Robert S. Kerr EPA/600/R-94/205

Environmental Research Laboratory

Ada, OK 74820

United States

Environmental Protection

Agency

Research and Development

Ground Water Sampling --

A Workshop Summary

Dallas, Texas

November 30 - December 2, 1993
i

Ground Water Sampling --

A Workshop Summary

Dallas, Texas

November 30 - December 2, 1993

Robert S. Kerr Environmental Research Laboratory

Office of Research and Development

U.S. Environmental Protection Agency

Ada, OK 74820

EPA/600/R-94/205
ii

Notice

The information in this document has been funded wholly or in part by the United States Environmental Protection Agency.

It has been subjected to the Agency’s peer review and administrative review, and it has been approved for publication as an

EPA document.

All research projects making conclusions or recommendations based on environmentally related measurements and funded

by the Environmental Protection Agency are required to participate in the Agency Quality Assurance Program. This project

did not involve environmentally related measurements and did not involve a Quality Assurance Project Plan. Mention of

trade names or commercial products does not constitute endorsement or recommendation for use.
iii

Foreword

EPA is charged by Congress to protect the Nation’s land, air and water systems. Under a mandate of national environmental

laws focused on air and water quality, solid waste management and the control of toxic substances, pesticides, noise and

radiation, the Agency strives to formulate and implement actions which lead to a compatible balance between human

activities and the ability of natural systems to support and nurture life.

The Robert S. Kerr Environmental Research Laboratory is the Agency’s center of expertise for investigation of the soil and

subsurface environment. Personnel at the laboratory are responsible for management of research programs to: (a) determine

the fate, transport and transformation rates of pollutants in the soil, the unsaturated and the saturated zones of the subsurface

environment; (b) define the processes to be used in characterizing the soil and subsurface environment as a receptor of

pollutants; (c) develop techniques for predicting the effect of pollutants on ground water, soil, and indigenous organisms; and

(d) define and demonstrate the applicability and limitations of using natural processes, indigenous to the soil and subsurface

environment, for the protection of this resource; and (e) provide technical assistance to characterize and remediate

contaminated soils and ground water.

The dissemination, review and implementation of new environmental research findings is essential in providing the

background information required for practitioners and policy makers working in the areas of environmental protection and

restoration. This information is critically needed in the area of ground-water sampling, where recent improvements in

technology have far outpaced our ability to evaluate and incorporate new methods into sampling protocols and technical

guidance documents.

The primary objective of this workshop was to provide a forum for the presentation and discussion of recent research

findings on ground-water sampling for researchers, practitioners, regulators and policy makers. Secondary objectives were:

to improve communication and the transfer of information between these diverse groups, encourage consistency in groundwater sampling programs where appropriate, and identify research and technology transfer needs. Participants included

representatives of universities, private industry, environmental consultants, the U.S. Environmental Protection Agency, the

U.S. Geological Survey, the Department of Energy, and several state environmental agencies.

Clinton W. Hall

Director

Robert S. Kerr Environmental

Research Laboratory
iv
v

Contents

Notice.................................................................................................................................................................................. ii

Foreword............................................................................................................................................................................ iii

1. Executive Summary ..................................................................................................................................................... 1

2. Agenda ......................................................................................................................................................................... 5

3. Extended Abstracts ....................................................................................................................................................... 7

4. Poster Abstracts .......................................................................................................................................................... 59

5. Small Group Discussions ........................................................................................................................................... 67

Appendices

Appendix A: Steering Committee and Other Attendees

Appendix B: Questions to Consider for Small Group Discussions

Appendix C: Bibliography

Appendix D: Glossary

Appendix E: Sampling Forms
vi
1

I. Executive Summary

Monitoring purposes have evolved in the past decade

reflecting an increasing emphasis on assessment and

remedial action performance over detection monitoring. The

recognition of many potential contamination sources as well

as the regulatory inclusion of a large number of sites in need

of investigation have spurred this evolution in practice. New

more efficient methods and tools for hydrogeochemical

characterization have been developed which can make site

investigations more reliable and cost-effective. Improved

field screening techniques, geophysical, portable analytical,

and computerized hydrologic data acquisition systems,

lighter drilling and boring tools, multi-level samplers, and

hydraulic “push” technologies are some of the tools which

may be applied to subsurface studies. Professional practices

and standards for all monitoring have lagged behind

methodological research and development. Regulatory

acceptance of new tools and methods has been slow in

general. However change is inevitable and, if properly

implemented, could lead to more uniformly reliable and less

expensive investigations. Improved training and

certification of hydrogeologic professionals could also aid in

this regard. Decreased reliance on wells as primary data

collection points follows on the recognition that many

inorganic and most organic contaminants have an

appreciable fraction of their mass associated with subsurface

solids. Also, wells designed for detection and assessment

monitoring purposes frequently become obsolete when

vadose or saturated zone remedial action has begun. It may

be anticipated that as the familiarity with and supporting

documentation for more effective methods grow, more

stringent standards of professional practice will evolve as

well. In summary, the state of current monitoring practice is

steadily changing to more reliable, cost-effective techniques

which should improve the spatial coverage, accuracy and

precision of data collection efforts.

The primary objective of this workshop was to provide a

forum for the presentation and discussion of recent research

findings on ground water sampling in the context of

continuing advances in environmental monitoring

technologies and changing environmental regulatory

requirements. Participants included researchers,

practitioners, regulators and policy makers from

governmental and non-governmental sectors. Secondary

objectives of the workshop were: to improve

communication and the transfer of information between

these diverse groups, encourage consistencey in ground

water sampling programs where appropriate, and identify

research and technology transfer needs.

Ground-Water Monitoring Goals and Objectives

One of the most important steps in the design and

implementation of a ground-water monitoring program

involves defining the data, analyses, and information

required to meet the monitoring program objectives.

Common examples of monitoring objectives may include

leak detection at hazardous and solid waste land disposal

facilities, hazardous waste site assessments, corrective

action evaluations, and ground-water resource evaluations.

In a broad sense, monitoring objectives define the data or

information that the investigator needs to support decisions

or conclusions. Monitoring objectives are developed to

satisfy regulatory requirements, support resource

assessments and research goals, and support the

development of site conceptual models.

In defining monitoring objectives, data quality objectives

(DQOS) are used to specify the type and quality of data

required to support decisions. DQOS describe the overall

level of uncertainty that a decision-maker is willing to

accept in results derived from environmental data. This

uncertainty is used to specify the quality of the measurement

data required, usually in terms of objectives for accuracy,

precision, bias, representativeness, comparability, and

completeness. DQOS are defined prior to the initiation of

the field and laboratory work. Also, DQOS are

communicated to field and laboratory personnel performing

the work to make informed decisions during the course of

the project to attain those DQOS. The procedures used to

characterize the hydrogeology of a site, to design and

construct a monitoring network, to collect and analyze

environmental samples, and to evaluate analytical results

should ensure that the data are of the type and quality

necessary to meet the objectives of the monitoring program.

The development and refinement of a site conceptual model

underlies all ground-water monitoring programs. A

conceptual model is an understanding of the hydrogeologic

characteristics of a site, and of how the hydrogeologic

characteristics (e.g., geology and geochemistry of the site

and the distribution of contaminant migration pathways) are

integrated into a hydrogeologic system that contains

interacting and dynamic components. Development of a site

conceptual model is an iterative process. After a groundwater monitoring system has been installed and numerous

ground-water samples have been collected, the conceptual

model for a site may be further refined, depending on the

DQOS.
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Design and Installation of Subsurface Sampling Points

The design and installation of sampling points for

subsurface investigations and monitoring have undergone

substantial change since the days when wells of one type or

another were the dominant data collection platforms. A

variety of gas, solid and liquid sampling techniques are in

use for field screening and to improve spatial coverage of

subsurface conditions, particularly for volatile organic

contaminants. These techniques may effectively substitute

for permanent sampling installations. They can be employed

during drilling or in conjunction with various “push”

technologies which rely on hydraulic or percussion

advancement principles.

The utilization of soil gas probes, piston-coring devices, and

“drill-tool” water sampling devices (e.g.,“ Hydropunch”,

screened augers/pumps, etc.) during drilling has led to an

improved ability to identify hydrostratigraphic units and

zones of contamination. In these instances, the location,

design, construction and performance of short-screened (i.e.,

<2m), narrow diameter monitoring wells or multi-level

samplers can enable more focused and reliable

hydrogeochemical data collection. Fewer drill holes and less

disturbance of subsurface conditions result from the use of

these emerging techniques which also reduce the time and

cost involved in monitoring efforts.

Wells are traditionally installed to address one or more of

the following objectives: regulatory monitoring; water level

measurement; hydraulic conductivity estimation; or to

measure or evaluate some other hydrogeochemical site

characteristic. Generally speaking, wells are designed to

yield enough water for sample collection for regulatory

purposes; however, this is not always practical in low wateryielding formations. Conventional monitoring well designs

are generally inadequate in these types of formation and

alternative designs are needed together with sampling

methodologies which do not introduce unwanted artifacts in

the collected samples.

Well Purging and Sampling

Traditional approaches to purging and sampling ground

water are undergoing significant reevaluation. The most

common method involves purging a well at a high pumping

rate or bailing, until a fixed number of casing volumes

(usually 3-5) is evacuated, followed by sample collection.

This approach has raised concerns about the

representativeness of samples collected using these

methods, especially if the sampling objectives include

monitoring of contaminants. Concerns include entrainment

of immobile particles and the possible need to filter samples

to remove those artifacts, costs of pumping and disposing of

large volumes of contaminated water, and uncertainties in

interpreting the source of the sampled water. Many of the

Workshop participants recommended a method which is

referred to as low-flow (with minimal-drawdown) purging

and sampling. The principal differences between this and

more traditional approaches centers on the rate of pumping

and the criteria for deciding that purging is complete. The

newer method calls for slow flow rates for purging and

sampling in order to minimize chemical and hydrological

disturbance in and around the well. Furthermore, the

completion of purging is gauged on site-specific criteria

(stabilization of water quality parameters) rather than on a

fixed number of well volumes pumped. Conceptually,

formation water flowing through the screened section of the

well is purged and then sampled no faster than it enters the

well bore under natural hydrological flow conditions. The

criteria for the appropriate rate for purging and sampling is

hydrological: pumping rates should produce no net (or at

least minimal) drawdown of the water table. Under these

conditions, low-flow sampling removes water from only the

screened zone and stabilization of water quality indicator

parameters can be used as a criteria for deciding when

formation water has been accessed and sampling can begin.

The ideal endpoint would be stabilization of the

concentration of a contaminant (or other species of interest);

however, some indicator parameters may be correlated with

different classes of contaminants (e.g., dissolved oxygen

with volatile organics, and turbidity with metals). A

conservative approach was recommended which included

the use of dissolved oxygen and specific conductance for

volatile contaminants, turbidity and specific conductance for

metals (and metalloids) and hydrophobic organics, and

perhaps also the use of oxidation-reduction (redox)

potentials for both cases.

There are several advantages to the low-flow, minimal

drawdown method, including the following:

• More Representative Samples — Minimal

disturbance of the sampling point and reduced stress

on the formation results in low turbidity samples

which are representative of the “mobile” load of

contaminants (dissolved and colloidassociated)

present in the formation. By minimizing “artifactual”

turbidity, this method also reduces the need for

filtration of samples and the costs of analyses of

filtered and unfiltered samples.

• Waste minimization— The volume of purge water

required to access formation water is much less than

for more traditional purging methods because lowflow sampling conditions remove water from only

the screened zone. This minimizes the volume of

water that will require waste disposal at

contaminated sites.

• Spatial Resolution in Sampling —A fundamental

benefit of the decreased purge volume is that a
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smaller volume of the aquifer is sampled. This

represents a significant improvement in our ability to

detect and resolve contaminant distributions, which

may vary greatly over small distances in threedimensional space. In fractured clay or rock, for

example, most of the water comes from the fractures.

Because the fracture porosity is so small, the

sampling process may draw in water from a very

large volume of the deposit. This could greatly dilute

the concentration of contaminants in the sample.

Analogous flow problems can occur in granular

aquifers due to vertical heterogeneities in hydraulic

conductivity in typically layered sediments.

Switching to the low-flow sampling method met with some

resistance on the part of sampling practitioners because of

potential problems with data comparison and interpretation

of temporal trends due to differences in sample collection

methods. There was also concern that increased time may be

required for purging and sampling at slow flow rates, and

additional equipment may be needed. It was also questioned

whether the method was practical in tight or low wateryielding formations where monitoring wells are often urged

to dryness. However, recognizing the disadvantages, the

advantages of the low-flow sampling method in providing a

higher quality sample that more closely represents the

mobile dissolved and colloidal components in the formation

suggest that this is the direction in which the state of

professional practice must proceed. In the case of low

water-yielding formations, extension of the low-flow

method to more “passive” sampling is proposed for further

study as an alternative to current practices in such geologic

settings.

Colloidal Transport and Ground-Water Sampling

Recognition of the potential role of colloids in facilitating

contaminant transport has heightened awareness of the need

to obtain ground-water samples that are representative of

naturally mobile colloids. Carefully collected field evidence

shows that commonly-used sampling protocols (bailing,

rapid pumping) produce ground-water samples in which

colloids have been artificially entrained. That is, bailed and

rapidly pumped samples often contain substantial turbidity

that is not representative of conditions within the

subsurface. In practice, the suspended particles causing this

turbidity have been removed from the samples by filtering

in the field. Usually, membrane filters with 0.45 m pores

have been used to remove turbidity despite biases

introduced by their use. The consensus of the workshop

endorsed low-flow sampling techniques (described above)

which make it possible to obtain ground-water samples that

are relatively free of turbidity, without resorting to filtering,

by withdrawing water at relatively slow rates which induce

little or no drawdown of the water level in a monitoring

well. The use of the term “low-stress” sampling in place of

low-flow was proposed to emphasize the importance of

minimizing disturbance or stress to the subsurface system.

Concern about the potential effect of colloid-facilitated

transport is limited to certain classes of low-volubility,

surface-reactive contaminants, including radionuclides (e.g.,

Pu, Am, U, Co, Sr, Cs), heavy metal cations (Cu, Pb),

inorganic contaminants typically in anionic form (Cr(VI),

As), as well as high molecular weight organic compounds

(polychlorinated biphenyls, polycyclic aromatic

hydrocarbons). For other contaminants, such as low

molecular weight, non-surface-reactive contaminants (e.g.,

volatile organic compounds), the significance of colloids

can be deemed insignificant, based on published partitioning

values. Further research is needed to clearly identify what

types of subsurface environments pose the greatest risk for

this mode of contaminant transport.

Filtration and Sample Handling

The decision to collect filtered or unfiltered ground-water

samples should be based on ground-water monitoring and

data quality objectives. Field filtration should not

necessarily be the default choice. Consideration must be

given to what the application of field filtration is attempting

to accomplish, and filtration should not be used as a

corrective measure for poor sampling practices. To estimate

truly dissolved concentrations of elemental species, the

smaller the filter pore size the better, with 0.1 pm generally

the most practical for field usage. Dissolved concentrations

of elemental species are required for geochemical modeling

purposes and other determinations (e.g., alkalinity). In-line

field filtration is considered the most desirable approach to

minimize sample handling, sample exposure to the

atmosphere, and facilitate the expeditious transfer of the

water sample to the sample container. For assessment of

colloidal mobility, samples must not be filtered. This places

more importance on the manner in which samples are

collected and the efforts taken to exclude non-mobile or

artifactual suspended particles from the sample.

Compatibility of unfiltered samples with the eventual

analytical method imposed on the sample must be

considered. Unfiltered samples collected to evaluate the

“mobile” contaminant loading (i.e., dissolved + colloidal)

and having high turbidity must undergo digestion prior to

analysis. This issue requires special attention in the sitespecific sampling plan.

Sample transfer from the sampling device to the sample

container should be accomplished with as little disturbance

as possible. This operation is relatively straightforward with

low-flow sampling techniques, however is problematic

using bailers. The excessive volume of sample required for

different regulatory programs was also seen as a major

impediment to improving our ability to collect
4

“representative” samples, particularly in low water-yielding

formations. Wells in these geologic settings may recharge at

extremely slow rates, requiring hours of sampling time to

fulfill regulatory sample volume requirements. In many

cases, current analytical requirements for sample volumes

are considerably less than “regulatory” requirements which

are based on outdated analytical methods and

instrumentation. Advantages of reduced sample volume

requirements are: lower sample container filling time at

lower flow rates, lower bottle costs, lower shipping costs,

and reduction of liquid wastes back at the laboratory.

Documentation and Technology Transfer

Despite the fact that more focused, real-time

hydrogeochemical data collection has been enabled by

recent technological advances, the growth of the knowledge

base and improvements in field sampling practice are

seriously lagging. Additional and better documentation is

required at virtually every step of the sampling process.

This will permit better interpretation of the collected data

and more assurance that data quality objectives are being

met. Improvements in technology transfer from the research

community to the user communities is also needed. Training

and perhaps certification of field sampling personnel should

be encouraged and efforts should be expanded in this area

by state and federal regulatory agencies.

Summary edited by Robert W. Puls, Robert S. Kerr

Environmental Research Laboratory, U.S. Environmental

Protection Agency and written by Michael J. Barcelona,

University of Michigan, John E McCarthy, Oak Ridge

National Laboratory, and James R. Brown and Robert W.

Puls, U.S. Environmental Protection Agency.
5

II. Agenda

TUESDAY, NOVEMBER 30, 1993

7:30 - 8:00 a.m. General Introduction Robert W. Puls

8:00 - 8:30 a.m. A Federal Perspective on the Acquisition of Representative James R. Brown and

Ground Water Samples: A Historical Review Andrew L. Teplitzky

8:30 - 9:00 a.m. Sampling Program Purpose and Design Considerations Michael J. Barcelona

9:00 - 9:30 a.m. The Relationship of Monitoring Well Design, Construction, and David M. Nielsen

Development to Turbidity in Wells, and Related Implications for

Ground Water Sampling

9:30 -10:00 a.m. Use of Low-Flow or Passive Techniques for Sampling Robert W. Puls

Ground Water

10:15 - 10:45 a.m. Sampling Colloids and Colloid-Associated Contaminants Debera A. Backhus,

in Ground Water J. N. Ryan, D.M. Groher,

J.K. MacFarlane, and

P.M. Gschwend

10:45 - 11:15 a.m. Need for Practical Approaches to Conduct Multilevel Sampling Gary A. Robbins

11:15 - 12:45 p.m. Effects of Well Design and Time of Pumping on Concentrations of Jacob Gibs

Volatile Organic Compounds in Ground Water Samples and Thomas E. Reilly

11:45 a.m. Lunch

1:00 -1:30 p.m. Common Sampling and Analytical Procedures Viewed in the William R. Mabey

Context of Data Quality Needs and Nancy Barnes

1:30 - 2:00 p.m. Considerations in Selecting Filtered or Unfiltered Samples for Dennis E. Reece

Analyses of Metals in Ground Water Samples

2:00 - 2:30 p.m. A Study of the Impact of Monitoring Well Purging and Filtering Carol A. White

Techniques on Metals Concentrations in Ground Water Samples

from the Auburn Road Landfill Site in Londondery, N.H.

2:30 - 3:00 p.m. Ground Water Sampling of Fractured Clay and Rock Larry McKay,

Kent Novakowski, and

John McCarthy

3:30 - 4:00 p.m. Evaluation of Field-Filtration Variables for Representative Samples Karl F. Pohlmann,

of Trace Metals in Ground Water Gary A. Icopini, and

Charlita G. Rosal

4:00 - 4:30 p.m. Monitoring Well Sampling—You Can’t Always Get What You Jack Connelly

Want, But Can You Get What You Need?
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4:30 - 5:00 p.m. Abstract of Statistical Comparison of Metal Concentrations in Robert Gibbons

Filtered and Unfiltered Ground Water Samples and Martin Sara

5:30 - 7:30 p.m. Poster Session

WEDNESDAY, DECEMBER 1, 1993

8:00 - 11:30 a.m. Small Group Discussions

Monitoring Goals and Objectives

Well Design, Construction, and Development

Well Purging and Sampling

Turbidity and Colloid Transport

Sample Handling and Analysis

11:30 a.m. Lunch

1:30 - 5:00 p.m. Small Group Discussions

Monitoring Goals and Objectives

Well Design, Construction, and Development

Well Purging and Sampling

Turbidity and Colloid Transport

Sample Handling and Analysis

THURSDAY, DECEMBER 2, 1993

8:00 - 11:00 a.m. Reports from Small Group Discussions Michael J. Barcelona,

Linda Aller, Robert W.

Puls, Joseph N. Ryan, and

Karl Pohlmann

11:00 - Noon Wrap-Up Robert W. Puls
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III. Extended Abstracts

The following extended abstracts are provided for the oral presentations made by invited speakers on the first day of the

Workshop. Speakers were selected by the Steering Committee and the topics were intended to provide some foundation for

subsequent discussions which occurred both formally and informally during the balance of the Workshop. The first day's

presentations covered a wide range of sampling-related topics from a diverse group of individuals active in ground-water

sampling. It should be noted that the abstracts were not part of the formal peer-review process which the remainder of this

document underwent, and represent opinions or personal points of view in many cases. As a result, some presentations are in

conflict with others. An attempt was purposely made to provide a forum for the exchange of conflicting views and data on

the first day, and thus stimulate discussions for the remainder of the Workshop.
8

A REVIEW OF FEDERAL

REGULATIONS AND GUIDANCE

FOR GROUND-WATER SAMPLING

James R. Brown and Andrew L. Teplitzky

Several Federal regulations mandate the collection and

analysis of ground-water samples to protect ground-water

resources and to determine the anthropogenic impacts on

ground-water quality: The Resource Conservation and

Recovery Act (RCRA); the Comprehensive Environmental

Response, Compensation, and Liability Act (CERCLA); the

Toxic Substances Control Act (TSCA); and the Federal

Insecticide, Fungicide, and Rodenticide Act (FIFRA).

Annually, these regulations result in the collection of

hundreds of thousands of ground-water samples. Some of

the regulations use general performance standards for

ground-water sample collection requirements. Other

regulations require specific procedures for the collection of

ground-water samples.

The RCRA program regulates, in part, owners and

operators of municipal solid waste landfills (MSWLFs),

hazardous waste management facilities, and underground

storage tanks. Ground-water monitoring regulations at

RCRA MSWLFs prohibit the filtration of ground-water

samples. RCRA hazardous waste ground-water

monitoring regulations and underground storage tank

standards do not specify whether the samples should be

filtered or not. Implementation of specific sampling

protocols for hazardous waste disposal facilities and

underground storage tanks is done at the State or EPA

Region level, mainly through technical guidance

documents. EPA’s ground-water sampling guidance for

hazardous waste disposal facilities is found in the RCRA

Ground-Water Monitoring Technical Enforcement

Guidance Document (TEGD) (USEPA, 1986), and RCRA

Ground-Water Monitoring: Draft Technical Guidance

(GWM) (USEPA, 1992).

The TEGD recommends:

1) the use of sampling equipment and procedures that

minimize sample agitation and reduce or eliminate

contact with the atmosphere;

2) that low-yielding wells be purged at a rate that does

not cause recharge water to be excessively agitated;

and

3) that sampling rates for volatile organic

compounds not exceed 100 milliliters per

minute.

The TEGD also recommends that samples collected for the

analysis of organic compounds not be filtered. However,

samples collected for the analysis of metals should be split

into two portions: one portion should be filtered and

analyzed for dissolved metals, and one portion should not be

filtered and analyzed for total metals.

 GWM recommends the use of low rate purging and

sampling procedures, discourages the use of bailers, and

generally does not recommend the filtration of ground-water

samples used for leak detection purposes.

The CERCLA program (commonly referred to as

“Superfund”) regulates the remediation of uncontrolled and

abandoned hazardous waste sites. The regulations specify

only general performance standards for collecting groundwater samples. Several guidance documents, however,

prescribe ground-water sampling procedures for various

sampling objectives.

A Compendium of Superfund Field Operations Methods

(USEPA, 1987), recommends that the sampling protocol be

dictated by the study objectives. The Compendium states

that if the study objective is to assess the migration

mechanisms in conjunction with migration pathways, then it

is necessary to know the concentration of dissolved and total

constituents.

The Risk Assessment Guidance for Superfund (USEPA,

1989), notes that data from filtered and unfiltered

ground-water samples are useful for evaluating chemical

migration in ground water, and that a comparison

between these samples can provide important

information on the form in which a chemical exists in

ground water. The Risk Assessment Guidance also

specifies the use of data from unfiltered samples for

estimating exposure concentrations.

A Superfund Ground-Water Issue Paper entitled, “GroundWater Sampling for Metals Analysis,” (Puls and Barcelona,

1989), also makes several ground-water sampling

recommendations for the Superfund program. The paper

recommends:

1) the collection of unfiltered samples to determine a

conservative estimate of contaminant loading in an

aquifer;
9

2) the use of small pore-size filters (<0.45 micron) to

determine the concentration of dissolved metals;

3) the use of low-rate purging and sampling

procedures (e.g., 100 milliliters per minute); and

4) that bailers not be used to collect ground-water

samples.

Ground-water samples are also collected under provisions of

the Toxic Substances Control Act (TSCA). TSCA requires

that materials containing concentrations of polychlorinated

biphenyls in excess of 50 parts per million must be disposed

of in a landfill with a ground-water monitoring network.

The TSCA regulations (40 CFR § 761.75(b)(6)(ii) and (iii))

outline general performance standards for ground-water

sampling methods, but do not address specifically whether

ground-water samples should be filtered or unfiltered.

Under § 3(c)(2)(B) of the Federal Insecticide, Fungicide,

and Rodenticide Act (FIFRA), EPA may require pesticide

registrants to submit monitoring data from ground-water

studies to support the registration of pesticide products.

These studies are performed when residues of the pesticide

have been detected in ground water or when EPA suspects

that the pesticide will leach to ground water based on a

review of the environmental fate data. FIFRA’s Draft

Guidance for Ground-Water Monitoring Studies (USEPA,

1988) recommends the filtration of ground-water samples;

however, this practice is being re-evaluated and revised

FIFRA guidance may change the sampling recommendation.

State implementation of the Federal RCRA ground-water

sampling requirements exhibits varying practices across the

nation. Information submitted to EPA by State

environmental agencies on ground-water sampling

procedures at MSWLFs and hazardous waste management

facilities reveals a non-uniform approach to the acquisition

of representative ground-water samples. During the

summer of 1993, all 50 States submitted publically available

information about ground-water sampling policies and

regulations to EPA. The data show that in both the

municipal solid waste and hazardous waste programs:

1) some States allow the filtration of ground-water

samples;

2) some States do not allow the filtration of groundwater samples;

3) some States require or recommend the collection of

both filtered and non-filtered ground-water

samples; and

4) some States allow either filtered or non-filtered

ground-water samples.

Figures 1 and 2 exhibit the distribution of these groundwater sampling practices throughout the United States for

the municipal solid waste and hazardous waste programs

respectively. The figures do not suggest any apparent

regional trends in sampling practices used by the various

State agencies. A comparison of these sampling practices to

a generalized hydrogeologic map of the United States also

fails to depict any deliberate consistency in sampling

practices within a distinct ground-water region (Figure 3).

Overall, that data show that ground-water sampling

practices lack consistency within EPA Regions, within

ground-water regions of the U.S., among States, and

between the municipal solid waste and hazardous waste

programs within States.

As made evident by this brief review of various Federal

environmental regulations requiring ground-water

monitoring, sampling requirements vary: some regulations

allow the filtration of ground-water samples and others do

not. Some Federal regulations are not specific with regard

to how the samples should be collected, relying instead

upon guidance from State environmental agencies to

develop the sampling protocol. A general survey of these

State sampling policies and regulations shows no apparent

consistency with respect to regulatory objectives or

hydrogeologic setting. Therefore, a need exits to develop

uniform ground-water sampling guidance that considers the

objectives of the ground-water monitoring regulatory

programs and incorporates site-specific hydrogeologic

information.
10

Figure 2. Ground-Water Sampling at Hazardous Waste Sites.

Figure 1. Ground-Water Sampling at Municipal Solid Waste Landfills.
11

References

Federal Insecticide, Fungicide, and Rodenticide Act, 7

U.S.C. § 3(c)(2)(B).

Ground-water Monitoring Requirements for Landfill

Disposal of PCBs, 40 CFR § 761.75(b)(6)(ii) and (iii),

(1992).

Puls, Robert W. and Michael J. Barcelona, (1989). GroundWater Sampling for Metals Analysis. Superfund GroundWater Issue Paper (EPA/540/4-89/001).

USEPA, (1986). RCRA Ground-Water Monitoring

Technical Enforcement Guidance Document, Office of

Waste Programs Enforcement and Office of Solid Waste and

Emergency Response, (OSWER-9950.1).

USEPA, (1987). A Compendium of Superfund Field

Operations Methods. Office of Emergency and Remedial

Response, (EPA/540/P-87/001; OSWER Directive: 9355.0-

14).

USEPA, (1988). Draft Guidance for Ground-Water

Monitoring Studies. Office of Pesticide Programs.

Figure 3. Generalized Hydrogeologic Map of the United States.

USEPA, (1989). Risk Assessment Guidance for Superfund:

Interim Final Guidance. Office of Emergency and Remedial

Response (EPA/540/1-89/002).

USEPA, (1992). RCRA Ground-Water Monitoring: Draft

Technical Guidance. Office of Solid Waste (EPA/530-R-93-

001).
12

SAMPLING PROGRAM PURPOSE

AND DESIGN CONSIDERATIONS

Michael J. Barcelona

Ground-water and subsurface monitoring programs have

diverse purposes and objectives which inevitably change as

detective efforts evolve into assessments and from there to

remedial-action performance evaluations. Common

objectives to many subsurface site characterization and

monitoring programs allow us to approach network designs

from a basic set of criteria for representativeness, accuracy,

precision, specifity, and sensitivity.

Detective monitoring programs have as their main

objectives: the characterization of the site and placement of

sampling points so as to permit detection of indicator

parameters (e.g. TOC, pH, conductance, metals or volatile

organic compounds (VOC’s) etc. Assessment monitoring

efforts would follow detection of releases and seek to

determine the specific extent and magnitude of contaminant

distributions. In turn, programs planned to support the

design and implementation of remedial actions increase in

detail to the point where real differences in contaminant

mass removal may be determined over time. Fundamental

to all of these purposes are the following objectives1:

1. Avoidance of gross errors2 (i.e. false

negative data collection due to poor

sampling techniques, choice of location or

focusing on symptoms rather than media

where the bulk of the contaminant mass

resides),

2. Minimization of costs in dollars, time and

human resources by avoidance of redundancy in data collection, while providing a

basis for detecting real trends3, and,

3. Complete data collection of both

hydrogeologic parameters and chemical

concentrations sufficient to permit decisionmaking at a known level of confidence.

In all of these efforts, representativeness, accuracy,

precision, specificity and sensitivity are of value to the

monitoring effort. Good professional standards of practice

apply and it is time that these standards are applied to both

field and laboratory techniques.

Representativeness

Though representativeness in sampling is often parroted

back in plans and reports, there exists a substantial gap

between what is commonly practiced and what we can

identify as standards for professional practice from the

scientific literature. In simplest terms, representativeness

stems from the purposes of the investigation recognizing

that purposes change (as does the dollar value of the data)

and all sites merit some level of specific detective and site

characterization effort. This comes from a recognition that

the basic geologic descriptions and a consistent hydrogeochemical framework which constitute a conceptual model of

a site have lasting value for the future.

Natural variability in background and “impacted”

hydrogeochemical conditions provides limits on the

distributions of chemical concentrations and aquifer

properties. These can be described in statistical terms.

Representativeness, therefore, implies that the sampled

population reflects at least some properties of the total

population. Values which lie beyond these limits will

require some explanation. The site’s unique characteristics

will determine the extent to which the statistical

distributions of critical parameters (e.g. major hydrostratigraphic units, hydraulic conductivity, transmissivity,

background and contaminant concentrations) must be

known. Clearly, presuming that the site has been

characterized to a degree that it would pass peer review

could establish if in fact good professional practice had been

performed. It is at this point that the basis for a thorough

monitoring effort may address major deficiencies within

program constraints.

The literature has shown numerous examples of deficiencies

which can and should be remedied in routine monitoring

efforts3,4,5. Progress has been in a number of operational

areas which deserve more in-depth consideration in ongoing

efforts.

Focus on the Media

A focus on the correct medium (i.e. solid associated

contaminants, rather than symptoms in soil gas or water) for

the major mass of contaminants is essential to accurate

monitoring efforts. Table 1 shows data which reflects the

dominant nature of solid-associated volatile organic

contaminant mass. This has also been observed by many

groups. Here, the guidance from the Agency with regard to

monitoring practice (e.g. bulk solid sampling without

preservation) is at odds with good professional performance.

If in fact, the correct medium is left under-represented with

respect to chemical data collection, it is often the case that
13

Table 1. Relative Masses (μg) of TCA in ground water and aquifer solids for a representative 1 liter aquifer

element.(25)

% Total

Well Ground MeOH Preserved Bulk Jar, 4oC TCA in

Water Solid Solid Solid

15 13.5 21.0 - 60

31 85.7 516.0 52 86

32 11.1 30.9 - 74

37 83.7 239 - 74

 (-) denotes no detectable levels of TCA in bulk jar sample by static headspace gas chromatography-Hall

electrolytic conductivity detection (7 day holding time) (Barcelona, M. J. and D. M. Shaw, 1992 unpublished

data).

Critical Considerations For Improving Professional

Practice

What is vitally important here in the judgement of good

professional practice? From the literature we can glean the

following:

1. Implement consistent field screening

techniques for both chemical and

hydrogeologic parameters with careful lab

confirmation of a percentage of the total

samples 8,9;

2. Minimize planned well completions where

they will afford the most long-term

information term and collect sufficient

background data for meaningful comparison;

3. Recognize that field sampling can often be

the most significant source of error. Avoid

the use of “different” well design, purging

and sampling techniques across the site so

that chemical concentration comparisons are

in fact statistically comparable, (this also

means rejection of biased purging and

sampling techniques (i.e. the bailer); and,

4. Permit sufficient time and flexibility in the

program’s directions to avoid “dead-end”

data collection which wastes time, human

resources and dollars to no useful end10,11.

The foregoing discussion stresses the value of a balanced

approach to site characterization and monitoring, which

redundant well completions rather than in-depth

hydrogeologic data collection and interpretation may have

been made. The major liability here is that though some

information exists for the major contaminants, both

background conditions and critical design parameters for

remedial action are lacking. The major pitfalls here are:

1. Overly rigid work plans which do not permit

needed exploratory field screening or

borehole/solid sampling for

hydrogeochemical parameters in

background and contaminated zones,

2. The use of known biased procedures in

water (e.g. bailer sampling for VOC’s) or

solids (e.g. bulk jar sampling) without

sufficient allowances for mineralogic, site

specific contaminant sorption/desorption

parameters, or hydraulic conductivity

determinations.

In addition, whether by dint of tradition or the “parrotsyndrome” (i.e. parroting back the format and detail of

earlier studies) monitoring efforts may fail to provide

sufficient hydrogeologic data and its integration with the

chemical data to suit the reasonable long-term interests of

the monitoring work6,7. From this perspective, it may be

irrelevant that precise, specific or sensitive analytical

determinations have been made since the focus of the

investigation may have been off the mark. It is far more

important that high quality decisions have been made in the

field. It true quality is the key (and why has this become

less of a value?), the quality of decision making can only be

assured if active peer-review at the planning stage becomes

a part of the overall field program.
14

Table 2. Overall Mean, Relative Standard Deviation and Percentage of Total Variance Attributable to

Laboratory or Field (Sampling) Error, and Natural Variability (November 1990-September 1992)

 Overall Relative Percent of Total Variability

Mean (Std. Dev.) Lab Field Natural

VOC (μg/L) % % % %

111 TCA 119.5 (36%) 1.29 3.26 95.45

TCE 29.8 (43%) 1.95 12.75 85.30

c12DCE 45.2 (32%) 1.69 4.72 93.59

11DCA 44.3 (28%) 1.02 5.22 93.76

11DCE 16.3 (31%) 3.61 4.15 92.24

values completeness in the data collection effort.

Refinement of the hydrogeochemical dataset via an

evolutionary, DQO-driven investigative effort will serve

both the regulated and regulating communities’ goals most

closely5. We must reject the use of poor practices and

educate the entire community that these sites will not simply

go away. They may yield eventually to a well-founded,

documented monitoring approach based on geologic and

hydrogeologic fact.

Table 2 contains an example of results of a controlled data

collection effort by using dedicated bladder pumps and

consistent purging and sampling procedures from a large

network for VOC’s in ground water. Here the magnitude of

natural variability (what we are trying to evaluate) far

outweighs the errors from analytical or sampling

procedures. In addition, the use of dedicated devices has

been shown to minimize costs associated with network

operation12.

Many other examples of controlled data collection can be

pointed out from the literature to aid future monitoring

network designs13. These approaches have the merit of

lower cost as well as a focus on the correct media for

decision-making purposes.

References

1. Barcelona, M.J., Overview of the Sampling Process, in

Principles of Environmental Sampling, Keith, L. H.

Ed., ACS Professional Reference Book, American

Chemical Society, Washinton, DC, 1988, Chapter 1.

2. Sanders, T.G., R.C. Ward, J.C. Loftis, T.D. Steele, D.D.

Adrian, and V. Yevjevich, Design of Networks for

Monitoring Water Quality, Water Resources

Publications, Littleton, CO, 1983, 328 pp.

3. Gammage, R.B., and B.A. Berven, Hazardous Waste

Site Investigations - Towards Better Decisions, Lewis

Publishers, 1992, 288 pp.

4. Barcelona, M.J., and Helfrich, J.A., Realistic

Expectations for Ground Water Investigation in the

1990’s, in Current Practices in Ground-Water and

Vadose Zone Investigations, Nielson, D. M. and Sara,

M. N., Eds., American Society for Testing and

Materials. Philadelphia, PA, 1992, 431 pp.

5. U.S.EPA. Data Quality Objectives for Remedial

Response Activities Development Process, U.S. EPA.

540/G-87/003, March 1987.

6. Calabrese, E.J. and P.T. Kostecki, Risk Assessment and

Environmental Fate Methodologies, Lewis Publishers,

Chelsea, MI, (1992), 150 pp.

7. National Research Council, Ground Water and Soil

Contamination Remediation Toward Compatible

Science, Policy and Public Perception, Water Science

and Technology Board, National Academy Press,

Washington, DC, (1990), 261 pp.

8. First International Symposium on Field Screening

Methods for Hazardous Waste Site Investigations,
15

U.S.EPA., U.S. Army Toxic and Hazardous Materials

Agency, Instrument Society of America, October, 1988.

9. Robbins, G. A., R. D. Bristol and V. D. Roe, A Field

Screening Method for Gasoline Contamination Using a

Polyethylene Bag Sampling System, Ground Water

Monit. Rev. 9(3):87-97, (1989).

10. National Symposium on Measuring and Interpreting

VOC’s in Soils: State of the Art and Research Needs.

Univ. of Wisconsin Extension, U.S. Environmental

Protection Agency, Oak Ridge National Laboratory,

U.S. Department of Energy, U.S. Toxic and Hazardous

Materials Agency, America Petroleum Institute.

January 12-14, 1993, Las Vegas, NV.

11. Black, S.C., Defining Control Sites and Blank Sample

Needs, Chapter 7, pp. 1077-117, in Principles of

Environmental Sampling, L. H. Keith (ed.). ACS

Professional Reference Book, American Chemical

Society, Washington, DC, (1988) 458 pp.

12. Lovejoy, S. and D.M. Eisenberg, Cost Effectiveness of

Dedicated Sampling Systems for Ground Water

Monitoring, pp. 89-96 in Proceedings of HAZMACON

’89 Hazardous Materials Management Conference and

Exhibition, April 18-20, 1989, Santa Clara, CA, T.

Bursztynsky and M. Loss, editors. Assoc. of Bay Area

Governments, P.O. Box 2050, Oakland, CA 94604-

2050.

13. Nielsen, D.M. and M.N. Sara, Current Practices in

Ground Water and Vadose Zone Investigations ASTM

1118, American Society for Testing and Materials,

Philadelphia, PA, (1992), 431 pp.
16

THE RELATIONSHIP OF

MONITORING WELL DESIGN,

CONSTRUCTION

AND DEVELOPMENT TO

TURBIDITY IN WELLS, AND

RELATED

IMPLICATIONS FOR GROUNDWATER SAMPLING

David M. Nielsen

A strong correlation exists between improper ground-water

monitoring well design, construction and development and

high levels of turbidity in ground-water samples. This

correlation is independent of the type of geologic material in

which the wells are installed. Research conducted by the

author, prior to the compilation of two recently approved

ASTM standards (D-5092, Standard Practice for Design and

Installation of Ground-Water Monitoring Wells in Aquifers;

D-5342, Standard Guide for Development of Ground-Water

Monitoring Wells in Granular Aquifers) indicates that

proper well design, construction and development can

alleviate turbidity problems in most unconsolidated

formation materials (sands and gravels). However, the same

research demonstrated that current well design, construction

and development practices are not sufficiently advanced to

limit turbidity in monitoring wells installed in

predominantly fine-grained unconsolidated formation

materials (silts and clays).

Work conducted on this subject by others (Paul et al., 1988)

has demonstrated th vigorous development of wells installed

in fine-grained glacial till actually aggravates turbidity

problems and that standard well design practices, even when

supplemented by additional controls on sediment

production, failed to ameliorate turbidity problems.

Additional research is required to develop suitable well

design, construction and development guidelines applicable

to predominantly finegrained formation materials. This is

particularly critical in waste disposal facilities, at which

monitoring wells are or well be required by regulation, are

purposely sited in areas where these geologic materials

prevail.

Recently proposed regulatory restrictions on ground-water

sample filtration appear to be founded primarily on the

premise that proper monitoring well design construction and

development practices can alleviate sample turbidity

problems in all wells. Current research demonstrates other

wise. Though proper well design, construction and

development are important steps toward eliminating

sedimentladen ground-water samples in some hydrogeologic

settings, these measures will not suffice in all situations.

