Passive Sampling of Groundwater Wells for Determination of 

Water Chemistry

Chapter 8 of

Section D. Water Quality

Book 1. Collection of Water Data by Direct Measurement

Techniques and Methods 1–D8

U.S. Department of the Interior

U.S. Geological Survey
A

F

G

H

B C D E

Cover. (A) Figure 15 from report, AGI Sample Module®. Photograph from Mark Arnold, Amplified Geophysical Imaging, LLC. 

(B) Figure 11A from report, an EON Products, Inc. Dual Membrane (DM) sampler®. Photograph by Bradley P. Varhol, EON Products, Inc. 

(C) Figure 7B from report a 2.5-inch-diameter regenerated cellulose dialysis membrane sampler with external supports after assembly. 

Photograph by Thomas E. Imbrigiotta, U.S. Geological Survey. (D) Figure 17A from report, A downhole semi-permeable membrane 

device (SPMD) sampler. Photograph and diagram by David A. Alvarez, U.S. Geological Survey. (E) A series of nylon screen samplers 

retrieved from a profile of the water column of a well showing capped bottles and the removed tops. The variation of iron-staining on the 

removed tops indicates stratified flow with different redox conditions occurs under ambient flow conditions in the well. Photograph by 

Philip T. Harte, U.S. Geological Survey. (F) Figure 5A from report, a polyethylene diffusion bag sampler. Photograph by Bradley P. Varhol, 

EON Products, Inc. (G) Figure 9 from report, a rigid porous polyethylene sampler, without protective mesh and with protective mesh, in a 

water-filled tube for shipment. Photographs by Leslie Venegas, ALS Global. (H) Figure 13A from report, QED Environmental Systems, Inc. 

Snap Sampler® with volatile organic compound bottle (40-milliliter vial). Photograph by Sanford Britt, QED Environmental Systems, Inc.
Passive Sampling of Groundwater Wells for 

Determination of Water Chemistry

By Thomas E. Imbrigiotta and Philip T. Harte

Chapter 8 of

Section D. Water Quality

Book 1. Collection of Water Data by Direct Measurement

Techniques and Methods 1–D8

U.S. Department of the Interior

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

DAVID BERNHARDT, Secretary

U.S. Geological Survey

James F. Reilly II, Director

U.S. Geological Survey, Reston, Virginia: 2020

For more information on the USGS—the Federal source for science about the Earth, its natural and living 

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Although this information product, for the most part, is in the public domain, it also may contain copyrighted materials 

as noted in the text. Permission to reproduce copyrighted items must be secured from the copyright owner.

Suggested citation:

Imbrigiotta, T.E., and Harte, P.T., 2020, Passive sampling of groundwater wells for determination of water chemistry: 

U.S. Geological Survey Techniques and Methods, chap. 8, section D, book 1, 80 p., https://doi.org/10.3133/tm1d8.

ISSN 2328-7055 (online)
iii

Contents

1.0 Introduction...............................................................................................................................................1

2.0 Overview of Groundwater Sampling ....................................................................................................2

2.1 Purge Methods................................................................................................................................2

2.1.1 Three-Well-Volume Purge.................................................................................................2

2.1.2 Low-Flow Purge ..................................................................................................................3

2.1.3 Field Physical and Chemical Characteristics Stabilization..........................................3

2.2 Passive Sampling............................................................................................................................3

3.0 Theory and Principles of Passive Sampling........................................................................................4

3.1 Kinetic and Equilibrium Sampling Regimes................................................................................4

3.2 Diffusive Chemical Exchange .......................................................................................................5

3.3 Well Communication and Hydraulics ..........................................................................................6

3.4 Sampler Materials and Constituents Sampled ..........................................................................6

3.5 Equilibration and Exposure Time..................................................................................................7

3.6 Common Advantages and Limitations of Passive Samplers ...................................................7

3.6.1 Advantages..........................................................................................................................7

3.6.2 Limitations............................................................................................................................9

4.0 Types of Passive Samplers.....................................................................................................................9

4.1 Polyethylene Diffusion Bag (PDB) Sampler .............................................................................10

4.1.1 Description and Operation ..............................................................................................10

4.1.2 Advantages and Limitations............................................................................................11

4.2 Regenerated Cellulose Dialysis Membrane (RCDM) Sampler..............................................11

4.2.1 Description and Operation ..............................................................................................13

4.2.2 Advantages and Limitations............................................................................................15

4.3 Rigid Porous Polyethylene (RPP) Sampler ...............................................................................15

4.3.1 Description and Operation ..............................................................................................15

4.3.2 Advantages and Limitations............................................................................................16

4.4 Nylon Screen (NS) Sampler........................................................................................................16

4.4.1 Description and Operation ..............................................................................................16

4.4.2 Advantages and Limitations............................................................................................16

4.5 EON Dual Membrane (DM) Sampler®......................................................................................17

4.5.1 Description and Operation ..............................................................................................17

4.5.2 Advantages and Limitations............................................................................................19

4.6 QED Snap Sampler®....................................................................................................................19

4.6.1 Description and Operation ..............................................................................................19

4.6.2 Advantages and Limitations............................................................................................20

4.7 AGI Sample Module®..................................................................................................................21

4.7.1 Description and Operation ..............................................................................................21

4.7.2 Advantages and Limitations............................................................................................22

4.8 Semi-Permeable Membrane Device (SPMD) Samplers ........................................................22

4.8.1 Description and Operation ..............................................................................................22

4.8.2 Advantages and Limitations............................................................................................22

4.9 Other Equilibrium-Membrane-Type Samplers ........................................................................22

4.10 Other Accumulation-Type Samplers........................................................................................23
iv

5.0 Considerations Prior to Use of Passive Diffusion Samplers...........................................................24

5.1 Data-Quality Objectives...............................................................................................................24

5.2 Hydraulic and Chemical Equilibration .......................................................................................24

5.3 Hydraulic and Hydrologic Well Considerations.......................................................................24

5.3.1 Geologic Formation ..........................................................................................................24

5.3.2 Age of the Well..................................................................................................................25

5.3.3 Monitoring History............................................................................................................25

5.3.4 Water Levels......................................................................................................................27

5.3.5 Well Construction .............................................................................................................27

5.4 Water-Quality Sampling Considerations...................................................................................27

5.4.1 Analyte Suitability Considerations.................................................................................27

5.4.2 Sampler-Size Considerations..........................................................................................28

5.4.3 Sampler-Depth Considerations ......................................................................................28

5.4.4 Equilibration Time and Exposure Time...........................................................................28

5.4.5 Sampler Hydration Considerations................................................................................29

5.4.6 Redox Considerations ......................................................................................................29

5.4.7 Biological Considerations ...............................................................................................30

5.4.8 Temperature and Density Effects...................................................................................30

5.5 Vertical Profiling............................................................................................................................30

5.5.1 Hydraulic-Flow Vertical Profiling ...................................................................................30

5.5.2 Chemical-Vertical Profiling .............................................................................................31

5.5.3 Profiling for Determining Deployment Depth ...............................................................31

5.5.4 Relation Between Borehole Flow and Water Chemistry ...........................................31

6.0 Decision Tools ........................................................................................................................................33

6.1 Passive Sampler Use....................................................................................................................33

6.2 Passive Sampler Capabilities .....................................................................................................33

6.3 Minimum Required Analytical Volumes ....................................................................................36

7.0 Sampler Deployment, Retrieval, and Sample Collection.................................................................38

7.1 Well Dimensions and Water Level.............................................................................................38

7.2 Installation of the Sampler..........................................................................................................38

7.3 Deployment Period .......................................................................................................................38

7.4 Sampler Retrieval..........................................................................................................................39

7.5 Sample Collection.........................................................................................................................39

7.6 Disposal and Decontamination ..................................................................................................40

8.0 Data Reporting Procedures .................................................................................................................40

9.0 Quality Assurance/Quality Control......................................................................................................40

9.1 Recommended QA/QC Samples.................................................................................................40

9.1.1 Deionized Water Source Blank ......................................................................................40

9.1.2 Equipment Blank and Field Blank...................................................................................41

9.1.3 Trip Blanks..........................................................................................................................42

9.1.4 Replicates...........................................................................................................................42

9.2 Acceptability of Passive Sampling Blanks and Replicate Variability...................................42

10.0 Data Evaluation ....................................................................................................................................42

10.1 Data Comparison.........................................................................................................................43

10.2 Potential Reasons for Differences between Purge and Passive Sampling Results........43
v

10.3 Potential Reasons for Differences Between Passive Sampler Replicate Samples ........46

10.4 Regulatory Acceptance for Switching from Purge Sampling to Passive Sampling........46

10.5 Cost Comparison Between Purge and Passive Sampling ...................................................46

Acknowledgments.......................................................................................................................................47

11.0 References Cited..................................................................................................................................47

Appendix A. Case Studies.......................................................................................................................56

Appendix B. Field Form for Deployment and Retrieval of Passive Samplers.................................72

Appendix C. Well Label for Deployed Passive Samplers...................................................................80

Figures

1. Diagram of passive sampling regimes......................................................................................4

2. Diagram of the chemical gradient across a membrane A, before equilibrium and 

B, after equilibrium.......................................................................................................................5

3. Diagram showing chemical gradient from the groundwater to the receiving phase

of the accumulation-type passive sampler..............................................................................6

4. Graph showing purge duration for 1- and 10-gallon-per-minute rates of pumping for

a 4-inch-diameter well.................................................................................................................8

5. Photographs of A, a polyethylene diffusion bag (PDB) sampler and B, a tripod used

for installation of PDB samplers in a well...............................................................................11

6. Diagram of multiple polyethylene diffusion bag samplers A, deployed in a well

screen under horizontal flow conditions, and B, multiple PDBs deployed under

complex vertical and horizontal groundwater flow conditions ..........................................12

7. Photographs of a 2.5-inch diameter regenerated cellulose dialysis membrane

sampler with external supports, A, prior to assembly, and B, after assembly.................13

8. Photographs of internal supports for regenerated cellulose dialysis membrane

samplers.......................................................................................................................................14

9. Photographs of a rigid porous polyethylene sampler A, without the protective

mesh, and B, with the protective mesh in a water-filled tube for shipment.....................15

10. Photographs of two different sized nylon-screen passive samplers A, V/A ratio of

6:1 and B, V/A ratio of 22:1.........................................................................................................17

11. Photographs of A, an EON Products, Inc. Dual Membrane (DM) sampler® and 

B, a vertical string of DM samplers being retrieved from a well........................................18

12. Diagram of an EON Products, Inc. Dual Membrane sampler® with large pore and

small pore membrane configurations .....................................................................................18

13. Photographs of the QED Environmental Systems, Inc. Snap Sampler® with A, a

volatile organic compound bottle (40-mL vial), and B, variously sized volatile organic

compound and inorganic constituent bottles ........................................................................19

14. Photographs of various views of the QED Environmental Systems, Inc. Snap

Sampler® operation in a well...................................................................................................20

15. Photograph of the AGI Sample Module® ..............................................................................21

16. Diagram of the installation of an AGI Sample Module® in a monitoring well .................21

17. Photograph of A, a downhole semi-permeable membrane device sampler and B, a

diagram of SPMD operation .....................................................................................................23

18. Diagrams showing hypothesized relation of passive sampler constituent

concentration responses to rates of well flushing and groundwater flow and

transport assuming constant sampler equilibrium rates for A, high-permeability, 

B, medium-permeability, and C, low-permeability formations............................................26
vi

19. Graphs showing example of vertical profiling with passive samplers, based on

borehole geophysical logs, water levels, and well construction in an alluvial

aquifer in New Mexico ..............................................................................................................32

20. Diagrams showing ambient borehole flow patterns and relation to vertical water

chemistry as measured by passive samplers: A, upward flow, B, convergent

outflow, C, mixed cross flow, and D, mixed stratified flow..................................................34

21. Photograph of tamper-resistant attachment of a weighted passive sampler

suspension line to an interior bolt............................................................................................39

22. Graph showing concentrations of cis-1,2-dichloroethene (cisDCE) from regenerated

cellulose dialysis membrane samplers in relation to concentrations of cisDCE

from low-flow purging, with a 1:1 linear relation line ...........................................................44

23. Graph showing concentrations of manganese from regenerated cellulose dialysis

membrane samplers in relation to concentrations of manganese from low-flow 

purging, with a 1:1 linear relation line .....................................................................................44

24. Graph showing concentrations of chloride from regenerated cellulose dialysis

membrane samplers in relation to concentrations of chloride from low-flow

purging methods, with a 1:1 linear relation line.....................................................................45

Tables

1. Dialysis membrane flat widths, filled diameters, and filled volumes for regenerated

cellulose dialysis membrane passive samplers ....................................................................14

2. Classifications of intervals in open borehole fractured-rock wells, based on

distinguishing hydraulic and chemical characteristics of zones .......................................35

3. Decision analysis summary of appropriateness of passive sampler use.........................35

4. Chemical constituents and corresponding sampling capability of passive samplers....36

5. Minimum volumes required for selected analytes from the U.S. Geological Survey

National Water Quality Laboratory..........................................................................................37

6. Identifiers and parameter codes for data associated with purge and passive

samples for input into the U.S. Geological Survey National Water Information

System database ........................................................................................................................41
vii

Conversion Factors

U.S. customary units to International System of Units

Multiply By To obtain

Length

inch (in.) 2.54 centimeter (cm)

inch (in.) 25.4 millimeter (mm)

inch (in.) 25,400 micron (μm)

foot (ft) 0.3048 meter (m)

mile (mi) 1.609 kilometer (km)

Area

square foot (ft2) 929.0 square centimeter (cm2)

square foot (ft2) 0.09290 square meter (m2)

square inch (in2) 6.452 square centimeter (cm2)

Volume

gallon (gal) 3,785 milliliter (mL)

gallon (gal) 3.785 liter (L)

gallon (gal) 0.003785 cubic meter (m3)

cubic inch (in3) 0.01639 liter (L)

cubic foot (ft3) 0.02832 cubic meter (m3)

Flow rate

cubic foot per second (ft3/s) 0.02832 cubic meter per second (m3/s)

cubic foot per day (ft3/d) 0.02832 cubic meter per day (m3/d)

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

Mass

ounce, avoirdupois (oz) 28.35 gram (g)

pound, avoirdupois (lb) 0.4536 kilogram (kg)

Density

pound per cubic foot (lb/ft3) 16.02 kilogram per cubic meter (kg/m3)

pound per cubic foot (lb/ft3) 0.01602 gram per cubic centimeter (g/cm3)

Transmissivity

foot squared per day (ft2/d) 0.09290 meter squared per day (m2/d)

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

 °F = (1.8 × °C) + 32.

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

 °C = (°F – 32) / 1.8.
viii

Datum

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

(NGVD 29).

Horizontal coordinate information is referenced to the North American Datum of 1983 (NAD 83).

Altitude, as used in this report, refers to distance above the vertical datum.

Supplemental Information

Specific conductance is given in microsiemens per centimeter at 25 degrees Celsius (μS/cm at 

25 °C).

Concentrations of chemical constituents in water are given in either milligrams per liter (mg/L), 

micrograms per liter (μg/L), or nanograms per liter (ng/L).

Abbreviations

ASTM American Society for Testing and Materials

cisDCE cis-1,2-dichloroethene

D Diffusion coefficient

DM Dual membrane

DO Dissolved oxygen

DQO Data-quality objective

EM Electromagnetic

IDW Investigation derived wastewater

ITRC Interstate Technology and Regulatory Council 

LDPE Low-density polyethylene

NS Nylon screen

NWIS National Water Information System

NWQL National Water Quality Laboratory

PAHs Polycyclic aromatic hydrocarbons

PCBs Polychlorinated biphenyls

PCE Tetrachloroethene

PDB Polyethylene diffusion bag

PFASs Poly- and perfluoroalkyl substances

PTFE Polytetrafluoroethylene

PVC Polyvinyl chloride

QA/QC Quality assurance/quality control
ix

RCDM Regenerated cellulose dialysis membrane

RPD Relative percent difference

RPP Rigid porous polyethylene

SC Specific conductance

SPMD Semi-permeable membrane device

SVOCs Semi-volatile organic compounds

TCE Trichloroethene

VOCs Volatile organic compounds

USGS U.S. Geological Survey

Passive Sampling of Groundwater Wells for Determination 

of Water Chemistry

By Thomas E. Imbrigiotta and Philip T. Harte

1.0 Introduction

Passive groundwater sampling is defined as the collection of a water sample from a well without the use of purging by a pump or retrieval by a bailer (Interstate Technology 

and Regulatory Council [ITRC], 2006; American Society for 

Testing and Materials [ASTM], 2014). No purging means 

that advection of water is not involved in collecting the 

water sample from the well. Passive samplers rely on diffusion as the primary process that drives their collection of 

chemical constituents. Diffusion is the transport of chemicals 

caused by the presence of a chemical gradient. Chemicals 

tend to move or diffuse from areas of higher concentration to areas of lower concentration to reach an average or 

equilibrium concentration. 

Passive sampling of groundwater relies on the ambient 

exchange of groundwater in the formation with water in the 

screened or open interval of a well. In this report, the term 

formation is used to describe all saturated hydrogeologic units 

that yield water to a well. If the well opening is unclogged and 

free of a film of deposits from physical turbidity or chemical 

precipitation, then the exchange of groundwater is likely adequate, and the water in the open interval will be representative 

of water in the formation. In some cases, the passive sample 

from the well opening can be more representative of groundwater from the formation than a sample collected by pumping 

if pumping induces mixing of water in the open interval with 

stagnant casing water that has undergone chemical alteration 

(Harte and others, 2018). In most cases, passive sampling will 

better represent the ambient groundwater chemistry flowing 

through the open interval of a well because pumping may capture water of different chemistry from downgradient or lateral 

areas that would not normally pass through the well. 

Three basic types of passive samplers are discussed in 

this report. The first type of passive sampler is the equilibriummembrane type, which includes a semi-permeable membrane 

through which chemicals diffuse or permeate. Permeation 

is simply the process of water or chemicals moving through 

openings in the membrane. The authors contend that permeation is dominated by diffusion for many of the passive samplers discussed in this report. Some passive equilibrium-membrane-type samplers allow most types of chemical constituents 

through, whereas others allow the diffusion of only selected 

groups of chemicals. Once the chemical constituents are inside 

the membrane, they are retained by the equilibration of concentrations inside the sampler with those outside the sampler.

The second type of passive sampler is an equilibriumthief type, which has no semi-permeable membrane. Chemical 

constituents simply move through the openings in the body of 

the sampler either initially through advection and dispersion or 

over time primarily by diffusion. Chemical constituents reach 

equilibrium between the water in the sampler and the water 

in the well and are captured in the sampler when the sampler 

is closed. 

The third type of passive sampler is an accumulation-type 

sampler that contains sorptive media. Selected chemical constituents are sorbed onto the media that the sampler contains 

for later extraction and analysis. 

Although passive samplers have been available for more 

than 15 years (from present [2020]), their use by U.S. Geological Survey (USGS) hydrologists and hydrologic technicians to monitor groundwater quality largely has been limited 

to selected research studies. The authors believe that this may 

be the result of (1) a lack of exposure of most USGS personnel 

to passive samplers and the uses of these samplers and (2) the 

lack of a USGS-approved protocol for the proper use of these 

samplers by USGS personnel. This report is an effort to fill 

those two needs. 

The focus of this report is on hydraulic, hydrologic, and 

chemical considerations in the application of passive samplers 

and interpretation of groundwater chemistry results obtained 

using passive samplers in wells. This report describes the 

differences between purging and passive sampling methods 

in groundwater and explains how and why passive samplers 

work. The report points out the advantages and limitations 

of passive samplers in general and for each particular type 

of passive sampler. Important considerations to be taken into 

account prior to the use of passive samplers are discussed, 

such as defining the data-quality objectives, the waterquality constituents to be sampled, sample volumes required 

for analysis, well construction of the sampling network, 

and the geologic formations that will be sampled. Potential 

applications of passive samplers also are discussed, such as 

chemical-vertical profiling of wells. A general field protocol 
2 Passive Sampling of Groundwater Wells for Determination of Water Chemistry

for the deployment, recovery, and sample collection using 

these devices is described, and some overall guidance for the 

practitioner with application examples is given. Comparison 

methods used to evaluate results from passive sampling versus 

purge sampling also are discussed. 

2.0 Overview of Groundwater Sampling

Over the past 51 years (1970–2020), knowledge of 

groundwater flow and transport processes has increased along 

with the development of innovative tools, techniques, and 

methods. Groundwater sampling has changed from simple 

bailing and standard purging methods to low-flow purging and 

passive sampling. In this section, we discuss the principle differences between purge and passive sampling to help qualify 

sample results from passive sampling. 

Purge and grab sampling can be categorized as the collection of instantaneous samples, whereas passive sampling is 

a time-integrated sampling method. There are differences also 

in the volume of the formation interrogated, degree of mixing, 

and flow conditions.

2.1 Purge Methods

Groundwater flow in the open interval of a well will 

differ under ambient and pumping conditions (Crisma and others, 2001; Elci and others, 2001). Flow differences are likely 

more pronounced in wells with long open intervals (>10 feet 

[ft]) because of the potential to intercept either differences in 

hydraulic head vertically across the well opening or in hydraulic conductivity (referred to as permeability in this report). 

In the case of the former, ambient flow will be dominated by 

inflow from the layer with the highest hydraulic head. In the 

case of the latter, pumping will induce flow from the layer 

with the highest permeability. If the layer with the highest 

hydraulic head and the layer with the highest permeability are 

not coincident, then the water sources differ, which may have 

implications for water chemistry. 

In some cases, there may be little difference in water 

under ambient and pumped conditions. Elci and others (2001) 

found that ambient flow in one well at the Savannah Test Site 

in Aiken, South Carolina, had a maximum upward flow of 

0.28 liter per minute (L/min) from a bottom inflowing layer 

to an upper outflowing layer. Under this scenario, the passive 

and the purge samples collected from this well would produce 

similar results for two reasons. The first reason is that in both 

the passive and the pumped samples, the water chemistry in 

the open interval will be dominated by the inflowing bottom 

layer. The second reason is that strong vertical flow may produce altered water chemistry in the aquifer in the outflow zone 

of the well such that even when a pump is drawing water into 

the well from the outflow zone, thereby reversing flow, that 

water likely represents the inflowing water from the bottom 

layer of the well. Thus, with both methods samples would be 

exposed to the same water chemistry. 

2.1.1 Three-Well-Volume Purge

The relatively high volume, active purge method called 

the three-well-volume method or volumetric purge is a benchmark sampling procedure used for many water-quality studies, 

including the USGS National Water Quality Assessment 

Project (Koterba and others, 1995), and is one of the methods presented in the USGS National Field Manual (USGS, 

2017). In this method, a portable or installed pump is set at 

the bottom of the casing directly above the well opening if the 

saturated water column extends to that depth. Purging is initiated and continues until a predetermined equivalent volume 

of water, typically equal to three volumes of the water column 

in the well, is evacuated or until stabilization of field physical 

and chemical characteristics (pH, specific conductance [SC], 

temperature, dissolved oxygen [DO], and turbidity) occurs 

within acceptable limits over three successive measurements. 

Purging the well is done to reduce or eliminate the inclusion of stagnant water in the well casing (Koterba and others, 1995). Purging also helps reduce the turbidity in the well 

caused by the deployment of a portable pump in the well (if 

one is used). The consequence of a volumetric purge is that the 

collected sample represents a flow-weighted, mixed, integrated 

sample dominated by groundwater from the more permeable 

hydrogeologic units with some contribution from the lower 

permeability units (Britt and Tunks, 2003). 

Barber and Davis (1987) incorporated well hydraulics 

with water chemistry differences between the well and formation to derive purge/volume times associated with achieving 

representative samples from wells. As expected, the aquifer 

permeability and storage play important roles in the time a 

particular well needs to be purged to ensure a representative 

sample. The initial water chemistry conditions of the well also 

played a role in that it took longer to achieve a representative 

value if the SC of the well water was initially higher than the 

SC of the formation water. In some cases, Barber and Davis 

(1987) found that more than three well-casing volumes of 

water were needed to ensure a representative sample, and in 

some low-permeability formations, as many as nine borehole 

volumes were needed.

Several pitfalls can result from volumetric purging that 

can alter the chemistry of the formation water in the well. 

These include the potential for in-well degassing from excessive withdrawals and pressure decreases (Roy and Ryan, 

2010), the need to extract and sometimes collect and treat 

large volumes of contaminated water, long purge times to 

achieve representative conditions, and unrepresentative mixing either in the well or formation. Mixing can alter the water 

chemistry from that of the groundwater in the formation. However, mixing in the well can be problematic for many sampling 

methods. Several of these processes are discussed in more 

detail in Section 10.2. 
2.0 Overview of Groundwater Sampling 3

2.1.2 Low-Flow Purge

A primary goal of low-flow purge sampling of groundwater (pumping at low rates, 0.1–0.5 L/min) is to minimize 

the amount of water pumped from in-well storage by avoiding drawdown in the well; consequently, in-well vertical flow 

from the stagnant water column in the well casing above the 

screened or open interval is minimized (Puls and Barcelona, 

1989; Barcelona and others, 1994; Pohlmann and others, 1994; 

Kearl and others, 1994; Shanklin and others, 1995; Puls and 

Barcelona, 1996; Barcelona and others, 2005). Hence, water 

within the screened or open interval typically is more representative of formation water than water in the casing (Kearl 

and others, 1992).

Additional benefits of low-flow sampling include small 

purge volumes, which minimizes the production of investigation-derived waste (IDW) caused by pumping contaminated 

water, and the collection of groundwater samples with low turbidity, which decreases the need for filtration. However, there 

are associated hydraulic and chemical concerns when purging 

and sampling using low rates of flow. According to the State 

of New Jersey sampling guidance (http://www.state.nj.us/dep/

srp/news/1997/9711_04.htm):

“The zone sampled within the well by low-flow 

methods is conceptually limited. If the contaminant 

distribution in the screened section of the aquifer is 

heterogeneous, which may be the case in most wells, 

the sample results obtained by low-flow sampling 

may be significantly biased low if the sampling 

device intake is not placed at the same depth as that 

of the highest contaminant concentration entering 

the well.”

A common assumption for low-flow groundwater 

sampling was that low purge rates capture primarily lateral 

inflow (horizontal laminar flow) through the screened interval 

from the formation at depths coincident with the pump intake 

(Stone, 1997). However, because even low-flow sampling 

causes some drawdown in the well, convergent, in-well, 

vertical flow is induced toward the pump intake from inflow 

across the entire well screen (Harte, 2017). Varljen and others 

(2006) show that the entire well screen is sampled during 

low flow with preferential sampling of high permeability 

layers under steady-state transport. Flow convergence toward 

the pump promotes mixing that is biased toward the capture 

of formation water from layers with the highest head and 

permeability that intersect the well screen (Divine and others 

2005). Because low-flow purge sampling uses lower rates 

of pumping and less volume is extracted from the well than 

for the three-well-volume purge method, the resultant lowflow sample tends to be more affected by the ambient flow 

(pre-purged) and initial-head distribution than three-wellvolume purge samples. Nevertheless, the low-flow sample can 

approximate either (1) a flow-weighted sample dominated by 

transmissive layers of the formation (similar to volumetric 

purge methods) or (2) a flux-averaged sample dominated by 

chemical mixing and averaging of chemical concentrations 

along the open interval or screen of a well. The former sample 

is called a flow-weighted sample, and the latter is called a 

volume-integrated sample. 

2.1.3 Field Physical and Chemical Characteristics 

Stabilization

Inherent in many active/purge sampling methods 

(volumetric and low-flow) is the requirement that, prior to 

collecting a sample, field physical and chemical characteristics 

such as pH, DO, SC, temperature, and turbidity achieve 

some degree of stability as an indicator of formation 

water recharging the well water. Harte (2017) found that 

stabilization of field physical and chemical characteristics 

monitored during purging was useful in diagnosing the 

contribution of in-well vertical flow and transport to the 

pump intake location. However, stabilization of field physical 

and chemical characteristics during purging may not always 

be a reliable indicator of the chemical stability for other 

chemical constituents. For example, during purging at sites 

in the Coastal Plain sediments of New Jersey, field physical 

and chemical characteristics at 10 wells typically achieved 

stabilization before 2 casing volumes were purged. However, 

the aromatic organic compounds being sampled took slightly 

more than 3 casing volumes of purging to stabilize (Gibs and 

Imbrigiotta, 1990). Researchers hypothesize that the primary 

factors affecting the difference between field physical- and 

chemical-characteristic stability and target-constituent stability 

include the physical and chemical heterogeneity of the 

formation, mixing of groundwater in the well, reactions within 

the wellbore external to the formation, and the presence of a 

well-skin effect that may alter flow and chemistry (Church and 

Granato, 1996; Reilly and LeBlanc, 1998). Therefore, relying 

on the stability of field physical and chemical characteristics 

alone may provide a false measure of success during purge 

sampling. Rather, knowledge of well and formation hydraulic 

characteristics with either purge or passive sampling 

will increase the likelihood of obtaining a representative 

groundwater sample from the formation. A coupled hydraulic 

and chemical monitoring approach is discussed in Harte 

(2017), and an analytical model is provided in Harte and 

others (2019) for such an analysis.

