INSTITUTIONAL CONTROL - IMPACTS ON HUMAN HEALTH
RISK ASSESSMENT EXPOSURE SCENARIO DEVELOPMENT
David L. Hippensteel, PG, REP
DOE/NV-ETD
North Las Vegas, NV.
ABSTRACT
The concept of institutional control has been present in the environmental industry since the advent of the Comprehensive Environmental Recovery, Compensation and Liability Act of 1976. Many federal facilities undergoing environmental remediation under this Act have made valuable use of institutional control as an interim remedial action and as an important portion of final remedial alternatives. The core concept of institutional control has been to put in place administrative policies or physical barriers between potentially exposed populations and a contaminant source to avoid unwanted exposures to those very receptor populations.
The concept of estimating the risk to humans from exposure to contamination and its use as a defining criteria as to whether a site must undergo active remediation have been around just as long. Institutional control and human health risk assessment are intimately linked as crucial parts of the greater remedial alternative analysis topic - human health risk assessment being a determining criteria for proceeding with active remediation and institutional control being one of those remedial alternatives.
Institutional control’s core concept has very dramatic influences on the science and practice of human health risk assessment. A vital portion of human health risk assessment involves defining probable human receptor populations using a set of criteria of which land use scenarios are a key part. A foundational goal of human health risk assessment has been to define realistic land use scenarios which can limit the number and types of potential exposed populations for which risk estimates must be calculated.
Institutional control by its regulatory definition limits potential land use on a given contamination site; therefore limiting the realm of potential (realistic) exposed populations that should be considered in a human health risk assessment. This relationship makes the early identification of institutional control as part of an overall final remedy paramount to conducting efficient realistic human health risk assessment. In successfully doing so, remedial action managers and risk assessors must closely confide in each other to determine the probability of institutional control as a viable remedial action. Such cooperative strategy saves resources for both the remedial action manager and the risk assessor by avoiding unnecessary work to account for improbable exposure scenarios which can drive unnecessary remediation.
A SUMMARY OF THE INTENT OF INSTITUTIONAL CONTROLS
Paraphrasing the Comprehensive Environmental Response, Compensation and Liability Act (CERCLA) from 40 Code of Federal Regulations (CFR) 300.430(a)(1)(iii)(D), institutional controls are "actions" which seek to restrict or limit human activities at or near hazardous substance sites or facilities. The intent of the restriction or limitation is to greatly reduce or temporarily eliminate exposure to those hazardous substances which might result in unacceptable risk to human health. Institutional controls can consist of (1) physical barriers, (2) land use restrictions, (3) well drilling prohibitions, (4) drinking water advisories and (5) restrictions on the use of other natural resources (Bakr et al., 1991). Traditionally, institutional controls do not involve active remediation of any hazardous substances to reduce the toxicity, volume or mobility of those materials. In reality, institutional controls are invoked when normal active remediation can not solve the problem or will not solve the problem quickly enough to avoid unacceptable exposure to receptors. EPA expects institutional controls to be protective of human health and the environment just like active remedies. EPA, also, expects institutional controls to not replace active remediation unless no other option exists. Normally, institutional controls are approved as interim remedial actions in lieu of future active remediation or as a part of final remedies which include some type of active remediation.
The concept of institutional controls as viable remedial options has been discussed in the context of federal and state regulations, but has only been defined in the National Oil and Hazardous Substances Pollution Contingency Plan (NCP) of CERCLA. EPA made very specific statements concerning its expectations for institutional controls in 40 CFR 300.430(a)(iii)(D):
"EPA expects to use institutional controls such as water use and deed restrictions to supplement engineering controls as appropriate for short- and long-term management to prevent or limit exposure to hazardous substances, pollutants, or contaminants. Institutional controls may be used during the conduct of the remedial investigation/feasibility study (RI/FS) and implementation of the remedial action and, where necessary, as a component of the completed remedy. The use of institutional controls shall not substitute for active response measures (e.g., treatment and/or containment of source material, restoration of ground waters to their beneficial use) as the sole remedy unless such active measures are determined not to be practicable, based on the balancing of trade-offs among alternatives that is conducted during the selection of remedy."
