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Multi Incremental Sampling. Lessons Learned. Alaska Forum on the Environment February, 2009 Alaska Department of Environmental Conservation. Sampling Theory Review. Heterogeneity – The Rule Impossible to sample the entire population - PowerPoint PPT Presentation
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Lessons LearnedLessons Learned
Multi Incremental Multi Incremental SamplingSampling
Alaska Forum on the Environment
February, 2009Alaska Department of Environmental
Conservation
Sampling Theory ReviewSampling Theory Review
Heterogeneity – The RuleHeterogeneity – The Rule
Impossible to sample the entire Impossible to sample the entire populationpopulation
Statistical methods must be used to Statistical methods must be used to determine a determine a representativerepresentative meanmean
Goal is to minimize sampling errorGoal is to minimize sampling error
Sampling ErrorSampling Error Compositional HeterogeneityCompositional Heterogeneity
Contributes to fundamental error (FE) - result Contributes to fundamental error (FE) - result of not representing proportional of not representing proportional concentrations of all of the particles in the concentrations of all of the particles in the population. population.
Distributional HeterogeneityDistributional Heterogeneity Contributes to grouping and segregation Contributes to grouping and segregation
error (GSE) – result of not collecting enough error (GSE) – result of not collecting enough random increments in enough locations to random increments in enough locations to capture spatial variability. capture spatial variability.
To minimize To minimize fundamental fundamental
error…error… collect enough collect enough
mass.mass.
To minimize grouping To minimize grouping and segregation and segregation error…error…
collect from many collect from many random locations.random locations.
Fundamental Error EquationFundamental Error Equation
m
dFE
)(20 3
WhereFE = Sampling fundamental error
20 = Sampling constant d = maximum particle size (centimeters)m = sample mass (grams)
GoalGoal
Maintain FE at 15% or lessMaintain FE at 15% or less
At least 30 g of sample analyzedAt least 30 g of sample analyzed 2 mm soil fraction2 mm soil fraction Grinding required for smaller Grinding required for smaller
sample size sample size
Composite or MI?Composite or MI? MI uses a defined decision unitMI uses a defined decision unit
BUTBUT Composite sampling does not Composite sampling does not
consider the decision unitconsider the decision unit
MI attempts to control FE and GSEMI attempts to control FE and GSE
BUTBUT Compositing is a simple combination Compositing is a simple combination
of discrete samples and does not of discrete samples and does not control FE or GSEcontrol FE or GSE
Decision Unit IdentificationDecision Unit Identification The area or volume in question The area or volume in question
(i.e. contaminated zone)(i.e. contaminated zone)
Systematic planning - Thorough documentation Systematic planning - Thorough documentation when setting decision unit boundarieswhen setting decision unit boundaries
Potential “dilution” effect and hot spot removal Potential “dilution” effect and hot spot removal must be consideredmust be considered
Decision units must be approved by DEC Decision units must be approved by DEC
Sampling LocationsSampling Locations
Increments collected from multiple Increments collected from multiple random locationsrandom locations
Different types of random sampling Different types of random sampling techniquestechniques Systematic random preferredSystematic random preferred
Sample depth considerationsSample depth considerations Sampling from the excavator bucketSampling from the excavator bucket
Current Procedure – Current Procedure – Non-VolatilesNon-Volatiles
Lab must meet MI-specific requirementsLab must meet MI-specific requirements Scoop at least 30 - 60 g into appropriate Scoop at least 30 - 60 g into appropriate
container from each random increment locationcontainer from each random increment location Sieve now or bag and sieve laterSieve now or bag and sieve later Sub-sample in field or labSub-sample in field or lab Approx. 500 – 1,000 g should be available after Approx. 500 – 1,000 g should be available after
sievingsieving Spread evenly and divide into sections (~30)Spread evenly and divide into sections (~30) One small scoop (about 1-2 g) from each One small scoop (about 1-2 g) from each
section into a 2-4 oz sample jar section into a 2-4 oz sample jar
Current Procedure - Current Procedure - VolatilesVolatiles
Volatile sample containersVolatile sample containers Small spoon, spatulaSmall spoon, spatula No sievingNo sieving Sample increments deposited into Sample increments deposited into
methanol at a minimum 1:1 ratiomethanol at a minimum 1:1 ratio Remove large clumps or rocks Remove large clumps or rocks 2-5 g from each increment location2-5 g from each increment location
QA/QCQA/QC
Triplicates collected to determine Triplicates collected to determine Relative Standard Deviation (RSD)Relative Standard Deviation (RSD)
Multiple, similar decision units may have Multiple, similar decision units may have a reduced triplicate sampling frequencya reduced triplicate sampling frequency
Do not collect triplicates from co-located Do not collect triplicates from co-located or adjacent locationsor adjacent locations
RSD is a measure of data precision expressed in RSD is a measure of data precision expressed in percentpercent Indication of representativeness of MI sampling of Indication of representativeness of MI sampling of
decision unitdecision unit
30% or less required30% or less required At RSDs >35%, the data distribution starts to become At RSDs >35%, the data distribution starts to become
non-normal and the confidence in the non-normal and the confidence in the representativeness on the MI sample results diminishes.representativeness on the MI sample results diminishes.
