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Establishing Background Concentrations in Soil to Support

Site ClosureTerry Griffin, PG

Terry.Griffin@CardnoTBE.com

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Primary Concerns

Soil excavation and removal is conducted at numerous environmental assessment sites

Excavation of soils with impacts not related to actual releases from the site is performed in many instances

Added cost of “unnecessary” soil excavation can prevent site closure or redevelopment

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What is Contamination?

Standards based on comparison to cleanup target levels (CTLs) (Chapter 62-777, F.A.C.) or water quality standards (Chapter 62-301 or 62-521, F.A.C.)

• Soil Contamination above CTLs– Direct Exposure Criteria– Leachability Criteria

• Soil Contamination Above Background Criteria, OR• Soil Contamination above Best Achievable Detection Limits(Chapter 62-785.680 F.A.C.)

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Establishing Alternative Cleanup Target Levels (Background)

What are Background Concentrations? Background Concentration

“Concentrations of contaminants that are naturally occurring in the groundwater, surface water, soil or sediment in the vicinity of the site” (Chapter 62-785(5) F.A.C.)

Anthropogenic Chemicals / Diffuse Anthropogenic Pollution (DAP)“...synthetic or natural substances that have been released to the environment as

a result of human activities, but are not related to specific activities conducted at the site” (FDEP Background Guidance, March 2008)

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Anthropogenic Background (Arsenic)

• Widespread use of arsenic pesticides

• Bio-accumulation of arsenic is shell material (fill material, road base)

• Arsenic in Florida Soils (2.1 mg/Kg direct exposure SCTL)– Study of 450 Un-impacted Soil Samples (Ma, et. al. www.AEHS.com)

• Conc. Range from 0.01 mg/Kg to 61.1 mg/Kg• Mean = 0.27 ppm / P95 = 3.54 mg/KG

– Study of 25 Urban soil samples (Chirenje & Ma, www.AEHS.com)• Conc. Range from 0 mg/Kg to 116 mg/Kg• Mean of 9.27 mg/KG

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FYI Possible Reduction in the Arsenic CTL

• EPA – Oral Slope Factor increase from 1.5 mg/kg-day-1 to 25.5 mg/kg-day-1

• New Residential DE CTL = 0.1 mg/kg

• New Industrial/Commercial DE CTL = 0.7 mg/kg

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Published Anthropogenic Background Concentrations for PAHs (Urban Soils)

1/ Toxicity equivalency factor used to calculate benzo(a)pyrene equivalents

PAH (in mg/kg) TEF1/

ATSDR (web) MA DEP (2002)

low high "Natural Soil"

Benzo(a)pyrene 1.00 0.17 0.22 2.00

Benzo(a)anthracene 0.10 0.17 59.00 2.00

Benzo(b)fluoranthene 0.10 15.00 62.00 2.00

Benzo(k)fluoranthene 0.10 0.30 26.00 1.00

Chrysene 0.00 0.25 0.64 2.00

Dibenz(a,h)anthracene 1.00 NR NR 0.50

Indeno(1,2,3-cd)pyrene 0.10 8.00 61.00 1.00

FDEP Residential SCTL (BaP equivalent standard) 0.10 2.50 21.02 3.1

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How to Address Background Contamination...

• Guidance for Comparing Background and Site Chemical Concentrations in Soil (FDEP March 2008)

– Draft guidance for groundwater (FDEP March 2009)

• Guidance for Characterizing Background Chemicals in Soil at Superfund Sites (EPA 540-R-01-003, June 2001)

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FDEP Guidance (March 2008)

• Background concentrations are used to help establish the area where liability for cleanup exists – where the chemical concentrations from the release become indistinguishable from concentrations present from other, non-specific sources”

• “If site concentrations are above background, and background concentrations are above risk-based criteria, cleanup to background levels may be warranted”

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Two Approaches for Comparing to Background Concentrations

• Non-Statistical Approach– Define the upper end of the range of background concentrations

• Statistical Approach– More robust method if sufficient data are available

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Case Study – Elevated Arsenic in Highly Organic “Muck” Soils Near Lake Okeechobee

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Approach 1 - Non-Statistical

• Upper end of range of background concentrations is lower of:

1. The maximum background concentration, or

2. Twice the mean background concentration

• 95% UCL non-statistical alternative (can be problematic)

