1996 Development of Connecticut's Risk-Based Remediation Standards (RSRs)

On January 30, 1996, the Connecticut Department of Environmental Protection promulgated the Remediation Standard Regulations (RSRs) that established the requirements for the remediation of contamination within Connecticut.  The regulations were organized by environmental media and relied, in part, on risk-based criteria that established remediation goals for various contaminants typically found at remediation sites. Numerical criteria for 88 compounds were established for soil, groundwater, and soil vapor. 
pie chart depicting 1996 criteria

Calculating Risk-Based Remediation Criteria

The RSRs were developed using a robust public process which included technical workgroups to support key areas of program development including the development of risk-based numeric criteria.  In addition to agency staff, these workgroups included scientists and technical staff from the regulated community who had experience and training with each workgroup topic.  The criteria workgroup fully vetted the equations, inputs and assumptions which went into the development of the final criteria for the RSRs.  Standard risk assessment practices were used to calculate concentrations of common pollutants in soil, groundwater and soil vapor which were protective of human health and the environment. These calculations took into account who could be exposed to the contamination, the degree of exposure, and the toxicity of each substance.
Prior to the development of the current RSR criteria, EPA published a collection of documents called the Risk Assessment Guidance for Superfund (RAGS). These documents were an important source of guidance for developing Connecticut’s risk-based remediation criteria.  A current version of RAGS is available at: http://www2.epa.gov/risk/risk-assessment-guidance-superfund-rags-part.  In addition to consulting federal sources, Connecticut also considered the Massachusetts Site Cleanup Regulations, which were adopted while Connecticut was developing the RSRs.  Current versions of the Massachusetts’s cleanup program documents are available at: 

Sources of Toxicity Information:
The primary source of toxicity information used to derive the criteria contained in the RSRs was the EPA Integrated Risk and Information System (IRIS) database of cancer potency values and reference values for non-cancer endpoints that were available at that time. The current IRIS database is available at: www.epa.gov/iris/
Exposed Populations:
Remediation criteria were established for two typical exposure groups: people within residential settings and workers in an industrial/commercial setting.  Within a residential setting, it was assumed that both adults and children would be present, and both were, therefore, included in the criteria calculations.  It was assumed that within an industrial/commercial setting only working adults would be exposed to site contamination. Exposure calculations for these receptors used upper bound but realistic estimates of contact rates with affected media, following the RAGS guidance from USEPA. 

Types of Risk-Based Remediation Criteria
Direct Exposure Criteria (DEC):
Direct Exposure Criteria were designed to establish health-protective concentrations of constituents in soil assuming that people may be exposed to such chemicals through incidental ingestion of soil.  For simplicity, other pathways such as absorption across the skin from dermal contact, inhalation of soil particulates, and ingestion of produce grown on affected soil were not included in the exposure estimates.
Pollutant Mobility Criteria (PMC):
Contaminants in soil can be transferred to and impact groundwater resources. Pollutant mobility criteria were developed to identify contaminant concentrations in soil which would not be expected to unacceptably impact groundwater. This was evaluated by considering the potential uses for groundwater as identified in the Connecticut Groundwater Water Quality Standards which were in development concurrent with the RSRs and were subsequently adopted.  The Connecticut Water Quality Standards establish designated uses for Connecticut’s groundwater resources.  For GA groundwaters, designated uses include, but are not limited to, drinking water resources and baseflow for hydraulically-connected surface water bodies.  For GB groundwaters, provision of drinking water is not a designated use but baseflow for hydraulically-connected surface water bodies remains a concern.  For both groundwater classifications, the groundwater must support other existing uses and must not pose a threat to public safety or public health.   It is assumed that substances in soil may leach from the soil and enter groundwater.  The pollutant mobility criteria were designed to establish environmentally protective concentrations of substances in soil that would support the attainment and maintenance of these designated uses for groundwater at remediation sites. 
The soil PMC was based upon the groundwater protection criteria (GWPC). PMC were calculated by multiplying the GWPC by a factor of 20. The factor of 20 was based on the dilution applied in the leaching-based analytical methods (SPLP or TCLP), and a unit conversion factor to adjust from micrograms (units from the GWPC) to milligrams (units from the PMC).  For GB PMC, an additional dilution factor of 10 is included in criteria derivation.

For inorganic chemicals, compliance with the PMC were based directly on the analytical results from leaching-based analytical methods (SPLP or TCLP).  PMC for inorganic chemicals were based on multiplying the GWPC by a unit conversion factor to adjust from micrograms (units from the GWPC) to milligrams (units from the PMC). For GB PMC, an additional dilution factor of 10 is included in criteria derivation.
Groundwater Protection Criteria (GWPC):
Groundwater Protection Criteria were designed to establish health-protective concentrations for constituents in groundwater assuming that people use the groundwater as a drinking water resource.  The 1996 criteria were modeled upon the risk-based assumptions used to derive federal drinking water standards.  These standards focus on the exposure of adults exposed for a 70 year lifespan to potential constituents in drinking water.