Field filtration of ground-water samples intended for metals

analysis, while not a suitable substitute for proper well

design and construction in coarse-grained formation

materials, is necessary to ensure comparability of analytical

data from wells installed in predominantly fine-graine

formation materials. To disallow field filtration of samples

from these wells is to fail to recognize the limitations of

current well design technology.
17

USE OF LOW-FLOW OR PASSIVE

SAMPLING TECHNIQUES FOR

SAMPLING GROUND WATER

Robert W. Puls

Introduction

It is generally accepted that monitoring wells must be

purged to access formation water to obtain “representative”

ground water quality samples. Historically anywhere from

3 to 5 well casing volumes have been removed prior to

sample collection to evacuate the standing well water and

access the adjacent formation water. However, a common

result of such purging practice is highly turbid samples from

excessive downhole disturbance to the sampling zone. This

disturbance includes the following: mixing of stagnant

casing water with water which resides in the screened

interval and the formation; aeration; degassing; and

excessive turbidity due to high pump rates or the continual

plunger action of bailers. The excessive turbidity created

can impact estimations for both “dissolved” and “total”

metals determinations, and cause other artifacts which may

adversely affect sample quality. An alternative purging

strategy has been proposed using pumps which permit much

lower flow rates (< 1 liter/min) and placement within the

screened interval of the monitoring well. The advantages of

this approach include less disturbance to the sampling zone,

increased spatial resolution of sampling points (i.e., sample

smaller portion of the aquifer), less variability, less purge

time (and volume), and low-turbidity samples. The overall

objective is a more passive approach to sample extraction

with the ideal being to match the intake velocity with the

natural ground water flow velocity (i.e. negligible

drawdown during purging). The volume of water extracted

to access formation water is generally independent of well

size and capacity and dependent upon well construction,

development, hydrogeologic variability and pump flow rate.

This is particularly evident where dedicated sampling

systems are employed. A detailed understanding of the

hydrogeochemistry of the sampling zone, particularly with

respect to aquifer heterogeneities, is important in both the

design of the sampling system and the interpretation of the

resultant sampling data for site assessment and remedial

evaluation purposes.

Required purge volume or purge duration is evaluated

through continuous monitoring of water quality parameters

(WQPs) such as dissolved oxygen, specific conductance,

oxidation-reduction (redox) potential and turbidity to

determine the presence of formation water. Research has

shown (Puls et al. 1992; Backhus et al. 1993; Barcelona et

al. 1994) that purging at these lower rates with various types

of pumps (peristaltics, low-speed submersibles, and bladder

pumps) does indeed produce low turbidity and generally

high quality samples. A perceived disadvantage of such

strategies however is the additional time required to purge

the wells. In general however, this same research has shown

that the volumes required to access formation water are less

than 2 casing volumes and in deeper wells are actually only

fractions of a casing volume, suggesting that the purge

volume is independent of well size or casing volume. This

previous research was conducted exclusively with

portable sampling systems. Studies which have utilized a

downhole camera during the purging process (Puls and

Powell, 1992; Kearl et al. 1992) have suggested that the

installation of the sampling devices themselves causes

the most disturbance to the sampling point. If

installation of the sampling system can be avoided

through the use of dedicated sampling systems, then this

could greatly reduce the time required to obtain

representative formation samples and also greatly reduce

the volume of water brought to the surface.

This study was conducted to evaluate the use of low-flow

purging methods in dedicated sampling installations in

routine monitoring wells. Stabilization of water quality

indicator parameters, together with time series sampling of

contaminants and water chemistry was employed to evaluate

the purge volume required to access formation water.

Study Site

The field site is located at the U.S. Coast Guard (USCG)

Support Center near Elizabeth City, North Carolina, about

100 km south of Norfolk, Virginia and 60 km inland from

the Outer Banks of North Carolina. The base is located on

the southern bank of the Pasquotank River, about 5 km

southeast of Elizabeth City. The topography of the site is

essentially flat and between two and three meters above sea

level. The river has a width of approximately 3.2 km along

the USCG base’s northern boundary and a depth about 3

meters. A chrome plating shop, located within an aircraft

hangar on the base, had been in use for more than 30 years,

and had discharged acidic chromium wastes through a hole

in the concrete floor into the soils immediately below the

shop’s foundation and the underlying aquifer (Puls et al.

1994).
18

The site geology consists of typical Atlantic coastal plain

sediments characterized by complex and variable sequences

of surficial sands, silts and clays. In the vicinity of the

plating shop, the surface soils are silty clays. These overlie

a thin sandy clay layer at about 1.5 m, which overlie a

sequence of sands and silty fine sands. In some locations, a

dense gray clay layer substitutes for the sandy clay layer at

1.5 m. Fine to medium sands dominate from 4 to 20 m. A

dense gray clay unit (Yorktown Confining Unit) persists at a

depth of 20 m. This depth is slightly variable and dips

gently from north to south.

Materials and Methods

Monitoring Wells and Sampling Pumps

Eight different monitoring wells at the site were used in the

study. With the exception of two of the wells, these were all

5 cm (2 in.) diameter schedule 40 polyvinylchloride (PVC)

wells with 0.25 mm (0.01 in) slotted screens. Other

characteristics of the sampled wells used in the study are

listed in Table 1. The wells ranged in depth from 4.6 to 15.2

meters below ground surface. System volume (Table 1)

refers to the volume of water in the tubing and the water

quality parameter measurement device (QED PurgeSaver).

Well volume (Table 1) refers to the water in the monitoring

well itself which varied somewhat over time due to

fluctuations in the water table level. Two of the wells (MW

25, MW 31) were installed without casing. For these two

wells, a permanently dedicated PVC bladder pump (QED

Inc.) and a permanently dedicated variable-speed

submersible pump (Redi-Flo 2, MP1; Grundfos Inc.) were

encased in 0.25 mm (0.01 in.) slotted screens, sealed and

connected with 0.63 cm (0.25 in.) teflon-lined polyethylene

tubing. These units were lowered inside 7 cm (2.75 in.)

hollow-stem augers to the desired depth and the formation

was allowed to collapse in around the units. For the caseless

Grundfos, a sandpack was used inside the screen, whereas

for the caseless QED pump glass beads were used as the

packing or filter material. These systems are referred to as

permanently dedicated, because they cannot be removed for

servicing. The same type pumps (Grundfos Redi-Flo2 and

QED bladder) and tubing were used in the traditional

monitoring wells as well.

Purging and Sampling Procedures

The pumps (except for the permanently installed pumps)

were set with the pump intake at approximately mid-screen.

Following installation (April, 1992), most of the pumps

remained in place throughout the study (April, 1992 - June,

1993). Data was first collected in August, 1992, and then

again in February, March, and June of 1993. The sampling

procedures described in previous publications (Puls et al.

1992; Puls and Powell, 1992) were generally followed,

except all purge water was collected in sequential 500 ml

increments for analysis of volatile organics

(trichloroethylene [TCE], dichloroethylene [DCE], and

vinyl chloride), major cations and metals, anions, and

chromium. Water levels were measured and recorded

prior to purging and monitored continuously while

purging to minimize drawdown (<0.1 m). Flow rates

ranged from 0.22-0.55 L/min. A flow-through cell with

data logger (QED PurgeSaver) was used to continuously

monitor pH, temperature, dissolved oxygen (DO), and

specific conductance. Purging and continuous sampling

continued beyond equilibration of water quality indicator

parameters to a maximum of 21 liters. Equilibration was

defined as three successive readings within ±10% for

DO and turbidity, ±3% for specific conductance, and

±0.05 for pH. At the flow rates utilized, these readings

were taken every three minutes. Equilibration criteria

were based on evaluation of preliminary plotted WQP

data and equipment accuracy. Temperature was recorded

but not used for stabilization.

Results and Discussion

Purging results in terms of water quality parameter

(WQP) equilibration and contaminant concentration

(CC) equilibration are shown in Table 1. WQP and CC

equilibration volumes were independent of well depth or

well volumes. WQP equilibration volumes ranged from

4 to 10 L, while CC equilibration volumes ranged from

2.5 to 7.5 L. The two dedicated permanent wells (MW

23, 31) had some of the lowest CC equilibration volumes

as might be expected due to the minimal stagnant well

water above the pump (0.64-0.81 L in buried pump

tubing). MW 22, the deepest well, had the smallest CC

equilibration volume for all wells used in the study,

while the largest CC equilibration volume was for the

shallowest well (MW 2).

The equilibration trends for the WQP’s were similar for

all wells in the study. Specific conductance increased

slightly and equilibrated prior to dissolved oxygen and

turbidity. Dissolved oxygen decreased and equilibrated

after specific conductance and prior to turbidity.

Turbidity followed a generally exponential decline.

Contaminant concentration equilibration volumes were

less than or equal to WQP equilibration volumes.

Differences in initial and final equilibration contaminant

concentrations were generally less than 20% for TCE, cDCE, vinyl chloride and chromium.

Using a spherical conceptual model for the aquifer volume

sampled, CC equilibration was achieved within a 13-16.5

cm radius (assuming a porosity of 0.38). Alternatively, if

casing volume is defined by only the water within the

screened interval of the well where the pumps are located,

CC equilibration was attained between 1.1-2.4 screened

interval casing volumes (SICV) for the dedicated pumps in

the 5 cm monitoring wells.
19

Summary and Conclusions

An alternative conceptual model is proposed which

considers the evacuation of only a portion of the screened

interval volume rather than the entire casing volume.

Depending upon well depth and the analytes of interest,

various types of pumps may be used with the pump intake

located within the screened interval and at the desired

sampling depth. Significant reductions in purge volume

have been attained using dedicated systems, and thorough

economic analyses may show this to be a cost-effective

alternative for routinely-sampled monitoring wells.

While this strategy works most effectively where well

screens are short (<1.5 m) and located within a relatively

homogeneous geologic zone, they may also be effective in

longer screened intervals and where geologic

heterogeneities may exist. This remains to be tested. The

utility of these techniques has not been explored in open

boreholes in fractured rock. Proper well construction and

well development and complete documentation of all

sampling activities becomes increasingly important where

such strategies are employed. A detailed understanding of

the hydrologic and geologic variability of the system is

essential in establishing sampling points and designing the

overall sampling program.

Disclaimer

Although the research described in this article has been

funded wholly or in part by the United States Environmental

Protection Agency, it has not been subjected to the Agency’s

peer and administrative review and therefore may not

necessarily reflect the views of the Agency and no official

endorsement may be inferred.

References

Backhus, D.A., J.A. Ryan, D.M. Groher, J.K. MacFarlane.

1993. Sampling Colloids and Colloid-Associated

Contaminants in Ground Water. Ground Water, 31(3), 466-

479.

Barcelona, M.J., H.A. Wehrmann and M.D. Varljen. 1994.

Reproducible Well Purging Procedures and VOC

Stabilization Criteria for Ground-Water Sampling. Ground

Water, 32(1).

Table 1. Characteristics of wells used in the study and water quality parameter and contaminant concentration

equilibration data, U.S. Coast Guard Support Center, Elizabeth City, NC.

Well Depth1 Screen2 Device3 WQPEV4 CCEV5 SystemVol.6 Well Vol.7

2 4.6 1.5 CS 7.5 7.5 0.6 5.6

13 4.6 1.5 CS 7.0 4.5 0.6 5.6

13 4.6 1.5 CS 7.0 7.0 0.6 5.6

14 6.1 1.5 BL 10.0 4.5 0.9 8.7

15 4.6 1.5 BL 6.0 5.5 0.8 5.6

16 4.6 1.5 CS 4.0 3.5 0.8 5.6

22 15.2 3.1 CS 7.5 2.5 1.3 27.2

23 7.1 0.9 BLp 7.5 3.5 0.8 0.5

31 4.9 0.5 CSp 6.5 3.5 0.6 0.3

1 Depth = well depth in m,

2 Screen = screen length in m,

3 CS = low-speed centrifugal submersible pump, BL = bladder pump, CSp = permanently buried low-speed

centrifugal submersible pump, BLp = permanently buried bladder pump.

4 WQPEV = water quality parameter equilibration volume in liters,

5 CCEV = contaminant concentration equilibration volume in liters,

6 System volume = volume (in liters) of tubing and flow-through cell,

7 Well volume = volume (in liters) of water in well casing and well screen.
20

Kearl, P.M., N.E. Korte, and T.A. Cronk. 1992. Suggested

Modifications to Ground Water Sampling Procedures Based

on Observations from the Colloidal Borescope. Ground

Water Monitoring Review, Spring, 1992, 155-160.

Puls, R.W. and R.M. Powell. 1992. Acquisition of

Representative Ground Water Quality Samples for Metals.

Ground Water Monitoring Review, 12(3), 167-176.

Puls, R.W., D.A. Clark, B. Bledsoe, R.M. Powell, and C.J.

Paul. 1992. Metals in Ground Water: Sampling Artifacts and

Reproducibility. Hazardous Waste and Hazardous

Materials, 9(2).

Puls, R.W., C.J. Paul, D.A. Clark, and J. Vardy. 1994.

Transport and Transformation of Hexavalent Chromium

Through Soils and into Ground Water. J. Soil

Contamination. To be published June, 1994.
21

SAMPLING COLLOIDS AND

COLLOID-ASSOCIATED

CONTAMINANTS

IN GROUND WATER

D.A. Backhus, J.N. Ryan, D.M. Groher, J.K.

MacFarlane and P.M. Gschwend

Groundwater monitoring wells are used to obtain general

information about groundwater quality and specific

information about concentrations and speciation of mobile

contaminants in the vicinity of a well. This information is

used to determine whether a given facility is currently in

compliance with regulations. In addition, data from

monitoring wells can be used to provide clues to as to the

processes affecting contaminant fate in the subsurface,

allowing development of models for accurate predictions of

spacial and temporal contaminant distributions. These

predictions allow for assessment of risks under various

scenarios and evaluation of alternative remediation

strategies. It is crucial that samples obtained from

monitoring wells accurately reflect in situ mobile

contaminant concentrations, as the cost of a bad decision

based on inaccurate data can be great.

In the past, it was generally assumed that contaminants

existed in the saturated zone either as associated with the

aquifer material and therefore immobile or dissolved in and

moving with the groundwater. Hence, when a turbid

groundwater samples was obtained from a monitoring well

it was assumed that the turbidity was an artifact of well

construction, preparation, or sampling procedures.

Filtration was and continues to be used to remove the

particles causing this presumed artifact turbidity. In recent

years, we have come to realize that in some subsurface

systems, turbidity causing materials may actually be present

in an aquifer as mobile colloidal species (see review by

McCarthy and Zachara, 1989). Filtration of groundwater

samples from these aquifers may remove both mobile

colloids and artifact particles. If the mobile colloids are

inherently hazardous (e.g., pathogenic bacteria, asbestos

particles, precipitates of radioactive materials or toxic

metals) or if significant quantities of contaminants sorb onto

these mobile colloids, then it is important that samples

analyzed to determine compliance, assess risks, and develop

models include these, as well as, dissolved contaminant

species. Removal of these mobile colloids from

groundwater samples could lead to underestimation of

contaminant concentrations and mobility, affecting

determinations of both compliance and current risks.

Failure to account for colloid- associated contaminants in

predictive models used for decision making could lead to

serious errors in setting clean-up priorities and in designing

cost effective remediation strategies.

Examination of the role of colloid-associated contaminants

in subsurface systems requires an ability to distinguish

between artifact particles and mobile colloids in

groundwater samples. We have designed and tested a

groundwater sampling system which avoids inclusion of

artifact colloids/particles in samples and minimizes losses of

mobile colloids and changes in colloid character during

sample collection and storage (Backhus et al., 1993). This

sampling system (Figure 1) incorporates slow prolonged

pumping using a positive-displacement pump with a low

sample contact surface area constructed of stainless steel

and teflon (model SP-202, Fultz, Inc., Lewistown, PA). The

pumping rate is controlled by a variable voltage AC-DC

converter powered by a generator, allowing minimum

steady pumping rates of about 100 mL/min to be maintained

at most wells. An inflatable packer or packers are used to

isolate the sampling zone. Groundwater from this sampling

zone is pumped to the surface through a continuous piece of

polypropylene (0.64 cm id) or aluminum (0.48 cm id)

tubing. At the surface, groundwater flows directly into a

flow-through monitoring cell to allow measurement of water

chemistry parameters (pH, Eh, dissolved oxygen (DO),

temperature, and specific conductance) during well purging.

In addition, samples are obtained periodically during well

purging to monitor turbidity. These samples are collected

by overfilling and tightly capping a cuvette or vial

and examined by using a submicron particle analyzer or

turbidity meter. Once the well is deemed sufficiently

purged, unfiltered groundwater samples for geochemistry

and colloid analyses are collected in glass bottles designed

to allow closure without inclusion of head space; therefore,

they minimize the exchange of gases between the sample

and the atmosphere during storage. Prior to sampling,

these bottles are filled with argon. Samples are collected by

inserting the sampling tube to the bottom of the bottle and

overfilling the bottle (by at least half of its volume).

Samples for specific contaminant analyses are collected in a

similar manner in suitable sampling vessels (e.g., 40 mL

glass vials or 4 L bottles). Additional groundwater colloid
22

samples are collected by joining the end of the sampling

tube to a 5 mL plastic syringe tip and allowing the plunger

to be displaced backwards to rinse and then fill the syringe.

The filled syringe is connected to a filter holder containing a

15 or 30 nm pore size Nuclepore polycarbonate membrane

filter. The sample is forced through the filter by pressure

from weights (0.8 kg/cm2), then rinsed with 5 mL of

distilled, deionized water, and placed in a covered

petri plate in a desiccator to dry.

Samples collected as indicted above should provide accurate

information about in situ groundwater geochemistry, mobile

colloid concentrations, and total mobile contaminant loads,

as well as, the characteristics of mobile colloids (e.g., size,

morphology, and elemental composition from scanning

electron microscopy/energy dispersive x-ray analysis of

colloids caught on field filters). This sampling scheme (1)

minimizes collection of artifact particles sheared from

aquifer materials by using slow pumping rates; (2) avoids

precipitation of artifact colloids and changes in the character

of mobile colloid by using flow-through sampling methods

and sample storage in DO bottles which minimize changes

in groundwater chemistry as the sample is brought to the

surface and sealed; (3) assures that prior to sampling, the

well is sufficiently purged of artifact particles which may

have been introduced during construction or formed due to

atmospheric exposure via the well casing; and (4) minimizes

losses of mobile colloids by avoiding filtration of groundwater samples.

Groundwater samples have been collected from numerous

sites across the United States using this careful sampling

scheme (Gschwend and Reynolds, 1987; Backhus and

Gschwend, 1990; Gschwend et al., 1990; Ryan and

Gschwend, 1990; Groher, 1990). Collectively, the results of

these studies provide information both about groundwater

sampling and about the existence of mobile colloids in the

subsurface. Regarding sampling, similar results were found

at most wells when groundwater turbidity was examined as

a function of time or volume of water removed from the

well. Initially high turbidity level, decreased to a stable

level after several hours of slow pumping (e.g., Figure 2).

At “background”wells, turbidity levels approached those

observed for distilled water blanks (e.g., Figure 2). At

contaminated wells (within a contaminant plume or where

geochemistry was altered due to natural processes), turbidity

Figure 1. Sampling setup for collection of ground water from monitoring wells when colloids or colloid associated

chemicals may be of importance.
23

levels stabilized at significantly higher levels (e.g., Figure

2) indicating that mobile colloids may be present. When the

timecourses of other monitored parameters were compared

with turbidity, some parameters (O2, pH, Eh) were generally

found to stabilize before turbidity (O2 vs turbidity in Figure

3). At some sites, a few parameters did not reach a stable

level during well purging and sampling (e.g., total

nonvolatile organic carbon, TOC and specific conductance,

Figure 3). At the one site where we monitored contaminant

concentrations as well as water chemistry parameters and

turbidity, the timecourse for lower solubility contaminants

(Pyrene, Chrysene, and Benzo (a) anthracene) were found to

closely mimic the turbidity timecourse (Figure 3). Little

variation was seen from the more soluble and more

abundant contaminant naphthalene. These data suggest that

turbidity may provide a better indication of required well

purging times than other typically monitored parameters for

the less soluble, possibly colloid-associated contaminants.

At a few sites, the effect of pumping rate on turbidity was

examined. Turbidity initially increased with pumping rate

(Figure 2 and Figure 4), but then decreased to a stable

level again after pumping at the higher rate for a while

(Figure 4). The stable level eventually achieved at the

higher rate was not always the same as that observed at the

slow rate (“Background” vs Contaminated well Figure 4).

At the “Background” well, the stable turbidity level was

higher at the increased flow rate, while at the contaminated

well, the same stable turbidity level was reached at both

pumping rates. Finally, comparison of bailed and slowly

pumped groundwater samples indicate that the method

chosen effects the results obtained (Figure 4). At the New

York site, bailed samples contained 10 - 100 times greater

colloid concentrations, and up to 750 times greater

polycyclic aromatic hydrocarbon concentrations than were

Figure 2. Turbidity timecourses from wells at the Delaware Site.

detected in slowly pumped samples. The results of our

sampling experiences indicate that both the parameter used

to judge the adequacy of purging efforts prior to sampling

and the sampling method (pumping rate, and pumping vs

bailing) may effect geochemistry parameters and

contaminant and colloid concentrations observed in

groundwater samples.

Regarding the existence of mobile colloids in aquifers, at

each of the sites where stable turbidity levels in

Contaminated wells were significantly greater than levels

found in “Background” wells, colloid size characteristics

(size, composition, surface charge, stability) and

groundwater geochemistry were examined to assess whether

colloids collected in the samples were likely to be natural in

situ colloids. Based on alteration of the regional

geochemical conditions by the “contaminated” plume and

expected colloid solubilities and surface charges,

explanations have been surmised for the presence of mobile

colloids at several of the sites sampled. At the

Massachusetts, it is hypothesized that the changes in

groundwater chemistry due to the influence of the plume of

secondarily treated sewage lead to precipitation of colloids

(Gschwend and Reynolds, 1987). At the New Jersey,

Delaware (Ryan and Gschwend, 1990), and Nevada sites

(Gschwend et al., 1990) it is hypothesized that changes in

groundwater chemistry lead to dissolution of secondary

mineral phases (iron oxyhydroxides or calcium carbonates)

which had cemented colloidal material to the aquifer solids

and consequently mobilization of colloidal material.

Results obtained at numerous sites using the careful

groundwater sampling protocol described above indicate

that mobile colloids do exist in the subsurface. However,

there is insufficient information available, at this point, to
24

Figure 4. The effect of pumping rate and sampling method on observed turbidity, NY site.

Figure 3. Monitored parameter timecourses from well D at the Connecticut Site.
25

judge the wide spread significance of mobile colloids.

There is sufficient information to warrant continued

examination of the role of mobile colloidal materials in the

transport of subsurface contaminants. Examination of the

role of colloids requires careful sampling methods which

incorporate: slow prolonged pumping, monitoring turbidity

during purging, maintaining in situ groundwater chemistry

conditions throughout sampling and storage, avoiding

filtration of samples which are used to assess colloid

concentration and total mobile loads of contaminants, and

collection of auxiliary data to confirm findings regarding the

existence of mobile colloids. If no evidence supporting the

existence of colloids and colloid-associated contaminants is

found at a given site, then more practical sampling schemes

may be instituted with comparable results.

References

Backhus, D.A., J.N. Ryan, D.M. Groher, J.K. MacFarlane,

and P.M. Gschwend. 1993. Sampling Colloids and ColloidAssociated Contaminants in Ground Water. Ground Water,

31(3): 466- 479.

Backhus, D.A. and P.M. Gschwend. 1990. Use of

fluorescent polycyclic aromatic hydrocarbon probes to study

the impact of colloids on pollutant transport in groundwater.

Environ. Sci. Technol. v. 24, pp. 1214-1223.

Groher, D.M. 1990. An investigation of the factors affecting

the concentrations of polycyclic aromatic hydrocarbons in

groundwater at coal tar waste sites. M.S. thesis. Dept of

Civil Eng., Massachusetts Institute of Technology. 145 pp.

Gschwend, P.M., and M.D. Reynolds. 1987. Monodisperse

ferrous phosphate colloids in an anoxic groundwater plume.

J. Contam. Hydrol. v.1, pp. 309-327.

Gschwend, P.M., D.A. Backhus, J.K. MacFarlane, and A.L.

Page. 1990. Mobilization of colloids in groundwater due to

infiltration of water at a coal ash disposal site. J. Contam.

Hydrol. v. 6, pp. 307-320.

McCarthy, J. F. and J. M. Zachara. 1989. Subsurface

transport of contaminants. Environ. Sci. Technol. v. 23, pp.

496-502.

Ryan, J. N. and P. M. Gschwend. 1990. Colloid

mobilization in two Atlantic Coastal Plain aquifers: Field

studies. Water Resour. Res. v. 26, pp. 307-322.
26

NEED FOR PRACTICAL

APPROACHES TO CONDUCT

MULTILEVEL SAMPLING

Gary A. Robbins

Robbins (1989), Robbins and Martin-Hayden (1991) and

Martin-Hayden et al. (1991) have shown that vertical mass

averaging in typical monitoring well results in water quality

samples that ate influenced by well screen length, vertical

concentration gradients, vertical variations in formation and

backfill hydraulic conductivity, the amount of water

removed for purging, and water levels achieved in a well

during purging and when sampling. Because of vertical

mass averaging, samples taken from wells can be highly

misleading in terms of the absolute and relative abundances

of water quality contituents. This in turn can lead to gross

misinterpretations of contaminant distributions, transport

properties, and physical, chemical and biological conditions

and processes that influence overall water quality. It

follows that efforts directed at obtaining representative

samples from typical monitoring wells are futile. Mass

averaging during well purging and sampling will result in a

well-biased and non-representative sample irrespective of

sampling method.

It should be kept in mind that monitoring wells were not

designed to provide representative samples. They are

simply an outgrowth of combining geotechnical engineering

practice (i.e., the availability of hollow stem augers),

everyday water well practice (i.e., constructing wells with

casing and screens), and public health practice (i.e.,

collection of samples for standard laboratory analysis). That

is, on a historical basis, monitoring well were not developed

in consideration of the three-dimensional nature of

groundwater flow and quality.

It is suggested here that research efforts be refocused on

developing practical approaches for conducting multilevel

sampling. Multilevel sampling issues requiring resolution

include: methods for constructing multilevel sampling nests

in hollow stem auger holes, methods for ground water

sampling using direct push technologies, methods for

collecting water quality samples during drilling, testing

seals between samplers, defining the vertical spacing

between samplers and their intake lengths, preventing intake

clogging in fine grain formations, and sampling contituents

exhibiting high vertical gradients. When dealing with nonaqueous phase liquids (NAPL), methods are needed for

sampling mobile and residual NAPLs, and avoidance of

cross contamination when samplers are constructed through

zones of NAPL.

References

Robbins, G.A., 1989. Influence of Using Purged and

Partially Penetrating Monitoring Wells on Contaminant

Detection, Mapping and Modeling. Ground Water Journal,

v. 27, No. 2, p. 155-162.

Robbins, G.A. and Martin-Hayden, J.M., 1991. Mass

Balance Evaluation of Monitoring Well Purging, Part I.

Theoretical Models and Implications for Representative

Sampling. Journal of Contaminant Hydrology, v. 8, p. 203-

224.

Martin-Hayden, J.M., Robbins, G.A., and Bristol, R.D.,

1991. Mass Balance Evaluation of Monitoring Well

Purgeing, Part II. Field Tests at a Gasoline Contamination

Site. Journal of Contaminant Hydrology, v. 8, p. 225-241.
27

Effects of Well Design and Time of

Pumping on Concentrations

of Volatile Organic Compounds in

Ground-Water Samples

Jacob Gibs and Thomas E. Reilly

Because a water sample collected from a well is an

integration of water from different depths along the well

screen, concentrations of analytes measured in the sample

can be biased if analyte concentrations are not uniform

along the length of the well screen. The concentration in the

sample is a function of variations in well-screen inflow rate

and analyte concentration with depth. These relations were

investigated at a site with gasoline-contaminated

groundwater in Galloway Township, Atlantic County, New

Jersey. Numerical simulation of the integration of water

along the well screen at this site and in a hypothetical

system was used to determine the total mass of selected

volatile organic compounds entering the screen by assuming

a layered porous medium in which each layer is

characterized by uniform hydraulic conductivity and

chemical concentration.

A well screen with seven short screened intervals was

designed and installed at two locations at the Galloway

Township site. Independent samples were collected from the

seven screened zones at each location. The sample

concentrations from each screened zone were flow-rate

weighted and integrated to simulate a sample concentration

from a 5-foot-long, 2.375-inch-outside-diameter

conventional wire-wound screen. The integrated volatile

organic compound concentration was as little as 28 percent

of the maximum concentration observed in samples from

the multiscreened well.

Numerical simulation of the integration of water along the

well screen at this site and in hypothetical heterogeneous

ground-water systems also was used to investigate the

temporal variation in water quality. Concentrations of

constituents that are not uniformly distributed along the

screened interval of the well can vary during purging and

continued pumping after purging as a result of vertical

variations in flow rate in the vicinity of the well screen. This

variation in water quality with time also can be affected by

well design characteristics, such as the use of a filter pack

and screen length. Results of numerical simulations of flow

associated with a hypothetical well design show that at a

constant pumping rate the percentage of total flow into the

screened zone at the ends of the screen that is derived from

increases in vertical flow as screen length decreases or when

a filter pack is used. Thus, a water sample collected from a

well in which the screen length is short or a filter pack is

used represents water from a vertical interval in the aquifer

that is larger than the actual length of the well screen.
28

COMMON SAMPLING AND

ANALYTICAL PROCEDURES

VIEWED IN THE CONTEXT OF

DATA QUALITY NEEDS

William R. Mabey and Nancy Barnes

The practice of sampling in the monitoring and investigation

of groundwater quality has experienced significant advances

in knowledge in the last decade. While some of the

methods now in use were adapted from the water supply

industry, many other methods reflect modifications that

resulted from the recognition of shortcomings of some

methods in obtaining water samples that provide reliable

chemical data. Research has been vital in recognizing these

shortcomings and developing better methods as well as

increasing our knowledge of groundwater chemistry,

hydrogeology, and remedial technologies. However,

incorporating these changes as acceptable professional

methods has been sometimes slow because of the

precedence of existing data with the older methods, costs of

equipment and training field personnel, and the lack of

familiarity and the uncertainties with the newer methods.

Recognizing that groundwater data are collected for specific

applications, it is appropriate to depart from historical

precedence, policy, or preoccupations regarding

uncertainties, and rather focus on the methods as they

provide quality data. Quality data can be defined as those

data that are fully described so that they may be intelligently

used (Campbell and Mabey, 1985). This definition is

consistent with the Data Quality Objectives (DQO) as set

forth in USEPA guidance. In this DQO context, data are

evaluated according to the criteria of accuracy,

representativeness, comparability, completeness and

precision. Clearly, data must have known qualities so that

the data user can decide whether the data can be applied to

the intended application.

The DQO objectives listed above are well-established in the

evaluation of analytical chemical data. The accuracy and

precision attainable for these data are measureable using

stated procedures. The data validation process according to

the Contract Laboratory Program (CLP) provide the basis

for expression of the quality of analytical data, and where

any qualifications on the data are valuably discussed in a

summary report format. A review of the analytical

procedures and CLP criteria shows that negative bias (that

is, lower concentrations than actually present) is reasonably

inherent in many methods because of losses during sample

handling and analyses. While a complete discussion of

analytical data quality is not the purpose of this paper, it is

important to recognize that data acceptable in the CLP

program may have losses of over 50% for some semivolatile organic chemicals (Guide to Environmental

Analytical Methods, 1992).

Appropriately, there is increasing concern for the quality of

data from groundwater monitoring and investigation

programs because of the way in which wells are

constructed, developed, purged, and sampled (Puls and

Powell, 1992). An evaluation of some procedures now in

common use shows that the accuracy of resulting data

should be of concern. In particular, some negative bias is

often likely because of losses as a result of some

groundwater purging and sampling procedures. As with

other measurements, good precision (that is, repeatability)

can be a misleading if accuracy is not also attained. It

should also be recognized that databases can have the effect

that the very qualities that contribute to a measured value

can be lost, and data from the database then are

inappropriate for comparison purposes.

It is ironic that the implementation of new sampling

methods can be viewed as a “conflict” between the DQO

criteria of comparability and representativeness. While the

established methods have merits of familiarity and

established use, research and other experience is showing

that some methods may not give representative samples

based on what can be shown or is reasonably of concern

based on the newly gained scientific knowledge. However,

attempts to develop methods that produce data more

representative of our understanding of groundwater

conditions are hampered by reasons presented in the

opening paragraph. Often overlooked is the realization that

some known bias in data may be acceptable for particular

applications, and that having the most accurate or

representative value may not be necessary.

One area where research has revealed a negative bias in

metals data because of sampling practices is in the filtration

of groundwater samples. Previously, turbid water samples

were often filtered, usually with a 0.45 micron filter, to

remove particulate materials from the water sample. The

rationale was that the turbidity was an artifact of well
29

construction and sampling, and filtering provided a true

dissolved concentration of analytes in the groundwater

sample. However, when research and some field

observations observed that colloidal material was mobile in

some saturated zone systems, filtration was discouraged to

avoid removing the collodial material (Puls and Barcelona,

1989). Thus, to remove a negative bias in metals

concentrations, the sampling procedure has changed to

possibly provide a positive bias in the data. As an

alternative procedure, the low flow rate purging and

sampling of a monitoring well has been employed to

achieve low turbidity and more representative groundwater

samples (Puls and Powell, 1992).

Several field sampling efforts by Montgomery Watson have

attempted to evaluate the significance of sample turbidity on

the concentrations of metals in groundwater samples. In

one project in California, wells previously installed in

another investigation study were found to have significant

turbidity and high metals concentrations. These wells were

purged at rates as low as 0.5 gallons/minute using a bladder

pump until the temperature, electrical conductivity (EC) and

turbidity parameters stabilized. Typically, turbidity was the

last parameter to stabilize according to DQO criteria, and

the times for stabilization ranged from one to seven hours,

with purge volumes ranging from 15 to 365 gallons (15 to

40 casing volumes). The wells were then sampled first

using the bladder pump, and then using a bailer. For each

sampling procedure a water sample was filtered using a 0.45

micron filter so as to provide a comparison of the effect of

filtration. Sampling with the bailer provided turbid samples

(>200 NTU) and the bailed, unfiltered water samples

typically showed two-fold higher concentrations of metals

present (including barium, chromium, copper, zinc, etc) than

the unfiltered water collected with a bladder pump (NTU

values of 4 and 5) . However, the metal concentrations of

the bailed, filtered samples were generally comparable to

those of the filtered and unfiltered samples collected with

the bladder pump (generally less than 10% difference)

These data then provide empirical evidence that filtration

can produce representative groundwater samples for some

monitoring wells at this site. It is also of note that for

several monitoring wells the iron concentrations in the

filtered water samples collected with the pump were higher

than the concentrations in the filtered, bailed water samples,

a result that is rationalized by the aeration of the bailed

sample, the subsequent oxidation of ferrous (iron) to the

ferric state, and removal of the solid ferric oxide/hydroxide

by filtration.

At another site, a Montgomery Watson sampling team

collected groundwater samples over a several month period

with varying pumping rates to develop an understanding of

the metals concentrations as a function of turbidty. The total

suspended solids (TSS) was also determined by the

laboratory as a quantitative measure of the particulate

content of the samples. A log/log plot of TSS against the

field-measured turbidity showed a roughly linear

relationship. Plots of TSS against the concentrations of

several metals also showed the expected relationship of

higher concentrations at higher TSS values. This

relationship was most notable for lead; however, when the

lead concentrations were divided by the iron or aluminum

concentrations the resulting ratios were roughly independent

of the TSS values. If it is accepted that the iron and

aluminum values are associated with their natural

abundances in soils, it is also reasonable that the lead

concentrations observed are also associated with the natural

abundance of soil constituents. Such a normalization

approach also has shown value in explaining high metal

concentrations in water samples at other sites.

Measures to improve the quality of sampling data clearly are

needed. The improvements may include improved sampling

procedures or obtaining additional information to support

the measured numbers. For example, measurement of redox

potentials or other groundwater chemistry parameters are

useful support the presence of reduction products such as

vinyl chloride. Because of the time and equipment costs of

the low flow rate purge/sample collection procedure, it also

seems reasonable that empirical evidence of the

comparability of the sample with that of a filtered water

sample may be the basis for planning a monitoring program,

where water samples may be filtered during three events in

a quarterly monitoring program while using the low flow

rate purge/sample collection procedure once a year as a

quality assurance measure.

While procedures to document measurement performance

have been developed for analytical data quality purposes,

such general procedures are difficult to implement for some

field sampling efforts because of the various sampling

methods and the differing hydrogeologic conditions

encountered. However, the quality of data would be

substantially improved if a more formal documentation

process for reporting well installation, development, purging

and sampling were applied, with any limitations or crucial

observations being reported and discussed in the text of the

report. This information is critical for future sampling and

evaluation of groundwater data where the qualities of the

water samples should be compared before the analytical

data are compared.

Finally, research observations or experience at unique sites

needs to be put in the appropriate context rather than being

put in general procedures that are incorporated in all

applications. For example, calculations indicate that the

contribution of a chemical sorbed on colloidal material to

the total measured concentration of a chemical in a

groundwater sample is likely to be negligible unless a large

amount of collodial material is present, the chemicals of

concern are detectable at very low concentrations, or they
30

are highly sorbed. Such an understanding is important for

collecting quality data in a cost effective sampling program.

In conclusion, it is important to recognize the qualities of

the groundwater samples for the correct use of the data. The

selection of sampling procedures should be made with

regard to the uses of the data and limitations of the data, and

this information needs to be documented for data users adn

for planning future sampling efforts.

The authors gratefully acknowledge the assistance of

Montgomery Watson colleagues Dr. Eric Wendlandt in

Walnut Creek, CA, Dr. Peter LeVon in Salt Lake City, UT,

and Mr. Marshall Pauly and Mr. Rodney Vlieger in Des

Moines, IA.

References

J.A. Campbell and W.R. Mabey. 1985. A Systematic

Approach for Evaluating the Quality of Groundwater

Monitoring Data, Groundwater Monitoring Review,

V(4):58-62.

R.W. Puls and M.J. Barcelona. 1989. Ground Water

Sampling for Metals Analyses. EPA/540/4-89/001

R.W. Puls and R.M. Powell. 1992. Acquistion of

Representative Ground Water Quality Samples.

Groundwater Monitoring Review, Summer.

R.E. Wagner, Editor. 1992. Guide to Environmental

Analytical Methods. Genium Publishing Co., New York.
31

Dennis E. Reece

A basic problem in establishing uniform groundwater

sampling procedures is that procedures that efficiently

provide representative samples for an intended use at one

site may not for others. The decision to use filtered or

unfiltered samples for metals can depend on a number of

site specific factors including:

• intended use of the data

• monitor well construction and conditions

• aquifer properties

• data quality objectives process (the data to be

collected and the associated procedures should be

developed to specifically make decisions or answer

questions for making decisions)

Analysis of unfiltered samples containing suspended solids

associated with well installation or sampling can result in

high metal concentrations which are not representative of

metal concentrations in the groundwater. Alternately, if

metal contaminants are present in the form of mobile

colloids, analysis of filtered samples may not identify the

colloidal fraction of the contamination.

The intended use for the data to be collected is important.

For detection monitoring the main concern is with

consistently identifying the concentrations of mobile

constituents present in the groundwater with adequate

reproduceability to allow determination of whether the data

indicate increases relative to site background conditions.

Determining the mobile concentrations of constituents is

often of primary concern during assessments and corrective

actions. Determining total (dissolved and solid phase)

concentrations present in a well is usually of prime concern

for use of the data in human health risk assessment or for

evaluating suitability of a well for use as a drinking water

supply.

Well construction and development practices and aquifer

properties influence the potential for significant well

siltation and for potential presence of contaminants in

mobile colloidal form.

The Data Quality Objectives process can be used on a site

specific basis to select sampling procedures which are

appropriate for the specific data uses and site conditions.

There is considerable variability in the experience and

CONSIDERATIONS IN SELECTING FILTERED

OR UNFILTERED SAMPLES FOR ANALYSES OF

METALS IN GROUNDWATER SAMPLES

technical knowledge among those involved in groundwater

sampling. Complex sampling requirements are often not

implemented appropriately. Cost of the procedures can also

be an important factor in how well the sampling procedures

are implemented. Selection of procedures for collecting

suitable groundwater samples should consider the

complexity and cost of implementation, and should be

practical for a wide range of site conditions rather than ideal

conditions. Required procedures should be implementable

and enforceable.

The selection of filtered or unfiltered samples should be

considered relative to two contradictory issues which may

be present at a site: siltation of monitor wells and possible

presence of contaminants in mobile colloidal form.

The severity of these problems is usually controlled

by:

• well construction

• well development

• aquifer properties

• sampling procedures

Siltation is a widespread problem which can have drastic

impacts on results for metals when unfiltered samples are

analysed. It is an easily identifiable problem and is

sometimes more easily addressed than the issue of whether

mobile colloids are present. Siltation is often greatest in

fine-grained low yield zones such as thin silty or clayey

intervals which are often required to be monitored. If the

sampling conditions result in high solids content or

nonreproduceable solids content in samples, analysis of

unfiltered samples for metals may result in useless data.

Siltation problems can often be mitigated at the well by

proper selection of procedures for well design and

construction, well development and sample collection.

However, experience indicates that these are not always

effective or practical for mitigating siltation.

Siltation problems (for metals analysis) may also be

mitigated by sample pretreatment such as decanting,

centrifuging, macrofiltration, microfiltration or analysis for

both filtered and unfiltered samples. These methods,

however, have limitations and pose a risk of introducing
32

contamination during pretreatment or of removing mobile

colloidal material actually present in the groundwater, thus

reducing the representativeness of the sample.

The issue of possible presence of mobile contaminants in

colloidal form is a less easily identifiable problem. Relative

to siltation, significant colloidal transport of contaminants is

probably a much less widespread problem. The impacts on

monitoring data are also probably less severe for most sites.

Transport of contaminants in colloidal form may be of more

concern in high yield aquifers than in low yield aquifers.

Geochemical conditions in the aquifer matrix may also be a

controlling factor in the potential importance of colloidal

transport.