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Sample ID Depth Value Source Sample ID Depth Value SourceHA-1 0.5' 3.7 Background SB-3 4' 3.1 SiteHA-1 2' 4.6 Background SB-6 0.5' 2.1 SiteHA-1 4' 2 Background SB-6 4' 1.6 SiteHA-2 0.5' 3.4 Background SB-15 4' 4 SiteHA-2 2' 7.6 Background SB-16 4' 2.2 SiteHA-2 4' 1.7 Background SB-6A 0.5 1.6 SiteHA-3 0.5' 2.8 Background SB-6A 2' 9.1 SiteHA-3 2' 3.5 Background SB-17 0.5' 4.9 SiteHA-3 4' 2.8 Background SB-17 2' 4.1 SiteHA-4 0.5' 2 Background SB-18 0.5' 5 SiteHA-4 2' 2.1 Background SB-18 2' 64 SiteHA-4 4' 0.99 Background SB-19 0.5' 3.7 SiteHA-5 0.5' 1.2 Background SB-19 2' 140 SiteHA-5 2' 14 Background SB-19 4' 34 SiteHA-5 4' 4 Background SB-20 0.5' 1.3 SiteHA-6 0.5' 2.7 Background SB-20 2' 21 SiteHA-6 2' 6.5 Background SB-20 4' 24 SiteHA-6 4' 7.7 Background SB-21 0.5' 2.3 SiteHA-7 0.5' 6.8 Background SB-21 2' 12 SiteHA-7 2' 5.6 Background SB-21 4' 8.2 SiteHA-7 4' 4 Background SB-22 0.5' 1.3 SiteHA-8 0.5' 5.9 Background SB-22 2' 11 SiteHA-8 2' 18 Background SB-23 0.5' 7.1 SiteHA-8 4' 7.2 Background SB-23 2' 10 SiteHA-9 0.5' 5.7 Background SB-23 4' 28 SiteHA-9 2' 13 Background SB-24 0.5' 2.4 SiteHA-9 4' 4.6 Background SB-24 2' 8.1 Site

HA-10 0.5' 3.6 Background SB-24 4' 7.4 SiteHA-10 2' 19 BackgroundHA-10 4' 4.6 BackgroundHA-11 0.5' 6.8 Background Statistic Background SiteHA-11 2' 14 Background Mean 5.34 15.13HA-11 4' 12 Background Median 4.00 6.05HA-12 0.5' 2 Background Range 18.00 138.70HA-12 2' 5.6 Background Variance 15.87 752.40HA-12 4' 9.1 Background Standard Deviation 3.98 27.43HA-13 0.5' 1.9 BackgroundHA-13 2' 11 Background Maximum Conc. 19 140HA-13 4' 7.6 Background 2 x Mean Conc. 10.7 30.3

Background Samples Site Samples

Qualifying Statistics

Non-Statistical Approach – Arsenic Study

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Approach 2 - Statistical • Parametric Tests (e.g., t-test)

– Best for normally distributed data

– Best used with large data sets (>25 samples) & few non-detects

– Sensitive to outlier data

• Non-parametric Tests (e.g., Wilcoxon Rank Sum test)

– Preferred unless compelling case for parametric tests

– No requirement for normal distribution

– Works well with non-detects

– Acceptable with smaller data sets (e.g., 15 – 20 samples)

• Incentives to collect more background samples (WRS Test 2)

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Wilcoxon Rank Sum (WRS) Test

• Test Form 1– Null hypothesis: mean Site concentrations ≤ the mean concentration in

background samples– Baseline assumption: chemical is Not a contaminant– Less conservative test

• Test Form 2 (Minimum Required by FDEP)– Null hypothesis: mean Site concentrations > background by more than a

specified concentration level– Baseline assumption: site concentrations reflect contamination– Site manager must decide what constitutes a substantial difference from

background• “Substantial difference = value above which sample is no longer considered a

result of variation in background concentrations and is deemed contaminated”

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WRS Test 1 – Arsenic StudySample ID Depth No. Spl. Value Location Site Rank Background Rank

HA-4 4' 1 0.99 Background 1HA-5 0.5' 2 1.2 Background 2SB-20 0.5' 3 1.3 Site 3.5SB-22 0.5' 4 1.3 Site 3.5SB-6 4' 5 1.6 Site 5.5

SB-6A 0.5' 6 1.6 Site 5.5HA-2 4' 7 1.7 Background 7HA-13 0.5' 8 1.9 Background 8HA-1 4' 9 2 Background 10HA-4 0.5' 10 2 Background 10HA-12 0.5' 11 2 Background 10HA-4 2' 12 2.1 Background 12.5SB-6 0.5' 13 2.1 Site 12.5