2.2 Passive Sampling

Field application of passive sampling started in the late 

1980s when passive sampling methods were first developed 

to sample organic vapors from air and soil gas (Vroblesky 

and others, 1991; Vrana and others, 2005). Soon thereafter, 

these methods were applied to sampling groundwater in wells. 

Accumulation-type and equilibration-type passive samplers 

were developed in the 1990s (Petty and others, 1995; Ellis 

and others, 1995; Vroblesky and others, 1996; Vroblesky 

and Hyde, 1997; Einfield and Koglin, 2000). Today (2020), 
4 Passive Sampling of Groundwater Wells for Determination of Water Chemistry

several different passive samplers are available that can be 

used to sample a wide variety of different chemical constituents in wells. These samplers are discussed in more detail in 

Section 4.

The idea behind passive sampling is simple; rather than 

purging a well and actively drawing water into a well, a passive sampler is lowered into the screened or open interval to 

sample the water flowing through it owing to natural groundwater gradients. Driven by the process of diffusion, chemical 

constituents in the passing groundwater can be collected in the 

sampler. This has benefits in that pumps requiring power are 

not needed; pumps and hoses do not have to be decontaminated between wells; and, at sites with contamination, large 

volumes of IDW water do not have to be collected and treated. 

Passive samplers collect samples that are representative of the water adjacent to the sampler, which in most cases 

represents water in the screened or open interval of a well. 

Because passive samplers do not induce flow into the well 

from the formation, they do not collect instantaneous samples. 

They also do not collect samples that are necessarily representative of a finite volume of water from the aquifer around the 

well, unlike purge samples. 

Because passive samplers function primarily by diffusion, they require a specified minimum deployment period in 

the well. The deployment period depends on the inflow and 

outflow patterns of a well, the degree of mixing of groundwater in a screened or open interval, the rate of groundwater flow 

through the screened or open interval, and the diffusion rates 

of constituents of interest. In general, samples obtained with 

a passive sampler will probably represent the time-weighted 

average concentration found in water flowing through the 

well over the most recent 3–4 days prior to sample collection 

(Vroblesky, 2001a, 2001b; ITRC, 2006). 

The general theory and principles of how and why 

passive samplers work, and their primary advantages and 

limitations, are discussed in Section 3. Individual types of 

passive samplers that have been developed for use in wells are 

discussed in Section 4.

3.0 Theory and Principles of Passive 

Sampling

Although many passive samplers appear simplistic in 

appearance, understanding the principles of operation will help 

ensure appropriate sample collection procedures are used. This 

section provides an overview of the physical and chemical 

principles of passive sampler operation.

3.1 Kinetic and Equilibrium Sampling Regimes

When a passive sampler is placed in a well, it encounters 

two primary sampling regimes. Initially, the mass of chemical taken up by the sampler increases somewhat linearly with 

time, and maximum relative change occurs during this time 

(fig. 1). This is known as the kinetic sampling regime. In the 

kinetic sampling regime, the longer the sampler is in the well, 

the more the chemical constituent of interest will diffuse or 

permeate into the sampler. This process can be represented 

by the first-order, one-compartment, mathematical model 

described by Vrana and others (2005): 

Cs(t) = Cw (k1/k2)(1–e-k2t) (1)

where

Cs(t) is the concentration of the constituent/analyte 

in the sampler at exposure time (t),

Cw is the constituent/analyte concentration in the 

well, and

k1 and k2 are uptake and offload rate constants, 

respectively.

The period of deployment for accumulation-type passive diffusion samplers that contain sorptive material to collect samples 

is restricted to the kinetic sampling regime.

Once the passive-sampler-deployment time exceeds the 

time period associated with the kinetic sampling regime, the 

relative rate of solute uptake of the constituent/analyte into the 

sampler decreases. Once the concentrations within the sampler 

are at equilibrium with the concentrations outside the sampler, 

the rate of uptake becomes essentially zero. This is referred 

to as the equilibrium sampling regime. In this regime, solutes 

may move into or out of the sampler in an attempt to maintain 

equilibrium with changes that may occur in water outside the 

sampler. During this period, equilibrium-type passive samplers 

rely on either diffusion of chemical constituents across a membrane (equilibrium-membrane type) or into a sample container 

(equilibrium-thief type) to collect samples that are equal to the 

concentrations of chemical constituents of interest in the well. Constituent mass uptake

Time

Transient sampling regime Equilibrium sampling regime

Kinetic sampling regime

Figure 1. Passive sampling regimes. Modified from figure 1 of 

Seethapathy and others (2008).
3.0 Theory and Principles of Passive Sampling 5

3.2 Diffusive Chemical Exchange

All equilibrium-type passive samplers rely primarily on 

the process of diffusion to collect samples of the constituents 

of interest from the well. Diffusion is governed by Fick’s Law 

(Seethapathy and others, 2008), which briefly stated says that 

solutes diffuse from areas of high concentration to areas of 

low concentration. For equilibrium-type passive samplers, 

the gradient that drives diffusion is the difference between 

the concentration of a chemical outside the sampler and the 

concentration of a chemical inside the sampler (fig. 2). At 

the initial time of deployment (t

i

=0), the concentration of the 

constituent to be sampled is essentially negligible (ci

=0) inside 

the sampler because it is filled with deionized water free of the 

constituent of interest. After deployment for some time (t>0), 

chemical exchange occurs according to Fick’s First Law of 

Diffusion, which states

M/t = D (A/L) (Cw–Cs

) (2)

where

M is the mass of the constituent collected by the 

sampler per unit time (t),

D is the diffusion coefficient (area/time),

A is the surface area of the diffusion path,

L is the diffusive path length,

Cw is the constituent concentration (mass/

volume) in the well, and

Cs

 is the constituent concentration in the sampler.

In a passive sampler with a semi-permeable membrane, A is 

the surface area of the membrane through which diffusion 

occurs, and L is the membrane thickness. Sample collection is 

complete when the concentration inside the sampler equals the 

concentration outside the sampler. This is shown graphically 

in figure 2.

Equation 2 can be rearranged to describe the relative 

uptake potential for water-filled passive samplers (Divine and 

others, 2005; Sanford and others, 1996). In this case, the rate 

of equilibrium between the concentration of the constituent of 

interest in the passive sampler and that of the well water can 

be expressed as 

 C   D L t e    1 m m At/ V

s

 (3)

where 

Cs

(t) is the ratio of the concentration inside the 

passive sampler to the concentration in the 

well water in contact with the sampler,

Dm is the diffusion coefficient of the constituent 

of interest across the membrane (solved),

A is the diffusive surface area of membrane,

t is the time of deployment,

V is the volume of sampler, and

Lm is the thickness of membrane.

For accumulation-type passive samplers, the concentration gradient that drives sample collection is between the 

concentration of a chemical in water outside the sampler 

and the concentration on the surface of the sorptive media. 

The net rate of uptake is controlled by the slower of the two 

processes: permeation through the membrane and diffusion 

through the boundary layer (Seethapathy and others, 2008). 

The two boundary layers are formed between the aqueous side 

of the membrane (well water) and the receiving side of the 

membrane (fig. 3). The sorptive media remove a constituent 

from solution, which creates a low-concentration zone on the 

receiving phase side of the boundary layer (fig. 3). Deployment time must be short enough that all the sorptive sites on 

the sampler are not saturated with the constituent of interest by 

the end of the deployment. 

Cwell Cwell

Csampler

Csampler

Membrane

Membrane

Before equilibrium After equilibrium

Distance Distance

A B Constituent concentration

Figure 2. The chemical 

gradient across a membrane 

A, before equilibrium and 

B, after equilibrium. Modified 

from Interstate Technology 

and Regulatory Council (2004). 

[C, concentration]
6 Passive Sampling of Groundwater Wells for Determination of Water Chemistry Membrane Constituent concentration

Distance

Aqueous phase Receiving phase

Diffusion/permeation distance Boundary layer Boundary layer

Figure 3. Chemical gradient from the groundwater to the 

receiving phase of the accumulation-type passive sampler. 

Modified from Seethapathy and others (2008).

3.3 Well Communication and Hydraulics

The hydraulic connection between the screened or open 

interval of a well and the formation is an important factor that 

affects a well’s ability to collect water representative of the 

water chemistry in the formation without the need to induce 

flow into the well by pumping. The ambient flow through the 

open interval of a well is dependent on well communication 

(ability to exchange groundwater with the formation); well 

construction (length of well opening in particular); formation 

characteristics, including physical and chemical heterogeneity; and position of the well relative to hydrologic boundary 

conditions, which affects horizontal and vertical hydraulichead gradients. All of these topics are discussed in more detail 

in Section 5.

Wells that are open to the formation distort the groundwater flow field because of the permeability contrast between the 

well (more permeable) and formation (less permeable). This 

distortion facilitates flushing or exchange of water in the well 

with the groundwater in the formation under ambient-flow 

conditions. Drost and others (1968) utilized tracers coupled 

with point-dilution theory to demonstrate the ambient flushing 

of water into a well. Mathematically, the distortion of groundwater flow is expressed as

qo = q/α (4)

where α is the convergence/divergence (distortion factor) of 

the groundwater flow in the vicinity of a well, water flux (qo

) 

in the formation, and water flux (q) through the well (Basu 

and others, 2006). A distortion factor of 0.9–2.4 was measured 

in wells by Verreydt and others (2015), indicating that flow 

through the well generally exceeded flow through the formation by as much as 2.4 times. 

3.4 Sampler Materials and Constituents 

Sampled

Passive samplers are constructed of a variety of materials. The material type depends on the type of sampler and 

the constituents to be collected. Passive samplers have been 

developed that can sample for a wide range of constituents, 

including major cations and anions, trace metals, nutrients, 

dissolved gases, volatile organic compounds (VOCs), semivolatile organic compounds (SVOCs), explosive compounds, 

poly- and perfluoroalkyl substances (PFASs), and pesticides. 

Different types of passive samplers vary in their ability to 

sample each of these categories of chemical constituents. 

Accumulation-type passive samplers are made of inert 

structural materials, such as stainless steel and Teflon, and 

organic media that adsorb organic compounds of interest. 

The sorbent media used include polymeric resins and triolein 

(ITRC, 2007). The accumulation-type passive samplers discussed in this report collect only organic compounds, such as 

VOCs, pesticides, and SVOCs and cannot be used to sample 

for inorganic constituents.

Equilibrium-thief-type samplers are constructed of 

relatively inert materials, such as stainless steel and Teflon. 

The sample collection containers are made of either glass 

or polyethylene. Equilibrium-thief-type passive samplers 

theoretically can collect any type of chemical that moves into 

them. The only constraint is that the material of the sample 

container cannot adsorb or leach the constituents of interest. This is important because the sample is not transferred: 

the collection container is submitted to the laboratory. Glass 

sample containers are used to collect samples for organic compounds, whereas polyethylene containers are used to collect 

samples for inorganic constituents and trace metals (Britt and 

others, 2010). 

Equilibrium-membrane-type samplers are constructed 

with many materials, the most important of which is the 

membrane material. Membranes have been made of polymers such as polyethylene, regenerated cellulose, cellulose 

acetate, nylon, polydimethylsiloxane, polysulfone, siliconepolycarbonate, polytetrafluoroethylene (PTFE), polypropylene, and polyvinyl chloride (PVC) (Seethapathy and others, 

2008; ITRC, 2007). The function of the membrane is to act as 

a semi-permeable barrier that allows the diffusion of selective 

groups of chemical constituents into the passive sampler. 

Equilibrium-membrane-type samplers are constructed 

with valves, mesh, and connectors, as well as membranes. 

All these components may sorb the constituents of interest. In 

general, however, such sorption or exchange is considered to 

not affect the sample quality as long as they do not add to the 

concentration of the constituents of interest and equilibration 

is reached during the deployment period.

Equilibrium-membrane-type passive samplers have 

been developed that can sample for VOCs, major cations 

and anions, most trace metals, nutrients, perchlorate, dissolved organic carbon, PFASs, and most explosive compounds. The constituents that these samplers collect depend 
3.0 Theory and Principles of Passive Sampling 7

on the membrane material. Some equilibrium samplers 

have been developed that sample only for certain types of 

organic compounds, whereas others allow for the collection 

of inorganic cation and anions and trace metals, as well as 

organic compounds. 

The selectivity of a semi-permeable membrane is due 

to several factors, such as its chemical characteristics, pore 

size, or hydrophobicity. The size of the pores of the membrane in relation to the size of the inorganic cation and anions 

or organic compounds can be a physical factor that prevents 

or allows constituents to diffuse through the membrane. The 

hydrophobic or hydrophilic characteristics of a membrane 

will allow some constituents to pass through and repel others. 

Characteristics of the constituents being sampled, such as 

solubility, volatility, diffusion coefficient, and partition coefficient, in relation to the chemical composition of the membrane 

will also affect whether a membrane will allow constituents to 

diffuse through it.

3.5 Equilibration and Exposure Time

Passive samplers must be deployed in a well for a 

predetermined length of time prior to their removal and 

sampling. Equilibrium-type samplers must be left in the well 

long enough to equilibrate to within at least 95 percent of 

the actual concentrations in the groundwater, yet not long 

enough for membrane degradation or clogging to occur. 

Accumulation-type samplers must be exposed to groundwater 

long enough to sorb detectable concentrations, yet not long 

enough to oversaturate all the sorption sites on the sampler. 

A general rule of thumb is that for most passive samplers, 

reasonable deployment times range from a few days to a few 

weeks for chemicals with diffusion coefficients greater than 

10-8 square centimeters per second (cm2

/s). Factors affecting 

equilibration and exposure time are discussed in more detail in 

Section 5.

3.6 Common Advantages and Limitations of 

Passive Samplers

The use of passive samplers has general advantages and 

limitations compared to the use of conventional pumps or bailers in sampling groundwater wells. Advantages and limitations 

that are common to most passive samplers are given below. 

3.6.1 Advantages

This section lists the common advantages that most passive samplers have over purging methods. Advantages specific 

to each type of passive sampler are provided where each 

sampler is discussed in Section 4.

No pump required: One of the advantages of using passive 

samplers is that they eliminate the need to purge water from 

the well during active sampling. This means that no pump or 

power source is needed to sample the well. This can save on 

equipment costs and operational costs.

Time in the field reduced: Purging a well prior to sampling 

frequently represents the largest amount of time spent in 

the field to collect a groundwater sample. Use of passive 

samplers can eliminate most of this field sampling cost. For 

example, Imbrigiotta and others (2007) found the typical time 

for low-flow purging of a well less than 100 ft deep to reach 

stabilization of field physical and chemical characteristics 

was 45–60 minutes (min). In comparison, passive samplers 

typically took 15 min to deploy and 15 min to retrieve 

from a well of this depth, so the field time and costs saved 

were substantial.

The savings in time and costs when using passive samplers 

rather than the three-well-volume purge method become more 

substantial as wells are deeper, well diameters are larger, and 

well volumes are greater. For wells where a three-well-volume 

purge is required prior to sampling, typical evacuation times 

on the order of 30–400 min for a 100-ft, 4-inch (in.) -diameter saturated column of water to 200–2,200 min for a 500-ft, 

4-in.-diameter saturated column of water are needed for a 

1-gallon-per-minute (gal/min) to 10-gal/min pumping rate 

(fig. 4). 

No purge water produced: Another advantage to using 

passive samplers instead of purging is that passive samplers 

produce very little leftover water or IDW. This is particularly 

important at groundwater hazardous waste sites where purge 

water must be drummed, transported, and treated. Passive 

sampling saves time and costs by eliminating the need to collect, transport, and treat the IDW.

No cleaning required: Most passive samplers are disposable and are constructed or purchased clean and ready for use. 

This is an important advantage over non-dedicated pumps that 

require cleaning or decontamination between wells.

Ease of use: Most passive samplers are easily deployed in 

a well by lowering them on a weighted suspension line to 

a selected depth in the open interval and tying off the line. 

Recovery is just the opposite; the sampler is untied and pulled 

up. Once the passive sampler is at the surface, minimal training is required for the field sampling personnel on the correct way to transfer the water from the sampler to the sample 

containers.

No filtration required: For equilibrium-type passive samplers, several do not require filtration because the membranes 

have very small openings (some smaller than 0.45 micron 

[μm]), which act as filters. This intrinsic filtering process can 

have the analytical advantage of reducing matrix interference 

from turbidity. 

One field trip to deploy and recover: Some equilibrium-type 

passive samplers that are constructed of non-biodegradable 

materials can stay in the well from one sampling event to the 

next for wells that are periodically sampled. Therefore, these 

passive samplers are not constrained by a maximum deployment period. Field personnel can retrieve and collect a sample 

from the equilibrated passive sampler, and then deploy a new 
8 Passive Sampling of Groundwater Wells for Determination of Water Chemistry

10

100

150

1,000

10,000

0 100 200 300 400 500 600

Time to evacuate three volumes, in minutes

Length of saturated water column in well, in feet

Range of purge time for pump rates between 1 and 10 gallons 

per minute required prior to groundwater sampling assuming 

evacuation of three well volumes of water

Typical deployment time for passive sampling;

deployment time (2 hours), and retrieval time (0.5 hour)

1 gal/min pump rate

10 gal/min pump rate

EXPLANATION

Figure 4. Purge duration 

for 1- and 10-gallon-perminute rates of pumping 

for a 4-inch-diameter well. 

(gal/min, gallon per minute)

passive sampler during the same field trip. The new passive 

sampler is then allowed to equilibrate until the next scheduled 

sampling event.

Easily adapted to long-term monitoring plans: In many 

cases, passive samplers are easily incorporated into longterm monitoring plans. As long as the results obtained with 

the passive sampler are accepted as being comparable to the 

purging results, wells can simply be switched from purging to 

passive samplers. 

Use to sample low-yield wells: Many passive samplers can be 

used to sample low-yield wells using long-term deployments 

to allow the chemical concentrations to come to equilibrium. 

Passive samplers save time in the field when field personnel 

otherwise would have to purge a low-yield well, wait for it to 

recover, and then pump it again to sample it. 

No depth limitations: Passive samplers can be used to sample 

at any depth in a well. The only depth restriction is the length 

of the suspension line. This is an advantage over some pumps 

that are limited by the depth they are able to lift water. 

Well sampling in high-traffic areas: Because the deployment 

and recovery times are usually short for passive samplers, they 

can be used to sample wells in high-traffic areas, such as wells 

in roadways or near airport runways provided proper safety 

procedures and conditions are met.

Integration of water-quality results: Equilibrium-membrane-type and equilibrium-thief-type passive samplers 

integrate a time-weighted average of the concentrations they 

are exposed to over the last 3–4 days of deployment. Accumulation-type passive samplers can integrate the concentrations 

of constituents they are exposed to during the entire time of 

their deployment. If the sorption sites are not saturated during 

the deployment period of an accumulation-type sampler, then 

the sampler will have the ability to measure episodic events. 

Therefore, passive sampling allows for a more cost-effective 

alternative to some active sampling methods, which are inherently instantaneous in operation.

Use in vertical profiling: Passive samplers can be used to 

provide an approximate vertical profile of the concentrations 

in the open or screened interval of a well for purposes of 

determining constituent input depths or chemical stratification 

in a formation because of their ability to interrogate a 

relatively small volume of water from a discrete depth 

(Vroblesky and Peterson, 2004; Divine and others, 2005). This 

differs from the purging method, which induces convergent 

flow to the pump intake and interrogates larger volumes of 

water. However, the ability of the passive sampler chemical 

profile to represent the chemical profile in the formation is 

a function of well-flow dynamics and the degree of in-well 

mixing under ambient conditions. 
4.0 Types of Passive Samplers 9

3.6.2 Limitations

Limitations common to the use of many passive samplers are 

discussed in this section. Limitations for individual types of 

passive samplers are discussed in Section 4.

Two field trips to deploy and recover: Passive samplers that 

are made with biodegradable materials and some accumulation-type samplers have limited deployment periods. Therefore, it is likely these types of samplers will require two trips 

to the field, one to deploy and one to retrieve, regardless of 

whether they are part of a periodic monitoring program. These 

samplers must be recovered before microbes perforate their 

membranes or before their sorptive media are saturated with 

the constituents of interest. 

Sample volume restrictions: A primary limitation to equilibrium-type passive samplers is the restricted volume most 

samplers can contain, particularly samplers utilizing water as 

an uptake medium (receiving phase). Some chemical constituents require a liter or more of water for analysis, and several 

passive samplers can only collect samples of 0.1 to 0.5 liter in 

volume. Volume requirements using some types of samplers 

can be met by deploying multiple samplers in a well at closely 

spaced vertical intervals. 

Flux versus concentration results: Accumulation-type passive samplers produce flux results (mass/time) rather than 

concentration results (mass/volume). This can be considered a 

slight limitation because concentration results are used more 

commonly than flux results. 

Extraction required prior to analysis: Accumulation-type 

passive samplers with unique receiving-phase media, such as 

lipids, carbon, or resins, require extraction or desorption of 

the target chemical constituent from the sorptive media into 

a liquid or gas phase prior to analysis. This extra step can be 

a limitation because it requires more preparation work in the 

laboratory and may restrict the number of laboratories that can 

do these analyses.

Potential difficulty in accurately measuring field physical 

and chemical characteristics: Measurements of common 

field physical and chemical characteristics, such as water 

temperature, DO, and redox potential, that typically are made 

using an in-line flow cell during well purging are likely to be 

more representative of field physical and chemical characteristics than measurements made in aliquots of water from a 

passive sampler. This is because chemical changes can easily 

take place in the sample when a passive sampler is exposed 

to oxygen or increased or decreased temperatures when it is 

removed from the water column in a well. However, pH and 

SC may be measured in water collected with some equilibrium-type samplers that allow the collection of dissolved ions. 

Accumulation-type samplers cannot be used to measure field 

physical and chemical characteristics.

Samplers must be kept hydrated: Several equilibriummembrane-type passive samplers must be kept hydrated or 

submerged in water between their construction and installation 

in a well. 

Chemical constituent limitations: Some passive samplers 

work only for a specific type or class of chemical constituents. For example, some samplers collect organic compounds 

but not inorganic constituents, whereas others cannot collect 

VOCs or dissolved hydrocarbons. 

Deployment time limitations: Some passive samplers have 

deployment time restrictions owing to biological degradation or chemical clogging of the membrane. In addition, some 

samplers have time restrictions owing to water loss through 

the membrane. Deployment times for accumulation-type 

samplers are uptake and sorption dependent. Deployment of 

several samplers that are retrieved at different durations may 

be required to ensure sorption sites are not saturated. Equilibrium-membrane-type samplers usually require deployment 

times of a couple weeks to minimize hydraulic disturbance 

during deployment and allow for chemical equilibration across 

the membrane. 

4.0 Types of Passive Samplers

The main types of passive samplers developed and used 

over the past decade (2010–20) have included 5 equilibriummembrane-type samplers (polyethylene diffusion bag [PDB] 

sampler, regenerated cellulose dialysis membrane [RCDM] 

sampler, rigid porous polyethylene [RPP] sampler, nylon 

screen [NS] sampler, and EON Dual-Membrane [DM] 

Sampler®), 1 equilibrium-thief-type sampler (QED Snap 

Sampler®), and 2 accumulation-type samplers (AGI Sample 

Module® [formerly GORE-SORBER® Module] and a semipermeable membrane device [SPMD] sampler). Each of these 

samplers is discussed in detail below. Other types of passive 

samplers are discussed briefly in Sections 4.9–4.10. 

Equilibrium-membrane-type passive samplers rely on 

diffusion of chemicals across a semi-permeable membrane to 

collect samples. The basic design for these samplers consists 

of a tube of semi-permeable membrane filled with distilled or 

deionized water. The sampler is deployed in the screened or 

open interval of a well for a sufficient length of time to reach 

chemical equilibrium. Once equilibrium has been reached, 

the constituent concentrations inside the sampler will be 

equal to those outside the sampler. The equilibrium sampler is retrieved, and water inside the membrane is collected 

in sample containers and sent for analysis of the chemical 

constituents of interest. This type of sampler results in a direct 

measurement of concentrations of chemicals (mass per volume) in the groundwater in a well. 

Equilibrium-thief-type passive samplers rely on diffusion 

or permeation of solutes into the open ends of the device. The 

basic design for equilibrium-thief-type samplers consists of a 

container, a container holder, and a closing mechanism made 

of mostly inert non-sorptive materials that will not interact 

with the groundwater sample. The sampler is deployed in the 

open position in the screened or open interval of a well for a 

sufficient length of time to reach chemical equilibrium. Once 
10 Passive Sampling of Groundwater Wells for Determination of Water Chemistry

equilibrium is reached, the sampler is remotely triggered to 

close and brought to the surface. The closed sample container 

is then sent directly to the laboratory for analysis. This type of 

sampler also results in a direct measurement of chemical concentrations (mass per volume) in the groundwater in a well.

Accumulation-type passive samplers rely on the diffusion 

and permeation of chemicals to reach the sorbent material of 

the sampler and sorb to it. The basic design for all accumulation-type samplers consists of a tube containing a material that 

is highly sorptive for the chemical constituents of interest. The 

sampler is deployed in the screened or open interval of a well 

for a length of time shorter than the time needed to completely 

saturate all the sorption sites on the sampler. The sampler is 

then recovered and sent to the laboratory for extraction and 

analysis. This type of sampler results in a direct measurement 

of the flux (mass per time) of chemicals in the groundwater 

coming into the well. Separate concentration comparison 

measurements may be made during the initial sampling to correlate the measured fluxes with chemical concentrations or an 

algorithm may be applied that approximates the concentrations 

on the basis of the measured fluxes and the estimated groundwater flow through the open interval of a well over the time of 

deployment of the sampler.

4.1 Polyethylene Diffusion Bag (PDB) Sampler

The PDB sampler is an equilibrium-membrane-type 

passive sampler. Polyethylene diffusion bag samplers were 

one of the first types of passive samplers developed in the late 

1990s for groundwater sampling. They are directly descended 

from polyethylene vapor diffusion samplers, which were 

initially developed to determine where VOCs in shallow 

groundwater were discharging to streams (Vroblesky and 

others, 1991; Vroblesky and others, 1996; Church and others, 

2002). Instead of having VOCs equilibrate with the headspace 

inside a glass vial with a low-density (LDPE) polyethylene 

membrane over the mouth, a tube-shaped LDPE membrane 

was filled with deionized water, installed in a well, and the 

VOCs in the groundwater were allowed to equilibrate with 

the water inside the membrane (Vroblesky and Hyde, 1997). 

Since then, PDB samplers have been extensively tested against 

purge sampling techniques and are now a widely accepted 

sampling method for VOCs in groundwater wells (Vroblesky 

and others, 2000; Vrobesky and Petkewich, 2000; Vroblesky 

and Peters, 2000; Harte and others, 2000; Vroblesky, 2001a; 

Vroblesky 2001b; Vroblesky and Campbell, 2001; Vroblesky 

and others, 2001; Vroblesky and Pravecek, 2002; Parker and 

Clark, 2002; ITRC, 2004; Archfield and LeBlanc, 2005; ITRC, 

2006; Huffman, 2015). 

PDB samplers can be used to collect samples for most 

VOCs, some SVOCs (naphthalene), and some dissolved 

hydrocarbon gases (methane, ethane, ethene). Several soluble 

polar VOCs, such as acetone, take a longer time to consistently diffuse through the LDPE membrane, so PDB samplers 

are not recommended for sampling of these VOCs (Vroblesky 

and Campbell, 2001). The small pore size (10 angstroms) 

of the LPDE membrane reduces matrix interference from 

turbidity and reduces volatilization loss from the possible 

formation of alkaline foams in alkaline waters (ITRC, 2006). 

Water samples collected with PDB samplers are shipped to the 

laboratory for direct analysis of concentrations of VOCs and 

dissolved hydrocarbon gases. An example of a study utilizing 

PDB samplers is given in Appendix A, Case Study A1. 

4.1.1 Description and Operation

PDB samplers consist of a deionized water-filled tube 

made of LDPE membrane material (typically 2–4 mils thick; 

fig. 5). A sampler is constructed by heat-sealing a length of 

LDPE tubing, filling with a volume of deionized water, and 

then heat-sealing the other end to form a water-filled tube. 

These samplers are commercially available pre-filled or with 

a port on one end to fill in the field or laboratory, and usually 

come in a protective polyethylene mesh sleeve to prevent 

abrasion during installation and recovery. Most PDB samplers 

are made of 1.25-in.- or 2.5-in.-diameter LDPE tubing and are 

1–2 ft in length, depending on the diameter of the well and 

the volume of the bottles to be filled. A 1.25-in.-diameter by 

12 in.-long PDB sampler filled with target analyte-free water 

has enough volume to easily fill four 40-milliliter (mL) vials 

for sampling of VOCs. 

