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Using Geostatistics and Risk Assessment to Minimize Remediation

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Mockingbird (site-wide exposure) Based on site-specific data ... Northern Mockingbird surrogate receptor to represent birds that prey upon soil invertebrates ... – PowerPoint PPT presentation

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Title: Using Geostatistics and Risk Assessment to Minimize Remediation


1
Using Geostatistics and Risk Assessment to
Minimize Remediation
  • Ronald J. Kotun, Ph.D.
  • Tetra Tech

2
Site Description
  • 85 Acres
  • Heavily forested
  • Land covered with detritus material
  • Ordnance disposal
  • Trap and skeet range
  • Lead and PAHs
  • No lead pellets present
  • Reuse Plan states that site is to be maintained
    as a Green Space

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6
Cleanup Level Development
  • Protective of recreational receptors (site-wide
    exposure)
  • Infrequent exposure
  • Ecological receptors
  • Shrew (2-acres)
  • Mockingbird (site-wide exposure)
  • Based on site-specific data

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Recreational Receptor (Chronic)
  • Exposure assumptions
  • Exposure Frequency 50 days/yr
  • Exposure Duration 20 yr
  • Soil Ingestion 50 mg/day
  • Body Weight 70 kg
  • EPA adult lead model
  • Exposure concentration is average lead
    concentration
  • CLEANUP LEVEL 3,281 mg/kg

10
Ecological Receptors
  • Least shrewsurrogate receptor to represent
    mammals that prey upon soil invertebrates
  • Northern Mockingbirdsurrogate receptor to
    represent birds that prey upon soil invertebrates
  • Literature data available for these species to
    develop PRGs (e.g., food consumption)

11
Ecological Receptors (con't)
  • CLEANUP LEVEL AVIAN 1,127 mg/kg
  • Applied site-wide
  • CLEANUP LEVEL SHREW 2,512 mg/kg
  • Applied to 2-acre units
  • Most conservative values based on a sensitivity
    analysis of variables
  • Exposure concentration is average lead
    Concentration

12
Site Conditions
  • Pre-remediation average 990 mg/kg
  • Pre-remediation Pb max 41,400 mg/kg
  • Pre-remediation Pb 2 acre-max 8,875 mg/kg
  • Recreational (site-wide) 3,281 mg/kg
  • Avian (site-wide) 1,127 mg/kg
  • Mammalian (2-acre) 2,512 mg/kg
  • 2 2-acre units have average Pb gt 2,512 mg/kg
  • Remediation to protect mammals would be required
    (remove soil with Pb gt 4,000 mg/kg in these two
    units)

13
LeadAcute Toxicity
  • Acute toxicity to a small child (single
    high-level exposure)
  • Child ingests large quantity of soil (10 g)
  • Conducted by University of Florida, EPA,
    Battelle Research Laboratory
  • Results in a not-to-exceed Pb of 6,500 mg/kg

14
Why an Acute Lead Level
  • Children are more sensitive to lead than adults
  • Higher soil ingestion rate
  • Smaller body weight
  • Greater extent of absorption
  • Developing nervous system sensitive to lead

15
Remediation
  • Remove all soil with Pb gt 6,500 mg/kg

Post-Remediation Average 577
mg/kg Post-Remediation Pb max 6,500
mg/kg Recreational (site-wide) 3,281
mg/kg Avian (site-wide) 1,127 mg/kg Mammalian
(2-acre) 2,512 mg/kg
16
Remediation Contours
  • Determined using geostatistics (kriging)
  • Uses the site-specific data to define an area of
    remediation that minimizes the volume (rather
    than connecting the dots)
  • Use spatial representation of data to develop
    areas of remediation

17
Establish the Variogram
  • Structural analysis for quantifying the
    correlation between data points
  • All pairs of sampling points are compared to each
    other in order to provide a consistent measure of
    their degree of spatial correlation.
  • Graph difference in concentrations vs distance
  • Can be done to show directional trends
    (correlation may be stronger in a certain
    direction)

18
Results of Variogram Analysis
  • Lead samples have a directional trend from
    northwest to southeast
  • Consistent with firing range activities (trend
    would be expected)
  • Strongest correlation was at 130
  • Range of correlation is up to 400 feet
  • Based on this information, can begin to estimate
    concentrations at points where no data are
    available

19
Pb gt 6500 MG/KG
20
Cleanup gt 4000 MG/KG in 2 2-Acre Units to Achieve
Mammalian Value of 2,512 MG/KG
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22
Remediation Areas
  • Geostatistical-Based Remediation 1.8 Acres
  • Pb gt3,281 mg/kg (recreational) 3.1 Acres
  • Pb gt 400 mg/kg (residential) 32.6 Acres

23
Conclusion
  • Best use of site-specific data
  • Lead concentrations
  • Site reuse
  • Most likely receptors
  • Geostatistics
  • Ultimately reduced costs associated with
    remediation with minimal impact to the site
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