Surface Impoundment Inspection and Response Actions

Last week we talked about the design and operation requirements for surface impoundments. Today we’re going to continue on that topic by covering the inspection and response actions that must be completed by surface impoundment operators. In case you’ve forgotten, surface impoundments are a lot like landfill cells. The main difference being that surface impoundments are used for temporary storage or treatment and a landfill cell is designated for final waste disposal.

What are the Inspection Requirements for Surface Impoundments?

To start, we must note that these inspection requirements must be completed in conjunction with the general inspection requirements in §264/265.226. The first additional requirement deals with design and structural integrity of the land disposal unit. According to the EPA, “the owner and operator must inspect liners and covers for any problems after construction or installation and continue inspections weekly and after storms to monitor for evidence of deterioration, malfunctions, improper operation of overtopping systems, sudden drops in the level of the impoundment contents, and severe erosions of dikes and other containment devices.”

The second additional requirement addresses leak detection sumps. According to this rule, on a minimum of a weekly basis owners and operators of land disposal units like surface impoundments must monitor their leak detection sumps in order to measure the amount of liquid within them and to determine whether or not the action leakage rate (ALR) has been exceeded. Doing so makes sure that both the liner and the leachate pump are working efficiently. If owners or operators discover that the ALR has been exceeded they must notify the Agency and respond “in accordance with the response action plan.”

What Response Actions must Surface Impoundments comply with?

Much like the inspection requirements, surface impoundments must also comply with two types of response actions. According to the EPA, “the response action for the performance of the unit is determined by the terms of the response action plan, triggered when the ALR has been exceeded (§264/265.223). If the action leakage rate has been exceeded, the owner and operator must notify the Regional Administrator or authorized state; determine what short-term actions must be taken (e.g., shut down of the facility for repairs); determine the location, size, and cause of any leak; and send the assessments to the Region or authorized state.”

The other response action deals with emergency repair provisions in the case of a unit design failure at permitted facilities. The EPA specifies that “if there is an indication of a failure of the containment system (e.g., a sudden drop in the level of the contents not attributable to changes in the flow in or out of the impoundment), the surface impoundment must be removed from service.” If this happens the owners and operators of the surface impoundment must follow the plans laid out in the contingency plan. This would include any emergency repairs that need to be made.

Quoted and EPA cited information (unless otherwise noted) for this blog post was gathered from the EPA document, Introduction to Land Disposal Units.” As always, this blog post is not intended to be comprehensive and it is always best to check with the EPA and local government for full, up-to-date, rules and regulations.

Surface Impoundments: Design and Operation

When the EPA was designing the cradle-to-grave system for managing hazardous wastes they developed nine different land disposal units. These units include landfill, surface impoundment, waste pile, injection well, land treatment facility, salt dome formation, salt bed formation, underground mine, and underground cave. Four of these nine unit types required additional technical standards set forth by the EPA. Today we will be covering the design and operating standards of one of those four, surface impoundments.

Surface impoundments are a lot like landfill cells in that, “both units are either a natural topographic depression, manmade excavation, or diked area formed primarily of earthen materials, such as soil.” Additionally, both may be lined with manmade materials. Their uses, however, are what make them so different. According to the EPA, “surface impoundments are generally used for temporary storage or treatment, whereas a landfill is an area designated for final waste disposal.” Because of this, the closure and post-closure standards are very different.

How are surface impoundments designed?

When the EPA began developing the design and operation standards for surface impoundments they operated with the goal of minimizing the formation and migration of leachate to the adjacent subsurface soil, groundwater, and surface water in mind.

According to the EPA, “these comprehensive technical requirements for surface impoundments are the minimum technological requirements (MTRs) mandated by RCRA. These sections require a double liner, a LCRS, and a leak detection system.” The MTRs are applicable to all new units, lateral expansions, and replacement units constructed or reused after July 29th of 1992.

First things first, we’ll talk about the double liner. This system includes, “a top liner to prevent migration of hazardous constituents into the liner and a composite bottom liner consisting of a synthetic geomembrane and three feet of compacted soil material.”

In addition to this liner system, the unit has to have a leachate collection and removal system (LCRS) which also serves as a leak detection system. According to the EPA, “The LCRS, along with the leak detection system drainage layers, must be designed with a bottom slope of at least one percent, be made of materials chemically resistant to the wastes placed in the unit, and be able to remove the liquids at a specified minimum rate. The LCRS itself must be designed to collect liquids in a sump and subsequently pump out those liquids. In addition to the performance and design requirements, the LCRS must be located between the liners immediately above the bottom composite liner, enabling the LCRS to collect the largest amount of leachate, while also representing the most efficient place to identify leaks.”

Making sure that material can’t leak back into the earth is not the only consideration that must be made, however. Surface impoundments also must be designed to prevent liquids from flowing over the top (called overtopping) and “ensure the structural integrity of any dikes.” The owner or operator must also develop a site-specific flow rate for leachate which is called the action leakage rate or ALR. This is used to indicate when a units system is not functioning as it should.

Because of the importance of these design regulations (and since none of the aforementioned technologies will work if the impoundment is not installed correctly or made of quality materials) the EPA requires a construction quality assurance (CQA) program to make sure that an impoundment meets all technical criteria. According to the EPA, “The CQA program requires a CQA plan that identifies how construction materials and their installation will be monitored and tested and how the results will be documented (§264.19). The CQA program is developed and implemented under the direction of a registered professional engineer, who must also certify that the CQA plan has been successfully carried out and that the unit meets all specifications before any waste is received.”

Quoted and EPA cited information (unless otherwise noted) for this blog post was gathered from the EPA document, Introduction to Land Disposal Units.” As always, this blog post is not intended to be comprehensive and it is always best to check with the EPA and local government for full, up-to-date, rules and regulations.