Colloidal material present in water samples may result from

either artificial means related to well construction and

sampling or from transport of colloidal material in the

groundwater. Proper well design, construction,

development and sampling procedures can reduce the

artificial sources. Microfiltration of the samples may

eliminate from the sample both undesired artificially

introduced colloids and mobile colloids actually present in

the groundwater. Analysis of unfiltered samples will

include colloidal material, if any is present, but will provide

representative data only if siltation does not result in

artificially high suspended solids content.

Groundwater data from three sites were examined to

illustrate the range of impact of siltation on metal results

when unfiltered samples are analyzed for metals.

Site 1 is a landfill site at which waste had not yet been

placed and at which there was no previous development or

use of the site. Four quarters of background monitoring had

been completed on unfiltered samples. The monitoring

system included five monitor well pairs. Each pair included

a monitor well completed in a shallow clayey unit and a

second monitor well completed in a deeper sand unit. The

wells were reportedly sampled using nondedicated

peristaltic or bladder pumps. Turbidity values for the

samples indicated relatively high and variable suspended

solids content in the shallow monitor wells in the clay unit.

Mean turbidity values for these wells varied from <100 to

7,000 ntu. Values for four of the sand unit wells were much

lower and less variable. Mean turbidity values for these

wells ranged from 15 to 25 ntu. One of the sand unit wells

exhibited higher turbidity values which were suspected to

have resulted from well construction or development

procedures. The high turbidity of the shallow clay unit

wells resulted in high and variable concentrations of some

metals for the unfiltered samples (in particular arsenic,

beryllium, cobalt, copper, nickel, chromium and zinc).

Relatively high correlations were observed between

turbidity values and metal concentrations for the shallow

clayey unit wells. Metal concentrations were highly

variable from quarter to quarter for each shallow clayey unit

well and among different wells due to variability of

suspended solids content. Analysis of the unfiltered samples

limited usefulness of intrawell or interwell statistical

comparison tests. Total dissolved solids values, by contrast

with turbidity values, were relatively constant from quarter

to quarter indicating that dissolved concentrations were

relatively constant. Further evaluation of the data did not

indicate that contamination was present at the site.

Site 2 was a site at which monitor wells were completed in a

relatively thick high yield sand and gravel aquifer. Twentyone wells were sampled using high yield dedicated pumps.

Both filtered (0.45 micron) and unfiltered samples were

collected and analyzed for thirteen metals. Turbidity was

low for all samples. Comparison of the results did not

indicate that filtering the samples lowered the

concentrations of metals.

Groundwater samples were collected at Site 3 from soil

borings using downhole tools without installation of

monitor wells. Sampling conditions at this site

approximated a worst case condition with respect to

siltation. All samples were very turbid and contained very

high suspended solids content. Comparison of results of

analyses for 23 metals for filtered (0.45 micron) and

unfiltered samples indicated markedly higher concentrations

in the unfiltered samples for all 23 metals except selenium

and thallium.
33

Carol White

Introduction

A study of the impact of various sampling techniques on

metals concentrations, in particular iron and arsenic, was

conducted as part of a larger remedial investigation at the

Auburn Road Landfill Site in Londonderry, N.H. A major

objective of the remedial investigation was the development

of a detailed understanding of the site geochemistry.

Collection of samples representative of the in-situ

groundwater chemistry was essential to the success of the

study. At the suggestion of EPA, a low flow-rate purging

and sampling method was employed to collect groundwater

samples from monitoring wells at the site.

Site Description

The Auburn Road Landfill Site is a Superfund site located in

southeastern New Hampshire in the Town of Londonderry.

Municipal and industrial wastes were disposed in three

separate landfills at the site. Contaminants present in the

groundwater at the site as a result of these disposal activities

include low levels several organic compounds: 2-butanone,

trichloroethane, tetrachloroethane, benzene and toluene, and

arsenic. The site consists of glacial outwash sands

overlying moderately fractured metamorphic bedrock. Over

150 monitoring wells have been installed at the site vicinity.

The majority of the wells are constructed of 2-inch diameter

polyvinylchloride screen and riser; screen lengths generally

range from 1 to 15 feet in length.

Sampling Methods

Prior to sample collection, all monitoring wells were purged

using either a peristaltic pump with dedicated tubing, or a

bladder pump. Where possible, dedicated tubing was

installed in each monitoring to mid-screen level several days

or weeks prior to sampling. This enabled the purging to be

conducted with minimal disturbance of the water column.

In general, purging rates ranged from 0.2 to 0.3 l/min.

During purging a flow-through cell equipped with pH, Eh,

specific conductance, dissolved oxygen and temperature

sensors was used to obtain in-line measurements. An

A STUDY OF THE IMPACT OF MONITORING

WELL PURGING AND FILTERING

TECHNIQUES ON METALS

CONCENTRATIONS IN GROUNDWATER

SAMPLES FROM THE AUBURN ROAD

LANDFILL SITE IN LONDONDERRY, N.H.

turbidimeter with a separate in-line flow-through cell was

utilized for turbidity measurements. Purging was

considered complete when turbidity measurements had

stabilized (± 10%). Initially, during the 1991 sampling

program, a minimum 2.5 well volumes were purged prior to

sampling. After a few sampling rounds it became clear that

generaly the in-line measurements stabilized within one well

volume or less, and the minimal well volume criteria was

dropped. All field measurements, purging volumes and

other pertinent sample data were recorded for each well

during the sampling episode.

Results and Discussion

Low-flow Purge Rate: Filtered vs. Unfiltered Samples

In 1991, the low-flow rate sampling methodology was used

to collect groundwater samples from 52 of the existing

monitoring wells at the site. Both filtered and unfiltered

samples were collected for iron and arsenic analysis. Prewashed, disposable 0.45 micron filters were used to collect

the filtered groundwater samples from the pump discharge.

As shown on Figure 1, samples collected from wells

included in this study showed an excellent correlation

between filtered and unfiltered arsenic concentrations.

Filtered and unfiltered iron concentrations were also well

correlated, except near the method detection limits.

Low-flow Rate Unfiltered vs. High-flow Rate Filtered

Samples

In 1992, a comparison of the unfiltered samples collected at

a low-flow purge rate (0.2 to 0.3 l/min) versus filtered

samples collected at a high-flow purge rate (≥ 0.5 l/min)

was conducted. A comparison of the sample results for iron

and arsenic are presented on Figure 2. In all cases, the

filtered samples obtained with high-flow rate method

yielded higher iron and arsenic concentrations than the

unfiltered, low-flow rate samples. These data suggest that

the high-flow rate sampling method may in fact mobilize

particles that can pass through a 0.45 micron filter resulting

in elevated metals concentrations. These results also suggest
34

Figure 1. Correlations between filtered and unfiltered iron (top) and arsenic (bottom).
35

Figure 2. Comparison of filtered vs. unfiltered, slow purge and filtered, fast purge unfiltered, slow purge in different

wells for iron (top) and arsenic (bottom).
36

that the data obtained with the low-flow rate sampling

method are more representative of the in-situ ground water

chemistry.

References

Baedecker, N.J. and W. Back. 1979. Hydrogeochemical

processes and chemical reactions at a landfill. Groundwater.

Vol. 17, No. 5 pp. 429-437

Barcelona, M.J., T.R. Holm, M.R. Schock and G.K George.

1989. Spatial and temporal gradients in aquifer oxidationreduction conditions. Water Resources Research Vol.

25,No. 5 pp. 991-1003.

Chapelle, F.H. 1993. Groundwater Microbiology and

Geochemistry. John Wiley and Sons, New York, NY. 424 p.

Puls, R.W. and M.J. Barcelona. 1989. Groundwater

sampling for metals analysis. Superfund Ground Water

Issue Paper USEPA-ORD, OSWER EPA/540/4-89/001. 6 p.

Sevee and Maher Engineers. 1992. Pre-Design Investigation

for the Remediation of Groundwater, Auburn Road Landfill

Site, Londonderry, N.H.

Sevee and Maher Engineers. 1993. Supplement II

Investigation Report, Supplemental Pre-Design

Investigation for the Remediation of Groundwater, Auburn

Road Landfill Site, Londonderry, N.H..

Walton-Day, K., D. Macalady, M. Brooks, V. Tate. 1990.

Field methods for measurement of groundwater redox

chemical parameters. Groundwater Monitoring Review.

Vol. 10, No. 4 pp. 81-89
37

Introduction

Deposits of fractured clay and rock are widespread and

many contaminated sites are located in such materials.

Groundwater flow and contaminant migration in these

materials are controlled by different factors than in granular

media and sampling/monitoring programs must reflect these

differences if they are to be effective.

Hydraulic Properties of Fractured Media

In a fractured porous medium, flow is largely controlled by

the distribution, orientation, length and aperture of fractures

or joints. In many materials flow through the blocks of

“matrix” between the fractures is much less than through the

fractures. Measurements of hydraulic conductivity are

largely dependent on how many hydraulically-conductive

fractures are intersected by the measurement zone (typically

in a borehole). As a result, measured values can vary greatly

and often depend on the length and orientation of the

measurement zone. Not all fractures are hydraulicallyconductive and at some sites investigators have found that a

few large aperture fractures may dominate an entire flow

system. One of the most critical parameters governing flow,

aperture, cannot be directly measured and is almost always

inferred from hydraulic or solute transport data, usually

using the “cubic law” (Snow, 1970). Hence there is always a

large degree of uncertainty associated with fracture aperture

values. The fracture porosity of a deposit generally

represents only a small fraction (10-2 to 10-5) of the total

volume of a deposit and is often much less than the

intergranular porosity of the deposit (<0.01 to 0.7).

Case Study - Borehole Flow Meter Survey at Oak Ridge

Reservation

Recent borehole flow meter surveys at the Oak Ridge

Reservation in Tennessee (Will, et al., 1992) illustrate some

of the problems encountered in fractured media. Based on

drilling records, core samples and geophysical/downholecamera surveys of a 405 foot deep borehole, CH-9, it

appeared that the shales at this site were highly fractured

with typical fracture spacings of a few inches to a few feet.

However, an electromagnetic flow meter survey under

ambient conditions (no pumping) indicated that flow was

restricted to two narrow zones at 135 and 330 foot depth.

Flow was found to enter the deeper zone, then flow up the

GROUNDWATER SAMPLING IN

FRACTURED CLAY AND ROCK

Larry D. McKay, Kent Novakowski, and John F. McCarthy

well bore and exit into the shallow fracture zone with a flow

rate of up to 0.2 gpm or about 700 gal per day. This presents

several potential problems: possible mixing of contaminated

and uncontaminated waters; and if you don’t have a flow

meter and the well is to be completed with a multilevel

sampler to prevent uphole flow, how do you decide where to

put the sampling zones?

Contaminant Transport in Fractured Porous Media

The transport of contaminants through fractured p.m. is

highly dependent on the physical properties of the

contaminants with solutes, colloids and immiscible phase

liquids behaving in radically different manners. Solute

transport is strongly influenced by matrix diffusion, which is

the transfer of solute mass from the zone of rapid flow

within the fractures into the relatively immobile pore water

in the blocks of matrix between fractures. Recent field

experiments (McKay et al., 1993) and model simulations

(ex: Sudicky & McLaren, 1992) have shown that matrix

diffusion is sufficient to retard migration of a non-reactive

solute by several orders of magnitude or more relative to

fracture flow velocities in fractured high porosity sediments.

Although we expect to see the greatest retardation in high

porosity clays and shales recent experiments (Birgersson &

Neretieks, 1990) indicate that this can be significant even in

granitic rock.

Colloidal contaminants, because of their larger diameters,

are not as strongly influenced by matrix diffusion and can

actually migrate faster than non-reactive solutes (McKay et

al., 1993). Immiscible phase contaminants, particularly

DNAPL’s (dense non-aqueous phase liquids) are also not

strongly influenced by matrix diffusion and can move

rapidly downwards through fracture systems with

movement controlled by the density and viscosity/interfacial

tension properties of the fluid, and the size of fracture

apertures (or openings). The residual DNAPL, which coats

the fracture walls, may then be slowly dissolved and

transported away by the flowing groundwater or may

diffuse directly into the matrix pore water (Keuper &

McWhorter, 1991).

Implications for Groundwater Monitoring

Some common problems which are expected in fractured

media include:
38

• contaminant plumes which are very irregular in shape

and relative concentration (due to variations in the

distribution of hydraulically-conductive fractures),

• difficulty in distinguishing which fractures are contributing to flow in a borehole and hence difficult to

determine where the contaminants are coming from.

• potential for ambient flow along the borehole,

resulting in mixing or (even worse) spreading of

contaminants into previously uncontaminated zones

• problems with sample dilution due to large volume of

sampling interval in conventional boreholes/wells

(Novakowski, 1992).

• purging prior to sampling may draw in water from a

large volume of the deposit (because of the very low

fracture porosity) and this water may not be

representative of what was initially in the fractures

and is likely not in equilibrium with pore water in the

matrix adjacent to the fractures. For example a 10

litre water sample taken from a well in a rock with a

fracture porosity of 10-4 could draw water from up to

100 m3 of the rock.

Improvement of Monitoring and Sampling Methods

Monitoring and sampling methods should be evaluated on a

site-specific basis with respect to both the properties of the

fractured media and to the type of contaminant. Possible

improvements for existing wells could include:

• use of downhole methods including flow meter logs,

temp. logs and conductivity logs to identify location

of hydraulically-conductive fracture zones.

• installation of packers or seals to minimize borehole

storage volumes and to prevent flow along the

borehole

• sampling using minimal purging

New monitoring programs could include

• angled or horizontal boreholes to increase the

probability of intersecting vertical fractures (where

needed)

• use of monitoring wells designed to minimize storage

volume and prevent flow along the borehole

(examples: Westbay system, Waterloo multi-level)

• sampling of matrix pore water directly from core

samples. In clays a variety of methods have been

developed including: leaching with de-mineralized

water, squeezing out pore water in high pressure

cells, displacement with toluene, and finally direct

measurement of vapour phase contaminants in small

holes drilled into the core sample.

• measurement of contaminant concentrations along

streams to identify specific fracture discharge zones

(Clapp et al., 1992)

References

Birgersson, L., and I. Neretnieks, Diffusion in the matrix

of granitic rock: Field test in the Stripa mine, Water Resour.

Res., 26(11), 2833-2842, 1990.

Clapp, R.B., D.S. Hicks, D.K. Solomon, D.M. Borders,

D.D. Huff, and H.L. Boston, Groundwater, surface water,

and movement of contaminants at the Oak Ridge

Reservation, Abstract presented at American Geophysical

Union meeting, San Francisco, CA, Dec., 1992.

Kueper, B.H., and D.B. McWhorter, The behaviour of

dense, non-aqueous phase liquids in fractured clay and rock,

Ground Water, 29(5), 716-728, 1991.

McKay, L.D., J.A. Cherry, R.C. Bales, M.T. Yahya, and C.P.

Gerba, A field example of bacteriophage as tracers of

fracture flow, Environ. Sci. and Technol., Vol. 27, No. 6, p.

1075-1079, 1993.

McKay, L.D., R. W. Gillham, and J.A. Cherry, Field experiments in a fractured clay till: 2. Solute and colloid transport,

Water Resour. Res., 29(12), 3879-3890, 1993.

McKay, L.D., and J.A. Cherry, Groundwater research in

clay-rich glacial tills in southwestern Ontario, Paper

presented at Intl. Assoc. of Hydrol. Conference, Hamilton,

Ontario, May, 1992.

Novakowski, K.S., The analysis of tracer experiments

conducted in divergent radial flow fields, Water Resour.

Res., 28(12), 3215-3225, 1992.

Snow, D.T., The frequency and apertures of fractures in

rock, J. Rock Mech. Min. Sci., Vol. 7, 23-40, 1970.

Sudicky, E.A. and R.G. McLaren, The LTG technique for

large-scale simulation of mass transport in discretely

fractured porous formations, Water Resour. Res., 28(2), 499-

514, 1992.

Will, A.S., J.R. Kannard, A.R. Day, and L.B. Shannon,

Additional borehole geophysical logging at waste area

grouping 1 at Oak Ridge National Laboratory, Oak Ridge,

TN, ORNL, Environ. Restoration Div., Technical

Memorandum 01-04, 1992.
39

EVALUATION OF FIELDFILTRATION VARIABLES FOR

REPRESENTATIVE SAMPLES OF

TRACE METALS IN GROUND

WATER

Karl F. Pohlmann , Gary A. Icopini and

Charlita G. Rosal

Abstract

Selected ground-water sampling and field-filtration methods

were evaluated to determine their effects on trace metal

concentrations in ground-water samples. The study focused

on conditions where traditional approaches may produce

samples with high particle concentrations and concomitant

elevated metals concentrations. These samples are often

filtered to remove suspended particles before laboratory

chemical analysis; however, filtration may also remove

colloidal particles that may be important to the transport of

trace metals. Two filtration variables were evaluated in this

study: (1) collecting samples without filtration, and (2)

filtering samples with 0.45-μm pore size filters. Samples

were collected with a bailer, a submersible pump at a “low”

rate of 0.3 L/min, and a submersible pump at a “moderate”

rate of 1.0 L/min. Pump discharge rates were controlled by

pump speed rather than by flow restrictors or valves.

The results showed that some sampling methods entrained

large quantities of particles greater than 0.45 μm in size.

The quantities and sizes of these particles suggested that

they were not mobile in ground water under natural flow

conditions but were primarily artifacts of well construction,

development, and purging. Analysis of unfiltered samples

containing high concentrations of these artifactual particles

and associated metals resulted in metal concentrations that

were often orders-of-magnitude higher than in

corresponding 0.45-μm-filtered samples. This effect was

most consistent and pronounced in bailed samples, because

operation of the bailer caused the greatest agitation in the

sampling zone. The use of pumps at low to moderate rates

resulted in minimal concentration differences between

unfiltered and 0.45-μm-filtered samples in all but the most

turbid wells, and reflected the entrainment of only minor

amounts of artifactual particles larger than 0.45 μm in size.

The three sample collection methods produced similar

results when samples from less turbid wells were filtered,

however, the pumping methods produced the most

consistent overall results. Little variation was evident

between filtered and unfiltered pumped samples, reflecting

minimal agitation in the sampling zone and sample during

purging and sample collection. Use of submersible pumps at

low speeds may reduce the uncertainty in results when

collecting samples of inorganic ground-water constituents

that have the potential to associate with particles in ground

water.

Introduction

Ground-water samples are commonly field-filtered to

remove sediments mobilized during well construction

and sampling because inclusion of these particles may

bias analytical determinations, leading to elevated and

erroneous concentrations of mobile contaminants (Puls

et al., 1991; Backhus et al., 1993). However,

indiscriminant field filtration using 0.45-μm filters

ignores the presence of colloidal particles in ground

water that may exist between the extremes of solutes and

sediments. The small size of colloids facilitates their

mobility in certain ground-water systems and provides

them with high ratios of surface area to mass, which

increases their relative sorptive capabilities (McDowellBoyer et al., 1986). The association of metals with

colloids has been shown to provide a potentially

important mechanism for transport of these metals in

ground water (McCarthy and Zachara, 1989).

Routine filtration of ground-water samples may have

particularly important implications for metal determinations

when metals are associated with particles larger than the

filter pore size and/or when turbid samples are collected.

Turbid samples may result when bailers or submersible

pumps operated at moderate to high discharge rates (greater

than 1 L/min) are used in inadequately designed,

constructed, or developed wells, or wells completed in

formations containing fine-grained sediments. Collecting

samples at rates that approach natural ground-water

advective flow velocities may minimize disturbance in the

sampling zone, reduce entrainment of normally immobile

species, and thereby alleviate the need to filter samples. This

approach to sampling has been advocated by several

researchers, with maximum suggested pumping rates of 100

to 300 mL/min (Ryan and Gschwend, 1990; Puls et al.,

1990; Backhus et al., 1993).

The U.S. Environmental Protection Agency (EPA) is

interested in the implications of field-filtration on metal
40

concentrations in ground-water samples. This paper

summarizes some of the results of a field study addressing

this issue (the work presented here is fully described in

Pohlmann et al., 1994). The objectives of the study were to

(1) evaluate the impacts on trace-metal concentrations of

filtration with 0.45-μm pore size filters versus not filtering;

and (2) investigate the effects of interactions between field

filtration and other sampling variables including sampling

device, pumping rate, and well turbidity. The study focused

on sampling in conventional standpipe monitoring wells

under conditions where traditional approaches to sampling

may produce turbid samples. Three field sites were visited:

an active municipal solid waste landfill in Wisconsin, a

closed solid waste landfill in Washington, and a site

contaminated by industrial waste in Nevada.

Methods and Materials

The monitoring wells sampled in this study were

constructed of polyvinyl chloride, and were 5.1 cm in

diameter, with the exception of one 10.2 cm diameter well.

The top of the well screens ranged from 2 to 19 m below

ground surface, with well screen lengths of 0.6 to 6.0 m.

The static water level ranged from 1 to 14 m below ground

surface. Volumes of water within the well screens ranged

from 1.2 to 50 L.

The results of three sample collection methods will be

described in this paper. The first method used a dual check

valve bailer with a volume of approximately 0.4 L. Samples

were transferred from the bailer directly to sample bottles

for unfiltered samples or to a filtration vessel for filtered

samples. Compressed nitrogen gas was used to drive the

samples through either membrane filters or disposable

cartridge filters. The second sampling method was a

submersible centrifugal pump (CP) operated at an

appropriate speed to produce a flow rate at the surface of

approximately 300 mL/min. Filtration was conducted online with disposable cartridge filters. The third method was

a bladder pump (BP) operated at an appropriate speed and

pressure to produce a flow rate at the surface of

approximately 1 L/min. Filtration was conducted in the

same manner as for the centrifugal pump. The pumps and

bailer were positioned to collect samples from about 0.6 m

below the top of the well screen.

Measurements of turbidity, dissolved oxygen (DO),

temperature, electrical conductivity (EC), and pH of the

pump discharge were made on-line, while measurements of

these parameters for the bailer discharge were made off-line.

Stabilization of these parameters provided an indication of

equilibrium between incoming ground water, the action of

the sampler, and stagnant water in the well; thereby

suggesting that purging was complete. The relative values of

these parameters also provided a means for comparing the

sampling methods with respect to their ability to minimize

disturbance in the sampling zone. Estimates of particle size

distribution were determined gravimetrically by serial

ultrafiltration using microfilters of 5.0 μm, 0.4 μm, 0.1 μm,

and 0.03 μm pore size.

Results and Discussion

The relative disturbance in the sampling zone caused by a

sampling method was most evident in the field

measurements of turbidity and DO, particularly under low

well-yield conditions. When the discharge rate exceeded the

well yield, the increasing hydraulic gradient between the

formation and the well mobilized large quantities of

particles, thereby elevating turbidity values. Continued

removal of water from the well dewatered the filter pack,

leading to gravity drainage of pore water and sediments and

continually increasing turbidity values. Bailer turbidity

values were further elevated by the surging action of the

bailer which mobilized large quantities of particles in the

well. Elevated DO values of the bailer and BP at 1 L/min in

low-yield wells reflect the formation of a large air-water

interface which increased the potential for oxygenation of

incoming ground water as the filter pack was dewatered.

The bailer caused additional aeration of the samples as a

result of the increased exposure to the atmosphere during

sample collection and transfer. The lower discharge rate of

0.3 L/min, which was generally closer to the well yield,

resulted in less variability and more representative values of

turbidity and DO, as well as lower purge volumes.

Somewhat less variable results were observed between

sampling methods in wells where the purging and sampling

rate did not exceed the well yield. Under these conditions,

hydraulic gradients into the well were minimal, the filter

pack was not dewatered, and turbidity was generally lower.

The two pumping methods produced similar values of most

field measurements, while the surging action of the bailer

produced turbidity values that were approximately two

orders of magnitude higher than those produced by the

pumps. Likewise, DO values in bailed samples were

elevated with respect to the pumped values, an artifact of the

bailing process. As a result, the pumps produced equilibrium

DO and turbidity conditions with relatively low purge

volumes, while the bailer produced high values of these

parameters and did not reach equilibrium after greater purge

volumes.

In almost every case, samples collected by bailer contained

higher particle concentrations than those collected by the

pumps, with the greatest differences occurring at the most

turbid wells. Furthermore, the size distribution of particles

in most bailed samples was highly skewed toward larger

particles, with over 96 percent larger than 0.45 μm, and

generally over 93 percent larger than 5.0 μm. The quantities

and sizes of these particles suggest that they were not

mobile in ground water under natural flow conditions but
41

were primarily the artifacts of well construction,

development, and purging and were mobilized by agitation

in the sampling zone caused by bailing. The particle size

distribution in samples pumped from the most turbid wells

(the low-yield wells) were also skewed toward larger

particles, but total particle concentrations were much lower

than in the bailed samples. In the less turbid (high-yield)

wells, total particle concentrations in pumped samples were

orders-of-magnitude lower than in bailed samples, reflecting

the lower degree of agitation caused by the pumping

methods. Also, particle sizes in the pumped samples were

generally more uniformly distributed; approximately 50

percent of the particles were larger than 0.45 μm.

Differences in metal concentrations between filtered and

unfiltered samples were most evident in low-yield and

highly turbid wells, particularly when the samples were

collected by bailer. In fact, several metals present in

unfiltered bailed samples were below detection levels in the

corresponding filtered samples. The large differences in

concentration between filtered and unfiltered bailed samples

reflect the association of metals with the high concentrations

of artifactual particles entrained during bailing. For

example, iron in the sampling zone likely existed as iron

hydroxide particles, particles containing elemental iron, and

ferrous iron sorbed to particle surfaces. Removal of the

majority of particles during filtration therefore greatly

reduced iron concentrations in the filtered samples. Other

metals likely existed as aqueous species sorbed to particle

surfaces, or as elemental components of particles originating

as aquifer solids, and their concentrations were similarly

reduced by filtration. Additionally, ferrous iron may have

oxidized and precipitated during bailing, transfer, and

filtering of the samples, and then removed during filtration.

Finally, the formation of a thick filter cake during filtration

of bailed samples likely reduced the effective pore size of

the filter membrane, thereby blocking passage of some

particles smaller than 0.45 μm; this would further reduce the

concentrations of associated metals in the sample.

Trace metal concentrations in unfiltered samples pumped

from low-yield and highly turbid wells were generally lower

than in unfiltered samples bailed from the same wells. This

reflects the lower degree of agitation associated with

pumping and, as a result, the lower artifactual particle

concentrations. Removal of the larger particles in the

pumped samples did, however, cause filtered samples to

contain lower metal concentrations than unfiltered samples,

though the differences in concentration were much lower

than in bailed samples. Unfiltered metal concentrations in

samples pumped at 1 L/min were often slightly higher than

in samples pumped at 0.3 L/min, but the concentrations in

the filtered samples from both pumps were essentially the

same. Furthermore, metal concentrations in filtered pumped

samples did not differ significantly from those in filtered

bailed samples.

In less turbid and high-yield wells, unfiltered bailed samples

usually contained the highest metal concentrations of all

samples, but the differences between these concentrations

and concentrations in filtered samples were much smaller

than for low-yield and turbid wells. Several metals showed

only slight differences between filtered and unfiltered

results in bailed samples. These results reflect the lower

proportion of artifactual particles removed during filtration

as compared to the low-yield and turbid wells, but also are

related to metal speciation at each well. Differences between

filtered and unfiltered pumped samples were minimal, and

the concentrations were essentially the same as those in the

filtered bailed samples, despite the variability in proportion

of particles smaller than 0.45 μm. This suggests that many

metals existed primarily as dissolved species and/or were

associated with particles smaller than 0.45 μm in the less

turbid and high-yield wells included in this study.

Conclusions

The effects of field filtration on trace metal concentrations

were most evident when a bailer was used to sample lowyield and/or turbid wells. Concentrations in unfiltered bailed

samples were up to several orders-of-magnitude higher than

in filtered bailed, filtered pumped, and unfiltered pumped

samples. Elevated metal concentrations in unfiltered bailed

samples reflected the entrainment of large quantities of

normally immobile artifactual particles and their associated

matrix metals, and unknown quantities of contaminant

metals. Pumping at low to moderate rates in low-yield and/

or turbid wells resulted in less agitation in the sampling

zone, lower particle concentrations, and reduced effects of

field filtration on metal concentrations.

The effects of field filtration were the least evident in highyield wells and/or wells having lower turbidity. Samples

bailed from these wells exhibited much smaller differences

between unfiltered and 0.45-μm-filtered samples. However,

bailing clearly mobilized artifactual particles that caused

elevated metal concentrations in most unfiltered bailed

samples. In contrast, samples pumped from these wells

exhibited virtually no differences between unfiltered and

filtered samples, reflecting the minimal entrainment of

artifactual particles larger than 0.45 μm during sampling at

low to moderate pumping rates. Concentrations in filtered

samples bailed from high-yield wells and/or from wells

having lower turbidity were generally equivalent to

concentrations in pumped samples. This reflects the removal

of larger, normally immobile artifactual particles and

associated metals from the bailed samples.

Although the three sample-collection methods generally

produced similar results when samples from less turbid

wells were filtered, the pumping methods produced the most

consistent overall results. Most metals showed little

variation between filtered and unfiltered pumped samples,
42

reflecting the minimal agitation in the sampling zone and

sample during purging and sample collection. Use of

submersible pumps at low speeds may reduce the

uncertainty in results when collecting samples of inorganic

ground-water constituents that have the potential to

associate with particles in ground water.

Acknowledgements

The authors wish to acknowledge the technical assistance of

James Brown, Jane Denne, Robert Puls, and Andrew

Teplitzky; and the logistical assistance of Jack Connelly,

Brian Haelsig, Nadine Romero, and Bernie Zavala. This

work was supported by the EPA Environmental Monitoring

Systems Laboratory, Advanced Monitoring Systems

Division, under Cooperative Agreement #CR815774 with

the University and Community College System of Nevada,

Desert Research Institute, Water Resources Center.

Notice

The U.S. EPA, through its Office of Research and

Development (ORD), prepared this extended abstract for a

workshop presentation and proceedings. It does not

necessarily reflect the views of the EPA or ORD.

References

1. Backhus, D.A., J.N. Ryan, D.M. Groher, J.K.

MacFarlane, and P.M. Gschwend. Sampling Colloids

and Colloid-Associated Contaminants in Ground Water.

Ground Water, 31 (3): 466-479, 1993.

2. McCarthy, J.F., and J.M. Zachara, Subsurface Transport

of Contaminants. Environmental Science Technology,

23(5): 496-502, 1989.

3. McDowell-Boyer, L.M., J.R. Hunt, and N. Sitar.

Particle Transport Through Porous Media. Water

Resources Res., 22(13): 1901-1921, 1986.

4. Pohlmann, K.F., G.A. Icopini, R.D. McArthur, and C.G.

Rosal. Evaluation of Sampling and Field-Filtration

Methods for the Analysis of Trace Metals in Ground

Water. U.S. Environmental Protection Agency, Las

Vegas, Nevada, in preparation, 1994.

5. Puls, R.W. and M.J. Barcelona. Groundwater Sampling

for Metals Analysis. EPA /540/4-89/001, U.S.

Environmental Protection Agency, Ada, Oklahoma,

1989, 6 pp.

6. Puls, R.W., J.H. Eychauer, and R.M. Powell. ColloidalFacilitated Transport of Inorganic Contaminants in

Ground Water: Part I. Sampling Considerations. EPA/

600/M-90/023, U.S. Environmental Protection Agency,

Ada, Oklahoma, 1990. 12 pp.

7. Puls, R.W., R.M. Powell, D.A. Clark, and C.J. Paul.

Facilitated Transport of Inorganic Contaminants in

Ground Water: Part II. Colloidal Transport. EPA/600/

M-91/040, U.S. Environmental Protection Agency, Ada,

Oklahoma, 1991. 12 pp.

8. Ryan, J.N. and P.M. Gschwend. Colloid Mobilization in

Two Atlantic Coastal Plain Aquifers: Field Studies.

Water Resources Res., 26(2): 307-322, 1990.
43

MONITORING WELL SAMPLING -

YOU CAN’T ALWAYS GET WHAT

YOU WANT BUT CAN YOU GET

WHAT YOU NEED?

Jack Connelly

Introduction

In 1985, Wisconsin was one of the first states to develop

guidelines for installing monitoring wells, and in 1990 we

became the only state to develop comprehensive rules for

monitoring well installation and development. Wisconsin’s

monitoring well installation rule includes many

requirements to ensure that the water produced from a

monitoring well is representative of groundwater.

Wisconsin also recognized the need for consistent sampling

procedures, so in 1987 we developed Groundwater

Sampling Procedures Guidelines that we require landfill

owners and consultants to follow. We are proud of both our

sampling procedures guidelines and our monitoring well

installation rule, and these documents are in demand by

many states’ researchers and regulators. The guidelines

require field filtering of groundwater samples collected for

inorganic analysis. This requirement is based upon our 15+

years of infield sampling experience and the geology of our

state. Therefore, when the final Subtitle D criteria were

published, we were shocked that EPA had banned the use of

field filtering. We were especially surprised that such a

rigid policy would be included in an otherwise flexible rule.

We surveyed those sampling Wisconsin landfills to

investigate the impact of changing our sampling

requirements. The results from 305 respondents (see

Appendix I for complete results) show that:

1. 80 percent of the samplers use a bailer to purge

their wells,

2. 89 percent use a bailer to retrieve samples from the

wells,

3. over 55 percent of the sampled wells are turbid.

Many of the landfill monitoring wells in Wisconsin are

turbid because we encourage locating landfills in finegrained soils to limit contaminant migration. Wells

screened in tight soils often do not clear up during

development, and if bailed samples are not filtered, metals

results are erroneously high, variable and misleading. Table

1 lists results from an upgradient unimpacted well at a

foundry landfill. We typically see very high metals values

in unfiltered samples (“Bailer Unfiltered” results) that also

vary from one sampling period to the next. The variability

and elevated metals results are caused by well turbidity, not

by groundwater contamination. Columns C and D in Table

1 more accurately represent groundwater quality. Many

such sites with turbid wells would be required to perform

Assessment Monitoring under Subtitle D because of falsely

elevated metals values.

The impact of banning field filtering in Wisconsin would be

significant. Wisconsin has 15 to 20 years of data based on

filtered samples. We have detected contamination and taken

action at many sites relying primarily on this method. To

determine which sites to investigate we do not rely on

unfiltered turbid samples that produce falsely elevated

metals values but instead rely on VOCs and trends in nonmetallic inorganic parameters.

Table 1. Metals Concentrations (μg/L) from

Unimpacted Well at Foundry Site

A B CD

Bailer Bailer Low Flow

MCL Unfiltered Filtered Unfiltered

Arsenic 50 120 <2 <1

Cadmium 5 9.2 <0.5 0.29

Chromium 100 450 <2 1.2

Lead 15 320 <5 <1

Recent advances in monitoring technology have produced

the relatively new low-flow pumping technique (LFPT),

improving the quality of unfiltered samples, and recent

experience shows that the LFPT for purging and sampling

can produce reliable samples. After review of the articles

referenced in the Subtitle D criteria as background to this

issue, we agree that colloidal material may indeed move

through some aquifers. Since contaminants may be

adsorbed on colloids, the filtering of groundwater samples
44

could remove one source of contamination. However, as

illustrated in the data from columns C and D of Table 1, the

significance of the colloidal source is unclear. Few studies

have actually compared results from contaminated samples

that have been bailed and filtered with results from samples

collected using the LFPT. The evidence from these studies,

discussed below, has been mixed and inconclusive. In

addition, there has not been a study of the practicality of

using the LFPT.

Is Low-Flow Pumping Practical?

EPA contracted with the Desert Research Institute (DRI) to

study the filtering issue for a year. Wisconsin’s Outagamie

County Landfill was one of three sites DRI chose. DRI

collected both filtered and unfiltered samples using the

LFPT one week after the County collected samples using a

bailer and field filtering. All three types of sampling results

were similar for metals. We were impressed with the

LFPT’s ability to minimize turbulence and aeration. The

LFPT produced “clear” samples from wells that had

produced highly turbid samples when bailed the previous

week.

We made the following additional observations about the

LFPT:

1. There is a significant amount of bulky equipment

required: a heavy reel, 100 feet of hose and

electrical cable, a regulator, a 60-90 pound

generator (or battery or nitrogen tank depending on

pump type), meters for measuring conductivity,

DO, pH, temperature and turbidity and a flow

through cell. (Many Wisconsin wells cannot be

reached by vehicle.)

2. It is time-consuming to transport and set-up the

equipment, purge the well and collect the sample.

(An average of two wells were sampled per day.)

3. The pump sometimes had difficulties pumping at

very low rates.

4. The equipment would be very difficult to operate in

Wisconsin type winter conditions (e.g. if the pump

turned off, water remaining in the tubing would

freeze in a matter of minutes).

5. Low-flow pumping could not be used in wells that

could be purged dry. (Many monitoring wells in

Wisconsin can be purged dry.)

One of our biggest practical concerns with the LFPT is the

amount of time required to sample wells. A typical

Wisconsin landfill remaining open under Subtitle D would

have 50 monitoring wells. It would take samplers 1 week to

sample such a site using a bailer and field filtering, while it

would take 3-5 weeks to sample the site using the LFPT. An

ideal set-up for sampling would be a dedicated low-flow

pump because there would be less equipment to transport

and freezing would be less likely since the tubing is in the

well, not exposed to the air and less time would be needed

for decontamination. However, it is not realistic to expect

that most landfill owners will install a dedicated pump

system in each of its monitoring wells immediately to

comply with the Subtitle D criteria. As part of our survey of

groundwater samplers we asked them what type of

dedicated sampling equipment they were using. Seventy-six

percent of the samplers did not use any type of dedicated

system, 16% used dedicated bailers and only 8% used

dedicated pumps. Although dedicated pumps have been

available for a number of years, most landfill owners in

Wisconsin are not choosing to use them.

We evaluated the LFPT at facilities with high levels of

metals, such as plating companies. At the Riverside Plating

Company a consultant sampled several monitoring wells

using a bailer and collected both a filtered and unfiltered

sample from each well. We sampled the same wells using

the LFPT during the month following the consultant’s

sampling. We experienced a number of problems during

this sampling. We had hoped to sample 3 to 4 wells in a day

but found our rate of sampling to be similar to DRI’s - a

maximum of 2-3 wells per day. The pump would shut off

unexpectedly while purging some of the wells. It had to be

restarted at a high rate which created added turbulence and

increased the purging time. It took approximately 45

minutes to set up and calibrate the equipment prior to

sampling each well and slightly less time to take down the

equipment following sampling. Purging and sampling,

excluding set up and take down time, took anywhere from

1-4 hours for each well.

How Do Results Compare?

To date, the metals results comparing bailing and field

filtering to low-flow pumping have been inconclusive.

Table 1 represents data collected at an unimpacted well in

Wisconsin where metals are high only in bailed and

unfiltered samples due to turbidity. The bailing and field

filtering and low- flow pumping produced very similar

results indicating no metals contamination. Researchers

sampling for arsenic using the two methods found

somewhat lower values using bailing and field filtering than

low-flow pumping (Puls et al. 1992 and Puls and Powell

1992), but the values were close enough that under our

enforcement standards and procedures, we would have

taken the same enforcement action using the results from

either method. Chromium results have varied depending on

the level of contamination. Table 1 illustrates similar results

at low levels of contamination. Table 2, representing

preliminary results from Wisconsin’s study, illustrates
45

Table 2. Chromium Concentrations (μg/L) at Two Impacted Wells - Riverside Plating Co.

Well P-3 Well P-4

Bailer Bailer Low Flow Bailer Bailer Low Flow

Unfiltered Filtered Unfiltered Unfiltered Filtered Unfiltered

Chromium 77 20 14 340 470 292

similar results for the two methods at medium levels of

chromium contamination (see Well P-3) and exaggerated

levels of contamination using bailing and field filtering at

high levels of chromium contamination (see Well P-4). Puls

et al. (1992) also found exaggerated levels of chromium

when using the bailing and field filtering method. However,

in a separate study Paul and Puls (1993) found “very little

difference” in chromium concentrations between the bailer

and low-flow pumps at high levels of chromium

contamination.

Conclusion

Wisconsin has over 9,000 landfill monitoring wells, of

which over 85 percent are bailed and over 50 percent

produce turbid samples. If turbid samples collected from

these wells are not filtered, the results will be erroneously

high for metals and these erroneously high values will force

many landfill owners into Assessment Monitoring under

Subtitle D.

A logical alternative to bailing is the low-flow pumping

technique, which can produce clear samples without

filtering in many circumstances. However, before requiring

landfills and others to use this technique two critical

questions need resolution:

1. Does bailing and field filtering produce

significantly different results from low-flow

pumping? (The results of the comparison to date

have been preliminary and inconclusive.)

2. Can the low-flow pumping technique be

implemented practically? (The evidence indicates

it would be difficult to implement in the field but

more evidence should be gathered.)

We propose postponing the ban on field filtering while EPA

and the states gather additional evidence to answer these

two questions. What risk is involved in postponing the ban?

Very little, if any, at municipal solid waste landfills. Our

experience has been that metals rarely migrate beyond 100

feet of our landfills. We have found that more mobile

constituents such as VOCs and chloride are far better

indicators of contaminant releases from landfills than are

metals.

In Wisconsin we have used results from our current

techniques of bailing and field-filtering for inorganics and

bailing without filtering for VOCs to require groundwater

investigations at 100 landfills and implement remedial

action at over 50 of these landfills. We believe that our

monitoring and remediation programs would not be

significantly improved by adding requirements for low-flow

pumping.

We suggest that EPA use some of the flexibility used

throughout Subtitle D, at least while we gather additional

data to answer the two questions posed above. We

recommend that EPA:

1. Lift the ban on field filtering until more research is

completed.

2. Collect additional metals data from individual

wells using both bailing and field filtering and lowflow pumping.

3. Determine whether there is a significant difference

between the metals values using the two

techniques.

4. Evaluate ways to improve bailing and field filtering

if there are significant differences between the two

techniques.

5. Evaluate the practicality of the low-flow pumping
46

technique, especially for sites in northern climates,

in fine grained soils where wells can be purged dry

and sites with a large number of monitoring wells.

No matter which sampling technique seems best

scientifically, if it can’t be implemented, it serves no

purpose. Returning to the title of my presentation, you can’t

always get what you want. What all of us would love to

have is the ideal, perfect sampling technique. But if you try

sometime, and balance the ideal with what works in the

field, you just might find, you get what you need.

