Hazard Ranking System Issue Analysis:
        Use of Significance in
    Determining Observed Release
                MITRE

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Hazard Ranking  System Issue Analysis:
           Use of Significance in
      Determining Observed Release
                  Richard D. Brown
                     July 1986
                     MTR-86W101
                      SPONSOR:
                U.S. Environmental Protection Agency
                     CONTRACT NO.:
                     EPA-68-01-7054
                  The MITRE Corporation
                     Metrek Division
                    7525 Colshire Drive
                  McLean, Virginia 22102-3481

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   Department Approval:
MITRE Project Approval
:   
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                              ABSTRACT
     This report deals with the question of what criterion should be
used to establish that the concentration of a released uncontrolled
hazardous substance is "significantly higher than the background."
The criterion would be used in determining an observed release under
the Hazard Ranking System (HRS), an Appendix to the National
Contingency Plan (NCP) for oil and hazardous susbstances created by
the Comprehensive Environmental Response, Compensation, and Liability
Act of 1980 (CERCLA).  The report examines options for HRS revision
including definitions of significance based on the limits of
detection and quantitation to discriminate between contaminant levels
at or in the vicinity of an uncontrolled hazardous substance facility
and background levels.  The report also examines the relevance of
EPA responses to public comments relating to significance issues,
general concepts and tests of significance, detection limits,  and
the nature and amount of data available for determining an observed
release.
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                           ACKNOWLEDGMENT
     The author wishes to recognize colleagues whose ideas were
incorporated within this report.  Jerry Fitzgerald contributed
insight on the degree of variation of the limit of detection
achieved in analytical laboratories.   Charming Johnson developed
the concept of utilizing the limit of quantitation as a basis for
determining significance when evaluating concentrations near the
limit of detection.  Thomas Wolfinger identified several factors to
be considered when evaluating air data.
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                          TABLE OF  CONTENTS


                                                                 Page

LIST OF TABLES                                                    vii

1.0  INTRODUCTION                                                  1

I.I  Background                                                    1
1.2  Purpose of Report                                             3
1.3  Organization of Report                                        4

2.0  CURRENT USE OF SIGNIFICANCE IN THE HRS                         7

2.1  Introduction                                                  7
2.2  Observed Release                                              7

3.0  ISSUES RAISED RELEVANT TO SIGNIFICANCE                        11

3.1  Interpretation of Data                                       11
3.2  Amount of Data                                               11
3.3  Definition of Significance                                   13

4.0  CONSIDERATIONS RELATING TO USE OF SIGNIFICANCE IN THE HRS    15

4.1  General Concepts of Significance                             15
4.2  Tests of Significance                                        17
4.3  Role of Detection Limits in Determining Significance         18
4.4  Interpretation of Analytical Data                            22

     4.4.1  Detection Limits                                      22
     4.4.2  Suspect Data                                          24

5.0  SUGGESTED REFINEMENTS FOR USE OF SIGNIFICANCE IN THE HRS     27

5.1  Definition of Limit of Detection                             27
5.2  Significance When Background Levels Are Below Limit          28
     of Detection

     5.2.1  Option 1.  Presence of Contamination                  28
     5.2.2  Option 2.  Quantitation of Contamination              29
     5.2.3  Comparison of Options                                 30

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                    TABLE  OF  CONTENTS  (Concluded)
                                                                  Page

5.3  Significance When Background Levels Are Above Limit           31
     of Detection

5.3.1  Option 1.  Minimum Difference                               32
5.3.2  Option 2.  Margin for Certainty                             32
5.3.3  Comparison of Options                                       34

5.4  Special Considerations                                        34
5.5  Use of Suspect Data                                           36

6.0  REFERENCES                                                    37
APPENDIX A  DETAILED REVIEW OF EPA RESPONSES TO COMMENTS           39
            RELATED TO SIGNIFICANCE
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                           LIST OF TABLES
Table Number                                                     Page

    5-1        Option 2.  Minimum Difference,  Between             33
               Background And Site Sample Concentration,
               Required Before Assigning  An Observed Release
               When Background Level of Contaminant is Above
               the Limit of Detection
                                vii

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1.0  INTRODUCTION




1.1  Background




     The Comprehensive Environmental Response,  Compensation,  and




Liability Act of 1980 (CERCIA) (PL 96-510) requires the President to




identify national priorities for remedial action among releases or




threatened releases of hazardous substances.   These releases are to




be identified based on criteria promulgated in the National




Contingency Plan (NCP).  On July 16, 1982, EPA promulgated the




Hazard Ranking System (HRS) as Appendix A to the NCP (40 CFR 300;




47 FR 31180).  The HRS comprises the criteria required under CERCLA




and is used by EPA to estimate the relative potential hazard posed




by releases or threatened releases of hazardous substances.




     The HRS is a means for applying uniform technical judgment




regarding the potential hazards presented by a release relative to




other releases.  The HRS is used in identifying releases as national




priorities for further investigation and possible remedial action by




assigning numerical values (according to prescribed guidelines) to




factors that characterize the potential of any given release to




cause harm.  The values are manipulated mathematically to yield a




single score that is designed to indicate the potential hazard posed




by each release relative to all other releases.  This score is one




of the criteria used by EPA in determining whether the release




should be placed on the National Priorities List (NPL).

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     During the original NCP rulemaking process and the subsequent

application of the HRS to specific releases, a number of technical

issues have been raised regarding the HRS.  These issues concern the

desire for modifications to the HRS to further improve its

capability to estimate the relative potential hazard of releases.

The issues include:

     •  Review of other existing ranking systems suitable for
        ranking hazardous waste sites for the NPL.

     •  Feasibility of considering ground water flow direction and
        distance, as well as defining "aquifer of concern," in
        determining potentially affected targets.

     •  Development of a human food chain exposure evaluation
        methodology.

     •  Development of a potential for air release factor category
        in the HRS air pathway.

     •  Review of the adequacy of the target distance specified in
        the air pathway.

     •  Feasibility of considering the accumulation of hazardous
        substances in indoor environments.

     •  Feasibility of developing factors to account for
        environmental attenuation of hazardous substances in ground
        and surface water.

     •  Feasibility of developing a more discriminating toxicity
        factor.

     •  Refinement of the definition of "significance" as it relates
        to observed releases.

     •  Suitability of the current HRS default value for an unknown
        waste quantity.

     •  Feasibility of determining and using hazardous  substance
        concentration data.