s
RSD100
95% UCL95% UCL
95 % UCL must be calculated for all 95 % UCL must be calculated for all decision unitsdecision units
Only the 95% UCL will be used to Only the 95% UCL will be used to evaluate the decision units evaluate the decision units
n
tsUCL %95
MI Sampling Projects ReviewMI Sampling Projects Review
ADEC Developed Draft Guidance in ADEC Developed Draft Guidance in March 2007March 2007
Approximately 40 projects have been Approximately 40 projects have been proposed using MI sampling since proposed using MI sampling since then with approximately 20 projects then with approximately 20 projects accomplished using MI samplingaccomplished using MI sampling
ADEC plans on updating the ADEC plans on updating the guidance in the near futureguidance in the near future
Lessons LearnedLessons Learned
• Sample DryingSample Drying• Sample grindingSample grinding• SW 846SW 846• VOCsVOCs• Decision UnitsDecision Units• SievingSieving• Risk Assessment and ITRCRisk Assessment and ITRC
Sample DryingSample Drying
Sieving wet samples can be difficult and Sieving wet samples can be difficult and might leave material behindmight leave material behind
Based on limited information, drying Based on limited information, drying samples for semi-volatile and non-volatile samples for semi-volatile and non-volatile analyses has not shown a significant analyses has not shown a significant decrease in contaminant concentrations decrease in contaminant concentrations ((e.g. e.g. weathered DRO)weathered DRO)
Contact ADEC if sample drying will affect Contact ADEC if sample drying will affect holding timesholding times
Sample GrindingSample Grinding
Grinding may be required for Grinding may be required for samples to be analyzed for metals or samples to be analyzed for metals or any other analytes where the any other analytes where the analytical sample size is smallanalytical sample size is small
Some out of state labs are offering Some out of state labs are offering grinding and MI prepgrinding and MI prep
Likely to become more common as Likely to become more common as more MI samples are collectedmore MI samples are collected
SW 846- General Test SW 846- General Test MethodsMethods
EPA Method 8330B- ExplosivesEPA Method 8330B- Explosives
““Various studies have shown that Various studies have shown that concentrations of energetic residues concentrations of energetic residues at military training ranges that were at military training ranges that were measured using the procedures in measured using the procedures in 8330B 8330B
(MI Sampling) were statistically more (MI Sampling) were statistically more representative relative to traditional representative relative to traditional sampling and analytical protocols”sampling and analytical protocols”11
VOC’sVOC’s
Using a spoon or spatula with wide Using a spoon or spatula with wide mouth jar results in loss of volatilesmouth jar results in loss of volatiles
Updated guidance will recommend Updated guidance will recommend using an Encore using an Encore TM TM Sampler or other Sampler or other similar coring device that will reduce similar coring device that will reduce the loss of volatiles and a narrow the loss of volatiles and a narrow mouth jarmouth jar
Decision UnitsDecision Units Should include only the release area, Should include only the release area,
if knownif known
Alternative decision units may be Alternative decision units may be proposed, if impacted area is not proposed, if impacted area is not known or has been reworkedknown or has been reworked
Decision units must be clearly Decision units must be clearly identified in a work plan and must be identified in a work plan and must be approved by ADECapproved by ADEC
SievingSieving
Highly organic soil types such as peat Highly organic soil types such as peat are not conducive to sieving, therefore, are not conducive to sieving, therefore, MI sampling is not appropriate without MI sampling is not appropriate without alternate sample collection and alternate sample collection and preparation procedurespreparation procedures
Contact ADEC for additional information Contact ADEC for additional information on MI sampling for this matrixon MI sampling for this matrix
Risk AssessmentRisk Assessment
EPA Region X Risk Assessment EPA Region X Risk Assessment Conference in 2008 included a Conference in 2008 included a presentation on MI sampling presentation on MI sampling MI sampling may be accepted for use in MI sampling may be accepted for use in
Risk Assessments in the futureRisk Assessments in the future
Contact ADEC to discuss how this Contact ADEC to discuss how this might impact your Risk Assessmentmight impact your Risk Assessment
ITRC WorkgroupITRC Workgroup
Will begin working on a guidance Will begin working on a guidance document for MI sampling in 2009document for MI sampling in 2009
For Best Results, Use MI For Best Results, Use MI Sampling…Sampling…
To find the mean concentration of a To find the mean concentration of a contaminant in surface soil that is contaminant in surface soil that is conducive to MI sample preparation conducive to MI sample preparation and analysisand analysis
Where the decision unit is easily Where the decision unit is easily identifiedidentified
When you’ve considered the potential When you’ve considered the potential outcome and are comfortable with it.outcome and are comfortable with it.
Consider another sampling Consider another sampling method when…method when…
Soil type is not conducive to MI Soil type is not conducive to MI sample preparation and analysessample preparation and analyses
Identifying hot spotsIdentifying hot spots Delineating the extent of Delineating the extent of
contaminationcontamination Determining the maximum Determining the maximum
concentrationconcentration
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