For the deployment of PDB samplers (and many other 

passive samplers), either a dedicated/disposable polypropylene line or a re-useable Teflon-coated line is used to suspend 

the sampler in a well at the desired depth. The PDB sampler 

is deployed in the open interval or screen of a well for about 

2 weeks to equilibrate (figs. 5 and 6). During this time, VOCs 

in groundwater passing by the sampler adsorb to the LDPE 

material, diffuse across the thin membrane, and re-equilibrate 

with the deionized water inside. The LDPE membranes are 

hydrophobic, so no actual physical transport of water occurs 

between the outside and the inside of the sampler. At the end 

of the equilibration period, the concentrations of VOCs inside 

the PDB sampler are equivalent to the concentrations of VOCs 

outside the sampler. The sampler is then retrieved, the contents 

transferred to standard VOC vials, and the samples are sent to 

the laboratory for analysis. VOC concentrations determined 

from PDB samplers represent average VOC concentrations 

present in the open interval of the well over the 3–4 days prior 

to sample collection.

A simplistic conceptualization of a string of passive samplers deployed in a well is shown in figure 6A, which depicts 

stratified horizontal flow into the well. In this case, water well 

chemistry varies with depth, and samplers will reflect the 

chemistry of the inflowing groundwater at the same depth. A 

more complex conceptualization is shown in figure 6B that 

depicts a number of flow processes in the well. In the latter 

case, the water well chemistry may not be reflective of the 

inflowing groundwater at that same depth given processes 

such as vertical flow, dispersion, well mixing, and diffusion.
4.0 Types of Passive Samplers 11

A B

Figure 5. A, A polyethylene diffusion bag (PDB) sampler and B, a tripod used for installation of PDB samplers in a well. 

Photographs by Bradley P. Varhol, EON Products, Inc.

4.1.2 Advantages and Limitations

The main advantages of using PDB samplers are that they 

are low cost to construct or purchase, they are disposable, they 

can be left in wells indefinitely without degrading, and they 

have an extensive track record of proven performance in VOC 

sampling that is based on years of comparison to low-flow 

purging and other sampling methods. Because PDB samplers 

will not biodegrade, they can be left in a well between longterm-monitoring sampling events. This allows the field technician to collect a sample from an equilibrated PDB sampler 

and install another new PDB sampler during one field trip. 

From that point on, only one field trip is necessary to collect 

samples using this passive sampler. The main limitation of 

PDB samplers is that they are unable to sample for inorganic 

constituents and most SVOCs.

4.2 Regenerated Cellulose Dialysis Membrane 

(RCDM) Sampler

The RCDM sampler is an equilibrium-membrane-type 

passive sampler. The earliest version of a downhole dialysis 

sampler was developed by Ronen and others (1986), Ronen 

and others (1987), and Magaritz and others (1989), but it was 

limited to 20-mL sample volumes at each sampled depth. The 

current version of the RCDM sampler was developed in the 

early 2000s specifically to meet the need to sample for more 

than just VOCs using a passive sampler. RCDM samplers 

were developed to sample for inorganic constituents and nonvolatile organic compounds, in addition to VOCs, particularly 

at groundwater contamination sites where monitored natural 

attenuation potential was being evaluated, which required the 

collection of ferrous and ferric iron, sulfate and sulfide, and 

carbon dioxide and methane. RCDM samplers have been used 

successfully to sample wells for a wide variety of organic 

and inorganic chemical constituents (VOCs, major cations 

and anions, trace metals, nutrients, dissolved organic carbon, 

dissolved hydrocarbon gases, perchlorate, some PFASs, and 

selected explosive compounds) (Vroblesky and others, 2002a, 

2002b; Vroblesky and Pravecek, 2002; Imbrigiotta and others, 2002; Vroblesky and others, 2003; LeBlanc, 2003; Ehlke 

and others, 2004; Harter and Talozi, 2004; Parsons, 2005; 

Imbrigiotta and others, 2007; Imbrigiotta and others, 2008; 

Imbrigiotta and Trotsky, 2011). Water samples collected with 

RCDM samplers are shipped to the laboratory for direct analysis of concentrations of organic compounds and inorganic 

constituents. Examples of studies utilizing RCDM samplers 

are given in Appendix A, Case Studies A3 and A4. 
12 Passive Sampling of Groundwater Wells for Determination of Water Chemistry

Clay

Coarse sand

Fine sand

Coarse sand

Coarse sand

Fine sand

Fine sand

Clay

Coarse sand

Fine sand

Coarse sand

Coarse sand

Fine sand

Fine sand

A B

EXPLANATION

Direction of primary groundwater flow

and advective transport

Direction of primary groundwater flow,

advective transport, and dispersion

Direction of secondary groundwater flow,

advective transport, and dispersion

 Diffusive transport

Passive diffusion bag without protective mesh

Weight to counteract buoyancy

Figure 6. Multiple polyethylene diffusion bag samplers A, deployed in a well screen under horizontal flow conditions, 

and B, multiple PDBs deployed under complex vertical and horizontal groundwater flow conditions. Modified from 

Vroblesky and others (2001). [Arrows indicate direction of groundwater flow.]
4.0 Types of Passive Samplers 13

4.2.1 Description and Operation

The RCDM sampler consists of a deionized water-filled 

tube of high-grade regenerated cellulose dialysis membrane 

(fig. 7). The regenerated cellulose membrane is tied in a 

knot at one end, and a valve is attached to the other end. The 

membrane is then inserted into a protective LDPE mesh, the 

tube is filled with deionized water, and the valve is closed. The 

protective LDPE mesh is then cable-tied shut at both ends. 

Weights are attached at the bottom to overcome buoyancy, and 

a dedicated polypropylene line is used to suspend the sampler 

in the well. The sampler may have protective PVC supports 

external to the dialysis membrane to prevent leakage or an 

internal perforated PVC pipe or rigid polypropylene mesh to 

support the membrane in high ionic strength waters (fig. 8). 

The sampler is deployed in a well at the chosen depth for 

1–2 weeks to reach equilibrium. Because the dialysis membrane is hydrophilic, water can diffuse through the membrane. 

While the sampler is deployed in the open or screened interval, higher inorganic constituent or organic compound concentrations in the well water will diffuse through the membrane 

into the sampler in response to the concentration gradient with 

the enclosed deionized water. At the end of the deployment 

period, the concentrations of constituents inside the sampler 

are equivalent to the concentrations of constituents outside the 

sampler. The sampler is retrieved from the well, and the water 

sample is drained through the valve into the sample containers required for analysis. The sampler diameter and length can 

be adjusted to fit down the well and to collect the volume of 

water required for the chosen analyses.

Regenerated cellulose dialysis membranes can be 

purchased in different widths. The filled diameters and 

volumes of the two most commonly used dialysis membrane 

widths used to construct samplers for 2- and 4-in.-diameter 

wells are listed in table 1. For example, RCDM samplers made 

to fit in 2-in.- and 4-in.-diameter wells that are 63 centimeters 

(cm; 24.8 in.) long will contain volumes of approximately 

500 mL and 2,000 mL, respectively. 

Fully constructed RCDM samplers are not currently 

available from any commercial vendor. Dialysis membranes 

can be ordered from various material vendors. Purchase of 

pre-cleaned regenerated cellulose dialysis membrane material 

is recommended, particularly if trace metals and sulfides are 

to be sampled, because these constituents will be present in 

the dry, uncleaned dialysis membrane material. The dialysis 

membrane should have a nominal molecular weight cut-off of 

8,000 Daltons with an average pore size of 0.0018 μm. The 

regenerated cellulose dialysis membrane remains useable for 

3–5 years if kept refrigerated in its preservative solution.

A B

Figure 7. A 2.5-inch diameter 

regenerated cellulose dialysis 

membrane sampler with 

external supports, A, prior to 

assembly, and B, after assembly. 

Photographs by Thomas E. 

Imbrigiotta, U.S. Geological 

Survey.
14 Passive Sampling of Groundwater Wells for Determination of Water Chemistry

A B

Figure 8. Internal supports for regenerated cellulose dialysis membrane samplers. Photographs by 

Thomas E. Imbrigiotta and Donald A. Vroblesky, U.S. Geological Survey.

Table 1. Dialysis membrane flat widths, filled diameters, and filled volumes for regenerated cellulose dialysis membrane passive 

samplers. From Imbrigiotta and others (2007).

[mm, millimeter; cm, centimeter; mL milliliter; ft, foot]

Well diameter 

(inches)

Lay-flat width 

(mm)

Filled diameter 

(mm)

Filled diameter 

(inch)

Filled volume 

(mL/cm)

Filled volume 

(mL/ft)

2 50 31.8 1.25 7.94 242

4 100 63.7 2.5 31.87 971
4.0 Types of Passive Samplers 15

4.2.2 Advantages and Limitations

The main advantages of RCDM samplers are that they 

can be used to collect samples for analysis for a wide variety 

of organic and inorganic chemical constituents, they are relatively low cost to construct, the samples they collect require 

no field filtration, and they are disposable. Their limitations are 

primarily that they must be filled and kept immersed in deionized water between construction and deployment, they can 

biodegrade in groundwater systems after 4–6 weeks so they 

cannot be left in a well for extended periods, and the process 

of dialysis causes these samplers to lose a small percentage of 

their water volume with time (<3 percent per week) until equilibrium is achieved. RCDM samplers need to be filled with 

oxygen-free deionized water if redox-sensitive constituents are 

to be measured.

4.3 Rigid Porous Polyethylene (RPP) Sampler

The RPP sampler is an equilibrium-membrane-type 

passive diffusion sampler. The RPP sampler was developed in the mid-2000s to meet the need for a polyethylene 

non-biodegradable diffusion sampler that could be used to 

sample for inorganic constituents and non-volatile organic 

compounds, in addition to VOCs, at groundwater contamination sites where monitored natural attenuation potential was 

being evaluated. 

The RPP samplers have been successfully used to sample 

groundwater for a wide variety of organic compounds and 

inorganic constituents (VOCs, major cations and anions, 

most trace metals, nutrients, dissolved hydrocarbon gases, 

perchlorate, hexavalent chromium, 1,4-dioxane, explosives, 

and phenols; Vroblesky, 2004; Parsons, 2005; LeBlanc and 

Vroblesky, 2008; Savoie and LeBlanc, 2012). Water samples 

collected with RPP samplers are shipped to the laboratory for direct analysis of organic compound and inorganic 

constituent concentrations. 

4.3.1 Description and Operation

The RPP samplers consist of a 1.5-in.-outside-diameter 

by 6-in.-long, rigid porous polyethylene tube with a cap at one 

end and a plug at the other end (fig. 9). The tube is constructed 

from thin sheets of foam-like porous polyethylene with pore 

A

B

Figure 9. A rigid porous polyethylene sampler A, without the protective mesh, and B, with the protective mesh in a water-filled tube for 

shipment. Photographs by Leslie Venegas, ALS Global.
16 Passive Sampling of Groundwater Wells for Determination of Water Chemistry

sizes of 6–15 μm. The sampler is filled with deionized water; 

closed at both ends; placed inside a mesh sleeve, which is 

subsequently attached to a deployment rope using cable-ties; 

and lowered into a well. This size sampler holds 90–100 mL 

of water.

While deployed in the open or screened interval of a well, 

solutes in the groundwater will diffuse through the pores of the 

porous polyethylene membrane, driven by the concentration 

gradient between the groundwater and the deionized 

water inside the sampler. After 2 weeks, the constituent 

concentrations in water inside the RPP sampler will equal the 

constituent concentrations outside the RPP sampler. Upon 

retrieval, the capped end is removed, and the contents of the 

sampler are poured immediately into sample containers. Water 

samples are then shipped to the laboratory for direct analysis 

of concentrations. 

RPP are commercially available for purchase. The RPP 

samplers can be stacked to collect larger sample volumes. RPP 

samplers are restricted to a 6-in. length; if they are longer, 

they have a tendency to leak water as a result of the pressure 

of the fluid column inside the sampler exceeding atmospheric 

conditions. Even at 6 in., RPP samplers can leak if exposed to 

the atmosphere for several minutes. 

4.3.2 Advantages and Limitations

The main advantages of RPP samplers are that they can 

be used to collect samples for analysis of a wide variety of 

organic compounds and inorganic constituents and that they 

are not biodegradable, so they may be left in a well between 

sampling events. Their primary limitations are that they 

must be filled and kept immersed in deionized water prior to 

deployment owing to the possibility of leakage, the sample 

volume is restricted, and relatively large pore sizes (6–15 μm) 

allow for sampling of larger-sized molecules but consequently 

may require 0.45-μm filtering of the water upon retrieval. The 

length of the sampler, which is constrained by the height of the 

water column inside the sampler and the membrane pore size, 

limits the volume to approximately 100 mL per sample. These 

samplers need to be filled with oxygen-free deionized water if 

redox-sensitive constituents are to be measured.

4.4 Nylon Screen (NS) Sampler

The NS sampler is an equilibrium-membrane-type passive sampler. The NS sampler was originally developed in the 

late 1990s to sample for trace metals in groundwater. These 

samplers were tested in the early 2000s for their ability to 

sample VOCs, trace metals, major cation and anions, dissolved oxygen, 1,4-dioxane, and perchlorate (Vroblesky and 

others, 2002a; Vroblesky and others, 2002b; Vroblesky and 

others, 2003; Parsons, 2005). In some cases, the NS sampler 

may take a longer time (at least 3 weeks) to equilibrate with 

concentrations in the well water. If sampled before equilibration, the constituent concentrations in samples may be underestimates of concentrations in well water. The volume of water 

inside the sampler (V) relative to the diffusion surface area (A) 

of the nylon screen may play a role in equilibration and may 

be constituent dependent. Further research is warranted for 

the ability of NS samplers to sample for trace metals (ITRC, 

2006). Water samples collected with NS samplers are shipped 

to the laboratory for direct analysis of organic compound and 

inorganic constituent concentrations. An example of a study 

utilizing NS samplers is given in Appendix A, Case Study A2. 

4.4.1 Description and Operation

Nylon screen samplers can vary in size but typically consist of a 175-mL polypropylene wide-mouth bottle (diameter 

of 62 millimeters [mm] at top, 58 mm at bottom, and a height 

of 58 mm) filled with deionized water, with a 125-μm mesh 

nylon screen placed across the opening, and covered with a 

cap that has an opening about 58 mm in diameter (fig. 10). The 

resulting V/A ratio is about 6:1 (Webster and others, 1998).

Different sizes of samplers and corresponding V/A ratios 

can be used as shown in figure 10. The sampler in figure 10A

has a V/A ratio of 6:1, whereas the sample in figure 10B has 

a V/A ratio of 22:1. The NS sampler diffusion uptake can be 

calculated using equation 3 for constituents of interest. 

For deployment in wells, the NS sampler is placed within 

a protective polyethylene mesh and attached to a weighted 

line. It is preferable to deploy the NS sideways in a well but 

owing to size restrictions it is usually necessary to deploy 

it facing downward to minimize mixing as the samplers are 

brought back to the surface. During deployment, chemicals 

in groundwater in the well diffuse through the nylon screen 

membrane and equilibrate with water inside the sampler. The 

sampler retains the water inside by a combination of surface 

tension between the water and the screen and the vacuum that 

develops in the inverted bottle. Once retrieved, the samplers 

are re-inverted and the contents of the sampler can be transferred to sample containers, or solid caps can be screwed over 

the membrane in place of the open caps, and the entire sampler 

can be sent to the laboratory.

Fully constructed NS samplers are not currently available 

from any commercial vendor. Nylon screen of varying mesh 

sizes can be ordered from a number of material vendors. The 

NS samplers can be stacked to collect larger volumes of water 

from a well.

4.4.2 Advantages and Limitations

The main advantages of NS samplers are that they can 

be used to collect samples for analysis for a wide variety of 

organic compounds and inorganic constituents, they are low 

cost to construct, and they are disposable. Their limitations are 

primarily related to the small volumes of sample collection, 

typically 175 mL per sample, and that samples may require 

filtration through a 0.45-mm filter if dissolved concentrations 

are needed. NS samplers must be filled and kept immersed 

in deionized water between the time of construction and 

deployment in a well. These samplers need to be filled with 
4.0 Types of Passive Samplers 17

A

B

Figure 10. Two different sized nylon-screen passive samplers 

A, V/A ratio of 6:1 and B, V/A ratio of 22:1. Photographs by Donald 

A. Vroblesky and Philip T. Harte, U.S. Geological Survey. [V, volume 

of sampler; A, diffusion surface area of opening of sampler].

oxygen-free deionized water if redox-sensitive constituents 

are to be collected. Further, extended periods of deployment 

(>3 weeks) may be needed to achieve equilibration for some 

trace metals. 

4.5 EON Dual Membrane (DM) Sampler®

The EON Products, Inc. Dual Membrane (DM) sampler® is an equilibrium-membrane-type passive sampler. It 

essentially combines a PDB sampler and a NS sampler using 

two semi-permeable membranes in one diffusion sampler. It 

was developed fairly recently (circa 2015; EON Products, 

Inc., 2016). Given its recent development, the sampler has not 

been used extensively. The DM sampler theoretically allows 

sampling of major cations and anions, some trace metals, 

nutrients, VOCs, and some PFASs. 

A comparison study of the results of samples collected 

with DM samplers and with low-flow purging at Kirtland Air 

Force Base, Albuquerque, New Mexico, showed relatively 

good agreement between the concentrations of two VOCs 

(1, 2-dibromoethane and benzene), major cations and 

anions, and selected trace metals (EA Engineering, Science, 

and Technology, 2016, 2017). More than 90 percent of the 

comparisons made between the two sampling methods were 

within a relative percent difference (RPD) of 20 percent and 

were comparable to the RPD between duplicate samples 

(EA Engineering, Science, and Technology, 2016, 2017). 

Water samples collected with DM samplers are shipped to 

the laboratory for direct analysis of organic compound and 

inorganic constituent concentrations.

4.5.1 Description and Operation

The DM sampler consists of a 1.75-in.-diameter by 

22-in.-long hollow cylindrical, perforated tube that forms a 

rigid sample chamber. The top 6 in. of the sample chamber is 

wrapped with a 125-μm mesh nylon screen material, whereas 

the bottom 16 in. of the sample chamber is wrapped with an 

LDPE membrane (fig. 11). Like many other passive samplers, 

they can be deployed in a vertical string to profile well chemistry (fig. 11). The large pores of the nylon screen in the top 

portion of the sampler allow diffusion of inorganic constituents and polar organic compounds into the sampler (fig. 12). 

The LDPE membrane in the lower part of the sampler allows 

diffusion of VOCs (fig. 12) and acts as a reservoir. The two 

membranes form one internal sample chamber. Equilibration 

occurs when the chemical constituents that enter through both 

membranes diffuse vertically and mix within the sampler, their 

concentrations become uniform throughout, and the concentrations match that in the water outside the sampler in the well. 

This sampler should be deployed in a well for at least 3 weeks 

to equilibrate for most constituents. When a DM sampler is 

removed from a well, the water in the nylon screen portion 

will leak out and only the water in the LDPE portion will 

be retained. Because of this, a DM sampler with the above 

dimensions will collect approximately 625 mL of water. 
18 Passive Sampling of Groundwater Wells for Determination of Water Chemistry

A B

Figure 11. A, An EON Products, Inc. Dual Membrane (DM) sampler® and B, a vertical string of DM samplers being retrieved from a 

well. Photographs by Bradley P. Varhol, EON Products, Inc. and Rebecca Travis, U.S. Geological Survey.

Constituents equilibrate by

diffusing through the

membranes and then mixing

vertically within the sampler

Large pore membrane

Small pore membrane

Permeable to large and small molecules

Permeable to non-polar VOCs

Sample “Reservoir”

Figure 12. An EON Products, Inc. Dual Membrane sampler® with large pore and small pore membrane configurations. Modified 

from diagram by Bradley P. Varhol, EON Products, Inc. [VOCs, volatile organic compounds]
4.0 Types of Passive Samplers 19

4.5.2 Advantages and Limitations

The advantages of the DM samplers are that they can 

be used to collect samples for a range of major cations and 

anions, trace metals, VOCs, and some PFASs; they are 

constructed of non-biodegradable materials, so they can 

remain in a well from one sampling event to the next; and 

they are disposable, so no decontamination is needed. The 

limitations of the DM samplers include, longer deployment 

times (at least 3 weeks) for equilibration of some constituents 

both into and within the sampler, and that filtration of samples 

through a 0.45-μm filter is required if dissolved concentrations 

are needed. The relatively small nylon membrane surface area 

compared to the larger internal volume of the DM sampler 

may lengthen equilibration times. Other limitations are that 

the samplers must be filled in the field or kept submerged in 

deionized water between the time of filling and deployment, 

the samplers need to be filled with oxygen-free deionized 

water if redox-sensitive constituents are to be collected, and 

the sample volume is restricted by the size of the sampler to 

625 mL. 

4.6 QED Snap Sampler®

The QED Environmental Systems, Inc. Snap Sampler® 

is an equilibrium-thief-type passive sampler. Snap Samplers 

were first introduced in 2004, initially to collect unaltered 

VOC samples from wells without purging (Britt and others, 

2010). The sampler has specialized containers that can be triggered to close and seal at depth in a well. During equilibration, 

the samplers are left open (on both ends) to allow for advective or diffusive compound exchange with the surrounding 

environment (in this case well water). Once recovered, the 

closed containers are capped and sent directly to the laboratory for analysis, so no volatilization losses can occur during 

sample transfer at the surface (Britt, and others, 2010). 

Snap Samplers can be used to collect samples for most 

constituents of interest including VOCs, 1,4-dioxane, cations, 

anions, trace metals, explosives, and methane, among others 

(Britt and others, 2010; Parker and others, 2011a; Parker and 

others, 2011b). Water samples collected with Snap Samplers 

are shipped to the laboratory for direct analysis of organic 

compound and inorganic constituent concentrations. 

4.6.1 Description and Operation

The Snap Sampler consists of a polytetrafluoroethene or 

stainless-steel module that holds a 40-mL glass VOC vialsized bottle that is open on both ends (fig. 13A). A 125-mL 

polyethylene bottle and 350-mL bottle are also available for 

collecting larger sample volumes (fig. 13B). The device keeps 

the spring-loaded caps open while the device is deployed 

in the well. After equilibration has occurred, a trigger line 

is pulled manually or by using a pneumatic device to allow 

the spring-loaded caps to snap shut and seal off the sample 

(fig. 14). The pneumatic trigger allows for deep deployment 

of the samplers (>2,000 ft). Upon retrieval from the well, caps 

are added to both ends of the sealed bottle, which is then sent 

to the laboratory for analysis. There is no sample transfer, 

so there is no exposure to air, no volatilization, and no loss 

of sample volume. As many as six Snap Samplers can be 

attached in series to collect a large-volume composite sample 

or to collect samples at six different depths.

A B

Figure 13. The QED Environmental Systems, Inc. Snap Sampler® with A, a volatile organic compound bottle (40-millileter vial), and 

B, variously sized volatile organic compound and inorganic constituent bottles. Photographs by Sanford Britt, QED Environmental 

Systems, Inc.
20 Passive Sampling of Groundwater Wells for Determination of Water Chemistry

Figure 14. Various views of the QED Environmental Systems, Inc. Snap Sampler® operation in a well. Photographs by Sanford Britt, 

QED Environmental Systems, Inc.

When the Snap Sampler is left in the well for 1–2 weeks, 

permeation/diffusion through the open ends causes the chemical concentrations in the well water to equilibrate with those 

in the water inside the sampler. When triggered to close, the 

sample inside is sealed at the temperature and pressure present 

at the sampling depth. 

4.6.2 Advantages and Limitations

The main advantage of the Snap Sampler is that it 

is the only passive sampler that can collect true “total” or 

“unfiltered” samples because it contains no membrane or 

sorptive media that might selectively filter out or sorb some 

chemicals. It can be used to collect samples for analysis of a 

wide variety of organic compounds and inorganic constituents, 

and it can be used to collect redox- and pressure-sensitive 

chemical constituents that may oxidize or degas upon retrieval 

at land surface. The primary limitations of the Snap Sampler 

are limited sample volumes of the individual bottles (40 mL, 

125 mL, or 350 mL), the samplers are relatively expensive 

to buy compared to some other passive samplers (but may 

be leased at a lower cost), and operation and sampling 

procedures may require some training (available from the 

manufacturer). The sampler modules (the bottle holder part) 

are usually dedicated to a well, and the bottles may either be 

re-useable or disposable. Given that the sampler module is 

usually dedicated, there may be some long-term cost savings 

for monitoring wells that are sampled on a recurring basis. If 

dissolved concentrations are needed, the samples collected by 

the Snap sampler must be filtered through a 0.45-μm filter.
4.0 Types of Passive Samplers 21

4.7 AGI Sample Module®

The AGI (Amplified Geochemical Imaging, LLC) Sample 

Module®, formerly known as the GORE-SORBER® Module, 

is an accumulation-type passive sampler. The AGI Sample 

Module was developed in the 2000s to sample for organic 

compounds in soil gas, tree borings, and groundwater (Einfeld and Koglin, 2001; ITRC, 2006, 2007). The device relies 

on diffusion and sorption to accumulate analytes onto resins 

in the sampler. The samplers are recovered from a well after 

a pre-determined deployment period and sent directly to the 

AGI Laboratory in Newark, Delaware, for analysis. Samples 

collected with these samplers are measured after extraction/

desorption at the laboratory and produce a mass flux or a total 

mass of organic compounds sorbed over the time of deployment. Concentrations of organic compounds can be approximated with an algorithm developed by the manufacturer or can 

be compared to field samples collected using another sampling 

method during deployment (ITRC, 2006, 2007). 

These devices have been used to detect VOCs and 

SVOCs, including halogenated solvents, aliphatic and aromatic hydrocarbons, ethers, alcohols, ketones, polycyclic 

aromatic hydrocarbons (PAHs), nitroaromatic explosives and 

their breakdown products, pesticides, herbicides, and polychlorinated biphenyls (PCBs) (ITRC, 2006, 2007).

4.7.1 Description and Operation

Each AGI Sample Module is approximately 1⁄4-in. in 

diameter and 13 in. in length and consists of a tube of GORETEX® membrane that contains a series of four small packets 

of sorbent material (figs. 15 and 16). The GORE-TEX® 

membrane is microporous, expanded PTFE and is relatively 

chemically inert. The hydrophobic nature of the membrane 

Figure 15. The AGI Sample Module®. Photograph from Mark 

Arnold, Amplified Geophysical Imaging, LLC.

Knot (Secure

to wellhead)

Line

Loop to attach

to line

Tag with unique

serial number

Sorbent

Weight

Screened

interval

Water table Water table

AGI Sorber

A B

Well

Aquifer Aquifer

Figure 16. The installation of an AGI Sample Module® in a 

monitoring well. Modified from diagram by Mark Arnold, Amplified 

Geophysical Imaging, LLC.

allows organic vapor migration to the inner sorbent material 

but prevents water and sediments from passing through. 

A typical sorber module is about 9.8 in. (25 cm) in length, 

0.12 in. (3 mm) in diameter, and contains four packets of a 

granular adsorbent material that is selected on the basis of the 

specific compounds to be detected. For VOCs and SVOCs, 

hydrophobic carbonaceous and polymeric resins are used, 

although the sorber packets can be custom designed for 

specific organic compounds.

Organic compounds dissolved in water, partition to the 

vapor phase according to Henry’s Law and move through the 

PTFE membrane to the sorbent. For groundwater monitoring 

applications, the module is suspended in a monitoring well on 

a length of weighted line. The narrow diameter of the module 

allows deployment in piezometers and wells of 1⁄2-in.-inner 

diameter and larger. 

Each AGI Sample Module is clean when it comes from 

the manufacturer and is contained in a sealed glass vial 

(fig. 15). Each module is labeled with a unique serial number. 

After the module is removed from the vial, it is placed at the 

desired depth in the screened or open interval (fig. 16), or 

several modules can be placed at multiple depths within the 

screened or open interval. After the exposure period (minutes 

to days, depending on the concentrations present), the module 

is retrieved and returned to the glass vial and shipping container. The glass vials containing the exposed modules, along 
22 Passive Sampling of Groundwater Wells for Determination of Water Chemistry

with trip blanks, are shipped overnight to AGI’s dedicated 

laboratory. It has been determined that the modules do not 

have to be kept cold for shipment and will keep in the glass 

vials without refrigeration until they are analyzed, usually 

within 4–6 days (ITRC, 2007). The volume of water sampled 

during an AGI Sample Module deployment is a function of 

the sampling rate for a particular chemical and the sampling 

duration. The cost of an AGI Sample Module includes the trip 

blank, deployment supplies, laboratory analysis, and reporting. 

Costs per sample are dependent on the organic compounds 

being tested.