SB-16 4' 14 2.2 Site 14SB-21 0.5' 15 2.3 Site 15SB-24 0.5' 16 2.4 Site 16HA-6 0.5' 17 2.7 Background 17HA-3 0.5' 18 2.8 Background 18.5HA-3 4' 19 2.8 Background 18.5SB-3 4' 20 3.1 Site 20HA-2 0.5' 21 3.4 Background 21HA-3 2' 22 3.5 Background 22HA-10 0.5' 23 3.6 Background 23HA-1 0.5' 24 3.7 Background 24.5SB-19 0.5' 25 3.7 Site 24.5HA-5 4' 26 4 Background 27HA-7 4' 27 4 Background 27SB-15 4' 28 4 Site 27SB-17 2' 29 4.1 Site 29HA-1 2' 30 4.6 Background 31HA-9 4' 31 4.6 Background 31HA-10 4' 32 4.6 Background 31SB-17 0.5' 33 4.9 Site 33SB-18 0.5' 34 5 Site 34HA-7 2' 35 5.6 Background 35.5HA-12 2' 36 5.6 Background 35.5HA-9 0.5' 37 5.7 Background 37HA-8 0.5' 38 5.9 Background 38HA-6 2' 39 6.5 Background 39HA-7 0.5' 40 6.8 Background 40.5HA-11 0.5' 41 6.8 Background 40.5SB-23 0.5' 42 7.1 Site 42HA-8 4' 43 7.2 Background 43SB-24 4' 44 7.4 Site 44HA-2 2' 45 7.6 Background 45.5HA-13 4' 46 7.6 Background 45.5HA-6 4' 47 7.7 Background 47SB-24 2' 48 8.1 Site 48SB-21 4' 49 8.2 Site 49HA-12 4' 50 9.1 Background 50.5SB-6A 2' 51 9.1 Site 50.5SB-23 2' 52 10 Site 52HA-13 2' 53 11 Background 53.5SB-22 2' 54 11 Site 53.5HA-11 4' 55 12 Background 55.5SB-21 2' 56 12 Site 55.5HA-9 2' 57 13 Background 57HA-5 2' 58 14 Background 58.5HA-11 2' 59 14 Background 58.5HA-8 2' 60 18 Background 60HA-10 2' 61 19 Background 61SB-20 2' 62 21 Site 62SB-20 4' 63 24 Site 63SB-23 4' 64 28 Site 64SB-19 4' 65 34 Site 65.5SB-22 4' 66 34 Site 65.5SB-18 2' 67 64 Site 67SB-19 2' 68 140 Site 68

Rank Sum: 1092.5 1253.5

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Statistical Approach - WRS Test Form 1

• Null hypothesis – mean concentration of site samples ≤ mean concentration in background samples

• WRS critical value for a one-sided test approximated using the following equation:

Wcrit = [ns(N+1)/2] + zα[(nsnb(N+1))/12]1/2

Where Wcrit = critical value for the WRS testns = # measurements in the site sample populationnb = # of measurements in the background sample populationN = ns + nbZα is the 100(1-α)th percentile of the standard normal distribution (zα =

1.645 for 95% confidence interval)

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WRS Test 1 – Arsenic Study

Rank Sum: 1092.5 1253.5

Wcrit = [ns(N+1)]/2 + Zα[(nsnb(N+1))/12]1/2

Wcrit = [29(69)]/2 + 1.645[(29)(39)(69)/12]1/2 = 1,000.5 + 132.7 = 1,133.1

The sum of Site Ranks (1,092.5) < Wcrit (1,133.1) . Therefore, the null hypothesis that the mean site arsenic concentrations < the mean

background concentrations is Supported ; i.e., the site is NOTcontaminated above background

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WRS Test Form 2 (minimum required by DEP)• Null hypothesis – mean arsenic concentration at the site exceeds the

mean background concentration by a specified amount• WRS critical value for a one-sided test approximated using the

following equation:Wcrit = [nb(N+1)/2] + zα[(nsnb(N+1))/12]1/2

Where Wcrit = critical value for the WRS testns = # measurements in the site sample populationnb = # of measurements in the background sample populationN = ns + nb

Zα is the 100(1-α)th percentile of the standard normal distribution (zα = 1.645 for 95% confidence interval)

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WRS Test 2 – Arsenic StudySample ID Depth No. Spl. Value Location Site Rank Background Rank

