40 C.F.R. § 257.3-4 : Protection of Environment — ENVIRONMENTAL PROTECTION AGENCY — SOLID WASTES — CRITERIA FOR CLASSIFICATION OF SOLID WASTE DISPOSAL FACILITIES AND PRACTICES — CLASSIFICATION OF SOLID WASTE DISPOSAL FACILITIES AND PRACTICES —4 - Ground water

(a) A facility or practice shall not contaminate an underground drinking water source beyond the solid waste boundary or beyond an alternative boundary specified in accordance with paragraph (b) of this section.
(b)
(1) For purposes of section 1008(a)(3) of the Act or section 405(d) of the CWA, a party charged with open dumping or a violation of section 405(e) with respect to sewage sludge that is not used or disposed through a practice regulated in 40 CFR part 503 may demonstrate that compliance should be determined at an alternative boundary in lieu of the solid waste boundary. The court shall establish an alternative boundary only if it finds that such a change would not result in contamination of ground water which may be needed or used for human consumption. This finding shall be based on analysis and consideration of all of the following factors that are relevant:
(i) The hydrogeological characteristics of the facility and surrounding land, including any natural attenuation and dilution characteristics of the aquifer;
(ii) The volume and physical and chemical characteristics of the leachate;
(iii) The quantity, quality, and direction of flow of ground water underlying the facility;
(iv) The proximity and withdrawal rates of ground-water users;
(v) The availability of alternative drinking water supplies;
(vi) The existing quality of the ground water, including other sources of contamination and their cumulative impacts on the ground water;
(vii) Public health, safety, and welfare effects.
(2) For purposes of sections 4004(a) and 1008(a)(3), the State may establish an alternative boundary for a facility to be used in lieu of the solid waste boundary only if it finds that such a change would not result in the contamination of ground water which may be needed or used for human consumption. Such a finding shall be based on an analysis and consideration of all of the factors identified in paragraph (b)(1) of this section that are relevant.
(c) As used in this section:
(1) Aquifer means a geologic formation, group of formations, or portion of a formation capable of yielding usable quantities of ground water to wells or springs.
(2) Contaminate means introduce a substance that would cause:
(i) The concentration of that substance in the ground water to exceed the maximum contaminant level specified in appendix I, or
(ii) An increase in the concentration of that substance in the ground water where the existing concentration of that substance exceeds the maximum contaminant level specified in appendix I.
(3) Ground water means water below the land surface in the zone of saturation.
(4) Underground drinking water source means:
(i) An aquifer supplying drinking water for human consumption, or
(ii) An aquifer in which the ground water contains less than 10,000 mg/1 total dissolved solids.
(5) Solid waste boundary means the outermost perimeter of the solid waste (projected in the horizontal plane) as it would exist at completion of the disposal activity.

40 C.F.R. §257.3-4

44 FR 53460, 9/13/1979, as amended at 46 FR 47052, 9/23/1981; 58 FR 9386, 2/19/1993