Section 615.204  Groundwater Monitoring System

a)         Except as provided otherwise in subsection (b), the groundwater monitoring system must consist of a sufficient number of wells, installed at appropriate locations and depths to yield groundwater samples, that:

1)         Represent the quality of background water that has not been affected by contamination from the facility or unit; and

2)         Represent the quality of groundwater at the compliance point or points.

b)         If a potable water well or other water well can be used as a monitoring well under this subsection, no additional monitoring wells are required under this Section.  A potable water well or other water well may be used as a monitoring well if:

1)         For a potable water well other than a community water supply well, a construction report has been filed with the Illinois Department of Public Health for such well, or such well has been located and constructed (or reconstructed) to meet the Illinois Water Well Construction Code [415 ILCS 30] and 35 Ill. Adm. Code 920;

2)         For a potable water supply well that was constructed before August 20, 1965, the enactment of the Illinois Water Well Construction Code [415 ILCS 30], and meets all of the following criteria:

A)        Construction must be done in a manner that will enable the collection of groundwater samples that represent in situ groundwater conditions;

B)        Casings and screens must be made from durable material resistant to expected chemical or physical degradation that does not interfere with the quality of groundwater samples being collected; and

C)        The annular space opposite the screened section of the well (i.e., the space between the bore hole and well screen) must be filled with gravel or sand if necessary to collect groundwater samples.  The annular space above and below the well screen must be sealed to prevent migration of water from adjacent formations and the surface to the sampled depth.

3)         For a water well other than a potable water well (e.g., a livestock watering well or an irrigation well), the owner or operator of the unit seeking to use the well as a monitoring well certifies to the Agency that a construction report has been filed with the Illinois Department of Public Health or the Illinois Department of Mines and Minerals for such well, or that such well has been located and constructed (or reconstructed) to meet the Illinois Water Well Construction Code [415 ILCS 30] and 35 Ill. Adm. Code 920; and

4)         The unit contains solely non-special waste if the unit is a surface impoundment.

c)         When a facility contains more than one unit, separate groundwater monitoring systems are not required for each unit if provisions for sampling the groundwater will enable detection and measurement of contaminants that have entered the groundwater from all units.

d)         All monitoring wells must meet the following requirements:

1)         Construction must be done in a manner that will enable the collection of groundwater samples;

2)         Casings and screens must be made from durable material that is resistant to expected chemical or physical degradation and that does not interfere with the quality of groundwater samples being collected; and

3)         The annular space opposite the screened section of the well (i.e., the space between the bore hole and well screen) must be filled with gravel or sand if necessary to collect groundwater samples.  The annular space above and below the well screen must be sealed to prevent migration of water from overlying adjacent formations and the surface to the sampled depth.

(Source:  Amended at 47 Ill. Reg. 7581, effective May 16, 2023)