4.7.2 Advantages and Limitations

The main advantages of this passive sampler are that it 

can be used to collect samples for a wide range of VOCs and 

SVOCs; requires minimal handling, which reduces possible 

field sampling errors; is single use so no decontamination is 

needed; and can be used in monitoring wells and piezometers 

as small as 1⁄2-in. in diameter. In addition, these samplers 

have simple shipping requirements (no ice or coolers needed) 

and lower shipping costs, and the modules contain duplicate 

samples. Depending on the site and the constituents of interest 

being sampled, short deployment times may require only one 

trip to the field to collect a sample.

The limitations of the AGI Sample Module include that it 

cannot be used to sample for inorganic constituents and gives 

only flux results (mass per time) not concentration results, 

so a companion study is needed to correlate flux results with 

organic compound concentrations in groundwater, or an algorithm must be used to approximate concentrations. In addition, 

these samplers come from only one supplier, so the cost is set 

and relatively high, and the samples can be analyzed by only 

the supplier’s laboratory. 

4.8 Semi-Permeable Membrane Device (SPMD) 

Samplers

The SPMD sampler is an accumulation-type passive sampler. The SPMD samplers were developed in the mid-1990s 

by personnel at the USGS Columbia Environmental Research 

Laboratory primarily for sampling hydrophobic semi-volatile 

organic compounds and pesticides in surface water (Petty and 

others, 1995; Ellis and others, 1995; Lebo and others, 1995; 

Lebo and others, 1996; Gustavson and Harkin, 2000). Since 

that time, the sampler has been adapted to collect samples for 

organic compounds in groundwater in wells (Alvarez, 2010). 

The structure of the SPMD sampler simulates the surface 

and fatty tissues of a fish. Samples collected with an SPMD 

sampler are analyzed after extraction at the laboratory and 

produce a mass flux or a total mass of organics sorbed over 

the time of deployment in a well. Concentrations of chemicals 

can be approximated with an algorithm or can be compared to 

field samples collected during sampling using another method 

(Alvarez, 2010). 

4.8.1 Description and Operation

The SPMD sampler consists of a length of lay-flat LDPE 

tubing containing triolein. Triolein is a triglyceride and is 

highly sorptive of semi-volatile organic compounds and 

pesticides. The triolein-containing membrane can be made to 

different lengths to vary the surface area for adsorption and is 

supported inside a stainless-steel protective housing, which is 

made to fit down 4-in. wells (fig. 17A). The LDPE membrane 

and the triolein approximate the scales and the fatty tissues of 

a fish. The sampler is suspended in the open interval of a well 

where groundwater passing through comes in contact with it. 

Dissolved organic compounds flowing past the sampler experience a strong concentration gradient to move into the sampler, 

then partition into and accumulate in the triolein (fig. 17B). 

After recovery, the sampler is taken to the laboratory where 

the triolein is removed, extracted with hexane, and analyzed. 

The result is a mass flux or the mass of organic compound 

sorbed over the time the sampler was deployed.

4.8.2 Advantages and Limitations

The advantage of the SPMD sampler is that it can be 

used to collect samples for a range of hydrophobic SVOCs 

(PAHs, PCBs) and pesticides. The primary limitation of the 

SPMD sampler is that it cannot sample for inorganic constituents, VOCs, or hydrophilic organic compounds. Also, a 

sample extraction step is required prior to analysis and this 

procedure is typically only available at one or two laboratories. In addition, SPMDs measure only chemical fluxes in 

wells and require an algorithm to estimate concentrations or a 

companion study to correlate flux results to organic compound 

concentrations in well water.

4.9 Other Equilibrium-Membrane-Type Samplers 

A discussion of other equilibrium-membrane-type 

samplers is provided in Vrana and others (2005). In addition, 

and of note here, Gardner and Solomon (2009) developed a 

passive headspace sampler for sampling of noble gases. Gaspermeable silicon tubing is connected to conventional metal 

tubing by a gas-exchange port that can be shut off in situ by 

pressurization. This allows sealing of gas samples at depth. 

The concentration of the gas within the sampler can be calculated using Fick’s second law of diffusion. Testing of the ability of the sampler to collect noble gases, such as argon, found 

that concentrations of argon from the sampler provided a good 

comparison (within 3 percent) with results from conventional 

sampling (Gardner and Solomon, 2009). 

A diffusion sampler to collect samples for dissolved 

hydrogen in groundwater has been developed to determine 

redox conditions (Vroblesky and others, 2007b). This diffusion sampler is constructed with nitrogen-filled high-density 

polyethylene 50-mL syringes that can be installed in a well 

indefinitely. Over time, dissolved hydrogen in the groundwater 
4.0 Types of Passive Samplers 23

Water

Water

Interior

SPMD

Membrane

75-90 μm thick

EXPLANATION

Lipid (triolein)

Contaminant molecule

Membrane pore size <10 A

A

B

Figure 17. A, A downhole semi-permeable 

membrane device (SPMD) sampler and B, a 

diagram of SPMD operation. Photograph and 

diagram by David A. Alvarez, U.S. Geological 

Survey. (μm, micron)

equilibrates through the syringe walls into the nitrogen. Once 

the sampler is retrieved from the well, the gas sample can be 

directly injected into a gas chromatograph equipped with a 

hydrogen detector for analysis (Vroblesky and others, 2007b).

4.10 Other Accumulation-Type Samplers

The diffusive gradient in thin-film (DGT) sampler is an 

accumulation-type passive sampler, so the sampler produces 

a flux measurement that is based on the mass of inorganic 

constituents sorbed over the period of time it is deployed in 

a well. It does not measure concentrations in the groundwater. The sampler accumulates analytes on a thin-film resin 

layer. Analysis of the sample requires elution of the analytes 

off the resins to measure the mass of the inorganic constituents of interest. The sampler has been shown to be effective 

in sampling of uranium (U) and U isotopes of 235U and 238U 

(Turner, 2013) as well as lead, copper, zinc, cadmium, nickel, 

iron, and manganese (Zhang and others, 1995; Dunn and others, 2003). 

The ceramic dosimeter is another accumulation-type 

passive sampler. The sample produces a flux measurement that 

is based on the mass of organic compounds sorbed over the 

period of time the sampler is deployed in a well (Martin and 

others, 2003; Boppa and others, 2005). It does not measure 

concentrations in the groundwater. A comparison of results for 

benzene and naphthalene fluxes from the ceramic dosimeter 

with results for fluxes that are based on conventional water 

sampling of wells shows good agreement for relatively shortterm (days) to long-term (months) deployments. The timeintegrated flux measurements from the ceramic dosimeters 

were within representative ranges of results of fluxes calculated from conventional water sampling. 
24 Passive Sampling of Groundwater Wells for Determination of Water Chemistry

5.0 Considerations Prior to Use of 

Passive Diffusion Samplers

This section provides information on sampling objectives 

and the performance of passive samplers relative to physical 

and chemical conditions in the well and subsurface environments. Because passive samplers are affected by hydrologic 

and chemical conditions, substantial discussion is devoted to 

describing the dynamics between those conditions. 

5.1 Data-Quality Objectives

Prior to the start of a passive sampling effort, data-quality 

objectives (DQOs) need to be clearly identified. Data-quality 

objectives frequently are defined by (1) project sampling 

goals, (2) target analytes, (3) hydrologic conditions, and 

(4) regulatory guidelines. These factors help formulate the 

type of water-quality data needed and how accurate and precise the data need to be to achieve the project goals.

If prior information is unavailable on groundwater quality 

or the type of contaminants present, then purge sampling is 

better as an initial reconnaissance tool than passive sampling 

because purge sampling can collect samples for a broader 

range of chemical constituents. For evaluating contaminant 

problems or general water chemistry in residential areas, purge 

sampling may more closely approximate the volume of the 

aquifer that is interrogated when pumping household supply wells. However, if the main sampling goal is to monitor 

the concentration of a known indicator class of contaminants 

over the long term in observation wells, passive sampling 

may be the better option because it will reflect the concentrations present in the water flowing into the well under ambient conditions and likely will be less expensive than purging 

methods. An added benefit of passive sampling is that it will 

affect the flow field around the well less than purge sampling 

and consequently may better reflect solute transport behavior 

in the formation. 

A primary consideration when deciding whether to use 

passive samplers and the type of passive sampler to use is to 

ensure that the sampler is able to collect the constituents of 

interest. For example, if sampling is for just inorganic constituents, then PDB samplers would not be a good choice because 

they sample only for VOCs. In this case, RCDM, RPP, or NS 

passive samplers that can collect inorganic constituents and 

organic compounds may be more appropriate.

If one of the DQOs is to collect samples under unstressed 

(non-pumping) conditions, then one of the passive sampler 

types would be an ideal choice. In contrast, if the objective is 

to collect samples under different levels of stressed conditions 

in an aquifer, then use of a variable speed pump would be an 

effective sampling option. 

The DQOs for the project may require the collection of 

samples by certain prescribed methods to produce results that 

are approved and accepted by a regulatory or water agency. 

Many times, purging a well with a pump to obtain samples 

may be written into guidelines. In other cases, the agency 

may have guidance on the accepted use of passive samplers in 

wells or may allow their use if comparisons between passive 

sampling results and purging results are favorable.

5.2 Hydraulic and Chemical Equilibration

Two types of equilibration, hydraulic and chemical, must 

take place in a well before any passive sampler can collect a 

representative sample. Hydraulic and chemical equilibrium 

in this case refers to achieving a hydraulic-flow pattern and a 

chemical distribution within the screened or open interval of a 

well that is stable over a predetermined time. When a passive 

sampler is lowered into a well, it physically mixes the water 

column in the well to a small extent and temporarily perturbs 

borehole flow and the pattern of groundwater flowing into and 

out of the screened or open interval: a partial analogy to this 

process is the lowering of a downhole flow meter tool that perturbs the flow in the well, as described by Bayless and others 

(2011). The ambient flow of groundwater from the formation 

into the well and past the sampler will take a finite amount of 

time to re-establish itself. Once in the screened or open interval of a well, passive samplers must either equilibrate chemically with the concentrations of constituents in the groundwater or sorb a mass of constituents from the water flowing past 

the sampler. These equilibration and sorption processes will 

both take a finite amount of time to occur. Only after hydraulic 

and chemical equilibration/sorption occur can a representative 

sample be collected.

5.3 Hydraulic and Hydrologic Well 

Considerations

Passive sampling relies on the ambient flow of groundwater into the screened or open interval of a well to bring 

water in contact with the samplers. Therefore, knowledge of 

the geologic formation adjacent to the screened or open interval of the well, the age of the well, the water level in the well, 

and the construction of the well is important in deciding the 

performance of passive samplers in a well. These factors are 

discussed in more detail in Sections 5.3.1–5.3.5.

5.3.1 Geologic Formation

The exchange of ambient groundwater in the aquifer 

formation with the water in the screened or open interval 

of a well will differ among geologic formations. In permeable sand-and-gravel formations, ambient flow through the 

screened interval occurs principally from the most permeable 

strata along the screened interval (Marsh and Lloyd, 1980; 

Kearl and others, 1994). In fractured rock formations, ambient flow occurs primarily from discrete fractures at different 

depths in the bedrock. On a relative scale, wells in porous 
5.0 Considerations Prior to Use of Passive Diffusion Samplers 25

media likely will encounter more uniform diffuse flow across 

the entire open interval than wells set in fractured rock where 

flow is channeled only through discrete fractures. Regardless 

of the type of flow regime, proper placement of passive samplers in a well is important in any formation where hydrogeologic units promote stratified horizontal flow into a well and 

where minimal mixing occurs in the well. 

If a well is completed in a permeable formation, it probably is in good hydraulic communication with the formation, 

and the water in the well probably is representative of water 

in the formation adjacent to the well opening. In such a well, 

a passive sampler will collect a sample that likely represents 

the groundwater chemistry in the formation for the deployment period. This can be confirmed by comparing concentrations in samples collected with passive samplers and purging 

methods in the same well. Harte (2002) found close agreement 

of tetrachloroethene concentrations measured in wells in very 

permeable sand-and-gravel glacial deposits using PDB passive 

samplers and purging.

If the well is screened in a less permeable or a hydraulically tight formation, the concentrations of constituents 

measured using a passive sampler may represent the concentrations in the well over the past few days but not the concentrations present in the formation. The reason for this is the 

slow flushing times of wells in low-permeability formations, 

where mixing or chemical reactions may be taking place in 

the well, such as volatilization losses of VOCs in the water 

column of the well (McAlary and Barber, 1987), which are not 

occurring in the formation. Mixing or chemical reactions may 

cause a passive sampler in such a well to collect samples with 

concentrations different from those in the formation.

To further illustrate the concept that the permeability of 

a formation and the relative rates of flow and transport can 

control the chemical concentrations recovered by a passive 

sampler, a schematic diagram of the relation between chemical 

concentrations from the well, formation, and sampler is shown 

in figure 18. Fundamentally there are two transport characteristics to consider when sampling with passive samplers. They 

are the rate of transport of constituents from the formation to 

the well and the rate of exchange between the well water and 

the sampler. The first characteristic is controlled by near-well 

transport in the formation (permeability and hydraulic gradients) and transport into and out of the well (well connectivity). 

The second characteristic is controlled by the passive sampler 

membrane and concentration gradient of the constituents of 

interest across the membrane. For extremely high-permeability 

formations (for example, karst environments) with high transport rates, equilibrium-membrane-type passive samplers will 

equilibrate over time but may not be able to monitor shortterm changes in concentrations in water flowing rapidly past 

the sampler (fig. 18A). For example, the passive sampler could 

equilibrate to some time-weighted average concentration, but 

this average may not be representative of the chemical concentration in the formation at any moment in time. However, for 

some slower transport rates, it would be a closer representation 

(fig. 18B). Alternatively, in low-permeability formations, the 

transport from the formation to the well may be so slow that 

the chemical concentration in the well water is not representative of the concentration in the formation because chemical 

changes can occur once the water enters the well (fig. 18C). As 

a rule of thumb, in all but very low-permeability formations, 

7–14 days has been found to be sufficient for the flow regime 

to re-equilibrate between the formation and the well. 

5.3.2 Age of the Well

Well age or the time since the well was installed can 

have an important effect on whether to use passive sampling. 

Because contact time of the sample water with the well 

material is longer for passive sampling than for purge 

sampling, well-material degradation or reactivity of the water 

with the well material has the potential to affect passive 

samples more than the short-contact time for purge samples. 

In addition, if flow through the well screen or filter pack is 

diminished because of clogging by physical or biological 

processes, then the ambient water in the well is less likely to 

freely exchange with formation water. In this case, because 

a purge sample can force inflow through the screen, purge 

sampling may produce a more representative sample than 

the passive sampler. In general, wells constructed with inert 

materials that are not easily corroded or degraded and wells 

with screened or open intervals that are not clogged are 

preferred wells for passive sampling.

Another age-related factor that may affect passive sampling is related to well installation. The disturbance of the flow 

field in the groundwater system during the well installation 

process is important and affects the ability to collect representative samples from the well for a period of time after well 

installation. Ideally, at least 1–3 months should elapse before 

trying to sample a newly installed well using purging methods. 

Passive sampling will require a greater time period after installation than purge sampling to allow for hydraulic and chemical 

equilibration. Although some methods of well drilling disrupt 

the groundwater chemistry and ambient flow in the aquifer 

more than others, as a rule of thumb, passive samplers are not 

to be used to collect a sample in a well before the well is a 

minimum of 6 months old. 

5.3.3 Monitoring History

New wells that have no monitoring history are not ideally 

suited for the use of passive samplers. Unless the new well 

is installed at a site that is well characterized for a specific 

constituent, the practitioner has little idea about which constituents to look for and, consequently, which passive sampler 

to choose. As discussed in Section 5.3.2, there is also the 

problem of flow into the well not equilibrating hydraulically or 

chemically for a long period of time after well installation. 

Wells that are used for long-term monitoring with a 

known historical record are ideally suited for the use of passive samplers. Long-term monitoring wells have well-known 
26 Passive Sampling of Groundwater Wells for Determination of Water Chemistry

Rate of well flushing≥

Rate of groundwater flow>

Rate of sampler equilibrium

Rate of well flushing>

Rate of groundwater flow<

Rate of sampler equilibrium 

Rate of well flushing≤

Rate of groundwater flow<

Rate of sampler equilibrium 

A

B

C

Flow-exchange relation

Cw=Cfm≠Cs

Cfm

Cs

Cw

Cfm=Cw=Cs

C Cs fm

Cw

Cs=Cw≠Cfm

Cfm

Cs

Cw

Well casing

Well screen Well screen Well screen Well screen Well screen

Well casing

Well casing

Passive

sampler

Passive

sampler

Passive

sampler

High-permeability

formation 

Medium-permeability

formation 

Low-permeability

formation 

Chemical relation

Figure 18. Hypothesized relation of passive sampler constituent concentration responses to 

rates of well flushing and groundwater flow and transport assuming constant sampler equilibrium 

rates for A, high-permeability, B, medium-permeability, and C, low-permeability formations. 

[Cs, constituent concentration in the sampler; Cfm, constituent concentration in groundwater in the 

formation; Cw, constituent concentration in the well bore; >, greater than; <, less than; ≥, greater 

than or equal to; ≤, less than or equal to]
5.0 Considerations Prior to Use of Passive Diffusion Samplers 27

hydraulic and chemical histories. This makes choosing a passive sampler that will collect the constituents of interest possible. Previous knowledge of the transmissivity of the well and 

the well construction helps with making decisions concerning 

the sampler depth and deployment/exposure time. 

5.3.4 Water Levels

Knowledge of the water-level fluctuations in a well is 

important to prevent potential exposure of passive samplers 

to the atmosphere. Passive samplers ideally would be suspended in the well so that they remain submerged below the 

water level for their entire deployment period. If the water 

level in a well drops substantially over the deployment period 

and exposes the passive sampler to the atmosphere, chemical concentrations in an equilibrium-membrane-type passive 

sampler may not reach complete equilibrium with the chemical concentrations in the well water, and an accumulation-type 

passive sampler risks sorbing a reduced chemical mass from 

the well water, consequently yielding a low estimate for the 

mass flux. 

Continuous submergence is usually not a problem for 

fully saturated screened or open intervals where the water 

levels in the well casing are well above the top of the screened 

or open interval. Continuous submergence is more problematic 

in partially saturated screened or open intervals or in wells 

with very little water above their openings. In the latter case, 

water-level declines may result in exposure of the passive 

sampler to the atmosphere. This is especially a problem when 

sampling for redox-sensitive constituents in formations with 

anaerobic water because contact with oxygenated water in the 

sampler could cause a chemical reaction that would affect concentrations in the sampler. For example, iron hydroxides could 

precipitate within the sampler and lower the dissolved iron 

concentrations. For sampling in aerobic waters, the exposure 

of the sampler is less stringent for redox-sensitive constituents 

because there is less of a chance that oxidation will affect the 

concentrations. 

VOCs are a class of organic compounds that may also be 

sensitive to sampler exposure to the atmosphere. If sampling 

is for VOCs and the water level drops exposing the passive 

sampler to air in the well, loss of VOCs from degassing is 

possible. However, if the water level rises and the sampler is 

re-submerged for the last several days of its required equilibration time immediately prior to recovery, the collected VOC 

concentrations should be valid. 

5.3.5 Well Construction

The construction of a well may have some effect on the 

use of passive samplers. If the well screen is properly sized for 

the aquifer sediments, open, and unclogged, the well hydraulic 

communication with the formation should be good, and the 

use of passive samplers should not be a problem. If, however, 

the screen is clogged with fine sediments or mineral deposits 

and not open to the formation, the well may not provide 

adequate exchange with groundwater for passive samplers to 

work properly. 

The length of a well opening can be a factor affecting the 

use of passive samplers because of the potential for vertical 

flow and mixing within the well. Well openings greater than 

10 ft have an increased probability of intersecting zones of 

differing permeability and hydraulic head and, therefore, an 

increased probability of vertical flow within the well opening. 

If vertical flow is prevalent in the well, the water chemistry 

of the well primarily reflects that of the units with the highest 

hydraulic head flowing into the screened or open interval. In 

contrast, where horizontal flow predominates, such as through 

short screens or longer screens intercepting little vertical variation in permeability and hydraulic head, the water chemistry 

of the well tends to reflect that of the formation approximately 

coincident with the sampler depth (Harte and Flanagan, 2011). 

A filter pack around a screened interval can affect ambient flow in the well by redistributing inflow and outflow. Consequently, filter packs facilitate mixing of groundwater, which 

can alter water chemistry and potentially camouflage any 

stratification of groundwater chemistry found in the formation. 

Filter packs that extend beyond the well opening can intercept 

units with unique flow and chemistry characteristics that could 

then be redistributed into the well opening by way of the filter 

pack. Harte and others (2001) found that a filter pack that 

extended above a well screen contributed to tetrachloroethylene (PCE) concentrations that were 50 percent greater near the 

upper part of a 10-ft-long well screen than in the remainder of 

the well screen because the filter pack intercepted a permeable 

unit that transported PCE from above the screened interval 

into the well screen. 

The diameter of a well will determine which passive 

samplers will fit down the well. All passive samplers discussed 

in this report are constructed to fit down a 4-in.-diameter well 

or greater. Versions of many of these samplers also have been 

constructed to fit down 2-in.-diameter wells or less. AGI Sample Modules will fit down wells as small as 1⁄2-in. in diameter.

5.4 Water-Quality Sampling Considerations

Water-quality considerations need to be taken into 

account before deciding whether to use a passive sampler and, 

if so, which sampler to use in the well. Issues like the materials used for sampler construction, the chemical constituents to 

be monitored, the size of the sampler, the deployment depth in 

the well, and the sampler deployment time in the well, among 

other things, will affect these decisions. These factors are 

discussed in Sections 5.4.1–5.4.8.

5.4.1 Analyte Suitability Considerations

The most important factor in choosing which passive 

sampler to use is that it must be able to sample for the 

constituents of interest. As pointed out in Section 4, each 
28 Passive Sampling of Groundwater Wells for Determination of Water Chemistry

passive sampler has a set of constituents for which the 

sampler has successfully been used to sample and some that 

it has not been able to sample. If, for instance, the site has 

VOC contamination, PDB samplers would be a good choice 

because they are inexpensive, reduce field sampling time, and 

have a proven track record of successful sampling for most 

VOCs. However, if there is a need to monitor for evidence 

of natural attenuation of the VOCs at the site, samples for 

ferrous and ferric iron, sulfate and sulfide, and carbon dioxide 

also will need to be collected. To sample for these additional 

inorganic constituents, a RPP sampler could be added in close 

proximity to the PDB sampler. Alternatively, a larger RCDM 

sampler could be used that would collect VOCs and inorganic 

constituents in one sampler. Additional discussion on the 

suitability of samplers for sampling specific constituents is 

presented in Section 6. 

5.4.2 Sampler-Size Considerations

Many of the equilibrium-membrane-type passive samplers are small in diameter so they can fit down 2-in.- and 

4-in.-diameter wells. As a result, most of these samplers collect small volumes of water. Before using a passive sampler 

in a well, one must be certain that enough water volume can 

be collected from the sampler to analyze for the constituents 

of interest. Once the sampler is constructed, the volume of 

water contained in any equilibrium-membrane type of passive 

sampler is fixed, so it is important to carefully determine at the 

outset of sampling the water volumes needed for analysis.

Volume limitations can be overcome by contacting the 

laboratory that will be analyzing the samples to discuss the 

minimum volumes necessary for the analyses. Frequently, laboratories ask for sample volumes that are several times larger 

than required simply to ensure that they have enough water 

for multiple analyses, dilutions, or reruns. Improvements in 

analytical technology have decreased the volumes required for 

many analyses. As an example, many anions are now analyzed 

by ion chromatography that requires only 5 mL of sample, 

whereas the laboratory may ask for a full 250-mL bottle for 

these analyses. Once the minimum volume has been agreed 

upon with the laboratory, this volume should be increased by 

10–20 percent to account for volume used to rinse bottles or 

losses during sample handling in the field. 

Some samplers can be made longer to increase their 

volume (PDB, RCDM), but some cannot because of poresize limitations or design (RPP, NS, Snap). For example, the 

RPP sampler can leak the fluid sample if it is longer than 6 in. 

Also, as the length of a passive sampler increases, the sampler 

becomes more difficult to protect from harm during installation and recovery, and handling during sample collection 

becomes harder. The ITRC (2004) states that a single passive 

sampler should not represent more than a 5-ft interval in a 

well, so no passive sampler should be longer than 5 ft. 

5.4.3 Sampler-Depth Considerations

The depth at which a passive sampler needs to be 

deployed must be known prior to going to the field so as to 

select the appropriate length of the suspension line required to 

deploy the sampler. Knowledge of the length and depth of the 

screened or open interval in a well is required. Screened and 

open intervals of 5 ft or less can be sampled by a single sampler suspended at their center point because vertical chemical stratification over this short distance is likely small. (The 

exception to this case is wells closer to hydraulic boundaries.) 

It is prudent, when initially using passive samplers in wells 

with screened or open intervals longer than 5 ft, to begin by 

deploying a string of passive samplers over the length of the 

open interval to decide whether the water is mixed or stratified, as discussed in Section 5.5. On the basis of the results of 

the initial vertical profiling and the DQOs of the project, the 

passive sampler typically is deployed at the depth where the 

highest concentration and (or) mass flux of the constituent of 

interest is found to be entering the well. 

Passive samplers have no depth limit for their operation. 

As long as the samplers can be deployed and recovered from 

the selected depth in the well, they will work. RCDM samplers have been used in wells to depths of 410 ft but should 

be useable at greater depths (Imbrigiotta and others, 2007). 

DM samplers have been used at depths >1,000 ft in wells in 

New Mexico (Rebecca Travis, U.S. Geological Survey, written 

commun., 2018). Samplers that, by their design, are prone to 

leakage with time, such as the RPP sampler, are best not used 

in wells with depths to water greater than 200 ft. 

5.4.4 Equilibration Time and Exposure Time

A variety of factors affect the equilibration time for 

equilibrium-type passive samplers and the exposure time 

for accumulation-type passive samplers. For equilibriumthief-type passive samplers, the primary consideration is 

re-establishing hydraulic equilibrium after installation of the 

sampler. Once hydraulic equilibrium is achieved, chemical 

equilibrium via diffusion must then occur prior to sampling. 

For equilibrium-membrane-type passive samplers, the 

rate of chemical equilibration of a constituent of interest 

between the sampler and the well water is dynamic and is a 

function of several factors: (1) the rate of ambient flow and 

transport past the sampler, (2) the physical characteristics 

of the membrane, (3) the affinity of the constituent of 

interest for the membrane material or materials of sampler 

construction, (4) the temperature of the groundwater, and 

(5) the diffusion coefficient of the constituent of interest. For 

most wells screened in sand-and-gravel deposits, fast flow 

through the screened interval allows for a quick and more 

complete exchange between equilibrium-type samplers and 

the groundwater. 

The physical characteristics of a membrane refer to 

its thickness, area, pore size, and effective pore size. Thin 

membranes will equilibrate faster than thick membranes. For 
5.0 Considerations Prior to Use of Passive Diffusion Samplers 29

example, equilibration through a 2-μm-thick LDPE membrane 

takes place faster than through a 4-μm-thick LPDE membrane. 

In general, membranes with large pores will equilibrate faster 

than membranes with small pores. The effective pore size 

depends not only on the size of the openings in the membrane, 

but also the tortuosity or length of the path a molecule must 

travel to diffuse through the membrane. 

The chemical affinity and permeability of a variety of 

membrane materials have been determined in the laboratory for a large number of organic compounds and inorganic 

constituents (Vroblesky and Campbell, 2001; Vroblesky and 

others, 2003; Martin and others, 2003; Divine and McCray, 

2004; Imbrigiotta and others, 2007; Britt and others, 2010). If 

a chemical constituent is strongly sorbed to a membrane material, equilibration will take longer to occur than if the chemical 

is not strongly sorbed because the strongly sorbed constituent 

passes through the membrane more slowly. 

Groundwater temperature can affect the length of the 

deployment of a passive sampler. Molecules of a chemical 

constituent dissolved in warm shallow groundwater will diffuse faster and presumably equilibrate faster than the same 

chemical in cold groundwater at the same location. 

The diffusion coefficient (D) of a chemical in water is an 

important factor in equilibration time because it is an important characteristic in Fick’s first law (eq. 2). VOCs like trichloroethene (TCE) have a relatively high D (1.5 × 10-5 cm2

/s) 

compared to the D for inorganic constituents like uranium or 

selenium (2 × 10-8 cm2

/s). Equilibrium time as expressed by 

the Cs

(t) term in equation 3 is shorter for higher values of D. 