SB-20 0.5' 1 1.3 Site 1.5SB-22 0.5' 2 1.3 Site 1.5SB-6 4' 3 1.6 Site 3.5

SB-6A 0.5' 4 1.6 Site 3.5SB-6 0.5' 5 2.1 Site 5SB-16 4' 6 2.2 Site 6SB-21 0.5' 7 2.3 Site 7SB-24 0.5' 8 2.4 Site 8SB-3 4' 9 3.1 Site 9SB-19 0.5' 10 3.7 Site 10SB-15 4' 11 4 Site 11SB-17 2' 12 4.1 Site 12SB-17 0.5' 13 4.9 Site 13HA-4 4' 14 4.97 Adjusted Background 14SB-18 0.5' 15 5 Site 15HA-5 0.5' 16 5.18 Adjusted Background 16HA-2 4' 17 5.68 Adjusted Background 17

HA-13 0.5' 18 5.88 Adjusted Background 18HA-1 4' 19 5.98 Adjusted Background 20HA-4 0.5' 20 5.98 Adjusted Background 20

HA-12 0.5' 21 5.98 Adjusted Background 20HA-4 2' 22 6.08 Adjusted Background 22HA-6 0.5' 23 6.68 Adjusted Background 23HA-3 0.5' 24 6.78 Adjusted Background 24.5HA-3 4' 25 6.78 Adjusted Background 24.5SB-23 0.5' 26 7.1 Site 26HA-2 0.5' 27 7.38 Adjusted Background 27SB-24 4' 28 7.4 Site 28HA-3 2' 29 7.48 Adjusted Background 29

HA-10 0.5' 30 7.58 Adjusted Background 30HA-1 0.5' 31 7.68 Adjusted Background 31HA-5 4' 32 7.98 Adjusted Background 32.5HA-7 4' 33 7.98 Adjusted Background 32.5SB-24 2' 34 8.1 Site 34SB-21 4' 35 8.2 Site 35HA-1 2' 36 8.58 Adjusted Background 37HA-9 4' 37 8.58 Adjusted Background 37

HA-10 4' 38 8.58 Adjusted Background 37SB-6A 2' 39 9.1 Site 39HA-7 2' 40 9.58 Adjusted Background 40.5

HA-12 2' 41 9.58 Adjusted Background 40.5HA-9 0.5' 42 9.68 Adjusted Background 42HA-8 0.5' 43 9.88 Adjusted Background 43SB-23 2' 44 10 Site 44HA-6 2' 45 10.48 Adjusted Background 45HA-7 0.5' 46 10.78 Adjusted Background 46.5

HA-11 0.5' 47 10.78 Adjusted Background 46.5SB-22 2' 48 11 Site 48HA-8 4' 49 11.18 Adjusted Background 49HA-2 2' 50 11.58 Adjusted Background 50.5

HA-13 4' 51 11.58 Adjusted Background 50.5HA-6 4' 52 11.68 Adjusted Background 52SB-21 2' 53 12 Site 53HA-12 4' 54 13.08 Adjusted Background 54HA-13 2' 55 14.98 Adjusted Background 55HA-11 4' 56 15.98 Adjusted Background 56HA-9 2' 57 16.98 Adjusted Background 57HA-5 2' 58 17.98 Adjusted Background 58.5

HA-11 2' 59 17.98 Adjusted Background 58.5SB-20 2' 60 21 Site 60HA-8 2' 61 21.98 Adjusted Background 61

HA-10 2' 62 22.98 Adjusted Background 62SB-20 4' 63 24 Site 63SB-23 4' 64 28 Site 64SB-19 4' 65 34 Site 65.5SB-22 4' 66 34 Site 65.5SB-18 2' 67 64 Site 67SB-19 2' 68 140 Site 68

Rank Sum: 866 1480

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WRS Test 2 – Arsenic Study

Rank Sum: 866 1480

Wcrit = [nb (N+1)]/2 + Zα[(nsnb(N+1))/12]1/2

Wcrit = [39(69)]/2 + 1.645[(29)(39)(69)/12]1/2 = 1,345.5 + 132.7 = 1,478.2

The sum of Adjusted Background Ranks (1,480) > Wcrit (1,478.2) . Therefore, the null hypothesis that the mean site arsenic concentrations > the mean background concentrations by at least 3.98 mg/kg is Rejected. Therefore, the site is NOT

contaminated substantially above background

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Arsenic Study Conclusions

• Mean concentrations of arsenic on the site is less than the mean concentration of background samples (Test 1 results)

• Site concentrations of arsenic are not higher than background samples by a factor > the standard deviation of the background sample population (3.98 mg/Kg) (Test 2 results)

• Mean site concentrations will exceed mean background concentrations for any value slightly less than 3.98 mg/Kg

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Questions?

Terry.Griffin@CardnoTBE.com