1. a) Natural attenuation, access controls, and point of use treatment shall not be considered engineered barriers. Engineered barriers may not be used to prevent direct human exposure to groundwater without the use of institutional controls.
2. b) For purposes of determining remediation objectives under Tier 1, engineered barriers are not recognized.

3. c) The following engineered barriers are recognized for purposes of calculating remediation objectives that exceed residential remediation objectives:

   1. 1) For the soil component of the groundwater ingestion exposure route, the following engineered barriers are recognized if they prevent completion of the exposure pathway:

      1. A) Caps or walls constructed of compacted clay, asphalt, concrete or other material approved by the Agency; and
      2. B) Permanent structures such as buildings and highways.

   2. 2) For the soil ingestion exposure route, the following engineered barriers are recognized if they prevent completion of the exposure pathway:

      1. A) Caps or walls constructed of compacted clay, asphalt, concrete, or other material approved by the Agency;
      2. B) Permanent structures such as buildings and highways; and

      3. C) Soil, sand, gravel, or other geologic materials that:

         1. i) Cover the contaminated media;
         2. ii) Meet the soil remediation objectives under Subpart E for residential property for contaminants of concern; and
         3. iii) Are a minimum of three feet in depth.

   3. 3) For the outdoor inhalation exposure route, the following engineered barriers are recognized if they prevent completion of the exposure pathway:

      1. A) Caps or walls constructed of compacted clay, asphalt, concrete, or other material approved by the Agency;
      2. B) Permanent structures such as buildings and highways; and

      3. C) Soil, sand, gravel, or other geologic materials that:

         1. i) Cover the contaminated media;
         2. ii) Meet the soil remediation objectives under Subpart E for residential property for contaminants of concern; and
         3. iii) Are a minimum of ten feet in depth and not within ten feet of any manmade pathway.

   4. 4) For the ingestion of groundwater exposure route, the following engineered barriers are recognized if they prevent completion of the exposure pathway:

      1. A) Slurry walls; and
      2. B) Hydraulic control of groundwater.
4. d) Unless otherwise prohibited under Section 742.1100, any other type of engineered barrier may be proposed if it will be as effective as the options listed in subsection (c).

(Source: Amended at 37 Ill. Reg. 7506, effective May 15, 2013)