tom purucker us environmental protection agency athens, georgia, usa protect working group oslo,...
TRANSCRIPT
Tom PuruckerUS Environmental Protection Agency
Athens, Georgia, USA
PROTECT Working GroupOslo, Norway Jan 28 2008
Spatial approaches for ecological screening and exposure
assessment of chemicals and radionuclides:
Application of Spatial Analysis and Decision Assistance (SADA) Freeware
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SADA General InformationWindows--based freeware designed to integrate scientific models with decision and cost analysis frameworks in a user-friendly manner. Can be used to analyze spatially referenced analytical data or to post-process model output for risk assessment purposes.
SADA has been supported by DOE, EPA, and the NRC. SADA Version 3.0 had about 11000 downloads. Version 4.0/4.1 has had 10000+ since January, 2005. Version 5 due this summer.
• Visualization/GIS
• Statistical Analysis
• Geospatial Interpolation
• Geospatial Uncertainty Analysis
• Human Health Risk Assessment
• Ecological Risk Assessment
• Custom Analysis
• Area of Concern Frameworks
• Cost Benefit Analysis
• Sampling Designs
• Export to Arcview/Earthvision
• MARSSIM
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Derivation and application of benchmarks
SADA is primarily chemical (though MARSSIM (dual level DCGL exposures) and BDAC BCGs accessible)
Not a rad model that competes with Resrad/Erica/R&D 128
Can be used to (back)calculate species/site-specific benchmarks using exposure models
Sample size and designs for collecting and comparing data against benchmarks
Find accurate percentiles of exposure when spatial correlation is present
Ecologically, SADA most often used to apply benchmarks (e.g. site pass/fail, risk quotient maps)
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Basic GIS Capabilities
Exposure modeling (in SADA) is spatial, not dynamic
Consistent with applying numerical target values (e.g., BDAC BCGs) and (chemical) dose
Spatial interpolation methods useful for soil/sediment exposures/benchmark applications
Surface water- applications of benchmarksGIS Capabilities- (Layers, Polygons, Vertical
layers, etc.)
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Sample DesignsSADA has a number of sample design strategies in Version 4. These strategies include initial and secondary designs. Some are based on data alone while others are based on modeling results. With the exception of a couple of exclusively 2d designs all are available in 3d dimensions.
Systematic, unaligned, & hotspot search grids
Random
Judgmental
Adaptive Fill
High Value
AOC Boundary
Initial Designs Secondary Designs
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Sample Analytical Data
Or transport model output files
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Data Formats
SADA can accept data in two formats: comma delimited files (csv) and Microsoft Access.
Requires the presence of certain fields in the data set.EastingNorthingDepthValueName
Can use other forms of information as wellMediaDetectionDateCAS Number
Any other form of meta data can be imported as well. User can plot and retrieve this meta data during an analysis.
SADA recognizes soil, sediment, surfacewater, groundwater, air, biota, and background, and the “basic” media type. Basic is assigned to data that have no media type.
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Scaleable interface
Interviews
Analysis Box Data Type Box Data Name Box Labels Box Layers Box
Results WindowSteps Window Parameters Window
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Basic Data ExplorationData/GIS Visualization
Spatial AggregationData Screening
3D visualizationStatistics
Spatial Data Query
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Classical StatisticsEPA DQO/DQA
Numerous univariate statistics
Non-parametric hypothesis testing
Power curve based sample sizes
Histograms and CDFs
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Calculate sample size based on Sign Test and WRS Test
Develop initial sample design incorporating DCGLS, Area Factors, Instrument sensitivity
Post sampling analysis (A site passes or fails)
Detecting and Defining Elevated Areas
MARSSIM Functionality
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Spatial Estimation
The estimated value Vo at an unsampled location is estimated as the weighted average of nearby values.
Search Neighborhood
Unsampled Point
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Modeling spatial auto-correlationSemi-variograms often do not conform to the well behaved monotonic increasing variogram
structures seen in text book examples.
Distance
Sem
ivar
Distance DistanceSADA provides 3 standard correlation models that provide flexibility in semi-variogram data: Spherical, Exponential, and Gaussian.
Autofit routines are available to assist in fitting correlation models. These models are then used to generate kriging maps.
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Comparing spatial models (Cross Validation)
Cross validation provides estimates of model error based on existing data.
Process of removing one sample at a time and predicting the concentration at that location, and measuring the error.
Statistic generated for all samples that can be used to make comparative statements between different spatial models:Mean of errorsAbsolute mean errorMean squared error
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Spatial Analysis
Spatial EstimationSpatial Uncertainty
Model Spatial Correlation
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Kriging MapsKriging provides an estimate with an associated kriging variance at
each grid node.
Allows one to be conservative (e.g. percentiles > .5)
Allows one to spatially ascertain the difference between an “optimistic, realistic, and pessimistic” (e.g. 25th, 50th, and 75th) maps.
