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Toxics Cleanup Program |
Policies and Guidance |
List of Policies...
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November 24, 1993
Implementation Memo No. 3
TO: Interested Staff
FROM: Steve Robb
Toxics Cleanup Program
SUBJECT: PQLs as Cleanup Standards
ISSUES
Two issues have been raised with regard to the use of practical quantitation limits (PQLs) in setting cleanup levels:
I. LONG-TERM LIABILITY
The Model Toxics Control Act (MTCA) states, "Where cleanup levels are below the PQL, compliance with cleanup standards will be based upon the PQL" (WAC 173-340-700(6) Measuring compliance). Also stated in the rule, "If those situations arise and the practical quantitation limit is higher than the cleanup level for that substance, the cleanup level shall be considered to have been attained, subject to subsection (4) of this section..." (WAC 173-340-707(2) Analytical considerations). Therefore, the PQL becomes the compliance value, and PLPs who attain the PQL are eligible for a covenant not to sue. WAC 173-340-707(4) places one additional burden, however, and that is a requirement for periodic review of the cleanup action in which the department, in reviewing the cleanup action, shall "...consider the availability of improved analytical techniques." Therefore, any covenant must have a reopener which would allow the department to take action if necessary.
Long-term monitoring is not required as long as the remedy does not specifically involve containment. However, it is possible that the remaining unquantified risk at a site could be sufficient to cause concern. This situation makes it very important for project managers to require PLPs to attempt to quantify those contaminants which have high PQLs. We need to avoid situations in which PLPs may leave unquantified contamination and that upon periodic review new analytical data demonstrates that further action is necessary. The rule supports the use of special analytical methods and/or institutional controls to address this situation.
WAC 173-340-707(3) gives project managers the flexibility to require special sampling and analytical methods. PQLs should not be used to justify unnecessarily high compliance levels. In cases where the risk-based cleanup level is less than the PQL, site managers should calculate, using the appropriate formula, the risk the contaminant would represent if it were present at the PQL concentration. As this risk approaches the 1x10-5 level, serious consideration should be given to use of surrogate measures of the hazardous substance or development of specialized sample collection and/or analysis techniques. If the risk posed by a contaminant concentration at the PQL level exceeds the 1x10-5 level, project managers should consider requiring special analytical methods which can quantify the contaminant concentration at least to the 1x10-5 level.
In support of this approach, the Responsiveness Summary (RS) acknowledges that in meeting its mission to protect human health and the environment, Ecology cannot ignore concentrations below current quantitation limits. In doing so, the RS states, we would be placing "...human health and the environment 'at the mercy of analytic quantitation limits' and would be inconsistent with the statute's overriding objectives" (p. 107).
Finally, WAC 173-340-440(1)(a) requires institutional controls "...when the department determines such controls are required to assure the continued protection of human health and the environment or the integrity of the cleanup action." In situations where the PQL is above cleanup levels (i.e. exceed the 1x10-5 level), project managers should evaluate the need for institutional controls, particularly if special analytical methods are inadequate.
II. RISK SUMMATION CALCULATIONS BASED ON PQLs
MTCA requires the development of cleanup levels that are protective of human health and the environment. For carcinogenic substances, protection is defined as a cumulative site risk that does not exceed 1 in 100,000 (1x10-5). However, our inability to reliably measure some contaminant concentrations at calculated risk-based levels hinders our ability to measure total site risk.
In some situations the risk posed by a single contaminant at the PQL concentration outweighs the risk of all the other contaminants put together. Using such a PQL risk value in the risk summation calculation will negate the usefulness of both the risk summation and the 1x10-5 cumulative site risk requirement. In this situation, to calculate overall site risk, use the risk-based cleanup level rather than the PQL. The other contaminant concentrations can then be adjusted downward, as necessary, so the adjusted total site risk does not exceed 1x10-5. The final list of compliance levels should show the single contaminant at the PQL value and the other contaminants at their adjusted levels.
When adjusting individual cleanup levels to meet the one in a hundred thousand total risk standard at sites with multiple contaminants becomes necessary, do not adjust a contaminant below its PQL. For example, the cleanup level for trichloroethylene (TCE) in groundwater is 3.98 ppb and the PQL is 0.5 ppb. If higher cleanup levels for other compounds required the TCE cleanup level to be adjusted downward, it should not be adjusted below 0.5 ppb.
One final clarification regarding risk summation is warranted. Method B specifically establishes cleanup levels based on a risk of one in a million for individual carcinogenic contaminants. When multiple contaminants and/or multiple pathways of exposure are involved, MTCA allows for a cumulative site risk of no more than one in a hundred thousand (e.g., WAC 173-340-720(5)). The one in a hundred thousand risk level is intended to serve as a cap, or ceiling, on the cumulative site risk at cleanup sites with multiple contaminants and is not a goal.
For example, when the cumulative site risk total is 8x10-5, cleanup levels for individual constituents must be adjusted downward until the cumulative site risk is equal to or less than 1x10-5. Alternately, at sites where the total cumulative site risk is 8x10-6, for example, no downward adjustment is necessary, since the risk does not exceed 1x10-5. However, adjustment upward for individual contaminants is not permitted under MTCA since individual contaminants must still meet the 1x10-6 (or 1x10-5 for Method C) limit.
Risk Communication
How we portray risk to the public is important to the implementation of the rules. When cleanup levels are based on PQL values, Ecology site managers should explain that technical limitations may prohibit us from measuring contaminants at levels that correspond to a risk of 1x10-6. This explanation should be part of the Cleanup Action Plan (CAP) and any public hearings where cleanup levels and risk are discussed. The CAP should include a list of risk-based levels as well as a list of the compliance levels.
Analytical Guidelines
What Are The PQLs?
There is no definitive list of PQLs. However, Ecology has put together tables of PQLs, MDLs (method detection limits), and comparisons to Method B numbers for groundwater, surface water, and soil. These tables are based on surveying published methods and laboratories. There are many factors that can produce a different PQL for one sample as compared to another. However, these tables can be useful guidance. Ecology refers you to the guidance for the use of the tables and also to a discussion on the meaning of PQLs. These are found as three additional parts to this memorandum. The four parts are:
Part I: Implementation Memo No. 3--PQLs as Cleanup Standards (this document)
Part II: Guidance For The Use of Tables
Part III: MDL, PQL, and Comparisons Tables
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Part IV: Appendix--Meaning of Quantitation Limits