As a general rule of thumb, the deployment time 

for many equilibrium passive samplers is on the order of 

1–3 weeks with 2 weeks being the most commonly used 

deployment time. However, in some cases for compounds with 

low diffusion coefficients, the deployment time could be much 

longer than 2 weeks. Deployment times can differ at a given 

site for given constituents, depending on the conditions present 

in the aquifer. For example, if a well in a high permeability 

formation is sampled for chlorinated VOCs, a RCDM passive 

sampler probably will hydraulically and chemically equilibrate 

in a matter of a few days to a week (Imbrigiotta and others, 

2007). On the other hand, if a well in a low-permeability 

formation is sampled for these same organic compounds, the 

RCDM sampler will probably take longer to hydraulically 

equilibrate, and the necessary deployment time will probably 

be closer to 2 weeks. The manufacturer of an equilibrium-type 

passive sampler always should be consulted when estimating 

deployment times for a sampler for various constituents.

For accumulation-type passive samplers, the exposure 

time needs to be determined on the basis of the constituents 

of interest and the concentrations present at the field site. 

The constituents of interest must be able to readily adsorb to 

the sorbent material of the sampler for effective sampling. 

For accumulation samplers, exposure time in the well should 

be shorter than the time it takes to completely saturate all 

the sorption sites on the sorbent material in the sampler, yet 

long enough to sorb sufficient mass to be able to detect the 

chemicals of interest at the lowest concentration of interest. 

Frequently, the exposure time is determined during the first 

sampling event by deploying multiple samplers in a well and 

removing them at different times (Martin and others, 2003) to 

determine when saturation occurs. For accumulation samplers, 

it is important to have some idea of the range of concentrations of the constituents of interest that are present in the well 

before deploying the samplers. The range of exposure times 

for accumulation-type samplers extends from minutes where 

constituent concentrations are high to several days or weeks 

where constituent concentrations are low.

5.4.5 Sampler Hydration Considerations

Some equilibrium-membrane-type passive samplers need 

to be kept hydrated after construction so the membrane will 

not dry out or to keep the sample chamber filled. Samplers 

such as the RCDM, RPP, NS, and DM samplers should be 

constructed and (or) filled within a few days of deployment, 

and all need to be kept immersed in deionized water between 

filling and deployment. If allowed to dry out, the membrane’s 

diffusive properties can change, or the sample chambers can 

lose fluid from within the sampler. 

5.4.6 Redox Considerations

The redox conditions of groundwater in the formation 

need to be considered prior to deployment of passive samplers 

when sampling for redox-sensitive constituents. For example, 

equilibrium-membrane-type passive samplers used to collect 

redox-sensitive constituents in anaerobic groundwater should 

be filled with water sparged with nitrogen or another relatively 

inert gas to remove the oxygen. Further, the sampler should 

not be exposed to atmospheric conditions prior to deployment 

because atmospheric oxygen will diffuse through the membrane into the sampler. De-oxygenated samplers can be transported to the field in a cooler full of sparged deionized water. 

If the samplers are used in an aerobic aquifer, then sparging 

the sampler-fill water is not necessary. 

The reason that de-oxygenated water is needed to sample 

redox-sensitive constituents in anaerobic systems is that 

oxygen within the sampler can potentially react with chemicals diffusing into the sampler. For example, an equilibriummembrane-type passive sampler filled with aerobic deionized 

water installed in a well with anaerobic groundwater and a 

high dissolved iron concentration can be problematic because, 

as dissolved iron diffuses across the membrane and contacts 

the oxygenated water inside the sampler, iron hydroxides can 

be precipitated out. This can result in lower dissolved iron 

concentrations being measured inside the sampler than in a 

pumped sample from the same depth in the well. 

Sorption of a redox-sensitive constituent to the membrane 

of an equilibrium sampler can also be a problem, but with 

the reverse effect. For example, if high concentrations of iron 

are sorbed to the membrane itself, the inward concentration 
30 Passive Sampling of Groundwater Wells for Determination of Water Chemistry

gradient may be increased between the membrane and the 

water inside the sampler. This may result in a higher concentration of dissolved iron being measured inside the sampler 

than that measured in a pumped sample from the same depth 

in the well (Imbrigiotta and others, 2007).

5.4.7 Biological Considerations

Some semi-permeable membranes can be perforated or 

clogged over time by bacteria present in groundwater systems. 

This can take the form of bacterial or fungal growth clogging or fouling the membrane or, in some cases, perforating 

the membrane, which can cause the sampler to fail. Previous 

researchers have noted that some RCDM membranes have 

become discolored or bio-fouled during extended equilibration 

periods ranging from 2 to 3 weeks in shallow wells with warm 

groundwater temperatures (about 21 degrees Celsius [°C]) 

(Vroblesky and others, 2002b; Vroblesky and Pravacek, 2002; 

Vroblesky and others, 2003). Imbrigiotta and others (2007) 

compared biodegradation of four identical RCDM samplers 

in an anaerobic groundwater system in a 75-ft-deep well with 

an average groundwater temperature of about 15 °C at the 

Naval Air Warfare Center, West Trenton, N.J. These samplers 

discolored only slightly and lasted 4–6 weeks before developing perforations. Iwakun and others (2008) found that RCDM 

samplers survived intact for 6 months at a site in Canada 

where the average groundwater temperature was 4 oC ± 1 oC. 

Because the RCDM samplers require only a 2-week deployment to equilibrate for most constituents of interest, biodegradation of the membrane was not considered to be a major 

limitation for these samplers.

5.4.8 Temperature and Density Effects

Small density differences in water of 0.005 percent 

(approximately 50 milligrams per liter [mg/L] in total dissolved solids) and small temperature gradients (0.2 o

C per 

meter) can induce mixing and the formation of thermal 

convective cells (Martin-Hayden, 2000). Thermal convection 

can induce vertical flow rates in a well to exceed 200 mL/min 

(Martin-Hayden, 2000). Thermal convection can inhibit the 

ability to determine depth-dependent concentrations. Instead, 

the concentrations derived would represent a mixed average 

concentration across depths contributing inflow within the 

convection interval. 

Thermal convection also can inhibit a sampler’s ability to 

collect representative redox-sensitive constituents of interest. In the winter in wells with a shallow depth to water, the 

shallower water can become colder than the deeper water in 

the well. The cold shallow water can sorb oxygen, initiate convection, and transport this DO to the deeper parts of the well. 

Thermal convection during the winter months was found to 

rapidly transport (within days) DO throughout much or all of 

the water column in wells with shallow depths to water (less 

than 30 ft) in South Carolina (Vroblesky and others, 2006, 

2007a). Therefore, well water under ambient conditions is not 

representative of groundwater in an anaerobic formation under 

the influence of thermal convection and DO transport. Given 

the potential effect of thermal convection, passive sampling for 

redox-sensitive constituents should not be done without mitigating thermal convection and DO transport. One approach to 

mitigating thermal convection is to use a simple, inexpensive 

baffle system (Vroblesky and others, 2006, 2007a). Although 

the simple baffle system is unlikely to prevent strong advective 

(head-driven) vertical flow in a well because of pressure differences forcing flow around the baffle, it is generally effective 

in mitigating thermal convection. Other more complex baffle 

systems, such as packers, could be used to mitigate both thermal convection and advective flow.

5.5 Vertical Profiling

Vertical profiling in a well can be of two types, hydraulicflow profiling and chemical profiling. Hydraulic-flow profiling refers to the determination of the depths where water is 

entering or leaving the open interval of a well and where there 

are zones within the open interval with no water movement. 

Hydraulic-flow profiling is useful for designing subsequent 

chemical-profiling surveys. Chemical profiling refers to the 

determination of the vertical distribution of chemical constituents within the open interval of a well under ambient (or 

pumped) conditions. Specific techniques used to conduct both 

types of profiling are discussed in the Sections 5.5.1–5.5.2.

5.5.1 Hydraulic-Flow Vertical Profiling

Hydraulic-flow vertical profiling to determine where 

groundwater is entering the well usually is done using either 

a straddle-packer pump setup or a borehole flow meter. The 

straddle packer with a pump in between the packers is used to 

seal off a zone in the well, measure the distribution of hydraulic head in the different zones, pump the zone, and watch the 

change in water level with time as it recovers. These data 

cannot only be used to determine whether water is entering 

the zone based on head measurements, but also can be used to 

calculate transmissivities of the packed-off zones. These zones 

can be portions of a long screen in unconsolidated aquifers 

in the absence of a sand pack or portions of an open bedrock 

borehole around discrete fractures. By moving up or down 

the open interval and repeating these tests, transmissivities at 

different depths can be determined, and the vertical change 

in transmissivities and the depths of groundwater inflow and 

outflow over the length of the open interval of a well can be 

evaluated (Shapiro, 2007).

Hydraulic-flow vertical profiling with borehole flow 

meters can be done with several different types of meters. For 

small flows (vertical flow rates of 0.01–0.5 gal/min) a heatpulse flow meter has been used. The heat-pulse flow meter 

tracks an initiated pulse of heat by measuring a temperature 

increase above or below the sensor and determines the vertical 
5.0 Considerations Prior to Use of Passive Diffusion Samplers 31

direction of groundwater flow. The rate of the heat-pulse 

transport can be measured and used to identify the vertical 

distribution of inflow and outflow in the well under ambient 

and pumped conditions. Also, the vertical variation in transmissivities with depth of layers intersecting the open interval 

of a well can be calculated under pumped conditions. Locations of vertical flow between layers or fractures in the well, or 

stagnant zones where there is negligible inflow or outflow, also 

can be determined. 

Many of the borehole-flow meters measure only vertical 

flow where horizontal flow between successive vertical flow 

measurements is inferred. Horizontal flow, specifically cross 

flow where inflow into the well equals outflow from the well 

at the same or similar depth, cannot be determined with these 

meters (Harte and others, 2014). In this case, other borehole 

flow meters will need to be used, including point-dilution 

meters (Masciopinto and Palmiotta, 2014). Annable and others 

(2005) developed a passive-flux meter that estimates horizontal flow through an open interval by measuring the rate of loss 

of a dye off a sorbent over a deployment period to calculate a 

flux through the open interval of a well.

Knowledge of inflow and outflow patterns in a well 

helps to guide deployment of passive samplers. The depth 

of deployment of a passive sampler is crucial to collecting 

a representative sample from the well and should not be 

arbitrarily chosen in a well where mixing is minimal. The 

passive sampler typically needs to be placed at a depth where 

the highest mass flux of the constituent of interest passes 

through the open interval of a well (ITRC, 2004). This means 

the vertical variation in groundwater chemical concentrations 

also needs to be determined.

5.5.2 Chemical-Vertical Profiling

Chemical-vertical profiling can be accomplished with 

passive samplers by deploying a series of equally spaced 

samplers over the entire length of a screened or open interval 

of a well. This is easily done because of the relatively small 

interrogation volume of the samplers (Harte and others, 2001; 

Vroblesky and Peterson, 2004; Divine and others, 2005). 

Analysis of samples collected with this series of passive 

samplers will give the vertical variation in concentrations of a 

constituent of interest. The vertical variation in concentrations 

can be used to assist in identifying which zones or fractures 

have inflowing groundwater containing the constituent 

of interest. Vertical chemical profiling also can help to 

corroborate flow patterns in open boreholes from various types 

of hydraulically active fractures if fracture water chemistry 

has been determined with discrete sampling. During vertical 

profiling with passive samplers, the use of baffles can be 

incorporated onto the suspension line to help segregate or 

isolate flow in the well.

Samplers can be spaced as close or as far apart as desired 

over the open interval of a well, constrained by the length 

of the sampler (Appendix A, Case Study A1). A minimum 

spacing distance equal to the length of the passive sampler is 

recommended to improve detection of distinguishable differences in vertical water chemistry while balancing the costs of 

analyses. For example, a 1-ft-long sampler would have a minimum spacing distance of 1 ft between the bottom of the upper 

sampler and the top of the lower sampler. Obviously, using 

more samplers in vertical profiling means more analyses, so 

the cost of the analyses is often the controlling factor in the 

number of samplers deployed in vertical profiling. In general, 

one passive sampler should represent no more than 5 ft of the 

open interval of a well (ITRC, 2004). 

Sampler deployment for vertical profiling can be 

designed on the basis of results from borehole geophysical 

logging (Appendix A, Case Study A2). Stratigraphy (geologic 

layering) and formational contacts are important considerations in vertical profiling. These data can be ascertained from 

lithologic logs and borehole geophysical logs, such as naturalgamma ray logs, which help map lithologic and mineralogic 

characteristics of a formation. Other borehole logs that are 

useful in deployment of samplers include electromagnetic 

(EM) induction conductivity, fluid conductivity, and temperature. The EM induction logs measure apparent conductivity 

induced from an EM signal. The EM induction log responds 

to electrical conductivity of the solids and groundwater. Fluid 

conductivity and temperature can be used to identify ambient 

flow circulation in the well. An example of vertical deployment that is based on stratigraphy and depths of inferred 

hydrogeologic contacts for an alluvial aquifer in New Mexico 

is shown in figure 19. A description of the study area and formations is presented in Appendix A, Case Study A2.

5.5.3 Profiling for Determining Deployment Depth

In wells with open intervals longer than 5 ft, the depth of 

deployment for a passive sampler ideally is not arbitrarily chosen but is based on the information collected from hydraulicflow profiling and chemical profiling. Some depths may have 

high constituent concentrations but not much groundwater 

flowing into the well. Other depths may have low constituent 

concentrations but most of the water coming into the well. In 

most cases, passive samplers should be positioned at the depth 

of highest mass flux of the constituent of interest. That is, the 

depth at which the product of the groundwater inflow rate and 

the constituent concentration gives the highest mass per unit 

time. Deployment at this depth allows for the collection of a 

sample of groundwater that has the highest transport potential 

of the constituent of interest in the well. 

5.5.4 Relation Between Borehole Flow and Water 

Chemistry 

Ambient flow can occur horizontally and vertically in 

a well. The direction of ambient flow is an important influence on samples obtained from a passive sampler. Horizontal 

flow through the screened or open interval is dependent on 

the hydraulic properties of the formation and the horizontal 
32 Passive Sampling of Groundwater Wells for Determination of Water Chemistry

100110

102030405060708090

0

0 50 100 150 200

Gamma

(2-foot moving average)

Depth in feet below land surface

Gamma counts, in counts per second Electromagnetic conductivity, in mmho/m

0 50 100 150 200

EM

Casing

Construction

Screen

Samplers

Deploymentwater level Recovery

water level

Sampler in casingSampler in screen

Figure 19. Example of vertical profiling with passive samplers, based on borehole geophysical logs, water levels, and well construction in an alluvial aquifer in New Mexico. [mmho/m, millimhos per meter; ft, feet; EM, electromagnetic]
6.0 Decision Tools 33

hydraulic gradients between the formation and the head in the 

well. A well dominated by stratified horizontal flow (fig. 6A) 

likely will have greater variability in vertical water chemistry 

than a well dominated by vertical flow from a single zone. 

Vertical flow in the well is dependent on the vertical-head 

gradients in the formation and differences in the permeability 

across the opening (fig. 6B). 

In-well mixing can obscure the ability of a sampler to 

identify vertical water chemistry in the formation (Church and 

Granato, 1996). The presence of sand packs in screened wells 

also can obscure the chemistry in the formation by redirecting ambient flow. Research on ambient flow indicates there is 

a tendency toward chemical homogenization in the screened 

interval of a well such that most wells experience strong 

redistribution effects of groundwater chemistry (Britt and others, 2014). However, some wells may maintain stratification 

or perhaps re-stratify differently from the surrounding formation (Britt and others, 2014). In some cases, the ambient flow 

in the well can be modified with use of baffles or packers that 

segregate flow vertically from in-well mixing (Vroblesky and 

others, 2007a).

Harte and others (2014) identified several different flow 

types of hydraulically active fractures in crystalline rock on 

the basis of borehole dilution logging. Flow types included 

inflowing fractures, outflowing fractures, and several different types of cross-flowing fractures. Deployment of passive 

samplers at hydraulically active fractures in this study helped 

identify chemical influent and confirmed inflowing groundwater at a fracture. In this case, three samplers were arranged vertically, in an upper, middle, and lower configuration, adjacent 

to three fractures to allow for delineation of chemical influent 

and vertical transport of influent in the borehole (fig. 20). 

Borehole-flow patterns in fractured rock can be complex 

and lead to well-mixed borehole fluid from differing chemical zones in the formation. Several examples of borehole flow 

are illustrated in figure 20. In some cases, the passive sampler 

positioned adjacent to a fracture may not measure the water 

chemistry of the adjacent fracture on the basis of flow patterns and the type of flow in the fracture (whether inflowing, 

outflowing, or cross flowing). Figure 20A shows an example 

of upward flow where the outflowing fracture (F1) receives 

water from all three fractures; the closest adjacent passive 

sampler (P1) to fracture (F1) is primarily sampling water from 

fractures F3 and F2 with some contribution from the inflowing side of F1. Figure 20B shows an example of a convergent 

flow to an outflowing fracture (F2) that is not contributing 

water chemistry to the adjacent passive sampler (P2). In other 

cases, the passive sampler collects a mixture of water chemistries from several fractures (fig. 20C; samplers P1 and P2). 

Lastly, the passive sampler may be relatively unaffected by 

any particular water chemistry from a fracture and instead 

may reflect the chemistry of stagnant borehole water (fig. 20D; 

sampler P3). 

Before using a passive sampler in a well, it is important 

to know whether there are stagnant zones where water is not 

flowing into the open interval. In fractured-rock wells where 

fracture frequency may be sparse, particularly in some deep 

wells (greater than 500 ft deep), flow may be focused in the 

shallow depth of the open interval. In such a case, the passive 

sampler should be suspended at a shallow depth to collect a 

sample from water in the formation. It is important to remember that passive samplers collect only samples that are representative of the water passing by them.

Passive samplers also have been deployed to measure primarily hydraulically inactive flow zones of a rock block. Harte 

and others (2015) and Harte and Brandon (2020) developed 

a screening methodology to utilize findings from chemicalvertical profiling with PDB samplers to identify the active 

and inactive flow zones of an open borehole in fractured rock 

at a cis-1,2-dichloroethene (cisDCE) contamination site. The 

screening methodology coupled borehole flow conditions and 

changes in vertical concentrations to identify flow- or diffusion-dominated processes in an open borehole set in fractured 

rock (table 2). 

6.0 Decision Tools

Prior to groundwater sampling, an assessment needs to be 

done to determine whether passive sampling is a viable alternative to other sampling methods. Decision tools are provided 

in the following sections to aid in determining (1) whether a 

passive sampler could be used at a particular well, (2) which 

passive samplers can be used to collect water for certain 

classes of chemical constituents, and (3) what are the minimum water volumes that can be collected to provide enough 

volume for the required analyses. The decision tools include 

several tables that can be used as general guides for addressing 

each topic. Obviously, each well, site, and analysis will have 

its own unique characteristics that will need to be considered.

6.1 Passive Sampler Use

Table 3 provides 10 questions that field personnel need 

to ask when deciding whether or not to use passive samplers 

in wells. The table has been modified from a similar one in the 

ITRC (2004) technical regulatory guide.

6.2 Passive Sampler Capabilities

It is important when considering the use of passive 

samplers to make sure that the selected sampler is capable of 

collecting a representative concentration of the chemical constituents in question. Table 4 presents groups of constituents 

that have been successfully sampled and analyzed in laboratory equilibration tests or in field tests and the type of passive 

sampler used to collect the sample. As more testing is done, 

this list likely will change and be expanded.
34 Passive Sampling of Groundwater Wells for Determination of Water Chemistry

F1

F2

F3

P1

P2

P3

F1

F2

F3

P1

P2

P3

F1

F2

F3

P1

P2

P3

F1

F2

F3

P1

P2

P3

P1=F1+F2+F3; P2=F1+F2; P3=F3

P1=F1; P2=F1+F2+F3; P3=F3

P1=F1; P2=F1+F3; P3=F3

P1=F2; P2=F2; P3=BOREHOLE

A B

C D

Figure 20. Ambient borehole flow patterns and relation to vertical water chemistry as measured by 

passive samplers: A, upward flow, B, convergent outflow, C, mixed cross flow, and D, mixed stratified 

flow. [P, passive sampler; F, inflowing or outflowing groundwater location of fracture; arrow, indicates 

direction of flow]
6.0 Decision Tools 35

Table 2. Classifications of intervals in open borehole fractured-rock wells, based on distinguishing hydraulic and chemical 

characteristics of zones. From Harte and Brandon (2020).

Hydraulic zones

Chemical zones

Static, negligible change in concentration along interval of wellIncrease in concentration 

along interval of well

Decrease in concentration 

along interval of well

Inflow (Active) Active-Static chemical zone Active-Influx chemical zone Active-Dilution chemical zone

Outflow (Active) Active-Nonparticipating chemical 

zone

Active-Mixed chemical zone (likely 

some small inflow present)

Active-Nonparticipating chemical 

zone

Non-flow (Inactive) Inactive-Chemical diffusion zone Inactive-Potential unidentified hydraulically active zone or back diffusion 

chemical zone

Inactive-Potential unidentified hydraulically active zone or adsorption 

chemical zone

Table 3. Decision analysis summary of appropriateness of passive sampler use. Modified from ITRC (2004).

[A negative answer to any of the following questions will require further action or investigation before passive samplers can be deployed. If all answers are 

affirmative, passive samplers are likely to be a viable option for the site. ft, foot; cm/s, centimeter per second; >, greater than; <, less than]

No. Question YES NO

1 Is sampling being done for long-term groundwater monitoring?

2 Has the groundwater chemistry at the site been fully characterized?

3 Can the passive sampler being considered collect samples for all constituents of interest?

4 Can the passive diffusion sampler being considered collect the sample volume necessary to analyze the constituents of 

interest given the well construction?

5 Have hydraulic and chemical vertical profiling been done in the wells to be sampled?

6 Are the monitoring wells to be sampled in an area where there is sufficient groundwater velocity (>0.5 ft/day)? Low 

groundwater velocity can result from either a low hydraulic conductivity (<10-5cm/s) or a low hydraulic gradient 

(<0.001).

7 Are the monitor wells currently free of dedicated pumps or other sampling equipment?

8 Has a cost evaluation shown the passive sampler being considered offers a cost savings compared to current sampling 

techniques?

9 Have you discussed the potential use of the passive sampler with site regulators?

10 Are the site regulators familiar with the passive sampler technology, and will they allow the data to be used for the same 

purposes as those obtained by purge sampling?
36 Passive Sampling of Groundwater Wells for Determination of Water Chemistry

Table 4. Chemical constituents and corresponding sampling capability of passive samplers.

[Ca, calcium; Mg, magnesium; Na, sodium; K, potassium; HCO3, bicarbonate; Cl, chloride; SO4, sulfate; F, fluoride; Br, bromide; NO3, nitrate, NO2, nitrite; 

NH4, ammonium; PO4, phosphate; Fe, iron; Mn, manganese; Al, aluminum; Ag, silver; Zn, zinc; BTEX, benzene, toluene, ethylbenzene and xylene; RDX, 

1,3,5-trinitro-1,3,5-triazinane; HMX, 1,3,5,7-tetranitro-1,3,5,7-tetrazoctane; TNT, trinitrotoluene; organoCl, organo-chlorine; organoP04, organo-phosphate; 

PAH, polycyclic aromatic hydrocarbons; BN, base-neutral organics; PCB, polychlorinated biphenyls; ClO4, perchlorate; PFOS, perfluorooctane sulfonic acid; 

PFOA, perfluorooctanoic acid; PFNA, perfluorononanoic acid, NT, not tested]

Passive diffusion samplers

Polyethylene diffusion bag 

sampler 

(PDB)

Regenerated 

cellulose 

dialysis 

membrane 

sampler 

(RCDM)

Rigid 

porous 

polyethylene 

sampler 

(RPP)

Nylon 

screen 

sampler 

(NS)

Downhole 

thief 

sampler 

(Snap)

Sorbent 

sample 

module 

(AGI)

Semipermeable 

membrane 

device 

sampler 

(SPMD)

Dual 

membrane 

sampler 

(DM)

Chemical constituents and characteristics

Field physiochemical characteristics 

(Temp, pH, SC, DO, ORP)

Some Some Some Some Some None None Some

Major cations and anions 

(Ca, Mg, Na, K, HCO3

, Cl, SO4, F, Br)

None All All All All None None All

Nutrients (NO3

, NO2, NH4, PO4) None All All All All None None All

Trace elements 

(Fe, Mn, Al, Ag, Zn and others)

None Most Most Most All None None Most

Perchlorate (ClO4

) None All All All All None None All

Organic carbon (dissolved or total) None All All All All None None All

Dissolved hydrocarbon gases

(Methane, ethane, ethene)

All All All All All None None All

Volatile organic compounds 

(Chlorinated solvents, BTEX)

Most Most Most Most All All None Most

Semi-volatile organics (1,4-Dioxane, BN, 

Phenols, PAH, PCB, dioxins, furans)

Some Some Some NT All Some Most NT

Pesticides (organoCl, organoPO4

) None NT NT NT All Some Most NT

Explosive compounds

(RDX, HMX, TNT)

None Most Most NT All Most NT NT

Poly- and perfluoroalkyl substances 

(PFASs)

None Some NT NT NT NT NT Some

6.3 Minimum Required Analytical Volumes

Because the volume of water that passive samplers 

typically collect is limited, it is a good idea to check with the 

laboratory to determine whether the laboratory can conduct 

all the analyses of interest with the volume that the selected 

sampler can collect. The volume of water typically requested 

by laboratories for each analysis is often larger than the volume actually needed for analysis in order to anticipate spills, 

reruns, or analytical difficulties. Table 5 shows the volume of 

water the USGS National Water Quality Laboratory (NWQL) 

typically requests for selected constituents and analytical 

methods, and the minimum volume the laboratory can use and 

still complete these analyses. Summing the minimum volumes 

will give the actual amount needed by the laboratory for all 

the analyses. Again, prior to the collection of any samples, 

it is advisable to check with the laboratory to be sure of the 

minimum acceptable water volume required by the laboratory for sample analyses. ITRC (2004) has a similar table for 

minimum volumes needed for U.S. Environmental Protection 

Agency analytical methods. 
6.0 Decision Tools 37

Table 5. Minimum volumes required for selected analytes from the U.S. Geological Survey National Water Quality Laboratory.

[Schedules and laboratory codes from internal USGS websites accessed online November 19, 2018; mL, milliliter; RU, raw untreated; FU, filtered untreated; 

FA, filtered acidified; FCC, filtered chilled; TDS, total dissolved solids; GCV, 40-mL glass vials; GCC, baked glass container; PCBs, polychlorinated biphenyls; 

NWQL, National Water Quality Laboratory; DOC, dissolved organic carbon; VOCs, volatile organic compounds; SVOCs, semi-volatile organic compounds; 

HNO3, nitric acid; NH4, ammonium; NO2, nitrite; NO3, nitrate; H2SO4, sulfuric acid; HCl, hydrochloric acid; °C, degrees Celsius]

Analyses

Filtration 

requirement/

preservation

Lab code 

(LC) or 

Schedule 

(SH)

Volume 

requested 

by NWQL 

(mL)

Minimum 

volume 

required by 

NWQL 

(mL)

Comments

Field physiochemical characteristics:

Specific conductance and pH

Raw, untreated, chilled 

(RU)

LC69 + 

LC68

250 100 Recommend collected 

in field (50 mL each)

Alkalinity Filtered, untreated, 

chilled (FU)

LC2109 250 100

Major cations and anions and silica: Bromide, 

Calcium, Chloride, Fluoride, Iron, Magnesium, Manganese, pH, Potassium, Total 

dissolved solids, Silica, Sodium, Specific 

conductance, Sulfate

Filtered, acidified 

w/HNO3 (FA)

SH1 250 50 Must measure specific 

conductance and pH 

in the field

Trace elements: Aluminum, Antimony, Arsenic, Barium, Beryllium, Boron, Cadmium, 

Chromium, Cobalt, Copper, Lead, Lithium, 

Manganese, Molybdenum, Nickel, pH, Selenium, Silver, Specific conductance, Strontium, Thallium, Uranium, Vanadium, Zinc

Filtered, acidified 

w/HNO3 (FA)

SH2710 250 50 Must measure specific 

conductance and pH 

in the field

Nutrients: Nitrogen, ammonia; Nitrogen, 

nitrite; Nitrogen, nitrite + nitrate; phosphorous, phosphate, ortho; Total nitrogen 

(NH3+NO2+NO3+organic)

Filtered, chilled (FCC) SH2755 125 80

Residue on evaporation (180 °C) (TDS) Filtered, chilled (FU) LC27 250 100 Must measure specific 

conductance in field

Dissolved organic carbon (DOC) Filtered, acidified 

w/H2SO4 (DOC)

LC2612 125 125

Volatile organic compounds (VOC) Raw, acidified w/HCl 

(GCV)

SH1307 or 

SH1380

3 × 40 3 × 40

Semi-volatile organic compounds:

Base/neutral/acids (SVOC)

Raw, untreated, chilled 

(GCC)

SH1383 1,000 500

Organonitrogen pesticides Raw, untreated, chilled 

(GCC)

SH1379 125 100

Halogenated organic compounds:

PCBs, pesticides

Raw, untreated, chilled SH8099 500 250
38 Passive Sampling of Groundwater Wells for Determination of Water Chemistry

7.0 Sampler Deployment, Retrieval, and 

Sample Collection

This section identifies critical information needed for passive samplers to collect water chemistry samples from wells. 

