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The term alternative endpoints includes a variety of formal designations permitted under specific Federal and State programs to shape groundwater remediation goals on a site-specific basis. Alternative endpoints are management approaches considered at highly complex sites where complete groundwater restoration is not likely possible within the next few decades using best available technologies. The approaches include technical impracticability (TI) waivers, alternate concentration limits (ACLs), groundwater reclassification, designations of points of compliance and more. These management approaches are typically used along with remediation technologies and institutional controls to protect human health and environment. This article describes several alternative endpoints, their regulatory basis, and the circumstances under which they can be considered at a site.

Related Article(s):

CONTRIBUTOR(S): Elisabeth Hawley and Dr. Rula Deeb

Key Resource(s):

• Assessing Alternative Endpoints for Groundwater Remediation at Contaminated Sites
• Groundwater Remediation and the use of Alternative Endpoints at Highly Complex Sites
• Remediation Management of Complex Sites

Introduction

Figure 1. TI Zone and other Remedy Components at the Koppers Oroville Wood Treatment Facility

Alternative endpoints and other approaches were first described in an ESTCP report titled “Assessing alternative endpoints for groundwater remediation at contaminated sites” and subsequently reiterated elsewhere. Several types of alternative endpoints include the following: TI waivers, other Applicable Relevant and Appropriate Requirements (ARAR) waivers, ACLs, state designations for technical impracticability, groundwater management/containment zones, and groundwater classification exception areas. Other organizations have since recognized the topic and discussed aspects of alternative endpoints in technical and regulatory guidance documents (e.g., ITRC in press). The following sections examine several examples of alternative endpoints and other approaches, as well as references for more information.

Technical Impracticability (TI) Waivers

Remediation goals in the Comprehensive Environmental Response Compensation and Liability Act (CERCLA) program, also known as the Superfund program, are based on ARARs. An ARAR may be waived due to “technical impracticability” if technical/engineering challenges preclude the complete restoration of contaminated groundwater within a reasonable time frame (CERCLA Section 121(d)(4)). For example, a drinking water Maximum Contaminant Level (MCL) may be waived for a particular groundwater contaminant due to the technical inability to reach the MCL within a reasonable timeframe at a given area of the site. The Record of Decision (ROD) or other final remedy decision document would cite the applicability of a TI waiver based on a detailed site-specific TI evaluation report and would specify the area of the aquifer within which the TI waiver applies (“TI zone”) as well as the lithologic unit or depth interval where the TI waiver applied. The ROD would also specify the remedial approach to meet ARARs outside of the TI zone and would describe how the TI zone would be protected (e.g., deed restrictions, groundwater use restrictions, slurry wall). As of 2012, TI waivers had been used at 85 CERCLA sites

A TI waiver may be considered during any stage of the remedial process. TI decisions have been made prior to or after full-scale remediation systems were implemented. In the former case, the decisions were supported by detailed site characterization data and analysis, and Feasibility study (FS) evaluations of potential remedial technologies and their inability to overcome critical limitations to groundwater restoration. In the latter case, data from the remediation system performance were used to evaluate technical impracticability along with information gained through remedy optimization and the evaluation of other potential remediation technologies. The primary guidance document on TI waivers was issued by the USEPA in 1993; Table 1 summarizes the key USEPA publications related to TI waivers.

Greater Risk and Other Applicable or Relevant and Appropriate Requirements (ARAR) Waivers

As stated in CERCLA Section 121(d)(4), a greater risk ARAR waiver is appropriate if compliance with the requirement would result in greater risk to human health and environment compared with non-compliance. Several ARARs have been waived because meeting them would entail the use of remedial actions that pose a greater risk to human health and the environment. Examples of scenarios that could constitute greater risk include the following:

• Mobilization of contaminants during remedial activity, causing greater risk to deeper or nearby drinking water aquifers
• Dewatering or land subsidence due to pump-and-treat
• Disturbance of wetlands or other sensitive ecosystem areas due to remedial activity
• Contaminant re-suspension and mobilization that would be caused by dredging, adversely affecting sediment and surface water quality
• Explosive hazards or other health and safety hazards associated with the implementation of specific remedial technologies (e.g., chemical oxidation remedies, excavation of pyrophoric wastes)
• Reduced natural flushing due to liner/cap installation, extending the timeframe for natural attenuation of underlying groundwater contaminants.