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     •  Feasibility of evaluating waste quantity on a hazardous
        constituent basis.

     •  Review of the adequacy of the target distance specified in
        the surface water pathway.

     •  Development of a sensitive environment evaluation
        methodology.

     •  Feasibility of revising the containment factors to increase
        discrimination among facilities.

     •  Review of the potential for future changes in laboratory
        detection limits to affect the types of sites considered for
        the NPL.

     Each technical issue is the subject of one or more separate but

related reports.  These reports, although providing background,

analysis, conclusions and recommendations regarding the technical

issue, will not directly affect the HRS.  Rather, these reports will

be used by an EPA working group that will assess and integrate the

results and prepare recommendations to EPA management regarding

future changes to the HRS.  Any changes will then be proposed in

Federal notice and comment rulemaking as formal changes to the NCP.

The following section describes the specific issue that is the

subject of this report.

1.2  Purpose of Report

     As a part of the current HRS process, a score is assigned to a

known ("observed") release for each pathway (ground water, surface

water, or air) for the migration of a hazardous substance away

from a facility.  The acceptable evidence indicating an observed

release primarily is data that show levels of a contaminant,

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attributable to the uncontrolled hazardous substance  facility,  to  be




significantly higher than the background level.   Guidance is not




provided in the HRS with respect to the meaning  of "significantly"




other than to state that it is "in terms of demonstrating that a




release has occurred, not in terms of potential effects."  The




purpose of this report is to examine the issue of "significantly




higher than the background" with respect to an observed release and




to suggest options for a more definitive method for determining an




observed release.




     Excluded from discussion in this report are other observed




release issues raised in public comment on the proposed HRS and the




proposed NPL and its revisions, such as the relationship of the




observed level of contamination to either environmental standards,




the permitted release of pollutants, the degree of perceived health




threat associated with a release, the validity of sampling and




analytical protocols, or the presence of substances commonly found




in the environment.




1.3  Organization of Report




     The rest of this report begins with a review (Chapter 2.0) of




the current use of significance in the HRS.  Chapter 3.0 is a summary




of EPA responses to relevant public comments on the issue of




significance.  These comments were raised with regard to HRS




promulgation and NPL proposals and promulgations.   A  detailed review




of the EPA responses is provided in Appendix A.   These two chapters

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examine the degree of consistency in,  and the pattern of public




comments on, EPA's position with respect to significance issues.



     Chapter 4.0 examines general concepts of significance,  tests of




significance, the role of detection limits in determining



significance, and the importance of interpreting analytical  data for




use in the HRS.



     Chapter 5.0 builds upon the preceding chapters to suggest




options for clarifications and/or refinements to the HRS.

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2.0  CURRENT USE OF SIGNIFICANCE IN THE HRS




2.1  Introduction




     The Hazard Ranking System (HRS) is Appendix A of the National



Oil and Hazardous Substances Contingency Plan (NCP) promulgated on



July 16, 1982 (47 PR 31219-31243).  The HRS is designed to estimate



the potential hazard presented by releases or threatened releases of




hazardous substances, pollutants, and contaminants.  The HRS is



applied to data from an observed or potential release to enable EPA




to calculate a "score" representing the relative hazard from such a



release.



     The calculation of the HRS score for a release involves




analyses of five "pathways" of exposure of humans or sensitive



environments:  1) ground water, 2) surface water, 3) air, 4) direct




contact, and 5) fire and explosion.  A composite migration score is




developed from scores for each of the first three pathways.  This



migration score is used to determine the eligibility of a site for




placement on the National Priorities List (NPL).  The last two




pathways are used to identify emergency situations that require




removal actions and are not considered in the placement of sites on



the NPL (47 FR 31187, July 16, 1982).




2.2  Observed Release




     Each of the three pathways used in determining an HRS migration




score incorporates a provision for determining the existence of a




release.  Provisions for determining an observed release for each

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pathway are described in the HRS Users Manual (contained  in




Appendix A of the NCP).




     For the ground water pathway, the determination of an observed




release is based on "direct evidence of release of a substance of




concern from a facility to ground water."  The "direct evidence of a




release must be analytical."  That is, "if a contaminant is measured




(regardless of frequency) in ground water or in a well in the




vicinity of the facility at a significantly (in terms of




demonstrating that a release has  occurred, not in terms of potential




effects) higher level than the  background level, then quantitative




evidence exists, and a release  has been observed."  Certain




"qualitative evidence of a release (e.g., an oily or otherwise




objectionable taste or smell in well water) constitutes direct




evidence only if it can be confirmed that it results from a release




at the facility in question" (47  FR 31224, July 16, 1982).




     For the surface water pathway, "direct evidence of release must




be quantitative evidence that the facility is releasing contaminants




into surface water."  The "quantitative evidence could be the




measurement of levels of contaminants from a facility in surface




water, either at the facility or downstream from it, that represents




a significant (in terms of demonstrating that a release has




occurred, not in terms of potential effects)  increase  over




background levels."   The direct  evidence  is not dependent on the



frequency of measurement (47  FR  31233,  July 16, 1982).






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     For the air pathway,  "the only acceptable evidence of release




is data that show levels of a contaminant,  at or in the vicinity of




the facility, that significantly exceed background levels




(regardless of the frequency of occurrence)."  "Data based on



transitory conditions due  to facility disturbance by investigative



personnel are not acceptable" (47 FR 31236,  July 16, 1982).

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3.0  ISSUES RAISED RELEVANT TO SIGNIFICANCE




     This chapter is a summary of EPA responses to significance




issues raised in public comments pertaining to HRS promulgation and




NPL proposals and promulgations.  A detailed review of the EPA




responses is provided in Appendix A.




3.1  Interpretation of Data




     Many commenters raised the issue that, in some instances,  the




levels reported for an observed release did not constitute a threat




to human health, particularly when subsequent sampling detected no




contaminants.




     The EPA position is that the HRS assigns a value for an




observed release when there is evidence that substances have




migrated from a site, indicating that more may do so in the future,




and not because the actual release is a health threat.  An observed




release is scored whenever contaminants are detected beyond their




place of deposition in concentrations "significantly higher" than




background levels.




3.2  Amount of Data




     Comments relevant to the amount of data required to document a




HRS score, including documentation of an observed release, are




conflicting.  Some commenters felt data requirements were overly




extensive, others felt that more data should be required.