In addition to these explanatory statements regarding the intent of institutional controls, the NCP preamble mentions that institutional controls are intended for facilities at which the released hazardous substances are fully expected to not migrate outside of the facilities physical boundaries. In cases where institutional controls are the proposed sole method of "remediation" the regulatory authority overseeing the remediation must ensure that all adequate precautions are in place to guarantee the reliability of those institutional controls.
With the application of institutional controls as part of or the entire remedy, EPA expected that the institutional controls would remain effective throughout any site operational and maintenance period during and following any active remediation.
Realizing the utility of institutional controls as "when all else fails" remedial options, EPA included the institutional controls concept in the proposed Subpart S (Corrective Action) Part 264 to the Resource Conservation and Recovery Act (RCRA). Within the preamble to this proposed rule, EPA indicated that (as with CERCLA sites) there could well be hazardous waste sites for which no active remedial options exist if the future land use is intended to be unrestricted. In such cases the only viable method to reduce the exposure risk to humans or the environment is to "control access" to the site and contamination; therefore greatly reducing the possibility of unacceptable risk. In particular, under RCRA proposed Subpart S, EPA noted that institutional controls may be a common occurrence at federal facilities due, primarily, to the large (areal) size of contamination problems and the technical complexity involved in remediation (not to mention the financial constraints created by the federal budget process)(White et al., 1992). Institutional controls are often proposed when contamination is so areally extensive, physically or chemically complex, or costly to remediate; being the only solution to protect human health and the environment. Unfortunately, proposed RCRA Subpart S does not specifically define what institutional controls are and the purpose as a sole remedy should be as was done in the NCP under CERCLA.
Getting back to CERCLA, EPA believed that institutional controls would be applied as secondary protective measures during the baseline risk assessment. Under CERCLA, the results of the baseline risk assessment serve as the basis for making remedial action decisions and justifying final remedial options based on the remaining risks following completion of the final remedy for each applicable future land use scenario.
EPA’s mandate in the final NCP was to ensure remedial actions were protective of human health and the environment. This could be attained by one of two means: (1) performing remediation which decreased or eliminated the toxicity, volume or mobility of the contaminants or (2) implementing actions that would control receptors opportunities for exposure to the contaminants. It is this second option that points to the relevance of institutional controls and clearly indicates the link between institutional controls and risk assessment exposure scenarios.
However, the EPA’s policy on land use and CERCLA remediation has changed. In 1996, EPA’s Office of Solid Waste and Emergency Response issued Directive #9355.7-04, "Land Use in the CERCLA Remedy Selection Process." This reference represents a drastic change in policy for the U.S. EPA in its direction for land use consideration for CERCLA remedy selection. The past incorrect broad application of "residential" land use scenarios to hazardous waste sites has resulted in far too costly remediation driven primarily by unrealistic future land use scenarios.
This EPA guidance directs remedial project managers to begin early talks and investigations into future land use of a site prior to deciding on potential remedial actions. Consultation with local land use coordinators should be a first step to establishing the public’s expectations for future land use of a given waste site. Additionally, the past and current land use history of the site in question must be a prime criteria for determining which future land use scenarios guide remediation.
A list of land use characteristics, including existing infrastructure, is provided to assist remedial project managers in identifying the most likely future land use scenarios based on existing characteristics and eliminate unreasonable future land use scenarios based on lack of necessary support elements.
This single piece of guidance creates a direct conflict with what appears in the NCP; however, the conflict is for the good of all involved in environmental remediation. The recommendation that remedial managers begin to investigate the reality of future land uses for a waste site long before actual remediation begins sets the stage for reducing the wholesale application of residential land use scenarios and enabling institutional controls to be proposed only when they are absolutely necessary because of true risks or technologically impossible remediation.
REALIZING RISK - BASIC NECESSITIES
The goal of risk assessment is to calculate (as close to reality as possible) the potential for harm (be it lethal or nonlethal) to a given receptor (human, other fauna or flora) from exposure to chemicals deemed hazardous and/or toxic to those receptors. The results of risk assessment are more often than not accompanied by a fair portion of uncertainty in almost every parameter used in the myriad of mathematical equations needed to produce a risk estimate from a contaminant’s concentration in any given environmental media. This uncertainty varies with the types of exposure scenarios risk assessor must consider during their work. However, one thing that is certain and every competent risk assessor agrees on is what is necessary to even "have" the potential for a risk.
