---
kind: "section"
citation: "40 C.F.R. § 265.278"
title: "40"
number: "265.278"
heading: "Unsaturated zone (zone of aeration) monitoring."
url: "https://uscodex.org/cfr/40/265.278"
---

# §265.278. Unsaturated zone (zone of aeration) monitoring.

- (a) The owner or operator must have in writing, and must implement, an unsaturated zone monitoring plan which is designed to:
  - (1) Detect the vertical migration of hazardous waste and hazardous waste constituents under the active portion of the land treatment facility, and
  - (2) Provide information on the background concentrations of the hazardous waste and hazardous waste constituents in similar but untreated soils nearby; this background monitoring must be conducted before or in conjunction with the monitoring required under [paragraph (a)(1)](#a-1) of this section.
- (b) The unsaturated zone monitoring plan must include, at a minimum:
  - (1) Soil monitoring using soil cores, and
  - (2) **Soil-pore water monitoring using devices such as lysimeters.**
- (c) To comply with [paragraph (a)(1)](#a-1) of this section, the owner or operator must demonstrate in his unsaturated zone monitoring plan that:
  - (1) The depth at which soil and soil-pore water samples are to be taken is below the depth to which the waste is incorporated into the soil;
  - (2) **The number of soil and soil-pore water samples to be taken is based on the variability of—**
    - (i) The hazardous waste constituents (as identified in § [265.273(a)](/cfr/40/265.273.md?p=a) and [(b)](/cfr/40/265.273.md?p=b)) in the waste and in the soil; and
    - (ii) The soil type(s); and
  - (3) The frequency and timing of soil and soil-pore water sampling is based on the frequency, time, and rate of waste application, proximity to ground water, and soil permeability.
- (d) The owner or operator must keep at the facility his unsaturated zone monitoring plan, and the rationale used in developing this plan.
- (e) The owner or operator must analyze the soil and soil-pore water samples for the hazardous waste constituents that were found in the waste during the waste analysis under § [265.273 (a)](/cfr/40/265.273.md?p=a) and [(b)](/cfr/40/265.273.md?p=b).

## Notes

### Authority

Authority: 42 U.S.C. 6905, 6906, 6912, 6922, 6923, 6924, 6925, 6935, 6936, 6937, and 6939g.

### Source

Source: 45 FR 33232, May 19, 1980, unless otherwise noted.