Surface Water Protection Criteria (SWPC):
Surface Water Protection Criteria were developed to address the assumption that contaminated groundwater could potentially discharge to a surface water body.  The criteria are applicable to groundwater and are designed to prevent unacceptable impacts to surface waters and the people and aquatic communities that use this resource.  SWPC were established using water quality criteria for surface water bodies, including Ambient Water Quality Criteria for the Protection of Human Health, which assume that fish may be caught and consumed from the surface water body, and also Ambient Water Quality Criteria for the Protection of Aquatic Life from chronic toxic impacts.  These values were established in accordance with EPA procedures and adopted into the Connecticut Water Quality Standards.  The 1992 Connecticut Water Quality Standards* were used to develop the SWPC in the 1996 RSRs.

Surface Water Protection Criteria were designed to be applied under low flow conditions, consistent with the requirements for ambient water quality criteria. The Water Quality Standards specify that Water Quality Criteria were to be applied under 7Q10 flow conditions, which represents a low flow which occurs approximately 1% of the time.  This flow was selected by EPA, as it is consistent with the short-term exposure assumptions on which the aquatic life criteria are based.  Human health based Water Quality Criteria have different exposure periods related to the mode of action of the chemical, either noncancer or cancer based endpoints.  This would translate to application under differing flows within the surface water, flows which were greater than the 7Q10 flow.  For noncarcinogens, EPA recommended applying the criteria under 30Q2 flows, which Connecticut determined to be approximately 2x the 7Q10 flow.  For carcinogens, EPA recommended applying the criteria under Mean Harmonic Flows, which Connecticut determined to be approximately 3x the 7Q10 flows.  CT DEP used these “flow factors” to address this issue.  The human health based Water Quality Criteria for noncarcinogens were multiplied by 2 and Water Quality Criteria for carcinogens were multiplied by 3 to allow for application under 7Q10 flows.   Exceptions to this were made for chemicals which were designated by EPA as known human carcinogens or for chemicals with a higher potential to bioaccumulate.  For these chemicals, a flow factor of 1 was used.  Appendix D of the 1992 Water Quality Standards provide this additional information for each chemical and designate noncarcinogens (Threshold toxicants, TT), carcinogens (C), known human carcinogens (A), or have a high potential to bioaccumulate (HB).
In addition to considering the river flows under which SWPC were to be applied, the default SWPC are based on an assumption of 10:1 dilution being available within the surface water body.
Volatilization Criteria (VC):
Substances from releases may be located under structures.  For volatile compounds, these substances may migrate from groundwater or soil vapor beneath a building into that structure.  The 1996 volatilization criteria were developed as health-protective concentrations for volatile substances in these media designed to insure that any volatilization of substances into overlying structures is protective of potential exposures to building occupants.  The criteria were derived using risk-based estimates of health-protective concentrations of substances in indoor air.  These values were then applied to a fate and transport model to derive associated environmental concentrations in groundwater and soil vapor that were unlikely to cause an exceedance of the Target Indoor Air concentrations. 

In 2003, CT DEP proposed an update to the derivation of Volatilization Criteria based on updated toxicity and exposure information, as well as an updated fate and transport model. 

Deriving Final Remediation Criteria

Final remediation criteria were established in 1996 using a process that considered risks to exposed populations, achievable analytical levels, and policy concerns such as general background concentrations for certain common substances and ceiling concentrations to prevent excessive contamination from being left in place.  Provisions were also included to allow for site-specific modifications to existing criteria or the development of remediation criteria for substances not included in the 1996 regulations.
Flow chart depicting criteria process
Ceiling Value:
Ceiling values were used as an upper bound value to prevent gross contamination from being overlooked or left in place.  The use of these values provided protection of the chemical, physical and biological integrity of the State’s environmental resources and recognized that risk-based evaluations represent the information available at the time the criteria were derived.  Should additional new toxicity information become available in the future which indicated that a substance was more toxic than originally thought, the ceiling value provided some measure of protection.  Additionally, ceiling values were useful to address other exposure conditions not explicitly included in criteria calculation such as odor thresholds, consideration of multiple pathways of exposure to the same, or similar compounds or to complex mixtures. 
Analytical Achievability:
Adjustments to risk-based values were made if it was not possible to reliably quantify the amounts of chemicals present using sensitive laboratory methods.  In these cases, the criteria value was adjusted upwards to the analytical reporting associated with sensitive methods that were routinely used at remediation sites.
Other Considerations:
While the goal of the RSRs was to develop health-protective, risk-based criteria, it  was recognized that there are cases in which other factors other than risk calculations may govern the establishment of a particular criterion.
General Ambient Concentrations - For risk-based values that are below general background environmental concentrations in Connecticut, the criteria were adjusted up from the risk-based value to one consistent with estimated Connecticut-based conditions.  Examples include soil criteria for arsenic.
Consistency with Federal Regulatory Programs - Criteria for Polychlorinated Biphenyls were established consistent with federal regulatory requirements. 

 - The calculated criteria values were rounded to provide a simpler presentation of the criteria, taking into account significant digits while not appreciably altering the level of environmental protection.
Content last updated August 29, 2017