To aid in passive sampler deployment and retrieval, a field 

form (Appendix B) has been developed by the authors as part 

of this report to help facilitate the use of passive samplers in 

collecting groundwater samples. The field form is referenced 

throughout this section when applicable. 

7.1 Well Dimensions and Water Level

Before going to the field to deploy the passive sampler, 

the casing and screened or open interval diameter, the total 

depth of the well, and the depth and length of the open or 

screened interval need to be obtained. This information typically can be found in the well construction log. The data need 

to be entered as reported well information on the field form 

(Appendix B). It is important to know the diameters of the 

well casing and screened or open interval because some wells 

telescope to smaller diameters with depth, thus having smaller 

diameter open intervals or screens than the casing. Some passive samplers can fit down 2-in.-diameter wells or screens, but 

others will require a minimum 4-in.-diameter well or screen. 

The current depth to water needs to be measured prior 

to installation of a passive sampler to ensure that the desired 

target depth of the sampler is completely below the water level 

in the well and is located within the screened or open interval. 

The total well depth also can be checked at this time if confirmation is needed (Appendix B, sounding depth). 

7.2 Installation of the Sampler

Prior to installation of a single passive sampler, the 

suspension line must be measured out, so the length will allow 

the sampler to be suspended at the chosen deployment depth 

in the screened or open interval. Sampler lengths, depths, and 

reference position used (top or midpoint) must be noted on the 

field form such as the one shown in Appendix B. The passive 

sampler is attached to the suspension line at the appropriate 

depth using cable ties or stainless-steel clips. A stainless-steel 

weight is attached to the end of the suspension line or the 

bottom of the passive sampler. The sampler is then lowered 

slowly into the well. Once submerged in the water column, the 

sampler should sink easily to the desired depth if it includes 

sufficient weight to overcome its buoyancy. If the suspension line is made of polypropylene and the passive sampler is 

deployed in a well greater than 100 ft deep, some line stretch 

may occur and needs to be taken into account when determining the actual depth of deployment. If the suspension line is 

made of Teflon-coated cable or stainless steel, it is unlikely to 

stretch even during deep deployments. 

During deployment, the sampler should be lowered 

slowly and carefully until the desired depth on the line is at 

the measuring point (MP) or other reference point, such as 

land surface. The phrase slowly and carefully is emphasized 

to minimize mixing of the water column in the well and to 

prevent abrasion of the sampler against the inside of the casing 

or open hole. The suspension line must be secured at the top of 

the casing, so the position of the sampler will not change during the period of equilibration. An example of securing a suspension line to the top of the well is shown in figure 21. The 

suspension line is attached to a bolt that is secured through the 

casing and bolted with nuts on both sides of the casing wall. 

When the attachment is covered by a locked well cap, the line 

and bolt are tamper resistant. In addition, a caution sign can 

be placed on a well, such as that shown in Appendix C, to 

indicate samplers are installed in the well. 

The installation of most passive samplers is easily 

accomplished by one person, but obviously can be done faster 

by two people. However, two people are recommended for 

vertical profiling of wells with the deployment of multiple 

passive samplers. 

The amount of weight to attach to the line for a passive 

diffusion sampler is based on the need to overcome the buoyant force, as described in Archimedes’ principle. Essentially, 

the upward buoyant force that is exerted on a passive sampler 

and its deployment line is equal to the weight of the fluid that 

the sampler displaces and acts in the upward direction at the 

center of mass of the displaced fluid. Since most passive samplers are filled completely with water, the buoyancy that must 

be overcome is from the weight of the materials of sampler 

construction and the deployment line. The greater the number 

of passive samplers attached to a line, the greater the material 

weight that will need to be overcome, and thus, the greater the 

amount of weight that will be needed on the end of the line. 

The deeper that the passive samplers are deployed, the greater 

the weight of the deployment line and the more weight that 

will be needed on the end of the line. Assuming minimal material is used in the construction of passive samplers, which is 

particularly true for PDB samplers, buoyancy can be roughly 

calculated by the volume (cubic feet [ft3

]) of water displaced 

by the suspension line, if water-filled samplers are used, multiplied by the density of water (62.4 pounds (lb) per ft3

). For a 

3/8-in.-diameter by 100-ft-long polypropylene suspension line, 

the amount of weight needed would be 0.03 lb per ft of line or 

3 lbs total.

7.3 Deployment Period

For equilibrium-membrane-type passive samplers, the 

deployment period, that is the time the passive sampler is left 

in a well, is dependent primarily on two factors: (1) the length 

of time it takes the flow regime passing through the well to 

re-stabilize after introduction of the sampler (time 1) and 

(2) the length of time it takes a passive sampler to chemically 

equilibrate with the water in the well (time 2). The minimum 
7.0 Sampler Deployment, Retrieval, and Sample Collection 39

Figure 21. Tamper-resistant 

attachment of a weighted 

passive sampler suspension 

line to an interior bolt. 

Photograph by Thomas E. 

Imbrigiotta, U.S. Geological 

Survey.

deployment period should be the longer of time 1 or 2. A more 

conservative approach is to make the deployment period the 

sum of time 1 and 2. In high-permeability formations, the 

flow re-stabilization may occur quickly, on the order of hours. 

In low-permeability formations, the flow stabilization may 

be quite slow, on the order of weeks. Prior to deployment, 

all passive samplers should be tested in the laboratory to 

determine how long it takes for a variety of chemicals to 

reach chemical equilibrium in test solutions containing known 

concentrations. Results of such tests are available in reports 

and papers published on the development of these samplers. 

Some passive samplers chemically equilibrate with some 

constituents in a day or two, whereas other constituents take 

weeks to equilibrate. As a general rule of thumb, unless you 

are dealing with a very low permeability formation or the 

constituent being sampled takes a very long time to chemically 

equilibrate because of a low diffusion coefficient (D <1 × 10-8

cm2

/s), 2 weeks is the most frequently used deployment time 

for most passive samplers.

7.4 Sampler Retrieval

After the appropriate deployment time, the passive 

samplers are retrieved. Visual inspection of the well should 

be done to identify whether tampering has occurred during 

deployment. Water levels should be measured prior to sampler retrieval and recorded on the field form (Appendix B). 

The start time of retrieval is recorded on the field form as the 

time when the suspension line begins its ascent to the surface. 

Once the sampler is at the surface, visual observations of the 

condition of the sampler should be made prior to transfer of 

the sample into the sample bottle (if required). Examples of 

possible changes to be noted are loss of volume, color change, 

the presence of biological growth, and any perforations in the 

membrane. After retrieval of the last passive sampler, the end 

time of retrieval is noted on the field form. 

7.5 Sample Collection

Sample collection should occur as soon as possible after 

retrieval of the passive sampler from the well. In most cases, 

the sample collection should occur within 10 min after the 

sampler is at land surface to avoid exposure of the sample to 

oxygen, lower pressures, and possible loss of volatile compounds. The time of sample transfer from the passive sampler 

to the laboratory bottle should be noted on the field form 

(Appendix B). 

Collection of water samples from passive samplers is 

most easily done by two field persons. For most samplers, one 

person holds and pours out the passive sampler while the other 

person holds and caps the sample container(s). All of these 

actions also can be done by one field person with a supported 

hook or clamp to act as a third hand. Sample collection likely 

will take longer with only one person. It is more of a challenge 

to retrieve and collect samples quickly if multiple samplers 

are used to vertically profile a well. Two persons are a benefit 
40 Passive Sampling of Groundwater Wells for Determination of Water Chemistry

in this case, where one person is sampling while the other is 

retrieving samplers from the well. If multiple bottles are filled 

from each sampler or it takes longer than 10 min to collect a 

sample, the remaining passive samplers still attached to the 

line can be carefully lowered down the well into the water 

column to prevent exposure to the air and to prevent drying of 

any membranes. 

For most of the passive samplers, sample collection is 

described in more detail in Section 4 and is briefly summarized here. For PDB samplers, the samplers are pierced with 

a straw or the corner of the bag is clipped off, and the sample 

stream is directed or poured into sample containers. For 

RCDM samplers, the sampler is inverted, the bottom valve is 

rinsed with deionized water to remove any particulates that 

may have fallen in from the well casing, and the sample is 

emptied through the valve directly into sample containers. For 

RPP samplers, the capped end of the sampler is removed, and 

the water sample is poured out directly into sample containers. For the NS samplers, the screened top of the NS sampler 

is removed, and the contents of the bottle are poured directly 

into the sample containers. In some cases, the same bottle can 

be used, and a solid cap is exchanged for the screened cap. 

For the DM samplers, the sampler is pierced with a straw, and 

the stream is directed into sample containers. For the Snap 

sampler, samples are collected by triggering the spring-loaded 

sample containers to close at depth in the well, bringing them 

to the surface, and then screwing caps onto both ends of the 

sample containers. For the AGI sample modules, the samplers 

are placed back in the glass container they were shipped in. 

For the SPMD samplers, the polyethylene membrane containing triolein is detached from the sampler body, rolled up, 

placed in an air-tight metal container, and chilled on ice for 

shipment to the laboratory. 

7.6 Disposal and Decontamination

If the passive sampler is sized correctly for the number 

and type of sample bottles being filled, essentially no water or 

only a minimal amount of water should be left over at the end 

of sample collection. With the exception of the Snap sampler, 

which has sample containers that may be cleaned and reused, 

and the SPMD sampler, which has a support structure that is 

cleaned and reused, passive samplers are made of disposable 

materials and can be discarded once the samples are collected. 

The suspension lines can be saved and dedicated to the same 

well for use in subsequent samplings. The stainless-steel 

weights should be saved, cleaned using standard equipment 

cleaning protocols, and baked to remove volatile contaminants, so they can be reused in subsequent samplings.

8.0 Data Reporting Procedures

The discrete nature of passive sampling lends itself 

to data collection, coding, and entry into databases that are 

different from the data collection, coding, and entry for 

standard purge sampling. For databases such as the USGS 

National Water Information System (NWIS), placement, 

time, and type of sample must be clearly identified to avoid 

confusion. The same station identifier needs to be used for all 

passive samples from the same well. Either single or multiple 

samplers used in vertical profiling need to be designated by a 

depth location in the well. The collection time differs between 

purge and passive sampling. Purging produces an instantaneous sample, whereas the passive sample needs to have a collection period equivalent to the last few days or weeks of the 

deployment period. Designation of sample type, whether filtered or total, should be based on the membrane pore size and 

whether it is coarser or finer than a 0.45-mm filter. A comparison of pertinent NWIS identifiers and parameter codes used 

for purge samples and passive samples are listed in table 6.

9.0 Quality Assurance/Quality Control

Quality assurance and quality control (QA/QC) with 

passive sampling includes a few procedures that differ from 

those for purge sampling. Many of the passive samplers 

require that a water source is tested for the presence of 

constituents of interest. Other differences and details are 

outlined in this section. 

9.1 Recommended QA/QC Samples

As with all groundwater sampling, QA/QC samples must 

be collected when using passive samplers. QA/QC samples 

help determine whether there is contamination in the water 

used to fill the samplers, contamination from the construction 

materials of the sampler, or cross-contamination in the cooler 

during shipment to the laboratory. QA/QC samples also can 

be used to explain the variability of the results from the water 

samples that the samplers produce.

9.1.1 Deionized Water Source Blank

Passive samplers that require filling with water in the laboratory or field (some PDB, RCDM, NS, and DM samplers) 

typically are filled with high-quality deionized water from 

a laboratory treatment system, such as ASTM Type 1 water 

(ASTM, 2014), or NWQL inorganic blank water or NWQL 

organic blank water. A sample of the blank water should be 

collected and analyzed for the constituents of interest for the 

project prior to its use in filling any passive samplers. Some 

commercially available passive samplers, such as PDB and 

RPP samplers, come pre-filled and enclosed in a sleeve of 

blank water. In this case, the manufacturer usually attaches a 

certificate stating the concentrations of chemicals in the water 

inside the sampler. 
9.0 Quality Assurance/Quality Control 41

Table 6. Identifiers and parameter codes for data associated with purge and passive samples for input into the U.S. Geological 

Survey National Water Information System database.

[STAID, station identifier; MEDIM, sample medium; STYPE, sample type; H, composite (through time), environmental sample; WG, groundwater; 

—, no data]

Identifier

Purge, bulk sample Passive, discrete sample

Description

Parameter 

code

Sub 

parameter 

code

Description Parameter code

Sub 

parameter 

code

Sample site identifier One unique site identifier STAID — One unique site identifier STAID —

Date of sample Begin date DATES — Begin and end date span the 

deployment period

DATES —

Time of sample Begin time (one sample 

per time)

TIMES — Begin and end times with time 

offset for each depth/deployed 

sampler

TIMES —

Deployment period Instantaneous with no 

duration

— — Begin and end date span the 

deployment period

— —

Medium Groundwater MEDIM WG Groundwater MEDIM WG

Type of sample Grab STYPE 9 Composite STYPE H

Total or dissolved Based on filter pore size — — Based on sampler membrane 

pore size

— —

Sample interval (feet) Well screen 00003 — Specified by position and depth 

of sampler (feet below land 

surface)

72015 (top of 

sampler) or

72016 (bottom 

of sampler)

—

Depth of well (feet) Depth including sump 72008 — Same as purge 72008 —

Depth of water level 

(feet below land 

surface)

Multiple readings for 

static and purge

72019 — Multiple readings for start and 

end deployment date

72019 —

Purpose of site visit Primary 50280 2001 Primary 50280 2001

Sample purpose Routine 71999 10 Routine 71999 10

Sampling method Peristaltic pump 82398 4080 Other 82398 8010

Sampling method Submersible pump 82398 4040 Passive diffusion 82398 140

Sampling type Purge, bulk sample — — Passive diffusion 84164 3090

9.1.2 Equipment Blank and Field Blank

An equipment blank is collected to determine whether 

the sampler construction materials are contributing any of the 

constituents of interest to the sample. An equipment blank 

should be collected from an extra sampler (typically the first 

sampler constructed) that is identical to all the others that are 

purchased or constructed for deployment. Once all samplers 

are deployed, this extra sampler can be handled in two different ways. First, it can be sampled immediately, and the 

sample sent to the laboratory for analysis of the constituents 

of interest. This is the preferred option because it reduces the 

possibility of additional exposure to contamination beyond 

the time of installation and best reflects initial conditions of 

deployment for all the samplers (option 1). Second, the extra 

sampler can be suspended in the same deionized water used to 

fill the sampler in a covered clean container in the laboratory 

or at the field site for the same length of time that the passive 

samplers are deployed in the wells in the field (option 2). After 

the deployment period is complete, the passive sampler stored 

in the deionized water container is sampled for an equipment 

blank, which is analyzed using the same identical method as 

the samples from the passive samplers recovered from the 

wells. For either option, the equipment blank will determine 

whether the constituents of interest are desorbing from the 

materials of the passive sampler itself. For option 2, it is 

assumed that the covered deionized water containers are clean 

at the start, do not contain materials that leach the constituents 

being sampled, and are not located in an area of the laboratory 

or field site during the deployment period that is contaminated 

with the constituents being collected by the passive samplers. 
42 Passive Sampling of Groundwater Wells for Determination of Water Chemistry

For most passive samplers, field blanks are essentially 

identical to equipment blanks because most of the passive 

samplers discussed in this report are single-use samplers. 

However, some passive samplers have containers and 

housings that are reused between sampling events, such as 

the Snap sampler and the SPMD sampler. Potential leaching 

of constituents from these reused, cleaned containers and 

housings warrants the collection of separate field blanks for 

these two types of passive samplers. Field blanks consist of 

the collection of a sample of deionized water poured over or 

through the reused, cleaned containers or housings, similar 

to field blanks collected for cleaned submersible pumps 

or bailers. 

9.1.3 Trip Blanks

A trip blank should be prepared in the laboratory, 

particularly if VOCs are being analyzed in the samples. A 

trip blank consists of vials filled with deionized water in the 

laboratory, preserved, brought to the field in the cooler used 

to store the other sample vials, and then sent to the laboratory 

for analysis along with the VOC samples collected from the 

passive samplers. A trip blank for VOCs helps to determine 

whether these compounds may have been introduced by 

cross contamination with other samples in the cooler during 

shipment to the laboratory. 

9.1.4 Replicates

Replicate samples are QA/QC samples collected to determine the variability in the passive sampler’s ability to collect 

reproducible chemical concentrations. Passive sampler replicates should be collected from identical samplers suspended 

either side-by-side at the same depth in the well or vertically 

adjacent in the well. Replicate samples should be collected at 

a rate of at least 1 for every 10 samples to determine the reproducibility of the passive sampling device. 

9.2 Acceptability of Passive Sampling Blanks 

and Replicate Variability

Deionized water source blanks should not contain concentrations of the chemical constituents exceeding detection 

levels. If the constituents of interest are found at greater than 

detection level concentrations, a cleaner source of deionized 

water should be found and utilized. Alternately, if the levels 

of the constituents of interest are much greater in the groundwater than in the deionized water, then the current source of 

water can still be used, and the concentrations can be adjusted 

by subtracting the small amount found in the blank.

Equipment blanks should not contain detectable levels of 

the chemical constituents being sampled at greater than their 

detection level concentrations. If the equipment blank results 

fail this test and it is determined that the deionized water is not 

a contributor, then the constituents may be desorbing from the 

materials of the passive sampler. In this case, different sampler 

construction materials should be found that contain no leachable concentrations of the chemical constituents of interest. 

Replicate variability from passive samplers is likely 

to be greater than replicate variability from purge sampling 

because two different samplers are typically used during passive sampling. Variability may be increased if the samplers 

are stacked vertically in the well and there are differences in 

the vertical water chemistry between the formation and the 

well. In general, for example, results from replicate samples 

collected using the same type of passive samplers should agree 

within an RPD of ±25 percent for VOC concentrations greater 

than or equal to 10 micrograms per liter (μg/L) and an RPD 

of ±50 percent for VOC concentrations less than 10 μg/L. If 

VOC concentrations are not within these ranges, the protocol 

for recovery and sampling of the passive samplers should be 

reviewed to determine what may be causing the difference. 

As a general rule of thumb, replicate variability from passive 

samplers should not exceed the variability in results from a 

vertical profile of passive samplers in the same well. 

10.0 Data Evaluation

If a well has been monitored previously using only 

purge sampling methods, some comparison of results from 

passive sampling methods may be needed to identify any 

differences. This comparison typically is done in one of two 

ways. First, the current concentrations of constituents of 

interest obtained from the passive sampler can be compared 

to historical concentrations obtained using previous purging 

methods. If the concentrations of the constituents of interest 

are similar between the current passive sampling results and 

the previously used purging results, then it can be reasonably 

concluded that the passive samplers are providing comparable 

results. If, however, the current passive sampling results do not 

compare favorably to the historical purging results, then some 

additional direct comparison of new sample results needs to 

be undertaken. The comparison to the historical results should 

incorporate time corrections and perceived temporal trends 

in the long-term water-quality record, if available. Further, 

constitution of a favorable comparison is case dependent on 

sampling objectives. Section 10.2 discusses considerations in 

comparative analysis between sampling methods.

The second type of evaluation is a side-by-side comparison of results from the passive sampler and the previously 

used purging method during the same sampling event. This 

type of comparison usually is carried out by deploying the 

passive sampler in a well at a specific depth and allowing it to 

equilibrate for the appropriate length of time. The sampler is 

then retrieved from the well and samples are collected. Then 

the pump is lowered into the well to the same depth as the 

deployed passive sampler and a purging procedure is used to 

flush the well, monitor field physical and chemical characteristics, and collect a sample. Results have shown that the process 
10.0 Data Evaluation 43

of retrieving passive samplers and lowering a pump, if done 

carefully, can maintain some degree of chemical stratification 

present in the well (Divine and others, 2005); however, logic 

would dictate that deviation from following an extremely careful approach has the potential to mix concentrations. 

The results of the passive sampler and purge sampling 

method allow a direct comparison of the two sampling methods at the same depth, representing a time-weighted sample 

from the passive sampler and an instantaneous sample from 

the purge method. The rate and volume of pumping used 

for the purge sample should be carefully considered for the 

comparison. The majority of the data evaluations have been 

done using a low-flow purge method; however, micropurging 

(a small volume extracted) and volumetric purging have also 

been compared (Harte and others, 2018; Appendix A, Case 

Study A2). 

If the concentrations of the constituent of interest generally compare favorably (see Section 10.2), then it is likely 

the formation is in good hydraulic communication with the 

water in the screened or open interval, and the use of passive 

samplers likely will be acceptable. If the concentrations from 

the side-by-side comparison are in poor agreement, there are 

a variety of possible reasons why this might occur, and further 

investigation may be needed to determine which of the two 

sampling methods is the preferred approach for achieving the 

data-quality objectives. Potential reasons for disagreement 

between the purge and passive sample results are discussed in 

Section 10.2.

10.1 Data Comparison

The most common way to compare constituent concentration results between the purging method and passive 

sampler methods is to tabulate the results and calculate a RPD 

between the recovered concentrations for the constituents of 

interest at that particular well. In general, the results should 

agree within an RPD of ±25 percent for VOC and trace metal 

concentrations greater than or equal to 10 μg/L and an RPD of 

±50 percent for VOC and trace metal concentrations less than 

10 μg/L. The results for major cations and anions should agree 

within an RPD of ±15 percent because these concentrations 

should be higher (in the milligrams per liter range). 

For each constituent of interest, one of the more effective ways to compare concentration results between purging 

methods and passive samplers is to plot the data on a 1:1 correspondence graph. Concentrations obtained with the passive 

sampler should be plotted on the x-axis and the concentrations 

obtained from the same well using the purging method should 

be plotted on the y-axis. If the two sampling methods collect 

the same concentrations, the points will plot on or close to the 

1:1 correspondence line (figs. 22–24). The three examples in 

figures 22–24 are for RCDM samplers in relation to low-flow 

purging for a VOC (cisDCE), a trace metal (manganese), and 

an anion (chloride), respectively. In general, there is good 

agreement in the three examples. If the points plotted far off 

the line, this would indicate that one sampling method was 

collecting higher concentrations than the other. The causes for 

any significant differences would need to be investigated. 

Another way to compare passive sampler and purging 

method results for a study is to plot the results on maps or 

cross sections to evaluate spatial tendencies. If the results 

agree approximately in some areas but not in others, the comparative results may provide insight into possible explanations 

for differences. 

Previous discussion in this section focused on comparisons of results from a single passive sample to those from 

a single purge sample from the same well. When multiple 

samplers are deployed for chemical-vertical profiling of a 

well, then considerations on how to compare results need to 

take into account the volume of water purged and the pump 

rate. For small purge volumes (either micropurge or low-flow 

methods), the pump can be placed at the same depth as one of 

the passive samplers, and samples can be compared similarly 

to the comparisons demonstrated in figures 22–24. For larger 

purge volumes (volumetric sample method), the results from 

the entire profile of passive samplers can be statistically summarized as a mean or another statistical indicator and then 

compared to the purge sample results. An example of the latter 

is found in Divine and others (2005). 

10.2 Potential Reasons for Differences between 

Purge and Passive Sampling Results

There are several reasons that passive sampler results 

may differ from purge sampling results for the same well. The 

primary reason results may differ is due to the physical mechanism of each sampling method used to collect samples and 

the differences between ambient flow and pumping-induced 

flow in the well. Specifically, these physical differences can be 

grouped into three categories: (1) temporal, (2) flow regime, 

and (3) volume of sample integrated during sampling. 

Passive samplers typically produce samples that represent 

the chemical concentrations in the water that the samples have 

been in contact with over the last 3–4 days prior to sampling, 

especially if the chemicals have relatively high diffusion coefficients. Purge sampling methods induce flow into a well and 

produce an instantaneous sample. Therefore, the two methods 

collect samples that may differ temporally. 

Passive samplers collect samples under an ambient flow 

regime. The degree of mixing in the well under ambient flow 

usually is substantially less than during purging. The difference in flow regime affects sampling tendencies. Passive 

sampling has a tendency to collect a volume-weighted sample, 

whereas purge sampling collects a flow-weighted sample 

(Divine and others, 2005). Samples from passive samplers 

reflect the chemistry of inflowing groundwater controlled 

by the distribution of hydraulic head and permeability along 

the open interval of the well under ambient conditions, 

whereas purge samples reflect the chemistry of the more 

permeable units along the open interval of the well under 

pumping conditions. 
44 Passive Sampling of Groundwater Wells for Determination of Water Chemistry

0.1

1

10

100

1,000

10,000

100,000

Concentration of cisDCE from low-flow purging, 

in micrograms per liter

0.1 1 10 100 1,000 10,000 100,000

Concentration of cisDCE from RCDM samplers, in micrograms per liter

Figure 22. Concentrations of cis-1,2-dichloroethene (cisDCE) from regenerated cellulose dialysis membrane (RCDM) samplers in 

relation to concentrations of cisDCE from low-flow purging, with a 1:1 linear relation line. Data from Imbrigiotta and others (2002, 2007).

Concentration of manganese from RCDM samplers, in micrograms per liter

Concentration of manganese from low-flow purging, in micrograms per liter

1 10 100 1,000 10,000

1

10

100

1,000

10,000

Figure 23. Concentrations of manganese from regenerated cellulose dialysis membrane (RCDM) samplers in relation to 

concentrations of manganese from low-flow purging, with a 1:1 linear relation line. Data from Imbrigiotta and others (2007).
10.0 Data Evaluation 45

1

10

100

1,000

1 10 100 1,000

Concentration of chloride from RCDM samplers, in milligrams per liter

Concentration of chloride from low-flow purging, in milligrams per liter

Figure 24. Concentrations of chloride from regenerated cellulose dialysis membrane (RCDM) samplers in relation to 

concentrations of chloride from low-flow purging methods, with a 1:1 linear relation line. Data from Imbrigiotta and others (2007).

The volume of sample and compositional mix of water 

interrogated during purging is independent of the depth of the 

pump intake if a steady-state flow field exists and sufficient 

time is allowed for in-well transport (Harte, 2017). The effects 

of in-well transport during pumping can be evaluated following methods described by Harte and others (2019). In contrast, 

the volume of the sample and compositional mix of water 

interrogated during passive sampling can be depth-dependent 

in the well. A difference in volume of samples interrogated 

using the two different sampling methods is important when 

vertical chemical stratification and hydraulic heterogeneities 

are present over the length of the screened or open interval. 

For example, if the well is in good hydraulic communication 

with transmissive zones intersecting the screened or open 

interval, most of the water pumped during purging will originate from those zones (Divine and others, 2005). If the passive 

sampler is not positioned at the same depth or affected by 

vertical flow that originates from those same zones, then the 

chemistry in water from the passive sampler will likely be different from the chemistry in the purge sample. Therefore, for 

wells undergoing stratified flow and where there is a tendency 

for the water to not be well mixed under ambient conditions, 

depth dependency of the sampler is important. 

Pressure changes from pumping can induce degassing 

of constituents of interest with high Henry’s Law coefficients 

(Roy and Ryan, 2010). Degassing of the water sample also 

may occur with passive sampling from exchange at land 

surface between the sampler and the final sample collection 

bottle. Some passive samplers can collect gas samples and 

minimize degassing by allowing the sampler to be sealed 

downhole in the well. Water from passive sampling may be 

more susceptible to volatilization under ambient conditions in 

the water column than water samples obtained from purging. A 

way to assess the effect of volatilization with passive sampling 

is to deploy multiple samplers in the well casing above the 

top of the well opening to identify the direction of chemical 

gradients (Harte and Brandon, 2020). If there is little vertical change in constituent concentrations in samples from the 

samplers in the well casing and samples from the open interval, then volatilization is unlikely. Thermal convection may 

cause inversions in the well water column and induce mixing 

between water in the casing and water in the screened interval 

(Vroblesky and others, 2006, 2007a). This process could affect 

passive and purge methods differently and camouflage volatilization losses in the water column.

There is a greater potential for water from the casing 

(especially if large volumes are present in the well) to mix 

with water from the open interval using purge sampling 

methods than using passive sampling methods because of 

the inducement of converging flow. Casing water can have 
46 Passive Sampling of Groundwater Wells for Determination of Water Chemistry

chemistry different from that of groundwater in the formation 

under anaerobic conditions because of exposure to the 

atmosphere at the top of the water column. In such a case, the 

mixed purge water may be more oxic than the open interval 

water in which the passive sampler is suspended during its 

deployment period. 

