Water's Journey Through the Shale Gas Drilling and Production ...

Jeffery Mathison
Fracing a horizontal Marcellus well may
use 2.5 million to 8 million gallons of water,
typically within about a week. This water
may come from surface or groundwater or
emerging alternate sources such as mine
drainage. It is usually transported to the
drilling site via truck, but in some cases
water pipelines are used.
Currently, in the Marcellus region two
to eight gas production wells typically
extend underground in various directions
from one 3- to 5-acre well pad. At the
well pad water is mixed with sand and
chemicals that may include oils, gels, acids,
alcohols, and various manufactured organic
chemicals. This solution, called “frac
water,” is then forced under high pressure
into the subsurface rock formation at
the appropriate depth. Depending on
the area within the Marcellus region,
between 60 and 90 percent of this water
remains underground, where it is trapped
within the shale formation itself. The
water that returns to the surface (called
“flowback water”) is the primary source
of wastewater from shale gas drilling
activities. Flowback water contains very
high amounts of total dissolved solids (salts
and metals) and may also contain naturally
occurring radioactive materials originating
from the shale.
Flowback water may be trucked to
a treatment facility and treated, and then
trucked to another well pad, where it is
stored in lagoons or tanks until it is reused.
Frac-related water treatment often occurs
farther from the drill pad than does water
acquisition.
Because only about 10 percent of the
frac water is recaptured as flowback water,
and some of that water is subsequently lost
during the treatment process, additional
water (termed “make-up water”) typically
has to be added to the treated flowback
water. Fresh water, or relatively clean
water from another source (such as treated
municipal wastewater, abandoned mine
drainage water, or nonpotable water sold
by public water supply agencies) is usually
used for make-up water. Treated water may
be discharged into a river, creek, lake, or
other surface water body only if it meets
stringent state discharge standards. Some
flowback water is disposed of without
treatment via underground injection
into suitable geologic formations very
far below the lowest fresh groundwater
zone, although this activity is extremely
limited in Pennsylvania. In Pennsylvania,
this process requires a permit from both
the U.S. Environmental Protection Agency
(EPA) and the Pennsylvania Department of
Environmental Protection (PaDEP).
The well development process
includes a number of points where
accidents, spills, or leaks could occur due
to mechanical failure or human error. More
detail about each of these processes is
included below.