In order for a risk to be present, a series of events must occur and this series of events must be "present" simultaneously of each other. Fire has its "triangle" of necessities and risk assessment has its "square." The following four necessities must be present simultaneously for a potential receptor to even have a chance at being "at risk:"
If one of these events does not occur, then a risk of exposure to a contaminant can not be realized. All the research into toxicity, dose-response, demographics, exposure scenario probability and contaminant fate and transport is for naught, if the situation does not satisfy the four risk assessment necessities listed above.
Each of these 4 necessities carries equal weight during the course of realizing a risk from contaminant exposure. Yet in the face of this clear fact, risk assessors are only asked to prove the existence of the first 3. The last crucial piece of the risk square, the presence of an actual receptor has always been forced upon the risk assessor by regulatory requirements or policy. Until very recently, around 1995, baseline risk assessments, whether they were being done under the authority of CERCLA or many other environmental regulations, were required to estimate risks for extremely conservative exposure scenarios for highly unlikely receptors - namely the "future residential land use scenario" which placed human receptors directly on top of a remediated waste site actively being exposed via every imaginable exposure route. In other words, the worst case scenario.
Institutional controls are used as remedial options at difficult-to-remediate waste sites because they eliminate the fourth piece of the risk square, available receptors. However, because institutional controls do not reduce the toxicity, volume or mobility of contamination, the NCP required and still requires baseline risk assessments to assess risks in the absence of institutional controls (White et. al., 1992). White et. al,. state that the exercise of doing risk estimations for the residential scenario on a waste site " ... is not a futile one." Under the NCP, baseline risk assessments must consider risk associated with future land uses which is often construed to include the residential scenario on top of the waste site. However, the NCP states that one should not assume future residential land use for a given waste site if it is not justifiable or if the probability is small due to the site’s characteristics (White et al., 1992). In cases where future land use is unclear, the NCP states that residential land use risk should be estimated and compared with risks associated with other land uses. It appears that while the NCP suggests relief from the "mandatory" residential land use scenario risk assessment, it only applies in cases where the future land use of a waste site is clearly limited to land uses exclusive of residential. Unfortunately, the NCP does not provide criteria for excluding residential land use from the arena of future land uses.
WHEN INSTITUTIONAL CONTROLS MEET RISK ASSESSMENT
The instance in which the use of institutional controls directly influence risk assessment involves the use of institutional controls as partial remedial options coupled with other active remediation techniques. To completely understand a common mistake in risk assessment exposure scenario development, a brief review of the relationship between institutional control as a remedial option and the necessary events to realize a risk is in order.
Institutional controls are designed to "control access" to hazardous and toxic substances which can not be immediately remediated or not remediated with current technology. In controlling access, institutional controls do not discriminate against contaminants. In other words, access is not intended to be restricted on a contaminant-by-contaminant basis. In fact, often it is one single contaminant (such as tritium) that makes the case of implementing one or more individual institutional controls.
Risk is realized only when 4 events occur and are present at the same time. If any of the 4 events are not present, a risk of exposure to a contaminant (and the subsequent toxic effects attributable to that exposure).
With these facts in mind, institutional controls, by restricting access to contaminants, actively eliminate the 4th requirement for realizing risk - viable receptors to be exposed. In cases of very complex contamination issues when institutional controls are the only viable option, the early proposal of such actions must be coordinated with risk assessors who may be expected to complete later risk assessments to justify final remedial technologies or support the use of risk-based cleanup levels. With an institutional control that actively restricts receptor access to the contamination, risk assessments should not include any exposure scenario that puts a potential receptor directly on the waste site. Such a scenario has a probability of zero given the implementation of institutional control.
Coordination between those who propose remedial actions and risk assessors who produce data to evaluate them is vital prior to completion of the risk assessment. Far too often the general public views the results of risk assessment as certain hazards applicable to entire receptor populations. The vast majority of the general public does not understand the intent of institutional controls and, therefore, can not realize that risks calculated for future residential land use are meaningless in the presence of long-term institutional control.
In cases in which an institutional control mechanism is only part of a remedial option, risk assessors must be made absolutely clear as to what environmental media the institutional control applies to. An illustrative example is in order.