     The EPA response consistently has been that the current data




requirements strike a balance between providing enough data for






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decision-making and the cost and time required to collect  data.   It




is important to note that placement on the NPL is only the first




step in considering a site for remedial response under CERCLA.   A




more detailed investigation, subsequent to NPL listing, could




indicate the hazard to be more or less of a threat to human health




or the environment.  Should subsequent data collection and analysis




indicate that remedial response is not needed, the site could be




removed from the NPL.  It is important to quickly list on the NPL




those sites which may pose serious threats to human health or the




environment.  The time required for acquisition of extensive data




prior to listing may inhibit remedial response actions which need to




be conducted in a timely manner.




     The question of the amount of data required for scoring an




observed release is important, if statistical tests of significance .




are utilized to document an observed release.  Generally, a large




number of  samples must be collected to provide a high degree of




confidence in statistical tests.  However, when  the HRS was




originally proposed, EPA stated that it was designed so that a site




could be scored without having to spend a lot of resources (e.g.,




time and money).  It was intended as a low-cost screening tool to




determine  which sites the Agency intended to further investigate




(47 FR 31186-31187, July 16, 1982).  Consequently, large amounts of




data are rarely available for use in scoring an observed release.
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Sometimes only two values are available,  one representing background




and one representing the site.




3.3  Definition of Significance




     Currently, data that show levels of a site-related contaminant




to be significantly higher than the background level constitutes the




most commonly reported acceptable evidence of an observed release.




Guidance is not provided in the HRS with respect to the meaning of



"significantly" other than to state that it is "in terms of




demonstrating that a release has occurred, not in terms of potential



effects."  Commenters have not questioned the lack of guidance, but



have questioned the validity of data used to score observed releases




in instances where the amount of contaminant detected is near the



limit of detection.




     As a general response to comments,  EPA stated that, if a



contaminant is observed in background and site samples and sample




concentrations are within 10 to 20 percent, the Agency cannot state




conclusively that an observed release has occurred.  Sometimes the




presence of a pattern of clustering of low and high values among




background and site samples, respectively, can demonstrate observed



release.




     The Agency also has stated that any detectable concentration of




a substance of concern above background levels can constitute




evidence of an observed release.  That is, any variation above




background can be considered an observed release if, in the judgment






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of the sampling and analysis authority (ultimately EPA),  the



variation indicates a release from the site.  However,  based on



the wording of the HRS, the inferred meaning of "above  background"



could be the concept of "significantly above background" based on




"quantitative evidence."  This inference still leaves open a




question as to the meaning of quantitation  and at what point one




concentration is considered to be  "significantly higher" than




another concentration.




     The Agency has attempted to clarify the HRS wording by stating




that in cases in which a  specific  contaminant is not detected in




background, any measurable quantity  of the  contaminant in the site




samples is considered  to  be "significantly  higher" than the




background and provides the basis  for scoring an observed release.




This clarification still  leaves open a question as to the meaning of




a "measurable" quantity.
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4.0  CONSIDERATIONS RELATING TO USE OF SIGNIFICANCE IN THE HR.S




     This chapter examines various considerations relevant to




revision of the method of scoring an observed release under the




HRS.  It begins (Section 4.1) with a discussion of general concepts




of significance, followed by a review (Section 4.2) of the current




use and relevance of tests of significance in hazardous waste




management.  Section 4.3 discusses the currently accepted definitions




of the limit of detection and limit of quantitation and their




relationship to concepts of significance.   Section 4.4 examines the




data available for scoring an observed release, their relationship




to the concepts of limit of detection and limit of quantitation,  and




their appropriateness for scoring an observed release.




4.1  General Concepts of Significance




     Use of the term "significance" generally is understood to infer




meaning.  If something is significant, it is considered important




and has meaning relevant to a normal state of affairs, events, or




facts.  Often, determination of significance is judgmental,




subjective, and is considered an expression of common sense.




     In the field of statistics, significance takes on a defined and




inflexible definition within a highly organized context of the




nature of assumptions, the type of mathematical distribution, and




the particular number and disparity of values.  When an observation




is very unlikely to have arisen by chance alone, it is considered




"statistically significant".  That is, it would be highly improbable






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that the observation occurred by chance and the difference between




the observation and normal occurrences must be accepted as a real




difference.




     Statistical significance is based on probability.  That is,




falling short of absolute certainty, it is expressed as a degree of




confidence in the reality of the difference between sets of values.




A difference that arises on the basis of pure chance only one time




in one thousand sampling efforts is considered highly significant.




The level of such probability is expressed as p=0.00l; i.e., there




is only one chance in a thousand of the result arising by chance




alone.




     A decision to apply a statistical test of significance to data




used to determine an observed release must be evaluated within the




HRS context.  In the abstract world of statistics, the only valid




foundation (in practice) for making such a determination is on the




basis of a statistical test of significance.  However, in the




evaluation of environmental data, practical considerations must also




be weighed, many of which cannot be represented precisely in




mathematical terms.  Common sense must be applied when considering




factors which cannot be adequately accounted for statistically when




few data are available.  Such factors include the natural




variability of the contaminant of concern within the environment,




the probable lack of any sources of the contaminant outside of the




site, the degree of precision and accuracy associated with the






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measurement (including influence of sample collection and




processing), and the representativeness of particular kinds of




environmental data.   Normally,  variability associated with




laboratory instrumentation and  techniques is taken into




consideration in the reporting  of analytical results (see




Section 4.3).  The natural variability of a contaminant may be




larger than variability attributable to the analytical process.




4.2  Tests of Significance




     For purposes of determining when a release is "significant"



under the RCRA (The Resource Conservation and Recovery Act) program,




EPA requires use of the Cochran's Approximation to the Behrens-Fisher




Student's t-test (published as  Appendix IV of 40 CFR 264).   The



Agency currently is considering another method, the averaged



replicate t-test, to determine  significance under the RCRA program.




     A problem associated with  incorporating such statistical tests




of significance within the HRS, which is different from the RCRA




context, is that the data available for scoring are highly variable




with respect to amount, source(s), and design of sampling programs.




Often, pre-HRS site investigation plans do not require that samples




be obtained systematically at specified times and places or contain




randomization schemes to ensure unbiased results.  In general,




sampling programs do not incorporate an experimental design to




produce data compatible with the application of a statistical test




for significance.  Statistical  tests of significance are useful only






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in instances when a large number of samples have been taken,  with




adherence to a well defined sampling plan, and the reported




concentrations are not near the level of detection.  It is not




within the scope of current pre-HRS data collection efforts to




generate the amount of data needed to effectively apply statistical




tests.




