(1) Site delineation concentration criteria. Satisfactory evidence of the definition of the horizontal and vertical delineation of soil or groundwater contamination for the purposes of this part may be determined on the basis of any of the following concentrations; provided, however, that the provisions of subparagraphs (B) and (C) of this paragraph shall not be used if the concentrations are higher than as provided in subparagraph (E) of this paragraph:

(A) Concentrations from an appropriate number of samples that are representative of local ambient or anthropogenic background conditions not affected by the subject site release;

(B) Soil concentrations less than those concentrations that require notification under standards promulgated by the board pursuant to Part 2 of this article;

(C) Two times the laboratory lower detection limit concentration using an applicable analytical test method recognized by the United States Environmental Protection Agency, provided that such concentrations do not exceed all cleanup standards;

(D) For metals in soils, the concentrations reported for Georgia undisturbed native soil samples as reported in the United States Geological Survey (USGS) Open File Report 8 1-197 (Boerngen and Shacklette, 1981), or such later version as may be adopted by rule or regulation of the board; or

(E) Default, residential cleanup standards;

(2) Exposure pathway. A site-specific exposure pathway shall be considered complete if there are no discontinuities in or impediments to constituent of concern movement, including without limitation controls, from the source of the release to the receptor. Otherwise, the exposure pathway shall be incomplete and there shall be no exposure pathway that requires evaluation;

(3) Representative exposure concentrations. Compliance with site-specific cleanup standards shall be determined on the basis of representative concentrations of constituents of concern in soils across each applicable soil exposure domain, and the representative concentrations for groundwater at a point of exposure;

(4) Point of demonstration monitoring for groundwater. Concentrations of site-specific constituents of concern in groundwater shall be measured and evaluated at a point of demonstration well to demonstrate that groundwater concentrations are protective of any established downgradient point of exposure;

(5) Cleanup standards for soil. Compliance with site-specific cleanup standards for soil may be based on:

(A) Direct exposure factors for surficial soils within two feet of the land surface;

(B) Construction worker exposure factors for subsurface soils to a specified subsurface construction depth; and

(C) Soil concentrations for protection of groundwater criteria (at an established point of exposure for groundwater as defined under this part) for soils situated above the uppermost groundwater zone.

Whenever such depth-specific soil criteria are applied, the voluntary investigation and remediation plan for the site shall include a description of the continuing actions and controls necessary to maintain compliance;

(6) Available cleanup standards. Any cleanup standard lawfully promulgated pursuant to Code Section 12-8-93 that is protective of human health and the environment and accomplishes the provisions, purposes, standards, and policies of this part may be used without demonstrating that a different cleanup standard is inappropriate or impracticable;

(7) Fate and transport parameters. Compliance with site-specific cleanup standards may be determined on the basis of any fate and transport model recognized by the United States Environmental Protection Agency or United States Geological Survey and using most probable representative values for model parameters as adopted by the board;

(8) Source material. Compliance with site-specific cleanup standards that require that source material be removed may be satisfied when such material is removed, decontaminated, or otherwise immobilized in the subsurface, to the extent practicable; and

(9) Technical impracticability. Site delineation or remediation beyond the point of technical impracticability shall not be required if the site does not otherwise pose an imminent or substantial danger to human health and the environment.