Herb LevineUS EPA, Region IX

SERDP‐ESTCP

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1. REPORT DATE NOV 2010 2. REPORT TYPE

3. DATES COVERED 00-00-2010 to 00-00-2010

4. TITLE AND SUBTITLE CERCLA Site Close Out. How Clean is Clean? An EPA Perspective

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6. AUTHOR(S) 5d. PROJECT NUMBER

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7. PERFORMING ORGANIZATION NAME(S) AND ADDRESS(ES) U.S. Environmental Protection Agency,Region 9,75 HawthorneStreet,San Francisco,CA,94105

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12. DISTRIBUTION/AVAILABILITY STATEMENT Approved for public release; distribution unlimited

13. SUPPLEMENTARY NOTES Presented at the 15th Annual Partners in Environmental Technology Technical Symposium & Workshop,30 Nov ? 2 Dec 2010, Washington, DC. Sponsored by SERDP and ESTCP.

14. ABSTRACT This talk will focus on a regulatory perspective related to site closure and attainment of cleanup standards.Often two major questions arise in evaluating the attainment of a cleanup standard (1) Is the site reallycontaminated because a few samples are above the cleanup standard? (2) Is the site really ?clean? becausethe sampling shows that the majority of samples are below the cleanup standard? Statistical methods allowfor decision making under uncertainty and permit valid extrapolation of information which can be usedwith confidence to determine whether the site meets the cleanup standard. A case study will be presentedwhich presents some of these methods.

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16. SECURITY CLASSIFICATION OF: 17. LIMITATION OF ABSTRACT Same as

Report (SAR)

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33

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Standard Form 298 (Rev. 8-98) Prescribed by ANSI Std Z39-18

Remediation and Management of Persistent Technical Session No. 1C Chlorinated Solvent Contamination

C-17

EPA PERSPECTIVE ON SITE CLOSURE: HOW CLEAN IS CLEAN?

MR. HERB LEVINE U.S. Environmental Protection Agency

Region 9 75 Hawthorne Street

San Francisco, CA 94105 (415) 972-3062

levine.herb@epa.gov

his talk will focus on a regulatory perspective related to site closure and attainment of cleanup standards. Often two major questions arise in evaluating the attainment of a cleanup

standard:

(1) Is the site really contaminated because a few samples are above the cleanup standard?

(2) Is the site really “clean” because the sampling shows that the majority of samples are below the cleanup standard?

Statistical methods allow for decision making under uncertainty and permit valid extrapolation of information which can be used with confidence to determine whether the site meets the cleanup standard. A case study will be presented which presents some of these methods.

T

Attainment of Cleanup StandardsCongressional mandate in CERCLA 121(d)(2)(A):“…remedial actions shall require a level …which at 

least attains MCLs established under the Safe  Drinking Water Act and water quality criteria  …section 304 or 303 of the Clean Water act, where 

such goals or criteria are relevant and appropriate  under the circumstances of the release….”

Attainment of Cleanup Standards Policy

NCP preamble sets forth EPA’s policy that for groundwater “ remediation levels generally should be attained throughout the contaminated plume, or at and beyond the edge of the waste management area when waste is left in place.”

Attainment of Cleanup Standards Technical Guidance

1992 Methods for Evaluating the Attainment of Cleanup Standards Volume 2:Groundwater, presents statistical methods which address attainment evaluation 

1994 Methods for Monitoring Pump and Treat Performance, Chapter four updates statistical methods 

Attainment of Cleanup Standards 1992 Guidance

Attainment hypotheses:

is the site really contaminated because of few samples are above the cleanup standard?

is the site really ‘clean’ because the sampling shows the majority of samples to be below the clean up standard?

Attainment of Cleanup Standards 1992 guidance

Definition of attainment:The groundwater in a well attains the cleanup standard 

if, based on statistical tests, it is unlikely that the  average concentration (or a percentile) is greater than 

the cleanup standard.

Region IX Groundwater SitesRegion IX has 128 sites on the NPL, 113 have groundwater contaminationLike other Regional offices RPMs are assigned many sites and have to prioritize their timeMany sites are not addressed due to lack of resourcesLow hanging fruit, closeout sites which have attained cleanup goals

Background informationMany Superfund Sites in California had releases of solvents in the 1980sThese sites performed removal actions at their source areas and initiated ground water extractionAfter initial success the extraction remedy effectiveness declined and were optimized and later shut off, relied on MNA w/o ROD amendment (State lead)Long term monitoring depicted a slow and steady decline towards contaminant clean up levels

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Attainment Evaluation at SiteResponsible Party presented an evaluation of attainment using existing wells using 1992 guidance.  That evaluation associated four wells into a group based on contaminant and sampling history, well construction, and geographical locationThe AM evaluation averaged the data into a single value and determined that the cleanup standard had been met everywhere throughout the plume

Attainment of Cleanup Standards 1992 Guidance

Two possible ways to evaluate attainment of multiple wells:

Assess each well individuallyAssociate selected wells into groups

Associate Wells  1992 guidance

Restrictions on associating wells into a group:             wells should be within similar concentration contourwells must not be outside of the plumewells should be screened in the same intervalwells should be sampled and analyzed at the same event

Intended  for data sets where concentrations fluctuate  above and below the clean up standard.

