Monterey Coal Mine #2 Site
Fact Sheet #2
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The Illinois Environmental Protection Agency (IEPA), prepared this fact sheet to address concerns about
groundwater contamination originating from the former Monterey Coal Mine #2, now known as
ExxonMobil Coal USA, Inc. (ExxonMobil), and potential effects on the surrounding private wells.
ExxonMobil began surface reclamation at the Mine #2 site early in 2005 and completed work in early
2007. After the required surface grading was completed in June 2005, a clay slurry wall was placed into
the Pearl Aquifer along the southern edge of the refuse disposal areas (RDAs). The placement of the
clay slurry wall was chosen because the groundwater in the Pearl Aquifer flows in a southwesterly
direction in the vicinity of the RDAs. The slurry wall functions as an impermeable barrier to redirect
contaminated water in the aquifer to the west, where it is pumped out by extraction wells and treated in
a series of vegetative drainage swales on-site before being discharged to the Kaskaskia River. After
installation of the slurry wall, ExxonMobil installed two new monitoring wells, MW-19 and MW-20 in
2006, south of the slurry wall, but on the ExxonMobil property.
What results were
found when the
wells were tested?
Both wells MW-19 and MW-20 contained high levels of iron and manganese, which
can come from coal mine waste. MW-20 also contained sulfate, which when found
at this location, pointed to the mine as the source of the contamination. These
results were confirmed by two samples from each well.
What action did As part of ExxonMobil’s Corrective Action Plan approved by IEPA in 2002,
Fact Sheet #2 - Monterey Coal Mine #2 Page 1 of 2
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ExxonMobil is required to conduct further investigation if significant increases in
existing contamination or new areas of contamination are found. ExxonMobil is
required by the Corrective Action Plan to conduct a study of the nature and extent
of contamination, and propose actions to IEPA that will correct the problem.
Yes. A number of temporary monitoring wells and permanent monitoring wells
were installed on the ExxonMobil property line, south of the RDAs. Because the
results of this study showed that the contamination had left the ExxonMobil
property in one area, additional monitoring wells were constructed on adjoining
property. The monitoring wells on the adjoining property did not contain mine
related contaminants. Therefore, it was determined that the mine contaminants
extend a few hundred feet off the ExxonMobil property at this time. As an added
precaution, IEPA and ExxonMobil’s consultants sampled four private wells near the
area where contamination had left ExxonMobil’s property. The samples were
analyzed by two different laboratories. The test results from both sets of samples
were similar. The private wells tested have not been contaminated by the mine.
How did the mine
When MW-19 and MW-20 were tested, it was found that MW-19, which was
closest to the RDAs, did not contain high levels of sulfate. However, MW-20 which
was further from the RDAs, did contain high levels of sulfate. Area groundwater
must flow past the MW-19 location before it reaches MW-20. Therefore, any
plume of contamination originating from the RDAs should be detected in MW-19
before contamination in reaches MW-20. Since these wells have not shown mine-related
contamination, it has been determined that contamination at MW-20 has
not been caused by a leak in the slurry wall.
The groundwater to the south of the RDAs used to be controlled by extraction
wells. These wells pumped groundwater to prevent contamination from spreading
south of the RDAs. During slurry wall construction, the extraction wells had to be
turned off so that large construction equipment could operate safely around power
lines. A likely scenario is that a slug of contamination may have escaped during
the time the wells were turned off, but before the slurry sealed the aquifer flow in
this direction in the vicinity of the RDAs.
proposed to fix the
the area around
As required by the Corrective Action Plan, ExxonMobil must propose a solution,
subject to IEPA approval, that will address groundwater contamination. In
discussions between IEPA and ExxonMobil, the company anticipates their
consultants will have a report containing the Company’s proposal complete in May
2007. IEPA will approve a remedy and keep the public informed.
Will there be other
studies or private
well sampling done
near Mine #2?
The IEPA plans to sample 3-5 additional private wells to the south and west of the
ExxonMobil property to assure residents of the safe quality of the groundwater
should they choose to drink it, or use it for other domestic and agricultural
purposes. Though no specific dates have been set, the IEPA plans to sample
selected private wells in early summer 2007, provided wells are accessible and
permission is given by well owners.
Jay A. Timm
Office of Community Relations
(217) 785-7725 (fax)
ILEPA Communications Manager
Central Management Services
Public Water Supplies
Fact Sheet #2 - Monterey Coal Mine #2 Page 2 of 2
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