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Much of the current concern about hydraulic fracturing revolves around the treatment
and disposal of wastewaters that come up out of the well after fracturing has occurred.
These “produced waters” and “flowback waters” in some cases are high in concentrations
of total dissolved solids (TDS), naturally occurring radioactive material (NORM),
and metals. There are currently many ways these wastewaters are managed including
being recycled on site, treated at commercial waste water treatment plants, or shipped
away for storage in federally permitted underground injection wells. This study suggests
that by supplementing wastewater with high-sulfate coal mine drainage (CMD), on site
recycling can be even more effective through the removal of high metal concentrations
and NORM from the wastewater. This could potentially allow for 100% waste water recycling,
saving local water resources, while a legacy environmental problem may be remediated.
This study was focused on the idea that by mixing coal mine drainage with flowback
or produced water, many of the negative characteristics of both fluids can be remediated.
The sulfate can be removed from the coal mine drainage, and with it, the barium and
radium can be removed from the coal mine drainage. Mix ratios of 1:4, 1:2, and 3:4
were used for this study and in almost every case a majority of the radium (100% for
each ratio), barium (75, 90, and 80% respectively), and sulfate (90, 75, and 40% respectively)
precipitated out of the mixture. Barium and radium concentrations were found to be
strongly correlated within each the sample (r2 of .815). In addition to that, the
removal of those solutes was also found to be correlated (r2 of .75). Finally, using
spatial analysis and a number of input factors, it was found that on average the use
of coal mine drainage is between $30 and $200 thousand more expensive to use per well
than fresh water.
These results indicate that mixing AMD and flowback water is an effect means of water
treatment for re-use as hydraulic fracturing fluid. Although not currently cost effective,
the potential to clean up a legacy environmental problem has inspired policy makers
to begin the process of making the use of coal mine drainage more cost effective with
less legal consequence.
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