Jump to main content.

Groundwater Monitoring Requirements for Treatment Storage and Disposal Facilities (TSDFs)

Pipe outfall with flowing water

The groundwater monitoring requirements for hazardous waste treatment, storage, and disposal facilities (TSDFs) are just one aspect of the RCRA hazardous waste management strategy for protecting human health and the environment from accidental releases of hazardous constituents. While land disposal restrictions and unit specific standards seek to reduce the toxicity of waste and prevent releases respectively, the groundwater monitoring requirements represent the last line of defense by ensuring that any releases are detected and remediated in a timely manner.

TSDFs that manage hazardous waste in landfills, surface impoundments, land treatment units, and some waste piles (referred to as “regulated units” in the regulations) are required to implement a groundwater monitoring program to detect the release of hazardous constituents to the underlying groundwater. The regulations for permitted facilities are found at 40 CFR Part 264, Subpart F-Releases from Solid Waste Management Units and the interim status regulations for facilities in operation before these rules came into effect are found at 40 CFR Part 265, Subpart F-Groundwater Monitoring.

The requirements for permitted and interim status TSDFs differ significantly. The major differences being:

Even with these differences, the overall goal of these requirements is the same: protect the groundwater in the uppermost aquifer from contamination by the hazardous constituents managed at the TSDF.

For more information, see:

Permitted Facilities

For permitted TSDFs, a groundwater monitoring program consists of three phases: detection monitoring (§264.98), compliance monitoring (§264.99), and corrective action (§264.100). The phases are sequential, with a facility able to move back and forth between phases as certain criteria are met. The regulations are written as performance standards that require each facility’s groundwater monitoring program to have a sufficient number of wells installed at the appropriate locations and depths that can yield representative samples of background conditions and water quality at the point of compliance in the uppermost aquifer (defined as the geological formation nearest the natural surface that is capable of yielding significant quantities of groundwater to wells or springs).

To meet these standards, each facility must design, install, and operate a groundwater monitoring program based upon the site’s specific geology and hydrology, as well as the type of waste management unit and the characteristics of the waste being managed. The monitoring wells must be appropriately designed and installed and consistent sampling and analytical procedures must be implemented to ensure accurate and representative samples are taken.

The specific sampling requirements and procedures (including frequency of sampling) are specified in the facility’s hazardous waste permit. Typically these requirements are included in a sampling and analysis plan. All data collected as part of a facility’s groundwater monitoring program must be maintained in the facility’s operating record.

Top of Page

Detection Monitoring

Detection monitoring is phase one of the groundwater monitoring program. Under this phase, facilities are monitoring to detect and characterize any releases of hazardous constituents into the uppermost aquifer. Samples are taken from the monitoring wells and analyzed for specific indicator parameters and any other waste constituents or reaction products that indicate that a release might have occurred. The EPA Regional Administrator designates in the facility’s permit the specific constituents and parameters to be monitored and establishes the frequency of sampling. At a minimum, four samples must be taken from each well semi-annually.

Samples taken from the point of compliance (i.e., the wells downgradient of the waste management unit) are compared to the background samples taken from the upgradient well(s). These samples are analyzed to determine if a statistically significant increase (SSI) in the levels of any of the monitored constituents has occurred. When analyzing the samples, facility owner/operators may use one of the following five methods:

If an SSI is detected, the facility must switch to a compliance monitoring program, unless the owner/operators can demonstrate that the SSI was due to a sampling, analysis, or statistical analysis error; or is due to natural variations in the groundwater chemistry. If unable to make this demonstration, the owner/operators must:

Top of Page

Compliance Monitoring

The purpose of a compliance monitoring program is to ascertain whether the constituents released to the uppermost aquifer are exceeding acceptable concentration levels and threatening human health and the environment. The first step in this process is establishing a groundwater protection standard (GWPS). As stated above, a facility must submit a permit modification application to switch from detection monitoring to compliance monitoring when an statistically significant increase (SSI) is detected. As part of this modified permit, the EPA Regional Administrator specifies the GWPS for the facility. The GWPS establishes:

During compliance monitoring, samples are taken at each well located at the point of compliance (four samples from each well) and compared to the GWPS. The frequency of sampling is determined by the EPA Regional Administrator and specified in the modified facility permit. At a minimum, samples must be taken at least semi-annually. The facility must also analyze samples for Part 264 Appendix IX constituents at least annually. If any new constituents are found to have an SSI, then they also must be added to the GWPS list of constituents.

If the level of any of the constituents exceeds the GWPS, the owner/operators must notify the EPA Regional Administrator in writing within 7 days. The owner/operators also must submit a permit modification application to establish a corrective action program. Compliance monitoring must be continued during this period.

Top of Page

Corrective Action

Once an exceedance of the groundwater protection standard (GWPS) has been detected, the facility must take action to bring the constituent concentration levels back into compliance with the GWPS. To achieve this the owner/operator must either remove the hazardous constituents or treat them in place. The EPA Regional Administrator will approve the facility’s selected corrective action method and specify the time frame in which it must take place. Any hazardous constituents that have migrated beyond the point of compliance also must be remediated. The facility must continue corrective action until the GWPS has not been exceeded for three consecutive years. At which point, the facility may return to compliance monitoring.

Visit EPA’s Corrective Action page for more information.

Top of Page

Interim Status Facilities

The interim status groundwater monitoring requirements apply only to those facilities with hazardous waste landfills, surface impoundments, or land treatment units in operation prior to the hazardous waste rules’ effective date. An interim status facility subject to the groundwater monitoring requirements must design and implement a groundwater monitoring system capable of representing the background groundwater quality and detecting any hazardous constituents that migrate from the hazardous waste management units. This system must consist of at least one upgradient and three downgradient monitoring wells that can collect representative samples for analysis. If a statistically significant increase (SSI) in any constituent is detected and confirmed during sampling, the owner/operators must notify the EPA Regional Administrator in writing within seven days. The owner/operators must then continue to monitor the groundwater quality. While the interim status regulations do not contain corrective action provisions, the EPA Regional Administrator may order cleanup under RCRA §3008(h) or §7003 authority, or when the facility permit is issued.

Visit EPA’s Corrective Action page for more information.

Top of Page


Handbook of Groundwater Protection and Cleanup Policies for RCRA Corrective Action This resource is a user-friendly, comprehensive publication designed to help TSDF owners/operators find and understand EPA’s policies concerning groundwater protection and cleanup.

RCRA Training Module: Introduction to Groundwater Monitoring (PDF) (29 pp, 231 K, about PDF) Provides an introduction to the groundwater requirements for TSDFs.

RCRA Orientation Manual: Chapter 5. Regulations Governing Treatment, Storage, and Disposal Facilities (PDF) (36 pp, 681 K, about PDF) Provides introductory information on the groundwater monitoring requirements for hazardous waste TSDFs.

RCRA Online Database Indexes thousands of letters, memoranda, publications, and questions and answers issued by EPA's Office of Resource Conservation and Recovery (ORCR). These documents represent EPA Headquarters interpretations of the RCRA regulations governing the management of solid, hazardous, and medical waste.

RCRA FAQ Database Enables users to search frequently asked questions, or submit their own question/comment on a variety of RCRA issues and topics.

Top of Page

Local Navigation

Jump to main content.