4.3  Role of Detection Limits in Determining Significance




     The Committee on Environmental Improvement of the American




Chemical Society (ACS) has defined a detection limit (DL; also




termed the limit of detection) as the lowest concentration level




that can be determined to be statistically  different from that




observed in a  blank (ACS 1983).




     Blanks are used to identify bias in  the final results due to




contamination.  There are two types of  blanks.  The first, called a




laboratory or  method blank, is intended to  detect bias resulting




from inappropriate handling in the analytical process.  These blanks




are prepared in the laboratory and carried  through the same



laboratory operations as the samples.   The  second, or field blank,




is designed to detect bias resulting from inappropriate handling



during the sampling process.  Field blanks  are prepared to accompany




samples collected in the field and are  treated as field samples in




all aspects, including exposure to the  type of sample bottle,




holding for the same time, and treatment with the same preservatives
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(EPA 1985a)-  Note that the ACS definition does not specify what




types of blanks are to be used.



     The EPA Contract Laboratory Program (CLP), which provides




analytical support to the CERCLA program (see 4.4.1), requires




analytical laboratories to verify the attainment of certain



laboratory detection limits (specifically,  instrument detection




limits or IDLs) which are determined in part  on the use of



laboratory blanks.  The IDLs must meet specific contract required




detection limits established under the Contract Laboratory Program.



Field blanks are not used in the determination of IDLs (Peter




Isaacson, VIAR, personal communication,  July  1986).




     Although the ACS definition of a DL has  become widely accepted,




other definitions have been used by chemists  when reporting data.




Non-statistical definitions have been used in which the DL is equated




to the background (naturally occurring concentration of a substance




within the environment), ten percent of the background, or some




arbitrarily determined level which does not represent a threat to




human health.  Various mathematical definitions of the DL range from




one to twenty times the standard deviation of net concentrations.




The net concentration of a sample is equal to the total analyte




value measured for a sample minus the analyte value measured for a



blank (Currie 1968).




     The question of detection is particularly important to the HRS




when an observed release is to be based on a  background level which






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is below the DL reported by an analytical laboratory.   Thus, with




respect to the ACS definition of the DL,  a question that needs to be




answered (when the measured background level is below the DL)  is




whether a measured sample value is significantly different from that




found for the sample blank.  The ACS has determined (for normal




distributions) that the difference between the value measured for a




sample and the value for the blank can be considered to be greater




than zero (at a high degree of confidence, i.e., at the 99 percent




confidence level) when that difference is greater than three times




the standard deviation of such differences observed in laboratory




data (net concentrations).  Thus, the ACS recommends that the DL




value, established by an analytical laboratory, be set at three




times the observed standard deviation for a particular series of net




concentrations (ACS 1983).




     The ACS position with respect to the DL is that a DL value set




at less than three standard deviations for such net concentrations




lies within the region of questionable detection (and is, therefore,




unacceptable).  A high degree of confidence that an analyte has been




detected exists at and above the three standard deviation value.




     The ACS also has defined the level above which quantitative




results may be obtained with a specified degree of confidence.  This




level is termed the limit of quantitation (LQ).  Confidence in the




apparent analyte concentration increases above the DL and attains a




high degree at the LQ.  Both the ACS and the National Bureau of






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Standards (NBS) agree that the lower limit of concentration (i.e.,



the lowest amount) of a substance that must be observed before a




method is considered to provide quantitative results is the LQ.



Both ACS and NBS agree that,  by convention,  the LQ is equal to ten




standard deviations (or 3.3 times the DL).   This LQ represents an




uncertainty of only plus or minus 30 percent in the measured value




at the 99 percent confidence  level.   The  LQ is useful for




determining the lower limit of the useful range of measurement




methodology (NBS 1985, ACS 1983,  EPA 1982a)-



     The ACS position with respect to the LQ is that a measured




value which is at or above the DL, but below ten standard deviations




(3.3 times the DL) lies in a  region of less-certain quantitation.  A




value 3.3 times the DL represents the limit of quantitation.  A




value above the LQ lies within the region of quantitation.




     For HRS purposes, sample results at  or near the DL (using the




ACS definition) are associated with two problems:  1) uncertainty




due to measurement variability can approach and even equal the




reported sample value, and 2) confirmation of the detection is




essentially impossible.  Identification of a contaminant is



dependent largely on the selectivity of the analytical method and




knowledge of the absence of sources of interference.  The problems




diminish when higher levels of analytes are present.  Thus, ACS




recommends that "quantitative interpretation, decision making, and
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regulatory actions should be limited to data at  or  above  the LQ"



(ACS 1983).




     The DL and the LQ have been established by  convention at  the




99 percent confidence level by ACS (1983), NBS (1985),  and EPA




(I982a,b).  For HRS purposes, a lower level of confidence (e.g.,




95 percent, resulting in lower values of DL and LQ could be




established.  The use of 99 instead of 95 percent places importance




on achieving a high state of certainty over the possibility of not




scoring an observed release on some sites when it would be desirable




to score an observed release, i.e., a 95 percent limit accepts




"false positives" in order to identify more "true positives."




4.4  Interpretation of Analytical Data




     4.4.1  Detection Limits




     Most of the data utilized in the HRS scoring procedure are




derived through the EPA Contract Laboratory Program (CLP).  The




Program is directed by the National Program Office, EPA Headquarter*s




Analytical Support Branch, Office of Emergency and Remedial Response.




The DLs utilized by the Program are Contract Required Detection




Limits (CRDLs; EPA I985b, 1984b, 1983b).  The CRDLs are minimum DLs




required by EPA of analytical laboratories performing analyses of




environmental samples under the CLP.  The CRDLs are conservative.




Many participating laboratories operate at or below the CRDLs  on a




routine basis.  The CLP laboratories are not required to report
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their own DLs associated with a particular data set, but are



required to relate sample values to the CRDLs (see Section 4.4.2).