The ability of the membrane used in the passive sampler 

to collect a representative sample of well water is an obvious 

factor in potential differences in results. If a passive sampler 

cannot collect samples for the constituents of interest, then the 

results will differ from those of purge sampling. An example 

of this would be the inappropriate use of a PDB sampler to 

sample for major cations and anions. Another possible reason 

that passive sampler results may differ from purge sampling 

results is that the passive sampler may have sustained damage 

during its deployment or retrieval that changed the diffusive 

properties of the membrane, which may alter the diffusion 

process across the membrane. For example, a perforated membrane damaged during installation may allow the collection 

of chemical constituents by the sampler that have not diffused 

through the membrane or equilibrated between the well and 

the sampler.

Passive samplers and purge sampling methods can yield 

different results if improper transfer techniques are used to 

fill sample containers. Passive samplers need to be sampled 

immediately after removal from the well. They should not 

be allowed to sit exposed to the atmosphere allowing loss 

of volatile compounds and the introduction of atmospheric 

oxygen, which can change the concentrations of redox species 

in the samples. 

10.3 Potential Reasons for Differences Between 

Passive Sampler Replicate Samples

Differences in results between replicate samples from 

passive samplers may be due to several factors. Samplers 

may not be constructed identically from the same materials or 

assembled in the same way. Samplers used for replicates may 

not be suspended at the same depth in a well that has a strong 

vertical chemistry difference. Differences may occur in postretrieval handling of the passive sampler and in transferring 

the sample to the sample container; for example, one replicate 

sampler might be recovered from a well and the sample transferred immediately, whereas the other sampler sits exposed to 

the atmosphere. 

10.4 Regulatory Acceptance for Switching from 

Purge Sampling to Passive Sampling

In most cases, State regulators will require some sort of 

“side-by-side” evaluation before allowing passive samplers to 

replace purge sampling methods. The number of comparison 

samples should be large enough (10–20) to produce a 

dataset that will allow confidence in the results. Prior to the 

comparison of sample results, the acceptable statistical range 

of results must be agreed upon with the regulator. As an 

example, State regulators at the New Jersey Department of 

Environmental Protection have approved the use of RCDM 

samplers in 50 wells in the long-term monitoring plan of the 

former Naval Air Warfare Center facility in West Trenton, 

N.J. The U.S. Navy contractor saves a considerable amount of 

time in the field by not having to pump the 50 wells to collect 

samples. The contractor does not have to decontaminate 

pumps in between these wells and does not need to collect, 

transport, and treat any contaminated IDW from these wells. 

Use of RCDM samplers is therefore saving the U.S. Navy a 

substantial amount of money annually in field sampling costs. 

More information is given about this example in Appendix A, 

Case Studies A3 and A4.

10.5 Cost Comparison Between Purge and 

Passive Sampling

Passive samplers have been shown to have many advantages in sampling groundwater wells. Sampling time in the 

field using a passive sampler is decreased by 67–83 percent 

(3–6 times less) compared to sampling time in the field using 

low-flow purging methods (Imbrigiotta and others, 2007; 

Parsons, 2005). Overall, collection of samples using a passive sampler is 50–75 percent less expensive (2–4 times less 

expensive) than using low-flow purging (Imbrigiotta and 

others, 2007; Parsons, 2005). Even higher savings would be 

anticipated using passive sampling rather than traditional 

3-volume purge sampling methods.

Passive samplers eliminate purge-water production and 

therefore IDW disposal costs. Many passive samplers exclude 

particulates from groundwater samples owing to the small 

pore size of their semi-permeable membranes, so in many 

cases no field filtration is required for samples collected with 

these devices. Most passive samplers are disposable, so there 

is no need for field decontamination. All of these attributes 

save money and time. 

Passive samplers have been used most frequently in 

long-term monitoring program wells because they substantially decrease sampling costs compared to purge sampling 

techniques. Cost savings are cumulative for periodic, longterm monitoring wells, and most of the savings come from a 

decrease in personnel time required to collect samples using 

passive samplers relative to the time spent to purge a well. 

Cost savings from sampling long-term monitoring wells 

can be substantial because these kinds of wells usually are 

designed to be sampled on a repeating basis over a period of 

20–30 years.
11.0 References Cited 47

Acknowledgments

The authors thank Cherie Miller and Michael Rosen 

of the U.S. Geological Survey (USGS) for encouraging and 

supporting the writing of this report. The authors also thank 

Don Vroblesky and Rebecca Travis of the USGS for their 

valuable peer reviews.

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Appendixes A–C
56 Passive Sampling of Groundwater Wells for Determination of Water Chemistry

Case Study A1

Title and location: Vertical profiling of a tetrachloroethene 

plume near a dense non-aqueous phase liquid source location (OK Tool facility), Savage Superfund Site, Milford, 

New Hampshire

Background: The Savage Superfund site in Milford, 

New Hampshire, consists of a large (several miles long) 

tetrachloroethene (PCE) plume that originated adjacent to a 

losing river reach of the Souhegan River (Harte and others, 

2001). The source of the plume is a former manufacturing 

facility (OK Tool facility; fig. 1.1 inset) that disposed of 

solvents in a pit near the facility. Fully penetrating (50-foot [ft] 

-long screen) wells were installed next to the pit to facilitate 

remediation of the dense non-aqueous phase liquid (DNAPL). 

Appendix A. Case Studies

The wells were left in place after surfactant-enhanced recovery 

pilot tests were performed. 

Study and sampling objectives: Vertically profile the fully 

penetrating wells over time to assess vertical changes in dissolved PCE and potential attenuation of the DNAPL source.

Geology: Glacial deposits of stratified drift overlying a basal 

till within the Souhegan River valley. 

Description of well network: Short-screened (5- to 10-ft 

screens) and long-screened (40- to 50-ft screens) wells finished in the overlying glacial drift. 

Sampling approach: Sampler type: (1) Passive diffusion bag 

(PDB); (2) Deployment in the well: Multiple samplers, uniformly spaced in the fully penetrating well screen; (3) Deployment duration: 2–3 weeks.

Berlin

Portsmouth

Aquifer boundary

0

0

10

10

20 MILES

20 KILOMETERS

0

0

0.5

0.5

1 MILE

1 KILOMETER

Milford 

Center VERMONT

CANADA

MAINE

MASSACHUSETTS

NEW

HAMPSHIRE

Keene Temple

Milford

Merrimack

Nashua

EXPLANATION

Inactive public-supply well

43o

44o

72o

45o

71o

Concord

Former OK 

Tool facility

General groundwater flow direction

Savage

well

Souhegan River

Stream

Figure 1.1. Location of the former OK Tool facility at the Savage Superfund site, Milford, New Hampshire.
Appendix A 57

Performance assessment: Concurrent low-flow samples at 

coincident depths were collected from a subset of wells, as 

reported in Harte and others (2001) and Harte (2002). Comparison of results from the two sampling methods (low flow 

and passive) showed good linear relation with a regression 

equation in the form of

PDB sample concentration = 0.9378 (low-flow sample 

concentration) + 102.8 with a coefficient of determination 

(R2

) of 0.966. (1)

Findings: Vertical profiling with PDB samplers (17 samplers) 

spaced uniformly in a fully penetrating, long-screened well 

adjacent to a known DNAPL source detected decreases of one 

order of magnitude of PCE concentrations from 2002 to 2007 

(fig. 1.2). For profiles in 2002 (January and March) and 2007, 

the highest PCE concentrations occurred at depth (below an 

altitude of 225 ft above the National Geodetic Vertical Datum 

of 1929 (NGVD 29)) near the contact between the stratified 

drift and underlying basal till, indicating some pooling of the 

DNAPL at that contact. The largest decreases between 2002 

and 2007 also occurred at that depth. The change in profile 

concentrations likely reflects decreases in mass of the adjacent 

DNAPL pool from a variety of processes. Concentrations of 

PCE were slightly higher in 2007 than 2002 above an altitude 

of 225 ft above NGVD 29. 

Utility of passive sampling: Vertical profiling with PDBs 

provided semi-discrete depth sampling in a long-screened well 

adjacent to a DNAPL pool, which allowed for documentation 

of apparent decreases in DNAPL mass. 

200

205

210

215

220

225

230

235

240

245

250

255

260

265

270

10 100 1,000 10,000 100,000

Altitude, in feet above NGVD 29

Tetrachloroethylene, in μg/L 

January 2002

March 2002

March 2007

EXPLANATION

Figure 1.2. Vertical chemical profile of tetrachloroethene concentrations from a long-screened (50-foot) well using uniformly 

spaced passive diffusion bag samplers, at the former OK Tool facility at the Savage Superfund site, Milford, New Hampshire, 2002–07. 

[μg/L, microgram per liter; altitude is referenced to National Geodetic Vertical Datum of 1929 (NGVD 29)]
58 Passive Sampling of Groundwater Wells for Determination of Water Chemistry

References Cited

Harte, P.T., Brayton, M.J., Ives, W., Perkins, S., and Brown, 

C., 2001, Testing and application of water-diffusion samplers to identify temporal trends in volatile-organic compounds: U.S. Geological Survey Open-File Report 00–196, 

91 p. [Also available at https://pubs.er.usgs.gov/publication/

ofr00196.] 

Harte, P.T., 2002, Comparison of temporal trends in VOCs 

as measured with PDB samplers and low-flow sampling methods: Ground Water Monitoring and Remediation, v. 22, no. 2, p. 45–47, accessed June 5, 2019, at 

https://doi.org/10.1111/j.1745-6592.2002.tb00311.x.

Case Study A2

Title and location: Vertical profiling for concentrations of 

uranium and selenium in groundwater of an alluvial aquifer, 

Homestake Superfund site, near Milan, New Mexico.

Background: The Homestake Mining Company Superfund 

site (Homestake Superfund site) is in the San Mateo Creek 

Basin of New Mexico, which is part of the Grants Mineral 

Belt where several geologic formations, such as the Morrison 

Formation, contain uranium (U) ore deposits. The site itself 

was a mill operation facility for processing of uranium ore 

from the local area. A large pile of residual U tailings sits atop 

the alluvial aquifer and is a local source of elevated U concentrations in excess of several hundred milligrams per liter 

(mg/L). An understanding of the difference in U concentrations between those in regional and local waters and those in 

water affected by leaching from the tailing pile is needed to 

assess sources of U. Selenium (Se) can be a co-contaminant 

with anthropogenic U from regional mines and mills in the 

upper San Mateo Creek Basin and is a good indicator of 

regional, anthropogenic-affected waters. 

Study and sampling objectives: The main objective of this 

study was the determination of regional and local occurrence 

of U by assessing the variation of U and Se concentrations 

(Se co-occurrence with U in regional waters) in groundwater. Observation wells completed in the alluvial aquifer were 

vertically profiled using passive samplers to determine the 

vertical variation in U and Se concentrations in groundwater. 

Results were compared to borehole geophysical logs of natural 

gamma-ray (NGR) and spectral gamma-ray to assess heterogeneity of the aquifer (Harte and others, 2019). 

Geology: Alluvial deposits of Quaternary age. Deposits are 

mostly composed of silts and fine sands with clay layers. 

Underlying the alluvium is a rock formation of the Chinle 

Group of Triassic age.

Description of well network: Five polyvinyl chloride (PVC) 

wells with screen lengths ranging from 20 to 40 feet (ft) and 

approximately 4 inches in diameter. One PVC well with a 

screen length of 80 ft. 

Sampling approach: (1) Sampler type: All passive samplers 

were nylon screen (NS) type and had 125-micron screen 

openings. (2) Deployment in the well: Multiple samplers 

(7–12), variably spaced in wells and deployed on the basis of 

borehole logs and inferred hydrogeologic contacts (fig. 2.2). 

(3) Deployment duration: 4–5 weeks.

Performance assessment: Concurrent micropurge samples 

(7) were collected at selected coincident depths with passive 

samplers from all wells (6) after retrieval of the passive samplers. The micropurge sampling is a minimal purge technique 

where samples are collected after pumping a volume of water 

equal to 1.5–2 times the volume of water contained in the 

pump and hose line. The pump intake was set at the same 

depth as a passive sampler. Approximately 1.5–2 liters of 

water were pumped prior to sampling. Neither the micropurge 

nor passive samples were filtered (total sample). Micropurge 

sampling allowed for collection of a semi-discrete instantaneous sample comparison of the results to those from the 

passive sampler. Comparison of results from the two sampling 

methods (micropurge and passive) showed a linear relation for 

U (R2 = 0.99) and Se (R2 = 0.98). However, the U and Se concentration from the NS samplers were found to be consistently 

low by a factor of 3.55 for U and 3.46 for Se between the 

passive samplers and micropurge samples (Harte and others, 

2018). Because of the excellent linear relation and consistent 

differences, results from the passive samplers were adjusted 

by these factors. Further, rates of concentration uptake of the 

NS samplers were evaluated by equation 3 and found to agree 

with these factors.

Purge samples also were collected by volumetric methods 

where the pump was set near the base of the casing and the 

top of the screen (if saturated), and samples were collected 

after three well volumes were purged. Comparisons also 

were made between passive sample results and volumetric 

sample results using two different approaches. Results from 

individual passive samplers from the closest depths to the 

pump intake of the volumetric sample were compared, and 

the results from the profile of passive samplers (the arithmetic 

mean of all samplers) were compared to the results from the 

volumetric sample. 

Findings: Table 2.1 summarizes U concentration results from 

the three different sampling methods at the seven wells. In 

the six wells sampled with both volumetric purge and micropurge methods, similar concentrations were found with both 

sampling techniques in all cases, indicating that well water 

within the screened interval of the well is representative of the 

formation. Therefore, volumetric sampling, which requires 

large amounts of purging, is not needed to collect a representative sample. The passive sampler concentrations were adjusted 

to the purge sampler concentrations according to methods 

described by Harte and others (2018). The variability in concentrations from the passive sampling profile can be identified 

by the relative magnitude of the standard deviation of U concentrations from the passive samplers (table 2.1).
Appendix A 59

Approximate subsurface fault location

Evaporation ponds

!(

!(

!(

!(

!(

!(

107°50'30"

35°16'30"

35°12'30"

0 0.5 1 MILES0 0.5 1 KILOMETERS

!(

!(

!(!(

!(

!(

!(!( !( !(

!(!(!(

!( !( !(!(!(!(!(

"

" "

"

Qa

Kmf

J

Ql

Tnv

Kml

Tmb

Kpl

Qb

Kdm

Kcc

Psa

Trc

Kmm

Kd

Jm

Kg

P

Jsr

Qe

Tnr

Kph

0 5 10 MILES

0 5 10 KILOMETERS

Q

ND

DD2

DD

T11

MV

Approximate subsurface fault location

Large tailings pileSmall tailings pile

Evaporation ponds

Quaternary

Qb Basalt Ql Landslide 

 Qe Eolian

Tertiary

Tnv/Tnr Volcanics Tmb basalts

Cretaceous

 Kmf Menefee Formation

Kpl/Kph Point Lookout SandstoneKm/Kmm/Kml Mancos ShaleKcc Crevasse Canyon Formation

 Kd/Kdm Dakota Sandstone and 

 Mancos Shale, undifferentiated

Kg Gallup Sandstone

Jurassic

Jm Morrison FormationJ undividedJsr San Rafael Group

Triassic

Trc Chinle Group

Permian

Psa San Andres FormationP undivided

EXPLANATION

Mill and mine site areas

San Mateo Creek Basin

A B

San Mateo Creek

107°53'30"

Fig. 1B

Treatment plant

Superfund site area

San Mateo Creek basin boundary

Base is copyright Esri, Inc. and its licensors; used under license

Albuquerque Grants

Gallup

Milan

San Mateo Creek Basin

NEW MEXICO

EXPLANATION

Sampled well, local well name, in alluvial aquifer MV 

35°16'30"N

35°16'0"N

35°15'30"N

35°15'0"N

35°14'30"N

35°14'0"N

35°13'30"N

35°13'0"N

35°12'30"N

107°50'30"W 107°51'30"W 107°52'30"W 107°53'30"W

Geology from NMBGMR (2003) Base from U.S. Geological Survey 10-meter digital elevation model 

of New Mexico

Figure 2.1. Location of A, Homestake Superfund site, San Mateo Creek Basin, and B, passive sampling wells, near Milan, New Mexico.
60 Passive Sampling of Groundwater Wells for Determination of Water Chemistry

Depth, below land surface, in feet

0

10

2030

40

50

60

70

80

90

100

110

0

10

2030

40

50

60

70

80

90

100

110

0

10

2030

40

50

60

70

80

90

100

110

2-ft moving average  of gamma count

Original gamma count

0

10

2030

40

50

60

70

80

90

100

110

0 50 100 200 150 0 50 100 1000 200 200 2,400 2,600 2800 150

Gamma counts, in cps Electromagnetic conductivity, in mmho/m Specific conductance, in microsiemens per centimeter

3,000 300 400

Uranium, in μg/L

EXPLANATION 

Sampler in casingSampler in screen

Figure 2.2. Borehole geophysical logs from well MV and uranium concentrations from passive samplers, Homestake Superfund site, near Milan, New Mexico. 

[cps, counts per second; mmho/m, millimhos per meter; μg/L, micrograms per liter; ft, foot]
Appendix A 61

Table 2.1. Summary of uranium concentrations obtained using different sampling methods, including passive sampling, Homestake 

Superfund site, near Milan, New Mexico.

[Uranium concentrations are in micrograms per liter (μg/L); none, no sample; —, use previous value from same well; **, concentrations adjusted by Harte and 

others (2018)]

Type of sample Parameter Sample description Units

Well name

ND MV Q DD DD2 DD2 T11

**Volumetric Total uranium Sample collected after evacuation of three well volumesμg/L 25 297 66 103 250 — 10,677

**Micropurge Total uranium Sample collected after evacuation of pump and hose volumeμg/L 31 353 61 90 263 257 10,353

**Passive Total uranium Passive sample located within 

casing (casing sample)

μg/L None 238 46 None 44 — None

Mean total uranium Mean concentration from profile 

of passive samples excluding 

sample from casing zone

μg/L 24 322 54 65 180 — 16,508

Standard deviation 

of total uranium

Exclude passive sample from 

casing zone

μg/L 6.4 23.4 3.7 23.8 50.5 — 7,502

The adjusted concentration of U for passive sampling shows 

small variations at two of the wells profiled (wells ND and Q; 

table 2.1) and larger variations at four of the wells (wells MV, 

DD, DD2, T11; table 2.1), as identified by the relative magnitude of the standard deviation of U concentrations from the 

passive samplers. Well T11 had the highest mean U concentration and largest standard deviation from the profile of passive samplers and is at the large tailings pile (fig. 2.1). Well 

ND had the lowest mean U concentration but not the lowest 

standard deviation from the profile of passive samplers and is 

upgradient from the tailings pile (base map). Well Q is upgradient from the tailings pile (base map) but downgradient from 

regional mills and mines in the upper part of the San Mateo 

Creek Basin. Well Q had the smallest standard deviation, 

which indicates that water in the well and potentially the formation is well mixed with little vertical variation in U concentrations. Wells DD, DD2, and MV are proximal to the tailings 

pile (fig. 2.1). Despite being in close proximity to well DD, 

well DD2 had a larger variation in U concentrations than well 

DD. Wells ND and Q are screened in predominantly silt and 

sands, whereas wells DD and DD2 are screened in interbedded clays, and silts and sands. Wells T11 and MV are screened 

in sands. Well MV had a vertical variation in U concentration 

similar to that of well DD, despite having a five-fold increase 

in mean U concentration. Well MV is downgradient from the 

tailings pile and likely receives U groundwater transport from 

the tailings. 

Physical heterogeneity of the alluvium likely affects U concentration variability. The interbedded clays at wells DD and DD2 

may contain reduced waters where U in the form of U(IV) 

may be sorbed onto sediments and in proximity to oxic waters 

that induce mobilization of U by converting U(IV) to mobile 

U(VI). Where there are primarily sands and silts (wells Q and 

ND), the aquifer is well mixed and shows less U variability. 

Se concentration results from the three different sampling 

methods at the seven wells are summarized in table 2.2. 

In the six wells where both volumetric purge samples and 

micropurge samples were collected, similar concentrations 

were found with both sampling techniques for four of the six 

wells. The passive sampler concentrations were adjusted to 

the micropurge sample concentrations, according to methods 

described by Harte and others (2018). The variability in concentrations from the passive sampling profile can be identified by the relative magnitude of the standard deviation of Se 

concentrations from the passive samplers (table 2.2).

Selenium variability is similar to U variability at wells T11 

and MV, which receive transport of anthropogenic U. This 

similarity indicates there is likely a local, anthropogenic 

source of Se. At two wells (ND and Q) that show little variation in U (table 2.1), Se shows greater variability (table 2.2). 

Well DD2 shows variability in U but little variability in Se 

(table 2.2). Selenium like U is affected by redox conditions, 

and Se (and U) is less mobile under reducing conditions. 

Well DD2 had low dissolved oxygen (DO) concentrations 

(<1 mg/L) and low Se concentrations. In contrast, well DD 

near well DD2 had high DO (>5 mg/L), and Se concentrations 

were higher at well DD than well DD2 (table 2.2). Well Q, 

despite showing little variability in U, had relatively high variability in Se. Well Q is downgradient from mines and mills in 

the upper San Mateo Basin and receives discharge of regional 

groundwater enriched in Se.

An example of a profile of U concentrations from the passive samplers in well MV is shown in figure 2.2. Two passive 

samplers straddling the inferred contact as determined from 

borehole logs were deployed to identify chemistry differences in aqueous uranium concentrations near a depth of 85 ft 

(fig. 2.2). Samplers were set at depths corresponding to low 
62 Passive Sampling of Groundwater Wells for Determination of Water Chemistry

Table 2.2. Summary of selenium concentrations obtained using different sampling methods, including passive sampling, Homestake 

Superfund site, near Milan, New Mexico.

[Selenium concentrations reported in micrograms per liter (μg/L); >0.5, less than detection level; none, no sample; —, use previous value from same well; 

μg/L, micrograms per liter; lsd, land surface datum; ft, foot; **, concentrations adjusted by Harte and others (2018); *, concentration of passive sampler potentially affected by low water column]

Type of 

sample Parameter Sample description Units

Well name

ND MV Q DD DD2 DD2 T11

Volumetric Total selenium Sample collected after evacuation of three well volumesμg/L 150 35 460 130 13 — 180

Depth of sample 

below lsd

ft 64 71 68 54 50 — 140

Micropurge Total selenium Sample collected after evacuation of pump and hose volumeμg/L 51 29 380 170 2 8 350

Depth of sample 

below lsd

ft 64 82 88 54 72 60 140

**Passive Total selenium Passive sample located within 

casing (casing sample)

μg/L None 4.3 381 *25 >0.5 — None

Mean total selenium Mean concentration from profile 

of passive samples excluding 

casing sample

μg/L 65 28.0 411.0 163.0 13.0 — 121

Standard deviation 

of selenium

Exclude sample from casing μg/L 23.7 8.2 20.8 23.7 3.3 — 75.1

NGR counts and low electromagnetic (EM) induction conductivity (two samplers), and high NGR counts and high EM conductivity (five samplers). Another sampler was placed in the 

casing (68-ft depth) to help understand the effect of stagnant 

water chemistry from the casing on passive sampler and purge 

method samples from the well. The results from the passive 

samplers show a slightly lower concentration of U, although 

not significantly different, from the samplers at depths corresponding to the relatively low NGR and low EM induction 

conductivity values, whereas higher concentrations of U are 

found from samplers at depths corresponding to relatively 

high NGR and EM induction conductivity (fig. 2.2). Because 

the fluid conductivity (specific conductance) log shows a large 

change along the screened opening, which indicates stratified 

and distinct well inflow from the two inferred units straddling 

the contact at the 85-ft depth, the relative similarity in U concentrations from the samplers above and below the inferred 

contact indicates that there are small differences in U concentrations in the two inferred units. 

Utility of passive sampling: Vertical profiling with passive samplers provided insight into the vertical variation in 

U concentrations in the alluvial aquifer. Vertical variation in 

U (and Se) can be compared to hydrogeologic units to identify 

the presence of constituents. At sites with limited wells for 

sampling, vertical profiling allows for an expanded view of 

the effects of physical and chemical heterogeneity on U and 

Se occurrence. 

References Cited

Harte, P.T., Blake, J., and Becher, K.D., 2018, Determination 

of representative uranium and selenium concentrations from 

groundwater, 2016, Homestake Mining Company Superfund Site, near Milan, New Mexico: U.S. Geological Survey 

Open-File Report 2018–1055, 40 p., https://doi.org/10.3133/

ofr20181055.

Harte, P.T., Blake, J., Thomas, J., and Becher, K.D., 2019, 

Identifying natural and anthropogenic variability of U in 

groundwater at the well scale by use of borehole geophysical and passive chemical profiling, Homestake Superfund site, Milan, New Mexico: Journal of Environmental 

Earth Science, v. 78, p. 95, accessed June 5, 2019, at 

https://doi.org/10.1007/s12665-019-8049-y.

Case Study A3

Title and location: Comparison of organic compound and 

inorganic constituent concentrations recovered by regenerated 

cellulose dialysis membrane (RDCM) passive samplers, polyethylene diffusion bag (PDB) passive samplers, and low-flow 

purging at the former Naval Air Warfare Center site in West 

Trenton, New Jersey.
Appendix A 63

Background: The former Naval Air Warfare (NAWC) site 

was a naval jet engine testing facility from the mid-1950s to 

1999 before the base was closed (fig. 3.1). Trichloroethene 

(TCE) was used as a refrigerant in a 25,000-gallon cooling system that allowed adjustment of engine test chamber 

temperatures. TCE was spilled or leaked from the system over 

the more than 40 years of operation and entered the underlying 

fractured bedrock. More than 100 wells were installed at the 

site to define the groundwater flow and contamination. Initially all wells were sampled for volatile organic compounds 

(VOCs) using a three-well-volume purge method. Because 

well diameters ranged from 4 to 8 inches and depths from 6 to 

410 feet (ft), this resulted in large volumes of contaminated 

purge water (IDW) being produced during sampling that 

needed to be drummed and transported to the onsite treatment 

plant. In 1995, low-flow purging was used in many wells to 

decrease the purge volumes produced. In 2002, PDB samplers 

were used at the site to collect VOC samples and to reduce the 

purge volumes further. Concentrations of VOCs from PDB 

samplers were found to compare well with concentrations 

from the low-flow purging method in most wells. In 2003, an 

investigation into the potential for natural attenuation of TCE 

at the site required the collection of samples of VOCs and 

inorganic constituents (chloride, ferrous iron, nitrate, sulfate, 

sulfide, methane). Regenerated cellulose dialysis membrane 

(RCDM) samplers were developed and tested as a way to 

collect organic compounds and inorganic constituents using 

passive samplers and to reduce the volume of purge water that 

had to be treated.

Study and sampling objectives: A study of low-flow purging, PDB samplers, and RCDM samplers was conducted to 

determine whether the three sampling methods gave comparable results for organic compounds and inorganic constituents 

(Imbrigiotta and others, 2007).

Geology and hydrology: The NAWC site is in the Newark 

Basin in central New Jersey. The site is underlain by a thin 

(<10 ft) layer of unconsolidated overburden over a thick 

(>200 ft) sequence of weathered and unweathered fractured 

mudstones and siltstones of the Lockatong Formation. Most 

of the groundwater flow in the aquifer takes place in bedding 

plane fractures between alternating layers of varying permeability in the mudstones and siltstones.

Description of the well network: More than 100 shallow and 

deep wells were installed at this site. Most shallow wells are 

constructed of low-carbon steel or polyvinyl chloride (PVC) 

casing and are screened in the overburden. All bedrock wells 

onsite are constructed using steel or PVC casing through 

the overburden and are open to the formation in the bottom 

10–25 ft of the borehole. 

Sampling approach: Passive samplers, both RCDM and 

PDB, were installed at known depths in the open interval of 

a group of wells and allowed to equilibrate. After 2 weeks, 

the RCDM and PDB samplers were retrieved and sampled. 

A variable-rate stainless-steel submersible pump was then 

lowered to the same depth. The wells were low-flow purged, 

field physical and chemical characteristics were monitored to 

stability, and samples were collected. 

Findings: Concentrations of TCE, cis-1,2-dichloroethene 

(cisDCE), and vinyl chloride (VC) were all recovered comparably by RCDM samplers versus low-flow purging, and 

RCDM samplers versus PDB samplers (figs. 3.2 A–F) (Imbrigiotta and others, 2007). The closer the data points are to the 

1:1 correspondence line in figure 3.2, the closer the results 

for each sampling method agree. The results presented on the 

graphs indicate that VOC samples can be collected using any 

of the three sampling methods, and all methods should yield 

basically the same result.

In addition, concentrations of inorganic constituents useful 

in assessing natural attenuation potential, such as chloride, 

ferrous iron, sulfate, and alkalinity, also were recovered 

comparably by RCDM samplers and low-flow purging 

(figs. 3.3 A–D) (Imbrigiotta and others, 2007). PDB samplers 

were not included in this comparison because they are not 

permeable to inorganic constituents. Again, the closer the data 

points fall to the line, the closer the sampling methods agree. 

