Ill. Admin. Code tit. 35, § 840.118 - Demonstration of Compliance
a)
Compliance with the on-site and off-site groundwater quality standards set
forth in Sections
840.116(a) and
(b) of this Subpart:
1) Compliance with on-site groundwater
quality standards will be achieved when no statistically significant increasing
trend that can be attributed to Ash Pond D is detected in the concentrations of
all constituents monitored in accordance with Section
840.114
of this Subpart at the down-gradient boundaries of the Hutsonville site for
four consecutive years after changing to an annual monitoring frequency
pursuant to Section
840.114(c).
2) Compliance with off-site groundwater
quality standards:
A) Compliance with off-site
groundwater quality standards set forth in Section
840.116(b)
of this Subpart will be achieved when:
i) A
statistically significant decreasing trend in concentrations of constituents
monitored in accordance with Section
840.114
of this Subpart in the upper zone of the underlying aquifer at the
down-gradient boundaries of the Hutsonville site is detected in the
concentrations of all constituents monitored for a period of four consecutive
years after changing to an annual monitoring frequency pursuant to Section
840.114(c);
ii) No statistically significant increasing
trend that can be attributed to Ash Pond D is detected in concentrations of
constituents monitored in accordance with Section
840.114
of this Subpart in the lower zone of the underlying aquifer at the
down-gradient boundaries of the Hutsonville site for four consecutive years
after changing to an annual monitoring frequency pursuant to Section
840.114(c);
and
B) If a
groundwater management zone for off-site properties with groundwater
contamination from Ash Pond D is established as provided in Section
840.116(b)
of this Subpart, the compliance points will be determined as set forth in the
GMZ approved in the closure plan or post-closure care plan, as
appropriate.
b) For purposes of demonstrating compliance:
1) The owner or operator of Ash Pond D must
perform an annual trend analysis for each monitoring well located at the
down-gradient boundaries of the Hutsonville site for all constituents monitored
in accordance with Section
840.114
of this Subpart, based on a minimum of four consecutive samples, by applying
Sen's Estimate of Slope.
2) If a
groundwater management zone for off-site properties with groundwater
contamination from Ash Pond D is established as provided in Section
840.116(b)
of this Subpart, the demonstration of compliance will be determined as set
forth in the GMZ approved in the closure plan or post-closure care plan, as
appropriate.
c)
Compliance with nondegradation standards during closure and post-closure care
periods:
1) If the results of sampling and
analysis show an increasing trend at any monitoring well located at the
down-gradient boundaries of the Hutsonville site , a Mann-Kendall analysis must
be performed at 95 percent confidence to determine whether the increasing trend
is statistically significant. The owner or operator of Ash Pond D must
investigate the cause of a statistically significant increasing trend as
determined under subsection (b) of this Section. If the statistically
significant increasing trend occurs during post-closure care, the investigation
must include more frequent inspection of the surface of the cover system and
evaluation of background concentrations and the effectiveness of the
groundwater collection trench required by Section
840.120
of this Subpart.
A) If an investigation
performed in accordance with subsection (c)(1) of this Section attributes a
statistically significant increasing trend to a superseding cause, the owner or
operator of Ash Pond D must notify the Agency in writing, stating the cause of
the increasing trend and providing the rationale used in that
determination.
B) If there is no
superseding cause for the statistically significant increasing trend and
sampling frequency has been reduced pursuant to Section
840.114(b) or
(c) of this Subpart to semiannual or annual
sampling, the owner or operator must return to a quarterly sampling schedule.
After four consecutive quarterly samples show no statistically significant
increasing trend, the frequency of groundwater monitoring may be returned to
either semiannual or annual, whichever frequency was utilized prior to the
return to quarterly sampling.
C)
For purposes of this subsection (c)(1), notifications concerning statistically
significant increasing trends and revisions of the sampling frequency must be
reported to the Agency in writing within 30 days after making the
determinations, as provided in Section
840.144(f)
of this Subpart.
2) If a
statistically significant increasing trend is observed to continue over a
period of two or more consecutive years and there are no superseding causes for
the trend, the owner or operator must perform the following:
A) A hydrogeologic investigation;
and
B) Additional site
investigation, if necessary.
3) Based on the outcome of the activities
required by subsection (c)(2) of this Section, the owner or operator of Ash
Pond D must take action to mitigate statistically significant increasing trends
that are causing, threatening or allowing exceedences of off-site groundwater
quality standards as set forth in Section
840.116(b).
These actions must be proposed as a modification to the post-closure care plan
within 180 days after completion of the activities required by subsection
(c)(2) of this Section.
Notes
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