     In general, the CRDLs are substantially higher than the DLs




realized by a particular laboratory.  And, since the DLs (and



consequently the LQs) depend on the precision (similarity of



repetitive measurements) attainable by an individual laboratory,




the DLs attained for a particular analytical method can be highly




diverse among laboratories.   Thus, analyte values reported near




the CRDLs can be viewed as being more reliable with respect to



quantitation than analyte values observed near the DL associated




with a particular laboratory for a given series of analytical




measurements.  Although difficult to determine, the LQs for the CLP




laboratories (and laboratories operating under the CLP guidelines)




with the best instrumentation and quality control practices may be




near the CRDLs (because the CRDLs are conservative and should be




attained readily by CLP laboratories).  The CLP is in the process of




evaluating CLP data reported to date for the purpose of determining




if the CRDLs could be lowered without diminishing the reliability




of reported data (Mike Carter, EPA, CLP, personal communication,



April 1986).




     Some data used for scoring sites are derived outside of the




CLP, e.g., data collected and analyzed by a consultant under




contract to a site owner.  These data are not accompanied by CLP
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CRDLs, but DLs of the laboratory performing the chemical analyses




usually accompany the data.




     4.4.2  Suspect Data




     Some data reported under the CLP is considered and identified




as suspect (flagged with the letter "J").  This procedure is part




of the CLP's quality assurance procedures.  The code letter "J"



indicates that the associated numeric value is an estimated quantity




because quality control criteria were not met.  Data reported as




suspect under the CLP reflect that the laboratory performance




requirements, specified by contract, have not been met or that other




factors may have affected the final result, causing the reported




data  probably to be biased.  Examples of factors which may cause




data  to be labeled as suspect are observed or inferred interferences




in laboratory blanks and/or samples, the exceeding of holding times,




and the lack of or inappropriate use of procedures for the




preparation of laboratory blanks, calibration standards, calibration




verification standards, laboratory control standards, and




interference check standards.  Narrative is to be provided with the




labeling  to indicate the cause of possible bias.




      Under the CLP, if the observed contaminant value is less than




the CRDL  (but equal to or greater than the measurement capability




of the analytical instrument), the CRDL is reported in brackets




(instead  of the observed contaminant value), e.g.  [10].  If an




inorganic substance (e.g., arsenic) was analyzed for but not






                                 24

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detected, the CRDL is reported together with a "U" (e.g.,  10U).



If an organic substance was analyzed for,  but not detected,  the



laboratory's own estimated sample quantitation limit is reported




with a "U".  Notations such as "10UJ" could indicate that  holding



times were exceeded, that the possibility  of false negatives may



exist, and that the laboratory DL for a particular sample  may be




elevated over the value reported (EPA 1986,  1985c).



     Suspect data should be used for HRS scoring  with caution.




Values reported at concentrations near the CRDL may not be reliable



for scoring an observed release,  unless the  associated narrative




indicates that the data can be considered  as valid under certain




circumstances.
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5.0  SUGGESTED REFINEMENTS FOR USE OF SIGNIFICANCE IN THE HRS




     Based on the review of EPA responses to public comments and




the considerations in Chapter 4.0, the following  suggestions for




revision of the HRS would be consistent with those responses.   The




suggestions would augment what has been stated by explaining what




is acceptable with respect to the meaning of the  HRS concepts of




"significantly higher" (e.g.,  47 FR 31224,  July 16,  1982) and




"measurable quantity" (e.g.,  49 FR 37078, September 21, 1984).




5.1  Definition of Limit  of Detection




     Determination of an  observed release is dependent on the




presence of a measurable  quantity of  a contaminant in site samples




that is significantly higher  than background.   When the contaminant




is not detected in background samples, any  measurable quantity of




the contaminant in the site samples is presently  considered




significantly higher than the background and provides the basis for




scoring an observed release (49 FR 37078,  September 21, 1984).




Thus, values of interest  in determining an observed release are the




DL and the LQ (which is based on the DL).




     Since the DL is determined at the laboratory, it is  suggested




that EPA utilize the DL as reported by the analytical laboratory as




the DL used for HRS scoring.   Since CLP laboratories usually report




only the CRDLs with analytical data, the CRDLs should be  used as the




DLs for CLP data.  Should a CLP laboratory report its DLs for a




particular set of data, its DLs should be used in place of the CRDLs.






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5.2  Significance When Background Levels Are Below Limit of Detection




     This section presents two options for refinement of the HRS




scoring of an observed release when background levels are below the




limit of detection.  The first option, discussed in Section 5.2.1,




is based only on the ability to detect contamination in a sample




associated with the site.  The second option, discussed in




Section 5.2.2, is based on the ability to quantitate the level of




contamination in a sample associated with the site.  These two




options are compared in Section 5.2.3.




     5.2.1  Option 1.  Presence of Contamination




     The ACS has defined the DL as the lowest concentration level




that can be determined to be statistically different from a blank.




That is, the level of contamination at the DL or higher can be




differentiated from that associated with the experimental error or




"noise" associated with the analytical protocol.  For Option 1, the




DL is the basis for the determination of an observed release against




a background of "none detected" for a particular contaminant.




     When background levels of a contaminant are below their DL, the




contaminant is considered to be not detected.  The actual background




concentration of the contaminant could be very near the DL and also




very close to the observed site concentration of the contaminant




(should the site value be near the DL).   Under these conditions, the




results of replicate analyses may be statistically indistinguishable,




given the unreliability of measurements  near the DL.   However,  the






                                 28

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detection of contamination can be reliable (at the 99 percent




confidence level) at and above the DL.




     Although one cannot be certain about the  actual level of




contamination when the concentration of  the site-related  sample is




near the DL, site contamination can be considered  to be present




(compared to a background of "none detected").   Thus,  it  can be said




that the migration of a hazardous substance has  occurred.   The




determination that migration has occurred is the only requirement




under the current HRS concept of an observed release (i.e.,




migration has been demonstrated).




     5.2.2  Option 2.  Quantitation of Contamination




     The ACS has  defined the region of certain quantitation at  3.3




times the DL.  For Option 2,  this relationship is  the basis for the




determination of  an observed release against a background of "none




detected" for a particular contaminant.   For practical use in




scoring, the HRS  could be revised to indicate  that any contaminant




value of three or more times the DL (in  a sample associated with the




site) reasonably  represents a measurable quantity, given  that the




contaminant is not detected in the background  sample(s).   This (3




times the DL reported by the analytical  laboratory) should provide a




reasonable and adequate margin to account for  uncertainty,




especially in light of the conservative  nature of  the CRDLs (which




have been specified by the CLP for many  of the most frequently




observed substances  at hazardous waste sites).  Under this option,






                                 29

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one could be highly confident that the site related sample




concentration represents a level of contamination that is higher




than that existing in background (even though the background




contaminant level is not detectable).