A waste site has contamination in groundwater and surface soils. The groundwater is contaminated with lead, vinyl chloride, phthalates and tritium. The surface soils are contaminated with lead, vinyl chloride and phthalates. The entire site is about 400 acres in total area. Both the groundwater and surface soil contamination is contained within the 400 acres - no "offsite" migration has occurred. Compared to the nonradionuclides, tritium in the groundwater accounts for the majority of exposure risk attributable to the groundwater exposure pathway. The presence of high levels of tritium in the groundwater (50,000 picoCuries/liter) drives a request from the party responsible for site remediation to implement the institutional control of prohibiting any use of the site’s groundwater (including drilling wells through the plume). While agreeing to the proposed institutional control for the groundwater operable unit, the regulatory authorities require remediation of the surface soil contamination to risk-based levels of 10E-6 for carcinogens and a hazard index of 1 for noncarcinogens. The risk assessment should only account for exposure pathways involving the surface soils even though the same contaminants are in the groundwater and many highly effective active remediation techniques exist for all of the groundwater contaminants except for tritium. The rationale for leaving the groundwater unremediated is the proposed institutional control which removes the potential receptors from the risk picture. This rationale remains valid for as long as the groundwater contamination remains within the physical boundaries of the waste site. Remediating the groundwater for the nonradionuclides would not solve the problem since tritium drives the risk in the groundwater.
The point of this ideal example is that proposing institutional controls automatically influences what risk assessors will do during any risk assessment at the respective waste site. This is particularly true for combinations of institutional controls and active remedial technologies. Any risk-based cleanup levels must account for the exposure pathways which institutional controls limit or eliminate depending on the extent of the proposed institutional control action.
Funding for environmental remediation is no longer the "blank check" it used to be. Risk-based remediation was born out of the need to ensure that limited finances were spent on environmental contamination that posed real risks. To identify real risks (or as close to reality as possible), risk assessors must be aware of anything that would influence any of the 4 risk realization necessities. Institutional control, by its very nature, brings reality to the development of exposure scenarios by influencing who and what is identified as a potential receptor and limiting future land use scenarios.
CONCLUSIONS
Institutional controls remain viable remedial alternatives for many environmental contamination problems. There still exists numerous highly toxic contaminants that have no viable cost-effective remediation technology. Until state-of-the-art technology catches up to these problem contaminants, institutional controls are the only solution to prevent unacceptable and unwanted exposure risks to receptors. The rationale being that if one can not clean up contamination with existing technology, one can prevent exposure by restricting access to the contamination for potential receptors.
When implementing institutional controls in combination with active remediation techniques, the derivation of risk-based clean-up levels must take into account which exposure scenarios are impacted by the institutional controls. Risk assessments completed to formulate risk-based levels should not calculate risks for exposure scenarios which are limited or prohibited by institutional controls. Institutional controls do not discriminate against contaminants. They are intended to restrict access to potential exposure and in doing so eliminate the opportunity for receptors to access the contamination, therefore, eliminating exposure scenarios.
Recent changes in EPA’s policy on considering future land use and its effects on CERCLA remedial actions brings the interrelationship between implementing institutional controls and performing risk assessments closer. EPA’s new policy of giving early consideration to realistic land use as a preliminary criteria for future remediation is a vivid example of recent change. Any remedial manager that proposes implementing any institutional control must coordinate the impacts with risk assessors who may be responsible for calculating risk-based remediation levels that are intended to be as close to reality as possible.
Proposing institutional controls as either an interim remedial action or part of a final remedial action directly influences the efficient and realistic completion of human health and ecological risk assessments relevant to waste sites and their respective contaminant releases. Any use of the results of such risk assessments for creating risk-based clean-up standards creates a direct link between the institutional controls and the materialistic and financial resources which must be expended to successfully complete the final remedial action. By not fully realizing the impacts of institutional controls on environmental risk assessment and planning accordingly during the; (1) risk assessment completion, (2) evaluation of the resulting risk estimates and (3) appropriation of resources to ensure remedial action implementation, time, money and materials are wasted and all parties involved in the remediation are deceived as to what the actual risks associated with the chosen remedial action can be.
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