References

Paul, C.J. and R.W. Puls. 1993. Comparison of GroundWater Sampling Devices Based On Equilibration of Water

Quality Indicator Parameters. EPA/600/A-93/005, 13 pp.

Puls, R.W. and R.M. Powell. 1992. FOCUS PAPER:

Acquisition of Representative Ground Water Quality

Samples for Metals. Ground Water Monitoring Review, v.

12, no. 3, pp. 167-176.

Puls, R.W., D.A. Clark, B. Bledsoe, R.M. Powell and C.J.

Paul. 1992. Metals in Ground Water: Sampling Artifacts

and Reproducibility. Hazardous Waste and Hazardous

Materials, v. 9, no. 2, pp. 149-162.
47

RESULTS OF WISCONSIN’S GROUNDWATER SAMPLING PROCEDURES SURVEY

This survey was sent on October 13, 1993 to those sampling groundwater at 470 Wisconsin landfills, of which 305

had replied at the time the results were compiled.

1. At about how many of the following types of Wisconsin landfills do you collect groundwater samples?

(e.g., if you sample at 2 municipal and 3 demolition landfills, fill in 2 in front of “Municipal Solid Waste”

and 3 in front of “Demolition”)

58% Municipal Solid Waste 8% Demolition

29% Industrial 5% Other

2. Of the above landfills, about how many are

31% Active (taking waste) 54% Closed

3. At about how many landfills do you use the following equipment to purge the wells? (e.g., if you use a

bailer at 3 landfills and a bladder pump at 2landfills, fill in 3 in front of “Bailer’ and 2 in front of “Bladder

Pump”)

80% Bailer 0.2% Gas Displacement Pump

12% Bladder Pump 1.6% Air Lift Pump

0.2% Centrifugal Pump 0.9% Peristaltic Pump

9% Submersible Pump 1.6% Suction Lift Pump

0.9% Others (list brand name of pump if unsure of type) ____________________________

4. About how many well volumes do you remove from the well when purging wells which you cannot purge

dry?

3.7 number of well volumes purged

5. About how much time elapses between the time you finish purging a well which recharges rapidly and the

time that you sample it?

 (Circle One)

None, we have no such well..................................................8.7%

less than 30 minutes ...............................................................60%

30 to 60 minutes .......................................................................6%

1 to 2 hours ............................................................................3.3%

2 to 4 hour .............................................................................1.1%

4 to 6 hours ............................................................................0.0%
48

6 to 12 hours .......................................................................... 1.1%

12 to 24 hours ......................................................................... 11%

25 to 48 hours ........................................................................ 4.3%

49 to 72 hours ........................................................................ 0.0%

6. At about how many landfills do you use the following equipment to retrieve the samples from the well?

40% Bailer 6% Submersible Pump

49% Bailer with Bottom .0% Gas Displacement Pump

Emptying Device

11% Bladder Pump 0.7% Peristaltic Pump

1.6% Centrifugal Pump 0.9% Suction Lift Pump

0.9% Others (List brand name of pump if unsure of type)

7. About what percent of all monitoring wells that you sample produce turbid water (i.e., water is not clear)?

18% < 25% 21% 25-50% 27% 51-75% 34% >75%

8. Do you filter samples for inorganics? 84% Yes 14% No

 (e.g., alkalinity, hardness)

If Yes, is filtering done in 66% Field

18% Lab

9. Do you filter samples for metals? 88% Yes 12% No

If Yes, is filtering done in 71% Field

17% Lab

10. If field filtering, do you use: 68% A transfer container

25% An in line filter system

11. About how long is it, on the average, between the time you take a sample and the time that it is filtered?

 (Circle One)

0 minutes (in line filtering).......................................... 18%

Less than 15 minutes. .................................................. 45%

15 to 60 minutes .......................................................... 16%

1 to 2 hours ................................................................. 6.5%
49

2 to 3 hours ................................................................. 3.3%

More than 3 hours ....................................................... 11%

12. About how many landfills that you sample have dedicated sampling equipment?

16% Landfills with dedicated bailers (separate bailers for each well)

7.6% Landfills with dedicated pump system (separate pump for each well)

13. Do you use distilled water (also includes deionized and reagent grade water) to rinse equipment between

wells?

95% Yes 5% No

If Yes, where is it usually obtained?

22% Grocery store

59% Laboratory

14% Other (please specify) most often: Culligan, or office purification equipment

If No, what do you use?

“River water” or “Just dry it off” were notable responses

Used to rinse equipment

The figures that follow graphically illustrate the answers to several of the sampling questions asked in the survey.
50
51
52
53
54

STATISTICAL COMPARISON OF

METAL CONCENTRATIONS IN

FILTERED AND UNFILTERED

GROUND-WATER SAMPLES

Robert D. Gibbons & Martin N. Sara

Introduction

The promulgation of Subtitle D on October 9, 1991 with it’s

restriction on filtering ground-water samples has generated

much controversy. From USEPA’s perspective, there is

concern that by filtering the sample potential contribution of

colloidal transport to off-site migration may be overlooked

(i.e., molecules of metals bound to particulate matter in the

ground water). From the states and regulated community

perspective, there is concern over what is being measured;

ground water or the formation adjacent to the monitoring

well. Increases in turbidity may lead to higher unfiltered

metal concentrations, and since waste disposal facilities

invariably have more downgradient than upgradient

monitoring wells, the probability of a turbid sample is more

likely in a downgradient well than an upgradient well by

chance alone. This type of “false positive” result will lead to

expensive and unneeded site assessment. Alternatively, if

higher turbidity or differences in formation are associated

with upgradient well measurements, effects of

contamination may go undetected (i.e., false negative

results).

Methodology

Paired measurements (i.e., filtered and unfiltered) were

obtained for 16 metals [calcium (Ca), magnesium (Mg),

sodium (Na), arsenic (As), cadmium (Cd), mercury (Hg),

selenium (Se), silver (Ag), chromium (Cr), copper (Cu),

lead (Pb), barium (Ba), manganese (Mn), potassium (K),

zinc (Zn), and iron (Fe)] in mg/l, and sample turbidity in

NTU, from each of 4 waste disposal companies. Each

company had paired data for upgradient and downgradient

monitoring wells from several different facilities. This

report is based solely on complete samples in which filtered

and unfiltered metal concentrations, and turbidity were

measured in the ground-water sample.

There were a total of 9689 complete records from 12 sites

and 155 monitoring wells. Sample sizes ranged from 506

complete measurements for Ba to 803 complete

measurements for Ca. For the purpose of illustration,

turbidity was divided into low (< l0 NTU), medium (11-50

NTU), and high (> 50 NTU). These cutpoints were based on

the empirical frequency distribution of turbidity such that

the sample would be roughly divided in thirds. The results

presented are not dependent on this classification system,

and can be replicated with the continuous turbidity

measurements as well.

Results

This section presents results from the comparison of filtered

and unfiltered samples using the entire database of complete

sample (i. e., those in which turbidity and both filtered and

unfiltered measurements were simultaneously available).

Summary statistics are presented in Tables 1 and 2. Table 1

displays detection frequency for filtered and unfiltered

samples by compound and sample turbidity level (~.e., low,

medium, and high). Table 2 displays the mean concentration

and standard deviation for those cases in which a metal was

detected in both filtered and unfiltered samples. Also, Table

2 lists results for each metal and turbidity level.

Table 3, displays summary statistics for Fe overall, and for

each turbidity level in 45 upgradient measurements. Table 3

reveals that the average upgradient unfiltered concentration

(see Total in Table 3) is five times higher than filtered

samples and the standard deviation i.e., variability) is six

times higher. Although variability is always higher in

unfiltered samples, the magnitude of the difference is

proportional to turbidity of the sample.

In addition to the effect of the increased variability of the

unfiltered samples on the false negative rate of the statistical

test, the relationship with turbidity can produce large

numbers of false positive results as well. Table 4 displays

the average and maximum iron concentrations for each of

the 11 downgradient wells at the facility for filtered and

unfiltered samples. Table 4 reveals widespread variability in

iron concentrations for the unfiltered samples across

downgradient wells. Some wells show consistently high (I

and 2) or consistently low (3, 4, 5, and 11) iron

concentrations whereas other wells show widespread

variation for unfiltered samples i.e., ratio of maximum to

mean values of 10 to 1). Results for the filtered samples

were far more consistent (ratio of maximum to mean of less

than 2 to 1).

The variance component estimates i.e., inter-site, inter-well,

and intra-well) for filtered, unfiltered and their difference

i.e., unfiltered-filtered) are displayed in Table 5. Table 5

reveals that variability from site to site is reasonably

consistent for filtered and unfiltered samples. Variability

from well to well is approximately twice as large for

unfiltered versus filtered samples. Variability within wells is

over five times as large for unfiltered versus filtered

samples.

These results suggest that if unfiltered samples are the basis

for these analyses, false negative rates i.e., failure to detect
55

contamination when it is present) will, in fact, be

considerably larger for than if filtered samples are used.

Conversely, the doubling of the well to well component of

variation for unfiltered samples relative to filtered samples,

will produce large numbers of false positive results as well,

particularly in upgradient versus downgradient detection

monitoring comparisons. Turbid sarnples will continuously

be mistaken for contaminated samples and needless site

assessments will be routinely performed. On the other hand,

an unscrupulous owner/operator might simply churn the

upgradient well sarnples i.e., inaease turbidity), and

meticulously collect downgradient samples, which would

greatly increase statistical limits and rarely result in

statistically significant differences whether contamination

was present or not. Such practice would have little or no

effect on filtered samples.

Summary

The data presented show how unfiltered measurements can

lead to increases in both false positive and false negative

rates due to increased variability of the unfiltered results

(i.e., false negative) and the relationship between

concentration and sample turbidity that can be mistakenly

interpreted as contamination (ie., false positive). The data

presented indicate that turbid samples will continuously be

mistaken for contaminated samples and needless technical

efforts will be expended by both the states’ and facility

owners’ staff. Conversely, by not filtering, upgradient

samples collected in turbid wells could mask releases in

downgradient wells where unturbid samples were carefully

collected.

The purpose of this report is to clearly demonstrate the

enorrnous price that is paid in both potential false positive

and false negative detection monitoring decisions when

unfiltered samples are used as the basis of testing statistical

hypotheses regarding site impact. It is clearly shown that

unfiltered sample concentrations exhibit extreme variability,

which is in large part due to sample turbidity and colloidal

transport. Furthermore, even if a statistical adjust for the

effects of turbidity was performed (i.e., in effect hold

turbidity constant), differences between unfiltered and

filtered metal concentrations still exist. Are these differences

due to colloidal transport or the effects of the formation? No

definitive conclusion can be readily drawn since these

effects are confounded in empirical data. It should be noted,

however, that there are special geological conditions that are

required for colloidal transport, but the increased variability

in unfiltered samples is seen consistently in all sites

examined regardless of whether conditions are conducive

for colloidal transport or not. In addition, the effects are

seen both in upgradient and downgradient wells indicating

that in these data, the increased concentrations associated

with unfiltered samples are not due to colloidal transport of

metals released from a facility.

From a statistical perspective, the question is whether

filtered or unfiltered samples lead to a preferential balance

between false positive and false negative results when used

in ground-water detection monitoring programs. To select

unfiltered samples to cover the possibility of colloidal

transport, at the expense of both greatly inaeased false

positive and false negative results is foolish at best. Analysis

of extensive monitoring data, from numerous waste disposal

facilities using upgradient and downgradient monitoring

wells in which both filtered and unfiltered samples were

simultaneously collected, clearly showed that filtered

samples dramatically minimize both false positive and false

negative rates relative to unfiltered samples. The principal

factor in this difference was due to the turbidity of the

sample.

The results of this study have profound implications for

public policy in relation to the monitoring of municipal solid

waste landfills. Use of unfiltered sarnples will dramatically

increase false negative results in those sites in which

upgradient wells exhibit turbidity or are drilled in different

formations that vary in terms of their concentration of tht

metal in question. Both conditions will lead to large

variability in upgradient samples and produce statistical

limit estimates that are quite large relative to what could be

obtained had filtered samples been used. In contrast, when

the small number of upgradient wells are not representative

of either the formations or turbidity in the far greater

number of downgradient wells, the variability in the

upgradient wells will underestimate the true background

variability for the site as a whole and large numbers of false

positive results will occur. The reason, of course, is that the

unfiltered samples are influenced heavily by sample

turbidity and geological formation, neither of which is

explicitly controlled in the detection monitoring process. To

the extent that there are far greater numbers of downgradient

wells, there is a correspondingly greater chance of having

turbidity or differences in formation adversely impacting the

concentration in a, downgradient well and falsely

concluding that it is the site that has impacted ground water.

Conversely, if the upgradient samples are highly turbid or

vary in turbidity, variability in the measured concentrations

will be large and statistical tests of contamination will be

powerless to detect real contamination when it occurs. All

analyses performed in this study yield exactly the same

conclusion.

The reader should note that the effects observed here were

consistent for both upgradient and downgradient wells. If

colloidal transport is the method by which contaminants are

transported off-site, why should the same types of

variability be observed in upgradient wells? These results

clearly show that whether colloidal transport is real or not,

the price paid for using unfiltered samples is enormous, both

in terms of missing real contamination when it exists and in

detecting contamination when it is not present.
56

Table 1 Detection Frequencies for Filtered and Unfiltered Samples (Expressed as a Proportion of Total Measurements)

Metal Low Turbidity Med Turbidity High Turbidity

Filtered Unfiltered Filtered Unfiltered Filtered Unfiltered

Ag .04 .07 .01 .06 .02 .12

As .08 .14 .13 .22 .32 .48

Ba .23 .31 .36 .48 .60 .70

Ca .99 1.0 1.0 1.0 .99 .99

Cd .10 .14 .07 .18 .06 .16

Cr .04 .09 .07 .15 .11 .55

Cu .22 .29 .12 .29 .28 .57

Fe .58 .87 .64 .98 .82 .99

Hg .01 .01 .01 .02 .02 .05

K .85 .87 .94 .95 .82 .83

Mg .99 1.0 .99 1.0 .98 1.0

Mn .75 .81 .84 .94 .88 .99

Na .92 .96 .98 .98 1.0 1.0

Pb .15 .-23 .07 .22 .24 .52

Se .05 .04 .04 .03 .14 .08

Zn .59 .68 .61 .78 .62 .76
57

Table 3 Summary Statistics for Iron (mg/l) in Filtered and Unfiltered Samples in

Upgradient Wells (1/2 MDL substituted for Nondetects)

Turbidity Filtered Unfiltered

 Mean SD N Mean SD N

Total .439 .760 45 2.044 4.530 45

Low .152 .305 32 .369 1.014 32

Medium .472 .348 5 1.970 1.066 5

High 1.569 1.145 8 8.790 7.682 8

Table 2 Mean and Standard Deviation (SD) of Metal Concentrations for Filtered and Unfiltered Samples When Both

were Detected

Metal Low Turbidity Med Turbidity High Turbidity

Filtered Unfiltered Filtered Unfiltered Filtered Unfiltered

Mean S D Mean S D Mean S D Mean S D Mean S D Mean S D

Ag .005 .001 .004 .001 .004 .000 .023 .000 .019 .043 .042 0.47

As .010 .018 .018 .024 .009 .008 .014 .016 .028 .055 .032 0.59

Ba .146 .174 .253 .649 .139 .112 .180 .153* .152 .144 .461 .995

Ca 93.4 139. 96.1 120. 102. 126. 108. 138. 356. 1152 465. 1341

Cd .005 .003 .007 .007 .009 .006 .008 .006 .011 .007 .011 .006

Cr .021 .016 .021 .013 .023 .031 .032 .032 .012 .013 .051 .053

Cu .091 .134 .111 .148 .143 .250 .152 .242 .070 .173 .146 .239

Fe 6.68 14.6 20.0 61.4* 10.5 23.5 20.1 48.8* 21.3 34.1 50.9 104*

K 11.9 27.0 13.2 31.7* 9.87 19.5 9.71 19.4 20.5 36.7 24.2 38.6*

Mg 121. 432. 114. 393. 184. 654. 171. 580. 163. 609. 179. 640.*

Mn 6.96 13.5 7.26 13.5* 4.60 8.11 4.76 8.00* 5.99 11.8 6.83 12.4*

Na 286. 1001 297. 1055 360. 1178 369. 1216 314. 1163 324. 1174

Pb .091 .034 .073 .278 .022 .030 .033 .033* .158 .124 .182 .134

Se .016 .030 .016 .031 .314 .483 .347 .549 .030 .036 .041 .059

Zn .350 .607 .385 .638* .194 .385 .217 .381 * .350 1.18 .602 1.26*

* indicates statistically significant difference between filtered and unfiltered sarnples based on a paired t-statistic
58

Table 4 Average and Maximum Iron Concentrations (mgA) in Downgradient Wells (1/2 MDL substituted for

Nondetects)

Well Filtered Unfiltered Turbidity

Mean Max Mean Max Mean Max

1 60.05 87.30 60.02 89.70 123 220

2 62.25 106.00 56.78 104.00 392 705

3 .S0 4.90 .90 5.60 9 49

4 .06 .08 .41 1.16 5 12

5 .06 .08 .85 1.98 21 85

6 .11 .94 2.65 29.50 16 55

7 .39 4.80 5.27 53.50 198 21 90

S .06 .08 8.62 53.60 235 1650

9 .06 .08 13.55 153.00 215 2550

10 5.90 7.89 12.58 24.40 741 3470

11 .43 .92 .49 1.00 2 8

Table 5 GLS Variance Component Estimates for Unfiltered, Filtered, and the Difference Between Filtered and

Unfiltered Results For Fe in mg/l

Effect Unfiltered Filtered Difference

Inter-Site SD 17.65 14.30 11.09

Inter-Well SD 27.43 13.30 20.59

Intra-Well SD 66.72 12.30 64.65

Variance components listed as standard deviations (SD)
59

IV. Poster Abstracts

PRESENTERS

John D. Gray, New York State Electric and Gas Company

Robert M. Powell, ManTech Environmental Technology, Inc.

Cynthia Paul, U.S. EPA/Robert S. Kerr Environmental Research Laboratory

Nic. E. Korte, Oak Ridge National Laboratory

Natalie Park, Westinghouse Savannah River Company

Daniel Ronen, Weizmann Institute

Gary Robbins, University of Connecticut (no abstract)
60

IN-LINE FILTERING OF GROUND WATER SAMPLES FROM MONITORING WELLS IN

GLACIAL TILL

John D. Gray

Richard E. Wardwell

ABSTRACT

New York State Electric & Gas (NYSEG) conducted an extensive research project at a solid waste (fly ash) landfill to

compare and evaluate the analytical results from filtered and unfiltered ground water samples. Two years of site-specific data

for dissolved (filtered) and total (unfiltered) concentrations of 22 metals were collected. Elemental analyses of the soil

constituents of the glacial till from the site were performed. In addition, field testing of alternative sampling techniques to

reduce turbidity in ground water samples was conducted.

The following results were determined from the research project:

• It is theoretically impossible to design a monitoring well filter pack which will prevent the movement of fines (silt

and clay) into a well bore during sampling.

• The high percentage of fines in the glacial till and fractured bedrock at the site makes it is impossible to assure a

turbid free sample from the site monitoring wells regardless of the well installation or sampling technique.

• The chemical composition of the native soil contains significant amounts of aluminum, chromium, copper, iron,

manganese and zinc.

• Unfiltered samples show increases in the fore mentioned metals in direct relation to the amount of turbidity in the

ground water sample.

• Filtering removes suspended soil particles but does not change the chemistry of the ground water samples collected

at the site.

The results from this study demonstrate that the use of unfiltered samples will produce elevated concentrations for those

metals which comprise the soil matrix. These elevated concentrations will trigger invalid exceedances of New York State

ground water standards and will mask any water quality trends associated with landfill activities. Therefore, filtered

(dissolved metals) concentrations are necessary for assessing the impacts of the landfill because they are more representative

of constituents actually moving in the ground water.
61

Passive Sampling of Ground Water Monitoring Wells without Purging: Multilevel Well

Chemistry and Tracer Disappearance

Robert M. Powell and Robert W. Puls

ABSTRACT

It is essential that the sampling techniques utilized in ground-water monitoring provide data that accurately depicts the water

quality of the sampled aquifer in the vicinity of the well. Due to the large amount of monitoring activity currently underway

in the U.S. it is also important that the techniques be efficient. It would be desirable to minimize the requirements of

sampling time, equipment, and quantity of contaminated waters pumped to the surface, without loss of data integrity. If

representative samples could be acquired without purging the wells, increased sampling efficiency could potentially be

achieved.

Purging of multiple borehole volumes is largely routine, based on studies that show changes in the water chemistry as it

stands in the casing and is subjected to atmospheric exposure at the top of the column. However, little data is available

depicting water chemistry in the screened intervals of wells at equilibrium flow conditions, i.e. with little or no disturbance to

the natural flow regime or disruption of the overlying casing waters.

This study examines the differences in water chemistry between the casing and screened interval volumes of four wells at a

field site, then compares the results to purged values for the same wells. Tracer experiments, utilizing both colloidal particles

and dissolved species as tracers, are presented to illustrate differences in natural flushing between the screened and cased

intervals. The data from the tracer removal was then utilized to estimate ground water flow velocities in the vicinities of the

boreholes.
62

Turbidity Effects on Volatile Organic Contaminants in Ground Water Samples

Cynthia J. Paul, Robert W. Puls and Lisa R. Secrest

ABSTRACT

According to the RCRA Ground Water Monitoring Technical Enforcement Document (TEGD), ground water samples

collected for contaminant analysis should have a turbidity of less than five nephelometric turbidity units (NTU). Some feel

turbidity levels greater than five NTUs would not be representative of the aquifer; however, many monitoring wells produce

samples with turbidity levels greater than five NTUs due to site-specific hydrogeochemistry or improper well design or

construction. However, our previous work has shown that proper sampling techniques can produce samples with low

turbidity values even in wells traditionally considered turbid. Little research has been conducted to determine the impact of

turbidity on volatile organic compounds (VOCs) in recovered ground water samples. This study was designed to

differentiate turbidity effects from unknown f1eld effects that could influence the apparent concentrations of VOCs in

ground water samples. Laboratory batch studies and field investigations were performed to evaluate the effects of solids

(turbidity) on VOC concentrations. Three different solids (recovered aquifer material, kaolinite, and Na-montmorillonite)

were used in the turbidity “spikes” to assess turbidity effects on sample quality. During the laboratory portion of this study,

these solids were used to determine sorption and volume displacement effects on VOC concentrations under controlled

laboratory conditions. The procedure included adding known amounts of solid to a simulated ground water solution and

then spiking each sample with varying amounts of TCE. The same solids were used in the field portion of the study to

differentiate turbidity effects on sampling methodology. Sample VOA vials were prespiked with known amounts of solids.

VOC samples were collected into these vials as well as vials containing no solids for comparison purposes. The field study

also included alteration of the sampling procedure to intentionally increase turbidity levels by entrainment of natural aquifer

materials in the collected samples. Water quality indicators (pH, dissolved oxygen, turbidity, specific conductance, redox,

and temperature) were monitored during well purging and samples were collected after all parameters reached equilibration.

Results of this study indicate that increased turbidity levels in ground water samples have no impact on VOC concentrations

(i.e., TCE and its degradation products). Sampling methodology appears to be the most important consideration when

collecting ground water samples for VOCs.
63

A Field Comparison of Micropurging and Traditional Groundwater Sampling Using Analytical

Data and Observations with the Colloidal Borescope

Nic E. Korte and Peter M. Kearl

ABSTRACT

The recent literature discusses micropurge sampling techniques as a possible replacement for traditional purge and sample

methods. Micropurge sampling involves a dedicated sampling pump, a sampling rate of approximately 100 mL/min, and

purging of only the sample pump and tubing. If micropurging can yield reliable groundwater samples, then significant

quantities of purge water can be eliminated, thereby reducing costs and minimizing waste. Unfortunately, evaluating

sampling methods for yielding representative water samples of natural groundwater systems is difficult. The monitoring well

represents an unnatural intrusion into the subsurface, and natural variations in the chemistry of the groundwater further

complicate the system. One approach to overcoming these problems is to duplicate groundwater sampling using both

conventional and repetitive micropurge sampling followed by a statistical comparison of the results. Using this approach, a

series of experiments is being conducted at two sites where samples are analyzed for selected organic and inorganic

constituents. Analysis of data collated to date using a paired t-test indicates that within a 95% confidence interval, there was

no significant difference between the sampling methods for both site contaminants and the majority of naturally occurring

analytes. Analytes that showed a significant difference were redox sensitive (e.g., iron and manganese) or were present in

such low concentrations that analytical reliability was a factor. The analytical results were supported by observations

performed with the colloidal borescope. Borescope observations demonstrated significant impacts on the hydrodynamic flow

system when using traditional sampling methods. Results of the study suggest replacing traditional purging and sampling

with micropurging, due to the reliability and cost-effectiveness of the method.
64

Random Variability of Metals Measurements in Ground Water Reduced through Revised

Sampling Techniques

Natalie M. Park

ABSTRACT

The potential to reduce the random variability or imprecision in metals measurements in groundwater samples by as much

as 90% was demonstrated through the application of revised groundwater sampling techniques. Revised ground water

sampling procedures incorporated recent research recommendations to cease filtering samples collected for metals analyses

and to move away from the conventional approach of "purge a minimum of 3 to 5 well volumes until pH, specific

conductance and temperature are stable." Since historical data indicted that pH and conductivity usually reached stability

within one to two well volumes, the new approach requires purging a minimum of two-well volumes (as a conservative

measure) and uses turbidity instead of temperature as a stabilization parameter. To reduce time, the first two well volumes

are purged at a rate that can be sustained without creating surging, generally 2-5 gal/min. Then the purging rate is reduced

to 0.25 gal/min and purging continued until pH, conductivity, and turbidity measurements stabilize. Samples collected for

metals analyses are not filtered, whereas previously 0.45 micron filters were used.

Dedicated, variable speed pumps replaced faster pumping, single speed submersible pumps in 40 wells. These wells

monitor a contaminant plume characterized by low pH (3-5), high nitrate (as N) and sodium concentrations, elevated

specific conductance (51 to 2200 μS/cm), and metals including aluminum, iron, manganese, barium zinc, copper, cobalt,

cadmium and zinc. Pumps are routinely set toward the bottom of the PVC screens to accommodate fluctuations in water

levels. The wells were installed using mud rotary drilling in Coastal Plain interbedded sands, silts and clays at depths of 20

to 70 feet (saturated screened intervals varied from 5 to 15 feet).

After a year of quarterly sampling using the revised method, comparisons with historical data revealed that for some wells

there was an average 75% to 90% reduction in random variability for measurements of aluminum, zinc, manganese,

barium, iron, cobalt, cadmium and copper. This average reduction in variability was observed for manganese data from

32% of all wells; for iron, zinc and barium data from 25% of all wells; and for 35% of the wells in which cobalt, copper,

and cadmium were present. On the average, the reduction in random variability was accompanied by a 50% decrease in

metal concentration. Turbidity measurements stabilized below 5 NTU in 38 of the wells sampled; stable values ranged

from 0.2 to 50 NTUs and were generally achieved within 15 minutes to 1.5 hours. Since the revised method did not use

filtering, the decrease in metals concentrations and variability can be attributed to a combination of the slower pumping rate

and the addition of turbidity as a stabilization parameters.
65

A Multi-Layer Sampler for the Study and Monitoring of Chemical Processes and Transport

Phenomena in Aquifers

Daniel Ronen

ABSTRACT

A multi-layer sampler (MLS) was developed and utilized for: a) sampling detailed undisturbed groundwater chemical

profiles; b) sampling gases in both the saturated and the unsaturated zone; c) deriving detailed vertical profiles of the

horizontal component of the specific discharge; d) characterizing suspended particles under natural gradient flow

conditions. Sampling is based on the dialysis-cell method; the sampling volume is defined by the desired sampling interval.

The MLS is portable, cheap and easy to operate.

The results of the field study conducted in Israel revealed: 1) intensive biochemical activity as reflected by the consumption

of dissolved O2 with the concomitant oxidation of organic matter and the development of an anoxic layer, and the

production of N2O (up to 400 μg/l) and CO2 (log PCO2 from -1.7 to -1.3); 2) the presence of an almost stagnant water layer

(q = 0.5 m/y) down to a depth of 60 cm below the water table; 3) the presence of microscale isothermal water parcels

(characteristic vertical and horizontal length dimensions on the order of less than 1 m) which differ from each other in their

chemical composition and density and are characterized by very sharp boundaries between them; 4) microscale Eulerian

variations in the flux, mineralogical composition and size of suspended particles under natural gradient flow conditions ( q

= 11 to 16 m/y). It is postulated that the gases produced during the biodegradation of the organic matter accumulate as a

distinct gas phase (bubbles) down to a depth of 1 m below the water table, reducing groundwater flow. The replenishment

of the aquifer by water of different chemical composition and the almost stagnant conditions prevailing at the water table

region (where mechanical dispersion by advection is negligible) lead to the development of microscale parcels of water of

different chemical composition. It is suggested that haline convection is a major transport and mixing mechanism at the

water table region. It is also postulated that due to the dramatic increase in pCO2 part of the carbonate cement of the rocks

dissolve and detritial CaC03, quartz and clay are released as colloidal particles. In the prevailing anoxic conditions of

groundwater at the study site (DO <1 mg/l) colloidal stability is enhanced by organic matter coating of particles.
66
67

V. Small Group Discussions Summaries

Prior to arriving at the workshop, participants were sent a package which included reference materials, brief abstracts for

presentations on the first day, small group discussion topics and focus questions for the small group discussion topics. In

addition, the participants were queried as to their preference for small group discussion assignment. These assignments were

made based on participants' responses, and each participant was assigned to two topical groups. The focus questions are

provided as Appendix B of this document. These questions were formulated by the Steering Committee in advance of the

workshop and as a result of formal meetings, phone conversations, and other communications. The small groups were

directed to attempt to answer as many questions as possible during their respective discussions, but were also granted the

latitude to let the group dynamics determine discussion direction as appropriate.
68

V. Small Group Discussions

Participants

(by topic area)

1. MONITORING GOALS AND OBJECTIVES

Group Leaders: Barcelona, Brown

Participants: Bourbon, Franks, Gronwald, Lee, Mabey, McKay, Park,

Reece, Rightmire, Romero, Stelz, Teplitzky, Willey, Zavala

2. WELL DESIGN, CONSTRUCTION, AND DEVELOPMENT

Group Leaders: Aller, Gardner

Participants: Connelly, Franks, Gray, Gronwald, McKay, Nielsen, Parker,

Sara, Stelz, Taylor

3. WELL PURGING AND SAMPLING

Group Leaders: Puls, McCarthy

Participants: Backhus, Barcelona, Connelly, Gibs, Hall, Korte, Mangion,

Martin, Park, Parker, Paul, Pohlmann, Powell, Robbins, Ronen,

White, Zavala

4. TURBIDITY AND COLLOID TRANSPORT

Group Leaders: Ryan, Mangion, Willey

Participants: Backhus, Lee, Martin, McCarthy, Puls, Reece, Rightmire,

Romero, Ronen, Sridharan, Taylor, Teplitzky, White

5. SAMPLE HANDLING AND ANALYSIS

Group Leaders: Pohlmann, Rosal, Beldsoe

Participants: Bourbon, Brown, Clark, Gibs, Gray, Hall, Korte, Mabey,

Nielsen, Paul, Powell, Robbins, Sara, Sridharan
69

Monitoring Goals and

Objectives

Michael J.Barcelona and James R. Brown

Introduction

This group considered a number of questions dealing with

the goals and objectives of monitoring efforts. From the

outset it was recognized that there are a wide variety of

monitoring purposes and programmatic goals--each with

their own objectives. The group acknowledged that main

objectives and the uses of data (i.e., both chemical and

hydrogeologic) collected in monitoring programs change

with time as the complexity and detail of subsurface

conditions become apparent. The participants also noted

that much has been learned about techniques which lead to

more accurate and reproducible data collection. It was

agreed that adoption of improved standards for professional

practice in monitoring network design, construction, and

operation should be encouraged; and that the use of errorprone monitoring techniques should be discouraged

accordingly. In this regard the newest revision of Agency

Guidance (“RCRA Ground-Water Monitoring: Draft

Technical Guidance,” EPA/530-R-93-001) goes a long way

towards highlighting the differences between currently

recommended practices and traditionally used practices.

Objectives of Monitoring Programs

Monitoring objectives include four main types (i.e.

detection, assessment, corrective-action evaluation and

resource evaluation), along with “hybrid” variations such as

site-assessments for property transfers and water availability

investigations. Monitoring purposes and objectives may

change as contamination or water quality problems are

discovered. However, there are a number of common

objectives for monitoring which should be recognized as

important regardless of initial purpose. These objectives

include: 1) Development of a conceptual model that

incorporates elements of the regional geology to the local

geologic framework. The conceptual model development

also includes initial site characterization efforts to identify

hydrostratigraphic units and likely flow-paths using a

minimum number of borings and well completions; 2) Costeffective and documented collection of high quality data

utilizing simple, accurate, and reproducible techniques; and,

3) Refinement of the conceptual model based on

supplementary data collection and analysis efforts which

evolve in complexity and the level of spatial detail. These

fundamental objectives would serve many types of

monitoring programs and provide a basis for future efforts

as purposes and objectives expand.

The Extent that Program Objectives, Site

Characteristics, or Constituents of Concern Provide

Criteria for Representativeness

The group noted from the outset that this topic applies to the

representativeness of chemical and hydrogeologic data

collected via wells, borings, piezometers, geophysical and

soil gas measurements, lysimeters, and temporary sampling

points. There is a need to get more quantitative about our

definition of what representativeness entails in the context

of controlled evolutionary site characterization and

monitoring efforts. Representativeness arises from a

recognition of the statistical variability of individual

subsurface physical properties, and contaminant or major

ion concentration levels with a need to explain extreme

values. Subsurface variability is a fact and good

professional practice should seek to maximize

representativeness by using proven accurate and

reproducible techniques to define limits on the distribution

of measurements collected at a site. An investigative site

characterization model was proposed to more systematically

approach the goal of consistent data collection.

The model emphasizes a recognition of the causes of the

variability (e.g., use of inappropriate technology such as

using bailers to purge wells; imprecise or operator

dependent methods) and the need to control avoidable

errors.

Flexible Sampling Designs for Meeting Multiple

Monitoring Objectives

Detailed site characterization is central to all purposes and

the basis for site characterization resides in the geologic

framework and identification of major hydro-stratigraphic

units. Fundamental data on subsurface lithology, headdifferences and background geochemical conditions for

example, should not change much (except to be refined

appropriately over time). Each sampling point has a proper

use or uses which should be documented at a level which is

appropriate for the program’s data quality objectives. While

these sampling points cannot always fulfill multiple

monitoring objectives (e.g., detection, assessment,
70

corrective action), the data that they yield will always

contribute to the fundamental information needed for any

monitoring program.

Elements of a Sampling Protocol: Accuracy, Precision

and Sensitivity Needed to Meet Monitoring Objectives

A sampling protocol is a documented set of procedures and

steps to accomplish a defined task. Since data quality

objectives (DQO’s) entail the identification of necessary

levels of accuracy, precision, sensitivity and completeness

for specific analytes (or subsurface properties), the DQO’s

should drive the complexity of the sampling protocols. It

was recognized that data validation methods which focus

solely on the analytical process do not assure that data will

be of sufficient quality to meet DQO’s. The major sources

of controllable error occur in the field (e.g., wrong locations,

poor technology choices, operator errors and incomplete

documentation), and it is vitally important to discourage the

continued use of methods proven to be inadequate to meet

DQO’s. Suggestions were made to expand educational

efforts on technology choices, and the potential usefulness

of QA summary reports which apply to field as well as

laboratory data collection efforts.

Application of Field-Screening Techniques and Related

Performance Criteria

The value of field-screening techniques to aid in

evolutionary site characterization and assessment efforts has

been documented in the literature. Since detection efforts

involve the evaluation of potential pathways for

contaminant movement, and assessment efforts focus on the

extent of movement through such pathways, their

monitoring objectives and DQO’s are comparable. The

levels of accuracy, precision and sensitivity for many

constituents of concern approachable by field techniques are

sometimes equal to laboratory-based analytical techniques.

In some cases (e.g., volatile organics) the use of field

techniques may be favored over lab analyses because

sample handling, storage, preservation steps are minimized

or eliminated prior to sample analysis. Laboratory methods

have the advantages of higher sensitivity and specificity

(e.g., mass-spectrometry). Their use should be encouraged

for confirmation purposes.

In all cases, the performance criteria for all screening

methods (including chemical analyses and hydrogeologic

analyses), should be determined by the data quality

objectives of the monitoring program. After the DQO's are

established, field screening procedures/tools can be selected

on the basis of their performance capabilities.

Criteria for the use of field screening methods should

include: 1) documentation of daily calibration and method

control with external standards/audits; 2) laboratory

confirmation of a percentage of samples; and, 3)

development of a field methods manual analogous to

laboratory CLP manuals under Agency auspices.

It is essential that continued training and overall quality

improvement should be undertaken to maintain/elevate field

practice to the state-of-the-art level. This should include

training courses, technical information transfer of important

scientific publications, and some form of certification and

auditing. The use of “ASTM-like” standards and quality

control summary reports would result in quality

improvement of hydrogeologic field work.

Program Objectives

Decision-Making

Data Quality Objectives

Sampling and

Analytical Protocols

Protocol Application

Refined Protocols

Evolutionary Site

Characterization
71

optimization techniques should be made more accessible to

the practitioners via technology improvement and transfer

efforts.

Documentation of Well Construction and Well

Development (Extends to demand criteria, threedimensional site characterization, and sampling

protocols)

The group was unanimous in acknowledging the need for

improved standards for professional well construction and

development practices. This need demands improved detail

in documentation of monitoring efforts. Useful inclusions

are: geologic descriptions of core material, grain-size

determinations prior to well screen design and construction,

and the development of meaningful criteria for well

development, purging and sampling. Extending the rigor of

traditional laboratory-based QA/QC procedures to all

aspects of field activities would result in substantial

improvements in practice and the value of monitoring data

for decision-making.

Factors (e.g., Sampling Techniques, Extraction Rates,

and Location ) that Influence Monitoring Objectives

The group consensus was that program objectives influence

the approach and complexity of the sampling and analytical

protocols, and not vice-versa. Program objectives are

usually motivated by regulation, although considerations of

experimental design establish monitoring objectives for

research projects. There will always be difficult situations

where the availability of water (e.g., low yielding

formations), accessibility of specific hydrostratigraphic

units, or unpredictable gradients may need to be factored

into the objectives; but the specifics of sampling protocols

should always be traceable to the DQO’s.

Chemical or Physical Speciation of Contaminants

Influence on the Design of a Monitoring Program

Speciation includes the individual physical (i.e., sorbed,

colloidal, etc.) and chemical (i.e., mineral, complexed,

varying oxidation states) forms of an element or compound

which make up the total amount present in a subsurface

sample. The potential for multiple species with differences

in mobility, toxicity, and stability should necessarily expand

the scope of program objectives and influence the detail and

rigor of DQO’s, sampling, and analytical protocols. In these

instances, renewed focus on the characterization of

background conditions and the total mass distribution of

contaminants becomes very important regardless of program

purpose. The proper selection of sample location and

sampling for the media in which the bulk of contaminant

mass may reside rather than symptoms (e.g. soil, gas or H2

O

for sorbed contaminants) are of major concern in this

regard.

In addition, the hydrogeochemical conceptual model of the

site is as important as the site’s geological conceptual

model. Ion balance and geochemical assessments should be

performed.

Alternative Methods for Designing Monitoring Networks

Given the fundamental value of a site geologic framework

consistent with regional hydrogeology and likely

contaminant behavior, alternative design methods include:

1) the diagnostic use of a flow and transport models to

select sampling locations where they can provide the most

information return; 2) Coupled field-screening/conceptual

model refinement and modeling work confirmed by further

site characterization and assessment efforts; 3) Integrated

use of geostatistical, stochastic fate and transport, and

optimization models applied in iterations to identify likely

limits on mass distributions and benchmarks for

performance as site-characterization proceeds. More

sophisticated methods such as decision-analysis/
72

Well Design, Construction and

Development

Linda Aller and Steven Gardner

The purpose of a monitoring well is to create a point within

the desired monitored zone such that an “unaffected”

representative sample can be collected. While the ease or

difficulty with which this can be accomplished is dependent

in part upon the hydrogeologic setting, additional questions

arise in almost any situation. These questions extend to

include whether or not even an effective water-level

sampling point can be designed in fine-grained materials

and fracture-flow dominated formations. More widespread,

pervasive questions arise as to what effects the process of

drilling and installing the well have on the analytical

samples that are desired to be collected from the well. The

purpose of this section is to focus on the “artifacts” that are

introduced in the well installation process and on the ways

and means that are currently available to minimize these

effects.

Artifacts can be defined as unwanted residual effects. These

effects are introduced through both the drilling process and

the well installation process (often through the materials

added) and may be either enhanced or minimized by the

development process. Other sources of artifacts, such as

interconnection of formations, are also of concern. A

discussion of the potential artifacts and possible

minimization of those artifacts is contained in the following

paragraphs. Areas where additional research is needed are

also noted.

Drilling Artifacts

Drilling Techniques

Drilling techniques are the crudest link in the drilling,

installation and sampling scenario. The drilling methods

employed to install monitoring wells were adapted from the

water well, soil dynamics and oil industry. None of the

technologies provided by this historical base have been

adequate to provide the rigorous quality control needed for

monitoring wells. This is clearly evident when the

complexities of the chemical environment being monitored

are carefully considered. Typical drilling techniques used

for monitoring well installation have been described by

Aller et al. (1989), Sara (1994) and USEPA (1992). As

such, it is only recently that these techniques are beginning

to be modified to reflect monitoring needs. Smearing of

borehole walls, compaction of borehole walls, transport of

formation material and drilling fluid into different zones are

all areas where artifacts are of concern.