     The above refinement would clarify EPA's current position that




any measurable quantity of a contaminant that is significantly



higher than background would provide the basis for scoring an




observed release.  The lower limit of the measurable quantity would




be the LQ for a particular set of data.   By definition,  any value at




or above the LQ would be measurable and significantly higher than




any value below the DL for a particular set of data.




     5.2.3  Comparison of Options




     A site is more likely to be scored for an observed release




using Option 1 than Option 2.  Under Option 1, the concept of




significance is based on the ability to reliably detect



contamination.  Option 1 is consistent with EPA's comments upon




promulgation of the first update of the NPL which infer that



detection represents a significantly higher concentration than a




concentration which is not detected (49 FR 37078, September 21,




1984).   The logic behind Option 1 vs.  Option 2 is that, if there




reasonably appears to be a demonstration of the migration of a




hazardous substance on a site (independent of the contaminant



concentration), it would be prudent to score for an observed release.
                                 30

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As currently practiced this would result in listing the site on the




NPL so that more definitive data can be obtained through detailed




site investigations.




     Under Option 2,  the concept of significance is based on the




ability to quantitate the amount of contamination.   This Option is




consistent with the viewpoint  that quantitation  is  implied in EPA




comments relating to  the existence of an observed release;  e.g.,  the




presence of "quantitative evidence"  (47 FR  31233, July  16,  1982),  a




"measurable quantity" (49 FR 37078,  September 21, 1984),  a "quantity




higher than background"  (48 FR 40665, September  8,  1983),  and a




"significantly higher concentration" than in background (49 FR 37078,




September 21,  1984).   The logic  behind  Option 2  vs.  Option 1 is




that, in order to determine that one value  is higher than another,




the basis for  decision-making  must be quantitative;  i.e.,  one must




have a high degree of confidence in the analyte  concentration.   Such




confidence does not exist near the limit of detection.




5.3  Significance When Background Levels Are Above  Limit of Detection




     This section presents two options  for  refinement of the HRS




scoring of an  observed release when background levels are above the




DL.  The first option, discussed in Section 5.3.1,  is based only on




the ability to quantitate the  concentration of the  site related




sample.  The second option, discussed in Section 5.3.2, is based on




the need to attain a degree of separation between site  and background
                                 31

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levels before an observed release is assigned.   These two options are




compared in Section 5.3.3.




     5.3.1  Option 1.   Minimum Difference




     This option for assigning an observed release when the




background level of the contaminant of concern is at or above the DL




requires that the site concentration must be above the background




level and at least equal to or above the LQ (3 times the DL).  This




option maintains a statistically justifiable separation between the




two values when the background level is near the DL; i.e., one can




be highly confident the site related sample concentration is higher



than background.  Confidence in the background concentration




increases as it increases above the DL.  When both background and




site related sample concentrations are above the LQ, a high degree



of confidence (99 percent level) is associated with each of the




sample values.  One can be highly certain that the site level is




higher than background (but cannot be certain that both values are




not reflective of general background contamination).



     5.3.2  Option 2.  Margin for Certainty




     This option is summarized in Table 5-1.  The option is based on




the premise that when a contaminant is observed in background, as




well as in site samples,  certainty of an observed release is




questioned by a possibility that the site concentration is merely a




reflection of widespread contamination in the general area of the
                                 32

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                              TABLE  5-1

     OPTION 2.  MINIMUM DIFFERENCE,  BETWEEN BACKGROUND AND SITE
         SAMPLE CONCENTRATION, REQUIRED BEFORE ASSIGNING AN
              OBSERVED RELEASE WHEN  BACKGROUND LEVEL OF
             CONTAMINANT  IS ABOVE THE LIMIT OF DETECTION
   When Background Level Isj

       iDL and<2DL


             and
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site.  The likelihood of this hypothesis being correct increases as




background levels increase.




     This option distinguishes between background and site sample




concentrations used for assigning an observed release, even when




both values are within the region of quantitation.   This option




provides for a margin of certainty to assure that the site value is




likely to represent an observed release, even in light of the




contaminant being observed in background.




     5.3.3  Comparison of Options




     A site is more likely to be scored for an observed release




under Option 1 in contrast to Option 2.  Option 1 simply treats one




sample concentration as higher than another, given the higher (site




value) is within the region of quantitation.  Option 2 provides an




additional margin to account for the possibility that the site value




is a reflection of some general contamination represented by the




background sample.




5.4  Special Considerations




     Situations occur when measurements of several contaminants




and/or a number of measurements of the same contaminant appear to




indicate that site-related concentrations are above background




(whether background is above or below the DL), yet data do not meet




the criteria set forth in Sections 5.2 or 5.3.  Under such




situations, one might conclude based on experience that a pattern




exists which indicates that an observed release has occurred.  Under






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these situations, it is suggested that determination of an observed




release be based only on the results of an appropriate statistical




test, given that enough data are available to apply a comparison




test where the results would be associated with a high (e.g.,  99




percent) degree of confidence.   The analysis should be documented




and verified by a trained statistician and/or chemist as appropriate.




     A characteristic,  not strongly associated with other media,




that confounds the interpretation of air data,  is that the




representativeness of the data  depend on highly variable




environmental conditions  such as temperature,  pressure,  wind speed,




and stability.   Thus, a single  pair of measurements is highly




unlikely to be representative of an observed release.




     Special atmospheric  conditions can result in a lower or higher




detection or emission level at  the time of sampling.   Special




atmospheric conditions  include  high wind speeds,  low temperature,




high relative humidity  (including precipitation), flat and open




terrain, and an unstable  atmosphere.  The reader should note that




detailed information on the effects of atmospheric conditions  on




airborne emissions from uncontrolled hazardous waste sites is




contained in another report under preparation.




     To a lesser extent,  similar special conditions are associated




with surface water, and even less with ground water.  Sometimes,




owing to limitations in sampling timeframes and the availability of




sampling personnel and equipment, sampling during these conditions






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cannot be avoided.  Special consideration should be given to




laboratory data reflecting background or site concentrations




generated from samples acquired under such conditions.




5.5  Use of Suspect Data



     The use of suspect data should be avoided,  if possible.  At




times, data which do not meet all contract (CLP) requirements are




released to facilitate the progress of projects  requiring the data.




The contract laboratory may be required to confirm the  data or to



reanalyze samples.  Under these circumstances, an attempt should be




made to obtain valid data through the CLP.



