xvEPA
                                  United States
                                  Environmental Protection
                                  Agency
                EPA/540/MR-93/505
                March 1993
                                  SUPERFUND INNOVATIVE
                                  TECHNOLOGY EVALUATION
                                   Demonstration Bulletin

                          Hydraulic Fracturing of Contaminated Soil

                             Risk Reduction Engineering Laboratory  and
                                       The University of Cincinnati
Technology Description:  Hydraulic fracturing is a physical
process that creates fractures in silty clay soil to enhance its
permeability. The technology, developed by the Risk Reduction
Engineering Laboratory (RREL) and the University of Cincinnati,
creates sand-filled horizontal fractures up to 1 in. in thickness
and 20 ft in radius. These fractures are placod at multiple depths
ranging from 5 to 30 ft below ground surface (bgs)  to enhance
the efficiency of treatment technologies such as soil vapor extrac-
tion, in situ bioremediation, and pump-and-treat  systems.

The fracturing process (see Figure 1  below) begins by using a
hydraulic jet to cut a disk-shaped notch extending 0.5 ft from the
borehole wall.  Water is injected  into the notch  until a critical
pressure is reached and a fracture is formetd. A proppant com-
posed of a granular material (sancl) and a viscous fluid (guar gum
and water mixture) is then pumped into the fracture  at a rate of
16 to 24 gal/min. After pumping, the sand holds the fracture open
while  an enzyme additive breaks down the viscous fluid. The
process is repeated at greater depths to create a stack of mul-
    , sand-filled hydraulic fractures.
The aboveground equipment includes a mixer, a slurry pump,
and gel storage tanks. The mixer continuously blends guar gum
gel, water, enzyme, and sand. The  slurry pump  is used to
transfer this mixture to the fractured area. The fracture aperture
can be estimated by measuring the ground uplift in the vicinity of
the borehole. A Ground Elevation  Measuring System (GEMS),
which uses a laser and an array of sensors, was developed to
measure uplift of the ground surface in real time during hydraulic
fracturing.

Waste Applicability:  The technology is designed for use in
low permeability silty clays contaminated with organic compounds.
This technology enhances other in situ remediation techniques
such as vapor  extraction and bioremediation. This technology
was developed by RREL and the University of Cincinnati at EPAs
Center Hill Research Facility. Factors that affect the technology's
performance were studied at this facility during 1991  and 1992.

Demonstration Results:  Hydraulic fracturing was demon-
strated at two sites, a Xerox site in Oak Brook, IL, in conjunction
Figure 1. Hydraulic fracturing in progress, the we V is located at the center of the photograph.
                                                                                    ^0?.  Printed on Recycled Papt >r

-------
with a vapor extraction system,  and a site near  Dayton, OH, in
conjunction with in situ bioremediation.

Xerox Site
Demonstration of this technology was conducled at the Xerox site
in  Oak  Brook, IL, where a vapor  extraction system has  been
operating since early 1991. The site  is  contaminated with
ethylbenzene,  1,1-dichloroethane,  trichloroethene,  tetra-
chloroethane, 1,1,1-trichloroethane, toluene, and  xylene. In July
1991, hydraulic fractures were created in two of the four wells, at
depths of 6, 10, and 15 ft below ground surface.  The vapor flow
rate, soil vacuum and  contaminant yields from the fractured and
unfractured wells were monitored  regularly. The site owner is
continuing with contaminant removal using the fracturing technol-
ogy in one more well. Results obtained to date  are as follows:

  * Over a 1 -yr period, the vapor yield from hydraulically fractured
    wells was an order of magnitude greater than from unfractured
    wells.
  • The hydraulically fractured wells enhanced remediation over an
    area 30 times greater than the unfractured wells.
  • The presence of pore water decreased the vapor yield from
    wells; therefore, water infiltration into areas where vapor extrac-
    tion is being conducted must be prevented

Dayton Site
The technology was also demonstrated at a site near Dayto i, OH,
where  in situ  bioremediation  was  being  used to  clean  up an
underground storage tank spill. The site is contaminated with
benzene, toluene, ethylbenzene, and xylene (BTEX), and  other
petroleum hydrocarbons. In August 1991, hydraulic fractures were
created  in one of two wells at 4, 6, 8, and 10 ft below ground
surface. Sampling was conducted before the demonstration and
twice during the demonstration at locations 5, 10, and 15 ft north
of the fractured and unfractured wells. Laboratory analysis in-
cluded moisture content; fluorescein diacetate analysis  (FDA),
which measures microbial  metabolic activity; number of  colony
forming  units (CPU), which indicates the number of  microbes that
have a capacity to degrade hydrocarbons; total petroleum hydro-
carbons (TPH); and BTEX. The flow rates of hydrogen peroxide
and nutrients were also measured in these two wells. Results
obtained to date are as follows:

  " The flow of water into the fractured well was two orders of
    magnitude greater than in the unfractured well.
  • The rate of bioremediation near the fractured well was 75
    percent  higher for BTEX and 77  percent higher for TPH
    compared to the rates near the unfractured well.

A Technology Evaluation Report (TER) describing  the complete
demonstrations will be available in early 1993.
For Further Information:

EPA Project Manager:
Naomi P. Barkley
U.S. EPA Risk Reduction Engineering Laboratory
26 West Martin Luther King Drive
Cincinnati, OH 45268
(513) 569-7854 FAX (513) 569-7620
    United States
    Environmental Protection Agency
    Center for Environmental Research Information
    Cincinnati, OH 45268

    Official Business
    Penalty for Private Use
    $300
                                  BULK RATE
                             POSTAGES FEES PAID
                                      EPA
                                PERMIT No. G-35
    EPA/540/MR-93/505

-------