The United States has vast reserves of natural gas within
shale and rock formations. During the past decade, extracting that gas has
become commercially viable as a result of the advances made in horizontal
drilling and hydraulic fracturing (fracking) techniques. With the rapid increase
in fracking has come the increase in concerns about its potential impacts on
drinking water. In response to public concern ignited by the film Gasland and
protests by anti-fracking groups, the US House of Representatives requested
that the US Environmental Protection Agency (EPA) examine the relationship
between fracking and drinking water resources in 2009. In 2011, the EPA began a series of research projects into the impacts and potential impacts of fracking on water. Also, in April 2012 EPA released the first federal air rules for natural gas wells that are hydraulically fractured, specificallyvrequiring operators of new fractured natural gas wells to use “green completion,” which is a series of technologies and practices to
capture natural gas and other volatile substance that might otherwise escape
the well during the completion period when most volatile release takes place.
Hydraulic fracturing has its own water cycle and involves
the pressurized injection of fluids commonly made up of mostly water and
chemical additives into a geologic formation. The pressure used exceeds the
rock strength and the fluid opens or enlarges fractures in the rock. As the
formation is fractured, a “propping agent,” such as sand or ceramic beads, is
pumped into the fractures to keep them from closing as the pumping pressure is
released. The fracturing fluids (water and chemical additives) are partially
recovered and returned to the surface. Natural gas will flow from pores and
fractures in the rock into the wells allowing for enhanced access to the
methane reserve. Two to five
million gallons of water are typically necessary to frack one horizontal well
in a shale formation. Water used for fracturing fluids is acquired from surface
water or groundwater in the local area. Wastewaters from the hydraulic
fracturing process (flowback or water produced in the well) may be disposed in
several ways. The water that flows back after fracturing may be returned
underground using injection well, discharged to surface waters after treatment
to remove contaminants, or applied to land surfaces. Not all fracturing fluids
injected into the geologic formation during hydraulic fracturing are recovered.
The EPA estimates that the fluids recovered range from 15-80% of the volume
injected depending on the site. The
long term fate of any residual fluid has not been studied.
Each stage of the fracking water cycle is a potential
area for impact to drinking water supplies especially from human error and
irresponsibly and improperly handling chemicals and contaminated water and poorly
managing and protecting our water resources. The steps in the fracking water cycle are:
Water acquisition. Chemical mixing. Pressurized Well
injection. Flowback and produced water (collectively referred to as “hydraulic
fracturing wastewater”) recovery. Wastewater treatment and disposal. Geology,
hydrology and human behavior will produce vastly different outcomes for
different regions of the county and different gas companies.
 |
| from US EPA |
EPA is engaged in a number of research projects that will
be the basis of their actions and future regulations for oil and gas operations.
Whether the EPA will regulate oil and gas exploration nationally or leave the
oversight in the hands of the states is an open question. There is an argument
that water resources and geology are very local phenomena and cannot be
generalized over the nation and that hydraulic fracturing should remain under
local oversight. The 2005 energy law exempts fracking from the Safe Drinking
Water Act based on the 2004 EPA study “Evaluation of Impacts to Underground
Sources of Drinking Water by Hydraulic Fracturing of Coalbed Methane Reservoirs.”
In that report EPA reviewed 11 major coal basins mined for coalbed methane and
saw no conclusive evidence that water quality degradation on underground
drinking water supplies had occurred as a direct result of the injection of
hydraulic fracturing fluids, but fracking of coalbeds generally involves a fraction
of the water used in hydraulic fracking of shale gas.
The current fracking projects are a series of studies. Existing
Data from multiple sources have been obtained for review and analysis. Well
construction and hydraulic fracturing records provided by well drillers are
being reviewed for 333 oil and gas wells across the United States; data within
these records are being examined to assess the effectiveness of current well
construction practices at containing gases and liquids before, during, and
after hydraulic fracturing. In addition information on the chemicals and
practices used in hydraulic fracturing has been collected from nine companies
that hydraulically fractured a total of 24,925 wells between September 2009 and
October 2010. Data on causes and volumes of spills of hydraulic fracturing
fluids and wastewater are being collected and reviewed from state spill
databases.
Computer models are being developed to identify conditions
that may lead to impacts on drinking water resources from hydraulic fracturing.
The EPA has created hypothetical scenarios for water acquisition, well injection, and
wastewater treatment and waste disposal stages of the water cycle that they
hope to have the models evaluate. Computer models are also being used to
explore the possibility of subsurface gas and fluid migration from deep shale
formations to overlying aquifers in six different scenarios. The effectiveness of the models would be dependent on how closely the model predicts transport behavior in rock and shale and the similarity in behavior of different formations.
Laboratory studies are being performed to identifying
potential impacts of inadequately treating hydraulic fracturing wastewater and
discharging it to rivers. Experiments are being designed to test how well
common wastewater treatment processes remove selected contaminants from
hydraulic fracturing wastewater, including radium and other metals. Since
wastewater treatment plants are not designed to remove more than biological
waste and bacteria, any removal of fracking chemicals and contaminants would be
incidental. I do not expect that wastewater treatment plants would be able to
treat flowback water for the contaminants associated with geological formations
and fracking chemicals.
The EPA has identified chemicals used in hydraulic
fracturing fluids from 2005 to 2011 and chemicals found in flowback and
produced water. The EPA is performing toxicity assessments based on chemical,
physical, and toxicological properties for chemicals with known chemical
structures. Existing toxicology models are being used to estimate properties in
cases where information is not available. The important thing that EPA is doing
is bringing together all the data and previous work to get as complete picture
of what we know about how hydraulic fracturing may be impacting our water
resources.
No comments:
Post a Comment