     If it is necessary to use suspect data,  the CLP or the non-CLP




laboratory should be contacted to determine how  the action, which




served as the reason for labeling the data as suspect,  introduced




bias and influenced the level of confidence.  Assurance from the CLP




or non-CLP laboratory must be documented with respect to the




validity of the data, and reliability of the associated DL, for use




in scoring an observed release.
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 6.0  REFERENCES

 American Chemical Society (ACS).  1983.  Principles of Environmental
Analysis.  Anal. Chem. 55: 2210-2218.

Bureau of National Affairs,  Inc. (SNA).  1986.   Statistical Test
Called Seriously Flawed.   Environment Reporter 1-24-86:   1780-1781.

Currie, Lloyd A.   1968.   Limits for Qualitative Detection and
Quantitative Determination.  Anal.  Chem.  40:  586-593.

National Bureau of Standards (NBS).   1985.  Principles of Quality
Assurance of Chemical Measurements.   NBSIR  85-3105  (PB85-177947).
U.S.  Department of Commerce, Gaithersburg,  Maryland.

U.S.  Environmental Protection Agency (EPA).   1986.  Laboratory Data
Validation:  Functional Guidelines  for Evaluating Inorganics
Analysis.   Office of Emergency  and Remedial Response,  U.S.
Environmental Protection,  Washington,  D,C.

U.S.  Environmental Protection Agency (EPA).   1985a.  Choosing
Cost-effective QA/QC Programs for Chemical  Analysis.   EPA 600/4-85-
056.   Environmental Monitoring  and Support  Laboratory, Cincinnati,
Ohio.

U.S.  Environmental Protection Agency (EPA).   1985b.  Statement of
Work for Organics Analysis (Revised).   Contract Laboratory Program,
Office of Emergency and Remedial Response,  U.S.  Environmental
Protection Agency, Washington,  D.C.

U.S.  Environmental Protection Agency (EPA).  1985c.  Laboratory Data
Validation:  Functional Guidelines  for Evaluating Organics
Analyses.   Office of Emergency  and  Remedial Response,  U.S.
Environmental Protection  Agency, Washington,  D.C.

U.S.  Environmental Protection Agency (EPA).  I984a.  Support
Document for the Revised  National Priorities  List - 1984.  Office of
Solid Waste and Emergency Response, U.S.  Environmental Protection
Agency, Washington, D.C.

U.S.  Environmental Protection Agency (EPA).  I984b.   Statement of
Work for Inorganics Analysis.   Contract Laboratory Program, Office
 of Emergency and Remedial Response, U.S. Environmental Protection
Agency, Washington, D.C.
                                 37

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U.S. Environmental Protection Agency (EPA).   I983a.   Support
Document for the National Priorities List.  Office of Solid Waste
and Emergency Response, U.S. Environmental Protection Agency,
Washington, D.C.

U.S. Environmental Protection Agency (EPA).   1983b.   Statement of
Work for Dioxin Analysis.  Contract Laboratory Program, Office of
Emergency and Remedial Response, U.S. Environmental Protection
Agency, Washington, D.C.

U.S. Environmental Protection Agency (EPA).   I982a.   Design of
30l(h) Monitoring Programs for Municipal Wastewater Discharges to
Marine Waters.  EPA 430/9-82-010 (PB83-153809).   Office of Water
Program Operations, U.S. Environmental Protection Agency,
Washington, D.C.

U.S. Environmental Protection Agency (EPA).   I982b.   Methods for
Organic Chemical Analysis of Municipal and Industrial Wastewater.
EPA 600/4-82-057.  Environmental Monitoring  and Support Laboratory,
Cincinnati, Ohio.
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                             APPENDIX A

            DETAILED REVIEW OF EPA RESPONSES TO COMMENTS
                       RELATED  TO  SIGNIFICANCE
     The following is a review of EPA responses on significance

issues raised in public comments pertaining to HRS promulgation and

proposed and final NPL and NPL revisions.

A.I  Preamble to the HRS

     When the National Contingency Plan was promulgated on July 16,

1982 (47 FR 31180-31243), EPA responded to public comments on the

proposed plan. Included in the EPA response was discussion of

certain comments which have some bearing on the use of significance

in determining an observed release.   Some of these comments related

to the amount of data needed to support an HRS score,  others focused

on the validity of scoring one-time or minor releases.

     A.1.1  Amount of Data Needed to Determine an Observed Release

     Many comments questioned the data requirements of the HRS.  The

frequent criticism was that the HRS fails to accurately distinguish

between the degree of hazard presented by different releases; the

result being that the HRS might give high scores to releases that

otherwise should not be included on the NPL (47 FR 31186).  Some

commenters suggested that the data required could be very expensive

to acquire and slow the remedial action process.  Others suggested

that more factors should be considered or that existing factors
                                 39

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should be considered at a higher level of detail through more




extensive data collection (47 FR 31187).




     The EPA response concerning the extent of data required in the




HRS was that the role and importance of the HRS and NPL must be kept




in perspective.  The NPL is merely the first step in considering a




release for Superfund-financed remedial response (CERCLA established




Superfund to investigate and clean up abandoned hazardous waste




disposal sites).  After a release is included on the NPL, a




subsequent remedial investigation would acquire more extensive




information which could indicate the hazard to be more or less




significant than originally thought (47 FR 31186-31187).




     With respect to conflicting comments on the amount of data



needed for the HRS, EPA felt that the amount of information to be




collected must be balanced against the cost and time required to




obtain the data.  Overall, the extent of information required must




be  consistent  with the costs of data collection, the large number of




releases which need to be investigated, and the resources available




for implementing the NCP.  EPA has tried to minimize the information




required for the HRS, so that releases which have not been




extensively investigated are not eliminated from the NPL.  The




Agency determined that the current HRS data requirements are




adequate without being unduly burdensome or costly (47 FR 31187).
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     A.1.2  One-time or Minor Releases




     Some commenters asserted that the frequency and quantity




of releases are not considered in the determination of  an observed




release.  Thus, one-time or minor releases would be treated as




equivalent to a frequent or chronic source of  release (47 FR 31188).




     The EPA response reflects the context within which an observed




release is viewed by the Agency.   The determination of  an observed




release indicates that the likelihood of  a release  is 100 percent.




