40 CFR § 146.4 - Criteria for exempted aquifers.

---
identifier: "/us/cfr/t40/s146.4"
source: "ecfr"
legal_status: "authoritative_unofficial"
title: "40 CFR § 146.4 - Criteria for exempted aquifers."
title_number: 40
title_name: "Protection of Environment"
section_number: "146.4"
section_name: "Criteria for exempted aquifers."
chapter_name: "ENVIRONMENTAL PROTECTION AGENCY"
subchapter_number: "D"
subchapter_name: "WATER PROGRAMS"
part_number: "146"
part_name: "UNDERGROUND INJECTION CONTROL PROGRAM: CRITERIA AND STANDARDS"
positive_law: false
currency: "2026-03-24"
last_updated: "2026-03-24"
format_version: "1.1.0"
generator: "[email protected]"
authority: "Safe Drinking Water Act, 42 U.S.C. 300f  Resource Conservation and Recovery Act, 42 U.S.C. 6901"
regulatory_source: "45 FR 42500, June 24, 1980, unless otherwise noted."
cfr_part: "146"
---


# 146.4 Criteria for exempted aquifers.

An aquifer or a portion thereof which meets the criteria for an “underground source of drinking water” in § 146.3 may be determined under § 144.7 of this chapter to be an “exempted aquifer” for Class I-V wells if it meets the criteria in paragraphs (a) through (c) of this section. Class VI wells must meet the criteria under paragraph (d) of this section:

(a) It does not currently serve as a source of drinking water; and

(b) It cannot now and will not in the future serve as a source of drinking water because:

(1) It is mineral, hydrocarbon or geothermal energy producing, or can be demonstrated by a permit applicant as part of a permit application for a Class II or III operation to contain minerals or hydrocarbons that considering their quantity and location are expected to be commercially producible.

(2) It is situated at a depth or location which makes recovery of water for drinking water purposes economically or technologically impractical;

(3) It is so contaminated that it would be economically or technologically impractical to render that water fit for human consumption; or

(4) It is located over a Class III well mining area subject to subsidence or catastrophic collapse; or

(c) The total dissolved solids content of the ground water is more than 3,000 and less than 10,000 mg/l and it is not reasonably expected to supply a public water system.

(d) The areal extent of an aquifer exemption for a Class II enhanced oil recovery or enhanced gas recovery well may be expanded for the exclusive purpose of Class VI injection for geologic sequestration under § 144.7(d) of this chapter if it meets the following criteria:

(1) It does not currently serve as a source of drinking water; and

(2) The total dissolved solids content of the ground water is more than 3,000 mg/l and less than 10,000 mg/l; and

(3) It is not reasonably expected to supply a public water system.

(Clean Water Act, Safe Drinking Water Act, Clean Air Act, Resource Conservation and Recovery Act: 42 U.S.C. 6905, 6912, 6925, 6927, 6974)

[45 FR 42500, June 24, 1980, as amended at 47 FR 4998, Feb. 3, 1982; 48 FR 14293, Apr. 1, 1983; 75 FR 77291, Dec. 10, 2010]