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Home | FAQs | SQuiRT cards and Screening |
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| FAQs related to the application of screening benchmarks contained on the Screening Quick Reference Tables |
Screening Quick Reference Tables (SQuiRTs) • top
Here are answers to questions about the information contained in the Screening Quick Reference Tables (SQuiRT) cards.
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Q. Why aren't full references provided?
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| A. Although we would have liked to have provided full references on the SQuiRT cards, space did not allow us to provide full bibliographic citations tied to each and every datum. Because some columns contain data from as many as six different sources, we could not include full references.
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Q. On page 2, what does the "Increasing" predicted toxicity gradient mean?
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| A. Each sediment quality guideline is intended to describe a particular--but unique--point in a spectrum of toxicity. These points range from lower thresholds, below which samples are presumably non-toxic, to upper thresholds of toxicity, above which samples are predicted. The guidelines have been ordered according to the level of toxicity each is intended to describe, from low to high.
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Q. Why don't the individual chemical values always increase across the predicted toxicity gradient?
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| A. The individual measurement endpoint for a UET or AET may be more sensitive than a PEL or ERM value, since PEL and ERM values incorporate several endpoints in their determination. A UET, therefore, may have a lower value than a PEL.
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Q. Why are background levels included?
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| A. Background levels have no development basis in risk characterization or toxicity evaluation. However, for purposes of screening samples which may be indicative of contaminant source areas (the main purpose of the SQuiRT cards is to aid you in doing this screening), background concentrations are useful for distinguishing possible contaminant sources.
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Q. Why does NOAA apply a default dilution factor of only 10x for the discharge of ground water to surface water?
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| A. We prefer to use site-specific information whenever it is available. But because such data have not been derived, we acknowledge that some level of dilution would occur. We chose to use a conservative, order of magnitude dilution factor for screening purposes to ensure a high degree of confidence that any contaminant source eliminated from further consideration is not likely to pose substantial risk. Conversely, this is not meant to imply that contaminant sources that do not pass this screening do pose risk.
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Q. Why isn't the value for total DDTs in the marine TEL/PEL, ERL/ERM, or AET benchmarks simply the sum of the individual three isomers?
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| A. This is a great example of why an understanding of the derivation of these various benchmarks is key to their proper application. The total DDT benchmark is not simply a mathematical summation of the other three benchmarks. It is derived by the same data evaluation process as any other compound. Therefore, it is responsive to the most potent of the isomers that were present in the samples used to generate the benchmark.
The total DDT benchmark should only be used for screening when there is no more specific information about the constituent composition of “total DDT.” Because each isomer has its own potency, individual concentrations of each should be screened whenever possible.
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Q. Will the cards be updated? If so, how often might that happen?
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| A. Yes, we plan to release updates whenever changes or additions are needed. A Nov 2006 update incorporates changes in Ambient Water Quality Criteria for cadmium, copper, and tin (pages 3 and 4), plus makes some minor additions.
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Q. If I am evaluating organic carbon normalized data, shouldn’t I adjust the sediment benchmarks (e.g., TELs, PELs, ERL, ERMs etc.) ?
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| A. Essentially, no. These benchmarks (as noted on the cards) were generally developed on a dry weight basis (there are some exceptions, such as the freshwater UETs). Adjusting the benchmarks to a default or assumed level of TOC would be inappropriate. It would be better to adjust the raw data back to a dry weight basis. This is typically the way a laboratory would have reported the raw data originally anyway.
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SQuiRT Cards Updates • top
Here are answers to questions about changes made to the SQuiRT cards.
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Q. What changes were made to AETs?
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| A. In December 1998 and again in June of 1999, Washington State issued draft, interim revisions to the Sediment Management Standards Rule, which included the addition of a new bioassay endpoint to the suite of confirmatory biological effects tests: a 20-day growth test using the juvenile polychaete Neanthes arenaceodentata. This endpoint lowered the lowest AET, the value reported on the SQuiRTs, for many contaminants.
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Q. Will the final AETs be different?
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| A. Since AET values are essentially determined by a single result (i.e., the highest non-toxic sample) as opposed to the entire distribution of results (e.g., as with a TEL or PEL), the final AET values used by the state may vary substantially depending on the outcome of their analyses.
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Q. What are Water Quality Criteria?
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| A. Section 304(a)(1) of the Clean Water Act requires EPA to develop criteria for water quality that accurately reflect the latest scientific knowledge. These criteria are based solely on data and scientific judgments on pollutant concentrations and environmental or human health effects. Section 304(a) also provides guidance to states and tribes in adopting water quality standards. Criteria are developed for the protection of aquatic life as well as for human health; the SQuiRT cards deal only with the aquatic life values.
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Q. What is the latest compilation?
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| A. From time to time, EPA revises their compilation to keep states and tribes informed about the most current recommended water quality criteria. EPA published the agency's current recommended 304(a) criteria by Federal Register notice, which first appeared on December 7, 1998 (Vol. 63 No. 234). Subsequent re-publications have clarified some textual matters, but the basic numerical criteria remained the same until changes in May 2005.
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Q. What is the status of existing criteria while they are under revision?
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| A. Water Quality Criteria published by EPA remain the agency's recommended criteria until EPA revises or withdraws them. EPA has consistently upheld the use of the current criteria and considers them to be scientifically sound until new, peer-reviewed scientific assessments indicate changes are needed.
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Q. What changes were made in the latest compilation?
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| A. There were many individual updates made in the latest compilation. However, many of the updates result from a few basic changes. These include expansion of available data through initiatives such as the National Toxics Rule, the California Toxics Rule, and Great Lakes Initiative Guidelines; expression of criteria for metals in terms of dissolved metal in the water column; and changes in the form of chemicals or valence state of metals for which criteria are published.
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Q. How do the SQuiRT cards deal with old and new criteria?
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| A. For metals' Ambient Water Quality Criteria (page 3), some changes are noted on the SQuiRTs in notations connected with the values. The SQuiRT cards have just been updated with the most recent values for cadmium, copper, and tin. The SQuiRT for Organics (pages 5-8) lists just the new values and does not attempt to indicate where changes have been made.
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Q. Why are the AET values interim?
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| A. The values reported represent preliminary values pending completion of additional technical work on individual AET values, reliability analyses, and discussions with other involved agencies. Washington State is still resolving some statistical issues of data analysis and classification of bioassay results.
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