1) Soil investigation.
A) Up to four borings must be drilled around
each independent UST field where one or more UST excavation samples collected
pursuant to
734.210(h),
excluding backfill samples, exceed the most stringent Tier 1 remediation
objectives of 35 Ill. Adm. Code 742 for the applicable indicator contaminants.
One additional boring must be drilled as close as practicable to each UST field
if a groundwater investigation is not required under subsection (a)(2) of this
Section. The borings must be advanced through the entire vertical extent of
contamination, based upon field observations and field screening for organic
vapors, provided that borings must be drilled below the groundwater table only
if site-specific conditions warrant.
B) Up to two borings must be drilled around
each UST piping run where one or more piping run samples collected pursuant to
Section
734.210(h)
exceed the most stringent Tier 1 remediation
objectives of 35 Ill. Adm. Code 742 for the applicable indicator contaminants.
One additional boring must be drilled as close as practicable to each UST
piping run if a groundwater investigation is not required under subsection
(a)(2) of this Section. The borings must be advanced through the entire
vertical extent of contamination, based upon field observations and field
screening for organic vapors, provided that borings must be drilled below the
groundwater table only if site-specific conditions warrant.
C) One soil sample must be collected from
each five-foot interval of each boring drilled pursuant to subsections
(a)(1)(A) and (B) of this Section. Each sample must be collected from the
location within the five-foot interval that is the most contaminated as a
result of the release. If an area of contamination cannot be identified within
a five-foot interval, the sample must be collected from the center of the
five-foot interval. All samples must be analyzed for the applicable indicator
contaminants.
2)
Groundwater investigation.
A) A groundwater
investigation is required under the following circumstances:
i) There is evidence that groundwater wells
have been impacted by the release above the most stringent Tier 1 remediation
objectives of 35 Ill. Adm. Code 742 for the applicable indicator
contaminants;
ii) Free product that
may impact groundwater is found to need recovery in compliance with Section
734.215 of
this Part; or
iii) There is
evidence that contaminated soils may be or may have been in contact with
groundwater, except that, if the owner or operator pumps the excavation or tank
cavity dry, properly disposes of all contaminated water, and demonstrates to
the Agency that no recharge is evident during the 24 hours following pumping,
the owner or operator does not have to complete a groundwater investigation,
unless the Agency's review reveals that further groundwater investigation is
necessary.
B) If a
groundwater investigation is required, the owner or operator must install five
groundwater monitoring wells. One monitoring well must be installed in the
location where groundwater contamination is most likely to be present. The four
remaining wells must be installed at the property boundary line or 200 feet
from the UST system, whichever is less, in opposite directions from each other.
The wells must be installed in locations where they are most likely to detect
groundwater contamination resulting from the release and provide information
regarding the groundwater gradient and direction of flow.
C) One soil sample must be collected from
each five-foot interval of each monitoring well installation boring drilled
pursuant to subsection (a)(2)(B) of this Section. Each sample must be collected
from the location within the five-foot interval that is the most contaminated
as a result of the release. If an area of contamination cannot be identified
within a five-foot interval, the sample must be collected from the center of
the five-foot interval. All soil samples exhibiting signs of contamination must
be analyzed for the applicable indicator contaminants. For borings that do not
exhibit any signs of soil contamination, samples from the following intervals
must be analyzed for the applicable indicator contaminants, provided that the
samples must not be analyzed if other soil sampling conducted to date indicates
that soil contamination does not extend to the location of the monitoring well
installation boring:
i) The five-foot
intervals intersecting the elevations of soil samples collected pursuant to
Section
734.210(h),
excluding backfill samples, that exceed the most stringent Tier 1 remediation
objectives of 35 Ill. Adm. Code 742 for the applicable indicator
contaminants.
ii) The five-foot
interval immediately above each five-foot interval identified in subsection
(a)(2)(C)(i) of this Section; and
iii) The five-foot interval immediately below
each five-foot interval identified in subsection (a)(2)(C)(i) of this
Section.
D) Following
the installation of the groundwater monitoring wells, groundwater samples must
be collected from each well and analyzed for the applicable indicator
contaminants.
E) As a part of the
groundwater investigation an in-situ hydraulic conductivity test must be
performed in the first fully saturated layer below the water table. If multiple
water bearing units are encountered, an in-situ hydraulic conductivity test
must be performed on each such unit.
i) Wells
used for hydraulic conductivity testing must be constructed in a manner that
ensures the most accurate results.
ii) The screen must be contained within the
saturated zone.
3) An initial water supply well survey in
accordance with Section
734.445(a)
of this Part.
