United States Environmental Office of Solid Wast# and ^
Protection Agency Emergency Response
oEPA Ground Water Forum
MONITORING WELL DEVELOPMENT GUIDELINES FOR
SUPERFUND PROJECT MANAGERS
Ruth izraeli* Doug Yeskls, Mark Collins, Kathy Davles, Bernard Zavala
The Ground Water and Engineering Forums were
established by EPA professionals in the ten EPA
Regional Offices, The Forums are committed to the
identification and resolution of scientific, technical
and engineering issues impacting the remediation of
Superfund and RCRA sites. The Forums are sup-
ported by and advise OSWER's Technical Support
Project, which has established Technical Support
Centers in laboratories operated by the Office of
Research and Development, Office of Radiation
Programs, and the Environmental Response Team.
The Centers work closely with the Forums in provid-
ing state-of-the-science technical assistance to EPA
project managers.
This document provides well development guidelines
and recommended additional sources of information.
It was developed by the Superfund Ground Water
Fotum and draws upon U.S. Army Corps of Engi-
neers and draft RCRA SW-846 field protocols.
Comments from ORD and Regional Superfund
hydrogeologists have been incorporated. These
guidelines are applicable to the great majority of
sites. However, unusual, site-specific circumstances
may require alternative approaches, in these in-
stances, the appropriate Regional hydrogeologist
should be contacted to establish alternative develop-
ment protocols.
Introduction
The goal of ground-water sampling is to obtain water
samples that best represent natural undisturbed
hydrogeological conditions. Adequate well develop-
ment is critical to minimize the Introduction of biases
into the sampling effort. Well development is neces-
sary because every drilling method disturbs the
geologic materials around the well bore to some
extent. Development processes are used to try to
ensure proper hydraulic connection between the well
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and the geologic materials in the vicinity of the well.
This is done by stressing the formation around the
screen so that mobile, artifact particulates are re-
moved. This process is necessary to obtain a ground
water sample which is as similar as possible to in situ
conditions.
One of the major goals of well development is to
produce a well capable of yielding ground-water
samples of acceptably low turbidity. Excess turbidity
may alter water quality and result in erroneous chemi-
cal analysis (particularly for unfiltered metals samples
which require acid preservation).
Turbidity in ground-water samples is minimized by
well development. Proper well development creates a
graded filter pack around the well screen. When
pumping is first initiated, natural materials in a wide
range of grain sizes are drawn into the well, producing
very turbid water. However, as pumping continues,
the natural materials are drawn into the filter, produc-
ing an effective filter pack through a sorting process.
This sorting process begins when the largest particles
of natural materials are retained by the filter pack,
resulting in a layer of coarse particles against the well
screen. With continued development, this process
produces progressively finer layers until an effective
graded filter is produced, which then minimizes
turbidity. Development is also necessary to remove
any foreign materials introduced during drilling, such
as drilling water and mud.
These guidelines are directed toward the development
of relatively permeable (i.e., K>10-® cm/sec) aquifers.
However, it is sometimes necessary to screen wells in
water-bearing zones containing significant quantities
of silt and clay, which would not normally be consid-
ered producing aquifers. Low-yielding wells located in
marginal aquifers often cannot be developed using
standard methods- For a discussion of the construc-
tion and development of wells in low-yielding forma-
Technology Innovation Office
Office of Solid Waste and Emergency Response
U.S. EPA, Washington, DC
Walter W. Kovaliek, Jr., Ph.D., Director
'Hazardous Waste Management Division
U.S. Environmental Protection Agency
Region VI
1445 Ross Avenue
Dallas, TX 75202
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tions, see Aller et al. (1989), Gass (1989), arid Paul
et al. (1988).
Wells constructed in bedrock may require special
protocols. For example, wells constructed as open
boreholes (cased to monitored zone) generally
should not be developed using a surge block due to
the potential for damaging the borehole walls. Bed-
rock wells constructed with screens may be devel-
oped in two stages, before and after the screen is
installed. Since bedrock wells may require special
development protocols other than those described
here for wells in unconsolidated aquifers, Regional
hydrogeologists should be consulted when designing
bedrock well development procedures.
