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Lessons Learned

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

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Lessons Learned

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  1. Multi Incremental Sampling Lessons Learned Alaska Forum on the Environment February, 2009 Alaska Department of Environmental Conservation

  2. Sampling Theory Review • Heterogeneity – The Rule • Impossible to sample the entire population • Statistical methods must be used to determine a representativemean • Goal is to minimize sampling error

  3. Sampling Error • Compositional Heterogeneity • Contributes to fundamental error (FE) - result of not representing proportional concentrations of all of the particles in the population. • Distributional Heterogeneity • Contributes to grouping and segregation error (GSE) – result of not collecting enough random increments in enough locations to capture spatial variability.

  4. To minimize fundamental error… collect enough mass.

  5. To minimize grouping and segregation error… collect from many random locations.

  6. Fundamental Error Equation Where FE = Sampling fundamental error 20 = Sampling constant d = maximum particle size (centimeters) m = sample mass (grams)

  7. Goal • Maintain FE at 15% or less • At least 30 g of sample analyzed • 2 mm soil fraction • Grinding required for smaller sample size

  8. Composite or MI? • MI uses a defined decision unit BUT • Composite sampling does not consider the decision unit • MI attempts to control FE and GSE BUT • Compositing is a simple combination of discrete samples and does not control FE or GSE

  9. Decision Unit Identification • The area or volume in question (i.e. contaminated zone) • Systematic planning - Thorough documentation when setting decision unit boundaries • Potential “dilution” effect and hot spot removal must be considered • Decision units must be approved by DEC

  10. Sampling Locations • Increments collected from multiple random locations • Different types of random sampling techniques • Systematic random preferred • Sample depth considerations • Sampling from the excavator bucket

  11. Current Procedure – Non-Volatiles • Lab must meet MI-specific requirements • Scoop at least 30 - 60 g into appropriate container from each random increment location • Sieve now or bag and sieve later • Sub-sample in field or lab • Approx. 500 – 1,000 g should be available after sieving • Spread evenly and divide into sections (~30) • One small scoop (about 1-2 g) from each section into a 2-4 oz sample jar

  12. Current Procedure - Volatiles • Volatile sample containers • Small spoon, spatula • No sieving • Sample increments deposited into methanol at a minimum 1:1 ratio • Remove large clumps or rocks • 2-5 g from each increment location

  13. QA/QC • Triplicates collected to determine Relative Standard Deviation (RSD) • Multiple, similar decision units may have a reduced triplicate sampling frequency • Do not collect triplicates from co-located or adjacent locations

  14. RSD is a measure of data precision expressed in percent • Indication of representativeness of MI sampling of decision unit • 30% or less required • At RSDs >35%, the data distribution starts to become non-normal and the confidence in the representativeness on the MI sample results diminishes.

  15. 95% UCL • 95 % UCL must be calculated for all decision units • Only the 95% UCL will be used to evaluate the decision units

  16. MI Sampling Projects Review • ADEC Developed Draft Guidance in March 2007 • Approximately 40 projects have been proposed using MI sampling since then with approximately 20 projects accomplished using MI sampling • ADEC plans on updating the guidance in the near future

  17. Lessons Learned • Sample Drying • Sample grinding • SW 846 • VOCs • Decision Units • Sieving • Risk Assessment and ITRC

  18. Sample Drying • Sieving wet samples can be difficult and might leave material behind • Based on limited information, drying samples for semi-volatile and non-volatile analyses has not shown a significant decrease in contaminant concentrations (e.g. weathered DRO) • Contact ADEC if sample drying will affect holding times

  19. Sample Grinding • Grinding may be required for samples to be analyzed for metals or any other analytes where the analytical sample size is small • Some out of state labs are offering grinding and MI prep • Likely to become more common as more MI samples are collected

  20. SW 846- General Test Methods • EPA Method 8330B- Explosives “Various studies have shown that concentrations of energetic residues at military training ranges that were measured using the procedures in 8330B (MI Sampling) were statistically more representative relative to traditional sampling and analytical protocols”1

  21. VOC’s • Using a spoon or spatula with wide mouth jar results in loss of volatiles • Updated guidance will recommend using an Encore TM Sampler or other similar coring device that will reduce the loss of volatiles and a narrow mouth jar

  22. Decision Units • Should include only the release area, if known • Alternative decision units may be proposed, if impacted area is not known or has been reworked • Decision units must be clearly identified in a work plan and must be approved by ADEC

  23. Sieving • Highly organic soil types such as peat are not conducive to sieving, therefore, MI sampling is not appropriate without alternate sample collection and preparation procedures • Contact ADEC for additional information on MI sampling for this matrix

  24. Risk Assessment • EPA Region X Risk Assessment Conference in 2008 included a presentation on MI sampling • MI sampling may be accepted for use in Risk Assessments in the future • Contact ADEC to discuss how this might impact your Risk Assessment

  25. ITRC Workgroup • Will begin working on a guidance document for MI sampling in 2009

  26. For Best Results, Use MI Sampling… • To find the mean concentration of a contaminant in surface soil that is conducive to MI sample preparation and analysis • Where the decision unit is easily identified • When you’ve considered the potential outcome and are comfortable with it.

  27. Consider another sampling method when… • Soil type is not conducive to MI sample preparation and analyses • Identifying hot spots • Delineating the extent of contamination • Determining the maximum concentration

  28. Questions and Discussion

  29. References • 1- DoD Environmental Data Quality Workgroup, Guide for Implementing EPA SW-846 Method 8330B July 7, 2008.

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