that the vertical change in TCE 

concentrations over a distance of about 5 ft was 

approximately 17,500 μg/L in well PW-66, approximately 7,300 μg/L in well PW-15, and approximately 

5,900 μg/L in well MW-12. At well MW-5, the 

1,1-DCE concentration changed by 3,410 μg/L, and 

the TCE concentration changed by 1,145 μg/L over a 

vertical distance of about 7 ft. Concentrations 

decreased with depth at some wells (PW-66 and 

MW-5) and increased with depth at others (MW-12 

and PW-15). The presence of stratification in well 

screens is important for ground-water sampling 

because small disturbances in the water column can 

mix the stratification, resulting in large variations in 

VOC concentrations from pumped samples. The data 

imply that care must be exercised when selecting a 

sampling depth. When using diffusion samplers in a 

well where chemical stratification is suspected within 

the screened interval, multiple diffusion samplers can 

be used to at least initially delineate the stratification. 

Analytical costs during such an investigation can b

minimized by using field gas chromatography or 

indicator-tube technology to delineate the stratificat

and to select particular samples for more detailed la

ratory analyses. 

The diffusion samplers deployed in buckets c

taining free-phase JP-5 and Stoddard solution collected from observation wells did not show evidenc

of structural integrity loss during the 2 months of 

equilibration. The VOCs detected in the free-phase 

fuel also were detected in water from the diffusion 

samplers. 

REFERENCES

Gefell, M.J., Hamilton, L.A., and Stout, D.J., 1999, A co

parison between low-flow and passive-diffusion ba

sampling results for dissolved volatile organics in f

tured sedimentary bedrock: Proceedings of the Petr

leum and Organic Chemicals in Ground WaterPrevention, Detection, and Remediation Conferenc

November 17-19, 1999, Houston, Texas, p. 304-31

OHM Remediation Services Corporation, 2000, Quarter

ground water report, Table 1: Summary of ground 

water VOC analytical results - UST 653 - Decembe

1999/January 2000: Consultant's Report to U.S. Na

Facilities Command Southwest Division, 9 p.

U.S. Environmental Protection Agency, 1999, On-line S

846 methods: accessed December 21, 1999, at URL 

tap://search.epa.gov/epaoswer/hazwaste/test/

tx8xxx.htm#8XXX

Vroblesky, D.A., and Hyde, W.T., 1997, Diffusion samp

as an inexpensive approach to monitoring VOCs in 

ground water: Ground Water Monitoring and Reme

tion, v. 17, no. 3, p. 177-184

Vroblesky, D.A., Nietch, C.T., Robertson, J.F., Bradley, 

P.M., Coates, John, and Morris, J.T., 1999, Natural 

attenuation potential of chlorinated volatile organic 

compounds in ground water, TNX flood plain, Sav

nah River Site, South Carolina: U.S. Geological Su

vey Water-Resources Investigations Report 99-407

43 p.

Vroblesky, D.A., Rhodes, L.C., and Robertson, J.F., 199

Locating VOC contamination in a fractured-rock a

fer at the ground-water/surface-water interface usin

passive vapor collectors: Ground Water, v. 34, no. 2

p. 223-230.

Vroblesky, D.A., and Robertson, J.F., 1996, Temporal 

changes in VOC discharge to surface water from a 

fractured rock aquifer during well installation and 

operation, Greenville, South Carolina: Ground Wat

Monitoring and Remediation, v. 16, no. 3, p. 196-2

Vroblesky and Peters - DIFFUSION SAMPLER TESTING AT NAVAL AIR STATION NORTH ISLAND,

SAN DIEGO COUNTY, CALIFORNIA, NOVEMBER 1999 TO JANUARY 2000

USGS WRIR 00-4182