Reportable Quantity Adjustment Methodology
Methodology for Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA) hazardous substances
The Agency evaluates the properties of hazardous substances (other than radionuclides) in a two-step process:
Step 1: Primary Criteria
Reportable Quantity (RQ) adjustment begins with an evaluation of the intrinsic physical, chemical, and toxicological properties of each substance. These intrinsic properties - called "primary criteria" - are aquatic toxicity, acute mammalian toxicity (oral, dermal, and inhalation), ignitability, reactivity, chronic toxicity, and potential carcinogenicity. EPA ranks hazardous substances for each intrinsic property (except potential carcinogenicity) on a five-tier scale, associating a specific range of values on each scale with a particular RQ value, from one to 5,000 pounds. For hazardous substances evaluated for potential carcinogenicity, each substance is assigned a hazard ranking of "high," "medium," or "low," corresponding to RQ levels of 1, 10, and 100 pounds, respectively. Each substance receives several tentative RQ values based on its particular intrinsic properties - the lowest of all the tentative RQs becomes the "primary criteria RQ" for that substance.
Step 2: Secondary Criteria
After the primary criteria RQs are assigned, substances are further evaluated for their susceptibility to certain degradative processes, which are used as secondary adjustment criteria. These natural degradative processes are biodegradation, hydrolysis, and photolysis (BHP). In general, if a hazardous substance degrades relatively rapidly in the environment to a less hazardous form by one or more of the BHP processes, its primary criteria RQ is raised one level. Conversely, if a hazardous substance degrades to a more hazardous product after its release, the original substance is assigned an RQ equal to the RQ for the more hazardous substance.
EPA has proposed (54 FR 35988, August 30, 1989) that substances be further evaluated after hazardous substances are evaluated for the primary and secondary criteria by applying the Emergency Planning and Community Right-to-Know Act (EPCRA) section 302 methodology for developing threshold planning quantities (TPQs). First, the screening criteria used to identify Extremely Hazardous Substances (EHSs) (51 FR 41570, November 17, 1986) would be applied to the hazardous substances being evaluated. Second, a level of concern would be established for each hazardous substance that meets the screening criteria. Third, the dispersion potential of each of these hazardous substances would be assessed by considering its physical state and volatility. The level of concern and dispersion potential would be combined to produce an index value, and the screened substances would be ranked according to this index value. Tentative RQs would be assigned to substances using a table of index value ranges. If the tentative RQ assigned in this way is lower than the primary and (if applicable) secondary criteria RQ, this tentative RQ resulting from application of the TPQ criteria would become the adjusted RQ. Until the addition of the TPQ methodology to the existing RQ methodology is finalized, however, RQs will continue to be adjusted according to the original RQ adjustment methodology.
Methodology for radionuclides
RQs for radionuclides were determined by estimating the quantity of a radionuclide that, if released into the environment under an assumed set of conditions, could result in an individual receiving a specified dose of radioactivity. To estimate this quantity for each radionuclide, a series of hypothetical (but conservative) exposure scenarios were analyzed to link a quantity released with an accepted dose level.
Specifically, hypothetical releases and exposures were analyzed for four different routes of exposure: inhalation, ingestion of water, ingestion of food, and direct exposure. For each exposure pathway, a "release value" was calculated for 757 radionuclides for which human health data and intake limits have been published. The Agency selected the lowest of the four values for each specific radionuclide. This lowest release value was then rounded down to the nearest decade to determine the RQ for that radionuclide. All radionuclides that do not have published intake limits have been assigned an RQ of 1 Ci. Available information on these radionuclides is insufficient to develop a specific RQ for individual radionuclides in this group. An RQ of 1 Ci was selected because it is the middle RQ category for radionuclides, and the majority of radionuclides (91 percent) examined individually have RQs at least at this level.