STANDING ROCK
GAMING AUTHORITY
STANDING ROCK INDIAN RESERVATION
FORT YATES, NORTH DAKOTA
March 2009
ACCOMPLISHMENTS
• Removed 3 USTs and 1 drum
• Installed 12 MWs
• Ground-water monitoring
• Conducted vapor exposure investigation
• Conducted ISCO pilot study
• Conducted 2 ISCO events
• Excavated and removed 260 yd3 of PCS
• Installed 2 replacement MWs
EPA Region 8 has performed this work in partnership
with the Standing Rock Sioux Tribe and with contract
support from Avanti Corporation.
PLANNED ACTIVITIES/
FUTURE STRATEGIES
• Groundwater monitoring
• Evaluate site closure
SITE HISTORY
The site was operated as a gasoline station from 1926
until 1980. The site is currently leased to the Standing
Rock Gaming Authority. In June 1998, an initial assess-
ment of the site was performed under the direction of
the North Dakota Department of Health, Underground
Storage Tank (UST) Program. The purpose of the
investigation was to determine (1) extent of petroleum
contamination and (2) source of petroleum vapor odors
in the building. Petroleum contamination was discov-
ered in the soil north of the Gaming Authority Office,
near the UST located under the northeast corner of the
building. A ventilation system was installed in the base-
ment of the building after this initial assessment. The site
became eligible for federal leaking underground storage
tank (LUST) funding in April 1999. Three USTs and one
drum were removed between July 1999 and June 2000.
Twelve monitoring wells (MWs) were installed and
limited soil excavation was performed. Investigations
for potential vapor exposure were conducted in 2001.
In 2008, a pilot study program was developed utilizing
in-situ chemical oxidation (ISCO) applied by direct
push injection to treat contaminated groundwater at
the site. Two subsequent ISCO events were designed
and conducted based on the success of the pilot study.
The ISCO events were successful in greatly reducing
the contamination levels in the treatment areas. Two
hundred sixty yd3 of petroleum contaminated soils
(PCS) were excavated and removed from the site and
replaced with clean fill. Two new MWs were installed at
the site replacing two wells that were damaged during
the excavation activities.
Fort Yates
,
ME
1 V 1 t— L_ 1
NE
1 1_
Site operated as a
gasoline station
1926-1980 > 1992 1993 1994
Federal LUST funding
eligibility determination
° 2 USTs and one drum
removed
Vapor exposure
investigations conducted
ISCO pilot study con-
ducted 2 additional
ISCO events 260
yd3 PCS removed • 2
replacement MWs
installed
1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 2006 2007 2008 2009 2010 1
Site assessment performed to '
determine extent of contamination *
K\V> Sty?.
%
Ventilation system installed in basement
of building
' — Waste oil UST removed
EPA began groundwa-
ter monitoring program
• 12 MWs installed
STANDING ROCK GAMING AUTHORITY
EPA Region 8 UST Program Technical Contact | Mr. Raymond Faliskie | (303) 312-6124 orfaliskie.raymond@epa.gov | www.epa.gov/region8/ust/
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