Incremental Sampling Methodology – an Innovative Approach to Soil Sampling

1. Incremental Sampling Methodology – an Innovative Approach to Soil Sampling Presented by Shannon H. McDonald, P.G. August 4, 2010

2. What is it? • Soil sampling approach designed to obtain contaminant concentrations more representative of your exposure unit/domain

3. Previously: • Collected discrete samples • Influenced by sampler bias • Not scientifically reproducible or, therefore, defensible • Expensive to collect sufficient samples to adequately represent a site • May miss ‘hot spots’ • Often biased upward or downward

4. Previously (cont.) • For Risk Assessments, commonly used either maximum concentration or 95% UCL concentration as representative concentration in exposure domain

5. Background on Incremental Sampling Methodology (ISM) • Theory of particulate sampling originally developed by geologist Pierre Gy for mining industry • Designed to address “Seven Sampling Errors” • FUNDAMENTAL ERROR • Address by collecting and analyzing sufficient sample mass • SEGREGATION ERROR • Address by collecting sample increments randomly • Collect samples in sufficient locations to capture spatial variability

6. Background (continued) • Formally developed: • By EPA • November 2006 • Method 8330B • For nitroaromatics (energetics and explosives) • Military munitions sites

7. Background (continued) • Commonly “Multi-Increment™ Sampling” • “Multi-Increment” is trademarked by Envirostat, Inc. • Incremental Sampling Methodology? • Began to be applied to other types of contaminants • Semi-volatile organic compounds • Metals • Pesticides • PCBs

8. Sampling Technique • Identify Decision Unit (DU) • Generally not the entire site; subdivide site into several Decision Units • Size will depend on goal of investigation • Important not to bias or dilute • Useless to draw around small source area • Should not include large areas known to be uncontaminated (“dilution effect”)

10. Sampling Technique (cont.) 2. Grid Decision Unit • Need sufficient increments to not “miss” contamination • Typically 30 to 50 increments (guidance and theory) • Addresses distributional heterogeneity • “Systematic random” approach reduces bias

11. 2. Grid Decision Unit (cont.) • Collect one sample increment per grid cell • Collect increments from same relative location within each grid cell • Start at random point in first grid cell

12. Grid Decision Unit (cont.)

13. 2. Grid Decision Unit (cont.) • Skipped increments? • Because “systematic random”, SKIP (don’t move) inaccessible increments (due to buildings, pavement, standing water, etc.) • Otherwise, introduce bias • For example:

14. 2. Grid Decision Unit (cont.)

15. Sampling Technique (cont.) 3. Collect same volume of soil at each increment • Work backward to calculate how much soil you will need at the end • Depends on analyses to be performed and how many replicate samples you plan to collect (discussed later) • For a site with lead and PAH contamination, TTL collected about 120 grams (4 ounces) of soil per increment

16. Sampling Technique (cont.) 3. Collect same volume of soil at each increment (cont.) • Can use soil probe, hand auger, geoprobe, etc. • Collect from specified depth at each increment location • Place each increment in intermediate container together • For example:

17. Sampling Technique (cont.)

18. Sampling Technique (cont.) 4. Sieve entire sample • Typically use #10 sieve (200-mesh) • Remove fraction of sample >2 mm in diameter (trash, gravel, etc.) • Sieve resultant “soil” into decontaminated 2nd container (bucket?) • May require air-drying (no elevated temps!) first • TTL used large stainless steel trays to air-dry no more than 2 hours (SVOCs, metals, etc.)

19. Sampling Technique (cont.) 4. Sieve sample (cont.)

20. Sampling Technique (cont.) 4. Grind sample? • Some guidance suggests grinding sample • Obtains uniform small particle size • Can further reduce Fundamental Sampling Error • Depends on analytes • ADEM does not use grinding step

21. Sampling Technique (cont.) 5. Subdivide sample • Spread sample out in thin layer (1/4-inch) on decontaminated surface

22. 5. Subdivide sample (cont.) • Grid into between 30 and 50 sections

23. 5. Subdivide sample (cont.) • Collect equal amounts of soil from each gridded section • Scale • Stainless steel scoop – FLAT (to scoop to bottom of sample; collect all particle sizes)

24. 5. Subdivide sample (cont.) • Place one scoop from each grid section into sample container • Number of containers to fill varies by state • Alaska and Hawaii recommend triplicate samples • Alabama recommends minimum of TEN ultimate samples for each analyte

25. 5. Subdivide sample (cont.) • After filling all sample containers:

26. Obtain analytical data • Relative standard deviation? • Some guidance suggests calculating the RSD of analytical results • Quality control measure • Ideally <30% • Indicates data distribution • Calculate 95% Upper Confidence Limit • Ideally requires 10 to 15 concentration measurements • Ensures representative concentration

27. Case Study • Ongoing investigation/remediation project • High concentrations of PAHs and metals • Approximate 85-acre parcel • Divided into 17 decision units • Using ISM on each unit, have been able to receive CLOCs without further remediation on 12 zones • Two zones pending CLOCs • Three zones require more remediation

28. Lessons Learned • Need careful planning before going out into the field • Coordinate with regulators before beginning to understand expectations

29. More Information • Alaska – Draft Guidance – March 2009 - http://www.dec.state.ak.us/spar/csp/guidance/multi_increment.pdf • ITRC Methodology Resources and Links – http://www.itrcweb.org/teamresources_79.asp • Hawaii Technical Guidance Manual - Nov. 2009 - http://www.hawaiidoh.org/tgm.aspx?p=0402a.aspx • USACE Interim Guidance – July 2009 - http://www.hnd.usace.army.mil/oew/policy/IntGuidRegs/IGD%209-02v2.pdf

30. Questions / Discussion??? Shannon H. McDonald, P.G. TTL, Inc. 4154 Lomac Street Montgomery, Alabama 36106 (334)244-0766 smcdonald@ttlusa.com