---
kind: "section"
citation: "40 C.F.R. § 146.4"
title: "40"
number: "146.4"
heading: "Criteria for exempted aquifers."
url: "https://uscodex.org/cfr/40/146.4"
---

# §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](/cfr/40/146.3.md) may be determined under [§ 144.7](/cfr/40/144.7.md) of this chapter to be an “exempted aquifer” for Class I-V wells if it meets the criteria in [paragraphs (a) through (c)](#a..c) of this section. Class VI wells must meet the criteria under [paragraph (d)](#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)](/cfr/40/144.7.md?p=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.**

## Notes

### Amendments

[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]

### Authority

Authority: Safe Drinking Water Act, 42 U.S.C. 300f et seq.; Resource Conservation and Recovery Act, 42 U.S.C. 6901 et seq.

### Source

Source: 45 FR 42500, June 24, 1980, unless otherwise noted.

### Amendments

[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]