The smearing of borehole walls is a concern where

conventional augering techniques are employed or where

casing is driven and then pulled back. The smearing effect

seals off fractures in fine-grained formations, thereby

potentially reducing the amount of flow to the well or even

sealing off the formation of concern entirely. Because

fractures are typically the most prominent pathways for

contaminant migration in the fine-grained formations, the

question arises as to whether or not the contaminant

pathway has been blocked such that the contaminant will be

present in the formation but not be found in the well. One

way to minimize smearing of the borehole wall is to

minimize auger rotation in the screened zone. The concept

is that if the auger can be simply “screwed” in and then

retracted without turning, the smearing will be less.

Although this can be performed relatively easily in most

formations, the typical drilling procedure used is to rotate

the auger to move cuttings up the annulus, thereby

minimizing the amount of shear that the rig must overcome

when withdrawing the augers. There is much practical

experience in this area, but little published research that

better defines the drilling process and the formation

constraints. The working group identified a research need

to develop more effective ways to minimize this smearing

artifact.

Compaction of borehole walls and transport of formation

material is of concern in both augering techniques, casing

driving, and in rotary drilling. Compaction of the borehole

walls is similar to smearing of the walls as discussed above

with the concern being that pathways and therefore

contaminants are possibly “shut off.” Transport of

formation material, along the borehole, downward into the

screened zone, is a concern where upper contaminant zones

are present. The amount of contaminated material necessary

to cause a detection with today’s detection limits of parts per

quadrillion is minimal. Several techniques for installing

monitoring wells in areas where this is a concern have been

successfully used. Keely and Boetang (1987) have written

about driving casing while augering. Other multiple casing
73

methods for installing surface casing through the

contaminated zone and then drilling deeper have also been

successful.

Drilling Fluids

There is substantial question created by the use of drilling

fluids during drilling with regard to artifact effects on the

monitoring well. Drilling fluids can be air, water or drilling

mud. Using air as a drilling fluid can cause chemical

changes in the formation due to oxidation. Lubricants in air

necessary for compressor operation can result in the

introduction of hydrocarbons through air entrainment into

the formation. Use of an in-line filter that has not reached

its useful life capacity can minimize this risk.

Adding water as a drilling fluid can: flush and dilute

indigenous water; change formation chemistry; precipitate

certain minerals, possibly seal off preferential pathways of

flow to the well, and substantially alter the soil and water

chemistry in the vicinity of the bedrock. Where water is

used, the amount of water added should always be measured

and the chemistry of the water should be known. Where

water is added, the question of how much water must be

removed in order to “get all the water back out” assumes

that no chemical changes have taken place and it is a matter

of just recovering the injected water. Although the amount

of water varies by formation and flow characteristics, the

rule of thumb for removal of three times the volume added

is frequently quoted. Using no water or minimizing water

use is the preferred alternative. One alternative is to pump

out and reuse formation water where the use of water is

needed. Some of the problems with the uses of drilling

fluids are discussed in Schalla (1986).

Other concerns related to drilling fluid include the use of

drilling mud and additives and the use of lubricants on

piping and joints. Drilling with mud involves the formation

of a filter cake on the borehole wall as an integral part of the

drilling process. Mud intrusion into the formation occurs as

part of the drilling process. The depth of intrusion is a

function of the geologic formations as imparted by other

factors such as wall cake thickness and character. There is

always concern that the mud filter cake (wall cake) will not

be completely removed during the development process.

The result will be that, once again, significant pathways of

contaminant migration are permanently sealed off

(particularly in fracture-controlled flow). Of concern also is

that the clay-sized particles in the mud will attenuate any

electrically charged contaminants that do migrate toward the

well. Because mud is difficult to remove during the

development process, the use of mud should be restricted.

The use of additives in mud to overcome drilling difficulties

is also inappropriate. This practice simply furthers the

potential to cause physical or chemical changes that will be

introduced and remain as a result of the particular additive.

Brobst and Brobka (1987) discuss the effects of drilling

fluid on sample chemistry.

The use of downhole hammer lubricants and petroleum-based

lubricants on rotary drill pipe connections are of concern in

monitoring well drilling. However, some type of lubricant is

necessary for the drilling machinery to operate without

damaging the equipment. Where lubricants are essential, there

are non-petroleum based synthetics that are better choices for

lubricants.

Installation Artifacts

Casing/Screen Artifacts

Installation artifacts are a result of casing and screen

materials and/or annular fill materials. Artifacts due to

casing and/or screen materials include: long-term

incompatibility of casing/screen materials with formation

water quality; short-term casing/screen impacts by sorption/

desorption and leaching; impacts by solvent cements; and

leakage through casing joints. The ability of the casing and

screen material to resist degradation by the water with

which it will come into contact is paramount from two

different standpoints. First, what are the immediate water

quality effects during sampling and second, what are the

water quality effects when the casing/screen materials

deteriorate and allow water to migrate along the borehole?

The corrosion of metal casing has long been a concern in

acidic environments. The swelling of polyvinyl chloride

(PVC) by solvents is also documented. These are real

concerns that should be addressed by choosing casing/

screen materials that are long-term compatible. When wells

are installed to meet short-term goals (ie. less expensive

materials that might not be longterm compatible), the well

may or may not stay a short-term well. Frequently, wells

are required to remain in place for a regulatory purpose. In

other situations, cost of abandonment may become a factor

as funding or priorities change and the well will remain.

Finally, personnel familiar with the concept of short-term

versus long-term well installation and any anticipated

incompatibility problems may be disengaged from the job.

With this loss, others may not recognize that a potential

problem exists and the well is left in place. Therefore,

prudent monitoring well installation does not employ

incompatible casing/screen materials.

Short-term effects on sample integrity due to: leaching of

analytes of interest or analytes that interfere with analyses;

sorption of analytes of interest; possible desorption of

analytes of interest should water quality improve; and

diffusion of organics through polymeric materials, are also

of concern in some environments. Significant discussions
74

of the “real effects” of different materials including PVC

and PTFE are included in the following papers: BianchiMosquera and Mackay (1992), Cowgill (1988), Gillham and

O’Hannesin (1990), Hewitt (1989), Hewitt (1992), Jones

and Miller (1988), Parker (1991), Parker (1992), Parker et

al. (1990), Reynolds et al. (1990), Miller (1982), Reynolds

and Gillham (1985), Barcelona and Helfrich (1986),

Barcelona and Helfrich (1988), Barcelona et al. (1983),

Barcelona et al. (1985), Barcelona et al. (1988), Marsh and

Lloyd (1980), Barcelona (1984), Junk et al. (1974), Boettner

et al. (1981), Curran and Tomson (1983), Parker and Jenkins

(1986), Tomson et al. (1979), and Rivett et al. (1991).

The use of solvent cements in joining polymer casings is

inappropriate due to dissolution of the cements and

subsequent detection in samples from the wells. Sosebee et

al (1983) have documented these problems. The industry,

therefore, uses flush-joint threaded casing. However, these

joints are of concern when, or if, they are not sealed

properly and allow water to enter the well. The use of orings and/or wrapping national pipe thread threads (NPT)

with polyfluoromer tape minimizes leakage potential. If

tape is used on threads that are not NPT, the tape may

actually increase the potential for the joint to leak. The

American Society for Testing and Materials (ASTM)

Standard F-480 specifies pressure ratings for the joints in

polymer casing. Usage of materials following this standard

with a pressure rating of 25 pounds per square inch (psi) or

greater will minimize the potential for joint leakage.

Annular Fill Artifacts

The materials that may be used in the annular space during

monitoring well installation include: the filter pack; fine

sand on top of the filter pack to minimize grout

contamination; bentonite; bentonite/cement mixtures and

cement. All materials may cause sampling artifacts if not

installed properly or used in inappropriate situations. A

filter pack should consist of inert, non-reactive materials.

Not all sands are silica and therefore the material used as a

filter pack should be verified during monitoring well

installation.

Bentonite is typically added to a monitoring well above the

filter pack to minimize grout contamination. The use of

bentonite as a “seal” against contaminants is a misnomer.

Bentonite is available in a variety of commercial forms and

is added either in solid form (by pellets) or in the form of a

slurry. If bentonite is introduced in such a manner that

formation water moving toward the well screen contacts the

bentonite, sorption of electrically-charged contaminants,

both organic and inorganic, sorption by the clay particles

will occur. In this setting, contaminants within the

formation may either be detected in the well in

concentrations less than the formation, or not at all. One

solution to this situation is to add a physical barrier between

the bentonite and the filter pack, such as a packer. Another

approach to this problem is to add a layer of fine sand

between the bentonite and the filter pack.

Many questions about the proper use of, and effective

emplacement of, bentonite have arisen. If granular

bentonite is added to a well and adequate time for hydration

is not allowed, the bentonite may not provide the intended

purpose. The time of hydration varies by pellet size, but it

is questionable whether or not a hydration time less than

two hours is appropriate in any situation. When granular

bentonite is added through a standing water column, there

are questions about whether or not the pellets will “bridge”

selectively and thus leave pathways for unwanted water to

enter the annular space. Although many pellets are “coated”

to delay instant hydration when falling in a water column, it

is generally agreed that the maximum column of standing

water through which pellets should be attempted to be

dropped is 30 feet. Documented studies by manufacturers

or researchers are necessary before this recommendation can

be changed.

Bentonite is a clay with a high shrink-swell potential.

This property makes it effective as long as it remains

hydrated. When the bentonite dries out, it shrinks and

cracks. The use of bentonite in the unsaturated zone is

questionable because of the ability of the bentonite to

stay hydrated in the unsaturated zone. Whether or not

fully hydrated bentonite will stay saturated in the

unsaturated zone in the presence of capillary action on

the clay is questionable. The conditions under which the

bentonite will remain hydrated are related to the

formation material with which it is in contact. If the

bentonite does not stay saturated, the clay will crack and

an unspecified amount of time and moisture will be

necessary to re-swell the clay. The concern is that these

cracks will allow rapid movement of contaminants along

the annular space in this area until sufficient moisture rehydrates the bentonite. Restricted use of bentonite in the

unsaturated zone is recommended until research has

been conducted to determine whether or not fully

hydrated bentonite placed the unsaturated zone will

remain fully hydrated. Field experience indicates that in

some cases, the bentonite dehydrates. Research is

needed.

Use of bentonite as an additive to cement is a popular

practice. Originally, the bentonite was added to control

shrinkage of the cement when it cured and to improve its

pumpability. Halliburton research on bentonite/neat cement

mixtures indicates that bentonite does not control

shrinkage. Research is needed to determine if and where

the use of bentonite/cement mixtures are appropriate and/or

desirable.

Cement is typically used to fill the annular space above a
75

bentonite “plug” to the surface. Cement, if it enters the

filter pack, can significantly raise the pH of the water.

Concerns about the precipitation of cations, and elevation of

specific conductance are valid if cement contamination of

the filter pack occurs. Steps should be taken to make sure

that either fine sand or properly emplaced and hydrated

bentonite is used in the well and properly separated from the

well screen. Mixing neat cement at a ratio of 5.5 to 6

gallons of water per 94 pound bag of cement will also

minimize grout infiltration by decreasing the mobility of the

grout. When adding cement to the well below the water

table, or in wells with an unsaturated zone greater than 20

feet, the grout should be emplaced using a tremie discharge

pipe and pumping grout from the bottom of the formation

until returns are seen at the surface. Emplacing cement

with a submerged discharge tremie pipe reduces the risk of

contamination, through weak zones developing in the grout.

Development

Development is the process by which all artifacts from

drilling are supposed to be removed from the well.

However, development becomes more difficult when it must

penetrate into the filter pack and/or formation. For example,

the cutting head of a 4.25-inch ID Central Mine Equipment

auger creates a borehole of 8.25 inches. However, Mobile

augers create an 11 inch borehole for a 4 inch ID auger

flight. If two inch monitoring wells are installed in this

borehole, the filter pack thickness will range between

approximately 3 inches and 4.5 inches if the screen is

perfectly centered in the borehole. Removing smearing

effects from the borehole wall through the filter pack is

difficult, if not impossible. Other methods have similar

limitations, particularly those such as mud rotary that

produce a “skin” effect on the borehole wall. It is very

difficult to remove this modified surface from the entire

screen length.

Other concerns about development relate to air entrainment,

addition of water, and problems caused by excessive

sediment in the well during development. Entrainment of

air in the formation has traditionally been associated with

development by air lifting. Acceptable methods of

development in monitoring wells do not include air lifting

because of the potential for the air to cause chemical

alteration of the formation water, to oxidize and/or

precipitate constituents within the formation and to

physically “block” the formation with air if the well

becomes “air-locked”.

The addition of water during the development process is a

questionable practice. The addition of water to the

formation dilutes the indigenous water and can cause

chemical changes resulting in undesirable chemical

reactions within the formation. Precipitation of constituents

can physically block pathways of migration for

contaminants. Water may not be able to be retrieved from

the formation and thus may alter the water chemistry

permanently. Most formations should yield enough water to

be developed using the formation water if proper methods

and techniques are utilized. The addition of water to

compensate for choosing an inappropriate technique is not

acceptable. If enough time is allotted, most wells can be

developed with formation water. This may involve the

process being repeated over a number of days in low yield

wells. If water is added, the amount of water that will need

to be removed varies based on formation, flow paths and

flow regimes. In the absence of better data, the rule of

thumb is to remove no less than three times the volume of

water added. The water should be removed as soon as

possible.

Excessive sediment in a monitoring well during

development is a concern because of the potential to force

the fine sediments into the formation and not be able to

retrieve the sediments. Clay-size particles and some clay

mineral particles have the potential to sorb contaminants

from ground water and also to reduce pathways of migration

for contaminants. The latter is especially true in formations

where flow is fracture-controlled. The problem of excessive

sediment in a monitoring well during development can be

minimized by using appropriate development methods and

proper techniques. The use of a well “sump” is not a

substitute for inadequate development or improper well

design.

Monitoring well development should be conducted using

only a combination of the following methods: surging/

pumping or overpumping/backwashing. Surging is

conducted by using a surging tool that is manufactured or

made in the field. The critical design elements of a surging

tool are a relatively close fit with the casing and means in

the tool by which the water may pass through the tool so

that the casing will not collapse during development. During

surging, the development takes place by surging an interval

(usually approximately two feet), beginning at the top of the

screen and continuing until the screen is completely

developed. The sediment-laden water must be removed

between every interval or two (depending on the amount of

fines in the water) to minimize forcing fine material too far

into the formation.

Overpumping and backwashing rely on the same principle

of moving water in and out of the formation to dislodge and

move the finer particles into and out of the well. Methods

that only pump in one direction are usually ineffective in

proper well development. Historically, a major problem has

been that most drilling rigs that are used to install

monitoring wells are not properly equipped to develop

monitoring wells. This is particularly true with regard to

surging and pumping, alternatively.
76

The most frequently made mistake in well development is

“giving up.” It is important to recognize that adequate

development takes time. Development time may range from

two hours to more than three days in order to be effective.

Remember that the thicker the filter pack, the longer the

development time required, and the greater the energy

requirement for surging.

Properly designed wells with appropriately sized well screen

and filter packs also minimize well development time.

Traditionally monitoring wells were installed with either a

10 or 20-slot screen and a filter pack of material that would

bridge (80% or more) on the selected slot size. This

“design” is often unsuitable in extremely fine-grained silts

and clays, with the resultant wells being high in turbidity

when sampled. Very little research has been done on very

fine grained, pre-packed filters, ceramic filters, etc. and their

impact on sample quality. References on monitoring well

design and found in the American Society for Testing and

Materials Standard D5092-90 (1990), Aller et al. (1989) and

Nielsen (1991).

Questions as to how much of a filter pack volume will be

removed during development and the effect that volume

reduction will have on the integrity of the well are

significant. Similarly, loss of the filter pack to the formation

and concomitant volume reduction and associated effects

were also questioned. It was agreed that appropriately

designing the well with a screen and filter pack picked for

the formation at hand should minimize this concern.

However, research into these related problems is warranted.

Other Artifacts

Other artifacts that may affect the chemistry of water in the

monitoring well include: microbial activity in the well;

interzonal leakage across a screened zone; and migration

along a casing due to ineffective grout adherence to casing

materials. Microbes in the well, particularly what are

known collectively as “iron bacteria”, are not uncommon.

These microbes have the capability to alter the natural

chemical environment and change reducing conditions to

oxidizing conditions and vice versa. The magnitude of the

effect of these organisms are not known because the

organisms are not well understood. In the water well

industry, these organisms are considered as a “nuisance”

because they are not toxic. The traditional methods of

rehabilitation that have been used to temporarily destroy

their protective sheaths are inappropriate in a monitoring

well due to addition of chemicals to the well. The chemical

methods used in water wells have been relatively ineffective

over time. The full effect of these organisms in monitoring

wells is not known. This is an area where research is

warranted. Clearly, field procedures are lacking.

Where screens cross more than one zone of flow with

different hydraulic gradients, two concerns are raised. First,

the potential for mixing in the borehole exists; and second

the opportunity for interzonal mixing through the well and

into the zone with the lower hydraulic head exists. The

concern can be minimized by understanding the flow

characteristics of the site, developing a site hydrogeologic

model and using short, specific screen lengths were the

situation is anticipated. It is commonly, and incorrectly

assumed, that there is generally “mixing” in an aquifer that

is considered to be hydraulically “isotopic”. This fails to

recognize that most samples are zone specific, and

dependent upon specific flow lines.

Questions as to the adherence of casing to certain types of

grout have been raised as a possible source of contamination

along the casing. Kurt and Johnson (1982) and Molz and

Kurt (1979) have looked at some of the issues of grout

adherence to casing and effects of temperature on casing

materials.

Well Design

Traditional Thinking

Many of the artifacts mentioned above are the result of the

acceptance and desire to install traditional monitoring wells

with traditional methods. Indeed the most frequently

installed size monitoring well is two inch ID, although some

states require four-inch wells in certain programs such as

hazardous waste monitoring or underground storage tanks.

Further, company policies may also dictate the installation

of four-inch monitoring wells. Some deeper wells are also

larger diameter and some older wells were built in the days

when sampling equipment required larger diameters.

Wells are traditionally installed to address one or more of

the following objectives: regulatory monitoring; water level

measurement; hydraulic conductivity determination; or “

other investigative reasons”. Inherent in the “typical

thinking” is the necessity to design a monitoring well that

will yield enough water to collect the volumes of water

necessary to test for regulatory purposes. While this may be

desirable, it may not always be practical in low-yield

formations.

Low Yield Formations

Conventional monitoring well designs are inadequate to

meet all the objectives of representative monitoring in lowyield formations. In order to obtain a reliable water quality

sample, it is desirable not to dewater the top of the screen

when collecting a water sample. It is desirable, in fact, not
77

to lower the water level at all. This either requires a change

in thought pattern or an inventive sampling methodology

(which was summarily decided to be outside the scope of

this group and to be determined by others).

If it is possible to change our frame of reference, then other

options for designing low yield wells exist. Perhaps special

purpose wells should be considered. The use of pore water

samples from cores may be appropriate in some situations.

McKay (1993) has used one-half inch well completions in

low yield formations in order to try to minimize many of the

artifacts previously discussed. Installation of a small

diameter well in a pushed shelby tube, split spoon hole or

with a drive point may minimize the smearing effect

associated with augering. These types of completions will

necessarily limit the sample volume available at any one

time. Typically the sample collection rate should be limited

to the recovery rate of the well. If the water level is held

constant in larger diameter wells, the effect is the essentially

the same.

Determination of what is a low-yield formation is

particularly important, but difficult with current methods

and thinking. It is inappropriate to use only grain size for

determination as to when a conventional well design is

appropriate. The depositional model, stratigraphic model

and diagenetic model are all essential. In fine-grained

formations, the fracture flow pathways may override the

significance of grain size. McKay et al. (1993a; 1993c) has

discussed flow and flow rates in fine grained deposits. One

strongly identified research need is for development of

better and more accurate ways to measure hydraulic

conductivity on a meaningful scale in low-yield formations.

Other traditional problems with turbidity in fine-grained

formations were raised. A research need was identified to

determine whether or not low flow sampling techniques

always yielded turbidity-free samples, (e.g. how is colloidal

transport being sampled?).

Fractured Rock Completions

Open hole completions have been common in the water well

industry in fractured rock in order to maximize the amount

of water that enters the borehole. However, open hole

completions in monitoring wells are not acceptable.

Fractured rock monitoring wells should be designed to

prevent cross contamination between zones of different

hydraulic head as discussed above. The identification of

specific zones to be monitored is often very difficult in a

rock hole. This technology is to be dealt with elsewhere.

Overall Monitoring Issues

The discussion about the “true” definition of aquifer in the

monitoring well context has been discussed since it has been

desirable to monitor low yield formations. However, the

important concept to remember is that monitoring of an

aquifer may be desirable, but monitoring of pathways for

migration is essential. This necessitates monitoring of zones

that have not traditionally been considered as aquifers.

An adequate monitoring well network cannot be designed

until a site investigation is completed. For site investigations

and monitoring well installation to be effective and to

reduce unwanted artifacts, qualified, trained geologists as

well as drillers and helpers are needed in the field.

Unfortunately, less experienced geologists are traditionally

relegated to the field while the “more experienced”

personnel move on to more prestigious office and

management assignments. This is due, in part, to costsaving measures by the customer as well as the provider.

Further, many of the “field personnel” are not adequately

trained, if at all, to make the important field decisions.

Indeed, many do not even know that they are making

important decisions. Either a complete attitude change is

necessary to assign trained individuals to the field, or a more

formalized training process is necessary for field personnel.

Certification is not necessarily the answer; training is.

Part of a successful site investigation is in depth description

of the geology and hydrogeology at the site. In order for the

appropriate level of detail to be developed complete and

accurate description of samples is necessary. Part of this

process relates to training and experience; part relates to the

type of information that needs to be collected. There are

many classification systems that provide guidance as to the

types of information to record when visually classifying

samples. The Unified Soil Classification System is most

frequently used because it was developed to identify

important engineering properties. While these

characteristics are important, additional descriptions such as

environment of deposition, diagenetic changes,

hydrostratigraphic units and lithofacies descriptions are

equally important for determining pathways of migration.

Characteristics, such as color, must be defined in a

reproducible manner. An accepted classification system or

combination of systems is necessary to adequately describe

lithology for monitoring well purposes. The use of standard

references, such as color charts for both soils and rock, add

reproducibility to the description. Descriptions of many of

the parameters that should be recorded are described in Sara

(1994).

Monitoring well design, construction and development are

the most important part of a monitoring system. When

compared with analytical costs, the installation and

development is the least expensive portion of the sampling

process. However, costs are typically cut during the

installation phase. Later, considerable sums of money are

spent on repeat analytical results to justify or rectify poor or

inadequate installation. Awareness needs to be raised as to
78

the importance of spending adequate sums of money upfront for long-term benefit.

Questions were raised as to whether or not it is appropriate

to make generalizations about design considerations for

hydrogeologic settings. The consensus was that for

overview purposes, generalizations were appropriate, but for

detailed design this approach was inappropriate. Site specific

information and monitoring objectives should always be

considered in lieu of using generalizations.

One last statement about monitoring well installation that

has been widely publicized, but that is still important is the

presence of adequate annular working space during

monitoring well installation. A minimum two inch working

annular space is necessary to minimize bridging of annular

fill materials and to maximize the central placement of the

screen within the well. However, it must be remembered

that where this annular space is filled with gravel or sandpack around the screen, the larger the annular space the

more difficult the development.

Summary of Important Items

General

Although many items were discussed the major points of

discussion are summarized as follows:

1) A site investigation must be completed before an

adequate monitoring well network can be chosen.

2) We are interested in monitoring “pathways of

migration”, not necessarily “aquifers” by

definition.

3) Do not skimp on monitoring well costs because

design, construction and development are the most

important parts of the system, and the least

expensive over the long haul.

4) Conventional monitoring well designs are

inadequate to meet all objectives in low hydraulic

conductivity formations. (Detection monitoring

water sample volumes may not be possible.)

Grain size alone should not be used to determine

when conventional wells are appropriate. We need

to change our frame of reference. We are not

monitoring system “averages” or “typical” zones.

We must monitor potential pathways of

contamination.

5) Methods are needed to monitor in low hydraulic

conductivity formations. Better ways to measure

and evaluate hydraulic conductivity in low

hydraulic conductivity formations are needed.

6) There is a need to expand (and possibly

standardize) existing visual classification systems

for samples (i.e. USCS or other) to include

geologic interpretation of environment of

depositions and hydrostratigraphic units.

7) The need for qualified, trained field personnel is

emphasized.

Special Considerations

The following were considered important special

considerations that should be considered in the future:

1) The use of special purpose wells in low hydraulic

conductivity formations (i.e. one half-inch well,

lysimeters) should be considered;

2) The use of pore water samples should be

considered in low hydraulic conductivity

formations;

3) Long, open-hole completions in fractured rock are

inappropriate due to the potential for interformation migration; and

4) Guidance on well design can be developed for

hydrogeologic settings where broad-scale overview

and knowledge transfer is the objective. However,

this approach is not appropriate for detailed well

design.

Research Needs

1) Smearing along borehole walls during monitoring

well installation, particularly in auger drilling, was

identified as a problem particularly in low

hydraulic conductivity formations and/or where the

clay content of the formation is relatively high and

flow is primarily in fractures. A research need was

identified to better define the components that

cause smearing and to suggest and/or design

alternatives to overcome and/or minimize this

problem.

2) Bentonite is sometimes used in the unsaturated

zone as an annular fill material. A research need

was identified to answer questions as to whether or

not fully-hydrated bentonite placed in the

unsaturated zone remains fully hydrated over time.

If the bentonite desiccates in only certain

situations, these circumstances need to be

identified.
79

3) Low hydraulic conductivity formations are difficult

to monitor using traditional monitoring well

designs. However, effectively defining a low

hydraulic conductivity formation is even more

difficult. Traditional methods for measuring

hydraulic conductivity have been proven to yield

hydraulic conductivity values orders of magnitude

too low. A research need was identified to develop

testing methods (both in the laboratory and in-situ)

that will be more representative of the flow

characteristics of the formation that intersects the

fractures as well as through the bulk of the

formation.

Guidance Needs

There was strong agreement that guidance on

wells in low conductivity formations needs to be

developed.

Reference Documents

There are many documents that will help to understand the

issues that were discussed by this group. The following

documents provide basic information and contain references

on additional subjects. The reference section contains

additional references that deal with more specific subject

matter.

1) American Society for Testing and Materials

Standard D5092-90, Standard Practice for Design

and Installation of Ground Water Monitoring Wells

in Aquifers, vol. 4.08, Philadelphia, Pennsylvania,

12 pp..

2) American Society for Testing and Materials,

(1994). Ground Water and Vadose Zone

Investigations, Philadelphia, Pennsylvania, 396 pp.

3) Aller, L., T. W. Bennett, G. Hackett, R. J. Petty, J.

H. Lehr, H. Sedoris, D. M. Nielsen and J. Denne,

1989. Handbook for the Suggested Practices for

the Design and Installation of Ground-Water

Monitoring Wells, National Water Well

Association, Dublin, Ohio, 398 pp.

4) USEPA, 1992. RCRA Ground-Water Monitoring:

Draft Technical Guidance, Office of Solid Waste,

EPA/530-R-93-001, PB93-139-350, Washington,

DC.

5) Sara, M. N., 1994. Standard Handbook for Solid

and Hazardous Waste Facility Assessments, Lewis

Publishers, Ann Arbor, Michigan.

6) Nielsen, D. M., ed., 1991. Practical Handbook of

Ground-Water Monitoring, Lewis Publishers,

Chelsea, Michigan, 717 pp.

7) Driscoll, F. G., 1986. Groundwater and Wells,

Johnson Division, St. Paul, Minnesota, 1089 pp.

References

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Specification for Thermoplastic Well Casing, Pipe and

Couplings, Made in Standard Dimension Ratio (SDR), SCH

40, SCH 80, Standard F-480-94, vol. 8.04 Philadelphia,

Pennsylvania, 25 pp.

Barcelona, M. J., 1984. TOC Determinations in Ground

Water, Ground Water, vol. 22, no. 1, pp. 18-24.

Barcelona, M. J., G. K. George and M. R. Schock, 1988.

Comparison of Water Samples form PTFE, PVC and SS

Monitoring Wells, United States Environmental Protection

Agency, Office of Research and Development,

Environmental Systems Monitoring Laboratory, Las Vegas,

EPA 600/X-88/091, 37 pp.

Barcelona, M. J., J. P. Gibb and R. Miller, 1983. A guide to

the Selection of Materials for Monitoring Well Construction

and Ground-Water Sampling, Illinois State Water Survey,

SWS Contract Report 327, Champaign, Illinois, 78 pp.

Barcelona, M. J., J. A. Helfrich and E. E. Garske, 1985.

Sampling Tubing Effects on Ground-Water Samples,

Analytical Chemistry, vol. 57, no. 2, pp. 460-464.

Barcelona, M. J. and J. A. Helfrich, 1986. Well

Construction and Purging Effects on Ground-Water

Samples, Environmental Science & Technology, vol. 20, no.

11, pp. 1179-1184.

Barcelona, M. J. and J. A. Helfrich, 1988. Laboratory and

Field Studies of Well-Casing Material Effects, Proceedings

of the Ground Water Geochemistry Conference, National

Water Well Association, Dublin, Ohio, pp. 363-375.

Bianchi-Mosquera, G. C. and D. M. Mackay, 1992.

Comparison of Stainless Steel vs. PTFE Miniwells for

Monitoring Halogenated Organic Solute Transport, Ground

Water Monitoring Review vol. 12, no. 4, pp. 126-131.

Boettner, E. A., G. L. Ball, Z. Hollingsworth and R. Aquino,

1981. Organic and Organotin Compounds Leached from

PVC and CPVC Pipe, United States Environmental

Protection Agency Report, EPA/600/1-81-062, 102 pp.
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Brobst, R. B. and Buszka, P. M., 1986. The Effect of Three

Drilling Fluids on Ground Water Sample Chemistry, Ground

Water Monitoring Review, vol. VI, no. 1, pp. 62-70.

Cowgill, U. M., 1988. The Chemical Composition of

Leachate from a Two-Week Dwell-Time Study of PVC Well

Casing and Three-Week Dwell-Time Study of Fiberglass

Reinforced Epoxy Well Casing, in A. G. Collins and A. I.

Johnson, eds., Ground-Water Contamination: Field

Methods, American Society for Testing and Materials,

Philadelphia, Pennsylvania, STP 963, pp. 172-184.

Curran, C. M. and M. B. Tomson, 1983. Leaching of Trace

Organics into Water from Five Common Plastics, Ground

Water Monitoring Review, vol. 3, no. 3, pp. 68-71.

Gillham, R. W. and S. F. O’Hannesin, 1990. Sorption of

Aromatic Hydrocarbons by Materials Used in Construction

of Ground-Water Sampling Wells, in D. M. Nielsen and A. I.

Johnson, eds., Ground-Water and Vadose Zone Monitoring,

American Society for Testing and Materials, Philadelphia,

Pennsylvania, STP 1053, pp. 108-122.

Hewitt, A. D., 1989. Leaching of Metal Pollutants from

Four Well Casings Used for Ground-Water Monitoring,

CRREL Special Report 89-32, U. S. Army Cold Regions

Research and Engineering Laboratory, Hanover, New

Hampshire.

Hewitt, A. D. , 1992. Potential of Common Well Casing

Materials to Influence Aqueous Metal Concentration,

Ground Water Monitoring Review, vol. 12, no. 2, pp. 131-

136.

Jones, J. N. and G. D. Miller, 1988. Adsorption of Selected

Organic Contaminants onto Possible Well Casing Materials,

in A. G. Collins and A. I. Johnson, eds., Ground-Water

Contamination: Field Methods, American Society for

Testing and Materials, Philadelphia, Pennsylvania, STP 963,

pp. 185-198.

Junk, G. A., H. J. Svec, R. D. Vick and M. J. Avery, 1974.

Contamination of Water by Synthetic Polymer Tubes,

Environmental Science and Technology, vol. 8, no. 13, pp.

1100-1106.

Keely, J. F. and K. Boetang, 1987. Monitoring Well

Installation, Purging, and Sampling Techniques - Part I:

Conceptualizations, Ground Water, v. 25, no. 3, pp. 300-

313.

Kurt, C. E. and R. C. Johnson, 1982. Permeability of Grout

Seals Surrounding Thermoplastic Well Casing, Ground

Water, vol. 20, no. 4, pp. 415-419.

Marsh, J. M. and J. w. Lloyd, 1980. Details of

Hydrochemical Variations in Flowing Wells, Ground Water,

vol. 18, no. 4, pp. 366-373.

McKay, L. D., J. A. Cherry and R. W. Gillham, 1993a.

Field Experiments in a Fractured Clay Till: 1. Hydraulic

Conductivity and Fracture Aperature, Water Resources

Research, vol. 29, no. 4, pp. 1149-1162.

McKay, L. D., R. W. Gillham and J. A. Cherry, 1993b.

Field Experiments in a Fractured Clay Till: 2. Solute and

Colloidal Transport, Water Resources Research, vol. 29, no.

12, pp. 3879-3890.

McKay, L. D., J. A. Cherry, R.C. Bales, M.T. Yahya and

C.P. Gerba, 1993c. A Field Example of Bacteriophage as

Tracers of Fracture Flow, Environmental Science and

Technology, vol. 27, no. 6, pp. 1075-1079.

Miller, G. D., 1982. Uptake and Release of Lead,

Chromium and Trace Level Volatile Organics Exposed to

Synthetic Well Casings, Proceedings of the Second National

Symposium on Aquifer Restoration and Ground-Water

Monitoring, National Water Well Association, Dublin, Ohio,

pp. 236-245.

Molz, F. J. and C. E. Kurt, 1979. Grout-Induced

Temperature Rises Surrounding Wells, Ground Water, vol.

17, no. 3, pp. 264-269.

Parker, L. V. and T. F. Jenkins, 1986. Suitability of

Polyvinyl Chloride Well Casings for Monitoring Munitions

in Ground Water, Ground Water Monitoring Review, vol. 6,

no. 3, pp. 92-98.

Parker, L. V., A. D. Hewitt and T. F. Jenkins, 1990.

Influence of Casing Material on Trace-Level Chemicals in

Well Water, Ground Water Monitoring Review, vol. 10, no.

2, pp. 146-156.

Parker, L. V., 1991. Discussion of The Effects of Latex

Gloves and Nylon Cord on Ground Water Sample Quality,

by J. L. Canova and M. G. Muthig, Ground Water

Monitoring Review, vol. 11, no. 4, pp. 167-168.
81

Parker, L. V., 1992. Suggested Guidelines for the Use of

PTFE, PVC, and Stainless Steel in Samplers and Well

Casings, Current Practices in Ground Water and Vadose

Zone Investigations, in D. Nielsen and M. Sara, eds.,

American Society for Testing and Materials, Philadelphia,

Pennsylvania, STP 1118, pp. 217-229.

Reynolds, G. W. and R. W. Gillham, 1985. Absorption of

Halogenated Organic Compounds by Polymer Materials

Commonly Used in Ground-Water Monitors, Proceedings of

the Second Canadian/American Conference on

Hydrogeology, National Water Well Association, Dublin,

Ohio pp. 125-132.

Reynolds, G. W., J. T. Hoff and R. W. Gillham, 1990.

Sampling Bias Caused by Materials Used to Monitor

Halocarbons in Groundwater, Environmental Science

Technology, vol. 24, no. 1, pp. 135-142.

Rivett, M., S. Feenstra and J. Cherry, 1991. Field

Experimental Studies of a Residual Solvent Source

Emplaced in the Ground Water Zone, Proceedings of the

Conference on Petroleum Hydrocarbons and Organic

Chemicals in Ground Water, National Water Well

Association, Dublin, Ohio, pp. 283-299.

Schalla, R., 1986. A Comparison of the Effects of Rotary

Wash and Air Rotary Drilling Techniques on Pumping Test

Results, Proceedings of the Sixth National Symposium and

Exposition on Aquifer Restoration and Ground Water

Monitoring, National Water Well Association, Dublin, Ohio,

pp. 7-26.

Sosebee, J. B., P. C. Geiszler, D. L. Winegardner and C.

Fisher, 1983. Contamination of Ground Water Samples

With Poly (Vinyl Chloride) Adhesives and Poly (Vinyl

Chloride) Primer From Monitor Wells, in Proceedings:

American Society of Testing and Materials Second

Symposium on Hazardous and Industrial Solid Waste

Testing, ASTM Special Publication #805, pp. 38-49.

Tomson, M. B., S. R. Hutchins, J. M. King and C. H. Ward,

1979. Trace Organic Contamination of Ground Water:

Methods for Study and Preliminary Results, III World

Congress on Water Resources, Mexico City, Mexico, vol. 8,

pp. 3701-3709.
82

Well Purging and Sampling

Robert W. Puls and John F. McCarthy

Traditional approaches to purging and sampling ground

water involve purging a well at a high pumping rate until a

fixed number of casing volumes (usually 3-5) is evacuated,

followed by sample collection at a lower pumping rate.

This approach has raised concerns about the

representativeness of samples collected using these

methods, especially if the sampling objectives include

monitoring of contaminants. Briefly, the concerns include

entrainment of immobile particles (Puls et al. 1992) and the

possible need to filter samples to remove those artifacts

(Puls and Powell, 1992; Backhus et al. 1993), costs of

pumping and disposing of large volumes of contaminated

water (Barcelona et al., 1994; Korte and Kearl, this report),

and uncertainties in interpreting the source of the sampled

water (Martin-Hayden and Robbins, in revision). The goal

of this discussion group was to evaluate approaches to

purging and sampling and determine if new techniques

should be recommended. Group discussions addressed

questions related to the objectives of purging, methods of

well purging and sampling, the advantages and

disadvantages of low-flow rate purging, site-specific

considerations in purging and sampling methods, and tradeoffs among sampling devices.

The general consensus of the discussion group was that, in

many cases, new methods should be adopted for purging

and sampling wells; the recommended method is generally

referred to as low-flow, minimal drawdown purging and

sampling. The principal differences between this and more

traditional approaches centers on the rate of pumping and

the criteria for deciding that purging is complete. The

newer method calls for slow flow rates for purging and

sampling in order to minimize chemical and hydrological

disturbance in and around the well. Furthermore, the

completion of purging is gauged on site-specific chemical

criteria (stabilization of water quality parameters) rather

than on a fixed number of well volumes pumped.

Objectives of Well Purging

The objective of well purging is to obtain formation water

from the targeted sampling point with no alteration of water

chemistry. The location within the subsurface from which

that formation water is actually drawn depends on a number

of factors including how we purge. There was general

agreement among the members of the discussion group that

water in the well casing, and perhaps even water in the

screened interval of the well, is different than the formation

water. This is due to a variety of factors including the

following: gas diffusion into and out of the standing water

column, potential alteration of water chemistry from contact

with the well casing, filter pack and annular sealing

materials, and surface infiltration. The similarity of the

water in the screened interval to that of the formation will

depend on the following: ground water flow velocity and

direction, screen length, well diameter, well depth, distance

from the screen to the water table, geologic and hydrologic

heterogeneities in the screened interval and the degree of

connectedness of the well to the aquifer. It was also

generally agreed that these same factors and considerations

would apply whether the sampling approach involved

'portable', or 'semi-permanent' dedicated sampling systems,

multilevel samplers or whether the sampling was carried out

in monitoring wells or using screening tools (e.g.

Geoprobe). The volume of water that needs to be purged to

obtain formation water will, however, depend on the

particular sampling approach, and monitoring system

selected, and the hydrogeologic characteristics of the site.

Methods of Well Purging and Sampling

It was generally agreed by the discussion group that

disturbance of the sampling zone or point should be

minimized and that purging methods which tend to alter

water chemistry or the integrity of the sample should be

avoided. The objectives of the sampling program should be

considered in selecting a purging method. There was

general agreement that consistency and adequate

documentation are essential and currently lacking in many

sampling programs.

For purposes of site assessment and remedial performance,

low-flow purging which produces minimal drawdown of the

water table was generally recommended, with no change of

flow rates during sampling. Conceptually, formation water

flowing across the screened section of the well is sampled

no faster than it enters the well bore under natural

hydrological flow conditions. The criteria for the

appropriate rate for purging and sampling is hydrological:

pumping rates should produce no net (or at least minimal)

drawdown of the water table. There are several advantages

to this method, a principal one being that the volume of

purge water is much less than for more traditional purging

methods. Low-flow sampling conditions have been

demonstrated to remove water from only the screened zone,

without the need for packers to isolate the stagnant
83

overlying casing water (Powell and Puls, 1993; Gillham et

al. 1985; Robin and Gillham, 1987). Although flow rates

are slower, much less water needs to be purged, with the

benefit that, in contaminated sites, a much smaller volume

of water will require subsequent waste disposal. More

fundamentally, however, a key benefit of the decreased

volume of purge water is that a smaller section or volume of

the aquifer is sampled. This represents a significant

improvement in our ability to detect and resolve

contaminant distributions, which may vary greatly over

small distances in three-dimensional space.

The traditional method of evacuating a standard 3-5 well

volumes samples a much larger portion of the aquifer, and

provides a larger volume-averaged concentration. That

averaged value is directly related to the volume of water

purged, the geologic setting, and the placement of the

sampling point. For some sampling objectives, such as

determining a large volume-averaged number for water

resource analysis purposes, the traditional approach may be

valid. However, much of the discussion centered around

contaminant detection and long-term monitoring at landfills

and hazardous waste sites. In most cases, the large volume

of aquifer sampled complicates interpretation of data

concerning the concentration and spatial distribution of

contaminants. If the well screen is long and intersects only

a small portion of a contaminant plume, a biased low

concentration value would be produced due to mixing of

uncontaminated portions of the aquifer. Similarly, in a

fractured clay or rock, most of the water comes from the

fractures. Because the fracture porosity is so small, the

sampling process may draw in water from a very large

volume of the deposit. This could greatly dilute the

concentration of contaminants in the sample.

Recent research has highlighted the significant chemical and

physical heterogeneities that exist even within porous media

(Davis et al. 1993; Nikolaidis et al. 1994). Flow problems

analogous to those associated with fractured rock can occur

in granular aquifers due to vertical heterogeneities in

hydraulic conductivity in typically layered sediments (Hess

et al. 1991). For this reason, it was generally agreed that for

many sampling purposes the use of smaller screen lengths

(1-5 ft) was best. Multi-level samplers, which are available

in combination with pumps or which use dialysis cells for

the 'passive' collection of water (Ronen et al. 1987), were

also recommended for further resolution of the spatial

distribution of contaminants in a formation. These sampling

devices may the best choice for sampling water in lowpermeability formations and in fractured rock (in

combination with packers). It was suggested that low-flow

purging and sampling techniques or the use of multilayered

sampling devices might also be capable of obtaining useful

information in long-screened wells. However, this would

depend on the establishment of good hydraulic connection

between the well and the adjoining formation. This topic

requires additional research.

