Technology Status Report: In Situ Flushing - CLU-IN

In Situ Flushing Project Summaries
GWRTAC Case Study Database
GWRTAC ID: FLSH0030
Project Name: Montana Pole & Treating, Butte, MT
City: Butte State/Province: MT
Primary GWRTAC Personal
Communication Source
(Name/Organization):
Project Summary:
Neil Marsh
Montana DEQ
Report(s)/Publication(s) (GWRTAC Source):
U.S. EPA, Nov. 1996: Innovative Treatment Technologies: Annual Status Report (Eighth Edition),
EPA 542-R-96-010, Number 8, U.S. EPA OSWER (5102G) TIO, Washington, DC
Internet URL http://www.epa.gov.superfund.htm
The following text is from notes from a July 1998 conversation with the Montana DEQ RPM:
The site has 10-15 acres of pentachlorophenol (PCP)-contaminated area bisected by an interstate
highway. The ROD calls for accessible soils to be excavated and treated aboveground via
landfarming and aerated biopiles. To date, soil excavation has taken place on the north side of the
interstate, and excavation on the south side of the interstate will begin in 1999.
A total of about 200,000 cubic yards of contaminated soils will be excavated and treated ex situ.
However, approximately 50,000 cubic yards of contaminated soil lies beneath the interstate
highway, and will be remediated via in situ flushing, although ozone injection is also under
consideration for these soils In situ flushing will also be used to remediate groundwater. Much
LNAPL at the site (comprised of diesel fuel and 5% PCP), was removed at the time of soil
excavation, however remaining LNAPL will also be targeted with in situ flushing. The remediation
goals for PCP for the site are 34 ppm in soil and 1 ppb in groundwater.
The geologic material of the subsurface area targeted for in situ flushing is comprised of sandy
alluvial material. The water table is present at approximately 5 to 8 feet below the ground surface.
At the time of soil excavation north of the interstate, the excavations were extended to about two
feet below the water table. The excavations were backfilled with clean soil, and recharge basins
were constructed to allow current recharge of treated groundwater for flushing. (In the future after
soils treated aboveground are replaced, the current recharge basin system will be replaced with a
subsurface manifold system to deliver the treated groundwater to the subsurface).
Two interception trenches (approximately 30 feet deep) have been installed north of the interstate.
The downgradient trench is designed to prevent contaminated groundwater from leaving the site.
Approximately 150 gpm groundwater is extracted from this trench and treated via carbon
absorption with discharge to surface water or recharge to groundwater through the
aeration/infiltration basins. The upgradient trench is designed to intercept both contaminated
groundwater and LNAPL before it reaches the north site excavated area. About 150 gpm
groundwater is exrracted, treated, and discharged. LNAPL is intercepted by a physical plastic
Ground-Water Remediation Technologies Analysis Center
Operated by Concurrent Technologies Corporation
Appendix - Page 65 of 164
Copyright GWRTAC 1998
Revision 1
Tuesday, November 17, 1998