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Figure7. Ammal A11-erage 1,1-Dicbloroetbeoe Concentraticms in Representative A-~ Mooitoring Wells, Applied Materials Building 1 mJ Vicinity, Santa Clua, Ca]ifomia

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Figure 8. 1,1-Dichloroethane Phtme R:umring Avenge, R.epresemative A-Znoe Mooi.toring Wells, Awlied Materials Building 1 and Vicinity, Santa Cla:ra, California

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Figure9. 1,1-Dichloroetbene PlumeR:umringAvenge, R.eprese.ntttiveA-'l.cmeMooitoring Wells, Applied Materials Building 1 and Vicinity, Santa Clara, California

Attainment of Cleanup Standards 1994 Guidance

Recommended time frame for attainment analysis is 2 to 5 years

 

Table 1: Spatial Average results and Statistics (2003 – 2010)

Sample Date

Spatial Average

Concentration [ug/L] All Wells

Standard Deviation

1,1-Dichloroethane (MCL 5) 1/9/2003 5.60 1.83 1/14/2004 3.84 2.36 1/12/2005 5.30 1.80 1/12/2006 4.51 1.60 1/16/2007 4.70 1.72 1/16/2008 2.97 1.95 1/20/2009 4.63 2.82 1/20/2010 4.20 2.72 1,1-Dichloroethene (MCL 6) 1/9/2003 9.18 1.45 1/14/2004 7.18 4.95 1/12/2005 7.65 3.53 1/12/2006 6.36 2.58 1/16/2007 6.88 1.95 1/16/2008 3.17 1.84 1/20/2009 5.45 2.21 1/20/2010 3.75 1.52 Notes: 1. Concentrations are averages for wells AM1-6, AM1-7, AM1-11 and AM1-5E for dates indicated. 2. The chart shows concentration vs. time with error bars representing the standard deviation for eachpoint 3. MCL are shown as straight line for DCA and DCE

Concentrations 

2006‐2010

90% 95% 99%

Well LCL UCL LCL UCL LCL UCL

name Min Max Mean Median SD

1,1 Dichloroethane   MCL 5

AM1‐11 1.8 4.6 2.96 2.2 1.33 1.69 4.22 1.309 4.611 0.22 5.698

AM1‐5E 4.9 7.2 5.88 5.8 0.83 5.09 6.67 4.85 6.9 4.17 7.59

AM1‐6 2 2.7 2.42 2.5 0.26 2.17 2.67 2.1 2.74 1.89 2.95

AM1‐7 2 8.1 5.68 6.2 2.24 3.55 7.82 2.9 8.46 1.07 10.29

1,1, Dichloroethene  MCL 6

AM1‐11 2.2 8.8 5.22 3.4 3.3 2.1 8.36 1.13 9.31 ‐1.566 12

AM1‐5E 2.9 5.5 4.42 4.5 1.01 3.4 5.43 3.1 5.71 2.23 6.61

AM1‐6 2.8 6.1 4.84 5 1.23 3.67 6.01 3.32 6.36 2.32 7.37

AM1‐7 1.1 8.3 6.02 8.1 3.2 3 9.05 2.1 9.9 ‐0.52 12.6

Spatial Average

1,1 DCA 2.42 5.88 4.24 4.32 1.8 2.1 6.4 1.4 7.1 ‐1 9.5

1,1 DCE 4.42 6.02 5.13 5.03 0.7 4.3 6 4 6.2 3.1 7.1

Attainment EvaluationSite conceptual model: site underlain by heterogeneous soils, remaining organic contaminants slowly diffusing out of marine mud into alluvial sandsRemedial actions taken: source removal, P&T with follow on MNA have reduced contaminant levels to or below the ROD specified cleanup levelsNo receptors at siteConclude site RAOs met using single well and 

multiple well statistics

Attainment ConclusionFor sites with similar CSM and data sets EPA Region IX goal is to close out these sites and delist from the NPL

EPA Region IX prefers an open approach using existing guidance, either individual wells or well groups.

EPA Region IX currently developing a policy document which reiterates national EPA policy and guidance and clarifies associating wells into groups.