The group consensus was that common water quality

indicator parameters, such as specific conductance,

dissolved oxygen and turbidity should be used to determine

the endpoint of purging, i.e., when formation water has been

accessed. Ideally, the concentration of a contaminant (or

other species of interest) would be measured over time

during purging to determine when its concentration

stabilized. In most cases, this approach would not be

practical. However, some studies (Puls et al. in review;

Barcelona et al. 1994; Backhus et al. 1993) have indicated

correlation of some indicator parameters with different

classes of contaminants (e.g. dissolved oxygen with volatile

organic compounds, and turbidity with metals and

hydrophobic organic compounds). While the measurement

of dissolved oxygen can be problematic at low

concentrations (< 1 ppm), many reliable field-portable

chemical measurement techniques (colorimetric) and

improved dissolved oxygen probes have recently been

developed which should help in obtaining more accurate

and stable measurements. A conservative approach was

recommended which included the use of dissolved oxygen

and specific conductance for volatile contaminants,

turbidity, dissolved oxygen and specific conductance for

metals (and metalloids) and semi-volatiles, and perhaps also

the use of oxidation-reduction (redox) potentials in both

cases. It must be recognized that erroneous or highly

variable parameter measurements can result from improper

methods of sample collection or analysis. Dissolved oxygen

or electrode potential measurements will change rapidly if a

sample is open to the atmosphere, and turbidity can increase

within a few minutes if air is introduced into a sample

containing ferrous iron. In many cases, sampling

practitioners are using flow-through cells which can be

connected in-line with the sampling system. These devices

generally include most of the above-mentioned indicator

parameters as well as pH and temperature. The latter two

measurements are useful data, but are generally insensitive

as purging indicators. In addition to measurements to

determine stabilization of the water quality parameters,

time-series measurements of the change in the depth to the

water table should also be recorded to assure hydrologic

stabilization with minimal drawdown of the water table.

The frequency for measurement of the indicator parameters,

and the criteria to decide that the parameters are stabilized

needs to consider pump flow rate and the precision of the

monitoring instruments. Some suggested criteria were

discussed: stabilization to within 10% (for turbidity and

dissolved oxygen) for three consecutive readings taken three

minutes apart under conditions where flow rates ranged

from 100-500 ml/min; three successive readings within five

times the reproducibility of the instrument; and, individual

well evaluation of indicator parameter stabilization plots.
84

exist, caution should be exercised in acquiring and

interpreting the data from such sampling points.

The most important parameters affecting purge volume

appear to be hydraulic and geologic heterogeneity, water

chemistry, pumping rate, device size and whether the

sampling devices are used in a portable or dedicated

fashion. Significant reductions in purge volume have been

noted when the problems associated with disturbances

during installation of pumps immediately prior to sampling

are avoided (Puls and Powell, 1992). This can be achieved

by installing portable pumps at least a day before sampling,

or through the use of dedicated pumps. A thorough

economic analysis may show dedicated systems to be a costeffective alternative for routinely-sampled monitoring wells.

In general, the advantages of low-flow purging include the

following:

• low turbidity samples which are representative of

the 'mobile' load of contaminants present

(dissolved and colloid-associated),

• minimal disturbance of the sampling point,

• reduced stress on the formation (minimal

drawdown),

• less mixing of stagnant casing water with

formation water,

• reduced need for filtration and therefore less time

required for sampling,

• smaller purging and sampling volume which

decreases waste disposal costs and sampling time.

Whereas the disadvantages of low-flow purging are:

• resistance to change on the part of sampling

practitioners due to lack of long-term data base,

• problems with data comparison and interpretation

of temporal trends due to differences in sample

collection methods,

• increased time that may be required for purging

and sampling at slow flow rates,

• the need for additional (& costly) equipment,

• difficulty of implementation, and

• potential for increased gas exchange and sorption

of contaminants onto tubing surfaces due to

increased residence time of fluid in the tubing.

Recognizing the disadvantages, the advantages of the lowflow-rate sampling in providing a higher quality sample that

more closely represents the mobile dissolved and colloidal

components in the formation suggest that this is the

direction that the state of professional practice must

proceed.

Regardless of the purging and sampling protocols selected

for a particular sampling objective, proper well construction

The same use of indicator parameters was recommended in

fractured rock settings.

Finally, it was concluded that education and training of

ground-water samplers should be expanded, and

certification programs possibly initiated. It was strongly

recommended that EPA be involved in these technologytransfer activities. Field sample collection currently

represents the greatest potential source of error in site

assessment and remedial evaluations. Increased education

and certification and the establishment of quality-assured

and consistent sampling protocols is critical to the future

success of multi-million dollar environmental restoration

programs.

Low-Flow Purging

Low-flow purging refers to the intake velocity of the

sampling device downhole and the resulting induced

formation water velocity, not the average flow rate at the

surface. The latter can be manipulated using flow valves or

other obstructions to produce low surface flow rates while

the subsurface induced flow may be extremely rapid and

impart significant disturbance within the sampled zone. The

overall objective is a more passive approach to sample

extraction with the ideal being to match the intake velocity

with the natural ground water flow velocity thus inducing

minimal drawdown of the water table.

Required purge volume or duration is evaluated through

continuous monitoring of water quality parameters such as

dissolved oxygen, specific conductance, oxidation-reduction

(redox) potential and turbidity for evaluation of the presence

of formation water. Research has shown that purging at

these lower rates with various types of pumps (peristaltics,

low-speed submersibles, and bladder pumps) does indeed

produce low turbidity and generally high quality samples

(Puls et al. 1992; Kearl et al. 1992). A perceived

disadvantage of such strategies is the additional time

required to remove the traditional 3 to 5 casing volumes. In

general, however, the volumes required to access formation

water are much less than 3 to 5 casing volumes, and in

deeper wells are actually only fractions of a casing volume.

Indeed the volume of water extracted to access formation

water is generally independent of well size and capacity

(Puls et al. in review; Puls, this report). The criteria for the

initiation of sampling are stabilization of the water quality

indicator parameters listed above. It should be noted that

excessively stringent stabilization guidelines may result in

longer purging. If chemically distinct zones exist within the

formation adjacent to the screened interval, they may be

accessed with prolonged pumping and result in changes in

water quality indicator values. The design of such sampling

points should be discouraged; however where they already
85

and well development is important and intimately

interrelated to the issue of well purging. A detailed

understanding of the hydrologic and geologic variability of

the system is also essential in establishing sampling points

and in designing the overall sampling program. There was

general agreement among the group from a technical

perspective, that minimal drawdown, low-flow purging was

a better way to sample for most ground water sampling

programs.

Site-Specific Considerations

The overall goals of the sampling program or the sampling

objectives will drive how the sampling points are located,

installed, and the choice of sampling methods. Likewise,

site-specific hydrogeologic factors will affect these

decisions. Unlike water supply wells, wells installed for

ground-water quality assessment and restoration programs

are often installed in low water yielding settings. In fact, it

was the consensus of the group that the use of "typical"

ground-water monitoring wells in such locations should

undergo a serious review. Alternative types of sampling

points and sampling methods are needed in these types of

environments. The discussions focused on five general

classes of hydrogeologic settings:

• high permeability formations, screened below the

water table;

• high permeability, water table wells (i.e. screened

across the water table);

• low permeability formations, deep, screened below

the water table;

• low permeability formations, screened across the

water table; and

• fractured rock.

For the high permeability wells, either screened deep and

below the water table or screened across the water table, it

was generally agreed that use of low-flow purging and

sampling techniques was the preferred method for sample

collection in most instances. The use of low-flow techniques

were also advocated for the low-permeability, deep wells,

with the caveat being to avoid dewatering of the screened

interval. This may require extremely low-flow purging (<

100 ml/min) and may be technology-limited. Where devices

are not readily available to pump at such low flow rates, the

primary consideration was still to avoid dewatering of the

well screen. This may require repeated recovery of the water

during purging while leaving the pump in place within the

well screen. It was suggested that comparisons be made

between samples recovered using low-flow purging

techniques and using passive sampling techniques. The

latter would essentially entail acquisition of the sample with

no or very little purging using a dedicated sampling system

installed within the screened interval.

The most problematic of the above settings were those in

low permeability water table wells and fractured rock. In

the former case, there was a serious concern that an

adequate sample could not be obtained using traditional

monitoring wells and standard sampling devices. The group

consensus was that, once again, the primary consideration in

purging such wells was to avoid dewatering the well

screens. Use of low-flow techniques may be impractical in

these settings, depending upon the water recharge rates.

The sampler and the end-user of data collected from such

wells needs to understand the limitations of the data

collected, i.e. a strong potential for underestimation of

actual contaminant concentrations for volatile organics,

potential false negatives for filtered metals and potential

false positives for unfiltered metals. Once again it was

recommended that more passive sampling techniques be

investigated and compared with current and low-flow

purging techniques.

In fractured rock formations, a low- to no-flow purge was

recommended in conjunction with the use of packers to

isolate the sampling zone in the borehole. It is imperative in

such settings to identify flow paths or water-producing

fractures prior to sampling, using tools such as borehole

flowmeters. The spatial resolution issue referred to above is

particularly of issue in fractured rock. That is, the volume

purged can make a dramatic difference on the constituent

concentrations obtained.

For low-yielding wells or fractured rock formations, the

unnecessarily large sample volumes often required by some

regulatory programs is a significant problem. For example,

in a rock with a fracture porosity of 10-4, the 10 L sample

volume required by many protocols could conceivably

include the water from a volume of 100 m3 of rock. This

could greatly dilute the concentration of contaminants in the

sample and the concentrations may not be in equilibrium

with the adjoining matrix (McKay, this report). It was

strongly recommended that the different EPA programs

review their sample volume requirements. In many cases

they are unnecessary, and in fact have the result of

encouraging poor sampling practices.

Sampling Systems and Devices

The use of standard monitoring wells and devices to sample

ground water in low permeability formations should be

reevaluated and research should be directed toward the

development of alternative approaches. In most other

settings, many currently available devices (e.g. bladder

pumps, low-speed centrifugal submersible pumps etc.) are

entirely appropriate and adequate for the collection of water

samples. There was extensive discussion on the merits of
86

using bailers of any type. The majority of participants

agreed with the statement that "the standards of professional

practice have passed bailers by" for most situations. Bailers

were deemed useful in water table wells and for sampling

light non-aqueous phase liquids (LNAPL's). Variability in

sampling technique was considered a major limitation to

their use in providing representative and reproducible data.

Production of excessive turbidity and aeration were also

seen as significant drawbacks or limitations.

It was recommended that studies be undertaken to evaluate

the cost-effectiveness of using dedicated sampling systems

as opposed to portable sampling systems for some sampling

programs. Research has indicated (Puls, this report;

Barcelona, 1994) that the benefits of low-flow purging and

sampling techniques are more fully realized in such

sampling systems. These include: less purge volume, time

savings in the field and in field preparation, less

decontamination and production of additional wastes from

decontamination procedures, and improvements in sampling

consistency and sampling results (e.g. better

reproducibility). The potential disadvantages from dedicated

systems were unknown effects from system deterioration

over the long term and up-front costs for installation and

implementation.

Documentation

Throughout the group discussions, the topic of

documentation of all sampling activities, including sampling

preparation and subsequent sample handling, transportation

and storage was brought up. It was unanimously agreed that

current documentation efforts and documentation

requirements are inadequate, regardless of environmental

program. This was targeted as a major need or area for

improvement in the ground-water sampling field. Included

in the appendix of this document are examples of a fieldsampling log forms which would be useful for providing

some of this information. Regardless of the sampling

objective or sampling approach employed, insufficient

documentation will make the interpretation of the resulting

data inadequate.

Research Needs

Identified research needs by the group included the

following:

• more thorough comparison of low-flow sampling

data (unfiltered) with filtered conventional

sampling data,

• comparison of low-flow sampling and "passive"

sampling techniques,

• evaluations of cost-effectiveness of dedicated

sampling systems,

• development of new methods and instruments for

acquiring water samples in low water-yielding

formations.

References

Backhus, D.A., J.N. Ryan, D.M. Groher, J.K. MacFarlane,

and P.M. Gschwend. 1993. Sampling Colloids and ColloidAssociated Contaminants in Ground Water. Ground Water,

31(3), 466-479.

Barcelona, M.J., H. Allen Wehrmann, and Mark D. Varljen.

1994. Reproducible Well Purging Procedures and VOC

Stabilization Criteria for Ground-Water Sampling. Ground

Water, 32(1), .

Davis, J.A., CC. Fuller, J.A. Coston, K.M. Hess, and E.

Dixon. 1993. Spatial Heterogeneity of Geochemical and

Hydrologic Parameters Affecting Metal Transport in Ground

Water. USEPA Environmental Research Brief, EPA/600/S93/006, 22 pp.

Gillham, R.W., M.J.L. Robin, J.F. Barker, and J.A. Cherry.

1985 Field Evaluation of Well Flushing Procedures. API

Publ. 4405, 110 pp.

Hess, K.M., S.H. Wolf, M.A. Celia, and S.P. Garabedian.

1991. Macrodispersion and Spatial Variability of Hydraulic

Conductivity in a Sand and Gravel Aquifer, Cape Cod,

Massachusetts. USEPA Environmental Research Brief, EPA/

M-91/005, 9 pp.

Kearl, P.M., N.E. Korte, and T.A. Cronk. 1992. Suggested

Modifications to Ground Water Sampling Procedures Based

on Observations from the Colloidal Borescope. Ground

Water Monitoring Review, Spring, 155-160.

Martin-Hayden, J.M. and G.A. Robbins. 1994. Plume

Distortion and Apparent Attenuation Due to Concentration

Averaging in Monitoring Wells. In revision for publication

in Ground Water.

McKay, L., K. Novakowski, and J. McCarthy. 1994.

Ground-water Sampling of Fractured Clay and Rock. In

Ground Water Sampling Workshop, USEPA, Nov. 30-Dec.

2, 1993, Dallas, TX.

Nikolaidis, N.P., G.A. Robbins, M. Sherer, B. McAninch, G.

Binkhorst, and S.L. Suib. 1994. Vertical Distribution and

Partitioning of Chromium in a Glacio-Fluvial Aquifer.

Ground Water Monitoring and Remediation, .
87

Powell, R.M. and R.W. Puls. 1993. Passive Sampling of

Ground-Water Monitoring Wells Without Purging:

Multilevel Well Chemistry and Tracer Disappearance. J.

Contam. Hydrol. 12, 51-77.

Puls, R.W. and R.M. Powell. 1992. Acquisition of

Representative Ground Water Quality Samples for Metals.

Ground Water Monitoring Review, Summer, 167-176.

Puls, R.W., D.A. Clark, B. Bledsoe, R.M. Powell, and C.J.

Paul. 1992. Metals in Ground Water: Sampling Artifacts and

Reproducibility. Hazardous Waste & Hazardous Materials,

9(2), 149-162.

Puls, R.W. 1994. Use of Low-Flow or Passive Techniques

for Sampling Ground Water. In Ground Water Sampling

Workshop, USEPA, Nov. 30-Dec. 2, 1993, Dallas, TX.

Puls, R.W. and C.J. Paul. 1995. Low Flow Purging and

Sampling of Ground-Water Monitoring Wells With

Dedicated Systems. Accepted, Ground Water Monitoring

and Remediation, Winter issue, 1994.

Robin, M.J.L. and R.W. Gillham. 1987. Field Evaluation of

Well Purging Procedures. Ground Water Monitoring

Review,.7(4). 85-93.

Ronen, D., M. Magaritz and I. Levy. 1987. An In Situ

Multilevel Sampler for Preventive Monitoring and Study of

Hydrochemical Profiles in Aquifers. Ground Water

Monitoring Review, 7(4), 69-74.
88

Turbidity and Colloid

Transport

Joseph N. Ryan, Steve Mangion and Dick

Willey

Background

Realization of the potential role of colloids in facilitating

contaminant transport (McCarthy and Zachara, 1989) has

heightened our awareness of the need to obtain ground

water samples that are representative of the naturally mobile

colloids. Carefully collected field evidence shows that the

commonly-used sampling protocols (bailing, rapid

pumping) produce ground water samples in which colloids

have been artificially entrained (Puls et al., 1992; Backhus

et al., 1993). In such samples, the naturally mobile colloid

fraction is overestimated. That is, bailed and rapidly

pumped samples often contain substantial turbidity that is

not representative of conditions within the subsurface. In

practice, the suspended particles causing this turbidity have

been removed from the samples by filtering in the field.

Usually, membrane filters with 0.45 μm pores have been

used to remove turbidity despite the biases introduced by

their use (Kennedy et al., 1974; Danielsson, 1982; Johnson

and Wangersky, 1985).

Recently, the Solid Waste Program of the U.S.E.P.A. issued

regulations that banned the field filtration of ground water

samples (40 CFR, 1993). The ban requires samples from

ground water monitoring systems be analyzed for the total

amounts of contaminants in unfiltered samples. If the

samples have been obtained using techniques that overly

stress the subsurface system, the resulting samples may be

highly turbid. Such samples, when analyzed, typically have

high contaminant concentrations.

The field research cited above has also demonstrated that

ground water samples relatively free of turbidity can be

obtained without resorting to filtering by withdrawing

ground water at relatively slow rates. Collecting ground

water samples following these low-stress protocols requires

an investment in equipment and time that some site

investigators contend that they cannot afford. It should also

be noted that low-stress protocols minimize the amount of

purge water that may need special handling and eliminate

time needed to conduct the field filtration step.

The goal of these subgroup discussions was to reach a

consensus on the best protocol (based on current scientific

knowledge) for obtaining ground water samples that are

representative of the actual mobile colloid load. As a

premise to these discussions, the attendees agreed that, for

certain low-solubility contaminants like radionuclides,

metals, and high-molecular weight hydrophobic organic

compounds, research has shown that colloid-facilitated

transport is significant. The discussions leading to

consensus on following four important topics will be

presented in this report:

1. Criterion for Adequacy of Well Purging

2. Distinguishing Dissolved and Colloid-Bound

Contaminants

3. Distinguishing Mobile Colloids and Artifactual

Colloids

4. Identifying Sites with Colloid-Facilitated Transport

Potential

Owing to the recent promulgation of the U.S.E.P.A. ban on

field filtering, the discussions often included debates over

the adequacy of collecting turbid ground water samples and

“fixing” the improperly collected samples by field filtering.

After summaries of the consensuses on the four topics listed

above, this report will address field filtering.

Criterion for Adequacy of Well Purging

A suspended sediment concentration criterion should be

established to obtain ground water samples that are

representative of the mobile colloid load. This criterion

should specify that the suspended sediment concentration

should reach a stable level during purging and prior to

sampling. This criterion should be applied in a manner

analogous with the monitoring of other parameters during

purging; i.e., the sample turbidity should be monitored

during purging and purging should continue until a stable

turbidity is achieved. The best means to achieve the stable

suspended sediment concentration is through pumping the

ground water from the well. Based on the scientific

evidence currently available, low-stress purging is

recommended. The best way to specify low-stress pumping

is to require minimal or no drawdown of the water level.

The scientific evidence presented at the workshop clearly

demonstrated that the suspended sediment concentration of

the sample decreases during purging to some stable level. It

is this stable suspended sediment concentration that is
89

representative of the actual mobile colloid load. Careful

field sampling has shown that this stable colloid

concentration range from <1 to as high as 100 mg L-1 with

higher concentrations typically occurring in shallow,

unconfined aquifers subjected to changes in pore water

chemistry (McCarthy and Degueldre, 1993).

In the field, the decrease in suspended sediment

concentration toward a stable level can be effectively

monitored by some type of light scattering technique. A

turbidity meter is the most practical instrument to use for

this purpose. The extracted ground water can be routed

through a flow-through cell in the turbidity meter for

constant monitoring of the suspended sediment

concentration (measured in nephelometric turbidity units,

NTU) without exposing the sample to the atmosphere. The

turbidity meter can be added to the suite of instruments used

to monitor the stabilization of other chemical parameters

during purging (pH, dissolved oxygen, specific

conductance, etc.). Careful field tests have shown that these

chemical parameters typically stabilize more rapidly than

the suspended sediment concentration of the extracted

ground water (Puls et al., 1992; Backhus et al., 1993).

A stable colloid concentration is easily achieved by

withdrawing ground water using a pump positioned at a

fixed depth during purging and sampling. Careful field

studies have demonstrated that low-stress pumping produces

samples with stable suspended sediment concentrations that

are two to three orders of magnitude lower than those

produced by bailing in the same wells (Puls et al., 1992;

Backhus et al., 1993). The tests by Backhus et al. (1992)

showed that bailing continued to produce samples with high

turbidity even after 60 pore volumes of purging and that

bailed samples also contained up to 750 times greater

concentrations of high molecular weight polycyclic

aromatic hydrocarbons than pumped samples from a coal

tar-contaminated site.

The careful field studies currently recommend that pumping

be performed at relatively slow withdrawal rates to

minimize suspension of “artifactual” colloids, or sediment

that is attached to sediments at natural ground water flow

velocities. Calculations have shown that a pumping rate of

about 100 mL min-1 will keep shear rates below those

believed to mobilize attached colloids in a typical

unconfined aquifer (Ryan, 1988). Rather than specify a

particular withdrawal rate, which is strongly dependent on

aquifer properties, a “minimal-” or “no-drawdown”

guideline appears to be the best way to assure that the

pumping-induced flow rates near the well were not

“stressing” the aquifer and causing artifactual colloid

mobilization. However, some field data shows that

pumping at a range of withdrawal rates has no effect on the

stable suspended sediment concentration (Puls et al., 1992).

In fact, at higher pumping rates, the stable level was reached

in a shorter purging time, although the higher pumping rates

produced larger colloids. Further research is needed to

elucidate the effect of pumping rate on the stable suspended

sediment concentration.

A particular concern of many of the attendees was sampling

from “borderline” aquifers -- formations with low

permeability. Sampling and purging requirements are

difficult, if not impossible to meet, in such formations.

However, it is clear that bailing samples from these

formations will exacerbate turbidity problems, while lowstress pumping (“minimal drawdown”) produce samples of

lower turbidity. Also, there is a possibility that passive

sampling techniques (Magaritz et al., 1990) may prove

especially valuable in such formations.

Distinguishing Dissolved and Colloid-Bound

Contaminants

A representative sample used to determine the transport of

the contaminant should include both the mobile dissolved

and mobile colloidal fractions of the contaminant. For some

contaminants (e.g., volatile organic compounds), the mobile

colloidal fraction may be deemed insignificant a priori

based on published partitioning values. If the transport

behavior of the contaminant capable of significant

partitioning to colloidal phases is to be determined and

predicted, then it is always necessary to measure and

distinguish between the dissolved and colloidal fractions.

However, in a monitoring mode, where only the presence of

the contaminant is to be determined, it is not necessary to

distinguish between the dissolved and colloidal fractions;

only the total mobile contaminant concentration is needed.

Scientific evidence shows that certain low-solubility

contaminants are susceptible to colloid-facilitated transport

(McCarthy and Zachara, 1989). These low-solubility

contaminants are generally those that are surface-reactive;

i.e., they adsorb strongly to mineral and organic colloids. In

the field, colloid-facilitated transport has been observed for

radioactive (e.g., Pu, Am, U, Co, Sr, Cs) and nonradioactive metal (Cu, Pb) in the cationic form (Means et

al., 1978; Buddemeier and Hunt, 1988; Magaritz et al.,

1990; Penrose et al., 1990). Laboratory experiments have

shown that the transport of metals and other inorganic

elements typically present in the anionic form (e.g., Cr(VI),

As) is facilitated by positively charged metal oxides.

Organic colloidal phases (NOM) also enhance the transport

of high molecular weight organic compounds (PAH,

pesticides, polychlorinated biphenyls, etc.) in laboratory

columns, but direct evidence of this phenomenon has not

been observed in the field.

For contaminants that do not fit into the categories listed

above, colloid-facilitated transport is unlikely. Once the

nature and abundance of the colloidal fraction is known,
90

specific estimates of the potentially colloid-bound fraction

can be estimated based on known partition coefficients.

Given some reasonable safety margin, it is reasonable to

state that colloid-facilitated transport can be ruled out for

many low molecular weight, non-surface-reactive

contaminants. In these cases, it is not necessary to obtain

representative samples of the mobile colloidal fraction;

hence, many of the added precautions (turbidity monitoring,

low-stress pumping) recommended for sampling for colloids

may not be needed. However, the site investigator should

keep in mind an important caveat before dispensing with the

colloid sampling precautions: samples collected without

taking precautions to avoid nonrepresentative suspended

sediment can never be used to make judgements about the

transport of contaminants that may be colloid-associated.

The need for quantifying separate dissolved and colloidal

fractions of contaminants depends on the reason for

collecting the data. If the ground water sample has been

collected solely to monitor the containment of the

contaminant (e.g., a landfill), then the site investigator need

only be concerned with total mobile contaminant

concentrations without regard for the dissolved or colloidal

fraction. Note, however, that sampling techniques designed

for colloids still must be used for this measurement because

part of the total mobile contaminant may be colloid-bound.

If the groundwater sample has been collected to assess the

fate and transport of the contaminant, then it is essential to

quantify both the dissolved and colloidal fractions because

the transport of each fraction will be different.

Uncertainty still exists concerning the best method for

distinguishing between the dissolved and colloidal fractions

of a contaminant. The most common technique to isolate

the dissolved fraction is filtration. Currently, the 0.45 μm

pore size filters are needed to accurately isolate the

dissolved fraction. Improvements in the separation have

been made by using membrane filters with pore sizes

ranging from 1.0 down to 0.01 μm; however, these filters

are subject to rapid clogging. A more efficient means of

isolating the dissolved fraction is high molecular weight

ultrafiltration (10 to 100K nominal molecular weight

cutoff). Ultrafiltration must be performed in the laboratory;

thus, it requires more careful sample handling and storage

techniques. Centrifugation, another laboratory technique,

may also be useful in separating the dissolved and colloidal

fractions (Salbu et al., 1985).

Distinguishing Mobile Colloids and Artifactual Colloids

Collecting samples following the low-stress protocol is our

best assurance that we have obtained samples representative

of the truly mobile colloid population. However, it is still

necessary to ascertain that the colloids retrieved truly

mobile or artifactual. At many sites, this may not be

“readily” achievable. Detailed knowledge of the site

hydrogeochemistry and proper characterization of the

colloids are necessary to make this decision. Colloid

“veracity” can be determined by consideration of colloid

size, composition, possible origin, and the geochemistry of

“background” vs. “contaminated” samples.

Even after collecting ground water samples using techniques

designed to obtain representative dissolved and colloidal

fractions of the contaminant, the site investigator must judge

whether the colloids in the sample are truly mobile or not.

To do this, the site investigator must characterize the

colloids and gain thorough knowledge of the site

hydrogeochemistry. Without this thorough analysis of the

“veracity” of the colloids, the site investigator runs the risk

of accounting for colloid transport when, in fact, the colloids

are not truly mobile.

Colloid characterization techniques are considered esoteric

by all but the research community; however, many of the

analyses are more “routine” and less expensive than many

site investigators may realize. Such analyses include

scanning electron microscopy (colloid size, morphology,

and concentration), energy- or wave-dispersive x-ray

spectroscopy (elemental composition), photon correlation

spectroscopy and other light scattering techniques (size and

concentration), microelectrophoresis (surface charge), and

x-ray diffraction (mineralogy). Detailed methods for these

characterization techniques have been summarized in the

literature (McCarthy and Degueldre, 1993).

Knowledge of the colloid character is not sufficient; the site

investigator must seek to gain a thorough understanding the

hydrologic, geologic, and chemical character of the site.

This necessarily includes knowledge of (1) the direction and

velocity of the ground water flow, (2) the mineralogic

composition of the aquifer, (3) chemical composition of the

groundwater. Also, the site investigator must know how

these properties have been changed or been influenced by

the contaminant plume. This knowledge can be used to

assess the likelihood of mobile colloids in the samples. The

presence of colloids in the ground water must “make sense”

in the hydrogeochemical setting at the site. To make this

judgement, site investigators must become familiar with the

basics of colloid transport.

Key to this assessment is the presence of wells sampling

both “background” and “contaminated” portions of the

aquifer. The background and contaminated samples can be

used to explain the possible effect of the contaminant plume

on colloid mobilization. The geochemical changes wrought

by the advancing plume may mobilize colloids through

some change in the pore water chemistry; in these cases,

colloid transport may advance no further than the

contaminant plume which caused its mobilization. In such a

case, detailed understanding of the colloid transport may not

be necessary. Currently, field data is needed to substantiate

this phenomenon.
91

Identifying Sites with Colloid-Facilitated Transport

Potential

Given a contaminant for which colloid-facilitated transport

is possible, the potential for colloid-facilitated transport

cannot be ruled out based on the hydrogeochemical

character of a site because colloids have been found

everywhere they have been sought. With our current

understanding of colloid mobilization and transport, it is

possible to identify geochemical conditions under which

colloid-facilitated transport would be likely.

Using careful sampling methods, colloids have been found

everywhere that researchers have looked for them

(McCarthy and Degueldre, 1993). The nature and

abundance of colloids varies widely from site to site;

however, colloids are apparently ubiquitous. Whether or not

the colloids present are capable of facilitating contaminant

transport is a question that must be addressed on a site-bysite basis. At each site, we must consider whether the

mobile colloids are present at a sufficiently high

concentration and are capable of sufficiently strong binding

of contaminants to significantly enhance contaminant

transport. Based on the hydrogeochemical characteristics of

sites, we cannot rule out the possibility of colloid-facilitated

transport a priori.

We can identify combinations of aquifer mineralogy and

pore water chemistry where we expect colloid mobilization

to be significant. Two good examples of aquifers

susceptible to colloid mobilization have been presented in

the literature. The first involves the infiltration of anoxic,

organic matter-rich water (an analog for a landfill leachate)

into a sediment composed of quartz sand coated by ferric

oxyhydroxides and kaolinite. The infiltrating water

promoted the mobilization of the kaolinite colloids by

dissolution and reversal of the surface charge of the ferric

oxyhydroxide cement (Ryan and Gschwend, 1990; 1992).

The second involves the infiltration of acidic, carbon

dioxide-rich water into a carbonate-cemented aquifer. The

carbonate cement dissolved and released aluminosilicate

mineral colloids (Gschwend et al., 1990; Ronen et al.,

1992). Based on field observations such as these and

general knowledge of colloidal interactions, we can predict

that colloid mobilization may be a particular problem for

certain sites.

Bailing and Field Filtering

The general consensus of the Turbidity and Colloidal

Transport subgroup was that, based on scientific evidence,

bailing and field filtering do not provide samples that are

representative of the mobile colloid fraction. Nevertheless,

a number of the attendees, particularly those representing

state regulatory agencies, contended that E.P.A. ban on field

filtering should be rescinded for detection monitoring at

solid waste facilities (subtitle D). These regulators were

solely concerned with ground water sampling for

monitoring purposes. They foresaw that the ban would

result in an unusually large number of “false positive”

analyses in samples collected by bailing, the most common

sampling method. Although the intent of monitoring is to

measure only the mobile form of the compound of interest,

analyses of unfiltered turbid samples would measure both

mobile and immobile forms of the compound of interest as

well as natural forms of the compound.

Metals leaching from landfills was the major concern of the

state regulators. Currently, many state regulations require

the routine monitoring of metals in samples from landfill

monitoring wells. Because metals interact with colloidal

mineral surfaces and organic matter, the importance of

accurately determining the truly mobile metal fraction and

the potential for colloid-facilitated transport is heightened.

Representatives from the states of Wisconsin and Michigan

were particularly concerned with highly turbid samples

taken from glacial till aquifers, which are common in those

states. Glacial till contain abundant clay that can be

mobilized by the high groundwater velocities induced by

bailing. It is thought that the metals adsorbed to the

mobilized clays are actually immobile in the aquifer, hence

the suspended sediment is currently filtered out using 0.45

μm filters to attempt to isolate the mobile fraction of the

metals. This filtrate is typically called the “dissolved”

fraction, although it is well known that (1) some dissolved

metals may become adsorbed to the suspended sediment

trapped on the filter and (2) some colloidal metal (associated

with colloids smaller than the pore size) may pass through

the filter.

The state of Washington representative was concerned with

the inability to distinguish between natural levels of certain

compounds and levels caused by contamination. Many

Washington ground waters and sediments contain high

levels of arsenic, making the distinction between natural

levels and contamination difficult. Bailed samples

containing abundant suspended sediments may contain

natural arsenic originally present in mineral lattices that is

released by sample acidification and analyzed as a

contaminant.

The state regulators agreed that current scientific evidence

shows that the low-stress pumping protocol for obtaining

metals samples is the best method. In defense of the bailing

and field filtering protocol, the state regulators (and others)

raised two issues: (1) cost and (2) consistency. The state

regulators asserted that most site investigators required to

monitor ground water cannot afford the equipment and time

required to sample ground water properly. They also point
92

out that a change in sampling techniques will render their

extensive data bases inconsistent with newly-acquired

results.

Some members of the subgroup, particularly those from

academic and federal research laboratories, countered these

arguments by reiterating that (1) the perceived necessity of

field-filtering highlighted the fact that bailing was

inappropriate for collecting samples for metals and (2)

filtering introduces an unknown bias into metals analysis

(i.e., filtering could result in either under- or overestimation

of the mobile metal concentration). The researchers pointed

out that the cost of making decisions on poorly-collected

samples is potentially much greater than the cost of

sampling correctly. Following the same reasoning,

continuation of inappropriate sampling methods for the sake

of consistency is not a valid reason -- if bad data were

collected before, that makes collection of good data even

more important.

Some of the researchers did not share the state regulators’

concern for “false positive” measurements of high metal

concentrations. High metal concentrations in a turbid

sample may simply indicate that metals adsorbed to the

sediments were pulled into the well by the vigorous bailing

action. These metals must have been mobile enough to

reach that point. The contention that high natural levels of

some metals obscures our ability to distinguish contributions

from leaking landfills was also not deemed a valid excuse to

continue poor sampling techniques (e.g., high As

concentrations in Washington). Increases in levels of metals

above natural levels should be evident from properly located

background wells. If such wells are not available, then it is

scientifically advisable to discontinue monitoring the

troublesome metal and substitute a more easily measured

parameter indicative of leachate (e.g., organic carbon,

chloride).

References

40 CFR Parts 257 and 258, Solid Waste Disposal Facility

Criteria; Final Rule. Federal Register 56 (196), 50978-51119

Backhus D.A., Ryan J.N., Groher D.M., MacFarlane J.K.,

and Gschwend P.M. (1993) Sampling colloids and colloidassociated contaminants in ground water. Ground Water 31,

466-479.

Buddemeier R.W. and Hunt J.R. (1988) Transport of

colloidal contaminants in groundwater: radionuclide

migration at the Nevada Test Site. Appl. Geochem. 3, 535-

548.

Danielsson L.G. (1982) On the use of filters for

distinguishing between dissolved and particulate fractions in

natural waters. Water Res. 16, 179-182.

Gschwend P.M., Backhus D.A., MacFarlane J.K., Page A.L.

(1990) Mobilization of colloids in groundwater due to

infiltration of water at a coal ash disposal site. J. Contam.

Hydrol. 6, 307-320.

Johnson B.D. and Wangersky P.J. (1985) Seawater filtration:

Particle flow and impaction considerations. Limnol.

Oceanogr. 30, 966-971.

Kennedy V.C., Zellweger G.W., and Jones B.F. (1974) Filter

pore-size effects on the analysis of Al, Fe, Mn, and Ti in

water. Water Resour. Res. 10, 785-790.

Magaritz M., Amiel A.J., Ronen D., and Wells M.C. (1990)

Distribution of metals in a polluted aquifer: A comparison of

aquifer suspended material to fine sediments of the adjacent

environment. J. Contam. Hydrol. 5, 333-347.

McCarthy J.F. and Degueldre C. (1993) Sampling and

characterization of colloids and particles in groundwater for

studying their role in contaminate transport. In

Environmental Particles (eds. Buffle J. and van Leeuwen

H.P.), Lewis Publishers, 247-315.

McCarthy J.R. and Zachara J.M. (1989) Subsurface

transport of contaminants. Environ. Sci. Technol. 23, 496-

502.

Penrose W.R., Polzer W.L., Essington E.H., Nelson D.M.,

and Orlandini K.A. (1990). Mobility of plutonium and

americium through a shallow aquifer in a semiarid region.

Environ. Sci. Technol. 24, 228-234.

Puls R.W., Clark D.A., Bledsoe B., Powell R.M., and Paul

C.J. (1992) Metals in groundwater: Sampling artifacts and

reproducibility. Haz. Waste Haz. Mater. 9, 149-162.

Ronen D., Magaritz M., Weber U., Amiel A.J., and Klein E.

(1992) Characterization of suspended particles collected in

groundwater under natural gradient flow conditions. Water

Resour. Res. 28, 1279-1291.

Ryan J.N. (1998) Groundwater Colloids in Two Atlantic

Coastal Plain Aquifers: Colloid Formation and Stability.

M.S. Thesis, Dept. Civil Eng., Massachusetts Institute of

Technology, Cambridge, MA.

Ryan J.N. and Gschwend P.M. (1990) Groundwater colloids

in two Atlantic Coastal Plain aquifers: Field studies. Water

Resour. Res. 26, 307-322.

Ryan J.N. and Gschwend P.M. (1992) Effect of iron

diagenesis on clay colloid transport in an unconfined sand

aquifer. Geochim. Cosmochim. Acta 56, 1507-1521.

Salbu B., Bjornstad H.E., Lindstrom N.S., Lydersen E.,
93

Brevik E.M., Rambaek J.P., and Paus P.E. (1985) Size

fractionation techniques in the determination of elements

associated with particulate or colloidal material in natural

fresh waters. Talanta 32, 907-913.
94

Sample Handling and Analysis

Karl F. Pohlmann, Charlita Rosal and Bert

Bledsoe

Objectives of Sampling Program

Program objectives must be sufficiently defined so that data

collection efforts are designed and carried out in a way that

will produce data appropriate for the needs of the program.

“Data quality objectives” are developed to define the types,

quality, and quantity of data required by the various aspects

of the program. In this sense, “data quality” addresses the

purpose(s) for which the data are to be used. Once these

data objectives are defined, appropriate sampling and

analytical methodology (protocol) are evaluated and chosen.

Examples of several types of programs that might have

different data quality objectives are detection and

assessment monitoring related to regulatory activities,

resource evaluation, and geochemical modeling.

Most decisions regarding sampling methodology are made

before field operations begin, however, flexibility must be

built into the sampling protocol to deal with unexpected or

changing conditions. The group leaned toward basing

decisions on well or site-specific conditions as opposed to

applying general rules governing all sites, regardless of sitespecific conditions.

Field Measurements

Three categories of field measurements were defined: in

situ, purging, and field analyses. “In situ measurements”

are absolute values of constituents of properties that,

because of their unstable nature, must be made under

conditions as close to in situ conditions as possible, usually

conducted in a well or in situ device. Examples include

temperature and dissolved gases. Note that project

objectives may not require the additional efforts required to

collect data of this resolution.

“Purging measurements” are conducted to evaluate the

progress or efficiency of monitoring well purging and are

usually conducted at the well head. Because these

measurements are made on samples that have been removed

from their native physicochemical environment, their

accuracy may be lower than for in situ measurements. Use

of a flow-through cell may make measurements easier but

doesn’t necessarily improve data accuracy or precision.

Examples of purging parameters include temperature, EC,

pH, DO, turbidity, other field analytes, and lab analytes.

Measurements of the constituents of interest to the sampling

program are preferred but are not often practical. Note that

the sampling device may influence the quality of certain

parameters; such as DO and turbidity from bailed samples,

and temperature from many devices. Therefore, these

parameters may not be equally weighted as purging criteria.

The last value measured is often taken as representing

sample conditions, however, the accuracy of these

measurements must be evaluated to determine whether they

meet data quality objectives. Field evidence suggests that if

measurements are made in-line, turbidity should be

measured first to avoid potential particle settling in flowthrough cells for other measurements. However, some

turbidimeters may heat the ground-water leading to error in

temperature measurements. Also, the effect of flow-through

cells on pump discharge rate should be considered; they can

act as flow restrictors. When they are disconnected for

bottle filling (as recommended), pump discharge rates may

increase dramatically.

“Field analyses” are made for the purpose of on-site

characterization or are measurements of constituents and

properties considered too unstable for laboratory analysis.

Field-deployable analytical techniques (GC, GC/MS, XRF,

ion chromatography, immunochemistry, fiber optics) may

be useful for both detection and assessment but will require

the development of strong, standardized protocols for

quality control. Current use is primarily for site

characterization, but application of these techniques to

routine monitoring may reduce the costs and uncertainty

associated with sample collection, handling, and analysis,

particularly for aromatic hydrocarbons. Examples of

unstable parameters that are usually best measured at the

well head include pH, turbidity, DO, metals speciation (Fe

II, Cr IV), alkalinity, sulfide, nitrite, dissolved gases, and

electrode potential (for Eh). Note that holding times for

some of these parameters is 24 hours. Constituents that

require preservation for later analysis are those traditionally

analyzed in the laboratory, including major ion chemistry,

trace metals, organics, colloids, etc. Preservation

techniques are described below.

Field Filtration

The decision to collect filtered or unfiltered samples must be

based on data quality objectives and, therefore, the
95

media, pore size, and others, must be addressed to identify

and minimize potential sources of uncertainty when filtering

samples.

In-line filtration was generally considered the most desirable

approach because it allows better consistency through less

sample handling, and minimizes sample exposure to the

atmosphere. In-line filtration can be accomplished through

the use of disposable filter cartridges or membrane filters in

an in-line filter apparatus. Disposable filter cartridges have

the advantage of greater sediment handling capacity when

compared to traditional membrane filters. The filter media,

including materials and pore structure may impact breakthrough of certain metals. To obtain truly dissolved

constituents, the smaller pore size the better. The smallest

pore size practical in the field seems to be 0.1 μm, but the

choice depends on particle loads, required sample volume,

and project objectives. Also, the commercial availability of

filter pore sizes less than 0.45 μm is limited.