The fact that some substances have been released from a site is a




good indication that substances at the site can escape  and increases




the likelihood of a substantial release.   Gathering more extensive




data than currently required (e.g., for the purpose of




differentiating between a minor occurrence vs.  a frequent or




substantial problem) would add inordinately to the  cost and time




needed to score releases.  Such extensive monitoring is more




appropriately considered during investigations subsequent to the




listing of a site on the NPL (47  FR 31188).




A. 2  Preambles to the NPL and NPL Updates




     A.2.1  NPL




     The NPL was proposed on December 30, 1982 (47  FR 58476-58485).




The NCP was amended to include the NPL on September 8,  1983




(48 FR 40658-40673).




     In the preamble to the final NPL, EPA responded to public




comments concerning low level observed releases.  The comments






                                 41

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focused on situations where values used for scoring observed




releases were "low" (e.g., below regulatory limits specified under




the Safe Drinking Water Act).




     The EPA response explained that concentrations of substances




migrating in the environment tend to show extreme variation through




time and space.  Given that only periodic sampling is feasible in




most instances (to gather data in support of an NPL listing),




requiring contaminants to exceed certain levels before assigning an




observed release could exclude many sites from the NPL which may be




endangering the public.  The Agency explained that the HRS scoring




instruction for an observed release is based on the fact that the




observed release factor is considered for the purpose of estimating




the likelihood that substances can migrate from a site.  When a




release is observed in any quantity, as long as the concentration is




above background level, that likelihood is 100 percent (48 FR 40665).




     A.2.2  NPL Update 1




     On September 8, 1983, EPA proposed the first update to the NPL




(48 FR 40674-40682).  The NPL was amended to include the update on




September 21, 1984 (49 FR 37070-37082).




     Some commenters reiterated the concerns raised when the NPL




was proposed with respect to assigning values for observed releases




when measured concentrations of the substances involved were below




regulatory limits.  The EPA response on this topic remained unchanged




from that given in the preamble for the final NPL (49 FR 37078).






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     Some commenters questioned the validity of one-time or low level




releases when subsequent sampling showed lower concentrations or the




absence of any contaminants at the time of sampling.  In response,




EPA explained that values are assigned based on the data even if



subsequent sampling failed to detect the same contaminants.  Such an




approach recognizes that many releases vary in concentration through




time or occur sporadically.  Thus, negative results during one or



more sampling intervals cannot refute a finding, when based on valid




sampling and analyses,  that an observed release has occurred




(49 FR 37078).




     Several commenters took issue with the use of significance with




respect to observed releases to ground waters.  The commenters




questioned the validity of sampling and analytical data used to




establish observed releases, particularly in instances where the




amount of contaminant detected in a sample is near the detection




limit of the appropriate analytical method.



     In response, the Agency explained its method of establishing




background levels and determining significantly higher



concentrations.  In cases in which a specific contaminant is not




detected in some site samples, the background level of that



contaminant is assumed to be some unknown value less than the



detection limit.  Any measurable quantity of contaminant in the site




samples is considered significantly higher than the background and
                                 43

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provides the basis for scoring an observed release.   The validity of




this assumption was cited as being supported by the statistical




analysis used to establish the detection limits for the method used




in analyzing the data (49 FR 37078).




     In situations in which a specific contaminant is detected in




all site samples, an observed release is sometimes more difficult to




determine than when the substance is  not detected in background




samples.  Generally, there are insufficient numbers of samples from




a site to apply conventional statistical tests for significance.




The scorer often must rely on inspection of the data to evaluate




whether an observed release has occurred.  If the data cluster into




a group of high values and a group of lower values,  particularly  if



the high values are attributed to sampling locations that are




apparently downgradient of a site, an observed release is confirmed.




If the analytical data from only one  sampling location are




significantly higher than from all other locations,  an observed



release also has occurred.  However,  if the contaminant




concentrations are similar among background and monitoring wells




(e.g., within a 10 to 20 percent range), EPA cannot state




conclusively that an observed release has occurred.   In addition,




low concentrations (e.g., less than 10 parts per billion) of




phthalates and other substances commonly found in ground water are




carefully examined along with any other evidence that might tend  to




corroborate or disprove that a release has occurred (49 FR 37078).






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A.3  Support Documents for the NPL and NFL Updates




     EPA's responses to site-specific public comments on the proposed




NPL and NPL updates, including an explanation of any score changes,




are contained in support documents (available in EPA dockets in




headquarters and regional offices).   This section is a review of the



comments and the Agency's responses,  contained in the support




documents, which are relevant to the  use of significance in



determining an observed release.




     A.3.1  NPL




     Based on the support document for the NPL (EPA I983a), three



commenters (pp. 3-79,  4-57,  and 11-7) felt that additional data




showing a decreased level of contamination over time should justify




a lower HRS score.   Another  commenter (p. 3-76) felt that low




concentrations of only one contaminant should not be the basis for




an observed release.  One commenter (p. 2-16) felt that additional




data showing an increased level of contamination over time should




justify a higher HRS score.   The response to these comments was that



the quantity of a substance  detected  is not relevant to scoring for




observed release, as long as the concentrations are greater than



background levels.   Any observed release is evidence of the ability




of substances to migrate from a site.



     A.3.2  NPL Update 1



     The support document for the first NPL revision is EPA I984a.




In a response (p. 3-44) to a comment  questioning the rationale for






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determining an observed release of airborne PCBs, the word




"substantially" was used to characterize the significant difference




between background and site-related contaminated levels (e.g.,




"...the on-site PCS concentration is substantially above the




background level...").  Although the background and site-related




data were not collected simultaneously, a three month monitoring of




background levels was determined sufficient to establish the range




of background concentrations.




     Two commenters (pp. 5-11 to 5-12 and 6-51 to 6-52) stated that




EPA's  reliance on a single set of analytical data containing levels




near the limit of detection is inappropriate as a basis to support




NPL listing.  The response stated that an observed release is scored




whenever substances of concern are detected in concentrations higher




than background levels regardless of frequency.  An additional




response to one of the comments (pp. 5-11 to 5-12) noted that many




of the substances were measured at levels substantially above



detection limits.  Some substances were measured at elevated levels




compared to background concentrations which were below the detection




limit.




     One commenter (p. 11-1 to 11-2) inferred that the low levels of




PCBs observed in ground water should not be considered evidence that




the compounds have migrated away from the site. The response was
                                 46

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that an observed release was scored  because  the  PCBs were  detected




in concentrations higher than background levels  (in this case, over




tenfold higher).
                                 47

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