“optimistic”
p=0.25
“realistic”
p=0.5
“pessimistic”
p=0.75
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Spatial Dose/Risk Assessment
Conventional Risk Assessment Limitations
Typically regulatory exposure assessment guidance recommends a summary statistic for the exposure concentration
Spatial information is lost when a summary statistic is used in the RA- exposure is assumed to be continuous in space and time
Often this lost info not recovered in the rest of the assessment/remediation process
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Spatial Dose/Risk Assessment
Reasons for incorporating spatial statistics into dose/risk assessment
Maximize the use of limited resources
Efficiently collect data
Retain collected spatial info in the risk assessment
Use all types of available data, including expert judgment
To more adequately characterize the exposure distribution
Extrapolate from known data to cover data gaps
Account for spatial processes related to exposure
Better understand uncertainties in the exposure assessment
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Ecological Capabilities in SADA
SADA implements EPA methods for conducting ecological risk assessments
Benchmark database for contaminant effects on ecological receptors
Exposure modeling for over 20 other terrestrial species
Contains EPA default exposure parameters for the risk models where available
Tabular screening and risk results
Point screens
Risk and dose mapping
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Ecological Functionality Setting Up Ecological Risk
Ecological Risk Assessment Procedure
Setting Physical Parameters
Description of Ecological Benchmark Database
Histograms of Benchmark Values
Tables of Benchmark Values
Setting Screening and Exposure Statistics
Area Result Tables (Screens, Ratios)
Map Result Values (Screens, Ratios)
Rematching a Single Contaminant
Checking Ecological Version
Terrestrial Dose Modeling
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Setup Ecological Risk
Identify source benchmarks database
Match contaminants in data to benchmark contaminants
Adds ecological information to SADA file
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Hazard v. Risk AssessmentEcological Hazard Assessment- a comparison of an environmental
concentration to an estimated toxic threshold for a particular contaminant
-most common method for examining effects of chemicals in environment
-comparison of environmental exposure concentration to a toxic threshold (benchmark)
-iterative (or tiered) implementation
-number of toxicity data sets for soil, sediment, and surface water available for screening
Ecological Dose/Risk Assessment- explicitly attempts to estimate the probability and magnitude of the effects of exposure to contamination
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Benchmark ScreeningMedia-specific concentration benchmarks
Choice of statistics (max, percentile, UCL95, etc.)
Hierarchy of media-specific benchmarks for screening
Spatial and tabular display of ratios
Derivation of Benchmarks:Toxicity testing (acute or chronic)
-regression of concentration-response data-hypothesis testing
Extrapolation from another benchmark
Simulation of an assessment endpoint
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Ecological Benchmark ScreeningSuitable for screening ERAs
Compilation of ecological benchmarks for surface water (14), soil (11), sediment (17), and biota (8)
Benchmarks a function of environmental variables where appropriate
Choice of statistics (max, percentile, UCL95, etc.)
Hierarchy of media-specific benchmarks for screening
Spatial and tabular display of ratios
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SADA Eco Rad screening/dose calculations
BDAC support, next version of eco risk library has:
BDAC BCG rad benchmarks to open up spatial screening tools for rads
Simple (DCF/BCF) aquatic/riparian/terrestrial dose calculation for rads, again to allow spatial dose calculations
We can turn this on in SADA V5 if there is interest
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Map Result Screens and Ratios
Screens concentration against benchmarks at each sample location
Places a box around locations that exceed benchmark
Can use one benchmark source or establish a site-specific hierarchy
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SADA Terrestrial Dose Modeling
SADA calculates dose (mg/kg BW d) from food ingestion, soil ingestion, dermal contact, and inhalation for terrestrial exposures as well as total dose summed over all pathways selected.
SSL, Female, Male, or Juvenile
Number of different speciesUse a polygon to identify
home rangeSelect species/sexClick exposure pathwaysReturns dose in mg/kg/day for
each exposure pathway
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Ecological Exposures Inputs and Outputs
a)
d)
c)
b)
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Calculate Exposure for Home Range
Use a polygon to identify home range
Select species/sex
Click exposure pathways
Returns dose in mg/kg/day for each exposure pathway
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Spatial Estimation + Risk/Dose MethodsCombining spatial methods with dose/risk assessment allows for decision support applications
Search Neighborhood
Unsampled Point
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Decision AnalysisSpatial Screens
Sampling Strategies
Cost Vs Risk Reduction
Spatial Risk
Area of Concern
Cost Benefit
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Selective Remediation
Process that achieves a local- and/or site-specific concentration level while minimizing cleanup volume.
Implementation requires:- data- spatial interpolation model- decision-maker cleanup criteria- spatial scale inputs
Results in a spatially explicit remedial design
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Determining Areas of Concern
Map of interpolated concentration values can be compared to ecological or human health risk criteria to develop areas of concern
SADA reports area or volume of exceedance and coordinates or areal extent
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Cost-Risk Curves for Soil/Sediment remediation
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3D Visualization
True 3d Views: Points, Blocks, and Isosurfaces
Source term definition, etc.
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If you don’t like all that, at least I have a hard copy of Till & Meyer for Nick
Although this work was reviewed by EPA and approved for presentation, it may not necessarily reflect official Agency policy. Mention of trade names or commercial products does not constitute endorsement or recommendation for use.