Conditioning is required to remove preservatives, wetting

agents, residues of filter manufacturing, and leachable

compounds from filter media. Volumes of sample water of

500 mL to 1 L are generally accepted, but the volume

necessary depends on sample turbidity. If turbidity is high,

the filters may have to be preconditioned with DI water. For

analysis of very low metal concentrations, the filters may

require acid-washing. Once filtration has begun, a filter

cake may develop as particles larger than the pore size

accumulate on the filter membrane. The result is that the

effective pore diameter of the membrane is reduced and

particles smaller than the stated pore size are excluded from

the filtrate. Possible solutions include prefiltering,

minimizing particle loads to begin with, and reducing

sample volume. Finally, an inert environment may be

necessary during off-line filtration to minimize oxidation of

highly reduced species and may be accomplished through

the use of oxygen-free sample bottles in a glove box. For

in-line filtration, oxygen-free bottles alone will suffice.

If the objective of the sampling program is total recoverable

constituents, whether they be major ions or trace metals,

then the samples must not be filtered. In particular, samples

for the analysis of colloid-associated constituents must be

collected unfiltered. Likewise, samples for certain classes

of analytes are generally collected unfiltered, such as many

organics and nutrients. Particle load may be immaterial to

analysis of certain types of organic compounds (Paul et al.,

in preparation).

Collecting unfiltered samples eliminates many of the

uncertainties associated with field-filtration but should not

be attempted without addressing the issue of sample

collection. For example, sampling methods that disturb the

sampling zone and sample may suspend normally immobile

objectives of the overall program. Field-filtering of certain

constituents should not be the default, however.

Consideration should be given to what the application of

field-filtration is trying to accomplish. The group agreed

that specific reasons exist for collection of both filtered and

unfiltered samples, as outlined below.

Under conditions of excessive turbidity caused by certain

geologic or sampling conditions, field filtration is often

suggested to reduce artifacts caused by the presence of

excessive loads of suspended sediments that threaten to bias

the analyses. However, potential implications on sample

accuracy and overall data quality must be recognized and

evaluated. For example, filtration with 0.45 μm filters may

remove particles important to transport of colloidallyassociated contaminants (both larger than the initial pore

size and smaller, as the filter cake builds up). It was

generally agreed that field-filtration should not be used to

correct for improperly designed or constructed monitoring

wells, inappropriate sampling methods, or poor sampling

technique. The objective should be to carry out all aspects

of sampling so as to produce a sample that is minimally

disturbed. Turbidity may be a good criterion to evaluate

sample disturbance and the question was raised as to

whether turbidity guidelines could be developed.

Truly dissolved concentrations of major ions and trace

metals are used for flow system analysis and equilibrium

geochemical modeling. Therefore, samples collected for

these purposes must be filtered because inclusion of

particulate material in the analyses may lead to erroneous

dissolved concentrations that will impact geochemical

equilibrium calculations. Alkalinity samples must also be

filtered if significant particulate calcium carbonate is

suspected. The presence of this material is likely to impact

the alkalinity titration although filtration itself may alter the

CO2

 composition of the sample and therefore affect the

results. Field filtration may also be conducted to maintain

consistency with historic data collected with routine fieldfiltration of samples. This approach may be appropriate in

certain situations (e.g. flow system analysis) but the

determination must be made as to whether filtration is

appropriate to program objectives. Samples for analysis of

colloid composition should be collected on membrane

filters or by field ultrafiltration (Backhus et al., 1993).

Although filtration may be necessary in the cases suggested

above, filtration of a sample may cause a number of

unintended changes to occur, possibly leading to filtrationinduced artifacts during sample analysis and uncertainty in

the results (Horowitz et al., 1992). Some of these

unintended changes may be unavoidable but the factors

leading to them must be recognized. Also, their effects can

be minimized by the consistent application of certain

filtration guidelines. These issues, which include filter type,
96

particles and entrain them in the sample (e.g. bailers and

pumps at high flow rates) leading to analysis of naturallyoccurring matrix metals and “false positive” results. This is

a particular problem in turbid wells, where excessive

turbidity may result from improper design, construction, and

development. The following approaches may be useful in

minimizing potential sources of uncertainty when collecting

unfiltered samples.

Well design, construction, and development must be

appropriate to hydrogeochemical conditions present at the

site. Disturbance of the geologic matrix during drilling

must be minimized to reduce the effects of well construction

artifacts. When purging and sampling, low pumping rates

(300 mL/min and below) have been demonstrated to

minimize disturbance of the sample zone and sample when

compared to high pumping rates and bailing. The key is to

minimize particle concentrations in the sample thereby

minimizing artifacts from well design, construction, and

installation; purging; and sampling. However, the pump

intake position must be carefully chosen when using low

pumping rates because water drawn into the pump

originates in a relatively small vertical segment of the well

intake. If the pump intake is positioned away from the zone

of contamination, dilution within the wellbore may prevent

detection of the contaminant of interest. A borehole velocity

survey may provide indication of most conductive zones;

other techniques may also be applied to detect contaminated

zones. The measurement of selected field parameters during

purging, particularly in-line measurements of DO and

turbidity, provides an indication of the progress of purging

and when parameter equilibrium conditions have been

attained. Other parameters may lead to underpurging while

turbidity may be too conservative. Disturbance of the

sampling zone may be minimized, in turn reducing purge

volumes, through the use of dedicated sampling systems

rather than portable systems.

Finally, compatibility of unfiltered samples with the

analytical method must be considered, especially if the

samples contain significant quantities of suspended

particles. Also, make sure the lab doesn’t filter the sample

that was painstakingly collected unfiltered in the field!

Preservation of Samples

It should be recognized that potential uncertainty associated

with sample preservation may be reduced or eliminated for

certain analytes by conducting the analyses in the field.

Although routine field analysis is not currently widespread,

it appears that present trends are leading in that direction.

For those analyses conducted in the laboratory, there are

several important issues that must be addressed to ensure

sample integrity is preserved from the field to the lab.

The transfer of the sample from the sampling device (bailer,

pump tubing) to bottle (or filtration device if filtration is

conducted off-line) must be accomplished with as little

disturbance to the sample as possible. This operation is

relatively straightforward when using low-speed pumps but

can be more problematic when using bailers , although

several techniques are currently available for simplifying the

transfer and reducing agitation of samples from bailers. If

field filtration is conducted, the operation must be carried

out in such a way that sample integrity is preserved, as

discussed above. To minimize oxidation of highly reduced

species, an inert environment may be necessary during offline filtration.

Chemical preservation is used to minimize reactions such as

precipitation of metal oxides and hydroxides and

biodegradation of organic compounds. Chemicals may also

be used to control a specific reaction; such as addition of

sulfuric acid to samples collected for ammonia

determination to lower the pH and form the stable

ammonium ion. These preservation techniques have

evolved over many years of laboratory analyses and appear

adequate in most cases (see SW-846). However, questions

remain about preservation of samples collected for analysis

of volatile organic compounds. Recommended chemical

preservatives include HC1, sodium bisulfate, sulfuric acid,

and mercuric chloride. These substances have proven

effective for preservation, particularly for aromatic

hydrocarbons, which are highly susceptible to

biodegradation, greatly increasing holding times past the

standard 14 days (Maskarinec et al., 1990; Roe et al., 1989).

Increasing the holding times of chemically-preserved

organic samples might reduce project costs associated with

resampling when holding times were not met. On the other

hand, some studies suggest that if not chemically preserved,

samples for volatile aromatic hydrocarbons may biodegrade

in very short time periods (Roe et al., 1989).

Physical preservation includes temperature of the samples

during transport to the laboratory and type of sample

containers. Maintenance of sample temperature at 4°C may

be critical to control biodegradation in organic samples that

are not chemically preserved. However, the question was

raised whether ice chests arrive at the laboratory at the

required temperature, and what actions are taken if the

samples are warmer. In contrast, SW-846 does not specify

cooling of samples collected for most metal analyses, but

this is a common practice in the field. Under certain

conditions, cooling of metal samples may lead to

precipitation of certain constituents. For very sensitive

analyses, maintaining the samples near in situ ground-water

temperature may be a better approach. Questions were

raised as to the effect of collecting samples in bottles that

may have been stored on ice (for convenience) and therefore
97

are much cooler than ground water. Likewise, concerns

were expressed about the effects on VOC concentrations of

filling VOA vials that had been warmed by exposure to the

sun.

The types of sample containers appropriate for a wide range

of analytes are given in SW-846. Because organic

compounds may diffuse through plastic bottles and caps,

glass bottles and PTFE-lined caps are specified for samples

collected for organic analyses. Though plastic bottles and

caps are considered acceptable for many inorganic analyses,

the use of glass bottles minimizes exchange of gases with

the atmosphere that might lead to sample degradation of

very sensitive constituents (e.g., oxidation of highly reduced

metals species). Likewise, stoppers designed to eliminate

headspace may also be necessary to minimize this sample

degradation. Other physical preservation requirements are

given in SW-846.

Reducing the volume of samples sent to the laboratory can

minimize some of the problems discussed above under

filtration. Other advantages of reducing sample volumes

include increased ability to collect samples in low-yield

wells, lower bottle filling times at low pumping rates, lower

bottle costs, lower shipping costs, and reduced sample

disposal problems at the laboratory. Sample volume can

easily be reduced over many present practices. For

example, a full suite of metals can easily be analyzed from a

50 to 100 mL sample, and only 5 mL is required for purge

and trap GC analysis of organics.

Shipment of samples to the laboratory remains

controversial. Sample preservation techniques and holding

times would suggest that certain samples (e.g., metal) could

be shipped via conventional ground methods. However, this

method causes samples from the same sampling event to be

“split up” since VOC samples are commonly shipped by

overnight carrier, and might possibly lead to chain-ofcustody problems.

Documentation

There was clear consensus that more and better

documentation is required at virtually every step of the

sampling process in order to better interpret data collected

(field and lab) and to aid identification of areas where data

quality objectives are not being met. Discussion of general

topics follow.

Detailed descriptions of all methods, activities, and data are

critical. Examples include field conditions (well, weather)

that might be significant to the results, personnel, purging

methods (device, depth, rate, indicator parameters),

sampling methods (device, depth, rate), field measurement

instrumentation (type, methods, calibration data), specific

preservation information (filtration, chemical, physical), and

shipping information. Standardization of documentation

(data forms) at some level was discussed. Generic

“templates” of various forms could be developed and

adapted for widespread or project-specific use. More

widespread and uniform documentation is facilitated by

standardizing data records. Likewise, detailed,

comprehensive forms prompt for information that might

otherwise go unrecorded.

Automation of documentation is a future direction and has

some very appealing advantages. For example, permanent

bar codes applied directly to sample bottles in the field

might streamline sample tracking from the field to the lab

and into the final report. Personal Data Assistants may

provide an effective means for field data entry and storage

(for example all purging data could be recorded directly). A

copy of the data diskette sent to the laboratory with the

samples would provide laboratory personnel with a better

understanding of conditions under which the samples were

collected, and how they have been preserved.

Communication between field and lab personnel must be

open and proceed in both directions. As examples, lab

personnel should be fully aware of field conditions and

measurements, while field personnel should be cognizant of

laboratory requirements and the results of QC sampling.

Sending field notes with samples may facilitate this

communication.

Field Operations

Virtually all hydrogeologic and hydrochemical analyses are

based on information that is either measured in the field or

analyzed from samples collected in the field. As a result, it

is imperative that field personnel be qualified to carry out

the tasks required to ensure that data are of the quality

required to meet program objectives. At a minimum,

structured training of field personnel should provide an

understanding of project objectives, background in the

operating principles of field instrumentation and other

equipment, overview of the principles of sample

preservation, and guidance in documenting the sampling

event. A certification program might be initiated if certain

minimum qualifications for field personnel could be

developed. Since certification programs exist for analytical

laboratories, it seems reasonable that some type of

certification be instituted at the point where the data

originates. Regular audits of field operations might also be

useful for ensuring that appropriate procedures are followed

to meet established data quality objectives (QA/QC

program).

Research Needs

1. Although there was general agreement that

minimizing disturbance of ground-water samples
98

5. There was concern about the inappropriate

application of low-flow techniques, particularly in

monitoring wells with long screens. If the pump

intake is positioned away from the zone of

contamination, dilution within the wellbore may

prevent detection of the contaminant. A borehole

velocity survey may provide indication of the most

conductive zones but may be impractical and

doesn’t detect the contaminated zones. Therefore,

alternatives should be investigated and reported.

References

1. Backhus, D.A., J.N. Ryan, D.M. Groher, J.K.

MacFarlane, and P.M. Gschwend. Sampling

Colloids and Colloid-Associated Contaminants in

Ground Water. Ground Water, 31 (3): 466-479,

1993.

2. Horowitz, A.J., K.A. Elrick, and M.R. Colberg.

The Effect of Membrane Filtration Artifacts on

Dissolved Trace Element Concentrations. Wat.

Res., 26 (6): 753-763,1992.

3. Maskarinec, M.P., L.H. Johnson, S.K. Holladay,

R.L. Moody, C.K. Bayne, and R.A. Jenkins.

Stability of Volatile Organic Compounds in

Environmental Water Samples during Transport

and Storage. Environ. Sci. Technol., 24 (11): 1665-

1670, 1990.

4. Roe, V.D., M.J. Lacy, J.D. Stuart and G.A.

Robbins. Manual Headspace Method to Analyze

for the Volatile Aromatics of Gasoline in

Groundwater and Soil Samples. Anal. Chem., 61:

2584, 1989.

provides higher quality data, questions remained

about the steps that must be taken to achieve

significant improvement in results. In particular,

there was some concern expressed as to whether

low-flow pumping/unfiltered samples actually

provided results that were of significantly higher

quality than more traditional approaches and

whether the improvements in results justified the

costs associated with major changes in sampling

protocol.

2. There was also a general interest in improving our

understanding of colloid-facilitated transport in

different hydrogeologic environments. Questions

such as How mobile are colloids? How far do they

travel? What are they composed of? and What

types of contaminants are likely to be associated

with colloids? were raised. In reality, many of

these questions are currently being addressed in the

literature. The overriding question was Are

colloids actually important to contaminant

transport at solid waste landfills, or is their role in

facilitating contaminant transport rather

insignificant? What might be needed to answer

this question is a comprehensive survey of the

colloid-transport literature to complement the work

that comes out of Group 4 (Turbidity and Colloid

Transport).

Guidance Needs

Several important issues were raised that may warrant the

development of technical guidance or recommendations and

are summarized below.

1. The important potential and increased use of fielddeployable analytical techniques requires the

development of strong, standardized protocols for

quality control.

2. Standardized turbidity guidelines should be

developed to assist evaluation of sample

disturbance.

3. The issues of sample holding times, chemical

preservation of certain classes of organic samples,

and sample shipment methods could be revisited to

update current practices.

4. Documentation could be improved and made more

uniform through development of standard data

forms, templates, etc.
A-1

Appendix A - Steering Committee

and Other Attendees
A-2

Appendix A - Steering Committee

Puls, Robert W.

U.S. EPA/RSKERL

919 Kerr Research Drive

P.O. Box 1198

Ada, OK 74820

405/436-8543

405/436-8529 (fax)

Barcelona, M. J.

Western Michigan University

1007 Everett Tower

Kalamazoo, MI 49008-5150

616/387-5501

616/387-4988 (fax)

Bledsoe, Bert

U.S. EPA/RSKERL

919 Kerr Research Drive

P.O. Box 1198

Ada, OK 74820

405/436-8605

405/436-8529 (fax)

Brown, James R.

U.S. EPA/OSW (5303W)

401 M Street, SW

Washington, DC 20460

703/308-8656

703/308-8617 (fax)

Denne, Jane

AMD/AMW

U.S. EPA/EMSL-LV

P.O. Box 93478

Las Vegas, NV 89193-3478

702/798-2655

Mangion, Steve

U.S. EPA/Region V

 HSRLT-5J

77 W. Jackson Blvd.

Chicago, IL 60604

312/353-7499

312/353-9176 (fax)

McCarthy, John F.

Environmental Sciences Div.

Oak Ridge National Lab

P.O. Box 2008

Oak Ridge, TN 37831-6036

615/576-6606

Rich Steimle

U.S. EPA/TIO (5102W)

401 M Street, SW

Washington, DC 20460

703/308-8846

703/308-8528 (fax)

Willey, Richard

U.S. EPA/Region I

 HSS-CAN7

JFK Federal Bldg.

One Congress Street

Boston, MA 02203

617/573-9639

617/573-9662 (fax)
A-3

Other Attendees

Gardner, Steven P.

U.S. EPA/ORD/EMSL-LV

944 E. Harmon Ave.

Las Vegas, NV 89119-6748

702/798-2580

702/798-2692 (fax)

Gibs, Jacob

U.S. Geological Survey

810 Bear Tavern Road,Suite 206

West Trenton, NJ 08628

609/771-3977

Gray, John D.

New York State Electric and Gas Company

Corporate Drive, Kirkwood Industrial Park

P.O. Box 5227

Binghampton, NY 13902-5227

607/762-8879

607/762-8457 (fax)

Gronwald, Keith

New York State DEC

50 Wolf Road

Albany, NY 12233-4013

518/457-1860

518/485-7733 (fax)

Hall, Steve

U.S. EPA/Region IV

960 College Station Road

Athens, GA 30605

706/546-3173

Korte, Nic E.

Oak Ridge National Lab

P.O. Box 2567

Grand Junction, CO 81502

303/248-6210

303/248-6147 (fax)

Lee, Roger W.

U.S. Geological Survey-WRD

8011 Cameron Road

Austin, TX 78754

512/873-3023

512/873-3090

Aller, Linda

Geodyssey

2700 E. Dublin-Granville Road

Suite 530

Columbus, OH 43231

614/882-4991

614/882-4260 (fax)

Backhus, Debera

Indiana University

School of Public and Environmental Affairs

10th St. and Fee Lane,Room 425

Bloomington, IN 47405

812/855-4944

812/855-7802 (fax)

Bourbon, John

U.S. EPA/Region II

2890 Woodbridge Ave.

Edison, NJ 08837-3679

908/321-6729

908/321-6788 (fax)

Clark, Don A.

U.S. EPA/RSKERL

919 Kerr Research Drive

P.O. Box 1198

Ada, OK 74820

405/436-8562

405/436-8529 (fax)

Connelly, Jack

Bureau of Solid & Hazardous Waste

Dept. of Natural Resources

101 S. Webster Street

Box 7921

Madison, WI 53707

608/267-7574

608/267-2768 (fax)

Franks, Charles

U.S. EPA/Region I (HER-CAN6)

JFK Federal Bldg.

One Congress Street

Boston, MA 02203

617/573-9678

617/573-9662 (fax)
A-4

Mabey, William R.

Montgomery Watson

365 Lennon Lane

Walnut Creek, CA 94598

510/975-3521

510/975-3412 (fax)

Martin, Jr., William A.

Florida Dept. of Environmental Protection

2600 Blair Stone Road

Twin Towers Office Bldg.

Tallahassee, FL 32399-2400

904/921-0190

904/922-4939 (fax)

McKay, Larry D.

Dept. of Geological Sciences

University of Tennessee

306 G&G Bldg.

Knoxville, TN 37996-1410

615/974-0821

615/974-2368 (fax)

Nielsen, David

Nielsen Ground-Water Science

4686 State Road 605 South

Galena, OH 43021

614/965-5026

Park, Natalie

Westinghouse Savannah

 River Company

Bldg. 773-57A

Savannah River Site

Aiken, SC 29808

803/725-5923

803/725-8041 (fax)

Parker, Louise

USACRREL

72 Lyme Road

Hanover, NH 03755

603/646-4393

603/646-4640 (fax)

Paul, Cynthia

U.S. EPA/RSKERL

919 Kerr Research Dr.

P.O. Box 1198

Ada, OK 74820

405/436-8600

405/436-8529 (fax)

Pohlmann, Karl

Desert Research Institute

P.O. Box 19040

Las Vegas, NV 89132-0040

702/895-0485

702/895-0427 (fax)

Powell, Robert M.

ManTech Environmental Technology

919 Kerr Research Drive

P.O. Box 1198

Ada, OK 74820

405/436-8676

405/436-8501 (fax)

Reece, Dennis

Woodward-Clyde Consultants

P.O. Box 66317

Baton Rouge, LA 70896

504/751-1873

504/753-3616 (fax)

Rightmire, Craig

Oak Ridge National Lab

P.O. Box 2008

Oak Ridge, TN 37831-6036

615/574-7285

Robbins, Gary

Dept. of Geology & Geophysics

University of Connecticut

U-45, Room 207

345 Mansfield Street

Storrs, CT 06269-2045

203/486-1392

203/486-1382 (fax)

Romero, Nadine

Washington Dept. of Ecology

P.O. Box 47600

Olympia, WA 98504-7600

206/407-6116

206/407-6102 (fax)

Ronen, Daniel

Weizmann Institute of Science

76100 Rehovot

Israel

972-8-342546

972-8-344124 (fax)
A-5

Rosal, Charlita

U.S. EPA/EMSL-LV

P.O. Box 93478

Las Vegas, NV 89193-3478

702/798-2179

702/798-2692 (fax)

Ryan, Joseph N.

University of Colorado

Campus Box 428

Boulder, CO 80309

303/492-0772

303/492-7317 (fax)

Sara, Martin

Rust Environment & Infrastructure

1240 E. Diehl Road

Neighborville, IL 60563

708/955-6686

Sridharan, Lakshmi

Bureau of Solid & Hazardous Waste

Dept. of Natural Resources

101 S. Webster Street Box 7921

Madison, WI 53707

608/266-0520

608/267-2768 (fax)

Stelz, William G.

U.S. EPA/OMMSQA (8205)

401 M Street, SW

Washington, DC 20460

202/260-5798

202/260-4346 (fax)

Taylor, Allan B.

Michigan Dept. of Natural Resources

Work Management Division

P.O. Box 30241

Lansing, MI 48909

517/373-4799

517/373-4797 (fax)

Teplitzky, Andrew L.

U.S. EPA/OSW (5306)

401 M Street, SW

Washington, DC 20460

202/260-4536

White, Carol

Sevee & Maher Engineers, Inc.

4 Blanchard Road

P.O. Box 85A

Cumberland Center, ME 04021

207/829-5016

207/829-5692 (fax)

Zavala, Bernie

U.S. EPA/Region X

1200 Sixth Ave.

Seattle, WA 98101

206/553-1562

206/553-0119 (fax)
B-1

Appendix B -

Questions to Consider

for

Small Group Discussions
B-2

Monitoring Goals and Objectives

1. What are the objectives of the monitoring programs?

2. To what extent do/should the program objectives, site characteristics, or constituents of concern

provide criteria for representativeness?

3. Can we identify purpose and objective-driven sampling designs if monitoring networks are to be

used for different purposes over the life of the networks (e.g., detection networks phased into

assessment networks which may later be phased into corrective action networks)?

4. Given a sampling protocol, will the data collected meet monitoring objectives? What accuracy and

sensitivity will the sampling and analysis protocol provide?

5. Can field screening techniques be applied equally to detection and assessment monitoring programs? How can we provide performance criteria for field analyses that are credible and reliable?

6. Knowing that contaminant concentration values are dependent upon how the sample is collected, its

rate of extraction, and the point where it's drawn - how do these factors influence monitoring objectives?

7. What effects do/should the physical/chemical speciation of contaminants play in the design of a

monitoring program?

8. What alternative methods are available for designing monitoring well networks?

9. Do we need better documentation of well construction and well development?
B-3

Well Design, Construction, Development

1. What artifacts are introduced by well design, construction, and development? How do these artifacts compare in magnitude to sampling procedure errors?

2. What procedures/criteria should be followed to reduce the artifacts associated with well design,

construction, and development? Can general guidelines be recommended? What existing guidance

documents are avilable for reference? Are there needs for new guidance?

3. What are reliable/effective monitoring well development techniques and criteria?

4. Can guidance on well design be developed for specific hydrogeologic settings (i.e., grain size/

sorting/uniformity coefficient/hydraulic conductivity ranges)?

5. Can we provide criteria for properly designed wells without identifying some grain size/sorting/

uniformity coefficient/hydraulic conductivity ranges for specific types of installations?
B-4

Well Purging and Sampling

1. Why do we purge wells? Are the reasons/justification the same for dedicated and non-dedicated

sampling systems?

2. How should wells be purged? What should be the endpoints of sufficient purging? Do we need

better documentation of how wells are purged? Is there a difference between different purging

methods?

3. What are the advantages and disadvantages of low-flow purging and sampling techniques?

4. Is one set of criteria of endpoints sufficient to define "acceptable" purging and sampling for all

cases, or will endpoints of purging be site-specific? (i.e., do hydrogeological conditions affect how

we should purge and sample, e.g., unconsolidated formations, fractured rock, low-yielding wells,

Karst solution cavities). How does purging and sampling affect the spatial resolution of information on contaminant distribution in different hydrogeological environments?

5. Can/should we formulate a short list of recommended types of sampling devices? What are the

trade-offs of dedicated vs. non-dedicated pumps? Are bailers useful and under what conditions?
B-5

Turbidity & Colloidal Transport

1. Is it advisable to have a turbidity criteria for well purging, and if so what would it be?

2. Does a representative sample always include the mobile solute and mobile colloids? Is it always

necessary to distinguish between dissolved and colloid-bound contaminants?

3. Can we readily distinguish between truly mobile colloids and immobile solids or artifacts solids

from sampling?

4. Can we identify hydrogeochemical characteristics for sites where colloidal mobility could be a

significant transport mechanism?
B-6

Sample Handling and Analysis

1. How does filtering/not filtering produce "representative" samples and/or address the objectives of

the sampling program?

What is "dissolved"? What is "mobile"? What is "total"?

2. If filtration is deemed necessary, how can sampling/filtering-induced error (artifacts) be reduced?

3. If a decision is made to not filter, what approach is required to reduce error, particularly with

regards to sample collection?

4. What ground-water constituents must be (or are easily) analyzed in the field and what constituents

require preservation for later analysis?

5. What must be done at the time of sample collection to best preserve samples for later analysis in the

laboratory?

6. Do we need better documentation of sample handling and preservation procedures used?
C-1

Appendix C -Bibliography
C-2

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C-8

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C-10

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C-12

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D-1

Appendix D - Glossary
D-2

 Appendix D - Glossary

Absorption The process by which one substance is taken into and included within another substance,

as the absorption of water by soil or nutrients by plants.

Acid-extractable metals The concentration of metals in solution after treatment of an unfiltered sample with hot

dilute mineral acid.

Adsorption The increased concentration of molecules or ions at a surface, including exchangeable

cations and anions on soil particles.

Advection The process by which solutes are transported by the motion of flowing ground water.

Aggregation The act of soil particles cohering so as to behave mechanically as a unit.

Aliquot One of a number of equal-sized portions of a water sample that is being analyzed.

Anisotropy The condition under which one or more of the hydraulic properties of an aquifer vary

according to the direction of flow.

Annular space, annulus The space between two concentric tubes or casings, or between the casing and the

borehole wall. This would include the space(s) between multiple strings of tubing/

casings in a borehole installed either concentrically or multi-cased adjacent to each other.

Aquifer A geologic formation, group of formations, or part of a formation that is saturated, and is

capable of providing a significant quantity of water.

Aquifer, confined An aquifer that is overlain by a confining bed. The confining bed has a significantly

lower hydraulic conductivity than the aquifer.

Aquifer, unconfined An aquifer in which there are no confining beds between the zone of saturation and the

surface. There will be a water table in an unconfined aquifer. Watertable aquifer is a

synonym.

Aquitard A lithologic unit that impedes ground water movement and does not yield water freely to

wells or springs but that may transmit appreciable water to or from adjacent aquifers.

Where sufficiently thick, may act as a ground water storage zone. Synonymous with

confining unit. (9)

Artifact A product of artificial character due to extraneous agency.

Assessment (investigation) The study of a particular area or region for defining the appropriateness of the area for

waste disposal.

Assessment monitoring An investigative monitoring program that is initiated after the presence of a contaminant

in ground water has been detected. The objective of this program is to determine the

concentration of constituents that have contaminated the ground water and to quantify the

rate and extent of migration of these constituents.

ASTM cement types Portland cements meeting the requirements of ASTM C 150 (Standard Specifications for

Portland Cement). Cement types have slightly different formulations that result in
D-3

various characteristics which address different construction conditions and different

physical and chemical environments. They are as follows:

ASTM Type I (Portland) A general-purpose construction cement with no special

properties.

ASTM Type II (Portland) A construction cement that is moderately resistant to sulfates

and generates a lower heat of hydration at a slower rate than ASTM Type I.

ASTM Type III (Portland; high early strength) A construction cement that produces a

high early strength. This cement reduces the curing time required when used in cold

environments, and produces a higher heat of hydration than ASTM Type I.

ASTM Type IV (Portland) A construction cement that produces a low heat of hydration

(lower than Borehole Log: The record of geologic units ASTM Types I and II) and

develops strength at a slower rate.

ASTM Type V (Portland) A construction cement that is a high sulfate resistant

formulation. Used when there is severe sulfate action from soils and ground water.

Bailer A hollow tubular receptacle used to facilitate withdrawal of fluid from a well or borehole.

Ballast Materials used to provide stability to a buoyant object (such as casing within a borehole

filled with water).

Bar A unit of pressure equal to one million dynes per square centimeter.

Baseline A surveyed condition which serves as a reference point to which later surveys are

coordinated or correlated.

Bedrock The more or less continuous body of rock which underlies the overburden soils.

Bentonite clay An altered deposit of volcanic ash usually consisting of sodium montmorillonite clay.

Blow-in The inflow of ground water and unconsolidated material into a borehole or casing caused

by differential hydraulic heads; that is, caused by the presence of a greater hydraulic head

outside of a borehole/casing than inside.

Borehole A circular open or uncased subsurface hole created by drilling.

Borehole geophysics The general field of geophysics developed around the lowering of various probes into a

well.

Borehole log The record of geologic units penetrated, drilling progress, depth, water level, sample

recovery, volumes and types of materials used, and other significant facts regarding the

drilling of an exploratory borehole or well.

Bulk density, soil The mass of dry soil per unit bulk volume. The bulk volume is determined before drying

to constant weight at 105 degrees Centigrade.
D-4

Bulk specific gravity The ratio of the bulk density of a soil to the mass of unit volume of water.

Bulk volume The volume. including the solids and the pores, of an arbitrary soil mass.

Caliper log A borehole log of the diameter of an uncased well.

Capillary forces The forces acting on soil moisture in the unsaturated zone, attributable to molecular

attraction between soil particles and water.

Capillary fringe The zone immediately above the water table, where water is drawn upward by capillary

attraction.

Casing Pipe, finished in sections with either threaded connections or bevelled edges to be field

welded, which is installed temporarily or permanently to counteract caving, to advance

the borehole, and/or to isolate the zone being monitored.

Casing, protective A section of larger diameter pipe that is emplaced over the upper end of a smaller

diameter monitoring well riser or casing to provide structural protection to the well and

restrict unauthorized access into the well.

Casing, surface Pipe used to stabilize a borehole near the surface during the drilling of a borehole that

may be left in place or removed once drilling is completed.

Cation-exchange The interchange between a cation and solution and another cation on the surface of any

surface-active material such as clay colloid or organic colloid. (1) Cation-exchange

capacity (CEC): The sum total of exchangeable cations that a soil can absorb. Expressed

in milli-equivalents per 100 grams or per gram of soil (or of other exchangers such as

clay).

Caving; sloughing The inflow of unconsolidated material into a borehole which occurs when the borehole

walls lose their cohesive strength.

Cement; Portland cement Commonly known as Portland cement. A mixture that consists of calcareous,

argillaceous, or other silica, alumina-, and iron-oxide-bearing materials that is

manufactured and formulated to produce various types which are defined in ASTM C

150. Portland cement is also considered a hydraulic cement because it must be mixed

with water to form a cement-water paste that has the ability to harden and develop

strength even if cured under water (see ASTM Cement Types).

Channels Voids that are significantly larger than packing voids. They are generally cylindrical

shaped and smooth walled, have regular conformation, and have relatively uniform crosssectional size and shape.

Chemical activity The molal concentration of an ion multiplied by a factor known as the activity

coefficient.

Clay films Coating of clay on the surfaces of soil peds and mineral grains and in soil pores. (Also

called clay skins, clay flows, illuviation cutans, argillans or tonhautchen.)

Clay (a) A soil separate consisting of particles > 0.002 mm in equivalent diameter. (b) A

textural class.
D-5

Clay mineral Naturally occurring inorganic crystalline material found in soils and other earthy

deposits, the particles being clay sized; that is, > 0.002 mm in diameter.

Coarse texture The texture exhibited by sand, loamy sands, and sandy loams except very fine sandy

loams.

Colloid The phase of a colloidal system made up of particles have dimensions of 10 - 10,000

angstroms (1 - 1000 manometers) and which is dispersed in a different phase.

Colloidal particles Particles that are so small that the surface activity has an appreciable influence on the

properties of the particle.

Conceptual model A written or illustrated visualization of geologic/hydrogeologic/environmental conditions

of a particular area.

Conductance (specific) A measure of the ability of the water to conduct an electric current at 770 F (250C). It is

related to the total concentration of ionizable solids in the water. It is inversely

proportional to electrical resistance.

Conductivity, hydraulic See soil water.

Confining bed A body of material of low hydraulic conductivity that is stratigraphically adjacent to one

or more aquifers. It may lie above or below the aquifer.

Confining unit A term that is synonymous with “aquiclude,” “aquitard,” and “aquifuge;” defined as a

body of relatively low permeable material stratigraphically adjacent to one or more

aquifers.

Contaminant An undesirable substance not normally present or an unusually high concentration of a

naturally occurring substance in water or soil.

d-10 The diameter of a soil particle (usually in millimeters) at which 10% by weight of the

particles of a particular sample are finer. Synonymous with the effective size or effective

grain size.

d-60 The diameter of a soil particle (usually in millimeters) at which 60% by weight of the

particles of a particular sample are finer.

Darcy’s law A law describing the rate of flow of water through porous media. (Named for Henry

Darcy of Paris who formulated it in 1856 from extensive work on the flow of water

through sand filter beds.)

Deflocculate (a) To separate the individual components of compound particles by chemical and/or

physical means. (b) To cause the particles of the disperse phase of a colloidal system to

become suspended in the dispersion medium. (1)

Degradation The breakdown of substances by biological action.

Degree of consolidation The ratio, expressed as a percentage of: (1) The amount of consolidation at a given time

(percent consolidation) within a soil mass, to (2) The total amount of consolidation obtainable under a given

stress condition.
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Degree of saturation The extent or degree to which the voids in rock contain fluid (water, gas, or oil). Usually

expressed in percent related to total void or pore space.

Density The mass or quantity of a substance per unit volume. Units are kilograms per cubic

meter or grams per cubic centimeter.

Deposit Material left in a new position by a natural transporting agent such as water, wind, ice. or

gravity, or by the activity of man.

Depression curve Record of profile of water table as a result of pumping.

Detection monitoring A program of monitoring for the express purpose of determining whether or not there has

been a contaminant release to ground water.

Diagenesis The chemical and physical changes occurring in sediments before consolidation or while

in the environment of deposition.

Differential water capacity The absolute value of the rate of change of water content with soil water pressure. The

water capacity at a given water content will depend on the particular desorption or

adsorption curve employed. Distinction should be made between volumetric and specific

water capacity.

Direct methods Methods (e.g., boreholes and monitoring wells) which entail the excavation or drilling,

collection, observation, and analysis of geologic materials and water samples.

Direct precipitation Water that falls directly into a lake or stream without passing through any land phase of

the runoff cycle.

Discharge area An area in which there are upward components of hydraulic head in the aquifer. Ground

water is flowing toward the surface in a discharge area and may escape as a spring, seep,

or baseflow, or by evaporation and transpiration.

Discharge velocity An apparent velocity, calculated from Darcy’s law, which represents the flow rate at

which water would move through an aquifer if the aquifer were an open conduit. Also

called specific discharge.

Direct methods Methods (e.g., boreholes and monitoring wells) which entail the excavation or drilling,

collection, observation, and analysis of geologic materials and water samples.

Discontinuity (a) Boundary between major layers of the Earth which have different seismic velocities.

(b) Interruption of the homogeneity of a rock mass (e.g. joints, faults, etc.).

Disperse (a) To break up compound particles, such as aggregates, into the individual component

particles. (b) To distribute or suspend fine particles, such as clay, in or throughout a

dispersion medium, such as water.

Disposal The discharge, deposit, injection, dumping, spilling, leaking, or placing of any solid

waste or hazardous waste into or on any land or water so that such solid waste or

hazardous waste or any constituent thereof may enter the environment or be emitted into

the air or discharged into any waters, including ground waters.
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Dissolved metals Those constituents (metals) of an unacidified sample that pass through a 0.45pm

membrane filter.

Dissolution The process where soluble organic components from DNAPL dissolves in groundwater

or infiltration and forms a groundwater contaminant plume. The duration of remediation

measures (either clean-up or containment) is determined by the 1) the rate of the

dissolution process that can be achieved in the field, and 2) the mass of soluble

components in the residual DNAPL trapped in the aquifer.

DNAPL A Dense Non-aqueous Phase Liquid. Also known as free product or a sinking plume

(sinker).

DNAPL entry location The area where DNAPL has entered the subsurface.

DNAPL site A site where DNAPL has been released and is now present in the subsurface as an

immiscible phase.

DNAPL zone The portion of a site affected by free-phase or residual DNAPL in the subsurface either

the vadose zone or saturated zone). The DNAPL zone has organics in the vapor phase

(unsaturated zone), dissolved phase (both unsaturated and saturated zone), and DNAPL

phase (both unsaturated and saturated zone).

Downhole geophysics Techniques that use a sensing device that is lowered into a borehole for the purpose of

characterizing geologic formations and their associated fluids. The results can be

interpreted to determine lithology, resistivity, bulk density, porosity, permeability, and

moisture content and to define the source, movement, and physical/chemical

characteristics of ground water.

Drawdown A lowering of the water table of an unconfined aquifer or the potentiometric surface of a

confined aquifer caused by pumping of ground water from wells.

Drill cuttings Fragments or particles of soil or rock, with or without free water, created by the drilling

process.

Drilling fluid A fluid (liquid or gas) that may be used in drilling operations to remove cuttings from the

borehole, to clean and cool the drill bit, and to maintain the integrity of the borehole

during drilling.

Dynamic equilibrium A condition in which the amount of recharge to an aquifer equals the amount of natural

discharge.

Effective porosity The amount of interconnected pore space through which fluids can pass, expressed as a

percent of bulk volume. Part of the total porosity will be occupied by static fluid being

held to the mineral surface by surface tension, so effective porosity will be less than total

porosity.

Effective solubility The actual aqueous solubility of an organic constituent in groundwater that is in chemical

equilibrium with a mixed DNAPL (a DNAPL containing several organic constituents).

The effective solubility of a particular organic chemical can be estimated by multiplying

its mole fraction in the DNAPL mixture by its pure phase solubility.
D-8

Equilibrium constant The number defining the conditions of equilibrium for a particular reversible chemical

reaction.

Equivalent diameter In sedimentation analysis, the diameter assigned to a non-spherical particle, it being

numerically equal to the diameter of a spherical particle of the same density and velocity

of fall.

Equipotential line A line in a two-dimensional ground-water flow field such that the total hydraulic head is

the same for all points along the line.

Equipotential surface A surface in a three-dimensional ground-water flow field such that the total hydraulic

head is the same everywhere on the surface.

Equivalent weight The concentration in parts per million of a solute multiplied by the valence charge and

then divided by its formula weight in grams.

Field capacity The maximum amount of water that the unsaturated zone of a soil can hold against the

pull of gravity. The field capacity is dependent on the length of time the soil has been

undergoing gravity drainage.

Fill Man-made deposits of natural soils or rock products and waste materials.

Film water A layer of water surrounding soil particles and varying in thickness from 1 or 2 to

perhaps 100 or more molecular layers. Usually considered as that water remaining after

drainage has occurred because it is not distinguishable in saturated soils.

Fine texture Consisting of or containing large quantities of the fine fractions, particularly of silt and

clay. (Includes all clay loams and clays; that is, clay loams, sandy clay loam, silty clay

loam, sandy clay, silty clay, and clay textural classes. Sometimes subdivided into clayey

texture and moderately fine texture.) See soil texture.

Fissure flow Flow of water through joints and larger voids.

Flow net The set of intersecting equipotential lines and flowlines representing two dimensional

steady flow through porous media.

Flow, steady The flow that occurs when, at any point in the flow field, the magnitude and direction of

the specific discharge are constant in time.

Flow, unsteady The flow that occurs when, at any point in the flow field, the magnitude or direction of

the specific discharge changes with time. Also called transient flow or nonsteady flow.

Fluid potential The mechanical energy per unit mass of fluid at any given point in space and time.

Flush joint or flush coupled Casing or riser with ends threaded such that a consistent inside and outside diameter is

maintained across the threaded joints or couplings.

Fracture A break in a rock formation due to structural stresses. Faults, shears, joints, and planes of

fracture cleavage are all types of fractures.
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Fracture trace The surface representation of a fracture zone. It may be a characteristic line of vegetation

or linear soil-moisture pattem or a topographic sag.

Free energy A measure of the thermodynamic driving energy of a chemical reaction. Also known as

Gibbs free energy or Gibbs function.

Free-phase DNAPL Immiscible liquid exiting in the subsurface with a positive pressure such that it can flow

into a well. If not trapped in a pool, free phase DNAPL will flow vertically through an

aquifer or laterally down sloping fine-grained stratigraphic units. Also called mobile

DNAPL or continuous phase DNAPL.

Free water Water that is free to move through a soil or rock mass under the influence of gravity.

(gravitational water)

(ground water)

(phreatic water)

Gamma-gamma A borehole log in which a source of gamma radiation as well as a detector are lowered

radiation log into the borehole. This log measures bulk density of the formation and fluids.

Geohydrology Science of the occuffence, distribution, and movement of water below the surface of the

Earth.

Geomorphology The description of the present exposed surfaces of the crust of the Earth, and seeks to

interpret these surfaces in terms of natural processes (chiefly erosion) which lead or have

led to their formation.

Geophysical borehole logging See Downhole Geophysics.