Finally, it is Important to note that there are some
hydrogeologic environments, such as fine-grained
"marginal" aquifers and karst terraines, where excess
turbidity may still exist even after optimizing well
construction (e.g., filter pack size and thickness,
screen size, drilling technique) and development.
Development Methods
The common methods for developing wells are
described by Aller et al, (1989) and Driscol! (1986)
and include:
¦ Overpumping
¦ iackwashing
¦ Surging
• Bailing
• Jetting
• Airlift pumping
»Air surging
Well development procedures that have the poten-
tial to alter ground-water quality should not be used.
Therefore, methods which involve adding water or
other fluids to the well, or use air to accomplish
development, are not recommended. Generally
unsuitable methods for monitoring well development
include jetting, airlift pumping, and air surging.
However, air development techniques may be used
if they offer site-specific advantages over other
methods, and extreme care is taken to prevent air
from contacting the screened interval. Air develop-
ment techniques must only be implemented by an
experienced operator.
Recommended monitoring well development
methods Include pumping, overpumping, bailing
and backwashing, in combination with some
form of surging. The most effective combination
and timing of these methods must be deter-
mined through field testing, or from experience
developing wells In similar hydrogeologic re-
gimes.
Movement of ground water into the well in one direc-
tion generally results in bridging of the particles, and a
means of inducing flow reversal is necessary to break
down the bridging and produce a stable filter. Alter et
al. (1989) state that one of the most effective and
efficient methods to induce flow reversal is through
careful use of a properly-constructed surge block. For
a more detailed description of proper usage of a surge
block and other methods of achieving flow reversal,
see Aller et al.
One example of a well development field protocol is
described below:
1. Record static water level and total well
depth.
2. Set the pump and record pumping rate and
turbidity. Pump until turbidity (as measured by
a nephelometer) reaches desired level or
stabilizes.
3. Discontinue pumping and surge the well.
4. Measure depth to the bottom of the well, If
more than 10% of the screen is occluded by
sediments, remove excess sediment by
bailing,
5. Reset the pump, recording pumping rate
and turbidity. Pump until turbidity reaches
desired level or stabilizes. If the well has been
properly designed, the amount of pumping
required to achieve the desired turbidity level
will be substantially less than required in the
first pumping cycle.
6. Repeat surging and pumping until the well
yields water of acceptable turbidity at the
beginning of a pumping cycle. A good way to
ensure that development is complete is to shut
the pump off during the last anticipated pump-
ing cycle, ieaving the pump in place, and
restart it some time later. The turbidity of the
discharge water should remain low.
The pumping rate used during development must be
greater than the highest rate expected to be used
during subsequent purging and sampling. In fact,
recent field experience suggests that extremely low
(i.e., 100 to 500 ml/min) purging and sampling pump-
ing rates may significantly reduce the turbidity of
ground-water samples (Puis et al., 1990). The pump
intake should be placed close to, or within, the well
screen interval.
The development techniques listed above are most
efficient in wells with screens having the greatest area
open to the aquifer. Therefore, continuous slot, or
wire wrapped screens are recommended for use in
formations where adequate development is expected
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to be difficult. The additional cost of continuous slot
screen is typically more than compensated for by
significantly less cost in development time and subse-
quent well purging times.
Development Criteria
Development should continue until clear, artifact-free,
formation water is produced. Water quality param-
eters such as specific conductance, pH, temperature,
and turbidity should be measured during development,
and should stabilize before development is stopped.
Turbidity measurements are the most critical develop-
ment criteria. Other parameters should be used to
provide supplemental Information regarding aquifer
conditions, and stabilization of these parameters is
indicative of the presence of formation water. If water
was added during well construction or development,
two to three times the volume of water added must be
removed. Finally, the well should be producing
visually clear water before development is stopped.