Table 1. Summary of Key USEPA Documents Pertaining to TI Waivers

DATE	USEPA DOCUMENT	DESCRIPTION
1993	Guidance for Evaluating the Technical Impracticability of Ground Water Restoration. EPA/540/R-93/080, OSWER Directive 9234.2-25	This is the primary USEPA guidance document on TI waivers that is still used today. It includes the definition of TI, summarizes technical challenges faced at remediation sites, describes what is and is not included in a TI waiver, outlines a consistent, site-specific approach for evaluating the TI of groundwater cleanup and establishing a protective alternative remedial strategy if restoration is determined to be technically impracticable within a reasonable timeframe.
1995	Memorandum: Consistent Implementation of the FY 1993 Guidance on Technical Impracticability of Groundwater Restoration at Superfund Sites. OSWER Directive 9200.4-14	This memorandum specified a process for maintaining consistency for TI waiver implementation among different EPA regions. (The number of CERCLA sites conducting TI evaluations was reportedly far less than expected; therefore, the process outlined in this memorandum was not fully implemented).
2007	Recommendations from the EPA Ground Water Task Force. EPA/500/R-07/001	The task force identified and prioritized groundwater issues. They recommended developing supplemental guidance on TI and a fact sheet describing program flexibilities and alternative cleanup goals for DNAPL source zones. The report included an attachment describing cleanup goals that may be appropriate for DNAPL source zones.
2009	Summary of Key Existing EPA CERCLA Policies for Groundwater Restoration. OSWER Directive 9283.1-33	This memorandum compiled key existing USEPA policies to enhance the transparency of USEPA decisions and to assist USEPA regions with making groundwater restoration decisions. The memo addressed expectations for groundwater restoration and TI waiver consideration in the context of principles for remediation. No new guidance or policy was included.
2011	Groundwater Road Map: Recommended Process for Restoring Contaminated Groundwater at Superfund Sites. OSWER Directive 9283.1-34	The Groundwater Road Map compiled relevant highlights of existing USEPA laws, policy and guidance into a roadmap for groundwater restoration. Included is a discussion of TI waivers, institutional controls, wellhead treatment and other topics to the extent that these may be part of a comprehensive groundwater remedy.
2012	Summary of Technical Impracticability Waivers at National Priorities List Sites. Report with General Technical Impracticability Site Information Sheets. OSWER Directive 9230.2-24	The report summarized TI waivers issued by USEPA regions, presented some summary statistics and included an appendix of brief site information sheets for each site where a TI waiver was adopted. A total of 91 waivers at 85 sites were identified.
2016	Clarification of the Consultation Process for Evaluating the Technical Impracticability of Groundwater Restoration at CERCLA Sites. OLEM Directive 9200.3-117	The memo provides clarification of existing relevant Superfund policy and guidance and recommendations for planning and developing TI evaluation packages and describes the recommended process for EPA internal review and approval. The memo transmits five new recommended products, including a consultation process flowchart, TI evaluation flowchart, regional TI evaluation work planning spreadsheet, EPA review routing slip, and a summary checklist for the TI evaluation.

Few CERCLA sites have implemented greater risk ARAR waivers (see examples in Deeb et al., 2011) and there is very little published guidance on how to evaluate the applicability of a greater risk ARAR waiver. Theoretically, any determination of greater risk should consider the magnitude, duration, and reversibility of the adverse impacts. Several CERCLA sites adopted ARAR waivers based on greater risk in the late 1980s and early 1990s. There are no recent examples of the successful adoption and integration of these waivers into a decision document. In addition to technical impracticability and greater risk, there are four other reasons to waive an ARAR at a CERCLA site: 1) Equivalent standard of performance, 2) Inconsistent application of state standards, 3) Fund-balancing and 4) Interim measures. Interim measures are commonly used at complex sites and are not expected to achieve ARARs. However, interim measures must eventually be replaced with a final remedy that does comply with ARARs and is therefore a temporary ARAR waiver. The other three types of ARAR waivers are described in CERCLA policy but do not appear to be used in practice.

Alternate Concentration Limits (ACLs)

The term ACL refers to an alternate concentration limit that site stakeholders agree upon as the cleanup level to replace a chemical-specific ARAR (at CERCLA sites) or risk-based criteria (at sites in the Resource Conservation and Recovery Act [RCRA] program). At CERCLA sites, ACLs can only be considered if site conditions meet the following three criteria (CERCLA Section 121(d)(2)(B)(ii)):

1. Groundwater discharges to surface water (through known or projected points of entry)
2. Groundwater discharge does not lead to a “statistically significant increase” in contaminants in surface water or any “accumulation” of contaminants downstream
3. Institutional controls prevent human exposure to contaminated groundwater between the facility boundary and the discharge points of groundwater into surface water

In addition to meeting these three criteria, a policy memorandum includes a list of other factors that must be considered before establishing an ACL at a CERCLA site. Site regulators must consider whether all groundwater plumes are discharging to surface water and the potential accumulation or effect of degradation byproducts in groundwater or surface water. ACLs were rescinded at one site based on the USEPA memorandum and a TI waiver was issued instead.

At RCRA sites, the term ACLs has a different meaning and is less prescriptive. ACLs can be used at RCRA sites if the alternate concentration does not pose a substantial risk to human health or environment (40 CFR 264.94). A determination is made after considering potential adverse effects on the quality of groundwater and hydraulically-connected surface water. Several factors to consider include the waste characteristics and mobility, hydrogeologic setting, groundwater flow, groundwater and surface water usage (current and future), surface water quality standards, existing groundwater and surface water quality and quantity, rainfall patterns, proximity of source zone to surface waters, potential for human exposure and related health risks, potential for other risks, and the permanence of potential adverse effects (40 CFR 264.94).

Several RCRA sites have used surface water quality criteria in conjunction with dilution calculations, mixing zone modeling, and/or fate and transport modeling to determine the numerical value of the ACL for groundwater. Other groundwater ACLs have been determined based on site-specific risk assessments. 

State Approaches

Adapted from ITRC 2012

State remediation programs have developed a variety of designations that can be used to establish zones where contaminated groundwater can be managed or within which alternative cleanup standards can be adopted. Each designation and its primary purpose varies from state to state; most states have a system for classifying groundwater aquifer use, value and vulnerability. Groundwater re-classification can therefore change remedial goals. Some states permit groundwater classification exceptions or site-specific groundwater classification. Others have designations similar to the CERCLA TI waiver where a TI zone can be established and managed to contain and monitor residual contamination. Finally, some state designations are primarily intended to track institutional controls and monitor/ track areas of groundwater contamination above permissible levels and their related institutional controls. These concepts are also consistent with the ability to designate alternative points of compliance as a way of monitoring protectiveness and managing residual contamination as remediation slowly proceeds. Table 2 lists examples of state-specific designations for groundwater.