Toxics Cleanup Program |
Policies and Guidance |
List of Policies...
Toxics Cleanup Program |
Policies and Guidance |
List of Policies...
GUIDANCE FOR THE USE OF TABLES:
PRACTICAL QUANTITATION LIMITS (PQLS),
METHOD DETECTION LIMIT (MDLS), AND
PQL COMPARISONS TO METHOD B CLEANUP LEVELS
This guidance is Part II of four parts. They are:
Part I: Implementation Memo No. 3--PQLs as Cleanup Standards
Part II: Guidance For The Use of Tables (this document)
Part III: MDL, PQL, and Comparisons Tables
Part IV: Appendix--Meaning of Quantitation Limits
The Model Toxics Control Act (MTCA) provides human health risk-based cleanup levels for contaminants at cleanup sites. For certain compounds the risk-based values (Method B values) are less than the lowest levels which can be routinely quantified and reported by a laboratory. These lowest levels are known as the "practical quantitation limits" (PQLs). The "method detection limit" (MDL) is used mostly by the laboratory analyst and not usually reported, but can provide useful information to the site manager.
To provide a cleanup site manager with information on PQLs and the MDLs, we prepared tables of these values including a comparison to the MTCA Method B levels.
The MDL and/or PQL for a substance can be useful when requesting analytical work to verify it is possible to achieve the desired analytical limit. With information in these tables about the MDLs and PQLs for different analytical methods the site manager can choose the appropriate method and avoid wasteful analytical work that does not provide the desired limit. The site manager can also use these tables to check data to verify that the reported analytical limit is indeed reasonable.
What if the PQL exceeds the MTCA cleanup level? Ecology may require the use of surrogate measures of contamination; the use or development of specialized sample collection or analysis techniques to improve the method detection limit or practical quantitation limits for the hazardous substances at the site; monitoring to assure the concentration of a hazardous substance does not exceed detectable levels; or institutional controls in the event that the uncertainty posed by the limits of technology is unacceptable. Ecology also shall consider the availability of improved analytical techniques when performing periodic reviews. Subsequent to those reviews, the department may require the use of improved analytical techniques with lower practical quantitation limits and other appropriate actions (see WAC 173-340-707 Analytical considerations).
The PQLs listed in the tables are from published methods and confirmed by a number of laboratories. However, the PQLs for a given set of samples may vary for numerous reasons (see a discussion on PQLs in Part IV, Appendix).
The attached PQL/MDL tables are not intended to replace Method B values or be used as "default cleanup values." They should be used for the purposes described above.
It is suggested at the time of sample submittal that the site manager discuss with the laboratory the available analytical methods. A particular method should be chosen to provide the required degree of protection as well as to keep analytical costs as low as possible. This is especially important when there are multiple contaminants but one contaminant "drives" the cleanup level. Choosing a method with a PQL lower than the cleanup level, if possible, will be very important.
The tables are for water (ground- and surface water) and soil. The following is a description of the columns found on the tables:
CAS: Chemical Abstract Service registry number; a unique number assigned to a specific chemical.
Chemical The chemicals listed in the PQL tables were derived from the
Name: "Washington Ranking Method for Site Hazard Assessment." Not all chemicals from the "Cleanup Levels and Risk Calculation" (CLARC II) database are contained within the PQL tables. Names of organic chemicals frequently are preceded by numbers or certain letters used to describe the structure of the chemical. For purposes of indexing chemical names, this structural information is placed at the end of the chemical name.
Method: Some of the method numbers listed in this column refer to analytical methods listed in "Test Methods for Evaluating Solid Waste", US EPA SW 846. The 3000 series number refers to procedures used to prepare sample for analysis; 7000 series numbers refer to atomic absorption test methods; 8000 - 8100 series numbers refer to gas chromatographic methods; 8310 series numbers refer to high pressure liquid chromatography methods; and 9000 series numbers refer to colorimetric (spectrophotometric methods).
Another source of analytical methods is the Code of Federal Regulations, Vol. 40, Parts 136 and 141 for establishing test procedures for the analysis of pollutants. The 200 series numbers apply to metals analysis; the 500 series numbers to the analysis of organics in potable water; and the 600 series numbers to the analysis of organics compounds in drinking and waste water.
These are the primary sources of methods used by Ecology. These and others are identified in WAC 173-340-830 Analytical procedures.
Detector: The detector is the device that responds to the presence of the chemical after separation. Detectors vary in sensitivity to the individual chemicals.
AA Atomic absorption spectroscopy
Color Colorimetric method, spectrophotometry
HPLC High pressure liquid chromatography
GC ECD Separation of contaminant mixtures into individual components using gas chromatography and an electron capture detector
GC FID Separation of contaminant mixtures into individual components using gas chromatography and a flame ionization detector
GC Hall Separation of contaminants mixtures into individual components using gas chromatography and a Hall electrolytic conductivity detector
GC MS Separation of contaminant mixtures into individual components using gas chromatography and mass spectrometry
GC NP Separation of contaminant mixtures into individual components using gas chromatography and a nitrogen/ phosphorous detector
GC PID Separation of contaminant mixtures into individual components using gas chromatography and a photoionization detector
GFAA Analysis by graphite furnace atomic absorption
GHAA Analysis by gaseous hydride atomic absorption
ICP Analysis by inductively coupled plasma emission
MDL: Method Detection Limit: The minimum concentration of a substance that can be measured and reported with 99% confidence that the analyte concentration is greater than zero. The MDL values provided in the tables are values derived from WAC 173-340-830(4); e.g., Test Methods for Evaluating Solid Waste, U.S. EPA, SW-846, and compiled by PTI Environmental Services.
PQL: Practical Quantitation Limit: This is the concentration that can be reliably measured within specified limits during routine laboratory operating conditions using Ecology approved methods (see Part IV). The PQL values provided in the tables are values derived from WAC 173-340-830(4); e.g., Test Methods for Evaluating Solid Waste, U.S. EPA, SW-846, and compiled by PTI Environmental Services. In cases where there are no known PQL values (such as from the Federal Registry 40 CFR 136 & 141; 500 and 600 series), a factor of 10 times the MDL is used for the PQL value.
NOTE: "Table I Water" is reported in ug/l (ppb), "Table II Soil" is reported in mg/kg (ppm).
PQL Range: The range of thirteen responses out of a survey conducted by Ecology of fifty independent environmental laboratories. The survey was conducted to determine the range of PQLs achievable by specific matrixes, methods, and detectors. The laboratories surveyed routinely conduct these types of environmental analyses.
In some instances (indicated by a "thumbs-up" icon in the tables), the laboratories were able to attain a PQL lower than the federal PQL. For example, Table II for soil indicates antimony using Method 6010 attains a PQL range of 1.5 - 10 mg/kg with a PQL of 16 mg/kg.
Method B: The 1x10-6 (for carcinogens) Method B values are provided in Tables I and II for purposes of comparison with MDL and PQL values. Only carcinogens are included because there are frequently both PQL and Method B values for the same compound, and non-carcinogens are usually higher and often do not list both a Method B value and a PQL.
PQL > GW These columns compare the PQL with the Method B groundwater or SW (GW); surface water (SW); or soil formula values in their or Soil respective columns/tables.
Method B
Below are the following displayed conditions:
A blank cell indicates either (1) the Method B values is greater than the PQL, or (2) there is no PQL value available for comparison;
The "bomb" icon indicates the PQL is greater than the Method B formula value;
The "flag" icon indicates there is currently no Method B value in Ecology's Cleanup Levels and Risk Calculations (CLARC II) available for comparison.
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