BER LAKE
CHEYENNE RIVER INDIAN RESERVATION
TIMBER LAKE, SOUTH DAKOTA
Timber Lake
March 2009
ACCOMPLISHMENTS
• Conducted RBCA assessment
• Installed 27 MWs
• Excavated and removed 422 yd3 of PCS
• Conducted 2 ISCO injection events
• Constructed interceptor trench for wellhead protection
• Conducted microbial analysis
• Ground-water monitoring
EPA Region 8 performed this work in partnership with the Cheyenne
River Sioux Tribe and with contract support from Avanti Corporation.
PLANNED ACTIVITIES/
FUTURE STRATEGIES
• Groundwater monitoring
• Continue ISCO injection and application events to treat groundwater
• Replacement of municipal drinking water well
• Utilize phytoremediation to compliment ISCO in 1 of the source
areas
• Evaluate other green remediation approaches for potential applica-
tion at site
SITE HISTORY
Water samples collected from Municipal Well No. 1 in the early 1990s
contained contaminants which exceeded federal drinking water stan-
dards. Site investigations conducted by the South Dakota Department
of Environment and Natural Resources (SDDENR) identified several
former gas stations and bulk fueling facilities as potential sources for
the contaminants, but no single, clear source was found. Petroleum was
stored at these facilities in both underground storage tanks (USTs) and
aboveground storage tanks (ASTs). Since 1993, EPA has monitored the
groundwater to evaluate site conditions. Contaminant levels for chemicals
of concern (COC) continued to exceed groundwater quality standards
in multiple monitoring wells (MWs). In 2007, a risk-based corrective
action (RBCA) assessment was conducted at the site. Nine new MWs
were installed, developed and sampled. Four MWs that were scheduled
for abandonment were repaired. Petroleum contaminated soil (PCS)
was identified in three locations at the site. Three separate source areas
were identified for the contaminated groundwater and soil at the site. In
2008,422 yd3 of PCS was excavated from three target areas. Additional
site assessment activities were conducted including the installation of
BENZENE IN GROUNDWATER (MW-13)
120.00
2100-00
S 80.00
£ 60.00
cp
c 40.00
o>
m 20.00
0.00
Jan
2008
TIMBER LAKE
EPA Region 8 UST Program Technical Contact | Mr. Raymond Faliskie | (303) 312-6124 or faliskie.raymond@epa.gov | www.epa.gov/region8/ust/
-------
seven soil borings, development and sampling of three new MW and
installation of one deep in-situ chemical oxidation (ISCO) injection well.
Two ISCO injection events were conducted at the site. In December
2008, an interceptor trench for wellhead protection was constructed. In
2009, a microbial analysis was conducted to identify benzene degrading
bacteria at the site.
TIME LINE
"Municipal Well No. 1
was drilled
• EPA began groundwater
monitoring
RBCA assessment
conducted 9 MWs
installed, 4 MWs
repaired 6 test pits
excavated
1978 > 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 2006 2007 2008 2009 2010
Contamination -
detected in
Municipal Well
No.1
SDDENRsite
investigations
identify several
potential sources
of contamination
422 yd3 of PCS excavated and
removed 2 ISCO injection
events 3 MWs and 1 deep
ISCO injection well installed
interceptor trench constructed
TT
Performed microbial
analysis Ground-
water monitoring
TIMBER LAKE
EPA Region 8 UST Program Technical Contact | Mr. Raymond Faliskie | (303) 312-6124 or faliskie.raymond@epa.gov | www.epa.gov/region8/ust/
------- |