The results for the VOC concentrations collected using the 

three different sampling techniques were compared using a 

non-parametric Kruskal-Wallis rank sum test. The results of 

the testing are given in table 3.1. VOCs with four or more 

comparable sampling results greater than the minimum detection limit collected with each of the three sampling methods 

were included in this analysis. For all chlorinated VOCs, no 

significant difference was found between samples collected 

using the RCDM sampler, PDB sampler, and low-flow purging 

(Imbrigiotta and others, 2007). Thus, even though the 1:1 correspondence plots seemed to indicate that some sampling 

techniques were better than others at recovering VOCs, these 

differences were not significant statistically. The results indicate that in most cases, RCDM samplers accurately collected 

chlorinated VOCs that varied widely in volatility, solubility, 

and Henry’s Law constant. 

Inorganic constituent and selected organic compound 

concentration data collected with the RCDM passive sampler 

and low-flow purging methods were compared using a nonparametric Wilcoxon signed rank test. The results of the 

testing are given in table 3.2. For all the inorganic constituents 

listed in table 3.2, no significant difference was found between 

samples collected using the RCDM sampler and low-flow 

purging (Imbrigiotta and others, 2007). Thus, even though 

the 1:1 correspondence points appeared to indicate one 

sampling technique or another was better at recovering some 

constituents, these differences turned out to be not significant 

statistically. These results indicated that in most cases, RCDM 

samplers were able to collect inorganic constituents and 

organic compounds as accurately as low-flow purging over a 

range of concentrations (Imbrigiotta and others, 2007). 
64 Passive Sampling of Groundwater Wells for Determination of Water Chemistry

00

500 FEET 250

50 100 METERS

40 ̊16’10”

40 ̊16’20”

74 ̊48’50” 74 ̊48’40” 74 ̊48’30”

Contamination area >1 μg/L

2014 TCE concentrations μg/L

≥1,000

100 to <1,000

1 to <100

< 1

Not sampled

EXPLANATION

FaultFenceRailroadGold Run

Studysite

NEW JERSEY

Figure 3.1. Location of former Naval Air Warfare Center site, West Trenton, New Jersey, trichloroethene contamination areas, and passive sampler wells. [TCE, trichloroethene; mg/L, micrograms per liter; <, less than; >, greater than; ≥, greater than or equal to]
Appendix A 65

0.001

0.01

0.1

1

10

100

1,000

10,000

0.001 0.01 0.1 1 10 100 1,000 10,000

Concentration of VC from PDB samplers, 

in micrograms per liter

Concentration of VC from RCDM samplers, 

in micrograms per liter

RCDM versus PDB samplers

for vinyl chloride

F E

0.001

0.01

0.1

1

10

100

1,000

10,000

0.001 0.01 0.1 1 10 100 1,000 10,000

Concentration of VC from RCDM samplers, 

in micrograms per liter

RCDM versus low-flow purging 

for vinyl chloride

Concentration of VC from low low-flow purging, 

in micrograms per liter

0.01

0.1

1

10

100

1,000

10,000

0.01 0.1 1 10 100 1,000 10,000

Concentration of cisDCE from PDB samplers, 

in micrograms per liter

Concentration of cisDCE from RCDM samplers, 

in micrograms per liter 

RCDM versus PDB samplers

for cisDCE

C D

0.01

0.1

1

10

100

1,000

10,000

0.01 0.1 1 10 100 1,000 10,000

Concentration of cisDCE from low-flow 

purging, in micrograms per liter

Concentration of cisDCE from RCDM samplers, 

in micrograms per liter 

RCDM versus low-flow purging 

for cisDCE

0.01

0.1

1

10

100

1,000

10,000

100,000

0.01 0.1 1 10 100 1,000 10,000 100,000

Concentration of TCE from RCDM samplers, 

in micrograms per liter

RCDM versus PDB samplers 

for trichloroethene

B

Concentration of TCE from PDB samplers, 

in micrograms per liter

A

0.01

0.1

1

10

100

1,000

10,000

100,000

0.01 0.1 1 10 100 1,000 10,000 100,000

RCDM versus low-flow purging 

for trichloroethene

Concentration of TCE from low-flow purging, 

in micrograms per liter

Concentration of TCE from RCDM samplers, 

in micrograms per liter

Figure 3.2. 1:1 Correspondence plots of concentrations of A, trichloroethene (TCE) collected with regenerated cellulose dialysis 

membrane (RCDM) samplers versus low-flow purging, B, TCE collected with RCDM samplers versus polyethylene diffusion bag (PDB) 

samplers, C, cis-1-2-dichlorothene (cisDCE) collected with RCDM samplers versus low-flow purging, D, cisDCE collected with RCDM 

samplers versus PDB samplers, E, vinyl chloride (VC) collected with RCDM samplers versus low-flow purging, and F, VC collected with 

RCDM samplers versus PDB samplers. [Data from Imbrigiotta and others (2007).]
66 Passive Sampling of Groundwater Wells for Determination of Water Chemistry 0.1

1

10

100

1,000

0.1 1 10 100 1,000

Concentration of chlroide from low-flow

purging, in milligrams per liter 

Concentration of chloride from RCDM samplers, 

in milligrams per liter

AC

RCDM versus low-flow 

purging for chloride

10

100

1,000

10,000

100,000

10 100 1,000 10,000 100,000

Concentration of ferrous iron from low-flow 

purging, in micrograms per liter

Concentration of ferrous iron from RCDM samplers, 

in micrograms per liter

B

RCDM versus low-flow 

purging for ferrous iron 

0.1

1

10

100

1,000

10,000

0.1 1 10 100 1,000 10,000

Concentration of sulfate from low-flow 

purging, in milligrams per liter

Concentration of sulfate from RCDM samplers, 

in milligrams per liter

RCDM versus low-flow 

purging for sulfate

0.1

1

10

100

1,000

10,000

0.1 1 10 100 1,000 10,000

Concentration of alkalinity from low-flow 

purging, in milligrams per liter as CaCO3

Concentration of alkalinity from RCDM samplers, 

in milligrams per liter as CaCO3

D

RCDM versus low-flow 

purging for alkalinity

Figure 3.3. 1:1 Correspondence plots of concentrations of 

A, chloride collected with regenerated cellulose dialysis membrane (RCDM) samplers versus low-flow 

purging, 

B, ferrous iron collected with RCDM samplers versus low-flow purging, 

C, sulfate collected with RCDM samplers versus low-flow purging, and 

D, alkalinity 

collected with RCDM sampler versus low-flow purging. [Data from Imbrigiotta and others (2007).]
Appendix A 67

Table 3.1. Chlorinated volatile organic compounds for which 

concentrations recovered by the regenerated cellulose dialysis 

membrane sampler, polyethylene diffusion bag sampler, and lowflow purging were compared using the Kruskal-Wallis Test and 

no significant difference was found.

[RCDM, regenerated cellulose dialysis membrane; PDB, polyethylene diffusion bag; (at p<0.05), the presence or absence of differences are significant 

at the 95-percent confidence level for the number of comparisons; (12), 

number of comparisons for the constituent at concentrations greater than the 

minimum detection limit]

Volatile organic compounds for which no significant difference 

was found between concentrations in samples collected with the 

RCDM sampler, PDB sampler, and low-flow purging (at p<0.05)

trichloroethene (12)

cis-1,2-dichloroethene (10)

1,1-dichlorethene (10) 

trans-1,2-dichloroethene (5)

vinyl chloride (9)

dichlorodifluoromethane (4)

Conclusions: RCDM diffusion samplers were effectively 

used to collect both organic and inorganic chemical constituents that are indicators of natural attenuation of VOCs 

in groundwater. A deployment time of 1–2 weeks was sufficient for equilibration of all chemical constituents monitored in the study. For chlorinated VOCs, RCDM samplers 

produced graphically and statistically identical results to 

results produced by PDB samplers and low-flow purging. For 

inorganic constituents, RCDM samplers produced graphically and statistically identical results to results produced by 

low-flow purging. 

On the basis of this comparison study, the New Jersey 

Department of Environmental Protection agreed to allow the 

U.S. Navy and its contractors to use RCDM and PDB passive 

samplers to replace low-flow purging in 50 wells at the NAWC 

site. The use of passive samplers saves the Navy as much as 

70 percent of the low-flow purging field sampling costs each 

time the wells are sampled.

Reference Cited

Imbrigiotta, T.E., Trotsky, J.S., and Place, M.C., 2007, Demonstration and validation of a regenerated cellulose dialysis 

membrane diffusion sampler for monitoring ground-water 

quality and remediation progress at DoD sites (ER-0313): 

ESTCP Final Technical Report for Project ER-0313, 136 p., 

accessed June 5, 2019, at http://www.estcp.org/Technology/

upload/ER-0313-FR.pdf.

Table 3.2. Inorganic constituents and selected organic compounds for which concentrations recovered by the 

regenerated cellulose dialysis membrane sampler and low-flow purging were compared using the Wilcoxon Signed 

Rank Test and no significant difference was found.

[RCDM, regenerated cellulose dialysis membrane; (at p<0.05), the presence or absence of differences are significant at the 95-percent confidence level for the number of comparisons; (22), number of comparisons for the constituent greater than the minimum detection limit]

Constituents for which no significant difference was found between concentrations in samples collected with the 

RCDM sampler and low-flow purging (at p<0.05)

Aluminum (22) Chloride (28) Selenium (8)

Arsenic (18) Chromium (5) Silica (28)

Barium (25) Fluoride (16) Sodium (28)

Bicarbonate/Alkalinity (27) Iron (23) Sulfate (25)

Bromide (8) Lead (14) Vanadium (7)

Cadmium (5) Magnesium (28) Zinc (18)

Calcium (28) Manganese (27) Nitrate (11)

Carbon dioxide (28) Molybdenum (11) Potassium (28)

Total dissolved solids (27) Methane (21) Ethene (9)

Dissolved organic carbon (27)
68 Passive Sampling of Groundwater Wells for Determination of Water Chemistry

Case Study A4

Title and location: Comparison of aromatic volatile organic 

compound concentrations recovered by regenerated cellulose 

dialysis membrane passive samplers, polyethylene diffusion 

bag passive samplers, and low-flow purging at the Naval Base 

Ventura County (NBVC) gas station site in Port Hueneme, 

California.

Background: The shallow sand-and-gravel aquifer underlying the NBVC was contaminated by leaking gasoline tanks 

from the primary base filling station over many years prior to 

discovery of the leak. The primary contaminants at this site 

were aromatic volatile organic compounds (VOCs) (benzene, 

toluene, ethylbenzene, xylene [BTEX] and methyl-tert-butyl 

ether [MTBE]) caused by the leakage of fuel into the aquifer. 

Long-term monitoring sampling costs for the well network 

were substantial for the U.S. Navy. 

Study and sampling objectives: A study of low-flow purging, 

polyethylene diffusion bag (PDB) samplers, and regenerated 

cellulose dialysis membrane (RCDM) samplers was conducted 

to determine whether all samplers gave comparable results for 

aromatic organic compounds. 

Geology and hydrology: The NBVC site is within 1 mile of 

the Pacific Ocean near Oxnard, California. The site is underlain by a shallow sand-and-gravel deposit. The groundwater 

flow in the aquifer moves from the northeast to the southwest 

towards the Pacific Ocean.

Description of the well network: Shallow wells were 

installed in the sand and gravel aquifer to investigate the contamination at this site. All shallow wells were constructed of 

polyvinyl chloride (PVC) casing and were screened 14–27 feet 

below land surface. Six wells were sampled for this study.

Sampling approach: Passive samplers, RCDM and PDB, 

were installed at known depths in the screened interval of the 

six wells and allowed to equilibrate. After 2 weeks, the RCDM 

and PDB samplers were retrieved and sampled. A variablerate stainless-steel submersible pump was then lowered to the 

same depth, the wells were low-flow purged, field physical 

and chemical characteristics were monitored to stability, and 

samples were collected. 

Findings: Concentrations of most BTEX compounds were 

recovered comparably by RCDM samplers versus lowflow purging and RCDM samplers versus PDB samplers 

(figs. 4.2 A–F) (Imbrigiotta and others, 2007). The closer the 

data points are to the 1:1 correspondence line in figure 4.2, the 

closer the agreement for the results of each sampling method. 

The results shown in the graphs indicate that aromatic VOC 

samples can be collected using any of the three sampling 

methods, and all methods should yield basically the same 

results (Imbrigiotta and others, 2007).

The results for the aromatic VOC concentrations in samples 

collected using the three different sampling techniques were 

compared using a non-parametric Kruskal-Wallis rank sum 

test. The results of the testing are given in table 4.1. Aromatic 

VOCs with five or more comparable sampling results greater 

than the minimum detection limit collected with each of 

the three sampling methods were included in this analysis. 

For all aromatic VOCs, no significant difference was found 

between samples collected using the RCDM sampler, PDB 

sampler, and low-flow purging (Imbrigiotta and others, 2007). 

Thus, even though the 1:1 correspondence plots appear to 

indicate that one sampling technique or the other was better 

at recovering some VOCs, most of these differences were not 

significant statistically. These results indicate that RCDM 

samplers accurately collected aromatic VOCs that varied 

widely in volatility, solubility, and Henry’s Law constant 

(Imbrigiotta and others, 2007). 

Conclusions: RCDM diffusion samplers were found to collect aromatic VOCs effectively from groundwater in wells. A 

deployment time of 1–2 weeks was sufficient for equilibration 

of all organic compounds monitored in the study. For aromatic 

VOCs, RCDM samplers produced graphically and statistically 

identical results to results produced by PDB samplers and lowflow purging. On the basis of this comparison, the Navy and 

its contractors were able to ask state of California regulators to 

use passive samplers to reduce long-term monitoring costs.

Reference Cited

Imbrigiotta, T.E., Trotsky, J.S., and Place, M.C., 2007, Demonstration and validation of a regenerated cellulose dialysis 

membrane diffusion sampler for monitoring ground-water 

quality and remediation progress at DoD sites (ER-0313): 

ESTCP Final Technical Report for Project ER-0313, 136 p., 

accessed June 5, 2019, at http://www.estcp.org/Technology/

upload/ER-0313-FR.pdf. 
Appendix A 69

0 100 200 300 FEET

0 46 92 METERS

Biobarrier

CBC–32

CBC–33

Parade Ground

General direction of groundwater flow in semiperched aquifer

23rd Ave.

Gas stationGas station

Dodson St.

Harris St.

CBC–8

CBC–9

CBC–2

CBC–4

CBC–5

CBC–3

CBC–6

CBC–7

CBC–17 CBC–30

CBC–31

CBC–32

CBC–16 CBC–20

CBC–22

CBC–21

CBC–19

CBC–11

CBC–14

CBC–10

CBC–15

CBC–12

CBC–13

CBC–27

CBC–26

CBC–25

CBC–24

CBC–29

CBC–18

CBC–28

CBC–23

BTEX contamination area boundary >1 μg/LWells with passive samplers, and Construction Battalion Center identifier

EXPLANATIONCBC–21

Map modified from U.S. Navy andU.S. Geological Survey sources

34°17”

119°20’

NEX Autoport Gas Station—Source  of contaminant plume 

Study sitePort Hueneme

CALIFORNIA

Figure 4.1. Location of the Naval Base Ventura County gas station site, Port Hueneme, Oxnard, California, aromatic volatile organic compound contamination area, and wells in 

which passive samplers were deployed. [BTEX, benzene, ethylbenzene, toluene, and xylene; mg/L, micrograms per liter]
70 Passive Sampling of Groundwater Wells for Determination of Water Chemistry

B

D

F

0.01

0.1

1

10

100

1,000

0.01 0.1 1 10 100 1,000

0.01

0.1

1

10

100

1,000

10,000

0.01 0.1 1 10 100 1,000 10,000

0.01

0.1

1

10

100

10,000

1,000

0.01 0.1 1 10 100 1,000 10,000

A

C

E

Concentration of benzene from low-flow purging,

in micrograms per liter

RCDM versus low-flow purging 

for ethylbenzene

Concentration of benzene from RCDM samplers,

in micrograms per liter

RCDM versus low-flow 

purging for benzene

Concentration of ethylbenzene from low-flow 

purging, in micrograms per liter

RCDM versus low-flow purging 

for o-xylene

Concentration of o-xylene from low-flow 

purging, in micrograms per liter

Concentration of o-xylene from RCDM samplers,

in micrograms per liter 

Concentration of ethylbenzene from RCDM samplers,

in micrograms per liter

0.01

0.1

1

10

100

1,000

10,000

0.01 0.1 1 10 100 1,000 10,000

RCDM versus PDB samplers

for benzene

0.01

0.1

1

10

100

1,000

10,000

0.01 0.1 1 10 100 1,000 10,000

0.01

0.1

1

10

100

1,000

0.01 0.1 1 10 100 1,000

Concentration of o-xylene from RCDM samplers, 

in micrograms per liter 

Concentration of o-xylene from PDB samplers, 

in micrograms per liter

RCDM versus PDB samplers 

for o-xylene

Concentration of ethylbenzene from RCDM samplers,

in micrograms per liter

RCDM versus PDB samplers 

for ethylbenzene

Concentration of benzene from RCDM samplers, 

in micrograms per liter

Concentration of benzene from PDB samplers, 

in micrograms per liter Concentration of ethylbenzene from PDB samplers, in micrograms per liter

Figure 4.2. 1:1 Correspondence plots of concentrations of A, benzene collected with regenerated cellulose dialysis membrane 

(RCDM) samplers versus low-flow purging, B, benzene collected with RCDM samplers versus polyethylene diffusion bag (PDB) 

samplers, C, ethylbenzene collected with RCDM samplers versus low-flow purging, D, ethylbenzene collected with RCDM samplers 

versus PDB sampler, E, o-xylene collected with RCDM samplers versus low-flow purging, and F, o-xylene collected with RCDM 

sampler versus PDB samplers. [Data from Imbrigiotta and others (2007).]
Appendix A 71

Table 4.1. Aromatic volatile organic compounds for which concentrations obtained using the 

regenerated cellulose dialysis membrane sampler, the polyethylene diffusion bag sampler, and lowflow purging were compared using the Kruskal-Wallis Test and no significant difference was found. 

[RCDM, regenerated cellulose dialysis membrane; PDB, polyethylene diffusion bag; (at p<0.05), the presence or 

absence of differences are significant at the 95-percent confidence level for the number of comparisons; (17), number 

of comparisons for the constituent at concentrations greater than the minimum detection limit]

Compounds for which no significant difference was found between concentrations in samples 

collected with the RCDM sampler, PDB sampler, and low-flow purging (at p<0.05)

ethylbenzene (17) benzene (13)

isopropylbenzene (17) toluene (15)

n-propylbenzene (14) m,p-xylene (17)

tert-butylbenzene (7) o-xylene (15)

naphthalene (12) styrene (6)

1,2,4-trimethylbenzene (17)

1,3,5-trimethylbenzene (13)

methyl tert-butyl ether (5)
72 Passive Sampling of Groundwater Wells for Determination of Water Chemistry

Appendix B. Field Form for Deployment and Retrieval of Passive Samplers
USGS Appendix B 73

Location Date:

Local well name USGS SID#

Weather conditions Temperature (degrees C or F)

Measurement point (MP) [eg. Top of Casing (TOC), Land Surface (LS), ETC.]

Stickup of outer casing (ft) [from LS]

Well material (inner pipe) [Eg. PVC, Steel] Stickup of inner casing (ft) [from LS]

Well Diameter (inner pipe) [Units; inches, feet, cm, m]

Units of Measurement below if not noted [Circle: M-meters; Ft-feet; other_______]

3 MP Distance Relative to Land Surface (Circle Inner or Outer for MP)

4 Sounding Depth of Well from MP [Source: Borehole Log, handheld reading, etc]

5 Depth to Water Level (DTW) from MP [Two readings]

6 Date/Time of water level

7 Corrected DTW (DTWLS)from Land surface (LS) (Line 5-3)

8 Reported Well Depth from LS

9 Reported Open Interval from LS Top= ; Bottom=

10 Reported water column length (Circle Datum LS or MP) [Depth to water - depth of well]

11 Reported water casing length (Circle Datum LS or MP) [Depth to water - depth to top of opening]

12 Reported water open interval length (Circle Datum LS or MP) Top= ; Bottom=

13 Reported Well Depth from MP [Same as line 8 if LS datum=MP]

14 Reported Open Interval from MP Top= ; Bottom = [Same as line 9 if LS datum=MP]

15 Reported water column interval from MP Top= ; Bottom = [Entire well]

16 Reported water casing interval from MP Top= ; Bottom = [Casing only]

17 Reported water open interval from MP Top= ; Bottom = [Open interval only]

18 Correction factor based on well sounding [Sounding depth (line 4)-reported depth (line 13)]

19 Corrected Well Depth (MP) from sounding [Adjusted by line 18]

(If sounding depth = reported depth from MP then no correction)

20 Corrected Open Interval (MP) from Sounding Top = ; Bottom = 

(If sounding depth = reported depth from MP then no correction)

21 Corrected water well column interval (MP) Top = ; Bottom = 

22 Corrected water well casing interval (MP) Top = ; Bottom = 

23 Corrected water well open interval (MP) Top = ; Bottom = 

24 Range of Passive Sampler Deployment from (MP) From: To:

25 Number and depths of samplers from MP to midpoint of sampler: # of samplers

Depths: 

Other Notes on Deployment Depths:

Passive Sampler Deployment Field Sheet-page 1

[Adjusted by line 18]

Is there an outer protective casing? Y or N (Circle)

[If line 12 > 0; same as line 9; otherwise, depth 

to top of opening - line 12]

[Adjusted by line 18]

[Adjusted by line 18]

[Adjusted by line 18]

[Mar. 2020

version 12
74 Passive Sampling of Groundwater Wells for Determination of Water Chemistry USGS

Type of sampler [Circle types: PDB,NSPS,RPP,RCDM, ETC.]

Length of sampler ; ; [Units]

Diameter of sampler ; ; [Units]

Mouth/opening diameter for NS sampler [Units]

Membrane material and size of pore ; [Pore Units]

Medium Type [D.I. water, other]

Medium Blank Sample Date Source of blank

Sampler housing [eg. polyethene mil type, mesh type]

Deployment Start Time: Deployment End Time:

Number of Samplers Deployed and Types

Suspension information [eg. line, weight, material]

Line length Add on length of weight [Feet,meters,other]

Units of Measurement below if not noted [Circle: M-meters; Ft-feet; other_______]

Sampler spacing distance (sampler midpoint) MP (top of inner pipe, bottom depth, other)

s#1First Deepest Sampler (ID), depth relative to MP (midpoint) Dups: y or n

s#2Next Sampler (I.D.), depth relative to MP (midpoint-midpoint ) Dups: y or n

s#3Next Sampler (I.D.), depth relative to MP (midpoint-midpoint ) Dups: y or n

s#4Next Sampler (I.D.), depth relative to MP (midpoint-midpoint ) Dups: y or n

s#5Next Sampler (I.D.), depth relative to MP (midpoint-midpoint ) Dups: y or n

s#6Next Sampler (I.D.), depth relative to MP (midpoint-midpoint ) Dups: y or n

s#7Next Sampler (I.D.), depth relative to MP (midpoint-midpoint ) Dups: y or n

s#8Next Sampler (I.D.), depth relative to MP (midpoint-midpoint ) Dups: y or n

s#9Next Sampler (I.D.), depth relative to MP (midpoint-midpoint ) Dups: y or n

s10Next Sampler (I.D.), depth relative to MP (midpoint-midpoint ) Dups: y or n

s11Next Sampler (I.D.), depth relative to MP (midpoint-midpoint ) Dups: y or n

s12Last Sampler (I.D.), depth relative to MP (midpoint-midpoint ) Dups: y or n

Duplication position relative to sampler: (+ means deeper than sample)

WELL Stickup Comments:

casing

Fm

open

interval

Sketch loc. of samplers

Passive Sampler Deployment Field Sheet-page 2 Well________
USGS Appendix B 75

Well I.D.

Additional notes:

Picture

Notes/Attachments-Page 3 Deployment
76 Passive Sampling of Groundwater Wells for Determination of Water Chemistry USGS

Location Date

Local well name USGS SID#

Weather conditions Temperature (degrees C or F)

Measurement point (MP) [eg. TOP OF PIPE, ETC.]

Well construction material [EG. PVC, Steel]

Well Condition [good or tampered] Well diameter [Units]

Units of Measurement below if not noted [Circle: M-meters; Ft-feet; other_______]

MP Distance Relative to Land Surface

Pre DTW from MP

Date and Time of DTW

Bottle or sampler type [Poly bottle size, RPPM etc]

Analytical consitiuent and method

Retrieval start time (Circle, all that applies)

s# Top Sampler I.D./condition / [Good, poor, any leakage, Staining, Fe, Mn, etc.) Dups: y or n

s# Next Sampler I.D./condition / [Good, poor, any leakage, Staining, Fe, Mn, etc.) Dups: y or n

s# Next Sampler I.D./condition / [Good, poor, any leakage, Staining, Fe, Mn, etc.) Dups: y or n

s# Next Sampler I.D./condition / [Good, poor, any leakage, Staining, Fe, Mn, etc.) Dups: y or n

s# Next Sampler I.D./condition / [Good, poor, any leakage, Staining, Fe, Mn, etc.) Dups: y or n

s# Next Sampler I.D./condition / [Good, poor, any leakage, Staining, Fe, Mn, etc.) Dups: y or n

s# Next Sampler I.D./condition / [Good, poor, any leakage, Staining, Fe, Mn, etc.) Dups: y or n

s# Next Sampler I.D./condition / [Good, poor, any leakage, Staining, Fe, Mn, etc.) Dups: y or n

s# Next Sampler I.D./condition / [Good, poor, any leakage, Staining, Fe, Mn, etc.) Dups: y or n

s# Next Sampler I.D./condition / [Good, poor, any leakage, Staining, Fe, Mn, etc.) Dups: y or n

s# Next Sampler I.D./condition / [Good, poor, any leakage, Staining, Fe, Mn, etc.) Dups: y or n

s# Bottom Sampler I.D./condition / [Good, poor, any leakage, Staining, Fe, Mn, etc.) Dups: y or n

Retrieval end time Post DTW from MP:

Notes on filling of bottles:

WELL Stickup Comments:

casing

Fm

open

interval

Sketch loc. of samplers and I.D.

Passive Sampler Recovery Field Sheet-page 1 Well__________________
USGS Appendix B 77

Well I.D.

Fill and Bottle notes:

s# Top Sampler I.D./condition / Time:

s# Next Sampler I.D./condition / Time:

s# Next Sampler I.D./condition / Time:

s# Next Sampler I.D./condition / Time:

s# Next Sampler I.D./condition / Time:

s# Next Sampler I.D./condition / Time:

s# Next Sampler I.D./condition / Time:

s# Next Sampler I.D./condition / Time:

s# Next Sampler I.D./condition / Time:

s# Next Sampler I.D./condition / Time:

s# Next Sampler I.D./condition / Time:

s# Bottom Sampler I.D./condition / Time:

Additional notes:

Picture

Notes/Attachments-Page 2 Recovery
78 Passive Sampling of Groundwater Wells for Determination of Water Chemistry USGS

Well I.D.

Additional Type of comparison______________________________________(Bailer, purge)

Date and time ____________________ DTW (FT) FROM MP

Depth of collection from MP (FT) MP

Samples collected 

Purge information:

Pump Type: Pump Placement (FT) from MP

samPump Time/Ref time Rate (m3/hRate (LPM) SC T PH DO FG

umhos/cm deg-c MG/L fluro units

Comparison Tests Notes-Page 3 Recovery
USGS Appendix B 79

Well I.D.

Additional Type of comparison______________________________________(Bailer, purge)

Date and time ____________________ DTW (FT) FROM MP

Depth of collection from MP (FT) MP

Samples collected 

Purge information:

Pump Type: Pump Placement (FT) from MP

samPump Time/Ref time Rate (m3/hRate (LPM) SC T PH DO FG

umhos/cm deg-c MG/L fluro units

Comparison Tests Notes-Page 4 Recovery
80 Passive Sampling of Groundwater Wells for Determination of Water Chemistry

Appendix C. Well Label for Deployed Passive Samplers

CAUTION! 

Do not disturb

Passive sampler installed in well

Please close cover carefully

Direct questions to:

Agency Name

Contact Name______; ph___________
For more information about this report, contact:

Director, New England Water Science Center

U.S. Geological Survey

10 Bearfoot Road

Northborough, MA 01532

dc_nweng@usgs.gov

or visit our website at

https://www.usgs.gov/centers/new-england-water

Publishing support provided by the West Trenton and 

Pembroke Publishing Service Centers
Imbrigiotta and Harte—Passive Sampling of Groundwater Wells for Determination of Water Chemistry—Techniques and Methods 1–D8

ISSN 2328-7055 (online)

https://doi.org/10.3133/tm1d8