Experience has shown that development may take
from less than an hour to several days, depending on
the formation, development procedures, and well
characteristics or construction. In some marginal
aquifers such as glacial tills and interbedded sands
and clays, it may not be possible to attain the 5 NTlls
turbidity target level used as guidance in RCRA,
However, poor well construction practices, failure to
emplace an adequate filter pack, poor selection of
screen slot size and sand pack materials, as well as
inadequate development may result in high turbidity
levels. In these situations, the PRP or contractor must
demonstrate that the well has been constructed
property and all reasonable efforts have been ex-
pended to develop the well. The determination of
whether to abandon the well or address the turbidity
problem during sampling and analysis should be
made by the project manager in consultation with a
Regional hydrogeologist.
After development is completed, wells should be allowed to
stabilize and re-equilibrate before sampling. The time
necessary for stabilization depends on the characteristics
of the aquifer and the geochemistry of the parameters to be
monitored. Generally, high permeability formations require
less time (i.e,, several days) than low permeability forma-
tions {i.e., several weeks).
Development Documentation
Monitoring well development must be thoroughly
documented to verify that foreign materials have been
removed, formation water is being sampled, and
turbidity has reached acceptable levels or stabilized.
The following data should be recorded before and
during well development:
1. Date and duration of development
2. Water level from the marked measuring
point on the top of casing before and 24 hours
after well development.
3. Depth from top of well casing to the top of
any sediment present in the well, before,
during, and after development,
4. Types and quantity of drilling fluids intro-
duced during drilling and development.
5. Field measurements (e.g., turbidity, specific
conductance, pH, dissolved oxygen, tempera-
ture) taken before, during, and after well
development.
6. Volume and physical characteristics of
developed water (e.g., odor, color, clarity,
particulate matter),
7. Type and capacity of pump and/or bailer
used and pumping rates.
8. Detailed description of all development
methods used.
Glossary
Backwashing The surging effect or reversal of
water flow in a well that removes fine-
grained material from the formation sur-
rounding the borehole. Only formation
water is used during this process.
Jetting Bursts of high-velocity water injected into
the well,
Qverpumping Pumping at rates generally greater
than those used during sampling or well
purging. Commonly combined with surging
of the well.
Surge Block A plunger-like tool,, consisting of
leather or rubber discs sandwiched between
steel or wooden disks that may be solid or
valved, that is used in well development,
Surging A well development technique
where the surge block is alternately lifted
and dropped within the borehole above or
adjacent to the screen to create a strong
inward and outward movement of the Water
through the well intake,
Turbidity Solids and organic matter suspended
in water.
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References
Aller, L.p T.W. Bennett, G. Hackett, R.J. Petty, J.H.
Lehr, H, Sedoris, D.M. Nielsen, and J.E. Denne, 1989.
Handbook of Suggested Practices for the Design and
Installation of Ground-water Monitoring Wells: Tech-
nology Support Center, Environmental Monitoring
Systems Laboratory, EPA600/4-89/034, United States
Environmental Protection Agency, 396pp.
Driscoll, Fletcher G,, 1986, Ground Water and Wells;
Johnson Division, St. Paul, Minnesota, 1089pp.
Gass, T.E., 1989. Monitoring Wells in Non-aquifer
Formations, Water Well Journal, v, XXXXII, no. 2, pp.
27-28.
Paul, D., C. Palmer, and D. Cherkauer, 1988. The
Effect of Construction, Installation and Development
on the Turbidity of Monitoring Wells in Fine-grained
Glacial Till. Ground Water Monitoring Review, v, 8,
no. 1, pp. 73-82.
Puis, R.W„ J.H, Eyehanerand R,M. Powell. Colloidal-
Facilitatflri Transport of Innmanin Contaminants in
Ground Water: Part I. Sampling Considerations.
Environmental Research Brief, USEPA, EPA/600/M-
90/023, December 1990,
U.S. Army Corps of Engineers, Missouri River Divi-
sion, 1990. Installation of Ground-water monitoring
wells and exploratory borings at hazardous waste
sites, Chapter 6; Well development, pp. 38-44.
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