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Opportunity for Stakeholder Input on Conceptual Model of Potential Impacts to Drinking
Water Resources from Hydraulic Fracturing
Natural gas plays a key role in our nation's clean energy future and hydraulic fracturing (HF) is one way
of accessing this vital resource. Over the past few years, the use of HF for gas extraction has increased
and has expanded over a wider diversity of geographic regions and geologic formations. For example, in
the 1990s, HF was predominantly used in coalbed methane extraction. In recent years, HF used in shale
formations to extract natural gas has led increases in the proved reserves in the United States. It is
projected that shale gas will comprise over 20% of the total U.S. gas supply by 2020. Given the
expanded application of HF techniques and the increasing concerns raised by the public, media and
Congress, EPA announced in March 2010 that it will study the relationship between hydraulic fracturing
and drinking water. To assist in the development of the study design, the conceptual model identifies the
key interactions between hydraulic fracturing and water resources. EPA seeks input from stakeholders
and the public regarding the model explained here.
The Hydraulic Fracturing Process
EPA is examining the entire HF process ~ from obtaining the water necessary for fracturing fluids to
operations to disposal of wastes ~ to assess the potential for HF to impact water resources. The HF
process is also referred to as the hydraulic fracturing lifecycle. The HF process, may pose risks to
drinking water supplies through the introduction of contaminants into the drinking water supply or by
reducing the volume of water available for drinking water supplies. The HF process could affect both
surface and ground water supplies.
The process of hydraulic fracturing begins with building the necessary site infrastructure including well
construction. Production wells may be drilled in the vertical direction only or paired with horizontal or
directional sections. Vertical well sections may be drilled hundreds to thousands of feet below the land
surface and lateral sections may extend several thousand feet away from the well.
Fluids, commonly made up of water and chemical additives, are pumped into a geologic formation at high
pressure during hydraulic fracturing. When the pressure exceeds the rock strength, the fluids open or
enlarge fractures that can extend several hundred feet away from the well. After the fractures are created,
a propping agent is pumped into the fractures to keep them from closing when the pumping pressure is
released. After fracturing is completed, the internal pressure of the geologic formation causes the injected
fracturing fluids to rise to the surface where it may be stored in tanks or pits prior to disposal or recycling.
Recovered fracturing fluids are referred to as flowback. Disposal options for flowback include discharge
into surface water after treatment or underground injection.
Potential Impacts to Water
Water is an essential component in the HF process. Figure 1 illustrates the role of water in the HF
lifecycle including:
(a) acquisition of water for well drilling and fracturing operations
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(b)	mixing water with chemicals and proppant (e.g., sand, ceramic beads) for the fracturing operation
itself, including injection and return of wastewater (flowback and produced water) to the surface
and
(c)	disposal, treatment, or recycling of resultant
Potential Impacts on Water Availability (Quantity)
The HF process could affect water availability because of the large volume of water used. It has been
estimated that each hydraulically fractured well uses approximately two to five million gallons of water to
drill and hydraulically fracture the well. The water used in the HF process could come from either ground
or surface water depending on the location of the well. Use of large volumes of water could stress
drinking water supplies, especially in drier regions where aquifer or surface water recharge is limited.
Large withdrawals of waters for HF could potentially lead to lowered water tables or dewatered drinking
water aquifers, decreased stream flows, and reduced volumes of water in surface water reservoirs (Table
1). This would affect the availability of water for drinking water and other uses in areas where HF is
occurring.
Potential Impacts on Water Quality
Underground sources of drinking water (USDWs) are typically accessed at depths of less than 1,000 feet;
however, deeper USDWs are present in the United States. In some cases, USDWs may occur at depths
coincident with oil and gas reservoirs. Natural gas production wells are typically drilled to depths that
range from 1,000 to 8,000 feet below the land surface. Wells may also be drilled directionally or
horizontally. Horizontal drilling may extend several thousand feet from the vertically drilled wellbore
During the hydraulic fracturing process, there are several potential mechanisms by which contaminants
could be introduced into drinking water supplies or USDWs including:
•	transport of contaminants through natural fractures in the rock into adjacent drinking water
aquifers;
•	transport of contaminants into underground drinking water zones through the fractures produced
during the hydraulic fracturing process;
•	transport of contaminants into drinking water through abandoned or pre-existing wells;
•	leakage of contaminants from production wells (e.g. improperly constructed or damaged wells);
•	leaching of contaminants from improperly lined storage or drilling pits; and
•	spills of the HF fluids into surface water bodies used for drinking water (Figure 1).
When HF fluids, flowback water, or produced water are introduced into the subsurface, they could
potentially alter the natural conditions that exist in the underground environment. Changes in the
geologic formation could lead to the release of naturally occurring metals, radionuclides, organic
contaminants and gases present in rock and/or cause the migration of contaminants from the natural gas
reservoir into adjacent geologic formations.
The HF process may also impact surface water quality. For example, total dissolved solids (TDS) can
increase significantly in surface water from discharges from wastewater treatment facilities or runoff of
wastewater into nearby surface waters. Wastewater treatment facilities that accept wastewater from HF
sites are sometimes not capable of reducing TDS to concentrations that the receiving water is capable of
diluting to safe levels. High TDS discharges can cause adverse impacts to receiving streams used for
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drinking water supplies.
Table 1. Potential impacts to surface and ground water resources from the hydraulic fracturing process.
\\ silcr in Hie	Surface W aler	Ground \\ aler
Impacts
Decreased surface water flows
Water Used in Fracturing
Fluids
Reduced well water levels
Hydraulic Fracturing
Potential runoff to streams from
leaks, spills, accidents
1.	Abandoned wells as conduits
to adjoining drinking water
aquifers
2.	Well failure, poor
construction, leading to
leakage to adjoining drinking
water aquifers
3.	Fractures, faults leading to
leakage to adjoining drinking
Storage of Wastewater
Storage pit water runoff to
streams from leaks, spills,
accidents
Pit water leaching to
underground source of drinking
water
Disposal, Treatment, Recycling
of Wastewaters
1.	Wastewater treatment plant
discharges to surface water
2.	Water storage, transport,
spills
Well failure, poor construction
leading to fluid migration into
adjoining drinking water aquifers
Stakeholder Input
EPA is seeking input from stakeholders and the public to help inform the development of the study
design. In particular, we would appreciate responses to these questions related to the conceptual model
presented here:
1.	Can you suggest additional pathways of exposure that could impact drinking water
resources from the hydraulic fracturing process?
2.	In your experience what are the most important processes and pathway(s) of exposure
that would adversely impact drinking water resources?
3.	What current practices in your region do you think pose the most threat to drinking water
resources from hydraulic fracturing?
4.	Can you provide data, studies, reports, or other information to help us assess the relative
importance of these potential impacts?
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Figure 1. Simplified Water Lifecycle in the Hydraulic Fracturing Process
Produced Water and Flowback
to Treatment or Disposal
Residential
Well	.
Surface
. Water
Hydraulic fracturing (HF) uses water from
public water supplies, or directly from surface
or ground water sources. Water requirements
can range from 250,000 to 5,000,000 gallons
per well, depending upon site characteristics.
At the production well site, chemicals and proppant
(sand or ceramic beads) are mixed with the water and
pumped into the well under high pressure to create
fractures in the target formation.
Surflclal Aquifer
Regional Aquifer
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At the completion of HF, water mixed with the fracturing fluids
(flowback and production water) is pumped
back to the surfacefor disposal, treatment, or recycling.
Waste Water
tment Discharge to
ant Surface Water
rips
Production Waste
Underground
Injection Well
Impoundment

Surficial Aquifer
Regional Aquifer

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