Geophysics The study of all the gross physical properties of the Earth and its parts, particularly

associated with the detection of the nature and shape of unseen subsurface rock bodies by

measurement of such properties and property contrasts. Small scale applied geophysics

is now a major aid in geological reconnaissance.

Geotechnical Pertaining to Geotechnics, which is the application of scientific methods to problems in

engineering geology.

Gradation (grain-size The proportions by mass of a soil or fragmented rock distributed in specified particle-size

distribution) (texture) ranges.

 Grading A‘well-graded’ sediment containing some particles of all sizes in the range concerned.

Distinguish from‘well sorted’, which describes a sediment with grains of one size.

Grain-size analysis The process of determining grainsize distribution.

(mechanical analysis)

(particle/size analysis)

Granule A natural soil aggregate or ped which is relatively nonporous. See soil structure and soil

structure types.

Gravelpack Common nomenclature for the preferred terminology, primary filter of a well (see

primary filter pack).
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Gravel Round or semirounded particles of rock that will pass a 3-in. (76.2 mm) sieve and be

retained on a No. 4 (4.75 mm) U.S. standard sieve.

Ground water (a) The water contained in interconnected pores located below the water table in an

unconfined aquifer or located in a confined aquifer. (b) The portion of the total

precipitation which at any particular time is either passing through or standing in the soil

and the underlying strata and is free to move under the influence of gravity.

Ground-water basin A rather vague designation pertaining to a ground-water reservoir which is more or less

separate from neighboring ground-water reservoirs. A ground-water basin could be

separated from adjacent basins by geologic boundaries or by hydrologic boundaries.

Ground water, confined The water contained in a confined aquifer. Pore-water pressure is greater than

atmospheric at the top of the confined aquifer.

Ground-water flow The movement of water through openings in sediment and rock which occurs in the zone

of saturation.

Ground water level The level below which the rock and subsoil, to unknown depths, are saturated.

Ground-water mining The practice of withdrawing ground water at rates in excess of the natural recharge.

Ground water, perched The water in an isolated, saturated zone located in the zone of aeration. It is the result of

the presence of a layer of material of low hydraulic conductivity, called a perching bed.

Perched ground water will have a perched water table.

Ground water regime Water below the land surface in a zone of saturation.

(ground water)

Ground water, unconfined The water in an aquifer where there is a water table.

Grout A low permeability material placed in the annulus between the well casing or riser pipe

and the borehole wall (i.e., in a single cased monitoring well), or between the riser and

casing (i.e., in a multi-cased monitoring well), to maintain the alignment of the casing

and riser and to prevent movement of ground water or surface water within the annular

space.

Head, total The sum of the elevation head, the pressure head, and the velocity head at a given point

in an aquifer.

Heterogeneous Pertaining to a substance having different characteristics in different locations. A

synonym is nonuniform.

Homogeneous Pertaining to a substance having identical characteristics everywhere. A synonym is

uniform.

Horizon See soil horizon.

Hydration The physical binding of water molecules to ions, molecules, particles, or other matter.

Hydraulic conductivity A coefficient of proportionality describing the rate at which water can move through a
D-11

permeable medium. The density and kinematic viscosity of the water must be considered

in determining hydraulic conductivity.

Hydraulic diffusivity A property of an aquifer or confining bed defined as the ratio of the transmissivity to the

storativity.

Hydraulic gradient The change in total head with a change in distance in a given direction. The direction is

that which yields a maximum rate of decrease in head.

Hydraulic head The elevation with respect to a specified reference level at which water stands in a

piezometer connected to the point in question in the soil. Its definition can be extended

to soil above the water table if the piezometer is replaced by a tensiometer. The

hydraulic head in systems under atmospheric pressure may be identified with a potential

expressed in terms of the height of a water column. More specifically it can be identified

with the sum of gravitational and capillary potentials, and may be termed the hydraulic

potential.

Hydrochemical facies Bodies of water with separate but distinct chemical compositions contained in an aquifer.

Hydrodynamic dispersion The process by which ground water containing a solute is diluted with uncontaminated

ground water as it moves through an aquifer.

Hydrograph A graph that shows some property of ground water or surface water as a function of time.

Hydrogeology The study of the natural (and artificial) distribution of water in rocks, and its relationship

to those rocks. Inasmuch as the atmosphere is a continuation of the hydrosphere, and is

in physical and chemical balance with it, there is a close connection with meteorology.

Hydrologic equation An expression of the law of mass conservation for purposes of water budgets. It may be

stated as inflow equals outflow plus or minus changes in storage.

Hydrologic unit Geologic strata that can be distinguished on the basis of capacity to yield and transmit

fluids. Aquifers and confining units are types of hydrologic units. Boundaries of a

hydrologic unit may not necessarily correspond either laterally or vertically to

lithostratigraphic formations.

Hydrostatic pressure A state of stress in which all the principal stresses are equal (and there is no shear stress).

Hydrostratigraphic unit A formation, part of a formation, or a group of formations in which there are similar

hydrologic characteristics allowing for grouping into aquifers or confining layers.

Hygroscopic water Water adsorbed by a dry soil from an atmosphere of high relative humidity, water

remaining in the soil after “air-drying” or water held by the soil when it is in equilibrium

with an atmosphere of a specified relative humidity at a specified temperature, usually

98% of relative humidity at 25 degrees Centigrade.

Ideal gas A gas having a volume that varies inversely with pressure at a constant temperature and

that also expands by 1/273 of its volume at 0°C for each degree rise in temperature at

constant pressure.
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Immobilization The conversion of an element from the inorganic to the organic form in microbial tissues

or in plant tissues.

Indirect methods Methods which include the measurement or remote sensing of various physical and/or

chemical properties of the earth (e.g., electromagnetic conductivity, electrical resistivity,

specific conductance, geophysical logging, aerial photography).

Infiltration The flow of water downward from the land surface into and through the upper soil layers.

Infiltration capacity The maximum rate at which infiltration can occur under specific conditions of soil

moisture. For a given soil, the infiltration capacity is a function of the water content.

Infiltration rate (a) A soil characteristic determining or describing the maximum rate at which water can

enter the soil under specified conditions, including the presence of an excess of water. (b)

The rate at which a soil under specified conditions can absorb falling rain or melting

snow; expressed in depth of water per unit time (cm/sec; in/hr).

Injection well A well drilled and constructed in such a manner that water can be pumped into an aquifer

in order to recharge it.

Interflow The lateral movement of water in the unsaturated zone during and immediately after a

precipitation event. The water moving as interflow discharges directly into a stream or

lake.

Intermediate zone That part of the unsaturated zone below the root zone and above the capillary fringe.

 Intrinsic permeability Pertaining to the relative ease with which a porous medium can transmit a liquid under a

hydraulic or potential gradient. It is a property of the porous medium and is independent

of the nature of the liquid or the potential field.

Ion exchange A process by which an ion in a mineral lattice is replaced by another ion which was

present in an aqueous solution.

Isotropy The condition in which hydraulic properties of the aquifer are equal in all directions.

Jetting When applied as a drilling method, water is forced down through the drill rods or casing

and out through the end aperture. The jetting water then transports the generated cuttings

to the ground surface in the annulus of the drill rods or casing and the borehole. The term

jetting may also refer to a development technique (see well screen jetting).

Kinematic viscosity The ratio of dynamic viscosity to mass density. It is obtained by dividing dynamic

viscosity by the fluid density. Units of kinematic viscosity are square meters per second.

Laminar flow That type of flow in which the fluid particles follow paths that are smooth, straight, and

parallel to the channel walls. In laminar flow, the viscosity of the fluid damps out

turbulent motion. Compare with Turbulent flow.

Law of mass action The law stating that for a reversible chemical reaction the rate of reaction is proportional

to the concentrations of the reactants.

Leach To cause water or other liquid to percolate through soil.
D-13

Leaky conflning layer A low-penneability layer that can transmit water at sufficient rates to fumish some

recharge to a well pumping from an underlying aquifer. Also called aquitard.

Lineament A natural linear surface feature longer than 1500 meters.

Lysimeter A field device containing a soil column and vegetation which is used for measuring

actual evapotranspiration.

Lysimeter (a) A device for measuring percolation and leaching losses from a column of soil under

controlled conditions. (b) A device for measuring gains (precipitation and condensation)

and losses (evapotranspiration) by a column of soil.

Maximum contaminant level The highest concentration of a solute permissible in a public water supply as specified in

the National Interim Primary Drinking Water Standards for the United States.

Molality A measure of chemical concentration. A one-molal solution has one mole of solute

dissolved in 1000 grams of water. One mole of a compound is its formula weight in

grams.

Morphology See soil morphology.

Multi-cased well A well constructed by using successively smaller diameter casings with depth.

Multiport systems A single hole device in which points are installed that are capable of sampling or

measuring at multiple levels within a formation or series of formations.

N-value The number of blows required to drive the sampler of the Standard Penetration test its

last 12 inches (300 mm).

Natural gamma radiation log A borehole log that measures the natural gamma radiation emitted by the formation

rocks. It can be used to delineate subsurface rock types.

Neat cement A mixture of Portland cement (ASTM 150) and water.

Negative pressure A pressure less than the local atmospheric pressure at a given point.

Neutron log A borehole log obtained by lowering a radioactive element, which is a source of neutrons,

and a neutron detector into the well. The neutron log measures the amount of water

present; hence, the porosity of the formation.

Observation well A nonpumping well used to observe the elevation of the water table or the potentiometric

surface. An observation well is generally of larger diameter than a piezometer and

typically is screened or slotted throughout the thickness of the aquifer.

Overburden The loose soil, sand, silt, or clay that overlies bedrock.

Overland flow The flow of water over a land surface due to direct precipitation. Overland now generally

occurs when the precipitation rate exceeds the infiltration capacity of the soil and

depression storage is full. Also called Horton overland flow.

Oxidation-reduction potential The potential required to transfer electrons from the oxidant to the reductant and used as

2 qualitative measure of the state of oxidation in wastewater treatment systems.
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Packer A transient or dedicated device placed in a well that isolates or seals a portion of the well,

well annulus, or borehole at a specific level.

Parent material The unconsolidated and more or less chemically weathered mineral or organic matter

from which the solum of soil is developed by pedogenic processes.

Particle density The mass per unit volume of the soil particles. In technical work, usually expressed as

grams per cubic centimeter. See bulkeny, soil.

Particle size The effective diameter of a particle measured by sedimentation, sieving, or micrometric

methods.

Particle-size analysis Determination of the various amounts of the different separates in a soil sample, will

usually be sedimentation, sieving, micrometry, or combinations of these methods.

Particle-size distribution The amounts of the various soil separates in a soil sample, usually expressed as weigbt

percentages.

Penetrability The ease with which a probe can be pushed into the soil. (May be expressed in units of

distance, speed, force, or work depending on the type of penetrometer used).

Percent saturation The ratio, expressed as a percentage, of. (a) The volume of water in a given soil or rock

(degree of saturation) mass, to (b) The total volume of intergranular space (voids).

Perched water table A water table usually of limited area maintained above the normal free water elevation by

the pressure of an intervening relatively impervious confining stratum.

Percolation The flow or trickling of a liquid downward through a contact or filtering medium. The

liquid may or may not fill the pores of the medium.

Permeability, soil (a) The ease with which gases, liquids, or plant roots penetrate or pass through a bulk

mass of soil or a layer of soil. Since different soil horizons vary in permeability, the

particular horizon under question should be designated. (b) The property of a porous

medium itself that relates to the ease with which gases, liquids, or other substances can

pass through it. Previously, frequently considered the “k” in Darcy’s law. See Darcy’s

law and soil water.

Permeameter A laboratory device used to measure the intrinsic permeability and hydraulic conductivity

of a soil or rock sample.

pH, soil The negative logarithm of the hydrogen-ion activity of a soil. The degree of acidity (or

alkalinity) of a soil as determined by means of a glass, quinhydrone, or other suitable

electrode or indicator at a specified moisture content or soil-water ratio, and expressed in

terrns of the pH scale.

Physical properties (of soil) Those characteristics, processes, or reactions of a soil which are caused by physical

forces and which can be described by, or expressed in, physical terms or equations.

Sometimes confused with and difficult to separate from chemical properties; hence, the

terms “physical-chemical” or “physiochemical”. Examples of physical properties are

bulk density, water-holding capacity, hydraulic conductivity, porosity, pore-size

distribution, etc.
D-15

Phreatic water Water in the zone of saturation.

Piezometer A nonpumping well, generally of small diameter, which is used to measure the elevation

of the water table or potentiometric surface A piezometer generally has a short well

screen through which water can enter.

Piezometer nest A set of two or more piezometers set close to each other but screened to different depths.

Piezometric surface (a) The surface at which water will stand in a series of piezometers. (b) An imaginary

surface that everywhere coincides with the static level of the water in the aquifer.

Piping An underground flow of water with a sufficient pressure gradient to cause scour along a

preferred path.

Piston sampler A tube with an internal piston used for obtaining relatively undisturbed samples from

cohesive soils.

Plume The zone of contamination containing organics in the dissolved phase. The plume

usually will originate from the DNAPL zone and extend downgradient for some distance

depending on site hydrogeologic and chemical conditions. To avoid confusion, the term

“DNAPL plume” should not be used to describe a DNAPL pool; “plume” should be used

only to refer to dissolved-phase organics.

Pool and lens A zone of free-phase DNAPL at the bottom of an aquifer. A lens is a pool that rests on a

fine-grained stratigraphic unit of limited areal extent. DNAPL can be recovered from a

pool or a lens if a well is placed in the right location.

Pollutant Any solute or cause of change in physical properties which renders water unfit for a

given use.

Pore-size distribution The volume of the various sizes of pores in a soil. Expressed as percentages of the bulk

volume (soil plus pore space).

Pore space The volume between mineral grains in a porous medium.

Porosity The ratio of the volume of void spaces in a rock or sediment to the total volume of the

rock or sediment.

Potentiometric surface A surface that represents the level to which water will rise in tightly cased wells. If the

head varies significantly with depth in the aquifer, then there may be more than one

potentiometric surface. The water table is a particular potentiometric surface for an

unconfined aquifer.

Primary filter pack A clean silica sand or sand and gravel mixture of selected grain size and gradation that is

installed in the annular space between the borehole wall and the well screen, extending an

appropriate distance above the screen, for the purpose of retaining and stabilizing the

particles from the adjacent strata. The term is used in place of “gravel pack.”

Profile, soil A vertical section of the soil through all its horizons and extending into the parent

material.
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PTFE tape Joint sealing tape composed of polytetrafluoroethylene.

Pumping cone The area around a discharging well where the hydraulic head in the aquifer has been

lowered by pumping. Also called cone of depression.

Pumping test A test made by pumping a well for a period of time and observing the change in

hydraulic head in the aquifer. A pumping test may be used to determine the capacity of

the well and the hydraulic characteristics of the aquifer. Also called aquifer test.

Radial flow The flow of water in an aquifer toward a vertically oriented well.

Rating curve A graph of the discharge of a river at a particular point as a function of the elevation of

the water surface.

Reaction, soil The degree of acidity or alkalinity of a soil, usually expressed as a pH value. Descriptive

terms commonly associated with certain ranges in pH are: extremely acid, less than 4.5;

very strongly acid, 4.5 to 6.0; slightly acid, 6.1 to 6.5; neutral, 6.6 to 7.3; slightly alkaline,

7.4 to 7.8; moderately alkaline, 7.9 to 8.4; strongly alkaline, 8.5 to 9.0; and very strongly

alkaline, greater than 9. 1.

Recharge area An area in which there are downward components of hydraulic head in the aquifer.

Infiltration moves downward into the deeper parts of an aquifer in a recharge area.

Recharge basin A basin or pit excavated to provide a means of allowing water to soak into the ground at

rates exceeding those that would occur naturally.

Recharge boundary An aquifer system boundary that adds water to the aquifer. Streams and lakes are typical

recharge boundaries.

Recovery The rise in water level in a pumping well and nearby observation wells after groundwater pumpage has ceased.

Regolith The upper part of the earth’s surface that has been altered by weathering processes. It

includes both soil and weathered bedrock.

Representativeness The characteristic of a specific scientific experiment that makes it an adequate sample of

the general case.

Representative point a) A location in surface waters or ground waters at which specific conditions or

parameters may be measured in such a manner as to characterize or approximate the

quality or condition of the water body; or b) A location in process or waste waters at

which specific conditions or parameters are measured and will adequately reflect the

actual condition of those waters or waste waters for which analysis was made.

Riser The pipe extending from the well screen to or above the ground surface.

Residual Immiscible phase liquid held in the pore spaces or fractures by capillary forces (negative

pressure on DNAPL), Residual will remain trapped within the pore of the porous media

unless the viscous forces (caused by the dynamic force of water against the DNAPL ) are

greater than the capillary forces holding the DNAPL in the pore. At most sites the

hydraulic gradient required to mobilize all of the residual trapped in an aquifer is usually

much greater than can be produced by wells or trenchers.
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Residual saturation The fraction of available pore space containing residual DNAPLS, or the saturation level

where free-phase DNAPL becomes residual DNAPL. In the vadose zone, residual

saturation range up to 20% of total pore volume while in the saturated zone residual

saturations range up to 50% of total pore volume.

Resistivity log A borehole log made by lowering two current electrodes into the borehole and measuring

the resistivity between two additional electrodes. It measures the electrical resistivity of

the formation and contained fluids near the probe.

Rock Natural solid mineral matter occurring in large masses or fragments.

Runoff The total amount of water flowing in a stream. It includes overland flow, return flow,

interflow, and baseflow.

Sand (a) A soil particle between 0.05 and 2.0 mm in diameter. (b) Any one of five soil

separates, namely: very coarse sand, coarse sand, medium sand, fine sand, and very fine

sand. See soil separates. (c) A soil textural class. See soil texture.

Sand model A scale model of an aquifer, which is built using a porous medium to demonstrate

ground-water flow.

Sanitary landflll The disposal of solids and, in some instances, semisolid and liquid wastes by burying the

material to shallow depths, usually in unconsolidated materials.

Saturated zone The zone in which the voids in the rock or soil are filled with water at a pressure greater

than atmospheric. The water table is the top of the saturated zone in an unconfined

aquifer.

Saturation A condition reached by a material, whether it be in solid, gaseous, or liquid state, that

holds another material within itself in a given state in an amount such that no more of

such material can be held within it in the same state. The material is then said to be

saturated on in a condition of saturation.

Secondary filter pack A clean, uniformly graded sand that is placed in the annulus between the primary filter

pack and the over-lying seal, or between the seal and overlying grout backfill or both, to

prevent movement of seal, or grout, or both into the primary filter pack.

Secondary porosity The porosity developed in a rock after its deposition or emplacement, through such

processes as solution or fracturing.

Sediment sump A blank extension beneath the well screen used to collect fine-grained material from the

filter pack and adjacent strata. The term is synonymous with rat trap or tail pipe.

Sedimentation The process of subsidence and deposition of suspended matter carried by water,

wastewater, or other liquids, by gravity. It is usually accomplished by reducing the

velocity of the liquid below the point at which it can transport the suspended material.

Seepage velocity The actual rate of movement of fluid particles through porous media.

Seismic refraction A method of determining subsurface geophysical properties by measuring the length of

time it takes for artificially generated seismic waves to pass through the ground.
D-18

Silt (a) A soil separate consisting of particles between 0.005 and 0.002 mm in equivalent

diameter. See soil separates. (b) A soil texture class. See soil texture.

 Single-cased well A monitoring well constructed with a riser but without an exterior casing. (9)

Single-point resistance log A borehole log made by lowering a single electrode into the well with the other electrode

at the ground surface. It measures the overall electrical resistivity of the formation and

drilling fluid between the surface and the probe.

Site assessment A formal means of exploring and characterizing a proposed waste management facility or

location so that all physical factors are identified and so quantified as to serve as the basis

of an environmentally sound design and operational plan.

Slug test An aquifer test made by either pouring a small instantaneous charge of water into a well

or by withdrawing a slug of water from the well. A synonym for this test, when a slug of

water is removed from the well, is a bail-down test.

Soil (a) The unconsolidated mineral material on the immediate surface of the Earth that serves

as a natural medium for the growth of land plants. (b) The unconsolidated mineral matter

on the surface of the Earth that has been subjected to and influenced by genetic and

environmental factors of: parent material, climate (including moisture and temperature

effects), macro- and microorganisms, and topography, all acting over a period of time and

producing a product, soil, that differs from the, material from which it is derived in many

physical, chemical, biological, and morphological properties and characteristics.

Soil auger A tool for boring into the soil and withdrawing a small sample for field or laboratory

observation. Soil augers may be classified into several types as follows: (a) Those with

worm-type bits, unenclosed; (b) Those with worm-type bits enclosed in a hollow

cylinder; and those with a hollow cylinder with a cutting edge at the lower end.

Soil mineral (a) Any mineral that occurs as a part of or in the soil. (b) A natural inorganic compound

with definite physical, chemical, and crystalline properties (within the limits of

isomorphism), that occurs in the soil.

Soil moisture The water contained in the unsaturated zone.

Soil morphology (a) The physical constitution, particularly the structural properties of the soil profile as

exhibited by the kinds, thickness, and arrangement of the horizons in the profile, and by

the texture, structure, consistency, and the porosity of each horizon. (b) The structural

characteristics of the soil or any of its parts.

Soil physics The organized body of knowledge concemed with the physical characteristics of soil and

with the methods employed in their determinations.

Soil science That science dealing with soils as a natural resource on the surface of the Earth including

soil formation, classification, and mapping, and physical, chemical, biological, and

fertility properties of soil per se; and these properties in relation to their management.

Soil separates Mineral particles, < 2.0 mm in equivalent diameter, ranging between specified size limits.

The names and size limits of separates recognized in the U.S.D.A. system are: very

coarse sand, 2.0 to 1.0 mm; coarse sand, 1.0 to 0.5 mm; medium sand, 0.5 to 0.25 mm;
D-19

fine sand, 0.25 to 0.10 mm; very fine sand, 0.10 to 0.05 mm; silt, 0.05 to 0.002 mm; and

clay, < 0.002 mm. The U.S.C.S. particle and size range are as follows: coarse sand, 2.0

to 4.76 mm; medium sand, 0.42 to 2.0 mm; fine sand, 0.074 to 0.42 mm; fines (silt and

clay), < 0.074 mm. (Note: U.S.C.S. silt and clay designations are determined by response

of the soil to manipulation at various water contents rather than by measurement of size.)

Soil solution The aqueous liquid phase of the soil and its solutes.

Soil structure The combination or arrangement of primary soil particles into secondary particles, units,

or peds. These secondary units may be, but usually are not, arranged in the profile in

such a manner as to give a distinctive, characteristic pattern. The secondary units are

characterized and classified on the basis of size, shape, and degree of distinctness into

classes, types, and grades, respectively.

Soil suction A measure of the force of water retention in unsaturated soil. Soil suction is equal to a

force per unit area that must be exceeded by an externally applied suction to initiate water

flow from the soil. Soil suction is expressed in standard pressure terms.

Soil texture The relative proportion of the various soil separates in a soil as described by the classes

of soil texture.

Soil water diffusivity The hydraulic conductivity divided by the differential water capacity (care being taken to

be consistent with units), or the flux of water per unit gradient of moisture content in the

absence of other force fields.

Soil water pressure The pressure (positive or negative), relative to the extemal gas pressure on the soil water,

to which a solution identical in composition to the soil water must be subjected in order

to be in equilibrium through a porous permeable wall with the soil water. May be

identified with the capillary potential defined above.

Soil water A general term emphasizing the physical rather than the chemical properties and bebavior

of the soil solution.

Soil-moisture tension See moisture tension (or pressure).

Solid waste disposal facilities A facility or part of a facility at which solid waste is intentionally placed into or on any

land or water, and at which waste will remain after closure.

Solubility product The equilibrium constant that describes a solution of a slightly soluble salt in water.

Specific capacity An expression of the productivity of a well, obtained by dividing the rate of discharge of

water from the well by the drawdown of the water level in the well. Specific capacity

should be described on the basis of the number of hours of pumping prior to the time the

drawdown measurement is made. It will generally decrease with time as the drawdown

increases.

Speciflc electrical conductance The ability of water to transmit an electrical current. It is related to the concentration and

charge of ions present in the water.

Speciflc retention The ratio of the volume of water the rock or sediment will retain against the pull of

gravity to the total volume of the rock or sediment.
D-20

Specific weight The weight of a substance per unit volume. The units are newtons per cubic meter.

Specific yield The ratio of the volume of water a rock or soil will yield by gravity drainage to the

volume of the rock or soil. Gravity drainage may take many months to occur.

Spontaneous potential log A borehole log made by measuring the natural electrical potential which develops

between the formation and the borehole fluids.

Stability The condition of a structure or a mass of material when it is able to support the applied

stress for a long time without suffering any significant deformation or movement that is

not released by the release of stress.

Stagnation point A place in a ground-water flow field at which the ground water is not moving. The

magnitude of vectors of hydraulic head at the point are equal but opposite in direction.

Subsoil In general concept, that part of the soil below the depth of plowing. (2)

Static water level The elevation of the top of a column of water in a monitoring well or piezometer that is

not influenced by pumping or conditions related to well installation, hydrologic testing,

or nearby pumpage.

Storage, specific The amount of water released from or taken into storage per unit volume of a porous

medium per unit change in head.

Storativity The volume of water an aquifer releases from or takes into storage per unit surface area

of the aquifer per unit change in head It is equal to the product of specific storage and

aquifer thickness. In an unconfined aquifer, the storativity is equivalent to the specific

yield. Also called storage coefficient.

Stratified Arranged in strata, or layers. The term refers to geologic material. Layers in soils that

result from the processes of soil formation are called horizons; those inherited from the

parent material are called strata.

Structure One of the larger features of a rock mass, like bedding, foliation, jointing, cleavage, or

brecciation; also the sum total of such features as contrasted with texture. Also, in a

broader sense, it refers to the structural features of an area such as anticlines or synclines.

See also soil structure.

Subsoil In general concept, that part of the soil below the depth of plowing. (2)

Surface sealing The orientation and packing of dispersed soil particles in the immediate surface layer of

the soil, rendering it relatively impermeable to water.

Suspended metals Those constituents (metals) of an unacidified sample that are retained by a 0.45 mm

membrane filter.

Target monitoring zone The ground water flow path from a particular area or facility into which monitoring wells

will be screened. The target monitoring zone should be a stratum (strata) in which there

is a reasonable expectation that a vertically placed well will intercept migrating

contaminants.
D-21

Target In detection monitoring programs, the ground water flow path from a particular area or

facility into which monitoring wells will be screened. The target monitoring zone should

be a stratum (strata) in which there is a reasonable expectation that a vertically placed

well will intercept migrating contaminants.

Tensiometer (a) A device used to measure the soil-moisture tension in the unsaturated zone. (b) A

device for measuring the negative pressure (or tension) of water in soil in situ; a porous,

permeable ceramic cup connected through a tube to a manometer or vacuum gauge.

Tension The condition under which pore water exists at a pressure less than atmospheric.

Tension, soil water The expression, in positive terms, of the negative hydraulic pressure of soil water.

Test pit A shallow excavation made to characterize Transpiration: water loss from leaves and

other plant the subsurface.

Total metals The concentration of metals determined on an unfiltered sample after vigorous digestion,

or the sum of the concentrations of metals in both dissolved and suspended fractions.

Throughflow The lateral movement of water in an unsaturated zone during and immediately after a

precipitation event. The water from throughflow seeps out at the base of slopes and then

flows across the ground surface as return flow, ultimately reaching a stream or lake.

Time-series A series of statistical data collected at regular intervals of time; a frequency distribution

in which the independent variable is time.

Total potential (of soil water) The amount of work that must be done per unit quantity of pure water in order to

transport reversibly and isothermally an infinitesimal quantity of water from a pool of

pure water, at a specified elevation and at atmospheric pressure, to the soil water (at the

point under consideration). The total potential (of soil water) consists of the following:

Transects In ecology, a sample area (usually elongate or linear) chosen as the basis for studying a

particular assemblage of organisms.

Transmissivity The rate at which water of a prevailing density and viscosity is transmitted through a unit

width of an aquifer or confining bed under a unit hydraulic gradient. It is a function of

properties of the liquid, the porous media, and the thickness of the porous media.

Tremie pipe A pipe or tube that is used to transport filter pack materials and annular sealant materials

from the ground surface into the borehole annulus or between casings and casings or riser

pipe of a monitoring well.

Turbidity Heavily suspended and colloidal organic and inorganic material in water.

Turbulent flow That type of flow in which the fluid particles move along very irregular paths.

Momentum can be exchanged between one portion of the fluid and another. Compare

with Laminar flow.

Undisturbed sample A soil sample that has been obtained by methods in which every precaution has been

taken to minimize disturbance to the sample.

Unsaturated flow The movement of water in a soil which is not filled to capacity with water.
D-22

Unsaturated zone The zone between the land surface and the water table. It includes the root zone,

intermediate zone, and capillary fringe. The pore spaces contain water at less than

atmospheric pressure, as well as air and other gases. Saturated bodies, such as perched

ground water, may exist in the unsaturated zone.

Uppermost aquifer The geologic formation nearest the natural ground surface that is an aquifer, as well as

lower aquifers that are hydraulically interconnected with this aquifer within the facility’s

property boundary.

Vadose water Water in the zone of aeration.

Viscosity The property of a fluid describing its resistance to flow. Units of viscosity are newtonseconds per meter squared or pascal-seconds. Viscosity is also known as dynamic

viscosity.

Void ratio The ratio of. (a) The volume of void space, to (b) The volume of solid particles in a given

soil mass.

Voids Entities which are interconnected with each other either through voids of dissimilar size

and shape, through narrow necks, or through intersection with voids of similar size and

shape.

Water content The ratio of the volume of soil moisture to the total volume of the soil. This is the

volumetric water content, also called volume wetness.

Water table The surface in an unconfined aquifer or confining bed at which the pore water pressure is

atmospheric. It can be measured by installing shallow wells extending a few feet into the

zone of saturation and then measuring the water level in those wells.

Weathering All physical and cbemical changes produced in rocks, at or near the earth’s surface, by

atmospheric agents.

Well completion diagram A record that illustrates the details of a well installation..

Well, fully penetrating A well drilled to the bottom of an aquifer, constructed in such a way that it withdraws

water from the entire thickness of the aquifer.

Well interference The result of two or more pumping wells, the drawdown cones of which intercept. At a

given location, the total well interference is the sum of the drawdowns due to each

individual well.

Well, partially penetrating A well constructed in such a way that it draws water directly from a fractional part of the

total thickness of the aquifer. The fractional part may be located at the top or the bottom

or anywhere in between the aquifer.

Well screen A filtering device used to retain the primary or natural filter pack; usually a cylindrical

pipe with openings of a uniform width, orientation, and spacing.

Well screen jetting When jetting is used for development, a jetting tool with nozzles and a high pressure

(Hydraulic Jetting) pump is used to force water outwardly through the screen, the filter pack, and sometimes

into the adjacent geologic unit.
E-1

Appendix E- Sample Forms
E-2

Project__________________ Site____________ Well No._________ Date___________

Well Depth__________Screen Length______ Well Diameter _______ Casing Type____

Sampling Device___________________ Tubing type____________________________

Water Level (before sampling)__________ Water Level (after sampling)_____________

Measuring Point_________________________ Other Info _______________________

_______________________________________________________________________

Sampling Personnel________________________________

Pump Rate______________

Type of Samples Collected__________________________________________________

Information: 2 in = 617 ml/ft, 4 in = 2470 ml/ft; Volcyl = πr2h, Volsphere= 4/3πr3

Ground Water Sampling Log

Time pH Temp Cond Time pH Temp Cond. Dis.O Dis.O2 Turb. [ ] Conc Notes 2 Turb []Conc Notes
E-3

Project__________________ Site____________ Well No._________ Date___________

Well Depth__________Screen Length______ Well Diameter _______ Casing Type____

Sampling Device___________________ Tubing type____________________________

Measuring Point_________________________ Other Info _______________________

_______________________________________________________________________

Sampling Personnel________________________________

Type of Samples Collected__________________________________________________

Information: 2 in => 617 ml/ft, 4 in => 2470 ml/ft; Volcyl = πr2h, Volsphere= 4/3πr3

Ground Water Sampling Log

(with automatic data logging for most water quality parameters

Time Pump Rate Turbidity [ ] Conc Notes Alkalinity
E-4

Job Number:_______________ Sample I.D.___________________

Well Number:__________________

Sampling Method:

Pump Submersible Bladder Piston Peristaltic

Bailer PVC Teflon Stainless

Field Instruments:

pH

Temperature

Conductivity

Turbidity

Dissolved Oxygen

Brand Serial / I.D. #

Measured Water Level Depth (before sampling) =

Measured Water Level Depth (after sampling) =

Description of Sample Water: ___________________________________________________

(include color, odor, etc.)

 Field Filtration Performed

Date Time Initials

Temp. (oC) pH (S.U.) Cond.

(units)

Turbidity

(NTU)

Dissolved

O2 (mg/l) Date Time Initials

Print Name:___________________________

Signature:_____________________________

Print Name:___________________________

Signature:_____________________________

SAMPLE MEASUREMENTS

WILLIAMS AIR FORCE BASE

SAMPLING INFORMATION FORM
E-5
E-6

Calibration

Temp .

(°C)

Electrical

Conductivity

(uMhos/cm) pH

Eh

(mv)

DO

(mg/l)

Turbidity

(NTU) Guidance Remarks Comments

Date

TimeType of Calibration e.g., standard KCL solution, Zobels solution, in air/water etc.

List 1st Standard e.g., pH = 7.02 @ 25°C, KCL solution= 1000uMhos/cmInstrument Reading actual reading from instrumentCalibrated to +/-? difference between calibrated instrument display and standardList 2nd Standard e.g., repeat calibration with 2nd buffer or by alternate method

Instrument Reading "

Calibrated to +/-?Correction Factor e.g., cell constant, "k"

Calib. Successful? enter YES or NOSatisfies Protocol? Did calibration meet criteria in the sampling protocol? (Y or N)

Calibration by Signature or initialsInstrument ID# serial # or other ID#

Location specify "field," "lab," "office," etc.

Location (Site/Facility Name)Project Name / #

Sampling Point (common name)

WELL PURGING - FIELD WATER QUALITY MEASUREMENTS FORM* Side 2 of 2*; Sheet___ of ___

Well Purging Equipment (more details):List/Describe Field Instruments:Discussion of Protocol Exceptions:Other Comments:

Form Completed by Date Form GWS # 1R
E-7

Sampling Device (type of pump/bailer)* Sample Medium (well water, LNAPL, etc.)*

Permanently Installed Pump? Dedicated Equipment? Used Same Equip. for Purge?

Pump Intake/Bailer Set at (ft below MP) Interval Samples Represent (ft below GS)

Date / Time Sampling Began Date / Time Sampling Finished

Depth to Water (ft below MP) Depth to Water (ft below MP)

QC Samples Collected? Sample Withdrawal Rate

All Field Protocols were followed with no exceptions (Y,N) Enter Protocol Codes* 1.____ 2. ____

Remarks (1)* (include protocol exceptions)

Form Completed by Date

 *Site 2 of this form contains definition of abbreviations, protocol codes, additional room for equipment specification, QC sample description and other comments

Y or N

Top = / Bottom =

Y or N Y or N

Y or N ( see reverse*)

Y or N ( see reverse*)

Form GWS #2

Revised 9-2-93

PID/FID Reading @ Wellhead* Concentration Background Conc.

Free Product (circle: LNAPL of DNAPL)* Detected/Sampled? Appearance

Well Purging Equipment Pump, bailer? Type*

Purging Date/Time Start Finish

Pump/Bailer Intake Set at Feet below MP Avg. Purge Rate

Amt. Purged before Sampling Gals/WC Volumes Purge Protocol of___ WCV's met?

ppm

Y or N

gpm

ppm

Y or N / Y or N

 Purging

GROUND WATER SAMPLING INFORMATION FORM* Sheet ____ of _____

Side 1 of 2*

Location (Site/Facility Name)

Project Name/#

Field Personnel

Sampling Organization

Weather ?

Sampling Point (common name)

Type (mon. well, spring, etc.)

Field Sample (Event) ID#*

Facility ID (for IGWIS data entry)

Station ID (for IGWIS data entry)

Well Depth (ft. below MP)

Static Depth to Water (below MP)

Water Column Length (L) (ft)

Condition: Securely Locked?

 Sampling Station (Well) Details

Read from left to right top -- bottom

Casing Diameter (inches)

Static DTW (ft below GS)

One WC Volume (cu ft)

Station (Well) Damaged?

(0.01 ft)

Y or N

(0.1 ft)

Y or N

Open Interval (depth below GS)

Date Time

One WC Volume (gals)

Surface Contamination (visible)

 General Information

(0.1 ft)

Y or N

Date/Time Measurements Began Purge Rate for Measurements (gpm)

Submersible Pump with direct line to Flow Cell used for all Field Water Quality Measurements?

All Field Measurement Instruments Calibrated according to Protocol?

All Field Water Quality Parameters Stabilized according to Protocol Criteria just before filling sample containers?

The Measurements below Represent: (1) stabiliization, (2) sample water collected, (3) both a and 2, (4) other*:

Sample Appearance: Odor:

Y or N

Y or N

Y or N

 Field Water-Quality Measurements and Observations

Temperature

Electrical Conductivity

Specific Conductance

pH

Dissolved Oxygen

Eh

Turbidity

°C

μMhos/cm

μMhos/cm

Standard Units

mg/l

mV

NTU

= meter reading x magnitude x k

EC corrected to 25 °C

Field Measurement Value Military Time Comments*

 Sample Collection
E-8

Side 2 of 2

GROUND WATER SAMPLING INFORMATION FORM*

(Reverse Side)

ABBREVIATIONS

ft. feet MP Measuring Point GS Ground Surface

DTW Depth to Water WC Water Column cu. ft. cubic feet

Y Yes (circle if appropriate) N No (circle if appropriate) gals gallons

PID Photo Ionization detector FID Flame Ionization detector ppm parts per million

gpm gallons per minute Amt. amount k cell constant

EC Electrical Conductivity LNAPL light non-aqueous phase liquid (floater) DNAPL dense non-aqueous phase liquid

(sinker)

GENERAL INFORMATION

The “Field Sample (Event) ID#” should be constructed from the date and time that the first sample container of a purposefully associated set of sample

containers is filled. This set of samples would normally be collected vary closely together in time and include containers for a number of analytical

parameters and QC samples. QC samples are normally assigned temporary aliases (see below). For example, if the first of a set of containers is filled at

1:30 PM on December 19, 1992, the Field Sample Event ID# for all containers in the set should be 9212191330.

WELL INFORMATION

The water column length (L) is calculated by subtracting the depth to water (DTW) from the well depth. L = well depth - DTW. However, both of these

distances must be referenced to the same datum: either from the measuring point (MP) or from ground surface (GS). This form was designed with the

assumption that both the well depth and static water level values are referenced to the MP.

For convenience, a blank was included to also enter depth to water below GS in case the well depth referenced to the MP is unknown or cannot be

measured directly. In addition, this value will indicate where the static water level is relative to the open (screened) interval which is referenced to GS. For

the calculation of L in this case, the “stick up”, the distance from the MP to GS, needs to be looked up or measured in the field. If the MP is above GS, then

the stick up is a positive number for this calculation. Enter the stick up distance here____ft. (to the nearest 0.1 ft.). DTW (from GS) = DTW (from MP) - stick

up; L = well depth (from GS) - DTW (from GS).

One water column volume = πr

2L. The units conversion from cubic feet to gallons is as follows: πr2

 [ft.2] L [ft.[ [7.48 gallons/ft3]. r = well radius in feet (since

well specifications are normally given as diameter in inches, the diameter must be converted from inches to feet and then divided by one-half to yield r, in

feet). Examples of well diameter/gallons per ft. of WC: 1"/0.041 gals; 2"/0.163; 4"/0.653; 6"/1.47; 8"/2.61.

PURGING

Measure the concentration of organic vapors inside the well immediately after removing the wellhead cap. On the front side of this form, circle whether a

PID or a FID was used, then enter wellhead and ambient background readings. Here specify the calibration gas _____ , lamp voltage______make & model

# of the instrument here_________.

If free product was detected, describe appearance, thickness, etc. (free product samples collected {Y, N }): ______________________________________

 Supplemental description of purging equipment: ____________________________________________________________________________________

FIELD WATER QUALITY MEASUREMENTS AND OBSERVATIONS

If a flow cell was not used, describe how measurements were taken (note whether or not measurements were taken down hole):

__________________________________________________________________________________________________________________________

Other Comments and Observations ______________________________________________________________________________________________

SAMPLE COLLECTION

Sampling equipment details (Mfgr., Model#, tubing, etc.): _____________________________________________________________________________

Quality Control Samples

Fictional sampling point name(s) end field sample event ID#(s) (aliases) can be used for QC samples on sample labels and chain of custody sheets to

distinguish them from primary samples without tipping off laboratories. List aliases here to document their association with primary sample identifiers on

front side of sheet. Name(s)/ID#(s) Indicate total # of QC samples collected: Replicates____Splits____Trip blanks_____Field ambient air blanks ______

Field methods blanks______

Protocol codes: 1. Indicate the type of sampling protocol followed by selecting from codes (A-F) below and entering it on the front of this form. Specify the

name of the agency_____and the name of the agency program_______that approved the protocol. If none, write "none. ") A slightly modified agency

program standard sampling protocol, approved as a non-site-specific protocol B) An unmodified or slightly modified agency program standard sampling

protocol, approved as a non site-specific protocol C) A non site-specific protocol approved by an agency D) A detailed but non agency-approved, sitespecific sampling protocol with adequate QA/QC procedures was followed; E) A detailed but non agency-approved sampling protocol without adequate QA/

QC procedures was followed; B) None of the above protocol conditions were known to be met (comment): ______________________________________

Protocol code: 2

A) Sampling observed by_______(agency) to meet all field protocols except as noted below: (agency signature)

B) Sampling observed by "neutral" observer (signature) all field protocols except as noted below;

C) Neither A or B applies (comment): _________________________________________________________________________________________________________________

PROTOCOL EXCEPTIONS

List/discuss protocol exceptions for sampling-related field work (attach additional sheet if necessary): ______________________________________________________________

Other Remarks(2) ________________________________________________________________________________________________________________________________